Author name code: schwenn
ADS astronomy entries on 2022-09-14
author:"Schwenn, Rainer"
------------------------------------------------------------------------
Title: Multi-spacecraft observed magnetic clouds as seen by Helios
mission
Authors: de Lucas, A.; Dal Lago, A.; Schwenn, R.; Clúa de Gonzalez,
A. L.
Bibcode: 2011JASTP..73.1361D
Altcode:
A large number of magnetic clouds (MCs) were observed during the
operation period of the Helios mission. Some of the MCs were observed
by multi-spacecraft, enabling a detailed study of their extension
in the inner heliosphere when they pass by more than one observation
location. In the present work, we analyzed 62 MCs, including 16 which
were observed by multiple spacecraft and 46 observed by a single
one. For those MCs observed by a single spacecraft, the cloud's axis,
obtained using minimum variance analysis (MVA) on magnetic field data,
could be an explanation for the fact that there were no observations
at the other spacecraft. Highly inclined MCs, defined as MCs whose
axes are inclined more than 45∘ from the ecliptic plane,
are less likely to be observed by two spacecraft that are close to
the ecliptic plane.
Title: Interplanetary shock wave extent in the inner heliosphere as
observed by multiple spacecraft
Authors: de Lucas, A.; Schwenn, R.; dal Lago, A.; Marsch, E.; Clúa
de Gonzalez, A. L.
Bibcode: 2011JASTP..73.1281D
Altcode:
For over an entire solar cycle, from the end of 1974 until the
beginning of 1986, the twin Helios spacecraft explored the inner
heliosphere. These in situ, high-resolution plasma and magnetic
field measurements covered heliocentric distances between 0.3 and 1
AU from the Sun and are of particular interest to studies of space
weather phenomena. During this period the two spacecraft detected
395 ICME-driven shocks and these waves were found to be driven
by interplanetary coronal mass ejections (ICMEs). Based on these
multi-spacecraft measurements, which include a third vantage point
with the observations from ISEE-3/IMP-8, the longitudinal extent of the
shock waves were measured in the inner heliosphere. It was found that
shock waves have about a 50% chance to be observed by two different
locations separated by 90°. In practice, one can expect with about a
50% chance that the shock driven by a limb coronal mass ejections (CMEs)
will hit the Earth, considering the expansion in longitude of shock
waves driven by their associated ICMEs. For a larger separation the
uncertainty increases, as only a few cases could be observed. With the
absence of simultaneous solar disk observations one can then no longer
unequivocally identify the shock waves observed at each spacecraft.
Title: Identification of prominence ejecta by the proton distribution
function and magnetic fine structure in interplanetary coronal mass
ejections in the inner heliosphere
Authors: Yao, Shuo; Marsch, Eckart; Tu, Chuan-Yi; Schwenn, Rainer
Bibcode: 2010JGRA..115.5103Y
Altcode: 2010JGRA..11505103Y
This work presents in situ solar wind observations of three magnetic
clouds (MCs) that contain cold high-density material when Helios 2
was located at 0.3 AU on 9 May 1979, 0.5 AU on 30 March 1976, and 0.7
AU on 24 December 1978. In the cold high-density regions embedded
in the interplanetary coronal mass ejections we find (1) that the
number density of protons is higher than in other regions inside the
magnetic cloud, (2) the possible existence of He+, (3)
that the thermal velocity distribution functions are more isotropic
and appear to be colder than in the other regions of the MC, and the
proton temperature is lower than that of the ambient plasma, and (4)
that the associated magnetic field configuration can for all three MC
events be identified as a flux rope. This cold high-density region is
located at the polarity inversion line in the center of the bipolar
structure of the MC magnetic field (consistent with previous solar
observation work that found that a prominence lies over the neutral
line of the related bipolar solar magnetic field). Specifically, for
the first magnetic cloud event on 8 May 1979, a coronal mass ejection
(CME) was related to an eruptive prominence previously reported as a
result of the observation of Solwind (P78-1). Therefore, we identify
the cold and dense region in the MC as the prominence material. It
is the first time that prominence ejecta were identified by both the
plasma and magnetic field features inside 1 AU, and it is also the first
time that the thermal ion velocity distribution functions were used to
investigate the microstate of the prominence material. Moreover, from
our three cases, we also found that this material tended to fall behind
the magnetic cloud and become smaller as it propagated farther away
from the Sun, which confirms speculations in previous work. Overall,
our in situ observations are consistent with three-part CME models.
Title: Identification of prominence ejecta by the proton distribution
function and magnetic fine structure in ICMEs in the inner heliosphere
Authors: Marsch, Eckart; Yao, Shuo; Tu, Chuanyi; Schwenn, Rainer
Bibcode: 2010cosp...38.1876M
Altcode: 2010cosp.meet.1876M
This work presents in-situ solar wind observations of three magnetic
clouds that contain certain cold high-density material, when Helios
2 was located at 0.3 AU, on 9 May 1979, 0.5 AU on 30 March 1976, and
0.7 AU on 24 December 1978, respectively. In the cold high-density
regions embedded in the ICMEs we find that (1) the number density of
protons is higher than in other regions inside the magnetic cloud (MC),
(2)the possible existence of He+, (3) the thermal velocity distribution
functions (VDFs) are more isotropic and appear to be colder than in the
other regions of the MC, and the proton temperature is lower than that
of the ambient plasma, (4) the associated magnetic field configuration
can for all three MC events be identified as a flux rope. This cold
high-density region is located at the polarity inversion line in the
center of the bipolar structure of the MC magnetic field (consistent
with previous work of solar observation that a prominence lies over
the neutral line of the related bipolar solar magnetic field ). It is
the first time that prominence ejecta are identified by both the plasma
and magnetic field features inside 1 AU, and that thermal ion velocity
distribution functions are used to investigate the microstate of the
prominence material. Overall, our in situ observations are consistent
with the three-part CME models.
Title: Multi-spacecraft observation of a magnetic cloud
Authors: de Lucas, Aline; Dal Lago, Alisson; Schwenn, Rainer; Clúa de
Gonzalez, Alicia L.; Marsch, Eckart; Lamy, Philippe; Damé, Luc; Curdt,
W.; Davila, J.; Defise, J. M.; Fineschi, S.; Heinzel, P.; Howard, R.;
Kuzin, S.; Schmutz, W.; Tsinganos, K.; Turck-Chièze, S.; Zhukov, A.
Bibcode: 2010cosp...38.1921D
Altcode: 2010cosp.meet.1921D
Classical externally-occulted coronagraphs are presently limited in
their performances by the distance between the external occulter and
the front objective. The diffraction fringe from the occulter and
the vignetted pupil which degrades the spatial resolution prevent
useful observa-tions of the white light corona inside typically 2-2.5
Rsun. Formation flying offers an elegant solution to these limitations
and allows conceiving giant, externally-occulted coronagraphs
us-ing a two-component space system with the external occulter on
one spacecraft and the optical instrument on the other spacecraft
at distances of hundred meters. Such an instrument has just been
selected by ESA to fly (by the end of 2013) on its PROBA-3 mission,
presently in phase B, to demonstrate formation flying. It will perform
both high spatial resolution imaging of the solar corona as well as
2-dimensional spectroscopy of several emission lines (in partic-ular
the forbidden line of FeXIV at 530.285 nm) from the coronal base out
to 3 Rsun using a Fabry-Perot interferometer. The classical design of
an externally-occulted coronagraph is adapted to the formation flying
configuration allowing the detection of the very inner corona as close
as 0.05 Rsun from the solar limb. By tuning the position of the occulter
spacecraft, it may even be possible to try reaching the chromosphere
and the upper part of the spicules. ASPIICS/PROBA-3 mission, payload
and scientific objectives are presented.
Title: Multi-spacecraft observation of a magnetic cloud
Authors: de Lucas, A.; Dal Lago, A.; Schwenn, R.; Clua de Gonzalez,
A. L.; Marsch, E.; Gonzalez, W. D.
Bibcode: 2009AGUFMSH13B1515D
Altcode:
During the time operation of the Helios mission, from 1974 to 1986,
a large number of magnetic clouds was identified by the magnetic
field and solar wind sensors onboard the probes. Among these magnetic
clouds, some of them were identified by at least two probes, provided
that IMP-8 and ISEE-3 were monitoring the dayside magnetosphere. The
magnetic cloud observed on from DOY 029 to DOY 030/1977 by Helios 1,
Helios 2, and IMP-8 represents a potential multi-spacecraft observed
magnetic cloud. Despite the interaction with the high-speed stream
that compressed the magnetic cloud, the minimum variance analysis
technique showed the same direction of rotation of the magnetic field
inside the magnetic cloud. This helped to associate the observation
of the magnetic cloud at multi-spacecraft.
Title: Multi-spacecraft observations to study the shock extension
in the inner heliosphere
Authors: de Lucas, Aline; Schwenn, Rainer; Marsch, Eckart; Lago,
Alisson Dal; de Gonzalez, Alicia L. Clúa; Echer, Ezequiel; Gonzalez,
Walter D.; da Silva, Marlos R.
Bibcode: 2009IAUS..257..481D
Altcode:
The two Helios probes traveled at variable longitudinal and radial
separations through the inner heliosphere. They collected most valuable
high resolution plasma and magnetic field data for an entire solar
cycle. The mission is still so successful that no other missions
will collect the same kind of data in the next 20 years. One of the
subjects studied after the success of the Helios mission was the
identification of more than 390 shock waves driven by Interplanetary
Coronal Mass Ejections (ICMEs). Combining the data from both probes,
we make a statistical study for the extension of the shock waves in
the interplanetary medium. For longitudinal separations of 90° we
found a cutoff value at this angular separation. A shock has 50%
of chance to be observed by both probes and the same probability
for not being observed by two spacecrafts at the same time, when the
angle between them is around 90°. We describe the dependence of the
probability for shocks to be observed by both probes with decreasing
spacecraft separation. Including plasma data from the ISEE-3 and IMP-8
spacecrafts improves our statistical evaluation substantially.
Title: Exploring the global shock scenario at multiple points
between sun and earth: The solar transients launched on January 1
and September 23, 1978
Authors: Berdichevsky, D. B.; Reames, D. V.; Wu, C. -C.; Schwenn, R.;
Lepping, R. P.; MacDowall, R. J.; Farrugia, C. J.; Bougeret, J. -L.;
Ng, C.; Lazarus, A. J.
Bibcode: 2009AdSpR..43..113B
Altcode:
We revisit the transient interplanetary events of January 1 and
September 23, 1978. Using in-situ and remote sensing observations at
locations widely separated in longitudes and distances from the Sun,
we infer that in both cases the overall shock surface had a very fast
“nose” region with speeds >900 and >1500 km-1
in the January and September events, respectively, and much slower
flank speeds (∼600 km-1 or less), suggesting a shock
surface with a strong speed gradient with heliospheric longitude. The
shock-nose regions are thus likely efficient acceleration sites of MeV
ions, even at 1 AU from the Sun. Our 3D magnetohydrodynamics modeling
suggests that a 24° × 24° localized disturbance at 18 solar radii
injecting momentum 100 times the background solar wind input over 1
h can produce a disturbance in semi-quantitative agreement with the
observed shock arrival time, plasma density and velocity time series
in the January 1978 event.
Title: Theoretical modeling for the stereo mission
Authors: Aschwanden, Markus J.; Burlaga, L. F.; Kaiser, M. L.; Ng,
C. K.; Reames, D. V.; Reiner, M. J.; Gombosi, T. I.; Lugaz, N.;
Manchester, W.; Roussev, I. I.; Zurbuchen, T. H.; Farrugia, C. J.;
Galvin, A. B.; Lee, M. A.; Linker, J. A.; Mikić, Z.; Riley, P.;
Alexander, D.; Sandman, A. W.; Cook, J. W.; Howard, R. A.; Odstrčil,
D.; Pizzo, V. J.; Kóta, J.; Liewer, P. C.; Luhmann, J. G.; Inhester,
B.; Schwenn, R. W.; Solanki, S. K.; Vasyliunas, V. M.; Wiegelmann, T.;
Blush, L.; Bochsler, P.; Cairns, I. H.; Robinson, P. A.; Bothmer,
V.; Kecskemety, K.; Llebaria, A.; Maksimovic, M.; Scholer, M.;
Wimmer-Schweingruber, R. F.
Bibcode: 2008SSRv..136..565A
Altcode: 2006SSRv..tmp...75A
We summarize the theory and modeling efforts for the STEREO mission,
which will be used to interpret the data of both the remote-sensing
(SECCHI, SWAVES) and in-situ instruments (IMPACT, PLASTIC). The
modeling includes the coronal plasma, in both open and closed magnetic
structures, and the solar wind and its expansion outwards from the Sun,
which defines the heliosphere. Particular emphasis is given to modeling
of dynamic phenomena associated with the initiation and propagation
of coronal mass ejections (CMEs). The modeling of the CME initiation
includes magnetic shearing, kink instability, filament eruption, and
magnetic reconnection in the flaring lower corona. The modeling of CME
propagation entails interplanetary shocks, interplanetary particle
beams, solar energetic particles (SEPs), geoeffective connections,
and space weather. This review describes mostly existing models of
groups that have committed their work to the STEREO mission, but is by
no means exhaustive or comprehensive regarding alternative theoretical
approaches.
Title: Analysis of the Fe X and Fe XIV line width in the solar corona
using LASCO-C1 spectral data
Authors: Mierla, M.; Schwenn, R.; Teriaca, L.; Stenborg, G.;
Podlipnik, B.
Bibcode: 2008A&A...480..509M
Altcode: 2009arXiv0903.0496M
Aims:The purpose of this paper is to analyze the variation in
the line width with height in the inner corona (region above 1.1
R⊙), by using the spectral data from LASCO-C1 aboard
SOHO. We used data acquired at activity minimum (August-October 1996)
and during the ascending phase of the solar cycle (March 1998).
Methods: Series of images acquired at different wavelengths across
the Fe X 637.6 nm (red) and Fe XIV 530.3 nm (green) coronal lines
by LASCO-C1 allowed us to build radiance and width maps of the
off-limb solar corona.
Results: In 1996, the line width of Fe
XIV was roughly constant or increased with height up to around 1.3
R⊙ and then it decreased. The Fe X line width increased
with height up to the point where the spectra were too noisy to allow
line width measurements (around 1.3 R⊙). Fe X showed
higher effective temperatures as compared with Fe XIV. In 1998 the
line width of Fe XIV was roughly constant with height above the limb
(no Fe X data available).
Title: Space weather explorer The KuaFu mission
Authors: Schwenn, R.; Donovan, E.; Marsch, E.; Wang, J. -S.; Xia,
L. -D.; Zhang, Y. -W.; KuaFu Working Team
Bibcode: 2008AdSpR..41..190S
Altcode:
The KuaFu mission is designed to explore the physical processes
that are responsible for space weather, complementing planned
in situ and ground-based programs, and also to make an essential
contribution to the space weather application. KuaFu encompasses
three spacecraft. KuaFu-A will be located at the L1 libration point
and have instruments to observe solar extreme ultraviolet (EUV) and
far ultraviolet (FUV) emissions and white-light coronal mass ejections
(CMEs), and to measure radio waves, the local plasma and magnetic field,
and high-energy particles. KuaFu-B1 and KuaFu-B2 will be in elliptical
polar orbits chosen to facilitate continuous (24 h per day 7 days
per week) observation of the northern polar aurora oval and the inner
magnetosphere. The KuaFu mission is designed to observe globally the
complete chain of disturbances from the solar atmosphere to geospace,
including solar flares, CMEs, interplanetary clouds, shock waves, and
their geo-effects, with a particular focus on dramatic space weather
events such as magnetospheric substorms and magnetic storms. The mission
start is targeted for the next solar maximum with launch hoped for
in 2012. The initial mission lifetime will be 3 years. The overall
mission design, instrument complement, and incorporation of recent
technologies will advance our understanding of the physical processes
underlying space weather, solve several key outstanding questions
including solar CME initiation, Earth magnetic storm and substorm
mechanisms, and advance our understanding of multi-scale interactions
in and system-level behavior of our Sun Earth space plasma system.
Title: Mexican Coronagraph "Mextli" Project
Authors: Muñoz Martínez, Guadalupe; Jacinto, Juan Soto; Vargas
Cardenas, Bernardo; Aguirre Marquez, Hector; Schwenn, Rainer
Bibcode: 2008cosp...37.2137M
Altcode: 2008cosp.meet.2137M
Space weather forecasts require a variety of data and information in
order to produce reliable results to predict important events affecting
the Earth and the surrounding environment. One of the most important
solar phenomena concerning the interplanetary conditions is coronal
mass ejections. These events transport important amount of material and
magnetic field to the interplanetary medium capable of interact with
the magnetosphere in different ways. The only source of clear evidence
of the early development of coronal mass ejections are, by now, white
light images, provided by ground based and space coronagraphs. From
these images the main kinematical parameters as speed and acceleration,
as projected on the plane of the sky, are obtained. Basic information
as the speed of the ejecta in the line of sight and the nature of
the material carried require spectrographic observations of the
phenomena. LASCO C1 on board of SOHO space mission provided valuable
information in this field but propagation speeds greater than 10 km/s
could not be detected from the images and it is not in operations
since 1998. The Argentinean ground based coronagraph MICA has a design
similar to C1 but using a narrow-band filters mechanism instead of the
Fabry-Perot interferometer of C1. The purpose or Mextli project is to
have a coronagraph with spectroscopic capabilities aimed to observe
the inner solar corona between 2.5 and 15 solar radii in the emission
of Fe XIV line at 530 +-N nm. Its main objective would be the early
detection of dynamical events and its kinematical characterization. In
order to achieve the objective pursued, the coronagraph will b e
provided with a high speed CCD camera and an electronic Fabry Perot
interferometer. The instrument will be constructed in Mexico in the
frame of a collaboration project between the UNAM, INAOE and IPN and
under the technical supervision of the MPS in Germany and the MICA
team from Argentina.
Title: A Statistical Analysis of Shock Wave Extension in the Inner
Heliosphere as observed by the two Helios probes
Authors: de Lucas, Aline; Schwenn, Rainer; Marsch, Eckart; Dal Lago,
Alisson; Clúa de Gonzalez, Alicia L.; Gonzalez Alarcon, Walter
Demétrio
Bibcode: 2008cosp...37..661D
Altcode: 2008cosp.meet..661D
The two Helios probes traveled at variable longitudinal and radial
separations through the inner heliosphere. They collected most valuable
high resolution plasma data for an entire solar cycle. The mission
is still so successful that no other missions will collect the same
kind of data in the next 20 years. One of the subjects studied after
the success of the Helios mission was the identification of more
than 390 shock waves driven by Interplanetary Coronal Mass Ejections
(ICMEs). Combining the data from both probes, we make a statistical
study for the extension of the shock waves in the interplanetary
medium. For longitudinal separations of 90° we found a cutoff value
at this angular separation. A shock has 50
Title: Consequences of the force-free model of magnetic clouds for
their heliospheric evolution
Authors: Leitner, M.; Farrugia, C. J.; Möstl, C.; Ogilvie, K. W.;
Galvin, A. B.; Schwenn, R.; Biernat, H. K.
Bibcode: 2007JGRA..112.6113L
Altcode: 2007JGRA..11206113L
We examine the implications of the widely used, force-free, constant-α
flux rope model of interplanetary magnetic clouds for the evolution
of these mesoscale (fraction 1 AU) structures in the heliosphere,
with special emphasis on the inner (≤1 AU) heliosphere. We employ
primarily events observed by the Helios 1 and 2 probes between 0.3 and
1 AU in the ascending and maximum phases of solar cycle 21 and by Wind
at 1 AU in a similar phase of solar activity cycle. We supplement these
data by observations from other spacecraft (e.g., Voyagers 1 and 2,
Pioneers 10 and 11, and others). Our data set consists of 130 events. We
explore three different approaches. In the first, we work with ensemble
averages, binning the results into radial segments of width 0.1 AU in
the range 0.3 ≤ rh ≤ 1 AU. Doing this, we find that in
the inner heliosphere the modeled average central axial field strength,
<B0>, varies with heliospheric distance rh
as <B0> [nT] = 18.1 · rh-1.64
[AU], and the average diameter increases quasi-linearly as <D>
[AU] = 0.23 rh1.14. The orientation of the axis
of the underlying magnetic flux tube in our data set is generally found
to lie along the east-west direction and in the ecliptic plane at all
values of rh, but there is considerable scatter about these
average directions. In the second, we monitor the evolution of magnetic
clouds in snapshot fashion, using seven spacecraft alignments. The
results are in broad agreement with the statistics reported under
step 1. In the final approach, we obtain the functional dependence
of B0 and D predicted by an analytic expression for a
freely expanding Lundquist flux tube. We find D to vary linearly with
rh, broadly similar to that obtained under approach 1. The
maximum field strength scales as rh-2 compared to
a rh-1.3 dependence obtained from statistics. We
compare our findings with those of Bothmer and Schwenn (1998), who used
a different methodology. The results obtained form a good background
to the forthcoming Solar Terrestrial Relations Observatory (STEREO) and
Sentinels missions and to multispacecraft studies of magnetic clouds.
Title: Study of a Solar Streamer on March 1998 using LASCO-C1
Spectral Data
Authors: Mierla, M.; Schwenn, R.; Teriaca, L.; Stenborg, G.;
Podlipnik, B.
Bibcode: 2007AIPC..895...75M
Altcode:
The slow solar wind is supposed to originate from coronal regions
associated with streamers. It is not clear yet how the closed magnetic
field structures of streamers are opening up in order to release
the plasma. An analysis of this subject, particularly of a streamer
on March 1998, is done using LASCO-C1 spectral data. LASCO-C1 is
an internally occulted coronagraph on the SOHO spacecraft. It has
a tunable Fabry-Perot interferometer which allows taking spectral
scans of selected coronal emission lines. From measured line profiles
we deduced physical quantities like temperature and flow velocities
along the line of sight. This way, we obtained information on the flow
pattern in the low corona.
Title: Solar Dynamics and Its Effects on the Heliosphere and Earth
Authors: Baker, D. N.; Klecker, B.; Schwartz, S. J.; Schwenn, R.;
von Steiger, R.
Bibcode: 2007sdeh.book.....B
Altcode:
No abstract at ADS
Title: The dynamics of the minimum solar corona during the period
August October 1996
Authors: Mierla, M.; Schwenn, R.; Teriaca, L.; Stenborg, G.;
Podlipnik, B.
Bibcode: 2007AdSpR..40.1049M
Altcode:
The paper presents the dynamics of the solar corona at the minimum
phase of the solar cycle (period August-October 1996), as inferred
from LASCO-C1 spectral data. LASCO-C1 is an internally occulted
coronagraph aboard the SOHO spacecraft. It has a tunable Fabry-Pérot
interferometer which allows taking spectral scans of selected coronal
emission lines. From measured line profiles we deduced physical
quantities such as temperature and flow velocities along the line of
sight. This way, we obtained information on the flow pattern in the
low corona (1.1-1.6 solar radii).
Title: Solar Wind Sources and Their Variations over the Solar Cycle
Authors: Schwenn, R.
Bibcode: 2007sdeh.book...51S
Altcode:
No abstract at ADS
Title: LASCO-C1 Spectral Analysis of Flows in the Inner Corona
Authors: Mierla, Marilena; Schwenn, Rainer; Teriaca, Luca; Stenborg,
Guillermo; Podlipnik, Borut
Bibcode: 2007RoAJ...17..167M
Altcode:
No abstract at ADS
Title: Coronal Mass Ejections
Authors: Kunow, H.; Crooker, N. U.; Linker, J. A.; Schwenn, R.;
von Steiger, R.
Bibcode: 2007cme..conf.....K
Altcode:
No abstract at ADS
Title: Petschek-type magnetic reconnection exhausts in the solar
wind well inside 1 AU: Helios
Authors: Eriksson, S.; Gosling, J. T.; Schwenn, R.
Bibcode: 2006AGUFMSM41A1437E
Altcode:
Petschek-type reconnection exhausts can be recognized in solar
wind plasma and magnetic field data as accelerated or decelerated
plasma flows confined to magnetic field reversal regions. Using that
characteristic signature, we have identified 28 reconnection exhausts
in the Helios 1 and 2 data, thus extending observations of exhausts
associated with local, quasi-stationary reconnection in the solar
wind inward to heliocentric distances of 0.31 AU. Most of the exhaust
jets identified in the Helios data had the same general physical
character as solar wind exhausts observed at greater heliocentric
distances and latitudes by ACE, Wind, and Ulysses. The magnitude of
the velocity change from outside to inside an exhaust was generally
comparable to, but somewhat less than (by a factor of 0.75 on average),
the inflow Alfven speed. In a few of the Helios events plasma number
densities within the exhausts were intermediate to densities observed
immediately outside, indicating that transitions from outside to inside
the exhausts were not always slow-mode-like on both sides. We have
identified pairs of closely spaced, but independent, reconnection
exhausts bounding regions where the heliospheric magnetic field
folded back toward the Sun. We find that plasma and magnetic field
conditions in the high-speed wind from coronal holes are not generally
favorable for sustained magnetic reconnection and for the formation
and propagation of Petschek-type exhausts. Finally, we have not yet
identified reconnection events common to both spacecraft, partly
because of a relative lack of times when high data rate observations
were available from both spacecraft.
Title: Petschek-type magnetic reconnection exhausts in the solar
wind well inside 1 AU: Helios
Authors: Gosling, J. T.; Eriksson, S.; Schwenn, R.
Bibcode: 2006JGRA..11110102G
Altcode:
Petschek-type reconnection exhausts can be recognized in solar
wind plasma and magnetic field data as accelerated or decelerated
plasma flows confined to magnetic field reversal regions. Using that
characteristic signature, we have identified 28 reconnection exhausts
in the Helios 1 and 2 data, thus extending observations of exhausts
associated with local, quasi-stationary reconnection in the solar wind
inward to heliocentric distances of 0.31 AU. Most of the exhaust jets
identified in the Helios data had the same general physical character
as solar wind exhausts observed at greater heliocentric distances and
latitudes by ACE, Wind, and Ulysses. The magnitude of the velocity
changes from outside to inside the exhausts was generally comparable
to, but somewhat less than (by a factor of 0.75 on average), the
inflow Alfvén speeds. In a few of the Helios events, plasma number
densities within the exhausts were intermediate to densities observed
immediately outside, indicating that transitions from outside to inside
the exhausts were not always slow-mode-like on both sides. We have
identified pairs of closely spaced, but independent, reconnection
exhausts bounding regions where the heliospheric magnetic field
folded back toward the Sun. We find that plasma and magnetic field
conditions in the high-speed wind from coronal holes are not generally
favorable for sustained magnetic reconnection and for the formation
and propagation of Petschek-type exhausts. Finally, we have not yet
identified reconnection events common to both spacecraft, partially
because of a relative lack of times when high data rate observations
were available from both spacecraft.
Title: Space Weather: The Solar Perspective
Authors: Schwenn, Rainer
Bibcode: 2006LRSP....3....2S
Altcode:
The term space weather refers to conditions on the Sun and in
the solar wind, magnetosphere, ionosphere, and thermosphere that
can influence the performance and reliability of space-borne and
ground-based technological systems and that can affect human life and
health. Our modern hi-tech society has become increasingly vulnerable
to disturbances from outside the Earth system, in particular to
those initiated by explosive events on the Sun: Flares release
flashes of radiation that can heat up the terrestrial atmosphere
such that satellites are slowed down and drop into lower orbits,
solar energetic particles accelerated to near-relativistic energies
may endanger astronauts traveling through interplanetary space, and
coronal mass ejections are gigantic clouds of ionized gas ejected
into interplanetary space that after a few hours or days may hit the
Earth and cause geomagnetic storms. In this review, I describe the
several chains of actions originating in our parent star, the Sun,
that affect Earth, with particular attention to the solar phenomena
and the subsequent effects in interplanetary space.
Title: Solar Wind Sources and Their Variations Over the Solar Cycle
Authors: Schwenn, R.
Bibcode: 2006SSRv..124...51S
Altcode: 2007SSRv..tmp...50S
In this paper I will briefly summarize the present status of our
knowledge on the four different sorts of solar wind, their sources
and their short- and long-term variations. First: the fast solar wind
in high-speed streams that emerges from coronal hole regions. Second:
the slow solar wind emerging from the non-active Sun near the global
heliospheric current sheet above helmet streamers and underlying active
regions. Third: the slow solar wind filling most of the heliosphere
during high solar activity, emerging above active regions in a highly
turbulent state, and fourth: the plasma expelled from the Sun during
coronal mass ejections. The coronal sources of these different flows
vary dramatically with the solar activity cycle.
Title: Foreword
Authors: Baker, D. N.; Klecker, B.; Schwartz, S. J.; Schwenn, R.;
von Steiger, R.
Bibcode: 2006SSRv..124D...7B
Altcode:
The topic of Solar Dynamics and its Effects on the Heliosphere and
Earth was addressed with a workshop at the International Space Science
Institute, under the auspices of the International Living with a Star
program, held in April 2005. It started out with an assessment and
description of the reasons for solar dynamics and how it couples into
the heliosphere. The three subsequent sections were each devoted to
following one chain of events from the Sun all the way to the Earth's
magnetosphere and ionosphere: The normal solar wind chain, the chain
associated with coronal mass ejections, and the solar energetic
particles chain. The final section was devoted to common physical
processes occuring both at the Sun and in the magnetosphere such as
reconnection, shock acceleration, dipolarisation of magnetic field,
and others.
Title: Observation of a bright coronal downflow by SOHO/EIT
Authors: Tripathi, D.; Solanki, S. K.; Schwenn, R.; Bothmer, V.;
Mierla, M.; Stenborg, G.
Bibcode: 2006A&A...449..369T
Altcode:
A distinct coronal downflow has been discovered in the course of a
prominence eruption associated coronal mass ejection (CME) imaged by
EIT (Extreme ultraviolet Imaging Telescope) and LASCO (Large Angle
Spectrometric Coronagraph) on board SOHO (Solar and Heliospheric
Observatory) on 5-Mar.-2000. Evolution of the prominences seen by EIT
was tracked into the LASCO/C2 and C3 field-of-view where they developed
as the core of a typical three-part CME. In contrast to the inflow
structures reported earlier in the literatures, which were dark and
were interpreted as plasma voids moving down, the downflow reported
here was bright. The downflow, which was only seen in EIT FOV had an
onset time that coincided with the deceleration phase of the core
of the CME. The downflow showed a rapid acceleration followed by a
strong deceleration. The downflow followed a curved path which may be
explained by material following the apex of a contracting magnetic loop
sliding down along other field lines, although other explanations are
also possible. Irrespective of the detailed geometry, this observation
provides support for the pinching off of the field lines drawn-out by
the erupting prominences and the contraction of the arcade formed by
the reconnection.
Title: CME Disturbance Forecasting
Authors: Siscoe, G.; Schwenn, R.
Bibcode: 2006SSRv..123..453S
Altcode: 2006SSRv..tmp...71S
CME disturbances at Earth arise from the sheath that arrives in front
of the ICME and from the ICME itself. The geoeffective environment is
qualitatively different in the sheath than within the ICME. Consequently
two types of forecast procedures using solar observations of phenomena
associated with the release of the CME as input parameters have been
developed to treat the two types of environment. This chapter surveys
efforts that have resulted in implementable (at least in principle)
forecast algorithms for sheath and ICME disturbances and discusses
uncertainties associated with both.
Title: Foreword
Authors: Kunow, H.; Crooker, N. U.; Linker, J. A.; Schwenn, R.;
von Steiger, R.
Bibcode: 2006SSRv..123....1K
Altcode: 2006SSRv..tmp...62K
No abstract at ADS
Title: Coronal Observations of CMEs. Report of Working Group A
Authors: Schwenn, R.; Raymond, J. C.; Alexander, D.; Ciaravella, A.;
Gopalswamy, N.; Howard, R.; Hudson, H.; Kaufmann, P.; Klassen, A.;
Maia, D.; Munoz-Martinez, G.; Pick, M.; Reiner, M.; Srivastava, N.;
Tripathi, D.; Vourlidas, A.; Wang, Y. -M.; Zhang, J.
Bibcode: 2006SSRv..123..127S
Altcode: 2006SSRv..tmp...58S
CMEs have been observed for over 30 years with a wide variety of
instruments. It is now possible to derive detailed and quantitative
information on CME morphology, velocity, acceleration and mass. Flares
associated with CMEs are observed in X-rays, and several different
radio signatures are also seen. Optical and UV spectra of CMEs both on
the disk and at the limb provide velocities along the line of sight
and diagnostics for temperature, density and composition. From the
vast quantity of data we attempt to synthesize the current state of
knowledge of the properties of CMEs, along with some specific observed
characteristics that illuminate the physical processes occurring during
CME eruption. These include the common three-part structures of CMEs,
which is generally attributed to compressed material at the leading
edge, a low-density magnetic bubble and dense prominence gas. Signatures
of shock waves are seen, but the location of these shocks relative
to the other structures and the occurrence rate at the heights where
Solar Energetic Particles are produced remains controversial. The
relationships among CMEs, Moreton waves, EIT waves, and EUV dimming
are also cloudy. The close connection between CMEs and flares suggests
that magnetic reconnection plays an important role in CME eruption
and evolution. We discuss the evidence for reconnection in current
sheets from white-light, X-ray, radio and UV observations. Finally, we
summarize the requirements for future instrumentation that might answer
the outstanding questions and the opportunities that new space-based
and ground-based observatories will provide in the future.
Title: Coronal Mass Ejections
Authors: Kunow, H.; Crooker, N. U.; Linker, J. A.; Schwenn, R.;
von Steiger, R.
Bibcode: 2006cme..book.....K
Altcode:
No abstract at ADS
Title: CME Disturbance Forecasting
Authors: Siscoe, G.; Schwenn, R.
Bibcode: 2006cme..book..453S
Altcode:
CME disturbances at Earth arise from the sheath that arrives in front
of the ICME and from the ICME itself. The geoeffective environment is
qualitatively different in the sheath than within the ICME. Consequently
two types of forecast procedures using solar observations of phenomena
associated with the release of the CME as input parameters have been
developed to treat the two types of environment. This chapter surveys
efforts that have resulted in implementable (at least in principle)
forecast algorithms for sheath and ICME disturbances and discusses
uncertainties associated with both.
Title: Coronal Observations of CMEs
Authors: Schwenn, R.; Raymond, J. C.; Alexander, D.; Ciaravella, A.;
Gopalswamy, N.; Howard, R.; Hudson, H.; Kaufmann, P.; Klassen, A.;
Maia, D.; Munoz-Martinez, G.; Pick, M.; Reiner, M.; Srivastava, N.;
Tripathi, D.; Vourlidas, A.; Wang, Y. -M.; Zhang, J.
Bibcode: 2006cme..book..127S
Altcode:
CMEs have been observed for over 30 years with a wide variety of
instruments. It is now possible to derive detailed and quantitative
information on CME morphology, velocity, acceleration and mass. Flares
associated with CMEs are observed in X-rays, and several different
radio signatures are also seen. Optical and UV spectra of CMEs both on
the disk and at the limb provide velocities along the line of sight
and diagnostics for temperature, density and composition. From the
vast quantity of data we attempt to synthesize the current state of
knowledge of the properties of CMEs, along with some specific observed
characteristics that illuminate the physical processes occurring during
CME eruption. These include the common three-part structures of CMEs,
which is generally attributed to compressed material at the leading
edge, a low-density magnetic bubble and dense prominence gas. Signatures
of shock waves are seen, but the location of these shocks relative
to the other structures and the occurrence rate at the heights where
Solar Energetic Particles are produced remains controversial. The
relationships among CMEs, Moreton waves, EIT waves, and EUV dimming
are also cloudy. The close connection between CMEs and flares suggests
that magnetic reconnection plays an important role in CME eruption
and evolution. We discuss the evidence for reconnection in current
sheets from white-light, X-ray, radio and UV observations. Finally, we
summarize the requirements for future instrumentation that might answer
the outstanding questions and the opportunities that new space-based
and ground-based observatories will provide in the future.
Title: A study of the CME geometry
Authors: Dal Lago, A.; Schwenn, R.; Gonzalez, W. D.
Bibcode: 2006cosp...36.1157D
Altcode: 2006cosp.meet.1157D
Coronal mass ejections are the main source of space weather disturbances
thus understanding their evolution is a crussial point for forecasting
their impacts at earth Near the sun 3 dimentional observations are not
available thus the 3D geometry of CMEs are still under debate Based on
2D observational parameters we investigate the possible 3D geometry
of coronal mass ejections These parameters are the perpendicular
expansion and the radial expansion Three cone models are annalized
and their evolution studied If the geometry of CMEs is known and
if it is possible to have a similar model for all CMEs this can be
used to correct and interpret the meaning of the plane-of-sky speeds
measured by coronagraph like SOHO LASCO This knowledge would improve
the forecasting of CME arrival time at earth models
Title: Radial Speed for Slow CMEs
Authors: Munoz, G.; Schwenn, R.
Bibcode: 2006cosp...36.3369M
Altcode: 2006cosp.meet.3369M
Coronal Mass Ejections CMEs have been registered since 1996 with The
Solar and Heliospheric observatory SoHO The diversity and sensitivity
of the instruments in SoHO have provided huge quantity of data for
CMEs and related phenomena Dynamical parameters of CMEs are evaluated
and published in the SoHO LASCO CME Catalogue A broad range of values
for the plane of the sky speed of CMEs results from these observations
in particular extremely slow events seem to be possible sim 40 km s
In this work we analyzed slow CMEs speed 400 km s for events during
2003 and 2004 using the expansion speed to determine the radial speed
We evaluated the projection effects on the determination of speed and
acceleration for these events The possible relation of these CMEs to
flares and prominences is studied as well in order to present a wide
panorama for slow CMEs
Title: KuaFu Mission: The scientific payload of KuaFu-B
Authors: Wang, J. -S.; Tu, C. -Y.; Schwenn, R.; Donovan, E.; Xia,
L. -D.; Zhang, Y. -W.; Kuafu Team
Bibcode: 2006cosp...36.2742W
Altcode: 2006cosp.meet.2742W
The KuaFu mission would consist an L1 satellite KuaFu-A and a polar
satellite pair KuaFu B1 B2 The mission is designed to explore the whole
cause-and-result chain in solar-terrestrial space The two KuaFu-Bs will
have the same payload sets and fly on the same polar orbit plane but
with a phase difference of half period The preferred perigee is 1 8
Re and the apogee is 7 Re This orbit design will support a 24 times 7
full-covered observation on the northern auroral oval by the onboard
aurora cameras The suggested payloads consist of a Far Ultraviolet
Auroral Monitoring Camera UVAMC a FUV Imaging Spectrometer FUVSI a Wide
Field Auroral Imager WFAI a Fluxgate Magnetometer FGM a High Energy
Charged Particle Experiment HECPE an Imaging energetic electron and
proton instrument IEPS a Neutral Atom Imager on KuaFu NAIK a Fast
Plasma Pitch Angle Instrument FPI an Ion Mass Spectrometer IMS FPI
and IMS were suggested to merge and a Tri-Band Beacon TBB
Title: KuaFu Mission: The Scientific Payload of KuaFu-A
Authors: Xia, L. -D.; Tu, C. -Y.; Schwenn, R.; Donovan, E.; Wang,
J. -S.; Zhang, Y. -W.
Bibcode: 2006cosp...36.2677X
Altcode: 2006cosp.meet.2677X
The KuaFu mission would consist of three satellites KuaFu-A and
KuaFu B1 and B2 KuaFu-A would be operated in the Sun-Earth L1 region
while the satellite pair KuaFu-B1 and -B2 fly on identical Earth polar
orbits The mission is designed to explore solar disturbances and their
ultimate effects on the near-Earth space including solar flares CMEs
interplanetary clouds shock waves and their respective geo-effects such
as magnetospheric substorms magnetic storms and auroral activities The
launch of KuaFu is suggested in 2012 KuaFu-A would be instrumented to
continuously observe the solar disk in EUV FUV emission to register
Coronal Mass Ejections CMEs in white light and Lyman-alpha radiation
to trace CME propagation by radio wave measurements and to measure
the local solar wind plasma and magnetic field and solar energetic
particles Besides measurements of hard X-ray and Gamma-ray spectrum
and solar irradiance would also be carried out on KuaFu-A In this
poster we outline the payload of KuaFu-A and its scientific and space
weather objectives
Title: Why KuaFu? The missing links in understanding Sun-Earth
connections
Authors: Schwenn, R.
Bibcode: 2006cosp...36.1962S
Altcode: 2006cosp.meet.1962S
Despite the enormous progress in recent years there is still a lack
in understanding of several key links in the long chain of actions
and reactions that connects our Earth to its parent star the Sun They
concern 1 the origin of disturbances at the Sun flares and CMEs and
our inability to forecast them 2 the propagation of their effects to
the Earth 3 their capability of entering the Earth system and 4 the
magnitude of the terrestrial effects I will review these processes
and point out where the KuaFu mission is supposed to achieve better
understanding in context with the Living With a Star program
Title: An introduction to KuaFu project (scientific goals, scientific
payloads, historical events, present status and perspectives)
Authors: Tu, C. -Y.; Schwenn, R.; Donovan, E.; Wang, J. -S.; Xia,
L. -D.; Zhang, Y. -W.; Kuafu Study Team
Bibcode: 2006cosp...36..984T
Altcode: 2006cosp.meet..984T
KuaFu mission is composed of three spacecraft KuaFu-A and KuaFu B1 and
B2 KuaFu-A will be located at the L1 Lagrangian point The satellite
pair KuaFu-B1 B2 will fly on the same polar Earth orbit but with
a phase difference of half-period KuaFu-A will be instrumented to
continuously observe the solar disk in EUV including Lyman alpha
emission to register Coronal Mass Ejections CMEs in white light
and Lyman alpha radiation to trace CME propagation by radio wave
measurements and to measure the local solar wind plasma and magnetic
field and solar energetic particles Another remote sensing instrument
will observe the hard X-ray and Gamma-ray spectrum KuaFu-B1 and -B2
will carry out continuous 24 hours a day observation of the northern
hemisphere auroral oval and the ring current as well as systematic
conjugate aurora observations KuaFu-B will also carry a limited suite
of in situ instruments including a fluxgate magnetometer and charged
particle detectors The KuaFu project is now a space science mission
selected by China National Space Administration CNSA The Comprehensive
Study project already began in which careful review of scientific
payload initial design of spacecraft platforms launch tracking and
control and data transferring will be addressed The KuaFu mission may
start at the next solar maximum launch in 2012 hopefully and with an
initial mission lifetime of two to three years The KuaFu mission will
be an essential element of the ILWS program The scientific goal is to
study globally the Sun-Earth complex system The mission is
Title: In-situ data from Helios 1 and 2 on the web in preparation
for STEREO
Authors: Schroeder, P.; Luhmann, J.; Schwenn, R.
Bibcode: 2006cosp...36.2112S
Altcode: 2006cosp.meet.2112S
Although flown in the 1970 s the Helios mission continues to provide
a unique science opportunity Not only were the twin Helios spacecraft
s orbits unusual but the in-situ instruments were capable of probing
heliospheric structures in a manner similar to the upcoming STEREO
mission For the first time we make the electron data from the Helios
Plasma Experiment readily available to the public We integrate this
electron data with data already available for protons SEPs and the
magnetic field from the Helios mission as well as in-situ data from the
IMP-8 and ISEE-3 missions into a single user-customizable browser and
make these data available for download and local analysis in a variety
of formats Not only will analysis of the full Helios data set give new
insights into the analysis of multi-point in-situ data in preparation
for missions like STEREO but the full Helios data set provides an
unprecedented opportunity to explore regions of the heliosphere that
remain largely unexplored
Title: LASCO-C1 Spectral Data Analysis of the Slow Solar Wind
Authors: Mierla, M.; Schwenn, R.; Teriaca, L.; Podlipnik, B.;
Stenborg, G.
Bibcode: 2005ESASP.600E..45M
Altcode: 2005dysu.confE..45M; 2005ESPM...11...45M
No abstract at ADS
Title: The Relative Distribution of the Magnetic and Plasma Kinetic
Energy Densities in the Inner Heliosphere (<1 AU)
Authors: Leitner, M.; Farrygia, C. J.; Osherovich, V. A.; Biernat,
H. K.; Ogilvie, K. W.; Schwenn, R.; Torbert, R.
Bibcode: 2005ESASP.592..743L
Altcode: 2005ESASP.592E.151L; 2005soho...16E.151L
No abstract at ADS
Title: On the Thickness of the Sheath of Magnetic Clouds in the
Inner Heliosphere: A Helios Wind Investigation
Authors: Leitner, M.; Farrugia, C. J.; Biernat, H. K.; Torbert, R.;
Erkaev, N. V.; Ogilvie, K. W.; Schwenn, R.
Bibcode: 2005ESASP.592..739L
Altcode: 2005soho...16E.150L; 2005ESASP.592E.150L
No abstract at ADS
Title: Evolution of Interplanetary Magnetic Clouds from 0.3 AU to
1 AU: A Joint Helios-Wind Investigation
Authors: Farrugia, C. J.; Leiter, M.; Biernat, H. K.; Schwenn, R.;
Ogilvie, K. W.; Matsuil, H.; Kucharek, H.; Jordanova, V. K.; Lepping,
R. P.
Bibcode: 2005ESASP.592..723F
Altcode: 2005ESASP.592E.146F; 2005soho...16E.146F
No abstract at ADS
Title: The association of coronal mass ejections with their effects
near the Earth
Authors: Schwenn, R.; dal Lago, A.; Huttunen, E.; Gonzalez, W. D.
Bibcode: 2005AnGeo..23.1033S
Altcode:
To this day, the prediction of space weather effects near the Earth
suffers from a fundamental problem: The radial propagation speed of
"halo" CMEs (i.e. CMEs pointed along the Sun-Earth-line that are known
to be the main drivers of space weather disturbances) towards the Earth
cannot be measured directly because of the unfavorable geometry. From
inspecting many limb CMEs observed by the LASCO coronagraphs on SOHO
we found that there is usually a good correlation between the radial
speed and the lateral expansion speed Vexp of CME clouds. This latter
quantity can also be determined for earthward-pointed halo CMEs. Thus,
Vexp may serve as a proxy for the otherwise inaccessible radial speed
of halo CMEs. We studied this connection using data from both ends:
solar data and interplanetary data obtained near the Earth, for a period
from January 1997 to 15 April 2001. The data were primarily provided
by the LASCO coronagraphs, plus additional information from the EIT
instrument on SOHO. Solar wind data from the plasma instruments on
the SOHO, ACE and Wind spacecraft were used to identify the arrivals
of ICME signatures. Here, we use "ICME" as a generic term for all
CME effects in interplanetary space, thus comprising not only ejecta
themselves but also shocks as well. Among 181 front side or limb full
or partial halo CMEs recorded by LASCO, on the one hand, and 187
ICME events registered near the Earth, on the other hand, we found
91 cases where CMEs were uniquely associated with ICME signatures in
front of the Earth. Eighty ICMEs were associated with a shock, and
for 75 of them both the halo expansion speed Vexp and the travel time
Ttr of the shock could be determined. The function Ttr=203-20.77*ln
(Vexp fits the data best. This empirical formula can be used for
predicting further ICME arrivals, with a 95% error margin of about
one day. Note, though, that in 15% of comparable cases, a full or
partial halo CME does not cause any ICME signature at Earth at all;
every fourth partial halo CME and every sixth limb halo CME does not
hit the Earth (false alarms). Furthermore, every fifth transient shock
or ICME or isolated geomagnetic storm is not caused by an identifiable
partial or full halo CME on the front side (missing alarms).
Title: Properties and geoeffectiveness of magnetic clouds in the
rising, maximum and early declining phases of solar cycle 23
Authors: Huttunen, K. E. J.; Schwenn, R.; Bothmer, V.; Koskinen,
H. E. J.
Bibcode: 2005AnGeo..23..625H
Altcode:
The magnetic structure and geomagnetic response of 73 magnetic clouds
(MC) observed by the WIND and ACE satellites in solar cycle 23 are
examined. The results have been compared with the surveys from the
previous solar cycles. The preselected candidate MC events were
investigated using the minimum variance analysis to determine if
they have a flux-rope structure and to obtain the estimation for the
axial orientation (θC, φC). Depending on the calculated inclination
relative to the ecliptic we divided MCs into "bipolar" (θC<45°)
and "unipolar" (θC>45°). The number of observed MCs was largest in
the early rising phase, although the halo CME rate was still low. It
is likely that near solar maximum we did not identify all MCs at 1AU,
as they were crossed far from the axis or they had interacted strongly
with the ambient solar wind or with other CMEs. The occurrence rate of
MCs at 1AU is also modified by the migration of the filament sites on
the Sun towards the poles near solar maximum and by the deflection of
CMEs towards the equator due to the fast solar wind flow from large
polar coronal holes near solar minimum. In the rising phase nearly
all bipolar MCs were associated with the rotation of the magnetic
field from the south at the leading edge to the north at the trailing
edge. The results for solar cycles 21-22 showed that the direction
of the magnetic field in the leading portion of the MC starts to
reverse at solar maximum. At solar maximum and in the declining
phase (2000-2003) we observed several MCs with the rotation from
the north to the south. We observed unipolar (i.e. highly inclined)
MCs frequently during the whole investigated period. For solar cycles
21-22 the majority of MCs identified in the rising phase were bipolar
while in the declining phase most MCs were unipolar. The geomagnetic
response of a given MC depends greatly on its magnetic structure and the
orientation of the sheath fields. For each event we distinguished the
effect of the sheath fields and the MC fields. All unipolar MCs with
magnetic field southward at the axis were geoeffective (Dst<-50nT)
while those with the field pointing northward did not cause magnetic
storms at all. About half of the all identified MCs were not geoffective
or the sheath fields preceding the MC caused the storm. MCs caused
more intense magnetic storms (Dst<-100nT) than moderate magnetic
storms (-50nT ≥Dst≥-100nT). <p style="line-height: 20px;">
</td> </tr>
Title: What have we learned with SOHO?
Authors: Schwenn, Rainer
Bibcode: 2005IAUS..226...19S
Altcode:
The Solar and Heliospheric Observatory (SOHO), a space mission of
international collaboration between ESA and NASA, has been operating
almost continuosly since early 1996. The Sun and the heliosphere went
through both: the minimum and maxumum of solar activity in 1996 and
2000, respectively. The perfectly working set of modern solar telescopes
and insitu instrumentation has been producing an unprecedented set of
most valuable observational data that are almost immediately available
to the public via the Internet. A wealth of new results has been
published in innumerable papers. For CME research in particular,
SOHO has started a new era. CME evolution can now be studied from
their initiation up to the arrival of the ejecta clouds at 1 AU. For
the first time, helioseismological observations reveal flow vortices
underneath sunspots, i.e., activity centers that are involved in
subsequebt eruptions. Combined EUV disk observations and coronagraph
images allow to differentiate between CMEs pointed towards to or away
from the Earth. Thus, space weather predictions have achieved a new
quality. The occurrence of "EIT waves" at CME onset was discovered, the
internal structure of CMEs (including "disconnection", magnetic topology
and helicity, etc.) was made visible, statitics about CME properties and
their change with solar activity were refined. Spectacular CME images
and animations have been attracting the public to an unexpected extent,
to the benefit of solar research in general.
Title: SoHO/EIT Observation of a Coronal Inflow
Authors: Tripathi, D.; Bothmer, V.; Solanki, S. K.; Schwenn, R.;
Mierla, M.; Stenborg, G.
Bibcode: 2005IAUS..226..133T
Altcode:
A distinct coronal inflow has been discovered after ∼90 min
of prominence eruption associated coronal mass ejection (CME) on
05-Mar-2000 by EIT (Extreme ultraviolet Imaging Telescope) aboard SoHO
(Solar and Heliospheric Observatory). Evolution of the prominence seen
by EIT was tracked into the LASCO/C2 and C3 field-of-view (FOV; 4-10
R⊙) where it developed as the core of a typical three-part
CME. The speed of the inflow, which was only seen in EIT FOV, was 70-80
km/s at a height between 1.5-1.2 R⊙ coinciding with the
deceleration phase of the core of the CME in LASCO/C2. In contrast to
dark inflow structures observed earlier and interpreted as plasma void
moving down, the inflow reported here was bright. The inflow showed a
constant deceleration and followed a curved path suggesting the apex
of a contracting magnetic loop sliding down along other field lines.
Title: Dynamics of the Solar Corona Using LASCO-C1 Spectral Data
Authors: Mierla, Marilena; Schwenn, Rainer; Teriaca, Luca; Stenborg,
Guillermo; Podlipnik, Borut
Bibcode: 2005RoAJ...15..137M
Altcode:
No abstract at ADS
Title: Using LASCO-C1 spectroscopy for coronal diagnostics
Authors: Mierla, M.; Schwenn, R.; Teriaca, L.; Stenborg, G.;
Podlipnik, B.
Bibcode: 2005AdSpR..35.2199M
Altcode:
The LASCO-C1 telescope was designed to perform spectral analysis of
coronal structures by means of a tunable Fabry-Pérot interferometer
acquiring images at different wavelengths. Results from spectral
scans of the Fe XIV 5303 Å green coronal emission line are
presented. Physical quantities like the ion temperature (line widths),
and the flow velocity along the line of sight (Doppler shifts) are
obtained over the entire corona.
Title: Preparing for STEREO - Revisit Helios!
Authors: Schwenn, R.
Bibcode: 2004AGUFMSH21D..02S
Altcode:
Exactly 30 years ago, the first Helios solar probe was launched into
an elliptical heliocentric orbit, with a perihelion of 0.3 AU. It had
a set of then modern particle and field instruments on board, but no
imagers. One year later, an almost identical probe was put into a very
similar orbit, approaching the Sun even a bit closer. For most of their
common lifetime of 4 years, the two probes were separated in longitude
by no more than about 30 degrees. Further, due to their special
orbits, they spent many months above the Sun's limb (as seen from
Earth). In conjunction with the Earth-orbiting IMP 7&8 satellites
and the Voyager 1&2, and the Pioneer 10&11 space probes, real
multipoint studies covering large parts of the heliosphere could be
performed successfully for the first time. The Helios mission resembled
the upcoming STEREO mission in several respects and was indeed of good
use for defining the STEREO science goals. For example, Helios could
reveal details about the longitudinal and latitudinal solar wind stream
structure, it allowed unique associations between limb CMEs and their
radial propagation towards an in-situ observer, and the propagation
of solar energetic particles could be studied. However, since then our
understanding of the heliosphere has improved considerably, thanks to
recent space missions (Ulysses, Yohkoh, SOHO, Wind, ACE) and to more
and more refined theoretical models. In view of these new results,
it appears worthwhile to revisit the huge Helios data sets since they
certainly keep hiding some answers that future observations from STEREO
might benefit from.
Title: The phase curve of cometary dust: Observations of comet
96P/Machholz 1 at large phase angle with the SOHO LASCO C3 coronagraph
Authors: Grynko, Ye.; Jockers, K.; Schwenn, R.
Bibcode: 2004A&A...427..755G
Altcode:
We have analyzed brightness and polarization data of comet 96P/Machholz,
obtained with the SOHO-LASCO C3 coronagraph at phase angles up to
167° and 157°, respectively. The polarization
data are characteristic of a typical dusty comet. Within error limits
the corresponding trigonometric fit describes the new data measured at
larger phase angles as well as those of the previously known range. In
the phase angle range from 110° to 167°
the brightness increases almost linearly by about two orders of
magnitude. The gradient is independent of wavelength. From the
absence of a diffraction spike we conclude that the grains contributing
significantly to the scattered light must have a size parameter x = 2π
r/λ ≥20, i.e. have a radius larger than 1 μm. Fits of the data with
Mie calculations of particles having a power law distribution of power
index ≈ 2.5 provide a best fit refractive index m = 1.2 + i0.004. In
the framework of effective medium theory and on the assumption of
a particle porosity P= 0.5 this leads to a complex refractive index
of the porous medium m = 1.43 + i0.009. A higher refractive index is
possible for more porous grains with very low absorption. The large
particle sizes are in qualitative agreement with findings derived
from the analysis of the motion of cometary dust under solar radiation
pressure (Fulle and coworkers, see \cite{fulle}; \cite{jockers} 1997)
and with the in-situ measurements of the dust of Halley's comet.
Title: Comparison Between Halo cme Expansion Speeds Observed on the
Sun, the Related Shock Transit Speeds to Earth and Corresponding
Ejecta Speeds at 1 au
Authors: Dal Lago, A.; Vieira, L. E. A.; Echer, E.; Gonzalez, W. D.;
de Gonzalez, A. L. C.; Guarnieri, F. L.; Schuch, N. J.; Schwenn, R.
Bibcode: 2004SoPh..222..323D
Altcode:
We have compared characteristics of 38 halo coronal mass ejections
observed on the Sun by the Large Angle and Spectrometric Coronagraph
onboard SOHO with their corresponding counterparts observed near Earth
by the magnetic field and plasma instruments onboard the ACE, WIND and
SOHO satellites, in the period from January 1997 to April 2001. We only
have selected events that have some associated interplanetary ejecta
structure at 1 AU and we have compared the lateral expansion speeds
of these halo CMEs and the corresponding ejecta speeds near Earth. We
found that there is a high correlation between these two speeds. The
results are very similar to the study done by Lindsay et al. (1999)
using observations made by Solwind and SMM coronagraphs, and Helios-1
and PVO plasma and interplanetary field data from the period of 1979
to 1988. Also, we reviewed the relation between the CME-related shock
transit speed to Earth and the ejecta speeds near Earth. This kind
of relation is very important to estimate ejecta speeds of events for
which no interplanetary observations are available.
Title: CMEs in the heliosphere
Authors: Schwenn, R.
Bibcode: 2004cosp...35.2442S
Altcode: 2004cosp.meet.2442S
Since their discovery in the Skylab era, almost exactly 30 years
ago, coronal mass ejections (CMEs) have been a fascinating topic in
the vast field of solar system research. Several thousands of these
spectacular bright gas clouds ejected spontaneously from the dynamic
Sun were portraied from space-borne coronagraphs (OSO-7, Skylab, P78-1,
SMM). Since 1996, a new generation of instruments on SOHO has kept
the Sun under almost continuous surveillance. Images and animations
are being made public in near real-time through the Internet and have
thus stirred wide-spread interest. Some exceptionally dramatic CMEs in
the recent past have emphasized the CMEs' key role in forming space
weather near the Earth and throughout the heliosphere. No wonder
that they have raised unprecedented attention even in the public
media. Scientific exploration of CMEs has also made major progress,
but some fundamental questions are still waiting to be answered.
Title: Plasma dynamics of a prominence associated coronal mass
ejection
Authors: Tripathi, D.; Bothmer, V.; Solanki, S. K.; Schwenn, R.;
Mierla, M.; Stenborg, G.
Bibcode: 2004IAUS..223..401T
Altcode: 2005IAUS..223..401T
An erupting prominence seen by SOHO/EIT was tracked into the field of
view of the LASCO C2 and C3 coronagraphs where it developed into the
core of a structured CME. The erupting prominence was deflected by an
angle of sim 20^{circ} towards the north pole whereas the consequent
core of the CME and it's leading edge propagated in the outer corona at
constant position angle. The prominence material underwent a constant
acceleration phase until a height of sim1.5 solar radii before it
started to decelerate up to a distance of 5.0 solar radii. An inflow
of plasma with a speed of about 70-80 km/s was discovered in the EIT
observations at a height of 1.5-1.2 solar radii in the course of the
prominence eruption, matching in time the prominence deceleration
phase. The downflowing material followed a curved path, suggestive
of the apex of a contracting magnetic loop sliding down along other
field lines.
Title: Structure of Solar Ejecta
Authors: Muñoz, G.; Cantó, J.; Lara, A.; González, R.; Schwenn, R.
Bibcode: 2004cosp...35.2642M
Altcode: 2004cosp.meet.2642M
Solar Ejecta (SE) have been of interest in the last years,
especially those which may reach Earth environment. It is possible
to observe the SE early evolution, when they are in the field of
view of coronagraphs. There are few indirect observations, as the
case of interplanetary scintillation, of SEs in the interplanetary
medium. Finally, we observe SEs in situ when they arrive at 1 AU.The SEs
structure and evolution are important to understand the origin of these
phenomena but to predict the possible effects in the space weather. It
is of general acceptance that SEs are "Erupting Flux Ropes" traveling
trough the Solar Wind. The "shapes" have been modeled as cylinders or as
"ice cream cones" in order to represent the many different projections
observed on Coronagraphs.We present a model of the SE evolution based
on purely Hydrodynamic considerations. This model reproduces in good
approximation some of the features observed in the images and in the
measures of the shocks near Earth.
Title: Exploring the global shock scenario at multiple points
between Sun and Earth: the launch of solar transients on January 1
and September 23, 1978.
Authors: Berdichevsky, Db; Reames, Dv; Wu, C. -C.; Schwenn, R.;
Lepping, Rp; MacDowall, Rj; Farrugia, Cj; Bougeret, J. -L.; Ng, C.;
Lazarus, Aj
Bibcode: 2004cosp...35.1774B
Altcode: 2004cosp.meet.1774B
We revisit the transient events of January and September 1978. In
the January event the ejecta (an interplanetary magnetic cloud, IMC)
was studied using multiple spacecraft observations [Burlaga et al.,
1981]. In the September event Reames et al., 1997 studied the spectral
characteristics of the energetic particles of this big particle
event with a driven shock passage observed at longitudes nearly 180°
apart. Here we present a combined analysis of the overall solar wind
and energetic particles (EP) features of the shock and the driver,
observed at different locations in longitude. We further evaluate the
Rankine-Hugoniot properties of the shock at the locations its passage is
observed and add modeling of the driven shock using a three dimensional
MHD code which, at this stage of the analysis, does not include the
magnetic structure of the ejecta. For the study of the shock velocity
we use remote type II radio burst observations from near Earth (the
September event), and at different longitude locations we examine:
(a) flux intensity of the energetic particles, (b) shock strength,
(c) timing of the shock structure and the driver passage at each
spacecraft to infer the possible location of the nose of the shock. A
preliminary assessment on the connection between the global nature
of the shock and the observed level of energetic particle flux will
be presented. The data sets include the kilometric radio measurements
on ISEE3, and the 3 to 80 MeV energetic proton flux data from IMP-8,
and a similar energy range from Helios at wide longitudinal locations
relative to Earth. For the solar wind parameters we use magnetic
field and plasma parameters from instruments at Helios 1, and 2,
Voyager 1 and 2, and ISEE3 and IMP-8. The data set is completed with
the Dst index (Kyoto). We acknowledge partial support from NSF and
NASA grants, and the NSSDC for on-line access to their space science
data archives. Burlaga LF, E. Sittler, F. Mariani, and R. Schwenn,
Magnetic loop behind an interplanetary shock: Voyager, Helios, and IMP-8
observations, J. Geophys. Res., 86, 6673, 1981. Reames, DV, SW Kahler,
, and CK Ng, Spatial and temporal invariance in the spectra of gradual
particles in gradual solar events, Astrophys. J., 491, 414, 1997.
Title: The association of CMEs their counterparts near the Earth
Authors: Schwenn, R.; dal Lago, A.; Huttunen, E.; Gonzalez, W.
Bibcode: 2004cosp...35.2634S
Altcode: 2004cosp.meet.2634S
The propagation speed of halo CMEs towards Earth cannot be measured
directly because of the unfavorable geometry. From inspecting many limb
CMEs observed by the LASCO coronagraphs on SOHO we found that there is
a good correlation between the radial speed and the lateral expansion
speed vexp of CME clouds. This latter quantity can also be
determined for earthward-pointed ``halo'' CMEs. Thus, the expansion
speed may serve as a proxy for the otherwise inaccessible radial speed
of halo CMEs. We studied this connection using data from both ends:
solar data and interplanetary data obtained near the Earth, for a
period from January 1997 to April 15, 2001. The data were primarily
provided by the LASCO coronagraphs, plus additional information from
the EIT instrument. Solar wind data from the plasma instruments on
the SOHO, ACE and Wind spacecraft were used to identify the arrivals
of ICME signatures. Among 163 front side or limb full or partial halo
CMEs we found 91 cases uniquely and another 48 possibly correlated
with ICME signatures right in front of the Earth, that is a total
of 85%. That also means that 15% of all these CMEs missed the Earth:
False alarms! About 25 % of all 151 detected transient shocks and 40
ICMEs without shocks were apparently not caused by an identifiable
partial or full halo on the front side: Missing alarms! For 75 out of
91 safe associations between CMEs and ICMEs we could determine both the
expansion speed Vexp near the Sun and the travel time of the
associated shock towards the Earth. An empirical formula was derived
which now allows to predict (for an isolated, undisturbed front side
halo CME) the shock/ICME arrival time at the Earth. There is a 95 %
probability that the shock will arrive within one day around that
predicted time, except if it is one of the 15 % of ICMEs that never
hit the Earth.
Title: Dynamic properties of the solar corona: SOHO/LASCO observations
Authors: Mierla, M.; Schwenn, R.; Stenborg, G.; Teriaca, L.;
Podlipnik, B.
Bibcode: 2004cosp...35.2275M
Altcode: 2004cosp.meet.2275M
With the launch of the SOHO spacecraft in December 1995, the quality of
corona observations has improved significantly. The LASCO instruments
with their field of view now extending from 1.1 Rs (C1) to 30 Rs (C3)
offer sufficient sensitivity to make an almost continuous outflow in
the streamer belt visible. We report on two different approaches to
study the plasma motion, both in the plane of the sky and along the
line of sight. 1. By means of a multi-resolution image processing
technique based on wavelet packets the boundaries and the internal
details of originally faint and diffuse structures are enhanced. This
approach allows unambiguous image interpretation and provides a means
for the quantification of stationary and dynamic coronal structures
required for conducting morphological studies. 2. The LASCO/C1 telescope
was designed to perform spectral analysis on coronal structures. The
tunable Fabry-Perot interferometer allows to obtain images at different
wavelengths. Results from spectral scans of the coronal green and
red emission lines are presented. From the line profiles physical
quantities like temperatures (from line widths), and flow velocities
(from Doppler shifts) along the line of sight are deduced.
Title: Forecasting interplanetary ejecta arrival at 1 AU
Authors: dal Lago, A.; Vieira, L. E.; Echer, E.; Gonzalez, W. D.;
Clua de Gonzalez, A. L.; Guarnieri, F. L.; Santos, J.; Schwenn, R.;
Schuch, N. J.
Bibcode: 2004cosp...35.3045D
Altcode: 2004cosp.meet.3045D
A big challenge in space weather forecasting is the prediction of
arrival of an interplanetary disturbance at earth. Many attempts
have been done, and some forecasting models have been proposed. We
focus on the subset of solar-interplanetary events which have shown
interplanetary ejecta at 1 AU. To identify interplanetary ejecta at 1 AU
we use visual inspection of the cases, based on the criterion of intense
and smooth magnetic field, observed by the Advanced Composition Explorer
(ACE). For forecasting the arrival of the interplanetary ejecta at 1
AU we used the lateral expansion speed of the coronal mass ejection,
measured approximately perpendicular to the single plane-of-sky CME
speed, as defined by Schwenn et al (2001), using observations from the
Large Angle and Spectroscopic Coronagraph (LASCO), aboard the Solar
and Heliospheric Observatory (SOHO). The data set is from January 1997
to mid April 2001, and a number of 38 LASCO CMEs were identified to
be correlated with interplanetary ejecta at 1 AU. Results indicate
that forecasting the arrival at 1 AU of the sub set of interplanetary
ejecta is very well done by LASCO CME speed observations, being much
better than the predictions for the complete set of interplanetary
disturbances, like shocks/sheath structures.
Title: Evolution of interplanetary magnetic clouds from 0.3 AU to
1 AU: A joint Helios-Wind Study
Authors: Biernat, H. K.; Farrugia, C. J.; Leitner, M.; Kucharek,
H.; Schwenn, R.; Berdichevsky, D.; Osherovich, V.; Lepping, R. P.;
Matsui, H.
Bibcode: 2003AGUFMSH42A0474B
Altcode:
A class of interplanetary configurations which interact strongly
with the Earth's magnetosphere are interplanetary magnetic clouds. A
desideratum of space weather predictions is that they be made from data
acquired by distant probes so as to guarantee as long a lead time as
possible. For this to be viable, one must have accurate knowledge of
how parameters evolve. To this end, we use observations of magnetic
cloud made by the spacecraft Wind at 1 AU, and Helios 1 & 2 between
0.3 and 1 AU. A model is constructed, regarding the magnetic cloud as
a cylindrically symmetric, force-free constant-alpha magnetic field
configuration, i.e. the cylindrically symmetric solution of ∇ B =
α B. We least--squares fit the model to the data and obtain model
parameters, e.g. the magnetic field strength on the axis of the tube,
the helicity, the orientation, the diameter, and its orientation. We
adopt two approaches: In the first we obtain statistically the way these
parameters evolve with distance from the Sun. In the second approach
we focus on line-ups of the spacecraft and determine directly how
parameters scale with distance. The two approaches are compared. This
work is supported by NASA Living with a Star under grant NAG 5-10883.
Title: Global heliospheric disturbances near 1 AU caused by the
launch of solar transients on January 1 and September 23, 1978.
Authors: Berdichevsky, D. B.; Reames, D. V.; Wu, C.; Schwenn, R.;
Lepping, R. P.; Farrugia, C. J.; MacDowall, R. J.; Bougeret, J.; Ng,
C. K.; Lazarus, A. J.; Richardson, I. G.
Bibcode: 2003AGUFMSM22A0219B
Altcode:
We revisit the transient events of January and September 1978. In
the January event the ejecta (an interplanetary magnetic cloud, IMC)
was studied using multiple spacecraft observations [Burlaga et al.,
1981]. In the September event Reames et al., 1997 studied the spectral
characteristics of the energetic particles of this big particle
event with a driven shock passage observed at longitudes nearly 180°
apart. Here we present a combined analysis of the overall solar wind
and energetic particles (EP) features of the shock and the driver,
observed at different locations in longitude. We further evaluate the
Rankine-Hugoniot properties of the shock at the locations its passage is
observed and add modeling of the driven shock using a three dimensional
MHD code which, at this stage of the analysis, does not include the
magnetic structure of the ejecta. For the study of the shock velocity
we use remote type II radio burst observations from near Earth (the
September event), and at different longitude locations we examine:
(a) flux intensity of the energetic particles, (b) shock strength,
(c) timing of the shock structure and the driver passage at each
spacecraft to infer the possible location of the nose of the shock. A
preliminary assessment on the connection between the global nature
of the shock and the observed level of energetic particle flux will
be presented. The data sets include the kilometric radio measurements
on ISEE3, and the 3 to 80 MeV energetic proton flux data from IMP-8,
and a similar energy range from Helios at wide longitudinal locations
relative to Earth. For the solar wind parameters we use magnetic field
and plasma parameters from instruments at Helios 1, and 2, and ISEE3
and IMP-8. The data set is completed with the Dst index (Kyoto). We
acknowledge partial support from NSF and NASA grants, and the NSSDC
for on-line access to their space science data archives. Burlaga
LF, E. Sittler, F. Mariani, and R. Schwenn, Magnetic loop behind
an interplanetary shock: Voyager, Helios, and IMP-8 observations,
J. Geophys. Res., 86, 6673, 1981. Reames, DV, SW Kahler,, and CK Ng,
Spatial and temporal invariance in the spectra of gradual particles
in gradual solar events, Astrophys. J., 491, 414, 1997.
Title: Long-distance Correlations of Interplanetary Parameters:
A Case Study with HELIOS
Authors: Matsui, H.; Farrugia, C. J.; Kucharek, H.; Berdichevsky, D.;
Torbert, R. B.; Jordanova, V. K.; Richardson, I. G.; Galvin, A. B.;
Lepping, R. P.; Schwenn, R.
Bibcode: 2003AIPC..679..770M
Altcode:
In recent work, promising agreement has been obtained between measured
indices of geomagnetic activity (Dst, and cross-polar cap potential)
and their predicted values using interplanetary input from probes in
the inner heliosphere (~0.7 AU) when the probe was close to, (5), and
even substantially displaced from, (4), the Earth-Sun line. Implicit in
this agreement is a good correlation of, at least, the basic temporal
profiles of the major interplanetary parameters at the two observing
sites. In this work we discuss a case study using Helios 1 and 2 data
when the spacecraft are lined - up and separated by an almost constant
radial distance of 0.2 AU. In the period studied, the interplanetary
medium consists of a fast stream being trailed by a magnetic cloud in
a slower flow. Good correlation is found between the plasma and field
observations at the two sites. Two lag times, reflecting the two types
of major structures in the interval chosen, are determined. Evidence
of evolutionary processes are briefly discussed. Spectral analysis
confirms the results obtained from time series analysis.
Title: Solar-Heliospheric-Magnetospheric Observations on March
23-April 26, 2001: Similarities to Observations in April 1979
Authors: Berdichevsky, D. B.; Farrugia, C. J.; Lepping, R. P.;
Richardson, I. G.; Galvin, A. B.; Schwenn, R.; Reames, D. V.; Ogilvie,
K. W.; Kaiser, M. L.
Bibcode: 2003AIPC..679..758B
Altcode:
We discuss the similarities and differences of two intervals of extreme
interplanetary solar wind conditions, separated almost precisely by
two solar cycles, in April 1979 and March-April 2001. The similarities
extend to various data-sets: Energetic particles, solar wind plasma
and interplanetary magnetic field. In April 1979 observations were made
by three spacecraft covering a wide longitudinal range (~ 70°) in the
heliosphere. Data are presented from Helios 2, located 28° East of the
Sun-Earth line at ~ 2/3 AU, and from near the Earth. Observations of
the 2001 interval are from Wind. We examine the geomagnetic activity
during each interval.
Title: Launch of solar coronal mass ejections and submillimeter
pulse bursts
Authors: Kaufmann, Pierre; GiméNez de Castro, C. Guillermo; Makhmutov,
Vladimir S.; Raulin, Jean-Pierre; Schwenn, Rainer; Levato, H.;
Rovira, M.
Bibcode: 2003JGRA..108.1280K
Altcode:
The rapid solar spikes (100-500 ms) recently discovered at submillimeter
waves bring new possibilities to investigate energetic processes near
the solar surface that might have an important role in the launch and
propelling of ionized mass away from the Sun. We present a study on
the association between the launch time of coronal mass ejections
(CMEs) observed by the LASCO instruments on the SOHO spacecraft
and the onset of the new kind of rapid solar spikes (100-500 ms)
observed at submillimetric waves (212 and 405 GHz) by the new Solar
Submm-wave Telescope (SST). We investigated six submm-wave events,
all found associated to CMEs. Seven related CME were identified. Five
of them were associated with flares with large GOES class soft X-rays,
presenting distinct time histories and associations at other energy
ranges, and two of them were related to flares behind the solar limb,
with simultaneous related activity observed in the visible solar
disk. Ultraviolet images from EIT on SOHO show some kind of small
or large-scale magnetic activity or brightening for all events. The
extrapolation of apparent CME positions to the solar surface show that
they occurred nearly coincident in time with the onset of submm-wave
pulses for all six events. These results suggest that pulse bursts might
be representative of an important early signature of CMEs, especially
for events beginning near the center of the solar disk, sometimes
identified as "halo" CMEs. They lead to several challenging questions
relative to the physical nature of the pulses and its association to
the launch and acceleration of coronal mass ejections. Although these
evidences may favor multiple rapid energy releases at the origin near
the solar surface, they require further research in order to better
understand both diagnostics and model descriptions.
Title: Solar Pulsating Bursts at Submillimeter Wavelengths
Authors: Kaufmann, P.; Giménez de Castro, C. G.; Makhmutov, V. S.;
Raulin, J. -P.; Schwenn, R.; Levato, H.; Rovira, M.
Bibcode: 2003EAEJA.....5652K
Altcode:
We report some characteristics of trains of pulses that are
frequently observed in the Sun at 212 and 405 GHz by the Solar
Submillimeter Telescope operated at El Leoncito Astronomical Complex,
Argentina Andes. Pulses time scales range typically from 100-500
milliseconds. Although pulsed bursts are usually associated to optical
flares or events at other energy ranges, there are various examples
without connection to any important activity in the solar disk. In
the submillimeter range of wavelength most pulsed bursts are detected
without any bulk emission component. There is a significant association
between the occurrence of submm-wave pulsed bursts and the launch
times of coronal mass ejections (CMEs). Pulses bursts might turn out
a reliable early signature of CME's, specially for those occurring
near the center of the solar disk, which produce the most important
geophysical effects. For solar event for which there are light curves
measured at submm-waves or at higher energy ranges (X-, gamma-rays),
there are qualitative indications that the time rate of pulse occurrence
and pulses amplitudes are proportional to the energy release rate with
time (fluxes). The submm-wave pulsed bursts might be representative
of multiple energy releases in complex magnetic structures where many
fast instabilities occur in small scale magnetic arcades or fluxules.
Title: A comparative analysis of the helios and istp era sun-earth
connection during solar minimum
Authors: Berdichevsky, D.; Reames, D.; Schwenn, R.; Lepping, R.;
Farrugia, C.; Richardson, I.; Wu, C. -C.
Bibcode: 2003EAEJA....13892B
Altcode:
We discuss the similarities and differences of two intervals of extreme
interplanetary solar wind conditions, separated almost precisely by
two solar cycles, in Feb-Apr 1976 and Jan-Apr 2001. The similarities
extend to various data-sets: Energetic particles, solar wind plasma
and interplanetary magnetic field. In Jan-April 1979 observations were
made by spacecraft at three locations covering a wide longitudinal range
(from ~30 to 70°) in the heliosphere. Data are presented from Helios 2,
Helios 1, and from near the Earth. Observations of the 1997 interval are
from Wind, and solar conditions from SOHO. We examine the geomagnetic
activity during each interval. This Study is partially supported by the
following Grants: ATM-0208414 (NSF), and NASA NASW-02025 and NAG 5-10883
Title: On the solar origin of interplanetary disturbances observed
in the vicinity of the Earth
Authors: Vilmer, N.; Pick, M.; Schwenn, R.; Ballatore, P.; Villain,
J. P.
Bibcode: 2003AnGeo..21..847V
Altcode:
The solar origin of 40 interplanetary disturbances observed in
the vicinity of the Earth between January 1997 and June 1998 is
investigated in this paper. Analysis starts with the establishment
of a list of Interplanetary Mass Ejections or ICMEs (magnetic clouds,
flux ropes and ejecta) and of Interplanetary Shocks measured at WIND
for the period for which we had previously investigated the coupling
of the interplanetary medium with the terrestrial ionospheric
response. A search for associated coronal mass ejections (CMEs)
observed by LASCO/SOHO is then performed, starting from an estimation
of the transit time of the inter-planetary perturbation from the Sun
to the Earth, assumed to be achieved at a constant speed (i.e. the
speed measured at 1 AU). EIT/SOHO and Nançay Radioheliograph (NRH)
observations are also used as proxies in this identification for the
cases when LASCO observations do not allow one to firmly establish the
association. The last part of the analysis concerns the identification
of the solar source of the CMEs, performed using a large set of solar
observations from X-ray to radio wavelengths. In the present study,
this association is based on a careful examination of many data sets
(EIT, NRH and H images and not on the use of catalogs and of Solar
Geophysical Data reports). An association between inter-planetary
disturbances and LASCO/CMEs or proxies on the disk is found for 36
interplanetary events. For 32 events, the solar source of activity
can also be identified. A large proportion of cases is found to be
associated with a flare signature in an active region, not excluding of
course the involvement of a filament. Conclusions are finally drawn on
the propagation of the disturbances in the interplanetary medium, the
preferential association of disturbances detected close to the Earth’s
orbit with halos or wide CMEs and the location on the solar disk of
solar sources of the interplanetary disturbances during that period.
Title: Continuous tracking of CMEs using MICA, and LASCO C2 and
C3 coronagraphs
Authors: Balmaceda, L.; Dal Lago, A.; Stenborg, G.; Francile, C.;
Gonzalez, W. D.; Schwenn, R.
Bibcode: 2003AdSpR..32.2625B
Altcode:
In this work we have tracked coronal mass ejections observed with the
ground based Mirror Coronagraph for Argentina (MICA) and the Large Angle
and Spectroscopic Coronagraph (LASCO) C2 and C3 on board of the Solar
and Heliospheric Observatory (SOHO). The MICA telescope is located at El
Leoncito (31.8 S, 69.3 W), San Juan (Argentina), since 1997 as part of
a bilateral scientific project between Germany and Argentina. SOHO is
a project of international cooperation between ESA and NASA. Together
these instruments are able to observe the solar corona ranging from
1.05 to 32 solar radii. MICA images the Fe XIV emission line corona
and LASCO coronagraphs observe the Thomson scattered white light
corona. We have selected events for which there are observations from
the three coronagraphs. Using the composite data we were able to obtain
height-time diagrams for the corresponding dynamical coronal features
traveling outwards in order to determine some of their kinematical
properties, i.e., plane of sky velocity and acceleration.
Title: Relation between the radial speed and theexpansion speed of
coronal mass ejections
Authors: Dal Lago, A.; Schwenn, R.; Gonzalez, W. D.
Bibcode: 2003AdSpR..32.2637D
Altcode:
We have selected 57 limb coronal mass ejections observed by LASCO
during the period of January1997 to April 2001. We used the related EIT
activity close to the limb to define these CMEs as "limbs". We measured
the radial speed of the leading edge close to the center of these CMEs
and the lateral expansion speed of the structures. Comparison of both
speeds revealed a high correlation between them, the radial speed being
around 88% of the expansion speed of the CME. The expansion speed can
also be measured for halo CMEs so that it can be used to infer their
radial speed toward earth, which is otherwise inaccessible.
Title: Causes of major magnetic storms near the latest solar maximum
Authors: Huttunen, K. E. J.; Koskinen, H. E. J.; Schwenn, R.; dal
Lago, A.
Bibcode: 2002ESASP.506..137H
Altcode: 2002svco.conf..137H; 2002ESPM...10..137H
We have studied the nine most severe magnetic storms (Dst < -200 nT)
that occurred during the period from 1999 to the end of the year 2001
i.e. near the last solar activity maximum. The investigated storms
showed large variety both in their solar and solar wind causes. Only
two of these storms were caused by a sheath region together with a
well-defined magnetic cloud event. Distorted magnetic fields preceding
the CME ejecta were the storm drivers in five cases.
Title: Variability of magnetospheric storms driven by different
solar wind perturbations
Authors: Huttunen, K. Emilia J.; Koskinen, Hannu E. J.; Schwenn, Rainer
Bibcode: 2002JGRA..107.1121H
Altcode:
We have investigated the solar wind drivers of magnetic storms during
the rising phase of solar cycle 23 from January 1996 to December
1999. We used observations of coronal mass ejections (CMEs) by the
Large Angle and Spectrometric Coronagraph instrument on SOHO and in
situ solar wind observations by Wind, IMP 8, and ACE spacecraft. The
storms were determined from both the Dst and Kp indices, and the study
was limited to storms with Dst <= -50 nT or Kp >= 5. We show
examples of different behavior of Dst and Kp indices during magnetic
storms caused by different types of solar wind drivers. Furthermore,
we have investigated cross-correlation between peak Dst and Kp values
of storms organized according to the associated solar wind driver. It
makes a difference whether a sheath region or the following ejecta
causes the storm. We found that almost all intense and stronger
magnetic storms (Dst <= -100 nT, or Kp >= 7-) were associated
with shocks and CMEs, but for moderate storms, driver statistics were
different in different phases of the solar cycle. We found different
behavior of the Kp and Dst indices during different types of solar wind
drivers. Intense and short-time disturbances, like postshock streams
and sheath regions, generated more Kp storms, and ejecta generated
more Dst storms. Thus one should be careful when comparing studies
based on any single activity index.
Title: A comparative study of Solar-Heliospheric Observations during
very active Sun intervals in the 21st and 23rd solar cycles (April
1979 and March-April, 2001)
Authors: Berdichevsky, D. B.; Farrugia, C. J.; Lepping, R. P.;
Richardson, I. G.; Galvin, A. B.; Schwenn, R.; Reames, D. V.
Bibcode: 2002AGUSMSH51A..01B
Altcode:
On March 24, 2001, the largest sun spot group in 10 years, consisting
of three or more active regions (ARs) centered near AR 9393, emerged
from behind the eastern limb of the Sun and began a 2-week passage
across the visible hemisphere. During the same time, the Sun showed
several other ARs so this period constituted a phase of unusually
intense solar activity that continued almost 18 days beyond the
disk passage of the largest sun spot group and included possibly
the most energetic solar flare event in modern records (a > X20
flare in soft X-rays). We shall present an overview of the associated
solar energetic particle events and an analysis of the thermodynamic
characteristics of the shocks observed in the Earth's vicinity. The
investigation includes cross-correlation analysis of interplanetary
plasma and magnetic field observations at ACE (SWEPAM/MAG level-2 data)
situated 250 Re upstream of Earth and at Wind (SWE/MFI data), which
was ahead of Earth and executing a distant prograde orbit with large
Y-coordinate. The interval under study bears a close resemblance to a
similar active period during April 1979 (i.e., 2 solar cycles earlier)
observed by the Helios 1/2 probes and Earth solar wind monitors (ISEE-3,
IMP). The similarities and differences between the two intervals are
examined further.
Title: Response of magnetic indices to different solar wind
disturbances
Authors: Huttunen, K. Emilia J.; Koskinen, H. E. J.; Schwenn, R.
Bibcode: 2002ESASP.477..339H
Altcode: 2002scsw.conf..339H
We have investigated the magnetic storms during the rising phase of
the solar cycle 23 from January 1996 to December 1999. We determined
the storm periods from both the Dst and Kp indices. Study was limited
to storms with Dst <= -50 nT or Kp >= 5. We have investigated
cross-correlation between the peak Dst and Kp values of storms
organized according to the asscociated solar wind driver. It makes a
difference whether the Earth's magnetosphere is hit by a CME ejecta
or by a compressed and heated sheath region plasma. We found different
behavior of the Kp and Dst indices during different types of solar wind
drivers. Intense and short-time disturbances, like post-shock streams
and sheath regions generated more Kp storms and ejecta generated more
Dst storms. Thus one should be careful when comparing studies based
on any single activity index.
Title: Interplanetary phenomena associated with very intense
geomagnetic storms
Authors: Gonzalez, W. D.; Tsurutani, B. T.; Lepping, R. P.; Schwenn, R.
Bibcode: 2002JASTP..64..173G
Altcode: 2002JATP...64..173G
The dominant interplanetary phenomena that are frequently associated
with intense magnetic storms are the interplanetary manifestations of
fast coronal mass ejections (CMEs). Two such interplanetary structures,
involving an intense and long duration Bs component of
the IMF are: the sheath region behind a fast forward interplanetary
shock, and the CME ejecta itself. Frequently, these structures lead
to the development of intense storms with two-step growth in their
main phases. These structures, when combined, lead sometimes to the
development of very intense storms, especially when an additional
interplanetary shock is found in the sheath plasma of the primary
structure accompanying another stream. The second stream can also
compress the primary cloud, intensifying the Bs field, and
bringing with it an additional Bs structure. Thus, at times
very intense storms are associated with three or more Bs
structures. Another aspect that can contribute to the development of
very intense storms refers to the recent finding that magnetic clouds
with very intense core magnetic fields tend to have large velocities,
thus implying large amplitude interplanetary electric fields that can
drive very intense magnetospheric energization.
Title: New insights on the onsets of coronal mass ejections from soho
Authors: Plunkett, S. P.; Michels, D. J.; Howard, R. A.; Brueckner,
G. E.; St. Cyr, O. C.; Thompson, B. J.; Simnett, G. M.; Schwenn, R.;
Lamy, P.
Bibcode: 2002AdSpR..29.1473P
Altcode:
Coronal mass ejections (CMES) are among the most dramatic forms of
transient activity occurring in the solar atmosphere. Despite over
twenty years of research, many basic questions related to the physics
of CMEs have remained unanswered. Observations with the LASCO and EIT
experiments on SOHO, combined with recent theoretical modeling, have
provided new insights on some of these outstanding questions and have
also raised many new ones that need to be addressed in the future. In
this paper, we present some of the new results from SOHO pertaining
to the source regions and onsets of CMEs, and their evolution in the
corona. We emphasize the important role that studies of CMEs will play
in the International Solar Cycle Studies program.
Title: Comparison between halo CME expansion speeds observed on the
sun, their average propagation speeds to earth and their corresponding
counterparts near earth
Authors: dal Lago, A.; Schwenn, R.; Huttunen, K.; Gonzalez, W.;
Gonzalez, A.; Vieira, L.; Echer, E.; Guarnieri, F.; Prestes, A.;
Balmaceda, L.; Schuch, N.
Bibcode: 2002cosp...34E.827D
Altcode: 2002cosp.meetE.827D
We have compared characteristics of 85 halo CMEs observed on the sun
by the Large Angle and Spectroscopic Coronagraph on SOHO with their
corresponding counterparts observed near earth by the magnetic field
and plasma instruments on board of ACE, WIND and SOHO satellites, in
the period from January 1997 to April 2001. First, we focussed on the
comparison between the lateral expansion speeds of these halos and
the corresponding ejecta speeds near earth. It is found that there
is a relation between these two speeds, but the scatter is high. If
one takes a subset from these data which includes only those CMEs that
showed magnetic cloud structures near earth (21 cases), the correlation
mentioned above increases. The results are very similar to the study
done by Lindsay et al (1999) using observations made from Solwind and
SMM coronagraphs, and Helios-1 and PVO plasma and interplanetary field
data from the period of 1979 to 1988. Also, we reviewed the relations
between the average CME propagation speed to earth and the ejecta
speeds near earth. We found a relation for this set of data which
differs from the relation derived by Cliver et al. (1990). This kind
of relation is very important to estimate ejecta speeds of events for
which no interplanetary observations are available.
Title: Relation between the radial speed and the expansion speed of
coronal mass ejections
Authors: dal Lago, A.; Schwenn, R.; Gonzalez, W.
Bibcode: 2002cosp...34E.828D
Altcode: 2002cosp.meetE.828D
We have selected 54 limb coronal mass ejections observed by LASCO
during the period of January 1997 to April 2001. We used the related
EIT activity close to the limbto define these CMEs as SlimbT CMEs. We
measured the radial speed of the leading edge close to the center of
these CMEs and the lateral expansion speed of the structures. Comparison
of both speeds revealed a high correlation between them, the radial
speed being around 88% of the expansion speed of the CME. The expansion
speed can also be measured for halo CMEs so that it can be used to infer
their radial speed toward earth which is otherwise unaccessible. The
associations of CME expansion speeds and their travel speeds to earth on
the one hand and the radial limb CME speeds and their measured travel
time to Solwind and Helios-1 spacecraft on the other hand show a lot
of similarities.
Title: The halo CME expansion speed as a tool for predicting their
travel time to earth: testing the tool.
Authors: dal Lago, A.; Schwenn, R.; Gonzalez, W.; Huttunnen, K.
Bibcode: 2002cosp...34E.826D
Altcode: 2002cosp.meetE.826D
Expansions speeds of 94 halo coronal mass ejections were measured
from LASCO C3 images obtained in the period of January 1997 to April
2001. They have been found to be a very useful tool for predicting their
travel time to earth. The expansion speed is defined by the expansion
of oppositely directed portions of the halo CME front l. Only CMEs with
unique interplanetary association were chosen, and their travel time
was determined from the first CME appearance in the LASCO C2 field of
view and the arrival of an interplanetary signature (shock or blob)
near earth, as observed by ACE, WIND or SOHO instruments. An empirical
model for CME propagation was developed based on these measurements
which assumes that there is deceleration of CMEs proportional to their
speed.This model allows to estimate the travel time to earth from the
halo expansion speed. Recently, we had several opportunities to test
this empirical model, and the predictions were usually very good.
Title: Continuous tracking of CME's using MICA and LASCO -C2 and
-C3 coronagraphs
Authors: Balmaceda, L.; dal Lago, A.; Stenborg, G.; Francile, C.;
Gonzalez, W.; Schwenn, R.
Bibcode: 2002cosp...34E1440B
Altcode: 2002cosp.meetE1440B
In this work we have tracked coronal mass ejections observed with the
ground based Mirror Coronagraph for Argentina (MICA) and the Large
Angle Spectroscopic Coronagraph (LASCO) C2 and C3 on board of Solar
and Heliospheric Observatory (SOHO). MICA telescope is located at
El Leoncito, (San Juan, Argentina) since 1997 as part of a bilateral
scientific project between Germany and Argentina and SOHO is a project
of international cooperation between ESA and NASA. Together these
instruments are able to observe the solar corona ranging from 1.05 to
32 solar radii. MICA images the Fe XIV emission-line corona while LASCO
coronagraphs observe the Thomsonscattered white light. We have selected
events for which there are observations from the three coronagraphs
in order to determine the outflow characteristics such as velocity,
acceleration or deceleration. Using this composite data we were able
to obtain height-time diagrams for coronal moving features.
Title: Major Storms During The Last Solar Activity Maximum: Solar
and Interplanetary Causes
Authors: Huttunen, K. E. J.; Koskinen, H. E. J.; Schwenn, R.;
Dallago, A.
Bibcode: 2002EGSGA..27.3428H
Altcode:
During the solar maximum the prediction of the magnetic storms is
more difficult than in the minimum as several CMEs may impart during
a day interacting with the ambient solar wind and possibly with each
other. We analyzed the eight most severe storms (Dst < 200 nT)
occurring during the years 1999-2001, i.e. around the last so- lar
maximum. For two of these storms the geoeffective structures (sheath
region and well-defined magnetic cloud) were easily identifiable in
the solar wind data, and it was possible to find unique associations
to CMEs observed by SOHO/LASCO. The other six storms were caused
by more complex solar wind structures. Four of these had more than
one suitable CME association and were probably caused by the inter-
action of multiple CMEs. One storm was caused by a very strong sheath
region and one by the interaction of the CME ejecta with a high-speed
stream. The prediction of the geoeffectivity for complex cases is more
difficult as they have several solar source candidates. Also, due to
their mutual interaction, they lack the simple magnetic cloud topology
known from isolated CMEs. We have investigated the differences and sim-
ilarities in solar events and solar wind conditions that led to these
major storms and tried to identify the origin of the geoeffective
structures, even for the complex cases.
Title: Improving space weather predictions - what is missing?
Authors: Schwenn, R.; Huttunen, E.; dal Lago, A.
Bibcode: 2002cosp...34E1361S
Altcode: 2002cosp.meetE1361S
With the arrival of SOHO and its modern instrumentation, space
weather predictions reached a new quality: 1) an almost continuous
patrol service for detecting halo CMEs early on is now in service,
2) simultaneous EUV disk observations allow to determine wheather a
halo is pointed towards or away from Earth, i.e., wheather an impact
at Earth is probable or not. Yet, the accurracy of actual predictions
is still deplorably bad. The actual arrivals at Earth are usually off
by many hours, about 10% of storms are not predicted at all, another
10% of predictions are false alarms, and predicting the strength and
exact timing of storms caused by the ICMEs seems to be that worthless
that it is not even tried. From our experience over the years we
pinpoint several issues where practical improvements appear feasible,
both on short and on long term. In addition, basic research work
remains indispensible, for finally identifying the warning signals of
imminent solar transients and for pre-determininig their propagation
characteristics using near-real-time computer models.
Title: Coronal mass ejection speeds measured in the solar corona
using LASCO C2 and C3 images
Authors: dal Lago, A.; Schwenn, R.; Stenborg, G.; Gonzalez, W.
Bibcode: 2002cosp...34E.830D
Altcode: 2002cosp.meetE.830D
In this work we present height-time diagrams of 3 halo coronal mass
ejections, observed on July 25th,1999, September 28th,1997, and June
29th,1999. The CMEs were observed by the Large Angle and Spectroscopic
Coronagraph (LASCO) which is an instrument on board of the Solar and
Heliospheric Observatory (SOHO observing the solar corona from 2 to 32
solar radii. To obtain these diagrams we divide the LASCO images of a
given sequence in angular slices, transform them into rectangular slices
(their width chosen proportional to the time distance to the next image)
and place them side by side. Thus, the speed profile of any pattern
moving in the particular latitudinal slice can be derived. With this
method we were able to identify even minor speed changes in several
angular positions for the chosen events. This technique is particularly
appropriate to identify acceleration or deceleration of structures in
halo CMEs. This information may be used to improve predictions of CME
travel times to earth. From the analysis of these 3 events we conclude
that: (a) the CME observed on September 28th,1997, started very slowly,
with initial speeds ranging from 107 to 178 km/s, and accelerated
in the C2 field of view reaching final constant speeds of 352 to 400
km/s in the C3 field of view; (b) the CMEs observed on July 25th,1999,
and June 29th,1999 started with initial speeds from 310 to 650 km/s
and 435 to 650 km/s, respectively. They decelerated smoothly in the
C3 field of view and reached a variety of speeds ranging from 150 to
330 km/s, depending on the direction around the sun.
Title: Solar orbiter, a high-resolution mission to the sun and
inner heliosphere
Authors: Marsch, E.; Antonucci, E.; Bochsler, P.; Bougeret, J. -L.;
Fleck, B.; Harrison, R.; Langevin, Y.; Marsden, R.; Pace, O.; Schwenn,
R.; Vial, J. -C.
Bibcode: 2002AdSpR..29.2027M
Altcode:
The scientific rationale of the Solar Orbiter is to provide, at high
spatial (35 km pixel size) and temporal resolution, observations of the
solar atmosphere and unexplored inner heliosphere. Novel observations
will be made in the almost heliosynchronous segments of the orbits at
heliocentric distances near 45 R⊙ and out of the ecliptic plane at
the highest heliographic latitudes of 30° - 38°. The Solar Orbiter
will achieve its wide-ranging aims with a suite of sophisticated
instruments through an innovative design of the orbit. The first
near-Sun interplanetary measurements together with concurrent remote
observations of the Sun will permit us to determine and understand,
through correlative studies, the characteristics of the solar wind
and energetic particles in close linkage with the plasma and radiation
conditions in their source regions on the Sun. Over extended periods
the Solar Orbiter will deliver the first images of the polar regions
and the side of the Sun invisible from the Earth.
Title: Solar Orbiter: a high-resolution mission to the sun and
inner heliosphere
Authors: Fleck, Bernhard; Marsch, E.; Antonucci, Ester; Bochsler,
Peter A.; Bougeret, J. L.; Harrison, R.; Marsden, R. P.; Coradini,
M.; Pace, Oscar; Schwenn, Rainer; Vial, Jean-Claude
Bibcode: 2001SPIE.4498....1F
Altcode:
The key mission objective of the Solar Orbiter is to study the Sun
from close-up (45 solar radii, or 0.21 AU) in an orbit tuned to solar
rotation in order to examine the solar surface and the space above from
a co-rotating vantage point at high spatial resolution. Solar Orbiter
will also provide images of the Sun's polar regions from heliographic
latitudes as high as 38 degrees. The strawman payload encompasses
two instrument packages: Solar remote-sensing instruments: EUV
full-sun and high resolution imager, high-resolution EUV spectrometer,
high-resolution and full-sun visible light telescope and magnetograph,
EUV and visible-light coronagraphs, radiometers. Heliospheric
instruments: solar wind analyzer, radio and plasma wave analyzer,
magnetometer, energetic particle detectors, interplanetary dust
detector, neutral particle detector, solar neutron detector. To
reach its novel orbit, Solar Orbiter will make use of low-thrust
solar electric propulsion (SEP) interleaved by Earth and Venus gravity
assists. Solar Orbiter was selected by ESA's Science Programme Committee
(SPC) in October 2000 as a Flexi-mission, to be implemented after the
BepiColombo cornerstone mission to Mercury before 2013. This paper
summarizes the science to be addressed with the Solar Orbiter, followed
by brief descriptions of the strawman payload, the mission profile,
and the spacecraft and ground segment designs.
Title: A Tool For Improved Space Weather Predictions: The CME
Expansion Speed
Authors: Schwenn, R.; Dal Lago, A.; Gonzalez, W. D.; Huttunen, E.;
St. Cyr, C. O.; Plunkett, S. P.
Bibcode: 2001AGUFMSH12A0739S
Altcode:
From inspecting limb CMEs we found that there is usually a good
correlation between the apparent radial speed and the lateral
expansion speed of CME clouds. In case of halo CMEs, the radial speed
is inaccessible because of the geometry, but the expansion speed can
still be determined. Thus, the halos' radial speed can be inferred
and their travel time to Earth be estimated and compared with the
observed travel time. We studied this connection using solar and
interplanetary data for a period from January 1997 to April 2001. The
data were primarily provided by the LASCO coronagraphs on SOHO, plus
additional information from the EIT instrument. Solar wind data from
SOHO, ACE and Wind were used to identify the arrivals of CME effects
at the earth. Out of 280 full and partial halo CMEs recorded by LASCO
we found 102 cases uniquely correlated with ejecta signatures right
in front of the earth. For 94 of them, both the halo expansion speed
Vexp and the travel time Ttr could be determined. The function Ttr =
220.8 - 22.75 * ln(Vexp) fits the data best.
Title: 3D Coronal Observations and Sun Earth Connections : from SOHO
to STEREO data
Authors: Portier-Fozzani, F.; Inhester, B.; Schwenn, R.; Dal Lago,
A.; Papadopoulo, T.
Bibcode: 2001AGUFMSH31B0715P
Altcode:
Recent progress in 3D visualization and reconstruction made possible
to follow the evolution of coronal plasma structures frozen by the
magnetic field. As optically thin coronal emission lines introduce
uncertainties on the reconstructions, it is needed to develop
constraints on stereoscopic methods to be able to use them in the
solar case. Basic geometric assumptions on structures made possible
to determine the main parameters on loops - including their twists -,
arcade loops structures or filament shapes, using the difference angle
due to solar rotation with SOHO/EIT. Tomographic techniques are being
adapted to coronagraphic data such as SOHO/LASCO. 3D analysis of flare
formation on April 7th, 1997 shows emerging flux near a sigmoid loop
with magnetic fields reconnection. October 13th, 1999 a twisted filament
becomes instable and creates a limb CME. April 6-7th, 1998 at the limb,
several ejections of twisted structures are observed. In all of these
cases, the role of the helicity in these instabilities formations
is analyzed. Consequences of the observed detwisting processes in
ejections of material into the interplanetary space up to aurora
formations are described. Then improvements expected in dynamical
cases due to simultaneous observations at various angle, provided by
the STEREO mission (launched in December 2004) are presented in the
context of the space weather forecast.
Title: Dependence of Geoeffective Interplanetary Parameters on
Heliographic Longitude: A Case Study for March 1979
Authors: Lepping, R. P.; Farrugia, C. J.; Jordanova, V. K.;
Berdichevsky, D. B.; Galvin, A.; Schwenn, R.; Richardson, I. G.
Bibcode: 2001AGUFMSH31A0703L
Altcode:
We inquire into how much information content is lost in using
interplanetary field and plasma parameters to predict the Dst index
from monitors in the inner heliosphere (distance R < 1 AU) and
displaced from the Sun-Earth line. To this end, we selected a period
in March, 1979, during which 2 major geomagnetic storms (Dst < -100
nT) occurred. Data are from ISEE 3, in orbit around the L1 Lagrangian
point, and from Helios 2 situated at R ~ 0.8 AU and at a substantial
separation from the Sun-Earth line are used. Scaling factors with
R are the same as those in Lindsay et al. (1999), irrespective of
interplanetary configuration. Previous investigations have recorded
good overall agreement between the measured Dst and that predicted from
Burton et al.'s formula (1975). However, there are occasional large
discrepancies even when input interplanetary parameters are from probes
near the Sun-Earth line. In computing the Dst in this study we shall
therefore contrast predictions using two approaches. One is based on
Burton et al.'s formula; the other is based on a numerical simulation
with our kinetic ring current model [3] driven by a magnetopsheric
electric field derived from the Weimer [2001] model. The twofold aim
of the work is thus to answer the two questions: (1) which part of the
Dst is still predicted from off the Sun-Earth line and what are the
corresponding interplanetary configurations?; (2) Is prediction improved
when the model of Weimer (2001) is used?. This work is supported by
NASA Living with a Star grant NAG5-10883. 1. Lindsay, G. M., et al.,
JGR, 104, 10,335, 1999. 2. Burton, R. K., et al., JGR, 80, 4204,
1975. 3. Jordanova, V. K., et al., JGR, 103, 79, 1998. 4. Weimer,
D. R., JGR, 106, 407, 2001.
Title: The eruptive events on September 30, 1998: 1. The jet
Authors: Bagalá, L. G.; Stenborg, G.; Schwenn, R.; Haerendel, G.
Bibcode: 2001JGR...10625239B
Altcode:
The jet on September 30, 1998, is part of a complex event that
involved also other eruptive phenomena. Changes in the coronal
magnetic field topology were observed during the ejection of the
jet, as deduced from the Fe XIV green line emission. The whole event
was well observed by both the H-Alpha Solar Telescope for Argentina
(HASTA) and the Mirror Coronagraph for Argentina (MICA), which are
installed in the German-Argentinean Solar Observatory at El Leoncito,
Argentina. The Soft X-ray Telescope (SXT) on board Yohkoh also observed
the jet. In this work, observations of the first part of this complex
event showing the evolution of the jet and release of blobs are
presented. Certain features observed are interpreted as signatures
of a magnetic reconnection process in the region. We conclude that
existing theoretical and phenomenological models based on magnetic
reconnection mechanisms could explain our observations, which span
three temperature regimes far apart from each other.
Title: Solar Orbiter, a high-resolution mission to the Sun and
inner heliosphere
Authors: Marsch, E.; Harrison, R.; Pace, O.; Antonucci, E.; Bochsler,
P.; Bougeret, J. -L.; Fleck, B.; Langevin, Y.; Marsden, R.; Schwenn,
R.; Vial, J. -C.
Bibcode: 2001ESASP.493D..11M
Altcode: 2001sefs.workD..11M
Solar Orbiter will provide, at very high spatial (35 km pixel size)
and temporal resolution, novel observations of the solar atmosphere
and unexplored inner heliosphere. It will achieve its wide-ranging
scientific aims with a suite of sophisticated instruments through an
innovative orbit design. Unprecedented observations will be made in
the heliosynchronous segments of the orbits at heliocentric distances
near 45 Rsolar and out of the ecliptic plane at the highest
heliographic latitudes of 30° - 38°. The first near-Sun interplanetary
measurements together with concurrent remote-sensing observations of
the Sun and its corona will permit us to determine and understand,
through correlative studies, the characteristics of the solar wind
and energetic particles in close linkage with the plasma and radiation
conditions in the source regions on the Sun. Solar Orbiter will deliver
the first images of the polar regions and the far side of the Sun
invisible from the Earth.
Title: Ionization state and magnetic topology of coronal mass
ejections
Authors: Henke, T.; Woch, J.; Schwenn, R.; Mall, U.; Gloeckler, G.;
von Steiger, R.; Forsyth, R. J.; Balogh, A.
Bibcode: 2001JGR...10610597H
Altcode:
Charge state distributions of heavy solar wind ions measured in
interplanetary space can be used to probe the physical conditions
in the solar corona. This paper presents a study of the charge state
distributions and the magnetic topology of 56 coronal mass ejections
(CMEs) observed in interplanetary space by the Ulysses spacecraft. The
analysis of the data from the Solar Wind Ion Composition Spectrometer
(SWICS) instrument and the Vector Helium Magnetometer (VHM) experiment
onboard Ulysses shows a clear correlation between the charge state
distributions and the magnetic topology of CMEs. Almost all CMEs whose
charge state distributions are shifted to higher charge states with
respect to the ambient solar wind have the structure of magnetic clouds,
whereas CMEs with the same charge state distributions as the surrounding
solar wind do not show magnetic cloud structure. This correlation
is found for CMEs observed at low, mid, and high solar latitudes. On
the basis of the numerical solution of the ionization/recombination
equations for oxygen and silicon, it is investigated which changes of
the electron temperature, electron density, and the speed of the ions
in the source region of the CMEs can reproduce the observations. It is
shown that the main reason for the observed enhancement of higher charge
states in the cloud CMEs is an increased electron temperature. However,
the evolution of the density and velocity of the CMEs before the charge
states freeze in cannot be neglected.
Title: Large Doppler Shifts in X-Ray Plasma: An Explosive Start to
Coronal Mass Ejection
Authors: Innes, D. E.; Curdt, W.; Schwenn, R.; Solanki, S.; Stenborg,
G.; McKenzie, D. E.
Bibcode: 2001ApJ...549L.249I
Altcode:
We report observations, taken with the Solar Ultraviolet Measurements
of Emitted Radiation spectrometer, of spatially resolved high red and
blue Doppler shifts (up to 650 km s-1) from X-ray-emitting
plasma in the corona above a flare. The high Doppler shifts are seen
minutes after a fast, faint optical front is seen racing through the
same part of the corona in images taken with the Mirror Coronagraph
for Argentina. The association of the large-scale fast optical emission
front with soft X-ray emission and high Doppler shifts suggests plasma
heating and acceleration in the wake of a shock.
Title: Solar Orbiter - A high resolution mission to the Sun and the
inner heliosphere (Oral papers and posters which were given at the
conference, but for which no manuscripts were submitted)
Authors: Marsch, E.; Fleck, B.; Schwenn, R.
Bibcode: 2001ohnf.conf..445M
Altcode:
No abstract at ADS
Title: Solar Orbiter, a High-Resolution Mission to the Sun and
Inner Heliosphere
Authors: Marsch, E.; Antonucci, E.; Bochsler, P.; Bougeret, J. -L.;
Fleck, B.; Harrison, R.; Marsden, R.; Schwenn, R.; Vial, J. -C.
Bibcode: 2001IAUS..203..565M
Altcode:
The scientific rationale of the Solar Orbiter (SO) is to provide,
at high spatial and temporal resolution, observations of the solar
atmosphere and unexplored inner heliosphere. The most interesting and
novel observations will be made in the almost heliosynchronous segments
of the orbits at heliocentric distances near 45 Rodot and
out-of-ecliptic at the highest heliographic latitudes of 38 degrees. The
SO will achieve its many and varied aims with a suite of small and
innovative instruments through a clever choice of orbits. The first
near-Sun interplanetary measurements together with concurrent remote
observations of the Sun will permit us to determine and understand,
through correlative studies, the characteristics of the solar wind and
energetic particles in close linkage with the plasma and radiation
conditions in their source regions on the Sun. The SO will, during
the high-latitude orbital passes, provide the first observations of
the Sun's polar regions as seen from outside the ecliptic and also
measure the magnetic field at the poles.
Title: Long-term variations of the flow direction and angular momentum
of the solar wind observed by Helios
Authors: Scherer, K.; Marsch, E.; Schwenn, R.; Rosenbauer, H.
Bibcode: 2001A&A...366..331S
Altcode:
The flow directions of solar wind protons were measured in situ by
the Helios spacecraft. A long-term average of the velocity shows a
systematic drift in the latitudinal flow angle of about +1o
north observed with Helios 1 and -1o south observed onboard
of Helios 2. The longitudinal flow angle migrates about +1o
west over a period of almost 10 years for Helios 1 and 6 years for
Helios 2. This systematic change with time of the plasma flow direction
may be caused by solar-cycle variations of the orientation of the Sun's
magnetic field which partially corotates with the Sun inside the Alfvén
surface (varying in distance between 10 Rsun over the poles
and 30 Rsun near the equator). These variations must have
been imprinted on the solar wind flow when it detached from corotation
with the Sun near the Alfvén point. The angular momentum of the wind
is intimately connected with the flow and field directions. The gain of
total angular momentum of the wind equals the loss of angular momentum
of the Sun, which is caused by the torque exerted on the rotating
Sun through the magnetic field of the expanding corona. Implications
of the Helios observations for models of the magnetic fields of the
Sun as well as the solar wind are discussed. We show evidence, that
changes of the solar magnetic field inside the Alfvén surface are
responsible for systematic drifts in the solar wind flow direction.
Title: Solar Wind: Global Properties
Authors: Schwenn, R.
Bibcode: 2000eaa..bookE2301S
Altcode:
The most fundamental problem in solar system research is still unsolved:
how can the Sun with a surface temperature of only 5800 K heat up its
atmosphere to more than a million K? In fact, the solar atmosphere is
so hot that not even the Sun's enormous gravity can contain it. Part
of it is continuously evaporating into interplanetary space: the SOLAR
WIND. As a highly ionized magnetized plasma it...
Title: First combined observations in the German-Argentinean solar
observatory: correlations in quiet and eruptive phenomena at the limb
Authors: Stenborg, G.; Bagalá, L. G.; Bauer, O. H.; Borda, R. F.;
Francile, C.; Haerendel, G.; Rovira, M. G.; Schwenn, R.
Bibcode: 2000JASTP..62.1553S
Altcode: 2000JATP...62.1553S
This is a first report of combined observations form the solar
instruments at the recently inaugurated German-Argentinean
Solar-Observatory at El Leoncito, San Juan, Argentina. The /Hα
telescope (HASTA) and the mirror coronagraph (MICA) daily image the
solar disk and the inner solar corona respectively with high temporal
and spatial resolution. The excellent weather conditions for solar
studies of the Observatory, and its south equatorial location allow a
complementary summer-condition data with respect to the majority of the
other observatories, mainly located in the northern hemisphere. In this
paper, we present four events in order to study possible correlations
between observations taken by both telescopes. Since each instrument
records data in quite different temperature regimes, correlation between
both set of data appears when the phenomena span a broad range of
temperatures. This is explicitly shown for two of the four set of data
presented here. On the other hand, the four cases are good examples
of the contributions the two instruments can provide to the better
understanding of the mechanisms at work in the inner solar atmosphere.
Title: The origin of the solar wind: an overview
Authors: Srivastava, Nandita; Schwenn, Rainer
Bibcode: 2000ohbp.conf...13S
Altcode:
A tutorial review of the origin of the solar wind is presented in this
chapter. At the outset, the concept of the solar wind is introduced and
its various components and their charactertistics are discussed. Also
outlined are some of the important space missions dedicated to the
study of the solar wind and a review of their observations. The salient
features of a three-dimensional model of the inner heliosphere are
presented on the basis of the observations. From these space-based
observations, it is now well established that there exists a close
relation between the 3D heliosphere and the underlying coronal
structure. Around solar activity minimum, large polar coronal holes
dominate the major part of the heliosphere through which emanates
the high-speed solar wind. On the other hand, another type of solar
wind which is relatively slow, is restricted to a narrow equatorial
belt of about ±30° width in latitude. The magnetic topology
is dominated by strong multipole components and multiple current
sheets in the upper corona and by a large-scale dipole field further
outside, respectively. In this review, the emphasis is laid on the
new observations and findings by several sophisticated instruments
aboard SOHO which observe both, the inner and outer corona. These have
revealed several clues to the solar origins or the source regions of the
two types of solar wind, viz., the fast and the slow solar wind. The
observations also unravel the finer details of the processes that are
responsible for their generation. Finally, we summarize the present
status of our knowledge on the origin of solar wind.
Title: Solar Orbiter --- A High Resolution Mission to the Sun and
Inner Heliosphere
Authors: Fleck, B.; Marsch, E.; Schwenn, R.; Antonucci, E.; Bochsler,
P.; Bougeret, J. -L.; Harrison, R. A.; Marsden, R.; Vial, J. -C.
Bibcode: 2000SPD....31.0296F
Altcode: 2000BAAS...32..828F
The scientific rationale of the Solar Orbiter (SO) is to provide,
at high spatial and temporal resolution, observations of the solar
atmosphere and unexplored inner heliosphere. The most interesting and
novel observations will be made in the almost heliosynchronous segments
of the orbits at heliocentric distances near 45 Rsun and
out-of-ecliptic at heliographic latitudes of up to 38o. By
going to 45 Rsun the SO will allow remote sensing of the
solar atmosphere with unprecedented spatial resolution, and the almost
heliosynchronous orbit segments will permit us to disentangle spatial
and temporal variations in the solar wind in close linkage with the
plasma and radiation conditions in the source regions of the Sun. The
strawman payload encompasses two instrument packages: Heliospheric
Instruments --- high-res visible light telescope and magnetograph
(<40 km), high-res X-ray/EUV imager (<30 km), high-res EUV
spectrometer (<100 km), EUV and visible-light coronagraphs, solar
neutron and γ -ray detectors, radiometers. Heliospheric Instruments
--- solar wind analyzer, magnetometer, energetic particle detectors, IP
dust detector, plasma wave analyser, radio experiment, neutral particle
detector. Using solar electric propulsion (SEP) in conjunction with
multiple planet swing-by manoeuvres, it will take SO two years to reach
a perihelion of 45 Rsun at an orbital period of 149 days,
with an inclination ranging from 6.7o to 23.4o
w.r.t. the ecliptic. During an extended mission phase of about 2
years the inclination will increase to 31.7o, leading to
a maximum heliographic latitude of 38.3o. The SO was one
of the about 40 responses to the Call for Proposals for the next two
"flexi-missions" (F2 and F3) within ESA's Scientific Programme. At
its meeting on 1 March 2000, ESA's Space Science Advisory Committee
recommended the Solar Orbiter among 5 other proposals for an assessment
study. Launch is expected by the end of the decade.
Title: Factors Related to the Origin of a Gradual Coronal Mass
Ejection Associated with an Eruptive Prominence on 1998 June 21-22
Authors: Srivastava, Nandita; Schwenn, Rainer; Inhester, Bernd;
Martin, Sara F.; Hanaoka, Yoichiro
Bibcode: 2000ApJ...534..468S
Altcode:
We present observations of a coronal mass ejection (CME) associated
with an eruptive prominence during 1998 June 21-22 by LASCO (Large
Angle Spectroscopic Coronagraph) aboard SOHO (Solar and Heliospheric
Observatory). Various features in the three-part structured, white-light
CME as observed by LASCO-C2 and C3 coronagraphs were compared with
features in the other wavelengths, for example, in Fe XIV and Fe X
emission lines obtained from LASCO C1, in Hα from Helio-Research and
at 17 GHz obtained from Nobeyama Radioheliograph. We have investigated
conditions in several data sets to understand the eruptive and the
pre-eruptive scenario of the CME. The CME and the eruptive prominence
accelerate up to ~20 Rsolar and then decelerate to the
velocity of the ambient slow solar wind. The analysis clearly shows
that this particular CME is a typical case of a very slow or gradual
CME for which it is difficult to define an exact onset time. The CME
could be tracked for about 30 hours until it crossed a distance of
30 Rsolar and disappeared from the field of view of the
LASCO-C3 coronagraph. The height-time profiles of various features of
this CME suggest that the leading edge of the CME and the top of the
prominence or the core follow similar pattern, implying a common driver
for both the CME and the eruptive prominence. The observations provide
strong evidence that the CME and the prominence eruption resulted from
a common cause which is the global restructuring of the magnetic field
in the corona in an extensive volume of space near and including the
CME. The restructuring in turn was a consequence of newly emerging
flux regions near and within the neighboring active regions close to
the base of the CME.
Title: Heliospheric 3d Structure and CME Propagation as Seen from
SOHO: Recent Lessons for Space Weather Predictions
Authors: Schwenn, R.
Bibcode: 2000AdSpR..26...43S
Altcode:
Observations from Skylab, Helios, Ulysses, and SOHO have demonstrated
how closely the 3D heliosphere is related to the underlying coronal
structure. Around solar activity minimum, the large polar coronal holes
dominate the major part of the heliosphere, through the high-speed
solar wind streams emanating from them. A distinctively different
type of solar wind is restricted to a narrow near-equatorial belt
(about 30° in latitude). Its magnetic topology is dominated by strong
multipole components and multiple current sheets. Owing to the new
telescopes on SOHO, various effects of CME disturbances propagating
through the heliosphere can now be observed in much greater detail:
optically from the photosphere out to 32 Rs, and later on by
in situ spacecraft. It appears that the prediction reliability of space
weather at Earth's orbit can be raised substantially in the near future
Title: Properties of coronal mass ejections: SOHO LASCO observations
from January 1996 to June 1998
Authors: St. Cyr, O. C.; Plunkett, S. P.; Michels, D. J.; Paswaters,
S. E.; Koomen, M. J.; Simnett, G. M.; Thompson, B. J.; Gurman, J. B.;
Schwenn, R.; Webb, D. F.; Hildner, E.; Lamy, P. L.
Bibcode: 2000JGR...10518169S
Altcode: 2000JGR...105.8169S; 2000JGRA..105.8169S
We report the properties of all the 841 coronal mass ejections (CMEs)
observed by the Solar and Heliospheric Observatory (SOHO) Large Angle
Spectroscopic Coronagraph (LASCO) C2 and C3 white-light coronagraphs
from January 1996 through June 1998, and we compare those properties to
previous observations by other similar instruments. Both the CME rate
and the distribution of apparent locations of CMEs varied during this
period as expected based on previous solar cycles. The distribution
of apparent speeds and the fraction of CMEs showing acceleration were
also in agreement with earlier reports. The pointing stability provided
by an L-1 orbit and the use of CCD detectors have resulted in superior
brightness sensitivity for LASCO over earlier coronagraphs; however, we
have not detected a significant population of fainter (i.e., low mass)
CMEs. The general shape of the distribution of apparent sizes for LASCO
CMEs is similar to those of earlier reports, but the average (median)
apparent size of 72° (50°) is significantly larger. The larger
average apparent size is predominantly the result of the detection of
a population of partial and complete halo CMEs, at least some of which
appear to be events with a significant longitudinal component directed
along the Sun-Earth line, either toward or away from the Earth. Using
full disk solar images obtained by the Extreme ultraviolet Imaging
Telescope (EIT) on SOHO, we found that 40 out of 92 of these events
might have been directed toward the Earth, and we compared the timing
of those with the Kp geomagnetic storm index in the days following
the CME. Although the ``false alarm'' rate was high, we found that 15
out of 21 (71%) of the Kp>=6 storms could be accounted for as SOHO
LASCO/EIT frontside halo CMEs. If we eliminate three Kp storms that
occurred following LASCO/EIT data gaps, then the possible association
rate was 15 out of 18 (83%).
Title: Coupling Between High and Low Latitudes as Observed with
Lasco in the Solar Corona and in Interplanetary Space
Authors: Schwenn, R.
Bibcode: 2000AdSpR..26..771S
Altcode:
From Skylab, Helios and Ulysses observations we had learnt already
how closely the 3D heliosphere is related to the underlying coronal
structure. Around solar activity minimum, large polar coronal holes
dominate the major part of the heliosphere, through the high-speed
solar wind streams emanating from them. A different type of solar
wind is restricted to a narrow near-equatorial belt (about 30
degrees in latitude). The magnetic topology is dominated by strong
multipole components and multiple current sheets in the upper corona,
and by a large-scale dipole field further outside, respectively. New
observations by LASCO on SOHO cover both regions and may reveal clues
to the processes responsible for the generation of the different types
of solar wind
Title: Coronal Mass Ejections and Large Scale Structure of the Corona
Authors: Maia, D.; Vourlidas, A.; Pick, M.; Howard, R.; Schwenn, R.;
Lamy, P.
Bibcode: 2000AdSpR..25.1843M
Altcode:
A comparative study of two events accompanied by both a flare and a
CME has been performed. The data analysis has been made by comparing
the observations of the LASCO/SOHO coronagraphs with those of the
Nancay radioheliograph. The observations show a clear connection
between coronal green and red line transient activity, burst radio
emission and the CME development which is due to successive loop
interactions. Signatures of these interactions are given by the radio
emission. One can identify successive sequences in the evolution
of the coronal restructuring leading to the full development of the
CME. Identification and timing of these sequences result from the radio
emission analysis. For flare-CME events , the evolution takes place
in the low corona and is extremely fast of the order, on a few minutes
Title: Hot Cores in Coronal Filament Cavities
Authors: Hudson, H.; Schwenn, R.
Bibcode: 2000AdSpR..25.1859H
Altcode:
Filaments represent cold intrusions in the corona, embedded in magnetic
configurations termed ``filament cavities.'' Such cavities may occur
without actually containing prominence material. A cavity then may
erupt, leading to a coronal mass ejection (CME). Studies of Yohkoh
soft X-ray images have previously shown that such eruptions may contain
elongated high-temperature regions closely aligned with the Hα filament
material. We report in this paper multi-wavelength observations of an
extremely stable filament cavity, observed by Yohkoh and SOHO during
July-September 1997. Hot multi-thermal structures persistently occupied
the core of this large-scale polar-crown cavity
Title: Coronal structure and dynamics near solar activity
minimum. Proceedings. E2.2 Symposium of COSPAR Scientific Commission
E held during the 32nd COSPAR Scientific Assembly, Nagoya (Japan),
12 - 19 Jul 1998.
Authors: Watanabe, T.; Schwenn, R.
Bibcode: 2000AdSpR..25.....W
Altcode:
The solar minimum between solar cycles 22 and 23 was considered the
first opportunity to investigate solar and heliospheric physics during
the solar activity minimum via a set of major space-born instruments. In
these proceedings the main results and their theoretical implications
are presented.
Title: Multi-wavelength Observations of the September 30, 1998 Event
at the German-Argentinian Solar Observatory
Authors: Bagalá, L. G.; Stenborg, G.; Schwenn, R.; Bauer, O. H.;
Fernández Borda, R.; Haerendel, G.
Bibcode: 1999ESASP.448..959B
Altcode: 1999mfsp.conf..959B; 1999ESPM....9..959B
No abstract at ADS
Title: On the Rotation Rate of the Emission Solar Corona
Authors: Stenborg, G.; Schwenn, R.; Inhester, B.; Srivastava, N.
Bibcode: 1999ESASP.448.1107S
Altcode: 1999mfsp.conf.1107S; 1999ESPM....9.1107S
No abstract at ADS
Title: Comparative Study of Coronal Mass Ejections Associated with
Eruptive prominences
Authors: Srivastava, Nandita; Schwenn, Rainer; Stenborg, Guillermo
Bibcode: 1999ESASP.446..621S
Altcode: 1999soho....8..621S
Coronal mass ejections associated with eruptive prominences often
display a classical 3-part structure in white light, viz., a bright
leading edge followed by a dark cavity devoid of material and an
embedded prominence or core. However, the initiation of such CMEs and
nature of their acceleration as they propagate outward in the corona
are some of the basic questions that remain unsolved. In particular, the
question of role of the prominence in triggering or driving the CME has
not been settled yet. In this paper, we report observations of coronal
mass ejections (CMEs) associated with eruptive quiescent prominences
that occurred on June 2,1998 and June 21-22, 1998. A comparative study
based on multi-wavelength observations is presented. Various features
in three part structured, white-light CME as observed by LASCO C2
and C3 coronagraphs aboard SOHO were compared with features in other
wavelengths, for example, in FeXIV green and FeX red emission lines
by LASCO-C1 coronagraph. These observations were combined with other
data-sets in H-alpha, X-ray and radio wavelengths. The comparison
provides an important clue to the understanding, the origin or the
initiation of the CMEs. Measurements of speed and acceleration of
these CMEs have also been made in order to understand the nature
of propagation of the CMEs in the outer corona and the driver that
triggers the onset of the CMEs.
Title: MICA Observations of Coronal Transients
Authors: Stenborg, G.; Schwenn, R.; Srivastava, N.
Bibcode: 1999ESASP.446..627S
Altcode: 1999soho....8..627S
Dynamical processes are well known to occur in the inner solar
atmosphere, many of them giving origin to spectacular eruptions known as
coronal mass ejections. The projected velocity of propagation of these
events ranges from less than 100 km/sec to greater than 1200 km/sec. In
order to study the initial evolution of the faster processes it is
necessary to image the inner corona at a very high cadence. Although
ground-based observations of the corona are strongly affected by
sky conditions they allow imaging at a high temporal resolution as
compared to coronagraphic observations from space. In the recently
inaugurated German-Argentinean Solar-Observatory at El Leoncito, San
Juan, Argentina, a mirror coronagraph (MICA) daily images the inner
solar corona with high temporal and spatial resolution in two spectral
ranges: the well known green (~1.8 MK) and red (~1.0 MK) coronal lines
at 5303 A and 6374 A respectively. It is essentially similar in design
to LASCO-C1 on board SOHO, its field-of-view ranging from 1.05 to 2.0
solar radii from the sun center. Thus, it is ideally suited to observe
the hot material and reveal the fast processes that occur in the coronal
plasma. In the last year MICA has recorded several fast and not so fast
green line transients at a high temporal resolution. In this work we
will present observations of a few such events. This study would allow
us to have a better understanding of the conditions that trigger the
coronal mass ejections and their propagation in the inner solar corona.
Title: SOHO, der ungetrübte Blick auf die Sonne.
Authors: Schwenn, R.; Wilhelm, K.
Bibcode: 1999S&WSp...4...38S
Altcode:
No abstract at ADS
Title: LASCO FeXIV and FeX observations of the solar coronal rotation
during the recent solar activity minimum
Authors: Inhester, B.; Stenborg, G.; Schwenn, R.; Srivastava, N.;
Podlipnik, B.
Bibcode: 1999AIPC..471..297I
Altcode: 1999sowi.conf..297I
We investigate the periodicity and recurrence of FeXIV and FeX emission
structures with heliospheric latitude and distance above the Sun's
surface. The data was observed by the LASCO C1 coronagraph on board
the SOHO spacecraft during the solar minimum activity from April 1996
to March 1997. For the green FeXIV emission line, reliable estimates
of the solar rotation period could be obtained between -60 and 60
degrees in latitude and between 1.1 and 2 solar radii. Our investigation
confirms the results of (3) of an almost ridgidly rotating equatorial
streamer belt with a rotation period of about 27.5+/-0.5 days. Even
coronal emissivity structures with a shorter life time between 14 and
27 days do not seem to rotate differentially. The FeX observations
on the other hand do yield some indication of a reduced rotation for
coronal structures over the solar poles. However, the error of the
derived rotation period estimates is considerable so that the analysis
of the FeX data does not allow a definite conclusion.
Title: Recent observations of the solar corona with a new ground-based
Coronagraph in Argentina (MICA)
Authors: Stenborg, G.; Schwenn, R.; Srivastava, N.; Inhester, B.;
Podlipnik, B.; Rovira, M.; Francile, C.
Bibcode: 1999AIPC..471..561S
Altcode: 1999sowi.conf..561S
As part of the new German-Argentinian Solar-Observatory in El Leoncito,
San Juan, Argentina, a new ground-based solar telescope (MICA: Mirror
Coronagraph for Argentina) began to operate in August 1997. MICA is an
advanced mirror coronagraph, its design being an almost exact copy of
the LASCO-C1 instrument. Since its installation, it has been imaging the
inner solar corona (1.05 to 2.0 solar radii) in two spectral ranges,
corresponding to the emission lines of the Fe XIV and Fe X ions. The
instrument can image the corona as fast as every minute. Thus, it is
ideally suited to study fast processes in the inner corona. In this
way it is a good complement for the LASCO-C1 instrument. We present
a brief review of the characteristics of the instrument, and some
recent observations.
Title: Radio signatures of a fast coronal mass ejection development
on November 6, 1997
Authors: Maia, D.; Vourlidas, A.; Pick, M.; Howard, R.; Schwenn, R.;
Magalhães, A.
Bibcode: 1999JGR...10412507M
Altcode:
The Oporto radiospectrograph and the Nançay radioheliograph recorded
a radio event on November 6, 1997, closely related in time with a flare
on National Oceanic and Atmospheric Administration (NOAA) active region
8100. At the beginning of the event the radio sources are located on a
rather small volume in the vicinity of the flare site. In a timescale of
only a few minutes the radio emission sites spread over a large volume
in the corona, covering a range of 100° in heliolatitude. During the
period of the radio event the Large Angle and Spectrometric Coronagraph
(LASCO) on board the Solar and Heliospheric Observatory (SOHO) observed
an extremely fast coronal mass ejection (CME), with a velocity around
2000 kms-1. This CME presents the particularity of having
a fast lateral expansion, giving it a shape reminiscent of a ``coat
hanger.'' There is a very good association between the latitudinal
extent and time development of the CME seen by LASCO and the radio
sources recorded by the radio instruments.
Title: Measurements of flow speeds and acceleration in gradually
evolving solar mass ejections as observed by LASCO
Authors: Srivastava, Nandita; Schwenn, Rainer; Inhester, Bernd;
Stenborg, Guillermo; Podlipnik, Borut
Bibcode: 1999AIPC..471..115S
Altcode: 1999sowi.conf..115S
We present observations of slowly evolving, balloon-type solar mass
ejections observed by the LASCO coronagraphs aboard SOHO. These
mass ejections are typically observed to rise gradually in the solar
corona for several hours (>20 hours) as large loops or balloons
crossing the entire field of view of the coronagraphs. Usually, their
angular extent does not change much. Analysis of several such cases of
balloon-type mass ejections show that they rise with very slow speeds
(less than 50 km s-1) up to a distance of 2 Rsolar and then
are accelerated to higher speeds until 5 Rsolar. From a
distance of about 20 Rsolar, the mass ejecta attain almost a
constant speed ranging between 300 and 500 km s-1. The speed profiles
obtained for individual mass ejections indicate that they trace out
the slow solar wind and, thus, provide an insight into the initiation
and the propagation of the CMEs into the solar wind.
Title: Combined Ulysses solar wind and SOHO coronal observations of
several west limb coronal mass ejections
Authors: Funsten, H. O.; Gosling, J. T.; Riley, P.; Cyr, O. C. St.;
Forsyth, R. J.; Howard, R. A.; Schwenn, R.
Bibcode: 1999JGR...104.6679F
Altcode:
From October 1996 to January 1997, Ulysses was situated roughly above
the west limb of the Sun as observed from Earth at a heliocentric
distance of about 4.6 AU and a latitude of about 25°. This presents the
first opportunity to compare Solar and Heliospheric Observatory (SOHO)
limb observations of coronal mass ejections (CMEs) directly with their
solar wind counterparts far from the Sun using the Ulysses data. During
this interval, large eruptive events were observed above the west
limb of the Sun by the Large Angle Spectrometric Coronagraph (LASCO)
on SOHO on October 5, November 28, and December 21-25, 1996. Using
the combined plasma and magnetic field data from Ulysses, the October
5 event was clearly identified by several distinguishing signatures
as a CME. The November 28 event was also identified as a CME that
trailed fast ambient solar wind, although it was identified only by
an extended interval of counterstreaming suprathermal electrons. The
December 21 event was apparently characterized by a 6-day interval
of nearly radial field and a plasma rarefaction. For the numerous
eruptive events observed by the LASCO coronagraph during December
23-25, Ulysses showed no distinct, individual CMEs, perhaps because
of intermingling of two or more of the eruptive events. By mapping the
Ulysses observations back in time to the Sun assuming a constant flow
speed, we have identified intervals of plasma that were accelerated
or decelerated between the LASCO and Ulysses observations.
Title: LASCO observations of the coronal rotation
Authors: Lewis, D. J.; Simnett, G. M.; Brueckner, G. E.; Howard,
R. A.; Lamy, P. L.; Schwenn, R.
Bibcode: 1999SoPh..184..297L
Altcode:
The near-rigid rotation of the corona above the differential rotation
of the photosphere has important implications for the form of the
global coronal magnetic field. The magnetic reconfiguring associated
with the shear region where the rigidly-rotating coronal field lines
interface with the differentially-rotating photospheric field lines
could provide an important energy source for coronal heating. We present
data on coronal rotation as a function of altitude provided by the Large
Angle Spectrometric Coronagraph (LASCO) instrument aboard the Solar and
Heliospheric Observatory (SOHO) spacecraft. LASCO comprises of three
coronagraphs (C1, C2, and C3) with nested fields-of-view spanning 1.1
R⊙ to 30 R⊙. An asymmetry in brightness, both of the Fe xiv emission
line corona and of the broad-band electron scattered corona, has been
observed to be stable over at least a one-year period spanning May
1996 to May 1997. This feature has presented a tracer for the coronal
rotation and allowed period estimates to be made to beyond 15 R⊙,
up to 5 times further than previously recorded for the white-light
corona. The difficulty in determining the extent of differential motion
in the outer corona is demonstrated and latitudinally averaged rates
formed and determined as a function of distance from the Sun. The
altitude extent of the low latitude closed coronal field region is
inferred from the determined rotation periods which is important to the
ability of the solar atmosphere to retain energetic particles. For the
inner green line corona (<2 R⊙) we determine a synodic rotation
period of (27.4±0.1) days, whereas, for the outer white- light corona,
(>2.5 R⊙) we determine a rotation period of (27.7±0.1) days.
Title: The Rotation of the Fe XIV Solar Corona During the Recent
Solar Activity Minimum
Authors: Inhester, B.; Stenborg, G.; Schwenn, R.; Srivastava, N.;
Podlipnik, B.
Bibcode: 1999SSRv...87..211I
Altcode:
We analyze data observed by the LASCO C1 coronagraph on board the
SOHO spacecraft during the solar minimum activity from April 1996
to March 1997. Using the phase dispersion technique, we investigate
the periodicity and recurrence of Fe XIV emission structures with
heliospheric latitude and distance above the Sun's surface with high
spatial resolution. We find no significant deviation from a rigidly
rotating Fe XIV corona with latitude or with distance from the Sun
even on these small scales. In agreement with earlier work, the coronal
rotation period at solar minimum is about 27.5 ± 1 days.
Title: MICA: The Mirror Coronagraph for Argentina
Authors: Stenborg, G.; Schwenn, R.; Srivastava, N.; Inhester, B.;
Podlipnik, B.; Rovira, M.; Francile, C.
Bibcode: 1999SSRv...87..307S
Altcode:
As part of the new German-Argentinian Solar Observatory in El Leoncito,
San Juan, Argentina, a new ground-based solar telescope (MICA) began
to operate in August 1997. MICA is an advanced mirror coronagraph, its
design being an almost exact copy of the LASCO-C1 instrument. Since its
installation, it has been imaging the inner solar corona (1.05 to 2.0
solar radii) in two spectral ranges corresponding to the emission lines
of the Fe XIV and Fe X ions. The instrument can image the corona as fast
as every minute. Thus, it is ideally suited to study fast processes in
the inner corona. In this way, it is a good complement for the LASCO-C1
instrument. After a brief review of the instrument, we present some
recent observations showing the capabilities of the instrument.
Title: Observaciones de la corona solar interior con un coronógrafo
de espejo
Authors: Stenborg, G.; Schwenn, R.; Francile, C.; Rovira, M.
Bibcode: 1999BAAA...43...22S
Altcode:
El plasma de la corona solar es un buen indicador de las líneas de
fuerza del campo magnético. Por lo tanto, el análisis de estructuras
coronales cuasiestacionarias en la corona da importante información
sobre el campo magnético y la actividad asociada. Se trata de poner
límites a los modelos teóricos existentes mediante el estudio
de distintas estructuras en la corona interior. En agosto de 1997
comenzó a operar el coronógrafo solar (MICA) en El Leoncito como
parte del Observatorio Solar Alemán-Argentino. Desde su instalación
obtiene imágenes de la corona solar (1.05 a 2.0 radios solares)
en 2 líneas espectrales correspondientes a la emisión de Fe XIV y
Fe X. El instrumento puede obtener imágenes cada minuto por lo que
es ideal para estudiar procesos rápidos. Presentamos observaciones
recientes que muestran la capacidad del coronógrafo así como la
evolución de algunos eventos dinámicos observados por MICA.
Title: Acceleration Profile of the Slow Solar Wind as Inferred from
Gradual Mass Ejections Observed by LASCO
Authors: Srivastava, Nandita; Schwenn, Rainer; Inhester, Bernd;
Stenborg, Guillermo; Podlipnik, Borut
Bibcode: 1999SSRv...87..303S
Altcode:
The slow solar wind (< 400 km s-1) appears to initiate
from the regions in the corona where magnetic fields are closed, or from
the interface between streamers and other coronal regions. The nature
of the acceleration of slow solar wind is not yet well known. LASCO
observations of gradually evolving mass ejections offer us a good
opportunity to study the speed and acceleration profiles of the slow
solar wind from a distance of 1.1 up to 30 R⊙. We present
speed and acceleration profiles of slow solar wind, derived on the
basis of measurements of mass flows in several cases of gradual mass
ejections and present them in perspective of earlier work.
Title: Differences in the O7+/O6+ ratio of
magnetic cloud and non-cloud coronal mass ejections
Authors: Henke, T.; Woch, J.; Mall, U.; Livi, S.; Wilken, B.; Schwenn,
R.; Gloeckler, G.; von Steiger, R.; Forsyth, R. J.; Balogh, A.
Bibcode: 1998GeoRL..25.3465H
Altcode:
On its trajectory to Jupiter and over the poles of the Sun
the Ulysses spacecraft has observed a considerable number of
Coronal Mass Ejection (CME) transients in slow and in fast solar
wind streams. The analysis of the magnetic field topology and the
O7+/O6+ charge state ratio of 56 of these events
has yielded strong evidence for a systematic connection between the
two features. Coronal mass ejections with magnetic cloud structure
have an increased O7+/O6+ ratio with respect
to the ambient solar wind whereas non-cloud CMEs do not show enhanced
O7+/O6+ ratios. We discuss possible mechanisms
based on the freezing-in concept that can account for the observation.
Title: Die neue Aktivität der Sonne.
Authors: Schwenn, R.
Bibcode: 1998S&W....37..724S
Altcode:
No abstract at ADS
Title: Joint Nancay Radioheliograph and LASCO Observations of Coronal
Mass Ejections - II. The 9 July 1996 Event
Authors: Pick, M.; Maia, D.; Kerdraon, A.; Howard, R.; Brueckner,
G. E.; Michels, D. J.; Paswaters, S.; Schwenn, R.; Lamy, P.; Llebaria,
A.; Simnett, G.; Lanzerotti, L. J.; Aurass, H.
Bibcode: 1998SoPh..181..455P
Altcode:
The development of a coronal mass ejection on 9 July 1996 has been
analyzed by comparing the observations of the LASCO/SOHO coronagraphs
with those of the Nancay radioheliograph. The spatial and temporal
evolution of the associated radioburst is complex and involves a
long-duration continuum. The analysis of the time sequence of the
radio continuum reveals the existence of distinct phases associated
with distinct reconnection processes and magnetic restructuring
of the corona. Electrons are accelerated in association with these
reconnection processes. An excellent spatial association is found
between the position and extension of the radio source and the CME seen
by LASCO. Furthermore, it is shown that the topology and evolution
of the source of the radio continuum involve successive interactions
between two systems of loops. These successive interactions lead to
magnetic reconnection, then to a large scale coronal restructuring. Thus
electrons of coronal origin may have access to the interplanetary
medium in a large range of heliographic latitudes as revealed by the
Ulysses observations.
Title: Geomagnetic storms caused by coronal mass ejections (CMEs):
March 1996 through June 1997
Authors: Brueckner, G. E.; Delaboudiniere, J. -P.; Howard, R. A.;
Paswaters, S. E.; St. Cyr, O. C.; Schwenn, R.; Lamy, P.; Simnett,
G. M.; Thompson, B.; Wang, D.
Bibcode: 1998GeoRL..25.3019B
Altcode:
(1) All but two geomagnetic storms with Kp ≥ 6 during the operating
period (March 1996 through June 1997) of the Large Angle Spectroscopic
Coronagraph (LASCO) experiment on the Solar and Heliospheric Observatory
(SOHO) spacecraft can be traced to Coronal Mass Ejections (CMEs). (2)
These geomagnetic storms are not related to high speed solar wind
streams. (3) The CMEs which cause geomagnetic effects, can be classified
into two categories: Halo events and toroidal CMEs. (4) The CMEs are
accompanied by Coronal Shock Waves as seen in the Extreme Ultraviolet
Imaging Telescope (EIT) Fe XII images. (5) Some CMEs are related to
flares, others are not. (6) In many cases, the travel time between
the explosion on the Sun and the maximum geomagnetic activity is about
80 hours.
Title: The Solar Minimum Active Region 7978, Its X2.6/1B Flare, CME,
and Interplanetary Shock Propagation of 9 July 1996
Authors: Dryer, M.; Andrews, M. D.; Aurass, H.; DeForest, C.; Galvin,
A. B.; Garcia, H.; Ipavich, F. M.; Karlický, M.; Kiplinger, A.;
Klassen, A.; Meisner, R.; Paswaters, S. E.; Smith, Z.; Tappin,
S. J.; Thompson, B. J.; Watari, S. I.; Michels, D. J.; Brueckner,
G. E.; Howard, R. A.; Koomen, M. J.; Lamy, P.; Mann, G.; Arzner, K.;
Schwenn, R.
Bibcode: 1998SoPh..181..159D
Altcode:
The first X-class flare in four years occurred on 9 July 1996. This
X2.6/1B flare reached its maximum at 09:11 UT and was located in active
region 7978 (S10° W30°) which was an old-cycle sunspot polarity
group. We report the SOHO LASCO/EIT/MDI and SOONSPOT observations before
and after this event together with Yohkoh SXT images of the flare,
radio observations of the type II shock, and GOES disk-integrated soft
X-ray flux during an extended period that included energy build-up in
this active region.
Title: Joint Nançay Radioheliograph and LASCO Observations of
Coronal Mass Ejections - I. The 1 July 1996 Event
Authors: Maia, D.; Pick, M.; Kerdraon, A.; Howard, R.; Brueckner,
G. E.; Michels, D. J.; Paswaters, S.; Schwenn, R.; Lamy, P.; Llebaria,
A.; Simnett, G.; Aurass, H.
Bibcode: 1998SoPh..181..121M
Altcode:
The development of a coronal mass ejection on 1 July 1996 has been
analyzed by comparing the observations of the LASCO/SOHO coronagraph
with those of the Nançay radioheliograph. This comparison brings new
insight and very useful diagnosis for the study of CME events. It
is shown that the initial instability took place in a small volume
located above an active region and that the occurrence of short radio
type III bursts implies a triggering process due to magnetic field
interactions. The subsequent spatial and temporal evolution of the
radio emission strongly suggests that the large scale structure becomes
unstable within the first minute of the event.
Title: LASCO observations of an Earth-directed coronal mass ejection
on May 12, 1997
Authors: Plunkett, S. P.; Thompson, B. J.; Howard, R. A.; Michels,
D. J.; St. Cyr, O. C.; Tappin, S. J.; Schwenn, R.; Lamy, P. L.
Bibcode: 1998GeoRL..25.2477P
Altcode:
Coronal mass ejections (CMEs) that occur near the center of the
solar disk are most likely to impact Earth. Detection of such
events as ‘halos’ in white-light coronagraphs has been somewhat
controversial in recent years. We present observations from the LASCO
coronagraphs on SOHO that provide convincing evidence of the detection
of an Earth-directed CME on May 12, 1997. The event began at about
04:35 UT and propagated outwards from the Sun with a projected speed
of around 250 km s-1. Using some reasonable assumptions
about the geometry of the CME, we estimate the true speed to be around
600 km s-1. The onset of the event in LASCO is coincident
(to within measurement uncertainties) with an eruptive event detected
in extreme ultraviolet observations of the solar disk by the SOHO
EIT. This is the first reported observation of a halo CME at projected
distances greater than 10 R⊙, with a clearly identifiable
solar origin. We discuss the possibility that at least some of the
enhanced brightness observed by LASCO may be due to a compressional
wave propagating in the corona.
Title: Origin of Streamer Material in the Outer Corona
Authors: Wang, Y. -M.; Sheeley, N. R., Jr.; Walters, J. H.; Brueckner,
G. E.; Howard, R. A.; Michels, D. J.; Lamy, P. L.; Schwenn, R.;
Simnett, G. M.
Bibcode: 1998ApJ...498L.165W
Altcode:
We investigate the nature and origin of the outward-moving density
inhomogeneities (``blobs'') detected previously with the Large Angle and
Spectrometric Coronagraph on the Solar and Heliospheric Observatory. The
blobs are concentrated around the thin plasma layer that surrounds
the heliospheric current sheet and that constitutes the outer streamer
belt; they represent only a small, fluctuating component of the total
density within the plasma sheet. As noted before in Sheeley et al.,
blobs are characterized by low speeds and are continually emitted
from the elongated tips of helmet streamers at 3-4 Rsolar
from Sun center. We suggest that both the blobs and the plasma sheet
itself represent closed-field material injected into the solar wind as
a result of footpoint exchanges between the stretched helmet-streamer
loops and neighboring open field lines. The plasma sheet is thus
threaded by newly reconnected, open magnetic field lines, which lend
the white-light streamer belt its filamentary appearance. Since in
situ observations at 1 AU show that the slow wind (with speeds below
500 km s-1) spreads over an angular extent much greater
than the <~3° width of the plasma sheet, we deduce that a major
component of this wind must originate outside the helmet streamers
(i.e., from just inside coronal holes).
Title: The November 6, 1997 event: Radio signatures of the CME
development
Authors: Maia, D.; Vourlidas, A.; Pick, M.; Howard, R.; Schwenn, R.;
Magalhaes, A.; Carneiro, J.; Agostinho, R.
Bibcode: 1998cee..workE..57M
Altcode:
The analysis of the November 6, 1997 event has taken advantage of the
new capabilities of the OPorto Radiospectrograph and of the Nanccay
Radioheliograph. The evolution of this event shows successive phases
in time scales of a fraction of a second. It is shown that the CME
observed by the LASCO/SOHO coronograph is the result of successive
interactions of multiple loop systems which occur over a latitude range
of about 100circ. These magnetic loop interactions lead to
the creation of several electron acceleration sites which are widely
separated in the corona. There is a close correspondance between the
evolution of the CME seen by LASCO and the extend of radio sources
seen by the radioheliograph. The association with particles detected
by in situ measurements in the interplanetary medium is also presented.
Title: Magnetic Reconnection Phenomena in Interplanetary Space
(invited)
Authors: Wei, F. S.; Schwenn, R.; Hu, Q.
Bibcode: 1998asct.conf..279W
Altcode:
No abstract at ADS
Title: European Plans for the Solar/Heliospheric Stereo Mission
Authors: Bothmer, V.; Bougeret, J. -L.; Cargill, P.; Davila, J.;
Delaboudiniere, J. -P.; Harrison, R.; Koutchmy, S.; Liewer, P.;
Maltby, P.; Rust, D.; Schwenn, R.
Bibcode: 1998ESASP.417..145B
Altcode: 1998cesh.conf..145B
No abstract at ADS
Title: The structure and origin of magnetic clouds in the solar wind
Authors: Bothmer, V.; Schwenn, R.
Bibcode: 1998AnGeo..16....1B
Altcode: 1998AnG....16....1B
Plasma and magnetic field data from the Helios 1/2 spacecraft have
been used to investigate the structure of magnetic clouds (MCs) in the
inner heliosphere. 46 MCs were identified in the Helios data for the
period 1974-1981 between 0.3 and 1 AU. 85% of the MCs were associated
with fast-forward interplanetary shock waves, supporting the close
association between MCs and SMEs (solar mass ejections). Seven MCs
were identified as direct consequences of Helios-directed SMEs, and
the passage of MCs agreed with that of interplanetary plasma clouds
(IPCs) identified as white-light brightness enhancements in the Helios
photometer data. The total (plasma and magnetic field) pressure in MCs
was higher and the plasma-<beta> lower than in the surrounding
solar wind. Minimum variance analysis (MVA) showed that MCs can best be
described as large-scale quasi-cylindrical magnetic flux tubes. The axes
of the flux tubes usually had a small inclination to the ecliptic plane,
with their azimuthal direction close to the east-west direction. The
large-scale flux tube model for MCs was validated by the analysis
of multi-spacecraft observations. MCs were observed over a range
of up to ~60° in solar longitude in the ecliptic having the same
magnetic configuration. The Helios observations further showed that
over-expansion is a common feature of MCs. From a combined study of
Helios, Voyager and IMP data we found that the radial diameter of MCs
increases between 0.3 and 4.2 AU proportional to the distance, R, from
the Sun as R0.8 (R in AU). The density decrease inside MCs was found to
be proportional to R-2.4, thus being stronger compared to the average
solar wind. Four different magnetic configurations, as expected from
the flux-tube concept, for MCs have been observed in situ by the Helios
probes. MCs with left- and right-handed magnetic helicity occurred
with about equal frequencies during 1974-1981, but surprisingly,
the majority (74%) of the MCs had a south to north (SN) rotation of
the magnetic field vector relative to the ecliptic. In contrast, an
investigation of solar wind data obtained near Earth's orbit during
1984-1991 showed a preference for NS-clouds. A direct correlation
was found between MCs and large quiescent filament disappearances
(disparition brusques, DBs). The magnetic configurations of the
filaments, as inferred from the orientation of the prominence axis,
the polarity of the overlying field lines and the hemispheric helicity
pattern observed for filaments, agreed well with the in situ observed
magnetic structure of the associated MCs. The results support the model
of MCs as large-scale expanding quasi-cylindrical magnetic flux tubes in
the solar wind, most likely caused by SMEs associated with eruptions of
large quiescent filaments. We suggest that the hemispheric dependence
of the magnetic helicity structure observed for solar filaments can
explain the preferred orientation of MCs in interplanetary space as
well as their solar cycle behavior. However, the white-light features
of SMEs and the measured volumes of their interplanetary counterparts
suggest that MCs may not simply be just H<alpha>-prominences,
but that SMEs likely convect large-scale coronal loops overlying the
prominence axis out of the solar atmosphere.
Title: Comparison of Observations of the Coronal FeXIV Emission and
the Solar Surface Magnetic Field
Authors: Inhester, B.; Schwenn, R.
Bibcode: 1997ESASP.415...47I
Altcode: 1997cpsh.conf...47I
No abstract at ADS
Title: The Dynamics of the Quiet Corona as Observed by the LASCO C2
and C3 Coronagraphs
Authors: Andrews, M. D.; Morrill, J. S.; Howard, R. A.; Biesecker,
D. A.; Schwenn, R.; Liebaria, A.
Bibcode: 1997ESASP.415..303A
Altcode: 1997cpsh.conf..303A
No abstract at ADS
Title: Evidence of an Erupting Magnetic Flux Rope: LASCO Coronal
Mass Ejection of 1997 April 13
Authors: Chen, J.; Howard, R. A.; Brueckner, G. E.; Santoro, R.;
Krall, J.; Paswaters, S. E.; St. Cyr, O. C.; Schwenn, R.; Lamy, P.;
Simnett, G. M.
Bibcode: 1997ApJ...490L.191C
Altcode:
A coronal mass ejection (CME) observed by LASCO exhibits evidence
that its magnetic field geometry is that of a flux rope. The dynamical
properties throughout the fields of view of C2 and C3 telescopes are
examined. The results are compared with theoretical predictions based
on a model of solar flux ropes. It is shown that the LASCO observations
are consistent with a two-dimensional projection of a three-dimensional
magnetic flux rope with legs that remain connected to the Sun.
Title: White-Light Coronal Mass Ejections: A New Perspective from
LASCO
Authors: St. Cyr, O. C.; Howard, R. A.; Simnett, G. M.; Gurman, J. B.;
Plunkett, S. P.; Sheeley, N. R.; Schwenn, R.; Koomen, M. J.; Brueckner,
G. E.; Michels, D. J.; Andrews, M.; Biesecker, D. A.; Cook, J.; Dere,
K. P.; Duffin, R.; Einfalt, E.; Korendyke, C. M.; Lamy, P. L.; Lewis,
D.; Llebaria, A.; Lyons, M.; Moses, J. D.; Moulton, N. E.; Newmark,
J.; Paswaters, S. E.; Podlipnik, B.; Rich, N.; Schenk, K. M.; Socker,
D. G.; Stezelberger, S. T.; Tappin, S. J.; Thompson, B.; Wang, D.
Bibcode: 1997ESASP.415..103S
Altcode: 1997cpsh.conf..103S
No abstract at ADS
Title: LASCO Observations of Disconnected Magnetic Structures Out
to Beyond 28 Solar Radii During Coronal Mass Ejections
Authors: Simnett, G. M.; Tappin, S. J.; Plunkett, S. P.; Bedford,
D. K.; Eyles, C. J.; St. Cyr, O. C.; Howard, R. A.; Brueckner, G. E.;
Michels, D. J.; Moses, J. D.; Socker, D.; Dere, K. P.; Korendyke,
C. M.; Paswaters, S. E.; Wang, D.; Schwenn, R.; Lamy, P.; Llebaria,
A.; Bout, M. V.
Bibcode: 1997SoPh..175..685S
Altcode:
Two coronal mass ejections have been well observed by the LASCO
coronagraphs to move out into the interplanetary medium as disconnected
plasmoids. The first, on July 28, 1996, left the Sun above the west
limb around 18:00 UT. As it moved out, a bright V-shaped structure
was visible in the C2 coronagraph which moved into the field-of-view
of C3 and could be observed out to beyond 28 solar radii. The derived
average velocity in the plane of the sky was 110 ± 5 km s-1
out to 5 solar radii, and above 15 solar radii the velocity was 269
± 10 km s-1. Thus there is evidence of some acceleration
around 6 solar radii. The second event occurred on November 5, 1996
and left the west limb around 04:00 UT. The event had an average
velocity in the plane of the sky of ∼54 km s-1 below
4 R⊙, and it accelerated rapidly around 5 R⊙ up to 310 ± 10 km
s-1. In both events the rising plasmoid is connected back
to the Sun by a straight, bright ray, which is probably a signature of
a neutral sheet. In the November event there is evidence for multiple
plasmoid ejections. The acceleration of the plasmoids around a projected
altitude of 5 solar radii is probably a manifestation of the source
surface of the solar wind.
Title: First View of the Extended Green-Line Emission Corona At
Solar Activity Minimum Using the Lasco-C1 Coronagraph on SOHO
Authors: Schwenn, R.; Inhester, B.; Plunkett, S. P.; Epple, A.;
Podlipnik, B.; Bedford, D. K.; Eyles, C. J.; Simnett, G. M.; Tappin,
S. J.; Bout, M. V.; Lamy, P. L.; Llebaria, A.; Brueckner, G. E.;
Dere, K. P.; Howard, R. A.; Koomen, M. J.; Korendyke, C. M.; Michels,
D. J.; Moses, J. D.; Moulton, N. E.; Paswaters, S. E.; Socker, D. G.;
St. Cyr, O. C.; Wang, D.
Bibcode: 1997SoPh..175..667S
Altcode:
The newly developed C1 coronagraph as part of the Large-Angle
Spectroscopic Coronagraph (LASCO) on board the SOHO spacecraft has
been operating since January 29, 1996. We present observations
obtained in the first three months of operation. The green-line
emission corona can be made visible throughout the instrument's full
field of view, i.e., from 1.1 R⊙ out to 3.2 R⊙ (measured from Sun
center). Quantitative evaluations based on calibrations cannot yet be
performed, but some basic signatures show up even now: (1) There are
often bright and apparently closed loop systems centered at latitudes
of 30° to 45° in both hemispheres. Their helmet-like extensions
are bent towards the equatorial plane. Farther out, they merge into
one large equatorial `streamer sheet' clearly discernible out to 32
R⊙. (2) At mid latitudes a more diffuse pattern is usually visible,
well separated from the high-latitude loops and with very pronounced
variability. (3) All high-latitude structures remain stable on time
scales of several days, and no signature of transient disruption of
high-latitude streamers was observed in these early data. (4) Within
the first 4 months of observation, only one single `fast' feature was
observed moving outward at a speed of 70 km s-1 close to
the equator. Faster events may have escaped attention because of data
gaps. (5) The centers of high-latitude loops are usually found at the
positions of magnetic neutral lines in photospheric magnetograms. The
large-scale streamer structure follows the magnetic pattern fairly
precisely. Based on our observations we conclude that the shape
and stability of the heliospheric current sheet at solar activity
minimum are probably due to high-latitude streamers rather than to
the near-equatorial activity belt.
Title: The Relationship of Green-Line Transients to White-Light
Coronal Mass Ejections
Authors: Plunkett, S. P.; Brueckner, G. E.; Dere, K. P.; Howard,
R. A.; Koomen, M. J.; Korendyke, C. M.; Michels, D. J.; Moses, J. D.;
Moulton, N. E.; Paswaters, S. E.; St. Cyr, O. C.; Socker, D. G.;
Wang, D.; Simnett, G. M.; Bedford, D. K.; Biesecker, D. A.; Eyles,
C. J.; Tappin, S. J.; Schwenn, R.; Lamy, P. L.; Llebaria, A.
Bibcode: 1997SoPh..175..699P
Altcode:
We report observations by the Large Angle Spectrometric Coronagraph
(LASCO) on the SOHO spacecraft of three coronal green-line transients
that could be clearly associated with coronal mass ejections (CMEs)
detected in Thomson-scattered white light. Two of these events, with
speeds >25 km s-1, may be classified as `whip-like'
transients. They are associated with the core of the white-light
CMEs, identified with erupting prominence material, rather than with
the leading edge of the CMEs. The third green-line transient has a
markedly different appearance and is more gradual than the other two,
with a projected outward speed <10 km s-1. This event
corresponds to the leading edge of a `streamer blowout' type of CME. A
dark void is left behind in the emission-line corona following each of
the fast eruptions. Both fast emission-line transients start off as a
loop structure rising up from close to the solar surface. We suggest
that the driving mechanism for these events may be the emergence of new
bipolar magnetic regions on the surface of the Sun, which destabilize
the ambient corona and cause an eruption. The possible relationship of
these events to recent X-ray observations of CMEs is briefly discussed.
Title: MHD Interpretation of LASCO Observations of a Coronal Mass
Ejection as a Disconnected Magnetic Structure
Authors: Wu, S. T.; Guo, W. P.; Andrews, M. D.; Brueckner, G. E.;
Howard, R. A.; Koomen, M. J.; Korendyke, C. M.; Michels, D. J.; Moses,
J. D.; Socker, D. G.; Dere, K. P.; Lamy, P. L.; Llebaria, A.; Bout,
M. V.; Schwenn, R.; Simnett, G. M.; Bedford, D. K.; Eyles, C. J.
Bibcode: 1997SoPh..175..719W
Altcode:
We present a qualitative and quantitative comparison of a single
coronal mass ejection (CME) as observed by LASCO (July 28-29, 1996)
with the results of a three-dimensional axisymmetric time-dependent
magnetohydrodynamic model of a flux rope interacting with a helmet
streamer. The particular CME considered was selected based on the
appearance of a distinct `tear-drop' shape visible in animations
generated from both the data and the model.
Title: EIT and LASCO Observations of the Initiation of a Coronal
Mass Ejection
Authors: Dere, K. P.; Brueckner, G. E.; Howard, R. A.; Koomen, M. J.;
Korendyke, C. M.; Kreplin, R. W.; Michels, D. J.; Moses, J. D.;
Moulton, N. E.; Socker, D. G.; St. Cyr, O. C.; Delaboudinière, J. P.;
Artzner, G. E.; Brunaud, J.; Gabriel, A. H.; Hochedez, J. F.; Millier,
F.; Song, X. Y.; Chauvineau, J. P.; Marioge, J. P.; Defise, J. M.;
Jamar, C.; Rochus, P.; Catura, R. C.; Lemen, J. R.; Gurman, J. B.;
Neupert, W.; Clette, F.; Cugnon, P.; Van Dessel, E. L.; Lamy, P. L.;
Llebaria, A.; Schwenn, R.; Simnett, G. M.
Bibcode: 1997SoPh..175..601D
Altcode:
We present the first observations of the initiation of a coronal mass
ejection (CME) seen on the disk of the Sun. Observations with the EIT
experiment on SOHO show that the CME began in a small volume and was
initially associated with slow motions of prominence material and a
small brightening at one end of the prominence. Shortly afterward,
the prominence was accelerated to about 100 km s-1 and
was preceded by a bright loop-like structure, which surrounded an
emission void, that traveled out into the corona at a velocity of
200-400 km s-1. These three components, the prominence,
the dark void, and the bright loops are typical of CMEs when seen at
distance in the corona and here are shown to be present at the earliest
stages of the CME. The event was later observed to traverse the LASCO
coronagraphs fields of view from 1.1 to 30 R⊙. Of particular interest
is the fact that this large-scale event, spanning as much as 70 deg in
latitude, originated in a volume with dimensions of roughly 35" (2.5
x 104 km). Further, a disturbance that propagated across
the disk and a chain of activity near the limb may also be associated
with this event as well as a considerable degree of activity near the
west limb.
Title: Origin and Evolution of Coronal Streamer Structure During
the 1996 Minimum Activity Phase
Authors: Wang, Y. -M.; Sheeley, N. R., Jr.; Howard, R. A.; Kraemer,
J. R.; Rich, N. B.; Andrews, M. D.; Brueckner, G. E.; Dere, K. P.;
Koomen, M. J.; Korendyke, C. M.; Michels, D. J.; Moses, J. D.;
Paswaters, S. E.; Socker, D. G.; Wang, D.; Lamy, P. L.; Llebaria,
A.; Vibert, D.; Schwenn, R.; Simnett, G. M.
Bibcode: 1997ApJ...485..875W
Altcode:
We employ coronal extrapolations of solar magnetograph data to interpret
observations of the white-light streamer structure made with the LASCO
coronagraph in 1996. The topological appearance of the streamer belt
during the present minimum activity phase is well described by a model
in which the Thomson-scattering electrons are concentrated around a
single, warped current sheet encircling the Sun. Projection effects
give rise to bright, jet-like structures or spikes whenever the current
sheet is viewed edge-on multiple spikes are seen if the current sheet is
sufficiently wavy. The extreme narrowness of these features in polarized
images indicates that the scattering layer is at most a few degrees
wide. We model the evolution of the streamer belt from 1996 April to
1996 September and show that the effect of photospheric activity on
the streamer belt topology depends not just on the strength of the
erupted magnetic flux, but also on its longitudinal phase relative
to the background field. Using flux transport simulations, we also
demonstrate how the streamer belt would evolve during a prolonged
absence of activity.
Title: The Green Line Corona and Its Relation to the Photospheric
Magnetic Field
Authors: Wang, Y. -M.; Sheeley, N. R., Jr.; Hawley, S. H.; Kraemer,
J. R.; Brueckner, G. E.; Howard, R. A.; Korendyke, C. M.; Michels,
D. J.; Moulton, N. E.; Socker, D. G.; Schwenn, R.
Bibcode: 1997ApJ...485..419W
Altcode:
Images of the green line corona made with the LASCO C1 coronagraph
on SOHO are analyzed by applying current-free extrapolations to the
observed photospheric field. The Fe XIV λ5303 emission is shown to
be closely related to the underlying photospheric field strength. By
modeling the observed intensity patterns as a function of latitude and
height above the solar limb, we derive an approximate scaling law of the
form nfoot ~ <Bfoot>0.9, where
nfoot is the density of the green line-emitting plasma and
<Bfoot> is the average field strength at the footprints
of the coronal loop. The observed high-latitude enhancements in the
green line corona are attributed to the poleward concentration of the
large-scale photospheric field. The strongest such enhancements occur
where the high-latitude unipolar fields become reconnected to active
region flux at lower latitudes; the global emission pattern rotates
quasi-rigidly at the rate of the dominant active region complex. The
validity of the current-free approximation is assessed by comparing
the topology of the observed and simulated green line structures.
Title: Measurements of Flow Speeds in the Corona Between 2 and 30
R⊙
Authors: Sheeley, N. R.; Wang, Y. -M.; Hawley, S. H.; Brueckner,
G. E.; Dere, K. P.; Howard, R. A.; Koomen, M. J.; Korendyke, C. M.;
Michels, D. J.; Paswaters, S. E.; Socker, D. G.; St. Cyr, O. C.;
Wang, D.; Lamy, P. L.; Llebaria, A.; Schwenn, R.; Simnett, G. M.;
Plunkett, S.; Biesecker, D. A.
Bibcode: 1997ApJ...484..472S
Altcode:
Time-lapse sequences of white-light images, obtained during sunspot
minimum conditions in 1996 by the Large Angle Spectrometric Coronagraph
on the Solar and Heliospheric Observatory, give the impression of
a continuous outflow of material in the streamer belt, as if we
were observing Thomson scattering from inhomogeneities in the solar
wind. Pursuing this idea, we have tracked the birth and outflow of
50-100 of the most prominent moving coronal features and find that:
1. They originate about 3-4 R⊙ from Sun center as
radially elongated structures above the cusps of helmet streamers. Their
initial sizes are about 1 R⊙ in the radial direction and
0.1 R⊙ in the transverse direction. 2. They move
radially outward, maintaining constant angular spans and increasing
their lengths in rough accord with their speeds, which typically
double from 150 km s-1 near 5 R⊙ to 300 km
s-1 near 25 R⊙. 3. Their individual speed
profiles v(r) cluster around a nearly parabolic path characterized
by a constant acceleration of about 4 m s-2 through most
of the 30 R⊙ field of view. This profile is consistent
with an isothermal solar wind expansion at a temperature of about
1.1 MK and a sonic point near 5 R⊙. Based on their
relatively small initial sizes, low intensities, radial motions, slow
but increasing speeds, and location in the streamer belt, we conclude
that these moving features are passively tracing the outflow of the
slow solar wind.
Title: Using LASCO Observations to Infer Solar Wind Flow Near the Sun
Authors: Sheeley, N. R., Jr.; Brueckner, G. E.; Dere, K. P.; Howard,
R. A.; Korendyke, C. M.; Michels, D. J.; Socker, D. G.; Koomen, M. J.;
Paswaters, S. E.; Wang, D.; Lamy, P. L.; Llebaria, A.; Schwenn, R.;
St Cyr, O. C.; Simnett, G. M.; Plunkett, S.; Biesecker, D. A.
Bibcode: 1997SPD....28.0301S
Altcode: 1997BAAS...29..907S
We have continued to track individual coronal features as they become
detached from helmet streamers and move outward from the Sun. The
composite speed profile for 50-100 features has a parabolic shape
with a constant acceleration of about 4 m/s(2) over the 2-30 R field
of view. This well-determined speed profile contrasts strongly with
the nearly uniform scatterplot obtained for about 50 nominal coronal
mass ejections (CMEs), and suggests that these detached bits of coronal
``debris'' are passively tracing the speed of the slow solar wind. We
have also begun the more difficult task of tracking outflow along
polar plumes and will summarize these results as of June 1997.
Title: Pressure enhancement associated with meridional flow in
high-speed solar wind: possible evidence for an interplanetary
magnetic flux rope
Authors: Tu, C. -Y.; Marsch, E.; Ivory, K.; Schwenn, R.
Bibcode: 1997AnGeo..15..137T
Altcode: 1997AnG....15..137T
A sizable total-pressure (magnetic pressure plus kinetic pressure)
enhancement was found within the high-speed wind stream observed by
Helios 2 in 1976 near 0.3 AU. The proton density and temperature and
the magnetic magnitude simultaneously increased for about 6 h. This
pressure rise was associated with a comparatively large southward
flow velocity component (with Vz <>~<> -100 km · s-1)
and magnetic-field rotation. The pressure enhancement was associated
with unusual features in the electron distribution function. It shows a
wide angular distribution of electron counting rates in the low-energy
(57.8 eV) channel, while previous to the enhancement it exhibits a
wide angular distribution of electron count rate in the high-energy
(112, 221 and 309 eV) channels, perhaps indicating the mirroring of
electrons in the converging field lines of the background magnetic
field. These fluid and kinetic phenomena may be explained as resulting
from an interplanetary magnetic flux rope which is not fully convected
by the flow but moves against the background wind towards the Sun.
Title: The Solar Minimum X2. 6/1B Flare and CME of 9 July 1996;
Part 1: Solar Data
Authors: Andrews, M. D.; Dryer, M.; Aurass, H.; DeForest, C.;
Kiplinger, A. L.; Meisner, R.; Paswaters, S. E.; Smith, Z.; Tappipn,
S. J.; Thompson, B. J.; Watari, S. I.; Lamy, P.; Mann, G.; Schwenn,
R.; Michels, D. J.; Brueckner, G. E.; Howard, R. A.; Koomen, M.
Bibcode: 1997ESASP.404..169A
Altcode: 1997cswn.conf..169A
No abstract at ADS
Title: Characterisation of Polar Plumes from LASCO-C2 Images in
Early 1996
Authors: Lamy, P.; Liebaria, A.; Koutchmy, S.; Reynet, P.; Molodensky,
M.; Howard, R.; Schwenn, R.; Simnett, G.
Bibcode: 1997ESASP.404..487L
Altcode: 1997cswn.conf..487L
No abstract at ADS
Title: The Solar Minimum X2. 6/1B Flare and CME of 9 July 1996;
Part 2: Propagation
Authors: Dryer, M.; Andrews, M. D.; Aurass, H.; DeForest, C.; Karlicky,
M.; Kiplinger, A.; Klassen, A.; Meisner, R.; Ipavich, F. M.; Galvin,
A. B.; Paswaters, S. E.; Smith, Z.; Tappin, S. J.; Thompson, B. J.;
Watari, S. -I.; Michels, D. J.; Brueckner, G. E.; Howard, R. A.;
Koomen, M. J.; Lamy, P.; Mann, G.; Arzner, K.; Schwenn, R.
Bibcode: 1997ESASP.404..331D
Altcode: 1997cswn.conf..331D
No abstract at ADS
Title: Acceleration of Coronal Mass Ejections in the Upper Corona:
Observations from Lasco/Soho
Authors: Simnett, G. M.; Tappin, S. J.; Brueckner, G. E.; Howard,
R. A.; Lamy, P.; Michels, D. J.; Schwenn, R.
Bibcode: 1997ICRC....1..181S
Altcode: 1997ICRC...25a.181S
No abstract at ADS
Title: Dynamical Evolution of a Coronal Mass Ejection (CME) to
Magnetic Cloud: A Preliminary Analysis of the January 6-10, 1997
CME Observed by LASCO/SOHO
Authors: Wu, S. T.; Guo, W. P.; Michels, D. J.; Andrews, M. D.;
Brueckner, G. E.; Howard, R. A.; Koomen, M. J.; Korendyke, C. M.;
Moses, J. D.; Socker, D. G.; Dere, K. P.; Bougeret, Jean-Louis; Lamy,
P. L.; Schwenn, R.; Simnett, G. M.
Bibcode: 1997ESASP.404..739W
Altcode: 1997cswn.conf..739W
No abstract at ADS
Title: EIT and LASCO Observations of the Initiation of a Coronal
Mass Ejection
Authors: Dere, K. P.; Brueckner, G. E.; Howard, R. A.; Koomen, M. J.;
Korendyke, C. M.; Michels, D. J.; Moses, J. D.; Moulton, N. E.; Socker,
D. G.; Delaboudiniere, J. P.; Hochedez, J. F.; Lamy, P. L.; Schwenn,
R.; Simnett, G. M.; Defise, J. M.; Catura, R. C.
Bibcode: 1997IAUJD..19E..18D
Altcode:
We present the first observations of the initiation of a corona mass
ejection (CME) seen on the disk of the Sun. Observations with the EIT
and LASCO experiments on SOHO show that the CME starts in a small volume
and is associated with slow motions of prominence material. At about
the same time, a shock wave is created that travels out into the corona
at a velocity of 400 km s^{-1} ahead of an eruptive prominence. This
shock wave is clearly the event that is later seen as a classical CME
when observed in the coronagraph above 1.5 solar radii. Although the
CME clearly starts in a small region, a chain of activity near the
limb may also be associated with this event.
Title: Mirror Coronograph for Argentina (MICA). Primera Luz
Authors: Stenborg, G.; Epple, A.; Schwenn, R.; Francile, C.; Rovira, M.
Bibcode: 1997BAAA...41..115S
Altcode:
En Julio de 1997 se terminó con la primera parte de la instalación del
``Coronógrafo de Espejo para la Argentina'' en la estación de altura
Carlos U. Cesco (El Leoncito), gracias al esfuerzo de la gente del Max
Planck Institut für Aeronomie (Alemania), del OAFA y del IAFE. Dicho
coronógrafo forma parte de un programa de ciencia bilateral entre
Alemania y Argentina. El propósito del mismo, en conjunción con otros
telescopios solares y terrestres, es contribuir a un mejor entendimiento
de cuestiones fundamentales de la física solar. Para ello, ya está
observando la corona de emisión en el verde (Fe XIV), rojo (Fe X)
y Hα entre 1.05 y 2 radios solares aproximadamente. El diseño del
instrumento, el cual fuera ya presentado en esta misma reunión en La
Plata en 1996, es esencialmente similar al del telescopio LASCO-C1 a
bordo del Solar Heliospheric Observatory (SOHO). La adquisición de
datos se realiza con un CCD de 1280x1024 pixels, codificando en 12
bits, pudiendo ser el mismo operado en forma remota. En esta reunión
presentaremos algunas de las observaciones realizadas durante la puesta
a punto del instrumento en el período julio-setiembre de 1997. Asimismo
expondremos cómo y por qué sus resultados complementarán a los de
su par en el espacio.
Title: Electronic Densities in Coronal Holes from LASCO-C2 Images
Authors: Lamy, P.; Quemerais, E.; Llebaria, A.; Bout, M.; Howard,
R.; Schwenn, R.; Simnett, G.
Bibcode: 1997ESASP.404..491L
Altcode: 1997cswn.conf..491L
No abstract at ADS
Title: Joint Radioheliograph and LASCO Observations of Coronal
Mass Ejections
Authors: Pick, M.; Maia, D.; Howard, R.; Kerdraon, A.; Brueckner,
G. E.; Lamy, P.; Schwenn, R.; Aurass, H.
Bibcode: 1997ESASP.404..601P
Altcode: 1997cswn.conf..601P
No abstract at ADS
Title: Visibility of Earth-Directed Coronal Mass Ejections
Authors: Michels, D. J.; Howard, R. A.; Koomen, M. J.; Plunkett, S.;
Brueckner, G. E.; Lamy, Ph.; Schwenn, R.; Biesecker, D. A.
Bibcode: 1997ESASP.404..567M
Altcode: 1997cswn.conf..567M
No abstract at ADS
Title: Non-Thermal Weak Radio Bursts: X-ray and/or EUV Counterparts?
Authors: Crosby, N.; Vilmer, N.; Chiuderi Drago, F.; Pick, M.;
Kerdraon, A.; Khan, J.; Schwenn, R.
Bibcode: 1997ESASP.404..299C
Altcode: 1997cswn.conf..299C
No abstract at ADS
Title: Analysis of a High Latitude Slow CME with Travelling Ejecta
Authors: Boulade, S.; Delanné, C.; Koutchmy, S.; Lamy, P.; Llebaria,
A.; Howard, R.; Schwenn, R.; Simnett, G.
Bibcode: 1997ESASP.404..217B
Altcode: 1997cswn.conf..217B
No abstract at ADS
Title: Enhancing the Spatial Resolution of Solar Coronagraph
Observations Using Dynamic Imaging
Authors: Zaccheo, T. S.; Karovska, M.; Cook, J. W.; Howard, R. A.;
Brueckner, G. E.; Korendyke, C. M.; Schwenn, R.
Bibcode: 1996ApJ...471.1058Z
Altcode:
The Large Angle Spectrometric Coronagraph (LASCO) Cl coronagraph on
board the Solar and Heliospheric Observatory (SOHO) is designed to
image the corona from 1.1 to 3.0 Rsun. The resolution of
C1 is defined by the size of its CCD pixels, which correspond to 5".6,
and not by the diffraction limit of the optical system, which may be as
small as 3". The resolution of Cl can be improved using the technique of
"dynamic imaging" the process of acquiring successive images of the same
scene using sub- pixel displacements of the steerable primary mirror. We
developed a technique we call the fractional pixel restoration (F PR)
algorithm that utilizes these observations to construct an image with
improved resolution. Simulations were used to test this algorithm and
to explore its limitations. We also applied the direct co-addition
and FPR algorithms to laboratory preffight images of a wire mesh
grid. These results show that the resolution of the C1 coronagraph can
be significantly enhanced, even in the presence of noise and modest
differences between successive images. In some cases, the results can
even reach the diffraction limit of the telescope.
Title: LASCO spectrometric Lyot coronagraph tunable passband filter
Authors: Socker, Dennis G.; Brueckner, Guenter E.; Korendyke, Clarence
M.; Lilley, D. N.; Steenson, James H.; Kohn, Preston M.; Lyons, Gail
M.; Owens, Michael L.; Moulton, Norman E.; Moye, Robert W.; Schwenn,
Rainer; Hemmerich, P.
Bibcode: 1996SPIE.2804..126S
Altcode:
Spectrometric and spectropolarimetric aspects of the Lyot coronagraph
flown aboard the ESA/NASA SOlar Heliospheric Observatory (SOHO) are
presented. The coronagraph is one of the three channels comprising
the LASCO coronagraph and the only channel with spectroradiometric
capabilities. Among the primary science objectives assigned to the
Lyot coronagraph are the determination of the mechanisms responsible
for the acceleration of the solar wind and the heating of the
corona. Spectrometric and spectropolarimetric coronal observations
made with the Lyot coronagraph are used in support of these and
other objectives. We describe the Lyot instrument design from the
imaging coronal spectrometer perspective. The rationale for use
of a tunable Fabry-Perot interferometer as the spectral resolving
element is outlined. The relationships between spectral resolving
power, interferometer diameter, telescope entrance stop diameter and
coronal field of view as it applies to LASCO is reviewed. Performance
requirements imposed on the interferometer by the coronal source and the
science objectives are described. The optical, mechanical, electronic
and semi-automated control designs as well as the interferometer
modes of operation are summarized. The actual flight model Fabry-Perot
interferometer performance allows the instrument to operate with high
luminosity and with finesse values high enough to provide approximately
optimal passband widths and reasonable tunable ranges about useful
spectral features. We conclude with some early results indicative of
the flight performance of the instrument.
Title: STEREO: a solar terrestrial event observer mission concept
Authors: Socker, Dennis G.; Antiochos, S. K.; Brueckner, Guenter E.;
Cook, John W.; Dere, Kenneth P.; Howard, Russell A.; Karpen, J. T.;
Klimchuk, J. A.; Korendyke, Clarence M.; Michels, Donald J.; Moses,
J. Daniel; Prinz, Dianne K.; Sheely, N. R.; Wu, Shi T.; Buffington,
Andrew; Jackson, Bernard V.; Labonte, Barry; Lamy, Philippe L.;
Rosenbauer, H.; Schwenn, Rainer; Burlaga, L.; Davila, Joseph M.; Davis,
John M.; Goldstein, Barry; Harris, H.; Liewer, Paulett C.; Neugebauer,
Marcia; Hildner, E.; Pizzo, Victor J.; Moulton, Norman E.; Linker,
J. A.; Mikic, Z.
Bibcode: 1996SPIE.2804...50S
Altcode:
A STEREO mission concept requiring only a single new spacecraft has been
proposed. The mission would place the new spacecraft in a heliocentric
orbit and well off the Sun- Earth line, where it can simultaneously view
both the solar source of heliospheric disturbances and their propagation
through the heliosphere all the way to the earth. Joint observations,
utilizing the new spacecraft and existing solar spacecraft in earth
orbit or L1 orbit would provide a stereographic data set. The new
and unique aspect of this mission lies in the vantage point of the
new spacecraft, which is far enough from Sun-Earth line to allow an
entirely new way of studying the structure of the solar corona, the
heliosphere and solar-terrestrial interactions. The mission science
objectives have been selected to take maximum advantage of this new
vantage point. They fall into two classes: those possible with the
new spacecraft alone and those possible with joint measurements using
the new and existing spacecraft. The instrument complement on the new
spacecraft supporting the mission science objectives includes a soft
x-ray imager, a coronagraph and a sun-earth imager. Telemetry rate
appears to be the main performance determinant. The spacecraft could
be launched with the new Med-Lite system.
Title: A method for shock determination and classification
Authors: Liu, Shuhui; Marsch, E.; Schwenn, R.; Rosenbauer, H.
Bibcode: 1996AIPC..382..376L
Altcode:
A new method to present, to determine and to classify shocks from in
situ measurements is developed, using normalized velocities up- and
down-stream in a velocity V1-V2 diagram. With
this method one can show how the observed shock solutions vary with
different time averages over the data from the up- and down-stream
region. Some shock events have been analyzed. The Helios measurements
show, that the solutions for the fast forward shock are confined well
in the 1-->2 region. The different solutions, obtained by means of
straightforward averages with different time intervals, are somewhat
distributed in the normalized V1-V2 diagram. But
only the shock solutions which are consistent with the Rankine-Hugoniot
relations and an entropy increase really define a particular shock.
Title: Mass ejections from the sun and their interplanetary
counterparts
Authors: Schwenn, R.
Bibcode: 1996AIPC..382..426S
Altcode:
Since the first observations of solar mass ejection events in the early
seventies by OSO 7 and Skylab, a few thousand of these remarkable
dynamic incidents have been observed, covering about two full solar
activity cycles. The mass ejecta mainly include hot coronal plasma and
cold prominence material in variable amounts. This is the reason why the
often used term CME (for coronal mass ejection) should be replaced by
the more neutral term SME (solar mass ejection). The ejecta are often
recognized in the form of interplanetary plasma clouds detected in the
distant solar wind by appropriately located spacecraft. Clouds which
have been energetic enough to drive large scale interplanetary shock
waves can be identified most readily, but clouds without associated
shocks do also occur. Plasma clouds can be characterized by a variety
of signatures, indicating that they actually originate from injections
of different material into the ambient solar wind. Quite a few crucial
problems still remain to be addressed by the upcoming SOHO mission.
Title: LASCO Observations of the 03Feb96 Streamer Blow-out
Authors: Andrews, M. D.; Korendyke, C. M.; Koomen, M. J.; Brueckner,
G. E.; Cook, J. W.; Dere, K. P.; Howard, R. A.; Michels, D. J.; Moses,
J. D.; Morrill, J. S.; Moulton, N. E.; Paswaters, S. E.; Socker, D. G.;
St. Cyr, O. C. St.; Wang, D.; Lamy, P. L.; Llebaria, A.; Bout, M. V.;
Schwenn, R.; Podlipnik, B.; Bedford, D. K.; Biesecker, D. A.; Eyles,
C. J.; Plunkett, S.; Simnett, G. M.
Bibcode: 1996AAS...188.3716A
Altcode: 1996BAAS...28..880A
The C2 and C3 telescopes on the Large Angle Spectrometric Coronograph
(LASCO) have recorded images of a Streamer Blow-out which occured
on 03Feb96. We will present a series of images produces by combining
data from the 2 coronographs. These images show a rapid evolution of
the coronal streamer belt over projected distances of 2 to 20 solar
radii. The streamer belt shows a dramatic brightening, which is seen to
propagate outward. A bubble-like structure is seen to move away from
the Sun and expand. At the end of this event, the equatorial corona
is significantly less bright than prior to the event.
Title: LASCO Observations of the Solar Corona to 32 Rsun
Authors: Cook, J. W.; Koomen, M. J.; Korendyke, C. M.; Brueckner,
G. E.; Dere, K. P.; Howard, R. A.; Michels, D. J.; Morrill, J. S.;
Moses, J. D.; Socker, D. G.; Paswaters, S. E.; Wang, D.; Moulton,
N. E.; Cyr, O. C. St.; Andrews, M. D.; Schwenn, R.; Podlipnik, B.;
Lamy, P. L.; Llebaria, A.; Bout, M. V.; Simnett, G. M.; Bedford,
D. K.; Eyles, C. J.; Plunkett, S.; Biesecker, D. A.
Bibcode: 1996AAS...188.3717C
Altcode: 1996BAAS...28..880C
The Large Angle Spectrometric Coronagraph (LASCO) was launched on
board the SOHO satellite on 2 December 1995. The C3 externally-occulted
coronagraph of LASCO observes the solar corona over a field from 3.7-32
R_ ⊙, using a 1024x1024 CCD detector with a pixel size corresponding
to 56 arc sec. Observations can be made using color filters ranging
from the blue (420-520 nm) to the near-IR (860-1050 nm), and through
polarizing filters. We report on early observations of the solar corona
out to 32 Rsun.
Title: Preliminary Photometric Calibration of LASCO C3 Coronagraph
Images using Pre-Flight Laboratory Images of Standard Sources and
In-Flight Images of Standard Stars
Authors: Korendyke, C. M.; Koomen, M. J.; Andrews, M. D.; Brueckner,
G. E.; Cook, J. W.; Dere, K. P.; Howard, R. A.; Michels, D. J.;
Moses, J. D.; Morrill, J. S.; Moulton, N. E.; Paswaters, S. E.;
Socker, D. G.; St. Cyr, O. C.; Wang, D.; Lamy, P. L.; Llebaria, A.;
Bout, M. V.; Schwenn, R.; Podlipnik, B.; Bedford, D. K.; Biesecker,
D. A.; Eyles, C. J.; Plunkett, S.; Simnett, G. M.
Bibcode: 1996AAS...188.3621K
Altcode: 1996BAAS...28..876K
The C3 coronagraph is a wide field (+/-8.0 degrees), externally
occulted, white light coronagraph. The instrument is one of three
coronagraphs comprising the Large Angle Spectrometric COronagraph
(LASCO) experiment mounted on the Solar Heliospheric Observatory
satellite. The satellite was launched on Dec. 2, 1996; C3 observations
began in early Jan. 1997. The coronagraph optical train includes a set
of five broadband color filters mounted in a wheel. Prior to flight,
an image was obtained through each color filter of a well characterized,
rear-illuminated, opal glass diffusing screen. The C3 in-flight images,
in addition to the coronal structures, also contain several hundred
bright stars. We present a comparison of the photometric calibration
derived from standard stars with the laboratory measurements. The
resulting calibration is then used to examine color variations in the
white light corona over the field of view. The LASCO experiment was
developed by a scientific consortium of members from NRL (USA), MPAe
(Germany), LAS (France) and U. Birmingham (United Kingdom).
Title: Signatures of fast CMEs in interplanetary space
Authors: Bothmer, V.; Schwenn, R.
Bibcode: 1996AdSpR..17d.319B
Altcode: 1996AdSpR..17..319B
While fast coronal mass ejections (CMEs) have been uniquely identified
as sources of transient shock-disturbances in interplanetary space,
it is less understood why different kinds of plasma and magnetic field
signatures are found in the individual post-shock flows. It is an
open question if CMEs can produce various types of solar wind ejecta,
e.g. magnetic flux ropes or flows without highly ordered internal
fields. To help further clarify the consequences of fast CMEs in
interplanetary space we have examined shock events measured by the
Helios 1 spacecraft during the years 1979-1981 for which the associated
CME has been directly observed with the coronagraph onboard the P78/1
satellite. Seventeen (68%) out of 25 shock-disturbances were followed
by clearly discernible driver gas signatures, but only 7 (41%) of the
driver gases were magnetic clouds.
Title: An Essay on Terminology, Myths and Known Facts: Solar Transient
- Flare - CME - Driver Gas - Piston - BDE - Magnetic Cloud - Shock
Wave - Geomagnetic Storm
Authors: Schwenn, Rainer
Bibcode: 1996Ap&SS.243..187S
Altcode: 1996IAUCo.154..187S
In the field of solar-terrestrial relations a clear and unique
terminology is needed in order to abolish and avoid unnecessary
confusion between the scientists from several involved disciplines. For
example, the widely used abbreviationCME (for coronal mass ejection)
has turned out to be somewhat misleading. Early on it had been known
that other than coronal material is often involved in such events. The
discoverers observed transient events of mass ejections from the sun,
which could be observed in the corona owing to the newly available
coronagraphs. This article is meant to clarify the terminology,
with emphasis on giving credit to the original discoverers and the
terms they introduced. With this aim in mind I suggest some minor
modifications of the terminology.
Title: Descripción del coronógrafo a ser instalado en Argentina
(MICA)
Authors: Stenborg, G.; Francile, C.; Schwenn, R.; Epple, A.; Rovira, M.
Bibcode: 1996BAAA...40R..42S
Altcode:
El ``Coronógrafo de espejo para Argentina'' es un telescopio solar
terrestre a ser colocado en el Observatorio Astronómico Félix Aguilar
(El Leoncito), antes de finalizar 1996, como parte de un programa de
ciencia bilateral entre Alemania y Argentina. Eclipses fotográficos
de alta resolución han revelado que la corona solar es altamente
estructurada y variable. De hecho, está contínuamente deformada y
moldeada por los movimientos convectivos de los extremos de los arcos
magnéticos en la fotosfera, estando, en muchas oportunidades, afectada
por explosivas liberaciones de energía. MICA, en conjunción con otros
telescopios solares espaciales y terrestres, tratará de contribuir al
entendimiento de cuestiones fundamentales de la física solar. Entre
ellas: cómo la corona está siendo calentada, dónde y cómo el
viento solar es acelerado, qué causa los transitorios coronales,
etc. Para ello investigará la distribución de los parámetros del
plasma y su evolución con el tiempo, la estructura espacial de la
corona en fina y gran escala, procesos que ocurren en los transitorios
coronales y factores que los disparan, etc. Para responder a estas
cuestiones MICA observará la atmósfera solar por sobre el limbo
entre 1.1 y 2 radios solares aproximadamente, usando un nuevo tipo
de sistema coronográfico que permite suprimir el brillo del disco
solar suficientemente bien, tomando las imágenes con una cámara CCD
de 1024x1024 pixels, codificada en 12 bits, pudiendo el mismo ser
operado en forma remota. En la presente exposición describiremos
las características del instrumento, cómo será controlado y
qué esperamos observar basados en las imágenes obtenidas por los
telescopios de similares características LASCO C1 a bordo del SOHO
y PICO (ubicado en el Observatorio de Pic du Midi, Francia).
Title: Observations of the comet Hyakutake by the LASCO coronagraph
on the SOHO satellite.
Authors: Andrews, M. D.; Paswaters, S. E.; Brueckner, G. E.; Korendyke,
C. M.; Dere, K. P.; Howard, R. A.; Michels, D. J.; Moses, J. D.;
Morril, J. S.; Moulton, N. E.; Socker, D. G.; St. Cyr, O. C.; Wang,
D.; Lamy, P. L.; Llebaria, A.; Bout, M. V.; Schwenn, R.; Podlipnik,
B.; Bedford, D. K.; Biesecker, D. A.; Eyles, C. J.; Plunket, S.;
Simnet, G. M.
Bibcode: 1996BAAS...28.1195A
Altcode:
No abstract at ADS
Title: The Large Angle Spectroscopic Coronagraph (LASCO)
Authors: Brueckner, G. E.; Howard, R. A.; Koomen, M. J.; Korendyke,
C. M.; Michels, D. J.; Moses, J. D.; Socker, D. G.; Dere, K. P.;
Lamy, P. L.; Llebaria, A.; Bout, M. V.; Schwenn, R.; Simnett, G. M.;
Bedford, D. K.; Eyles, C. J.
Bibcode: 1995SoPh..162..357B
Altcode:
The Large Angle Spectroscopic Coronagraph (LASCO) is a three
coronagraph package which has been jointly developed for the Solar
and Heliospheric Observatory (SOHO) mission by the Naval Research
Laboratory (USA), the Laboratoire d'Astronomie Spatiale (France),
the Max-Planck-Institut für Aeronomie (Germany), and the University
of Birmingham (UK). LASCO comprises three coronagraphs, C1, C2, and C3,
that together image the solar corona from 1.1 to 30 R⊙ (C1:
1.1 - 3 R⊙, C2: 1.5 - 6 R⊙, and C3: 3.7 - 30
R⊙). The C1 coronagraph is a newly developed mirror version
of the classic internally-occulted Lyot coronagraph, while the C2 and
C3 coronagraphs are externally occulted instruments. High-resolution
imaging spectroscopy of the corona from 1.1 to 3 R⊙ can
be performed with the Fabry-Perot interferometer in C1. High-volume
memories and a high-speed microprocessor enable extensive on-board image
processing. Image compression by a factor of about 10 will result in
the transmission of 10 full images per hour.
Title: Particle fluxes observed in the magnetic pileup regions of
comets Halley and Grigg-Skjellerup
Authors: Kirsch, E.; McKenna-Lawlor, S.; Korth, A.; Schwenn, R.
Bibcode: 1995AdSpR..16d..29K
Altcode: 1995AdSpR..16...29K
Energetic particles (E_H_2_O >= 60 keV) as well as plasma ions of a
few KeV in energy have been measured in the magnetic pileup region and
in the cavity of comet Halley (13/14 March 1986) by the instruments
EPA/EPONA, RPA and IMS. The Pileup region of comet Grigg-Skjellerup
(G-S) was traversed on 10 July 1992. Similarities and diversities in
the encounter conditions, particle fluxes and acceleration processes
at both comets are discussed.
Title: Mass ejections from the sun and their interplanetary
counterparts
Authors: Schwenn, R.
Bibcode: 1995sowi.confR..45S
Altcode:
Since the first observations of solar mass ejection events in the early
seventies from OSO 7 and Skylab a few thousand of these remarkable
dynamic incidents have been observed by now, covering about two full
solar activity cycles. The mass ejecta include mainly hot coronal
plasma, plus cold prominence material in variable amounts. The
ejecta are often recognised in the form of interplanetary plasma
clouds detected in the distant solar wind by appropriately located
spacecraft. Clouds which have been energetic enough to drive large
scale interplanetary shock waves can be identified most readily, but
clouds without associated shocks do also occur. The plasma clouds
are characterized by a variety of signatures indicating that they
actually originate from injections of different material into the
ambient solar wind. Usually only a few of the signatures are found
simultaneously. Apparently the bidirectional streaming of halo electrons
is a most reliable criterion, indicating a magnetic bottle or plasmoid
topology of the clouds. The discussion of the most recent discoveries
in this context will show that quite a few crucial problems still
remain to be addressed by the upcoming SOHO mission.
Title: Statistical analysis of interplanetary shock waves observed
during a complete solar activity cycle
Authors: Khalisi, E.; Schwenn, R.
Bibcode: 1995sowi.conf...99K
Altcode:
During the Helios mission a total of 391 fast forward non-corotating
interplanetary shock waves was identified. For most of the 12 years
between 1974 and 1986 unique shock detection was possible for more than
80 % of the time. The occurrence rate (in shocks per day) varied from
0.02 at activity minimum in 1976 to 0.17 in 1979 and 0.22 in 1982 with
a significant drop to 0.13 in 1980, i.e. right at activity maximum. The
average properties of all events as functions of solar distance. phase
in the solar cycle, heliographic and -magnetic latitude and others
are discussed.
Title: Ground-based observations of the corona in the visible and
NIR spectral ranges
Authors: Epple, Alexander; Schwenn, Rainer
Bibcode: 1995sowi.conf...60E
Altcode:
Since late 1993 we have been using a mirror coronagraph on Pic du Midi
(PICO) to observe the solar emission corona in several spectral lines
of (FE-X), (FE-XIII), and (FE-XIV). For good meteorological conditions
the diffuse corona and coronal holes in between can be seen out to
1.2 solar mass for sun center. Active regions can be mapped to bond
1.5 solar mass in the green and infrared lines. Recent observations
of PICO are presented.
Title: PICO - A Mirror Coronagraph on Pic Du Midi
Authors: Epple, A.; Schwenn, R.
Bibcode: 1995itsa.conf..233E
Altcode:
No abstract at ADS
Title: PICO - a mirror coronograph on Pic Du Midi
Authors: Epple, A.; Schwenn, R.
Bibcode: 1994ESASP.373..399E
Altcode: 1994soho....3..399E
No abstract at ADS
Title: Eruptive prominences as sources of magnetic clouds in the
solar wind
Authors: Bothmer, V.; Schwenn, R.
Bibcode: 1994SSRv...70..215B
Altcode:
Large amounts of coronal material are propelled outward into
interplanetary space by Coronal Mass Ejections (CMEs). Thus one might
expect to find evidence for expanding flux ropes in the solar wind
as well. To prove this assumption magnetic clouds were analyzed and
correlated with Hα-observations of disappearing filaments. When clouds
were found to be directly associated with a disappearing filament,
the magnetic structure of the cloud was compared with that of the
associated filament. Additionally the expansion of magnetic clouds
was examined over a wide range of the heliosphere and compared with
the expansion observed for erupting prominences.
Title: Book-Review - Physics of the Inner Heliosphere - V.2 -
Particles Waves and Turbulence
Authors: Schwenn, R.; Marsch, E.; Schwartz, S. J.
Bibcode: 1993SSRv...64..371S
Altcode:
No abstract at ADS
Title: Comparison of CMEs, magnetic clouds, and bidirectionally
streaming proton events in the heliosphere using helios data
Authors: Webb, D.; Jackson, B.; Hick, P.; Schwenn, R.; Bothmer, V.;
Reames, D.
Bibcode: 1993AdSpR..13i..71W
Altcode: 1993AdSpR..13...71W
Coronal Mass Ejections (CMEs) are large, energetic expulsions of mass
and magnetic fields from the Sun; they can significantly affect large
volumes of the heliosphere and appear to be a key cause of geomagnetic
storms. We have compiled a list of all significant CMEs detected by
the HELIOS white light photometers from 1975-1982. We are studying the
characteristics of these CMEs, and present preliminary results of their
associations with in-situ features, especially magnetic ``clouds'' and
periods of bidirectionally streaming ions, two classes of structures
considered indicative of interplanetary loops. Advantages of this data
set include reliable association in the interplanetary medium of the
white light CME plasma with the in-situ features, and observations of
a large number of events over a long time base.
Title: Status of the LASCO Instrument Development Program
Authors: Moses, D.; Brueckner, G. E.; Howard, R. A.; Koomen, M. J.;
Korendyke, C. M.; Michels, D. J.; Socker, D. G.; Lamy, P.; Schwenn,
R.; Simnett, G. M.
Bibcode: 1993BAAS...25.1192M
Altcode:
No abstract at ADS
Title: Book-Review - Solar Wind Seven
Authors: Marsch, E.; Schwenn, R.; Woan, G.
Bibcode: 1993Obs...113..151M
Altcode:
No abstract at ADS
Title: Book-Review - Physics of the Inner Heliosphere - Part Two -
Particles Waves and Turbulence
Authors: Schwenn, R.; Marsch, E.; Jackson, B. V.
Bibcode: 1993SoPh..145R.405S
Altcode:
No abstract at ADS
Title: Book-Review - Physics of the Inner Heliosphere - Part One -
Largescale Phenomena
Authors: Schwenn, R.; Marsch, E.; Jackson, B. V.
Bibcode: 1993SoPh..145Q.405S
Altcode:
No abstract at ADS
Title: Books-Received - Solar Wind Seven
Authors: Marsch, E.; Schwenn, R.
Bibcode: 1993Sci...259.1634M
Altcode:
No abstract at ADS
Title: Analysis of Comet Halley's Heavy Ion- and Micro-Dust Fluxes
and Discussion of Possible Acceleration Processes
Authors: Kirsch, E.; McKenna-Lawlor, S.; Thompson, A.; O'Sullivan,
D.; Korth, A.; Schwenn, R.; Wenzel, K. -P.
Bibcode: 1993penp.conf...89K
Altcode:
No abstract at ADS
Title: Landolt-Börnstein: Numerical Data and Functional Relationships
in Science and Technology - New Series " Gruppe/Group 6 Astronomy and
Astrophysics " Volume 3 Voigt: Astronomy and Astrophysics. Extension
and Supplement to Volume 2 " Instruments, Methods, Solar System
Authors: Baars, J. W.; Beer, H.; Durrant, C. J.; Graser, U.; Guinot,
B.; Hoffmann, M.; Hopp, U.; Ip, W. -H.; Jessberger, E. K.; Klecker, B.;
Lemke, D.; Meisenheimer, K.; Möbius, E.; Palme, H.; Rahe, J.; Röser,
H. J.; Schubart, J.; Schwenn, R.; Solf, J.; Soltau, G.; Staubert,
R.; Stewart, R.; Trümper, J.; Vanysek, V.; Weigelt, G.; Wolf, R.
Bibcode: 1993lbor.book.....B
Altcode:
No abstract at ADS
Title: Quiet Sun and Quiet Solar Wind (Abstract)
Authors: Schwenn, R.
Bibcode: 1993stp2.conf...90S
Altcode:
No abstract at ADS
Title: The Large Angle Spectroscopic Coronagraph (LASCO): visible
light coronal imaging and spectroscopy.
Authors: Brueckner, G. E.; Howard, R. A.; Koomen, M. J.; Korendyke,
C.; Michels, D. J.; Socker, D. G.; Lamy, P.; Llebaria, A.; Maucherat,
J.; Schwenn, R.; Simnett, G. M.; Bedford, D. K.; Eyles, C. J.
Bibcode: 1992ESASP.348...27B
Altcode: 1992cscl.work...27B
The Large Angle Spectroscopic Coronagraph (LASCO) is a triple
coronagraph being jointly developed for the SOlar and Heliospheric
Observatory (SOHO) mission by the Naval Research Laboratory (USA),
the Laboratoire d'Astronomie Spatiale (France), the Max Planck
Institut für Aeronomie (Germany), and the University of Birmingham
(UK). LASCO comprises three nested coronagraphs (C1, C2, and C3)
that image the solar corona from 1.1 Rsun to
30 Rsun.
Title: Origin of the solar wind and coronal mass ejections.
Authors: Schwenn, Rainer
Bibcode: 1992ESASP.346..205S
Altcode: 1992ssts.rept..205S
Theories on the origin of solar wind, theories that are derived from
Parker's first theory on the existence and evolution of solar wind, are
discussed. It is suggested that knowledge on how the corona is heated
would lead to insight into the problem of solar wind acceleration. From
observations of solar wind stream structure through almost three
solar activity cycles, four different types of solar wind and their
respective coronal sources have been discerned. Each of these are
discussed: high speed wind in highspeed streams, low speed wind of the
'interstream' type, low speed wind of the 'maximum' type, and coronal
mass ejecta following interplanetary shocks. For each type of solar
wind, the following parameters are given: high speed, low density,
low particle flux, helium content, and source. A list of the most
urgent questions in context with the solar wind origin is given.
Title: LASCO - Large Angle Spectrometric Coronagraph for SOHO
Authors: Howard, R. A.; Brueckner, G. E.; Dere, K. P.; Korendyke,
C. M.; Koomen, M. J.; Michels, D. J.; Moses, D.; Socker, D. G.;
Schwenn, R.; Inhester, B.; Lamy, P.; Maucherat, A.; Simnett, G. M.;
Eyles, C.
Bibcode: 1992AAS...180.3307H
Altcode: 1992BAAS...24..781H
No abstract at ADS
Title: Observations of Plasma Dynamics in the Coma of P/Halley by
the Giotto Ion Mass Spectrometer
Authors: Goldstein, B. E.; Goldstein, R.; Neugebauer, M.; Fuselier,
S. A.; Shelley, E. G.; Balsiger, H.; Kettmann, G.; Ip, W. -H.;
Rosenbauer, H.; Schwenn, R.
Bibcode: 1992JGR....97.4121G
Altcode:
Observations in the coma of P/Halley by the Giotto ion mass spectrometer
(IMS) are reported. The high-energy range spectrometer (HERS) of
the IMS obtained measurements of protons and alpha particles from
the far upstream region to the near ionopause region and of ions
of mass 12-32 at distances of about 250,000 to 40,000 km from the
nucleus. Plasma parameters from the high-intensity spectrometer (HIS)
of the IMS obtained between 150,000 and 5000 km from the nucleus
are also discussed. The distribution functions of water group ions
(``water group'' will be used to refer to ions of 16-18 m/q, where m
is in atomic mass units and q is in unit charges) are observed to be
spherically symmetric in velocity space, indicating strong pitch angle
scattering. The discontinuity known as the magnetic pileup boundary
(MPB) is apparent only in Proton, alpha particle, and magnetometer
data, indicating that it is a tangential discontinuity of solar wind
origin. HERS observations show no significant change in the properties
of the heavy ions across the MPB. The issue of whether a cometopause
was unambiguously observed at comet Halley is discussed; it is concluded
that the observations do not convincingly support the idea of a boundary
due to internal cometary processes (as opposed to convected solar wind
discontinuities). A comparison of the observations to MHD models is
made. The plasma flow directions at all distances greater than 30,000
km from the nucleus are in agreement with MHD calculations. However,
despite the agreement in flow direction, within 200,000 km of the
nucleus the magnitude of the velocity is lower than predicted by MHD
models, and the density is much larger (a factor of 5 or more for
distances 60,000-160,000 km from the comet). Within 30,000 km of the
nucleus there are large theoretical differences between the MHD model
flow calculations for the plane containing the magnetic field and for
the plane perpendicular to the magnetic field. The observations agreed
much better with the pattern calculated for the plane perpendicular to
the magnetic field. The data obtained by the HERS that are published
herein have also been provided to the International Halley Watch
archive.
Title: Magnetic cloud observations by the HELIOS spacecraft
Authors: Bothmer, V.; Schwenn, R.
Bibcode: 1992sws..coll..599B
Altcode:
A possible interpretation for the observed characteristics of an
interplanetary magnetic cloud is the passage of a magnetic flux
rope. For simplification the flux rope might be considered as a
cylindrically symmetric structure with the magnetic field lines being
directed parallel to the axis at its center and circular at its outer
edges. Near the center of this flux rope the magnetic field strength
would be strongest. The minimum variance technique was applied to
several magnetic clouds observed by the Helios spacecraft between 0.3
and 1 AU in order to determine the orientations of the magnetic flux
rope axis. The calculated orientations are examined with respect to the
global solar wind stream structure, the surrounding solar wind flow,
the radial distance to the sun and their solar origin.
Title: Solar Wind Seven; Proceedings of the 3rd COSPAR Colloquium,
Goslar, Germany, Sept. 16-20, 1991
Authors: Marsch, E.; Schwenn, R.
Bibcode: 1992sws..coll.....M
Altcode:
The present conference discusses topics in coronal heating and solar
wind acceleration, the large-scale structure of the interplanetary
medium, minor ions and cosmic rays in the heliosphere, solar wind
kinetics and turbulence, and heliospheric dynamic phenomena. Attention
is given to the origin of high speed solar wind streams, density and
temperature structure of a coronal hole, a two-fluid model of the solar
wind, solar wind temperature observations in the outer heliosphere,
the solar wind transonic region, and the spectral structure evolution
of interplanetary medium parameters. Also discussed are MHD modeling
of the heliospheric interface, the magnetic field in the heliosheath,
radioastronomy of travelling interplanetary disturbances, Bernstein
waves in the solar wind, multifractals in the solar wind, solar
MHD turbulence, surface and body waves in solar wind flow tubes,
magnetospheric LF nonresonant ion-beam turbulence, nearly incompressible
fluid dynamics, and the interaction of intense magnetic clouds with
ambient solar wind streams.
Title: Magnetic structures at sector boundaries in the inner
heliosphere
Authors: Bothmer, V.; Schwenn, R.
Bibcode: 1992sws..coll..151B
Altcode:
The strong deflections of the IMF out of the ecliptic plane that
have been noted at sector boundaries, and are therefore related to
the heliospheric current sheet, have north-to-south turnings in the
case of magnetic field deflections at sector boundaries that point
to an origin for this phenomenon in magnetic field lines that remain
parallel to the inclined current sheet. The plasma and magnetic field
properties at sector boundaries closer to the sun may show interesting
coronal streamer belt features.
Title: Synoptic maps of heliospheric Thomson scattering brightness
from 1974-1985 as observed by the HELIOS photometers
Authors: Hick, P.; Jackson, B. V.; Schwenn, R.
Bibcode: 1992sws..coll..187H
Altcode:
We display the electron Thomson scattering intensity of the inner
heliosphere as observed by the zodiacal light photometers on board
the Helios spacecraft in the form of synoptic maps. The technique
extrapolates the brightness information from each photometer sector
near the Sun and constructs a latitude/longitude map at a given solar
height. These data are unique in that they give a determination
of heliospheric structures out of the ecliptic above the primary
region of solar wind acceleration. The spatial extent of bright,
co-rotating heliospheric structures is readily observed in the data
north and south of the ecliptic plane where the Helios photometer
coverage is most complete. Because the technique has been used on the
complete Helios data set from 1974 to 1985, we observe the change in
our synoptic maps with solar cycle. Bright structures are concentrated
near the heliospheric equator at solar minimum, while at solar maximum
bright structures are found at far higher heliographic latitudes. A
comparison of these maps with other forms of synoptic data are shown
for two available intervals.
Title: Comparison of Doppler scintillation and in situ spacecraft
plasma measurements of interplanetary disturbances
Authors: Woo, Richard; Schwenn, Rainer
Bibcode: 1991JGR....9621227W
Altcode:
Results are presented of detailed comparisons between Doppler
scintillation and in situ plasma measurements to improve the
understanding of Doppler scintillation transients. During a combined
observing period of nearly 3 mo in 1981-1982 near solar maximum,
22 transients were observed by the Pioneer Venus Orbiter spacecraft
and 23 shocks were observed by Helios 1. It is found that at least
84 percent of the transients are shocks, while at least 90 percent of
the shocks are transients. Although the temporal profiles of Doppler
scintillation and mass flux density are similar, the magnitudes of
the Doppler scintillation transients may not simply reflect those
of mass flux density. Only one pronounced solar wind event that was
observed in the mass flux density measurements showed no signature
in the scintillation data; field and particle measurements by Helios
1 suggest that it is a noncompressive density enhancement and/or a
magnetic cloud. It is shown that Doppler scintillation measurements
can now be used by themselves to detect and locate interplanetary
shocks near the sun with a relatively high degree of certainty.
Title: Heavy ions and micro dust fluxes recorded during the
Giotto-Halley flyby
Authors: Kirsch, E.; McKenna-Lawlor, S.; Korth, A.; Schwenn, R.;
O'Sullivan, D.; Thompson, A.
Bibcode: 1991ICRC....3..370K
Altcode: 1991ICRC...22c.370K
No abstract at ADS
Title: Synoptic maps for the heliospheric Thomson scattering
brightness as observed by the HELIOS photometers
Authors: Hick, P.; Jackson, B. V.; Schwenn, R.
Bibcode: 1991A&A...244..242H
Altcode:
A method for displaying the electron Thomson scattering intensity in the
inner heliosphere as observed by the zodiacal light photometers on board
the Helios spacecraft in the form of synoptic maps is presented. The
method is based on the assumption that the bulk of the scattering
electrons along the line of sight is located near the point closest to
the sun. Inner-heliospheric structures will generally be represented
properly in these synoptic maps only if they are sufficiently long-lived
(that is, a significant fraction of a solar rotation period). The
examples of Helios synoptic maps discussed (from data in April 1976 and
November 1978), indicate that it is possible to identify large-scale,
long-lived density enhancements in the inner heliosphere. It is expected
that the Helios synoptic maps will be particularly useful in the study
of corotating structures (e.g., streamers), and the maps will be most
reliable during periods when few transient featurs are present in the
corona, i.e., during solar minimum.
Title: Observations of plasma dynamics in the coma of P/Halley by
the Giotto Ion Mass Spectrometer
Authors: Goldstein, B. E.; Goldstein, R.; Neugebauer, M.; Fuselier,
S. A.; Shelley, E. G.; Balsiger, H.; Kettmann, G.; Ip, W. -H.;
Rosenbauer, H.; Schwenn, R.
Bibcode: 1991sicd.reptQ....G
Altcode:
Observations in the coma of P/Halley by the Giotto Ion Mass Spectrometer
(IMS) are reported. The High Energy Range Spectrometer (HERS) of the
IMS obtained measurements of protons and alpha particles from the
far upstream region to the near ionopause region and of ions from
mass 12 to 32 at distances of about 250,000 to 40,000 km from the
nucleus. Plasma parameters from the High Intensity Spectrometer (HIS)
of the IMS obtained between 150,000 to 5000 km from the nucleus are
also discussed. The distribution functions of water group ions (water
group will be used to refer to ions of 16 to 18 m/q, where m is in AMU
and q is in unit charges) are observed to be spherically symmetric
in velocity space, indicating strong pitch angle scattering. The
discontinuity known as the magnetic pile-up boundary (MPB) is apparent
only in proton, alpha, and magnetometer data, indicating that it is a
tangential discontinuity of solar wind origin. HERS observations show
no significant change in the properties of the heavy ions across the
MPB. A comparison of the observations to an MHD model is made. The
plasma flow directions at all distances greater than 30,000 km from
the nucleus are in agreement with MHD calculations. However, despite
the agreement in flow direction, within 200,000 km of the nucleus the
magnitude of the velocity is lower than predicted by the MHD model and
the density is much larger (a factor of 4). Within 30,000 km of the
nucleus there are large theoretical differences between the MHD model
flow calculations for the plane containing the magnetic field and for
the plane perpendicular to the magnetic field. The observations agreed
much better with the pattern calculated for the plane perpendicular
to the magnetic field. The data obtained by the High Energy Range
Spectrometer (HERS) of the IMS that are published herein were provided
to the International Halley Watch archive.
Title: Book-Review - Physics of the Inner Heliosphere - Part One -
Largescale Phenomena
Authors: Schwenn, R.; Marsch, E.
Bibcode: 1991Sci...251..578S
Altcode:
No abstract at ADS
Title: Physics of the Inner Heliosphere II. Particles, Waves and
Turbulence
Authors: Schwenn, Rainer; Marsch, Eckart
Bibcode: 1991pihp.book.....S
Altcode: 1991PCS....21.....S
No abstract at ADS
Title: Synoptic maps constructed from brightness observations of
Thomson scattering by heliospheric electrons
Authors: Hick, P.; Jackson, B.; Schwenn, R.
Bibcode: 1991AdSpR..11a..61H
Altcode: 1991AdSpR..11Q..61H
Observations of the Thomson scattering brightness by electrons in the
inner heliosphere provide a means of probing the heliospheric electron
distribution. An extensive data base of Thomson scattering observations,
stretching over many years, is available from the zodiacal light
photometers on board the two Helios spacecraft. A survey of these
data is in progress, presenting these scattering intensities in the
form of synoptic maps for successive Carrington rotations. The Thomson
scattering maps reflect conditions at typically several tenths of an
astronomical unit from the Sun. We discuss some representative examples
from the survey in comparison with other solar/heliospheric data,
such as in situ observations from the Helios plasma experiment and
synoptic maps constructed from magnetic field, Hα and K-coronameter
data. The comparison will provide some information about the extension
of solar surface features into the inner heliosphere.
Title: Spatial structures in high-speed streams as signatures of
fine structures in coronal holes.
Authors: Thieme, K. M.; Marsch, E.; Schwenn, R.
Bibcode: 1990AnGeo...8..713T
Altcode: 1990AnG.....8..713T
During solar eclipses one can observe fine ray-like structures in
coronal holes. In order to determine whether these structures might
be preserved in the evolving interplanetary high-speed solar wind the
authors used plasma and magnetic field data obtained by the two Helios
solar probes. For the time period from 1974 till 1977 they analysed
41 high-speed solar wind streams which were measured between 0.3 and 1
AU. They investigated the velocity of protons and α-particles as well
as the combined gas pressure of protons, α-particles, and electrons,
the magnetic pressure, and the total pressure. The authors found many
time periods with a strong anticorrelation between the variations in
the gas pressure and the magnetic pressure while the total pressure
was roughly constant. They interpret these features as structural
relics of coronal origin. To get an estimation of the mean angular
diameter of these structures they did a statistical analysis with the
entire set of 41 high-speed solar wind streams. The resulting data
show characteristic variations on an angular scale being of the same
order as the angular size of the structures in the coronal holes.
Title: New technology mirror coronagraph with extended applications
Authors: Smartt, Raymond N.; Koutchmy, Serge L.; Colley, Stephen A.;
Caron, R.; Schwenn, Rainer; Restaino, Sergio R.
Bibcode: 1990SPIE.1236..206S
Altcode:
General design considerations of objective-mirror coronagraphs are
presented. A 1-m-focal-length prototype reflecting coronagraph based on
a 5.5-cm aperture spherical superpolished silicon mirror objective is
described. The design is simple off-axis reflection from the objective
to a conventional coronagraph optical system (occulting disk, field
lens, Lyot stop, and imaging system). This instrument has produced the
first images of the emission corona using a ground-based reflecting
coronagraph. A second prototype instrument based on a 15-cm aperture
superpolished fused-silica mirror is also described.
Title: Large-scale variations of thermal electron parameters in the
solar wind between 0.3 and 1 AU.
Authors: Pilipp, W. G.; Muehlhaeuser, K. -H.; Miggenrieder, H.;
Rosenbauer, H.; Schwenn, R.
Bibcode: 1990JGR....95.6305P
Altcode:
Variations of thermal electron parameters in the solar wind are
investigated using data obtained from the Helios probes in the years
from 1974 to 1976, shortly before solar minimum, at heliocentric
distances ranging from 0.3 to 1 AU. The main part of the present
analysis is based on Helios 2 data obtained in 1976. Variations across
the sector structure of the interplanetary magnetic field (IMF) and
across the plasma stream structures are studied. These studies support
the hypothesis that the thermal electron properties, i.e., the electron
temperatures, the core temperatures, the heat flux, and the normalized
heat flux, are strongly correlated with the distance from the neutral
sheet in the IMF (implying also a correlation with the plasma stream
structures). The results do not indicate significant electron heating
in compression regions. Also, power laws for the variations of the
electron parameters with distance from the Sun as well as polytrope laws
are derived for different solar wind structures and distance ranges.
Title: Giotto IMS measurements of the production rate of hydrogen
cyanide in the coma of comet Halley.
Authors: Ip, W. -H.; Rosenbauer, H.; Schwenn, R.; Balsiger, H.;
Geiss, J.; Meier, A.; Goldstein, B. E.; Lazarus, A. J.; Shelley, E.;
Kettmann, G.
Bibcode: 1990AnGeo...8..319I
Altcode: 1990AnG.....8..319I
The ion composition measurements in the ionosphere of comet Halley by
the ion mass spectrometer (IMS) experiment on the Giotto spacecraft are
used to estimate the relative abundance of HCN. From a comparison of the
normalized number density of ions with mass-to-charge (M/q) ratio of
28 AMU/e with steady-state photochemical models, it can be determined
that the production rate of HCN directly from the central nucleus is
Q(HCN) ⪉ 2×10-4Q(H2O) at the time of Giotto
encounter. The related photochemical model calculations also indicate
that Q(NH3)/Q(H2O) ≡ 5×10-3 in
agreement with recent determinations from ground-based observations. The
estimated value of Q(HCN) is lower than the relative abundance of
Q(HCN)/Q(H2O) ≍ 10-3 as derived from radio
observations of the 88.6 GHz emission of the J = 1-0 transition of
HCN. The difference may be the result of time-variations of the coma
deposition and dynamics as well as other model-dependent effects.
Title: First results of measurements of ions of Martian origin and
the discovery of a plasma sheet in the Martian magnetosphere in the
TAUS experiment on Phobos-2
Authors: Rosenbauer, H.; Shutte, N.; Apathy, I.; Verigin, M.; Witte,
M.; Galeev, A.; Gringaus, K.; Grunwaldt, H.; Jockers, K.; Kiraly,
P.; Kotova, G.; Livi, S.; Marsch, E.; Remizov, A.; Richter, A.;
Riedler, W.; Szego, K.; Hemmerich, P.; Schwenn, R.; Schwingenschuh,
K.; Steller, M.
Bibcode: 1990PAZh...16..368R
Altcode:
TAUS measurements showed that the Martian magnetosphere is considerably
filled with fluxes of heavy ions originating from the planetary
atmosphere. A plasma sheet was found in the magnetotail, which also
consisted mainly of heavy ions. The flux of heavy ions leaving Mars
through the tail is tentatively estimated to be (0.5-2) x 10 to the
25th per sec.
Title: First Measurements of Ions of Martian Origin and Observation
of a Plasma Layer in the Magnetosphere of Mars - the TAUS Experiment
on the Spacecraft PHOBOS-2
Authors: Rosenbauer, H.; Shutte, N.; Apathy, I.; Verigin, M.; Witte,
M.; Galeev, A.; Gringauz, K.; Grunwaldt, H.; Jockers, K.; Kiraly,
P.; Kotova, G.; Livi, S.; Marsch, E.; Remizov, A.; Richter, A.;
Riedler, W.; Szego, K.; Hemmerich, P.; Schwenn, R.; Schwingenschuh,
K.; Steller, M.
Bibcode: 1990SvAL...16..156R
Altcode:
No abstract at ADS
Title: On Representing the Large-scale Structure of the Inner
Heliosphere in Synoptic Maps
Authors: Hick, P.; Jackson, B. V.; Schwenn, R.
Bibcode: 1990BAAS...22..810H
Altcode:
No abstract at ADS
Title: Cometary ion flow variations at comet P/Halley as observed
by the Giotto IMS experiments.
Authors: Kettmann, G.; Ip, W. -H.; Rosenbauer, H.; Schwenn, R.;
Balsiger, H.; Meier, A.; Goldstein, B. E.; Shelley, E. G.
Bibcode: 1990AnGeo...8..229K
Altcode: 1990AnG.....8..229K
Using the combined data sets from the angle analyzer and the mass
analyzer of the Giotto IMS-HIS experiment, the authors have derived
the three-dimensional plasma flow properties of cometary ions for
masses ≥12 AMU. The results are in agreement with the theoretical
model of charge exchange loss of the hot cometary ions.
Title: Introduction
Authors: Marsch, E.; Schwenn, R.
Bibcode: 1990pihl.book....1M
Altcode:
No abstract at ADS
Title: Large-Scale Structure of the Interplanetary Medium
Authors: Schwenn, R.
Bibcode: 1990pihl.book...99S
Altcode:
No abstract at ADS
Title: Physics of the Inner Heliosphere I. Large-Scale Phenomena.
Authors: Schwenn, Rainer; Marsch, Eckart
Bibcode: 1990pihl.book.....S
Altcode: 1990PCS....20.....S
Physics of the Inner Heliosphere gives for the first time a
comprehensive and complete summary of our knowledge of the inner solar
system. Using data collected over more than 11 years by the HELIOS
twin solar probes, one of the most successful ventures in unmanned
space exploration, the authors have compiled 10 extensive reviews of
the physical processes of the inner heliosphere and their connections
to the solar atmosphere. Researchers and advanced students in space and
plasma physics, astronomy, and solar physics will be surprised to see
just how closely the heliosphere is tied to the sun and how sensitively
it depends on our star. The four chapters of Volume I of the work deal
with large-scale phenomena: - observations of the solar corona - the
structure of the interplanetary medium - the interplanetary magnetic
field - interplanetary dust.
Title: Observations of a shock and a recombination layer at the
contact surface of comet Halley
Authors: Goldstein, B. E.; Altwegg, K.; Balsiger, H.; Fuselier, S. A.;
Ip, W. -H.; Meier, A.; Neugebauer, M.; Rosenbauer, H.; Schwenn, R.
Bibcode: 1989JGR....9417251G
Altcode:
Observations in the vicinity of the contact surface (ionopause)
of comet Halley obtained by the Giotto ion mass spectrometer (IMS)
are reported. Two specific events in this region were observed on the
inbound pass. Two seconds before the contact surface was encountered,
a burst of energized ions (about 20 eV, much greater than thermal
energies) was detected by the angle analyzer; the flux of these ions
decreased as the contact surface was approached. The burst of energized
ions coincided with a pulse in magnetic field strength interpreted by
Neubauer (1988) as a fast mode shock traveling away from the contact
surface. At the contact surface, a sharp spike in ion densities was
observed by the mass analyzer. This pileup region was at least 0.75
s in duration (about 47 km in width); there may also have been a
region of less enhanced densities extending inward another 47 km. The
spike in densities was centered approximately at the inner edge of
the magnetically determined contact surface. The exact magnitude of
the density increase is uncertain due to instrumental limitations,
but the increase above the ambient external density appears to have
been at least a factor of 3.5, and appears to have been more than an
order of magnitude for some species. The sharp spike in ion density
is interpreted as a boundary layer into which the radial ionospheric
flow enters, piles up, and in which the density increase is limited
by recombination.
Title: Ions of martian origin and plasma sheet in the martian
magnetosphere: initial results of the TAUS experiment
Authors: Rosenbauer, H.; Shutte, N.; Apáthy, I.; Galeev, A.; Gringauz,
K.; Grünwaldt, H.; Hemmerich, P.; Jockers, K.; Király, P.; Kotova,
G.; Livi, S.; Marsch, E.; Richter, A.; Riedler, W.; Remizov, T.;
Schwenn, R.; Schwingenschuh, K.; Steller, M.; Szegö, K.; Verigin,
M.; Witte, M.
Bibcode: 1989Natur.341..612R
Altcode:
UNLIKE plasma instruments used on previous space missions to Mars,
the TAUS instrument on Phobos 2 was designed so that the energy per
charge and angular spectra of three species of ions could be measured
separately. These species were H+ and He2+
characteristic of the solar wind, and 'heavy ions' collected in
one integral channel covering the mass per charge (M/q) range 3 to
infinite, which we anticipated to find predominantly in the near-martian
regime. In all spacecraft orbits around Mars we found a sharp boundary,
separating the shocked solar wind from the martian magnetosphere which
was characterized by the absence of solar-wind-like plasma. As the
plasma inside the magnetosphere, and particularly in the tail, was
dominated by heavy ions with number densities orders of magnitude
higher than found in the solar wind, we assumed it was mainly of
martian origin. Typically, heavy ions of low tailward flow velocity
were seen near the boundary of the magnetotail, whereas high-speed
tailward plasma flows of such ions were detected deeper inside the
tail, a region not investigated before. Near the centre of the martian
magnetotail a plasma regime, comparable to the terrestrial as well
as the venusian1 plasma sheet, was detected, characterized by highly
supersonic tailward streams of heavy ions. The flux of planetary ions
leaving Mars through its magnetotail is tentatively estimated to be
of the order of a few times 1025 s-1. Such loss
rates would be significant for the dissipation of the martian atmosphere
on cosmological timescales.
Title: Large-scale propagation properties of interplanetary
disturbances revealed from IPS and spacecraft observations
Authors: Watanabe, Takashi; Schwenn, Rainer
Bibcode: 1989SSRv...51..147W
Altcode:
Interplanetary scintillation (IPS) observations may be used to study
large-scale propagation properties of transient interplanetary
disturbances in a three-dimensional manner, although current IPS
observations have several limitations, e.g., poor time resolution and
line-of-sight integration. Comparative studies with spacecraft solar
wind and white-light coronal mass ejection (CME) observations are
quite helpful in interpretation of IPS observations. An interplanetary
disturbance apparently in association with a disappearing solar
filament, which took place near the central meridian of the Sun on
late 22 April, 1979, is discussed to examine previous deductions from
IPS observations. Three-station IPS observations of the flow speed and
spacecraft observations suggest that a quasi-spherical interplanetary
disturbance was formed around the Sun-Earth line, whereas the center
of the disturbance derived from the distribution of enhanced IPS across
the sky (g-maps) is located to the east of the Sun-Earth line.
Title: Large-scale propagation properties of an interplanetary
disturbance in association with a 'halo' coronal mass ejection on
27 November 1979
Authors: Schwenn, Rainer; Watanabe, Takashio; Kakinuma, Takakiyo;
Kojima, Masayoshi
Bibcode: 1989NURIA..36...11S
Altcode:
Propagation properties of an interplanetary disturbance in association
with a halo coronal mass ejection (CME), which was observed with the
Solwind coronagraph from 08:22 to 09:58 UT on November 27, 1979,
are examined utilizing IPS and spacecraft observations. Detailed
model-fitting showed that a dip of the propagation speed of the
disturbance was situated in the radial direction of the heliospheric
current sheet. Quick deceleration of the disturbance along the current
sheet is suggested.
Title: Ground-Based Mirror Coronograph: First Results
Authors: Smartt, R. N.; Koutchmy, S.; Schwenn, R.
Bibcode: 1989BAAS...21..848S
Altcode:
No abstract at ADS
Title: Interplanetary Solar Wind Brightness Synoptic Maps from the
HELIOS Zodiacal Light Photometers
Authors: Hick, P. L.; Jackson, B. V.; Schwenn, R.
Bibcode: 1989BAAS...21..858H
Altcode:
No abstract at ADS
Title: The density of cometary protons upstream of comet Halley's
bow shock
Authors: Neugebauer, M.; Goldstein, B. E.; Balsiger, H.; Neubauer,
F. M.; Schwenn, R.; Shelley, E. G.
Bibcode: 1989JGR....94.1261N
Altcode:
Cometary protons picked up by the solar wind were detected by the
high energy range spectrometer of the Giotto ion mass spectrometer
starting at a cometocentric distance of ~12×106 km. On the
average, the density of cometary protons varied approximately as the
inverse square of the cometocentric distance, reaching a value of 0.11
cm-3 just outside the bow shock. The data can be
successfully fit to models that include substantial amounts of both slow
(~1 km/s) and fast (>=8 km/s) H atoms beyond the bow shock. Large
local variations in the density of picked-up protons can be explained on
the basis of variations in the direction of the interplanetary magnetic
field in upstream regions where pitch angle scattering was weak.
Title: Coronal mass ejections and their manifestation in the three
dimensional heliosphere
Authors: Schwenn, R.
Bibcode: 1989AdSpR...9d.268S
Altcode: 1989AdSpR...9..268S
No abstract at ADS
Title: Transport of Energy and Mass to the Outer Boundary of the
Earth System
Authors: Schwenn, R.
Bibcode: 1989step.conf...13S
Altcode:
No abstract at ADS
Title: Type II Interplanetary Radio Bursts and Electron Plasma
Oscillations Associated with Interplanetary Shocks, Superthermal
Electrons, and Low/Medium Energy Protons
Authors: Kikuchi, H.; Gurnett, D. A.; Anderson, R. R.; Keppler, E.;
Richter, A. K.; Schwenn, R.; Marsch, E.; Pilipp, W. G.; Richter, K.;
Rosenbauer, H.
Bibcode: 1989lsp..conf..415K
Altcode:
No abstract at ADS
Title: Relationship of Coronal Transients to Interplanetary Shocks:
3D Aspects
Authors: Schwenn, R.
Bibcode: 1989lsp..conf..369S
Altcode:
No abstract at ADS
Title: Are structures in high-speed streams signatures of coronal
fine structures?
Authors: Thieme, K. M.; Schwenn, R.; Marsch, E.
Bibcode: 1989AdSpR...9d.127T
Altcode: 1989AdSpR...9..127T
Interplanetary plasma and magnetic field data were measured by the
two Helios solar probes from 1974 until 1986 and from 1976 until 1980,
respectively, between 0.3 and 1 AU. We used these data to investigate
plasma parameters of high-speed streams, especially velocities,
densities, and temperatures of protons and α-particles. The possibility
is discussed that the variability in these parameters is due to spatial
structures which are remnants of the underlying coronal structures
(supergranulation cells) preserved in the outflowing solar wind.
Title: Ion Temperature and Flow Profiles in Comet Halley's Close
Environment
Authors: Schwenn, R.; Ip, W. -H.; Rosenbauer, H.; Balsiger, H.;
Buhler, F.; Goldstein, R.; Meier, A.; Shelley, E. G.
Bibcode: 1989lsp..conf..583S
Altcode:
No abstract at ADS
Title: LASCO: A wide-field white light and spectrometric coronagraph
for SOHO
Authors: Michels, D. J.; Schwenn, R.; Howard, R. A.; Bartoe, J. -D. F.;
Antiochos, S. K.; Brueckner, G. E.; Cheng, C. -C.; Dere, K. P.;
Doschek, G. A.; Mariska, J. T.
Bibcode: 1988sohi.rept...55M
Altcode:
The scientific objectives of the LASCO (light and spectrometric
coronagraph) project in the SOHO (solar and heliospheric observatory)
mission are described. These include investigation of mechanisms
for heating of the corona and acceleration of the solar wind, causes
of coronal transients, and their role in development of large scale
coronal patterns and interplanetary disturbances. The distribution
and properties of dust particles, including those released from
sun-grazing comets are investigated. Interactions of coronal plasma
with the dust are studied. The corona is analyzed spectroscopically
by a high-resolution scanning, imaging interferometer. The spectral
profiles of three emission lines and one Fraunhofer line are measured
for each picture point, giving temperatures, velocities, turbulent
motions and volume densities. Polarization analysis yields the direction
of coronal magnetic fields.
Title: Chemical Composition and Ionisation States of the Solar Wind -
Plasma as Characteristics of Solar Phenomena.
Authors: Schwenn, R.
Bibcode: 1988RvMA....1..179S
Altcode:
No abstract at ADS
Title: An Interpretation of the Ion Pile-Up Region Outside the
Ionospheric Contact Surface
Authors: Ip, W. H.; Schwenn, R.; Rosenbauer, H.; Balsiger, H.;
Neugebauer, M.; Shelley, E. G.
Bibcode: 1987A&A...187..132I
Altcode:
An analysis interrelating some of the results of plasma measurements
by the Giotto spacecraft in the inner coma of comet P/Halley suggests
that the formation of the plasma pile-up region at a distance of 10,000
km - 30,000 km may be the result of accumulation of ion density in
a stagnant flow region with a sharp electron temperature transition
forming a recombination front at about 10,000 km.
Title: The Composition and Dynamics of Cometary Ions in the Outer
Coma of Comet p/ Halley
Authors: Balsiger, H.; Altwegg, K.; Buhler, F.; Fuselier, S. A.;
Geiss, J.; Goldstein, B. E.; Goldstein, R.; Huntress, W. T.; Ip,
W. H.; Lazarus, A. J.; Meier, A.; Neugebauer, M.; Rettenmund, U.;
Rosenbauer, H.; Schwenn, R.; Shelley, E. G.; Ungstrup, E.; Young, D. T.
Bibcode: 1987A&A...187..163B
Altcode:
During its flyby at comet Halley, the Giotto spacecraft encountered
high densities of cometary ions inside approximately 200000 km from
the nucleus. Their properties changed drastically as the comet was
approached. We present here density profiles of solar wind alpha
particles and of the major cometary ions as obtained by the IMS-HERS
sensor between 340000 km and 60000 km from the nucleus. Typical mass
spectra at various distances are presented and angular and velocity
distributions of the cometary ions are discussed.
Title: Ion Temperature and Flow Profiles in Comet p/ Halley's Close
Environment
Authors: Schwenn, R.; Ip, W. H.; Rosenbauer, H.; Balsiger, H.; Buhler,
F.; Goldstein, R.; Meier, A.; Shelley, E. G.
Bibcode: 1987A&A...187..160S
Altcode:
The HIS instrument of the ion mass spectrometer on board the Giotto
spacecraft identified the contact surface at 4800 km distance from
the comet nucleus. This boundary is clearly seen by a drastic drop
in the temperatures of different ion species from about 2000 K
outside to values as low as 300 K inside. Also, inside the contact
surface an outflow speed of >1 km s-1 was measured,
in contrast to a value around zero right outside. We discuss how
these numbers might be affected by a potential charge-up of the
spacecraft. Outside the contact surface, the ion temperature rises
gradually with increasing distance. Between 9000 and 10000 km distance
the ion density increases by a factor of 4. This "ion pile-up" is not
yet explained uniquely. Between 25000 and 28000 km distance there is
again a rather abrupt jump to significantly higher temperatures and
higher outflow speeds.
Title: Giotto / IMS Observations of Ion Flow Velocities and
Temperatures Outside the Magnetic Cavity of Comet p/ Halley
Authors: Goldstein, B. E.; Neugebauer, M.; Balsiger, H.; Drake, J.;
Fuselier, S. A.; Goldstein, R.; Ip, W. H.; Rettenmund, U.; Rosenbauer,
H.; Schwenn, R.; Shelley, E. G.
Bibcode: 1987A&A...187..174G
Altcode:
Fluid parameters for He2+ ions obtained from the Giotto
Ion Mass Spectrometer HERS sensor are presented; also investigated
are proton densities and velocities and thermal speeds of protons,
alpha particles, and heavy ions in the hour before closest approach. A
bow shock transition lasting ten minutes is observed. A region of
enhanced He2+ ion densities, and velocity, and decreased
temperature is observed from 20:26 to 21:45. Sharp decreases in the
proton density are observed at 23:30 and at 23:41; there are also
sharp drops in alpha particle density and temperature at 23:30. There
is a relative flow velocity between alpha particles and oxygen ions of
approximately 20 km s-1 during a period roughly from 22:55
to 23:10; by 23:30 the difference in flow velocity is less than the
experimental uncertainities.
Title: The variation of protons, alpha particles, and the magnetic
field across the bow shock of comet Halley
Authors: Neugebauer, M.; Neubauer, F. M.; Balsiger, H.; Fuselier,
S. A.; Goldstein, B. E.; Goldstein, R.; Mariani, F.; Rosenbauer, H.;
Schwenn, R.; Shelley, E. G.
Bibcode: 1987GeoRL..14..995N
Altcode:
Data from the Ion Mass Spectrometer and the magnetometer on the Giotto
spacecraft are used to examine the structure of the inbound crossing
of the comet Halley bow shock on March 13, 1986. It is found that the
velocity decrease, the field strength increase, and the heating of
picked up cometary protons occurred over a broad region corresponding
to several heavy-ion gyroradii. The solar-wind protons and alphas,
on the other hand, were compressed and heated at a narrow structure,
which might be called a subshock, on the leading edge of the broad
shock region. The electrostatic potential difference across the shock
was less than 40 V.
Title: Solar activity and heliosphere-wide cosmic ray modulation
in mid-1982
Authors: Cliver, E. W.; Mihalov, J. D.; Sheeley, N. R., Jr.; Howard,
R. A.; Koomen, M. J.; Schwenn, R.
Bibcode: 1987JGR....92.8487C
Altcode:
A major episode of flare activity in June and July 1982 was accompanied
by a pair of heliosphere-wide cosmic ray modulation events. In each
case, a large Forbush decrease (FD) at earth was followed in turn
by apparently related decreases at Pioneer 11 (P11) and Pioneer 10
(P10). The Pioneer spacecraft were separated by ~155° in ecliptic
longitude. We reviewed white light coronagraph and near-sun (<=1 AU)
satellite data to identify plausible solar origins of these modulation
events. The first widespread intensity decrease (FD 1) can be attributed
to the combined effects of a backside flare on June 3 from solar active
region 18382/18383, located 23° in ecliptic longitude from Pioneer 10,
and a visible disk flare from 18405 on June 6, when this region was
9° from Pioneer 11. The second widespread modulation event during this
period (FD 2) may be linked to flares from active region 18474 on July
12 and 22. The July 12 flare was located 34° in azimuth from Pioneer
11, and the July 22 flare was 24° from Pioneer 10. Since even fast
shocks would take ~1 month to propagate to Pioneer 11 (12 AU) and ~2
months to reach Pioneer 10 (28 AU) in mid-1982, these ``one-to-one''
associations must be regarded with caution. The processes of entrainment
and coalescence can cause a given traveling interplanetary disturbance
to lose its identify enroute to the outer heliosphere. The fact that
we were able to identify plausible solar flare candidates for each of
the four Forbushlike decreases observed at the Pioneer satellites (two
each at P10 and P11), however, removes the need to invoke a chock from
a single flare as the sole cause of either FD 1 (at both P10 and P11)
or FD 2. Such single-flare scenarios have recently been suggested by
several investigators to account for the widespread intensity decreases
in mid-1982. Instead, the heliosphere-wide modulation during this
period appears to result primarily from a sustained episode of powerful
flares from a relatively narrow range of active solar longitude. A
significant fraction (1/2 to 3/4) of the major coronal mass ejections
(CMEs) and near-sun shocks observed during June and July 1982 originated
in flares occurring in a 45° band of Carrington longitude. Because
of solar rotation these flares occur over the full range of ecliptic
longitude and can generate an outward propagating shell of CMEs and
shocks that encompasses the sun to produce the observed azimuthal
symmetry in the cosmic ray modulation. The prolonged high-speed wind
stream at P10 in the second half of 1982 may have resulted, at least
in part, from the coalescence of a series of fast transient streams
directed toward that distant spacecraft into an extended compound
stream.
Title: The ion mass spectrometer on Giotto
Authors: Balsiger, H.; Altwegg, K.; Benson, J.; Buhler, F.; Fischer,
J.; Geiss, J.; Goldstein, B. E.; Goldstein, R.; Hemmerich, P.;
Kulzer, G.; Lazarus, A. J.; Meier, A.; Neugebauer, M.; Rettenmund,
U.; Rosenbauer, H.; Sager, K.; Sanders, T.; Schwenn, R.; Shelley,
E. G.; Simpson, D.; Young, D. T.
Bibcode: 1987JPhE...20..759B
Altcode:
The design of the Giotto ion mass spectrometer (IMS) system, its
calibration, and the initial flight performance are discussed. The IMS
system consists of two sensors: one optimized for the outer coma, the
other for the inner coma, with each sensor obtaining complementary
information in the region for which it was not optimized. Both
sensors feature mass-imaging characteristics, permitting simultaneous
measurements of several ion species by means of multi-detector arrays,
with resultant mass per charge resolution of not less than 20. In
addition to mass per charge, the energy per charge and the elevation
and azimuth of the incident ions were measured during the Giotto flight.
Title: The solar wind
Authors: Schwenn, R.
Bibcode: 1987ESASP.268..131S
Altcode: 1987sass.conf..131S
Parker's theoretical model of the solar wind, i.e., a continuous
outflow of particles from the solar corona is found to be in basic
agreement with observations. More sophisticated models and more
detailed measurements reveal significant gaps in understanding. The
high values of flow speed in high speed streams cannot be explained,
and identifying coronal sources of the slow solar wind reveals severe
topological problems. It appears as if there are basic differences in
the acceleration mechanism for slow and fast solar wind. The variation
of the average solar wind during the solar activity cycle is only
a minor effect. Modulation of galactic cosmic radiation by solar
activity is probably due to transient effects on the Sun. Coronal mass
ejections in association with solar flares or eruptive prominences
drive interplanetary shock waves into the solar wind throughout the
heliosphere. However, there are gaps in understanding of reactions
between the Sun's surface and the outer solar system.
Title: The pick-up of cometary protons by the solar wind
Authors: Neugebauer, M.; Lazarus, A. J.; Altwegg, K.; Balsiger, H.;
Goldstein, B. E.; Goldstein, R.; Neubauer, F. M.; Rosenbauer, H.;
Schwenn, R.; Shelley, E. G.
Bibcode: 1987STIN...8719342N
Altcode:
The High Energy Range Spectrometer (HERS) of the Ion Mass Spectrometer
on the Giotto spacecraft measured the 3-dimensional distribution of
picked-up cometary protons over a distance of approximately 8 million km
upstream of the bow shock of Comet Halley. The protons were observed to
be elastically scattered out of their original cycloidal trajectories
such that they were nonuniformly distributed over a spherical shell
in velocity space. The shell radius (relative to its expected radius)
and thickness increased as the bow shock was approached. Downstream
of the shock, the cometary protons could not be distinguished from
the heated solar wind protons.
Title: Unusual electron distribution functions in the solar wind
derived from the Helios plasma experiment: Double-strahl distributions
and distributions with an extremely anisotropic core
Authors: Pilipp, W. G.; Miggenrieder, H.; Montgomery, M. D.;
Mühlhäuser, K. -H.; Rosenbauer, H.; Schwenn, R.
Bibcode: 1987JGR....92.1093P
Altcode:
Electron distribution functions with unusual features, which have been
observed on rare occasions in the solar wind by the Helios probes,
are presented. Two examples show a strong symmetric bidirectional
anisotropy in the energy regime of the halo up to particle energies of
800 eV (double-strahl distributions). Another example shows an unusually
strong bidirectional anisotropy in the energy regime of the core (below
150 eV). The infrequently observed double-strahl distributions provide
evidence that magnetic field loops can exist in the solar wind where
electrons are trapped. In addition, they provide evidence that in the
case of electrons trapped in closed magnetic field structures the break
in the energy spectrum separating the core from the halo is produced
only by collisions. On the other hand, the class of distribution
functions with strongly anisotropic cores indicates that in the case
of ``open'' magnetic field lines the break between core and halo is
largely determined both by the interplanetary electrostatic potential
and by collisions.
Title: Characteristics of electron velocity distribution functions
in the solar wind derived from the helios plasma experiment
Authors: Pilipp, W. G.; Miggenrieder, H.; Montgomery, M. D.;
Mühlhäuser, K. -H.; Rosenbauer, H.; Schwenn, R.
Bibcode: 1987JGR....92.1075P
Altcode:
The shapes of three typical examples of electron distribution functions,
which have been observed by Helios 2 in the solar wind, are analyzed and
compared with theoretical predictions. We have considered a distribution
function with a ``narrow strahl'' (narrow beam), which is extremely
anisotropic and skewed with respect to the magnetic field direction
at particle energies above 100 eV, a distribution function with a
``broad strahl'' (broad beam), which is less anisotropic and skewed,
and finally a nearly isotropic distribution function which, however,
shows a slight bidirectional anisotropy. The main results are
as follows: (1) For each distribution function we may discern a
``break,'' i.e., a sudden change in the slope of the distribution
function, separating the ``core'' at lower energies from the ``halo''
at larger energies. For the anisotropic distributions a significant
break is observed in velocity directions opposite to the strahl and
perpendicular to it but not along the strahl. Here the energy of the
break (breakpoint energy) may be determined both by the interplanetary
electrostatic potential and by collisions. In contrast, for the nearly
isotropic distribution function, a significant break is observed for
all velocity directions, and the breakpoint energy may be determined
by collisions only. (2) The strahl observed at larger energies in the
anisotropic distribution functions can be qualitatively explained by
existing theoretical approaches describing the propagation of electrons
in the solar wind. However, at least for the distribution function
with the broad strahl as well as for the nearly isotropic distribution
function, the halo electrons should be scattered by unknown anomalous
scattering processes, which do not show a strong energy dependence. (3)
For the anisotropic distribution functions we find a velocity shift
between the peak of each distribution function and the solar wind
bulk velocity, which is typically 100 kms-1
to 300 kms-1. This shift is drastically reduced
compared to the shift predicted by exospheric theory, indicating strong
frictional processes between electrons and ions. However the
results do not settle the question whether this friction is provided by
the combined action at wave-particle interactions and Coulomb collisions
or by Coulomb collisions only. For the nearly isotropic distribution
function this shift is probably not significantly different from
zero. In this scae it may be determined by some anomalous processes
and/or trapping in closed magnetic field structures. (4) For the
anisotropic distribution functions the heat flux is carried mainly by
the strahl. For the nearly isotropic distribution function most of the
heat flux is carried by the core electrons. For this distribution, part
of the halo electrons carry heat flux in the opposite direction, and the
total heat flux is probably not significantly different from zero. (5)
The pitch angle distribution in the energy regime of the halo may
provide some indications for the global structure of the magnetic field.
Title: Variations of electron distribution functions in the solar wind
Authors: Pilipp, W. G.; Miggenrieder, H.; Mühlhaüser, K. -H.;
Rosenbauer, H.; Schwenn, R.; Neubauer, F. M.
Bibcode: 1987JGR....92.1103P
Altcode:
Variations of electron distribution functions in the solar wind have
been investigated using the electron data observed aboard Helios 2
during the first four months of its mission in 1976 in the distance
range between 0.3 and 1 AU. In particular, variations across the sector
structure of interplanetary magnetic field and across the plasma stream
structures have been studied. It has been found that there is a strong
correlation between the electron properties and the sector structure
of the magnetic field. Within the interior of magnetic sectors the
electron distribution functions are extremely anisotropic and skewed
with respect to the magnetic field direction at high particle energies
(above 100 eV); i.e., the distribution functions have a narrow strahl
(beam) directed along the magnetic field away from the sun. Often
a slight indication of a second strahl directed along the magnetic
field toward the sun has been found. Toward sector boundaries the
electron distribution functions become less anisotropic and less
skewed. Right at sector boundaries the electrons are relatively cool,
and their distributions are nearly isotropic, often showing a slight
bidirectional anisotropy. These observations have been interpreted to
indicate that scattering of electrons with energies above 100 eV is
weak within the interior of magnetic sectors but anomalous scattering
increases drastically toward sector boundaries for all energies in
the halo regime up to several hyndred eV. There is evidence for closed
magnetic field structures, probably occurring frequently in the solar
wind, where the magnetic field lines should usually be connected to
the sun outside sector boundaries but may or may not be disconnected
from the sun at sector boundaries.
Title: Relationship between Structures in the Solar Wind and Their
Source Regions in the Corona
Authors: Thieme, K. M.; Marsch, E.; Schwenn, R.
Bibcode: 1987sowi.conf..317T
Altcode:
No abstract at ADS
Title: Doppler Scintillation Observations of Interplanetary
Disturbances within 0.3 AU
Authors: Woo, R.; Armstrong, J. W.; Schwenn, R.
Bibcode: 1987sowi.conf..266W
Altcode:
No abstract at ADS
Title: An interpretation of the ion pile-up region outside the
ionospheric contact surface
Authors: Ip, Wing-H.; Schwenn, R.; Rosenbauer, H.; Balsiger, H.;
Neugebauer, M.; Shelley, E. G.
Bibcode: 1986ESASP.250a.219I
Altcode: 1986ehc1.conf..219I
An analysis inter-relating some of the published results of the plasma
measurements by the Giotto spacecraft in the inner coma of comet Halley
suggests that the formation of the plasma pile-up region at a distance
of 10,000 km - 30,000 km may be the result of accumulation of ion
density in a stagnant flow region with a sharp electron temperature
transition forming a recombination front at about 10,000 km.
Title: Ion temperature and flow profiles in Comet Halley's close
environment
Authors: Schwenn, R.; Ip, Wing-H.; Rosenbauer, H.; Balsiger, H.;
Buehler, F.; Goldstein, R.; Meier, A.; Shelley, E. G.
Bibcode: 1986ESASP.250a.225S
Altcode: 1986ehc1.conf..225S
The HIS instrument of the ion mass spectrometer on board the GIOTTO
spacecraft identified the contact surface in 4800 km distance from
the comet nucleus. This boundary is clearly seen by a drastic drop
in the temperatures of different ion species from about 2000K outside
to values as low as 300K inside. Also, inside the contact surface an
outflow speed of >1 km s-1 was measured, in contrast to a
value around zero right outside. The authors discuss how these numbers
might be affected by a potential charge-up of the spacecraft. Outside
the contact surface, the ion temperature rises gradually with increasing
distance. Between 9000 and 10,000 km distance the ion density increases
by a factor of 4. This "ion pile-up" is not yet explained uniquely. At
27,000 km distance there is again a rather abrupt jump to significantly
higher temperatures, higher outflow speeds and lower densities.
Title: Giotto-IMS observations of ion flow velocities and temperatures
outside the contact surface of Comet Halley
Authors: Goldstein, B. E.; Neugebauer, M.; Balsiger, H.; Drake,
J.; Fuselier, S. A.; Goldstein, R.; Ip, Wing-H.; Rettenmund, U.;
Rosenbauer, H.; Schwenn, R.
Bibcode: 1986ESASP.250a.229G
Altcode: 1986ehc1.conf..229G
Fluid parameters for He++ ions obtained from the GIOTTO
ion mass spectrometer HERS sensor are presented; also investigated
are proton densities and velocities and thermal speeds of protons,
alpha particles, and heavy ions in the hour before closest appraoch. A
region of enhanced He++ ion densities, and velocity, and
decreased temperature is observed from 20:26 to 21:45. Sharp decreases
in the proton density are observed at 23:30 and at 23:41. There is
a relative flow velocity between alpha particles and oxygen ions of
approximately 30 km/sec during a period roughly from 22:55 to 23:10;
by 23:30 the difference in flow velocity is less than the experimental
uncertainties. The flow properties of protons observed during this
period are also discussed.
Title: Tangential discontinuities in the solar wind: Correlated
field and velocity changes in the Kelvin-Helmholtz Instability
Authors: Neugebauer, M.; Alexander, C. J.; Schwenn, R.; Richter, A. K.
Bibcode: 1986JGR....9113694N
Altcode:
Three-dimensional Helios plasma and field data are used to investigate
the relative changes in direction of the velocity and magnetic
field vectors across tangential discontinuities, (TDs) in the solar
wind at solar distances of 0.29-0.50 AU. It is found for tangential
discontinuities with both Δv and ΔB/B large that Δv and ΔB are
closely aligned with each other, in agreement with the unexpected
results of previous studies of tangential discontinuities observed at
1 AU and beyond. It is shown that this effect probably results from
the destruction by the Kelvin-Helmholtz instability of TDs for which
Δv and ΔB are not aligned. The observed decrease in the number of
interplanetary discontinuities with increasing solar distance may be
associated with the growth of the Kelvin-Helmholtz instability with
decreasing Alfvén speed.
Title: Formation of a compound stream between 0.85 AU and 6.2 AU
and its effects on solar energetic particles and galactic cosmic rays
Authors: Burlaga, L. F.; McDonald, F. B.; Schwenn, R.
Bibcode: 1986JGR....9113331B
Altcode:
During September 1979, Helios B (HB) and Voyager 1 (V1) were near
0.85 AU and 6.2 AU, respectively, and they were radially aligned
with respect to the sun within 20°. A slow transient stream, two
corotating streams, and two unusually fast transient streams passed
HB during a 17-day interval in that order. (A stream is defined here
as a flow in which the speed is always greater than 475 km/s.) As the
streams moved outward from HB to V1, they coalesced to form a single
large ``compound stream'' which moved past V1 in 20 days. The compound
stream was produced by motion of fast plasma away from slower plasma
behind and by the interaction of the fast streams with slower streams
ahead. The maximum speed observed was 1270 km/s at HB and 860 km/s at
V1. Closely associated with this compound stream was one of the
largest solar energetic particle events (protons 0.4-69 MeV) observed
beyond 5 AU. The maximum intensity was in the region of increasing
speed. The intensity-time profile of the solar energetic particles was
closely related to the speed profile. There is evidence of channeling
and trapping of particles in a region following the highest speeds,
where the magnetic field was strong and the magnetic field lines were
nearly radial. The high-energy protons (>150 MeV) and MeV electrons
are believed to be accelerated in solar flare events. Interplanetary
acceleration appears to play a major role in the low-energy particle
population. The galactic cosmic ray intensity remained low throughout
the passage of the compound stream, recovering slowly as the speed
decreased. The long ``recovery time'' is thus related to the large
extent of the flow.
Title: Hot ions observed by the Giotto ion mass spectrometer inside
the Comet Halley contact surface
Authors: Goldstein, R.; Young, D. T.; Balsiger, H.; Buehler, F.;
Goldstein, B. E.; Neugebauer, M.; Rosenbauer, H.; Schwenn, R.; Shelly,
E. G.
Bibcode: 1986ESASP.250a.207G
Altcode: 1986ehc1.conf..207G
Just inside the contact surface (approx. 4700 km) the High Energy
Range Spectrometer (HERS) sensor of the Giotto ion mass spectrometer
detected a sudden, intense burst of ions that lasted until the HERS
sensor ceased transmitting data at a distance 3000 km from comet
Halley. During this interval ions with M/Q=1, 2, 12, 14, 16, 19, 24 and
28 were observed. The heavier ions appear in two populations (in the
S/C frame): a very low energy, almost omnidirectional distribution,
and a more energetic (approx. < ram speed) population coming from
the ram direction. The low energy ions may belong to the natural
Halley environment or be generated at the spacecraft by dust and
gas bombardment. The ions may also be related to spacecraft charging
processes on Giotto.
Title: The pick-up of cometary protons by the solar wind
Authors: Neugebauer, M.; Lazarus, A. J.; Altwegg, K.; Balsiger, H.;
Goldstein, B. E.; Goldstein, R.; Neubauer, F. M.; Rosenbauer, H.;
Schwenn, R.; Shelley, E. G.
Bibcode: 1986ESASP.250a..19N
Altcode: 1986ehc1.conf...19N
The HERS detector of the Ion Mass Spectrometer on the Giotto spacecraft
measured the 3-dimensional distribution of picked-up cometary
protons over a distance of 6 million km upstream of the bow shock. The
protons were observed to be elastically scattered out of their original
cycloidal trajectories such that they were nonuniformly distributed over
a spherical shell in velocity space. The shell thickness increased as
the bow shock was approached. Inside the shock, the cometary protons
were difficult to distinguish from the heated solar wind protons.
Title: Relationship of Coronal Transients to Interplanetary Shocks -
3d Aspects
Authors: Schwenn, R.
Bibcode: 1986SSRv...44..139S
Altcode:
More than 1000 coronal mass ejections (CMEs) caused by different
types of coronal transients have been analyzed up to now, based on
the images from white light coronagraphs on board the OSO 7, Skylab,
P78-1, and SMM spacecraft. In many cases, the CME images lead us to
the impression of loop-like, more planar structures, similar to those
of prominence structures often seen in Hα pictures. There
is increasing evidence, though, for a three-dimensional bubble- or
cloud-like structure of CMEs. In several cases, CMEs directed toward the
earth (or away from it) were identified, as their outer fronts emerged
on all sides of the coronagraph's occulting disk, thus suggesting a
bubble-like appearance. There now appears to be unanimity about the
crucial role that magnetic reconnection plays during the transient
process. Recently, direct evidence was found for the ‘pinch-off of
CMEs, both from optical observations and from in situ measurements of
isolated ‘magnetic clouds' following transient shock waves. However,
the detailed sequence of events during the generation of a CME is
still unclear. Interplanetary shock waves associated with the CMEs are
usually restricted in latitudinal extent to about the angular width
of the optically observed CMEs. They may be somewhat less restricted
in longitudinal extent. A nearly 1 ∶ 1 association between CMEs and
shock waves measured in situ from spacecraft (Helios 1 and 2, IMP 7
and 8, ISEE 3, Pioneer Venus) can be established, provided the CME and
the spacecraft were in the same longitudinal and latitudinal range and
the CME speed exceeds ∼ 400 km s-1. Around the past solar
activity minimum all CMEs observed were centered at solar latitudes of
less than 60°. Around solar maximum, a significant fraction of CMEs
also originated from the polar regions. Thus, there is a good chance
that the Ulysses spaceprobe will encounter many shocks caused by both
low- and high-latitude CMEs, when it finally starts its journey over
the Sun's poles.
Title: Ion composition and dynamics at comet Halley
Authors: Balsiger, H.; Altwegg, K.; Buhler, F.; Geiss, J.; Ghielmetti,
A. G.; Goldstein, B. E.; Goldstein, R.; Huntress, W. T.; Ip, W. -H.;
Lazarus, A. J.; Meier, A.; Neugebauer, M.; Rettenmund, U.; Rosenbauer,
H.; Schwenn, R.; Sharp, R. D.; Shelly, E. G.; Ungstrup, E.; Young,
D. T.
Bibcode: 1986Natur.321..330B
Altcode:
The ion mass spectrometer aboard the Giotto spacecraft measured the
composition and velocity distributions of cometary ions at distances
of ~7.5×l06 to ~1,300 km from the nucleus of comet
Halley. Well outside the bow shock, pick-up cometary H+
ions were found in a diffuse shell-like distribution. Heavier ions
(C+, H2O+-group, CO+
and S+) with similar distributions have been identified
at <=3×l05 km. Solar-wind He2+ was found
throughout the coma to as close as ~5,000 km; He+ produced
by charge exchange was seen inside ~2×105 km. Deeper
within the coma the main cometary hot-ion species identified were
H+, H2+, C+, O+,
OH+, H2O+, H3O+,
CO+ and S+. A pile-up of heavy cometary ions
was found at ~104 km from the nucleus. Giotto crossed the
contact surface at ~4,600 km, based on changes in ion flow velocity
and temperature. Inside, ion temperatures as low as ~340 K and outflow
velocities of ~1 km s-1 were found. Outside the contact
surface ion densities vary as r-2, with a transition to an
r-l dependence approximately at the contact surface. A large
C+ abundance throughout the coma indicates an unexpected
direct source of atomic carbon. The nitrogen abundance, on the other
hand, is relatively low.
Title: In-Situ Observations of the Latitudinal Gradients of the
Solar Wind Parameters during 1976 and 1977
Authors: Bruno, R.; Villante, U.; Bavassano, B.; Schwenn, R.;
Mariani, F.
Bibcode: 1986SoPh..104..431B
Altcode:
Interplanetary observations from Helios 1, Helios 2, and IMP-8
spacecraft during 1976 and 1977, namely the early portion of solar
cycle 21, have been used to investigate the latitudinal gradients of the
solar wind parameters with respect to the angular displacement from the
current sheet inferred from synoptic HAO white-light maps of the solar
corona at 1.75 solar radii. A latitudinal belt of ±25 deg around the
current sheet has been investigated. Large gradients for solar wind
flow speed, proton density and temperature have been found. Smoother
gradients were also found for particle flux, kinetic, gravitational
and thermal energy density flux. All these gradients revealed to become
smoother going towards the solar cycle's maximum. Neither latitudinal
nor temporal variations were identified for magnetic and thermal
energy density. A remarkable result of this study is that the momentum
flux density and the total energy flux density which other authors
found to be independent of any longitudinal stream structure were
also found to be independent of any latitudinal structure. Moreover,
these two parameters did not show any temporal variation during the
period of interest.
Title: The Giotto ion mass spectrometer
Authors: Balsiger, H.; Altwegg, K.; Buehler, F.; Fischer, J.;
Geiss, J.; Meier, A.; Rettenmund, U.; Rosenbauer, H.; Schwenn, R.;
Neugebauer, M.
Bibcode: 1986gmis.rept..129B
Altcode:
The Giotto Ion Mass Spectrometer (IMS) consists of two sensors: one
optimized for the outer and the other for the inner coma, with each
obtaining complementary information in the region for which it is not
optimized. The outer coma is characterized by the interaction between
solar wind and comentary plasmas, the inner coma by the outflow of
cometary neutrals and their ionization products. Both sensors feature
mass imaging characteristics, permitting simultaneous measurements of
several ion species by multidetector arrays. Resultant mass-per-charge
resolution is greater than or = 20. Energy per charge, and the elevation
and aximuth of incident ions are measured. Calibration and in-flight
solar-wind data show that the IMS will meet its scientific goals for
the Halley encounter.
Title: Cosmic ray variations and turbulent flow systems: 0.3-1.0
AU; 1977-1980
Authors: Burlaga, L. F.; Goldstein, M. L.; McDonald, F. B.; Lazarus,
A. J.; Mariani, F.; Neubauer, F. M.; Schwenn, R.
Bibcode: 1986JGR....91.2917B
Altcode:
Relations among the relative counting rates of cosmic ray protons
and the magnetic fields and flows observed by Helios 1 between
0.3 AU and 1 AU in the period January 1977 to August 1980 are
discussed. Isolated corotating or transient flows are associated with
short-term depressions in cosmic ray intensity, but the effects are
localized in longitude. Systems of corotating streams do not produce a
long-term modulation effect, although temporary, short-term depressions
in cosmic ray intensity are associated with individual streams and
interaction regions. Spectra of fluctuations of the magnetic field and
magnetic helicity for systems of corotating flows often do not have the
form f-5/3 at frequencies
>=10-5 Hz, and accordingly, the hydromagnetic
fluctuations in corotating streams near the sun do not appear to
represent fully developed turbulence at low frequencies. Systems of
transient streams containing shocks that might encircle the sun are
associated with long-lasting decreases in cosmic ray intensity. The
magnetic field fluctuations in such flow systems are often turbulent,
with f-5/3 spectra extending
from below 10-5 Hz to the Nyquist frequency
of the data. The turbulence is likely to be confined to sheets with
thickness of the order of 0.1 AU, possibly associated with shocks. We
conclude that long-term modulation of cosmic rays inside 1 AU is
associated with turbulence in transient disturbances that probably
encompass a large longitudinal extent around the sun. In mixed flow
systems the effects are intermediate between those of corotating and
transient systems. The net modulation may be relatively small, with
large short-term variations associated with individual streams.
Title: The Giotto Ion Mass Spectrometer.
Authors: Balsiger, H.; Altwegg, K.; Bühler, F.; Fischer, J.; Geiss,
J.; Meier, A.; Rettenmund, U.; Rosenbauer, H.; Schwenn, R.; Benson,
J.; Hemmerich, P.; Säger, K.; Kulzer, G.; Neugebauer, M.; Goldstein,
B. E.; Goldstein, R.; Shelley, E. G.; Sanders, T.; Simpson, D.;
Lazarus, A. J.; Young, D. T.
Bibcode: 1986ESASP1070..129B
Altcode:
The Giotto Ion Mass Spectrometer (IMS) consists of two sensors: one
optimised for the outer and the other for the inner coma of Halley's
comet. Both sensors feature mass imaging characteristics, thereby
permitting simultaneous measurements of several ion species by means
of multi-detector arrays. Resultant mass-per-charge resolution is
≥20. In addition to mass per charge, the energy per charge, the
elevation and azimuth of incident ions are measured.
Title: Relationship of Coronal Transients to Interplanetary Shocks:
3-D Aspects
Authors: Schwenn, R.
Bibcode: 1986shtd.symp..119S
Altcode:
No abstract at ADS
Title: Shock and Statistical Acceleration of Energetic Particles in
the Interplanetary Medium
Authors: Valdes-Galicia, J. F.; Moussas, X.; Quenby, J. J.; Neubauer,
F. M.; Schwenn, R.
Bibcode: 1985ICRC....4..162V
Altcode: 1985ICRC...19d.162V
Definite evidence for particle acceleration in the solar wind came
around a decade ago. Two likely sources are known to exist: particles
may be accelerated by the turbulence resulting from the superposition
of Alfven and Magnetosonic waves (Statistical Acceleration) or they may
be accelerated directly at shock fronts formed by the interaction of
fast and slow solar wind (CIR's) or by traveling shocks due to sporadic
coronal mass ejections. Naurally both mechanisms may be operative. In
this work the acceleration problem was tackled numerically using Helios
1 and 2 data to create a realistic representation of the Heliospheric
plasma. Two 24 hour samples were used: one where there are only wave
like fluctuations of the field (Day 90 Helios 1) and another with
a shock present in it (Day 92 of Helios 2) both in 1976 during the
STIP 2 interval. Transport coefficients in energy space have been
calculated for particles injected in each sample and the effect of
the shock studied in detail.
Title: Origin of the Solar Wind
Authors: Gabriel, A.; Schwenn, R.
Bibcode: 1985ESASP.235..231G
Altcode: 1985fmsh.work..231G
No abstract at ADS
Title: Latitudinal gradients of the solar wind parameters during
1976 and 1977: HELIOS 1, 2 and IMP in-situ observations
Authors: Bruno, R.; Villante, V.; Bavassano, B.; Schwenn, R.
Bibcode: 1985STIN...8628902B
Altcode:
Interplanetary observations from Helios 1, Helios 2 and IMP spacecraft
during the early portion of solar cycle 21 were used to investigate
the latitudinal gradients of solar wind parameters with respect to the
angular displacement from the current sheet inferred from synoptic
white-light maps of the solar corona at 1.75 solar radii. Large
latitudinal gradients for solar wind flow speed, proton density, and
temperature are found. All these gradients become smoother towards
the solar cycle maximum. Neither latitudinal nor temporal variations
for magnetic flow and thermal energy density are identified.
Title: Doppler scintillation observations of interplanetary shocks
within 0.3 AU
Authors: Woo, Richard; Armstrong, J. W.; Sheeley, N. R.; Howard,
R. A.; Koomen, M. J.; Michels, D. J.; Schwenn, R.
Bibcode: 1985JGR....90..154W
Altcode:
Near-sun spacecraft Doppler scintillation observations have been
combined with Solwind coronagraph and Helios 1 plasma measurements to
provide more definitive measurements of the evolution and propagation
of interplanetary shock waves between the sun and earth orbit than
have been available from previous observations. This study shows that
substantial deceleration of fast shocks (shock speeds exceeding 1000 km
s-1) takes place near the sun and that the amount
of deceleration increases with shock speed. This is consistent with
the significantly lower and rather narrow range of shock velocities
observed by direct spacecraft near earth orbit. When coronal mass
ejection (CME) speeds are available for the fast shocks, they are
considerably lower than the speeds measured farther out but near the
sun. This implies that either the fast shocks first accelerate before
decelerating on their way out from the sun (assuming the CME front
is identified with the shock) or the CME speeds do not represent and
substantially underestimate the shock speeds in the outer corona. If
the CME speeds underestimate the shock speeds of the fast shocks, they
do not appear to do so for the slow shocks. If the shocks are being
driven over distances indicated by the acceleration region or to the
point where deceleration begins, then their velocity profiles imply
that the slower shocks are being driven farther out than the faster
shocks. The analysis of one piston-driven shock shows the velocity of
the contact surface is about 0.58 that of the shock front velocity.
Title: Coronal mass ejections and interplanetary shocks
Authors: Sheeley, N. R., Jr.; Howard, R. A.; Michels, D. J.; Koomen,
M. J.; Schwenn, R.; Muehlhaeuser, K. H.; Rosenbauer, H.
Bibcode: 1985JGR....90..163S
Altcode:
A comparison between Solwind observations of coronal mass ejections
(CME's) and Helios 1 observations of interplanetary shocks during
1979-1982 indicates that 72% of the shocks were associated with large,
low-latitude mass ejections on the nearby limb. Most of the associated
CME's has speeds in excess of 500 km/s, but some of them had speeds in
the range 200-400 km/s. An additional 26% of the shocks may have been
associated with CME's, but we were less confident of these associations
because the sizes and locations of the CME's did not seem appreciably
different from those of the numerous CME's without Helios shocks. Only
2% of the shocks clearly lacked CME's. As the average level of sunspot
activity declined during 1982, the shock frequency also declined, but
the observed shocks and some of their associated CME's had unusually
high speeds well in excess of 1000 km/s.
Title: Review of interplanetary shock phenomena near and within 1 AU
Authors: Richter, A. K.; Hsieh, K. C.; Luttrell, A. H.; Marsch, E.;
Schwenn, R.
Bibcode: 1985GMS....35...33R
Altcode:
A review of the more recent observations regarding interplanetary shock
waves and shock-related phenomena near and within 1 AU is presented. In
particular, the observations of interplanetary fast mode shocks are
summarized in terms of (1) their solar and interplanetary origin,
(2) their observed characteristics with respect to the solar cycle,
(3) the solar wind stream-structure, and (4) the heliocentric radial
distance; and in terms of (5) their three-dimensional propagation
properties in the inner part of the heliosphere. Postshock large-scale
flows and structures and some recent 'field and particle' observations
associated with interplanetary fast shocks are also reviewed.
Title: Interplanetary flow systems associated with cosmic ray
modulation in 1977-1980
Authors: Burlaga, L. F.; McDonald, F. B.; Ness, N. F.; Schwenn, R.;
Lazarus, A. J.; Mariani, F.
Bibcode: 1984JGR....89.6579B
Altcode:
The hydromagnetic flow configurations associated with the cosmic ray
modulation in 1977-1980 were determined using solar wind plasma and
magnetic field data from Voyager 1 and 2 and Helios 1. The modulation
was related to two types of large-scale systems of flows: one containing
a number of transients such as shocks and postshock flows, the other
consisting primarily of a series of quasistationary flows following
interaction regions containing a stream interface and often bounded
by a forward-reverse shock pair. Each of three major episodes of
cosmic ray modulation was associated with the passage of a system of
transient flows. Plateaus in the cosmic ray intensity-time profile
were associated with the passage of systems of corotating streams.
Title: Mean free paths and diffusion coefficients for energetic
protons at small heliodistances calculated using HELIOS 1 and 2 data
Authors: Valdes Galicia, J. F.; Moussas, X.; Quenby, J. J.; Neubauer,
F. M.; Schwenn, R.
Bibcode: 1984SoPh...91..399V
Altcode:
Pitch angle scattering of energetic particles (100 MeV) in the
interplanetary medium are studied using Helios 1 and 2 magnetometer
and plasma data during 1976 near the minimum of solar activity. An
IMF configuration was used in the computer experiments which allowed
the pitch angle diffusion coefficient, Dμμ and hence the
parallel mean free path, λ∥, to be determined. The radial
mean free path was found to vary as λr ≡ r-0.9
between 0.4 and 1 AU, but between 0.3 and 0.4 AU it decreases
significantly. To reconcile the authors' value of λr at
1 AU, lying between 0.01 and 0.02 AU, with the average prompt solar
proton event profile an increasing value of λr at lower
radial distances would be required.
Title: Solar Radio Burst and In-Situ Determination of Interplanetary
Electron Density
Authors: Bougeret, J. -L.; King, J. H.; Schwenn, R.
Bibcode: 1984SoPh...90..401B
Altcode:
We review and discuss a few interplanetary electron density scales
which have been derived from the analysis of interplanetary solar
radio bursts, and we compare them to a model derived from 1974-1980
Helios 1 and 2 in situ density observations made in the 0.3-1.0
AU range. The Helios densities were normalized to 1976 with the
aid of IMP and ISEE data at 1 AU, and were then sorted into 0.1
AU bins and logarithmically averaged within each bin. The best
fit to these 1976-normalized, bin averages is N(RAU) =
6.1R-2.10 cm-3. This model is in rather good
agreement with the solar burst determination if the radiation is assumed
to be on the second harmonic of the plasma frequency. This analysis
also suggests that the radio emissions tend to be produced in regions
denser than the average where the density gradient decreases faster
with distance than the observed R-2.10.
Title: Report of ESA's topical team on solar and heliospheric physics.
Authors: Christensen-Dalsgaard, J.; Delache, P.; Hoyng, P.; Priest,
E. R.; Schwenn, R.; Stenflo, J. O.
Bibcode: 1984ESASP1070...26C
Altcode:
No abstract at ADS
Title: Synoptic observations of coronal transients and their
interplanetary consequences
Authors: Michels, D. J.; Sheeley, N. R., Jr.; Howard, R. A.; Koomen,
M. J.; Schwenn, R.; Mulhauser, K. H.; Rosenbauer, H.
Bibcode: 1984AdSpR...4g.311M
Altcode: 1984AdSpR...4..311M
A small coronagraph has been placed in orbit to monitor the sun's
outer corona from 2.5 to 10.0 solar radii, and five years of nearly
continuous synoptic observations have now been completed. Rapid and
sensitive image processing techniques have been developed to screen
the data for transient phenomena, particularly coronal mass ejections
(CMEs). About 50,000 coronal images have been examined, out of a
five-year total of 68,000, and a standardized listing of more than 1,200
coronal transients for the period 1979-1982 has been prepared. These
data have been analysed in the light of other available information,
particularly on conditions in the interplanetary plasma. The dynamical
characteristics of the active corona, as they are beginning to emerge
from the data, are presented. We find that coronal mass ejections
exercise significant influence on the interplanetary solar wind. They
are the source of disturbances that are frequent and energetic,
that tend to be somewhat focussed, that often reach shock intensity,
and that propagate to large heliocentric distances, sometimes causing
major geomagnetic storms.
Title: Ten years solar wind experiments on HELIOS 1 and HELIOS 2
Authors: Schwenn, R.; Rosenbauer, H.
Bibcode: 1984GeCAS.......66S
Altcode:
The Helios solar wind experiment is reviewed. The experiment measures
low energy ions and electrons which run through an electrostatic or
electrodynamic deflection system. A stepwise registration of energy
spectra is performed, and the direction of particle arrival is also
determined. Velocity distribution functions for the different particle
species are used to deduce solar wind properties. The instruments
operate without any major malfunctions. The long life of Helios 1
allowed it to collect a set of solar plasma data of almost identical
quality over a full solar activity cycle.
Title: Data analyis of electron measurements of the Plasma Experiment
aboardthe Helios probes.
Authors: Philipp, W. G.; Miggenrieder, H.; Mühlhäuser, K. -H.;
Rosenbauer, H.; Schwenn, R.
Bibcode: 1984MPERp.185.....P
Altcode:
The methods to derive distribution functions for solar wind electrons
from the measurements of the "Plasma Experiment" aboard the Helios
probes are outlined. Electrons are measured in the energy range from 0.5
to 1660 eV with a one-dimensional angular resolution along the ecliptic
plane. From these measurements electron distribution functions with
high time resolution (typically 18 s) but poor angular resolution in
velocity space (45 degrees) and electron distribution functions with
high angular resolution (better than 5 to 10 degrees) but poor time
resolution (typically several minutes to few hours) have been derived.
Title: Interplanetary flow systems associated with cosmic ray
modulation in 1977 - 1980
Authors: Burlaga, L. F.; McDonald, F. B.; Ness, N. F.; Schwenn, R.;
Lazarus, A. J.; Mariani, F.
Bibcode: 1983STIN...8418149B
Altcode:
The hydromagnetic flow configurations associated with cosmic ray
modulation in 1977 to 1980 were determined using solar wind plasma and
magnetic field data from Voyagers 1 and 2 and Helios 1. The modulation
was related to two types of large scale systems of flows: one containing
a number of transients such as shocks, post shock flows and magnetic
clouds; the other consisting primarily of a series of quasi-stationary
flows following interaction regions containing a stream interface and
often bounded by a forward reverse shock pair. Each of the three major
episodes of cosmic ray modulation was characterized by the passage of
the system of transient flows. Plateaus in the cosmic ray intensity
time profile were associated with the passage of systems of corotating
streams.
Title: Associations between coronal mass ejections and interplanetary
shocks.
Authors: Sheeley, N. R., Jr.; Howard, R. A.; Koomen, M. J.; Michels,
D. J.; Schwenn, R.; Muhlhauser, K. H.; Rosenbauer, H.
Bibcode: 1983NASCP.2280.693S
Altcode: 1983sowi.conf..693S
The authors are in the process of comparing nearly continuous
complementary coronal observations and interplanetary plasma
measurements for the years 1979 - 1982. Their preliminary results
show that almost all low-latitude high-speed coronal mass ejections
(CME's) were associated with shocks at HELIOS 1. Some suitably directed
low-speed CME's were clearly associated with shocks while others may
have been associated with disturbed plasma (such as NCDE's) without
shocks. A few opposite-hemisphere CME's associated with great flares
also seemed to have been associated with shocks at HELIOS.
Title: The "average" solar wind in the inner heliosphere: structures
and slow variations.
Authors: Schwenn, R.
Bibcode: 1983NASCP.2280.489S
Altcode: 1983sowi.conf..489S
Measurements from the HELIOS solar probes indicated that apart
from solar activity related disturbances there exist two states
of the solar wind which might result from basic differences in the
acceleration process: the fast solar wind (v 600 kms(-)1) emanating
from magnetically open regions in the solar corona and the "slow" solar
wind (v 400 kms(-)1) correlated with the more active regions and its
mainly closed magnetic structures. In a comprehensive study using all
HELIOS data taken between 1974 and 1982 the average behavior of the
basic plasma parameters were analyzed as functions of the solar wind
speed. The long term variations of the solar wind parameters along the
solar cycle were also determined and numerical estimates given. These
modulations appear to be distinct though only minor. In agreement
with earlier studies it was concluded that the major modulations are
in the number and size of high speed streams and in the number of
interplanetary shock waves caused by coronal transients. The latter
ones usually cause huge deviations from the averages of all parameters.
Title: Dynamical evolution of interplanetary magnetic fields and
flows between 0.3 AU and 8.5 AU: entrainment.
Authors: Burlaga, L. F.; Schwenn, R.; Rosenbauer, H.
Bibcode: 1983NASCP2280..729B
Altcode:
No abstract at ADS
Title: Solar radio burst and in situ determination of interplanetary
electron density
Authors: Bougeret, J. L.; King, J. H.; Schwenn, R.
Bibcode: 1983STIN...8335989B
Altcode:
A few interplanetary electron density scales which were derived from the
analysis of interplanetary solar radio burst are discussed and compared
to a model derived from 1974 to 1980 Helios 1 and 2 in situ density
observations made in the 0.3 to 1.0 AU range. The Helios densities were
normalized to 1976 with the aid of IMP and ISEE data at 1 AU, and were
then sorted into 0.1 AU bins and logarithmically averaged within each
bin. The best fit to these 1976-normalized, bin averages is N(R(AU))
= 6.1 R(-2.10)/cu cm. This model is in rather good agreement with the
solar burst determination if the radiation is assumed to be on the
second harmonic of the plasma frequency. This analysis also suggests
that the radio emissions tend to be produced in regions denser than
the average where the density gradient decreases faster with distance
than the observed R(-2.10).
Title: Acceleration and spatial diffusion of energetic particles
obtained with Helios data.
Authors: Valdes-Galicia, J. F.; Mousas, X.; Quenby, J. J.; Neubauer,
F.; Schwenn, R. S.
Bibcode: 1983ICRC...10..104V
Altcode: 1983ICRC...18j.104V
Numerical simulations have been performed to evaluate the transport
coefficients for energetic particles in the interplanetary medium
using Helios 1/2 IMF data at distances from 0.3 to 0.67 AU from the
sun, and the results are reported. The data are also used to obtain
the statistical acceleration of these particles.
Title: Determination of the solar wind angular momentum flux from
the HELIOS data - an observational test of the Weber and Davis theory
Authors: Pizzo, V.; Schwenn, R.; Marsch, E.; Rosenbauer, H.;
Muehlhaeuser, K. -H.; Neubauer, F. M.
Bibcode: 1983ApJ...271..335P
Altcode:
In situ attempts to measure the sun's angular momentum loss in the
solar wind and thereby to test the Weber and Davis description of the
magnetic coupling between stellar rotation and winds have thus far
produced widely divergent and inconclusive results. A new estimate
for the solar loss rate in the ecliptic plane has been derived from
the Helios spacecraft data. By intercomparing measurements made by
the twin probes over the full 0.3-1.0 AU baseline of their orbits,
it is possible to eliminate the systematic instrumental offsets from
the true radial direction that have plagued previous efforts. The main
observational findings are that (1) the total angular momentum flux
loss rate (field + particles) near the solar equator is ∼0.2-0.3
× 1030 dyn cm sr-1, about one-quarter the
Weber and Davis prediction and much lower than previous spacecraft
estimates, and (2) the distribution of that flux between particles
and field stresses is very near the 1:3 ratio of the model, when
an important contribution from the heretofore neglected solar wind
α-particles is accounted for. Though few by number in the solar wind,
the α-particles' flow speed and direction in general differ from that
of the protons, largely offsetting the latters' angular momentum content
(+0.15-0.2 × 1030 for the protons, -0.1 × 1030
for the α-particles, plus being in the direction of corotation with
the Sun). As to the small value reported for the total flux, theory
and observation can be reconciled by moving the mean Alfvén radius,
rA, in to 12 Rsun, a figure that is consistent
with coronal models more realistic than the single polytrope formulation
used by Weber and Davis. There is a distinct tendency for slow solar
wind to carry positive total flux and for fast wind, negative; this
can probably be explained in terms of stream-interaction dynamics in
the super-Alfvénic region. It thus appears that the Weber and Davis
theory adequately describes angular momentum loss in solar-type winds,
insofar as simple magnetic stresses are taken as the dominant coupling
mechanism. However, in the general astrophysical application, it is
suggested that a more accurate treatment of coronal acceleration be
incorporated to properly locate rA (and hence fix the total
loss rate) and that some allowance for three-dimensional effects be
made. Also, should large speed differentials between α-particles and
protons occur well inside rA, a three-fluid version of the
Weber and Davis model may be in order.
Title: Dynamical evolution of interplanetary magnetic fields and
flows between 0.3 AU and 8.5 AU: Entrainment
Authors: Burlaga, L. F.; Schwenn, R.; Rosenbauer, H.
Bibcode: 1983GeoRL..10..413B
Altcode: 1983STIN...8319667B
The radial evolution of interplanetary flows and associated magnetic
fields between 0.3 AU and 8.5 AU was analyzed using data from Helios 1
and Voyager 1, respectively. During a 70-day interval in 1980 Voyager
1 observed two streams which appeared to be recurrent and which had
little fine structure. The corresponding flows observed by Helios 1
were much more complex, showing numerous small streams, transient
flows and shocks as well as a few large corotating streams. It is
suggested that in moving to 8 AU the largest corotating streams swept
up the slower flows (transient and/or corotating streams) and shocks
into a relatively thin region in which they coalesced to form a single
large-amplitude compression wave. We refer to this combined process of
sweeping and coalescence as "entrainment". The resulting large-amplitude
compression wave is different from that formed by the steepening of a
corotating stream from a coronal hole, because different flows from
distinct sources, with possibly different composition and magnetic
polarity, are brought together to form a single new structure. As a
result of entrainment, memory of the sources and flow configurations
near the sun is lost. Small-scale features are erased as the flows move
outward and energy is transferred from small scales to large scales
by entrainment. Thus in the outer solar system the structure of the
solar wind may be dominated by large scale pressure waves (compressions
followed by rarefactions) separated by several AU. Beyond several AU
most of the compression waves are no longer driven by streams, and
the compression waves expand freely. At large distances (≳ 25 AU)
they will have interacted extensively with one another producing yet
another state of the solar wind, with fewer large-scale non-uniformities
and more small-scale non-uniformities.
Title: On the equaton of state of solar wind ions derived from
Helios measurements
Authors: Marsch, E.; Muehlhaeuser, K. H.; Rosenbauer, H.; Schwenn, R.
Bibcode: 1983JGR....88.2982M
Altcode:
Observations of solar wind ion velocity distributions made by the Helios
spacecraft between 0.3 and 1 AU are used to study the radial evolution
of the so-called adiabatic invariants, for example, the ion magnetic
moments. Significant differences between the parameters of protons and
α particles have been found in dependence on the wind velocity. On
the average, adiabaticity is observed to be violated. We interpret this
violation of adiabatic invariance as evidence that protons are heated
perpendicular to the field in fast streams and, with less statistical
significance, that α particles are cooled more strongly than for
adiabatic expansion parallel to the magnetic field. The contribution
of the differential streaming energy to the total internal energy of
the ions is briefly investigated. Also, average heliocentric radial
profiles for the ion heat fluxes are presented, and the possible
role of the ion heat flux in supplying thermal energy during the
radial expansion of the wind is examined. Our findings suggest that
wave-particle interactions and (or) Coulomb collisions (or other yet
unknown processes) have to be invoked in order to explain the thermal
energy state of solar wind ions and their radial temperature profiles.
Title: Direct Correlations Between Coronal Transients and
Interplanetary Disturbances
Authors: Schwenn, R.
Bibcode: 1983SSRv...34...85S
Altcode:
Major interplanetary shock waves have often been successfully associated
with major solar flares. The interplanetary response to weaker solar
events, e.g., eruptive prominences (EP) and slow coronal transients,
is far less pronounced. Recently, progress has been made by combining
the newly-available data of white-light-coronagraph measurements from
the earth-orbiting satellite P78/1 (these data show the development of
coronal transients between 2.5 and 10 R bd, in-situ plasma
measurements from the HELIOS solar probes positioned mostly above
the Sun's limb at solar distances between 60 and 200 R bd
(showing the reactions of the interplanetary plasma), ground based
Hα-coronagraphs (showing in a few cases the evolution of EP's from
the Sun's limb up to 1.5 Abd). In the years 1979 to 1981
about 25 uniquely associated events were identified, 19 of which
allow some detailed analysis. The events can be sorted into three main
categories: The ‘flare-type’: 13 events, probably all of them
flare-related, transient speeds v t from 560 to 1460 km
s-1, no evidence for post-acceleration of the transient
(indicating impulsive injection), all transients followed by drastic
interplanetary shock waves, some of them probably involving magnetic
clouds. The ‘EP-type’: 4 events, none of them flare-related,
at least one was observed as an Hα-EP, transient speed from 200 to
410 km s-1, all post-accelerated (indicating ‘driven’
injection), all followed by shocks with at least one magnetic cloud,
one showing presence of He+ and O2+ behind
the shock. The ‘NCDE-type’: 2 events, one observed as an
Hα-EP, the other without known solar source, v t , = 130
and 470 km s-1, one post-accelerated, the other one not,
considerable density increase in interplanetary plasma (however, in
pressure equilibrium with surroundings), one event including shock, the
other not. These two events may not belong to the same category. Our
results are not completely consistent with previous work which is
mainly based on data from the Skylab era, 1973/74. This could be due
to the different phase in the solar cycle. The study is being continued.
Title: A magnetic cloud and a coronal mass ejection
Authors: Burlaga, L. F.; Klein, L.; Sheeley, N. R., Jr.; Michels,
D. J.; Howard, R. A.; Koomen, M. J.; Schwenn, R.; Rosenbauer, H.
Bibcode: 1982GeoRL...9.1317B
Altcode:
An interplanetary magnetic cloud observed by the Helios 1 spacecraft
was found to be associated with a coronal mass ejection observed by the
NRL Solwind coronagraph on the spacecraft P78-1. The magnetic cloud was
observed on June 20, 1980 when Helios 1 was at 0.54 AU and nearly 90°
west of the earth-sun line. This was associated with a large loop-like
coronal mass ejection observed over the west limb on June 18, 1980,
moving toward Helios 1. The speed of the front of the event at Helios
1 was (470 ± 10) km/s, which is close to the mean transit speed (∽
500 km/s). The magnetic cloud was similar to others described in the
literature: The magnetic field strength was higher than average; the
density was relatively low; the magnetic pressure greatly exceeded
the ion thermal pressure; and the magnetic field direction changed
through the cloud by rotating parallel to a plane which was highly
inclined with respect to the ecliptic.
Title: Processing and evaluation of the data from the plasma
experiment onboard the HELIOS solar probes
Authors: Schwenn, R.; Rosenbauer, H.
Bibcode: 1982mpia.rept.....S
Altcode:
The data processing and evaluation procedure for the plasma experiment
on board the HELIOS solar probes is described. The instruments of
the HELIOS plasma experiment investigate the interplanetary plasma
characteristics. Most of the intermediate data processing steps are
explained and the resulting data plots are shown in their various
forms. The most important computer programs are enclosed, together
with basic explanations.
Title: Observation of flare-generated shock waves by Helios-2 near
the sun
Authors: Volkmer, P. M.; Neubauer, F. M.; Schwenn, R.
Bibcode: 1982SSRv...32..131V
Altcode:
We present the observation of three flare generated shock waves
which were measured by Helios-2 at a radial distance from the Sun
of 0.476 AU, 0.444 AU, and 0.297 AU. These results show that two of
the shocks fulfill the classification scheme of ‘F-events’ stated
in the past while the third shock profile is that of a ‘R-event’
being interpreted as a driven wave. Because of the close distance to
the Sun a flare-association was possible. Only in one case there is
some evidence for a piston in the downstream region of the shock. One
of the shocks is characterized by a distinct hole in the frequency
distribution of directional discontinuities in the downstream region.
Title: Solar wind protons: Three-dimensional velocity distributions
and derived plasma parameters measured between 0.3 and 1 AU
Authors: Marsch, E.; Schwenn, R.; Rosenbauer, H.; Muehlhaeuser,
K. -H.; Pilipp, W.; Neubauer, F. M.
Bibcode: 1982JGR....87...52M
Altcode:
A survey of solar wind three-dimensional proton velocity
distributions as measured by the Helios solar probes between
0.3 and 1 AU is presented. A variety of nonthermal features like
temperature anisotropies, heat fluxes, or proton double streams has
been observed. The relative speed of the second proton component
increases on the average with increasing wind speed and decreasing
heliocentric radial distance and shows a correlation with the local
Alfvén speed. A marked anisotropy in the core of proton distributions
with a temperature larger perpendicular than parallel to the magnetic
field (T∥c<T⊥c) is a persistent feature
of high speed streams and becomes most pronounced in the perihelion
(~0.3 AU). Fairly isotropic distributions have only been measured
very close to and directly at magnetic sector boundaries. Low and
intermediate speed distributions usually show a total temperature
anisotropy T∥p/T⊥p>1 frequently caused by
'high-energy shoulders' or a resolved second proton component. No clear
radial gradient of the temperature anisotropy could be established
in these cases. The average dependence of the proton temperature on
heliocentric radial distance is given by a power law R-α,
where α~1 for T⊥p and 0.7<α<1 for T⊥p
are compatible neither with isothermal nor adiabatic expansion. Flattest
radial temperature profiles are obtained in high-speed streams. These
observations indicate that local heating or considerable proton heat
conduction occurs in the solar wind. Some consequences of nonthermal
features of proton distributions for plasma instabilities are discussed
as well as kinetic processes that may shape the observed distributions.
Title: Solar wind helium ions: obsevations of the Helios solar probes
between 0.3 and 1 AU
Authors: Marsch, E.; Rosenbauer, H.; Schwenn, R.; Muehlhaeuser,
K. -H.; Neubauer, F. M.
Bibcode: 1982JGR....87...35M
Altcode:
A survey of solar wind helium ion velocity distributions and
derived parameters as measured by the Helios solar probes between
0.3 and 1 AU is presented. Nonthermal features like heat flux or
He2+ double streams and temperature anisotropies have been
frequently observed. Fairly isotropic distributions have only been
measured close to sector boundaries of the interplanetary magnetic
field. At times in slow solar wind, persistent double-humped
helium ion distributions constituting a temperature anisotropy
T∥α/T⊥α> have been reliably
identified. Distributions in high-speed wind generally have small
total anisotropies (T∥α/T⊥α>1)
with a slight indication that in the core part the temperatures
are larger parallel than perpendicular to the magnetic field, in
contrast to simultaneous proton observations. The anisotropy tends to
increase with increasing heliocentric radial distance. The average
dependence of helium ion temperatures on radial distance from the
sun is described by a power law ~R-β with 0.7<~1.2 for
T∥α and 0.87<~β<~1.4 for T⊥α. In
fast solar wind the T⊥α profile is compatible with
nearly cooling. Pronounced differential ion speeds Δvαp
have been observed with values of more than 150 km/s near perihelion
(0.3 AU). In fast streams Δvαp tends to approach the local
Alfvén velocity vA, whereas in slow plasma values around
zero are obtained. Generally, the differential speed increases with
increasing proton bulk speed and (with the exception of slow plasma)
with increasing heliocentric radial distance. The role of Coulomb
collisions in limiting Δvαp and the ion temperature ratio
Tα/Tp is investigated. Collisions are shown to
play a negligible role in fast solar wind, possibly a minor role in
intermediate speed solar wind and a distinct role in low-speed wind
in limiting the differential ion velocity and temperature.
Title: Pronounced proton core temperature anisotropy, ion differential
speed, and simultaneous Alfvén wave activity in slow solar wind at
0.3 AU
Authors: Marsch, E.; Rosenbauer, H.; Schwenn, R.; Muehlhaeuser,
K. -H.; Denskat, K. U.
Bibcode: 1981JGR....86.9199M
Altcode:
In the Helios 2 perihelion (0.3 AU) im May 1978, pronounced ion
differential speeds Δvop>0 and large proton temperature
anisotropies T∥p/T⊥p<1 have been observed
in slow solar wind, in distinct contrast to earlier observations during
the phase of solar activity minimum. These features of ion distributions
occurred simultaneously with high Alfvénic wave activity. Coulomb
friction between the two ion species can be shown to play a minor role,
thus obviously favouring the establishment of a large differential ion
speed by preferentially accelerating wave forces. The observations
may also indicate that strong waves sometimes only heat the protons
without creating a fast solar wind.
Title: The instruments of the plasma experiment onboard the HELIOS
solar probe
Authors: Rosenbauer, H.; Schwenn, R.; Miggenrieder, H.; Meyer, B.;
Gruenwaldt, H.; Muehlhaeuser, K. H.; Pellkofer, H.; Wolfe, J. H.
Bibcode: 1981mpia.reptQ....R
Altcode:
The plasma experiment on board the solar probe HELIOS, consisting of
four instruments designed to investigate the interplanetary plasma,
or solar wind, is discussed. The velocity distribution functions of the
different kinds of particles are measured. Hydrodynamic parameters of
the solar wind plasma can then be derived. Three instruments analyze
the positive component of the solar wind (protons and heavier ions
with energy-per-charge values from 0.155 to 15.32 kV). Two of them
permit an angular resolution in both directions of incidence. One
instrument measures electrons in the energy range from 0.5 to 1660 eV
with a one-dimensional angular resolution.
Title: Magnetic loop behind an interplanetary shock: Voyager, Helios,
and IMP 8 observations
Authors: Burlaga, L.; Sittler, E.; Mariani, F.; Schwenn, R.
Bibcode: 1981JGR....86.6673B
Altcode: 1981STIN...8125009B
Magnetic field and plasma data from five spacecraft (Voyager 1 and 2,
Helios 1 and 2, and IMP 8) were used to analyze the flow behind an
interplanetary shock. The shock was followed by a turbulent sheath
in which there were large fluctuations in both the strength and
the direction of the magnetic field. This in turn was followed by
a region (magnetic cloud) in which the magnetic field vectors were
observed to change by rotating nearly parallel to a plane, consistent
with the passage of a magnetic loop. This loop extended at least
30° in longitude between 1 and 2 AU, and its radical dimension was
approximately 0.5 AU. In the cloud the field strength was high, and
the density and temperature were relatively low. Thus the dominant
pressure in the cloud was that of the magnetic field. The total
pressure inside the cloud was higher than outside, implying that the
cloud was expanding as it moved outward, even at the distance of 2
AU. The momentum flux of the cloud at 2 AU was not higher than that
of the preshock plasma, indicating that the cloud was not driving
the shock at this distance. It is possible, however, that the shock
was driven by the cloud closer to the sun where the cloud may have
moved faster. An extraordinary filament was observed at the rear of
the cloud. It was bounded by current sheets whose orientations were
preserved over at least 0.12 AU and which were related to the plane
of maximum variance of the magnetic field in the cloud.
Title: The Giotto Ion Mass Spectrometer
Authors: Balsiger, H.; Geiss, J.; Young, D. T.; Rosenbauer, H.;
Schwenn, R.; Ip, W. -H.; Ungstrup, E.; Neugebauer, M.; Goldstein,
R.; Goldstein, B. E.; Huntress, W. T.; Shelley, E. G.; Sharp, R. D.;
Johnson, R. G.; Lazarus, A. J.; Bridge, H. S.
Bibcode: 1981giot.proc...93B
Altcode:
No abstract at ADS
Title: Two States of the Solar Wind at the Time of Solar Activity
Minimum - Part One - Boundary Layers Between Fast and Slow Streams
Authors: Schwenn, R.; Mohlhauser, K. H.; Rosenbauer, H.
Bibcode: 1981sowi.conf..118S
Altcode:
No abstract at ADS
Title: Some Characteristics of Proton Velocity Distributions in the
Solar Wind as Observed by the HELIOS Solar Probes
Authors: Marsch, E.; Pilipp, W. G.; Schwenn, R.; Mohlhauser, K. H.;
Rosenbauer, H.
Bibcode: 1981sowi.conf..273M
Altcode:
No abstract at ADS
Title: Solar wind and its interaction with the magnetosphere:
measured parameters.
Authors: Schwenn, R.
Bibcode: 1981meth.conf....3S
Altcode:
No abstract at ADS
Title: Correlation of solar radio bursts associated with electron
plasma oscillations, solar particles and shock waves
Authors: Kikuchi, H.; Gurnett, D. A.; Keppler, E.; Richter, A. K.;
Schwenn, R.; Rosenbauer, H.
Bibcode: 1981ICRC...10....1K
Altcode: 1982ICRC...10....1K; 1981ICRC...17j...1K
A model for the generation mechanism of type III solar radio bursts
(SRB) was originally proposed by Ginzburg-Zhelenznyakov (1958),
and consists of a two-step process. The first process causes local
electron plasma oscillations at the electron plasma frequency. During
the second process, these electron plasma oscillations (EPO) are
converted to electromagnetic radiation. Concerning the first process,
the question arises, whether all of the electron plasma oscillation
events be caused by nonthermal solar flare electrons ejected directly
from the sun. Correlating EPO-SRB events with solar particle and shock
wave observations, the present investigation indicates that there are a
considerable number of EPO-SRB events which are not correlated with low
energy electrons, but some of them are correlated with interplanetary
shocks and/or low energy electrons.
Title: Solar wind and its interaction with the magnetosphere:
Measured parameters
Authors: Schwenn, R.
Bibcode: 1981AdSpR...1l...3S
Altcode: 1981AdSpR...1....3S
The earth's magnetosphere absorbs only a minor fraction (~
10-3) of the incident solar wind energy. Variations of
the solar wind can often cause lively reactions in the earth's close
environment. However, the physical mechanisms involved are not yet
understood. It appears now that the combined action of the solar
wind momentum flux, the direction of the interplanetary magnetic
field as well as its fluctuations might play the dominant role. The
behaviour of these parameters is governed in some characteristic way
by the solar wind stream structure which reflects the condition of
the solar corona and its magnetic field topology. Transients in the
sun's atmosphere associated with solar activity cause reactions in
the interplanetary medium which also show some typical, though very
different, signatures. Taking into account the interdependence of the
solar wind parameters in context with the underlying solar phenomena,
we may be able to pinpoint the mechanism which controls the action of
the solar wind on the magnetosphere.
Title: Properties of Alfvenic Fluctuations Near the Sun - HELIOS-1
and HELIOS-2
Authors: Denskat, K. U.; Neubauer, F. M.; Schwenn, R.
Bibcode: 1981sowi.conf..392D
Altcode:
No abstract at ADS
Title: HELIOS - Indications of Resonant Wave-Particle Interaction
in Fast Stream Solar Wind Ion Distributions
Authors: Rosenbauer, H.; Marsch, E.; Mohlhauser, K. H.; Pilipp, W.;
Schwenn, R.
Bibcode: 1981sowi.conf..353R
Altcode:
No abstract at ADS
Title: Two States of the Solar Wind at the Time of Solar Activity
Minimum - Part Two - Radial Gradients of Plasma Parameters in Fast
and Slow Streams
Authors: Schwenn, R.; Mohlhauser, K. H.; Marsch, E.; Rosenbauer, H.
Bibcode: 1981sowi.conf..126S
Altcode:
No abstract at ADS
Title: Kalte Schauer von der Sonne.
Authors: Schwenn, R.
Bibcode: 1981Umsch..81..438S
Altcode:
No abstract at ADS
Title: Initial Results on Solar Wind Alpha Particle Distributions
as Measured by HELIOS Between 0.3AU and 1AU
Authors: Marsch, E.; Mohlhauser, K. H.; Pilipp, W.; Schwenn, R.;
Rosenbauer, H.
Bibcode: 1981sowi.conf..443M
Altcode:
No abstract at ADS
Title: Electron Characteristics in the Solar Wind as Deduced from
HELIOS Observations
Authors: Pilipp, W. G.; Schwenn, R.; Marsch, E.; Molhauser, K. H.;
Rosenbauer, H.
Bibcode: 1981sowi.conf..241P
Altcode:
No abstract at ADS
Title: The Solar Origin of An Interplanetary Shock
Authors: Sheeley, N. R., Jr.; Howard, R. A.; Koomen, M. J.; Michels,
D. J.; Rompolt, B.; Schwenn, R. W.; Mihalov, J. D.
Bibcode: 1980BAAS...12..920S
Altcode:
No abstract at ADS
Title: Interplanetary particles and fields, November 22 to December 6,
1977: helios, voyager, and imp observations between 0.6 and 1.6 AU
Authors: Burlaga, L.; Lepping, R.; Weber, R.; Armstrong, T.; Goodrich,
C.; Sullivan, J.; Gurnett, D.; Kellogg, P.; Keppler, E.; Mariani,
F.; Neubauer, F.; Rosenbauer, H.; Schwenn, R.
Bibcode: 1980JGR....85.2227B
Altcode:
In the period November 22 to December 6, 1977, three types
of interplanetary flows were observed: a corotating stream, a
flare-associated shock wave, and a shock wave driven by ejecta. Helios
2, Imp 7, 8, and Voyager 1, 2 were nearly radially aligned at ?0.6, 1,
and 1.6 AU, respectively, while Helios 1 was at ?0.6 AU and 35° east of
Helios 2. The instruments on these spacecraft provided an exceptionally
complete description of the particles and fields associated with the
three flows and corresponding solar events. Analysis of these data
revealed the following results. (1) A corotating stream associated
with a coronal hole was observed at 0.6 and 1 AU, but not at 1.6
AU. The stream interface corotated and persisted with little change
in structure even though the stream disappeared. A forward shock was
observed ahead of the interface and moved from Helios 2 at 0.6 AU to
Voyager 1, 2 and 1.6 AU; although the shock was ahead of a corotating
stream and interface, the shock was not stationary. (2) An exceptionally
intense type III burst was observed in association with a 2B flare of
November 22, The exciter of this burst (a beam of energetic electrons)
and plasma oscillations (presumably caused by the electron beam)
were observed by Helios 2. (3) A nonspherical shock was observed
in association with the November 22 flare. This shock interacted
with another shock between 0.6 and 1 AU, and they coalesced to form
a single shock that was identified at 1 and at 1.6 AU. (4) A shock
driven by ejecta was studied. In the ejecta the density and temperature
were unusually low, and the magnetic field intensity was relatively
high. This regio was preceded by a directional discontinuity at which
the magnetic field intensity dropped appreciably. The shock appeared to
move globally at a uniform speed, but locally, there were fluctuations
in speed and direction of up to 100 km/s and 40°, respectively. (5)
Three types of electrostatic waves were observed at the shocks, in
different combinations. The detailed wave profiles differed greatly
among the shocks, even for spacecraft separations of <~0.2 AU,
indicating a strong dependence on local conditions. However, the same
types of fluctuations were observed at 0.6 and at 1.6 AU. (6) energetic
(50-200 keV) protons were accelerated by the shocks. The intensities
and durations of the fluxes varied by a factor of 12 over longitudinal
distances of ?0.2 AU. The intensities were higher, and the duratjions
were lower, at 1.6 than at 0.6 AU, suggesting a cumulative effect. (7)
Energetic (?50 keV) protons from the November 22 flare were observed
by all the spacecraft. During the decay, Helios 1 observed no change
in intensity when the interface moved past the spacecraft, indicating
that particles were injected and moved uniformly on both sides of the
interface. Helios 2 observed an increase in flux not seen by Helios 1,
reaching maximum at the time that a shock arrived at Helios 2. The
intensity dropped abruptly when the interface moved past Helios 2,
indicating that the 'extra' particles seen by Helios 2 did not penetrate
the interface.
Title: Singly-ionized helium in the driver gas of an interplanetary
shock wave
Authors: Schwenn, R.; Rosenbauer, H.; Muehlhaeuser, K. -H.
Bibcode: 1980GeoRL...7..201S
Altcode:
The interplanetary shock wave observed on Jan. 29, 1977 by the HELIOS-1
plasma instruments shows an unusual feature: In the cold tenuous
piston plasma following this shock, there appears a third peak in the
energy per charge (E/q) spectra, in addition to the normal proton
and α-particle peaks. The peak is located at E/q = 4 and persists
for about 14 hours, with slowly varying intensities. Independent
simultaneous measurement of these particles’ charge yields a value
of ≈ 1. These ions are thought to be 4He+
ions travelling with the same speed as protons and α-particles. The
occurrence of 4He+ indicates the possibility
that during eruptive prominences or other solar transients “cold”
chromosperic plasma might escape from the sun without undergoing the
normal coronal heating process.
Title: The plasma experiment on Helios (E 1).
Authors: Rosenbauer, H.; Schwenn, R.; Meyer, B.; Miggenrieder, H.;
Wolfe, J.
Bibcode: 1980hsp..conf....6R
Altcode:
No abstract at ADS
Title: Ion acoustic waves and related plasma observations in the
solar wind
Authors: Gurnett, D. A.; Marsch, E.; Pilipp, W.; Schwenn, R.;
Rosenbauer, H.
Bibcode: 1979JGR....84.2029G
Altcode:
This paper presents an investigation of solar wind ion acoustic
waves and their relationship to the macroscopic and microscopic
characteristics of the solar wind plasma. Comparisons with the
overall solar wind corotational structure show that the most
intense ion acoustic waves usually occur in the low-velocity
regions ahead of high-speed solar wind streams. Of the detailed
plasma parameters investigated, the ion acoustic wave intensities
are found to be most closely correlated with the electron to
proton temperature ratio Te/Tp and with the
electron heat flux. Investigations of the detailed electron and
proton distribution functions also show that the ion acoustic waves
usually occur in regions with highly non-Maxwellian distributions
characteristic of double-proton streams. The distribution functions
for the double-proton streams are usually not resolved into two
clearly defined peaks, but rather they appear as a broad shoulder on
the main proton distribution. Two main mechanisms, an electron heat
flux instability and a double-ion beam instability, are considered
for generating the ion-acoustic-like waves observed in the solar
wind. Both mechanisms have favorable and unfavorable features. The
electron heat flux mechanism can account for the observed waves
at moderate to large ratios of Te/Tp but has
problems when Te/Tp is small, as sometimes
occurs. The ion beam instability appears to provide more flexibility on
the Te/Tp ratio; however detailed comparisons
using observed distribution functions indicate that the ion beam
mode is usually stable. Possible resolutions of these difficulties
are discussed.
Title: Plasma wave turbulence associated with an interplanetary shock
Authors: Gurnett, D. A.; Neubauer, F. M.; Schwenn, R.
Bibcode: 1979JGR....84..541G
Altcode:
In this paper we give a brief summary of the interplanetary shocks
detected and analyzed to date from the Helios 1 and 2 spacecraft and
present a detailed analysis of the plasma wave turbulence associated
with one particular shock, on March 30, 1976. This event was selected
becaused a very clearly defined burst of plasma wave turbulence occurs
at the shock with otherwise quiet conditions in the solar wind upstream
and downstream of the shock. The shock is an oblique shock and the
upstream parameters are characterized by a low Mach number, a low
beta, and an unusually large electron to ion temperature ratio. Three
types of plasma waves are detected in association with this shock
(1) electron plasma oscillations, (2) electrostatic ion-acoustic or
Buneman mode turbulence from about 1 to 30 kHz, and (3) whistler-mode
magnetic noise. Because of the high velocity of the shock and the quiet
conditions in the solar wind this event provides a particularly good
determination of the scale size and characteristics of the precursor
waves upstream of the shock and the electric magnetic field turbulence
in the wake behind the shock. The primary burst of electric and magnetic
field noise at the shock occurs a few seconds after the jump in the
magnetic field, with a broad maximum in the electric field intensities
at about 3 kHz and a monotonically decreasing magnetic field spectrum
below about 1 kHz. Many of the characteristics of this shock are found
to be closely similar to, and are compared with, previous observations
of plasma wave turbulence associated with the earth's bow shock.
Title: Acceleration of ≥ 80 KEV Ions by Interplanetary Shocks
Between 0.3 - 1 AU Observed by HELIOS 1/2: a Survey
Authors: Richter, A. K.; Keppler, E.; Schwenn, R.; Hsieh, K. C.;
Denskat, K. U.
Bibcode: 1979ICRC....5...56R
Altcode: 1980ICRC....5...56R; 1979ICRC...16e..56R
Fifteen interplanetary shocks were observed by the Helios 1 and 2
spaceprobes between 0.3-1 AU during their primary missions in 1974/75
and 1976, respectively. By the use of plasma and magnetic field data
these shocks are analyzed and classified according to the theory of
collisionless shocks. Variations in intensity of greater than or equal
to 80 keV ions are then examined in relation to these shocks. Results
are compared with existing theories on particle acceleration by
interplanetary shocks.
Title: Energetic Particles at Interplanetary Shock Waves: the April
29 1978 Event
Authors: Richter, A. K.; Hsieh, K. C.; Keppler, E.; Schwenn, R.;
Van Hollebeke, M. A. I.; McDonald, F. B.; Denskat, K. U.
Bibcode: 1979ICRC...12..312R
Altcode: 1980ICRC...12..312R; 1979ICRC...16l.312R
On April 29, 1978 a low-energetic particle event originating from a
3B flare at N22 E38 was observed by HELIOS 1 at 0.31 AU and W 38 and
by HELIOS 2 at 0.29 AU and W 67 simultaneously with an interplanetary
shock wave. Using plasma and magnetic field data these shocks were
classified; the time variations were examined along with the angular
and spectral distributions in the ecliptic plane of the intensities
of 80 or more keV ions.
Title: On the radial expansion of the solar wind plasma between 0.3
and 1.0 astronomical units.
Authors: Cuperman, S.; Levush, B.; Dryer, M.; Rosenbauer, H.;
Schwenn, R.
Bibcode: 1978ApJ...226.1120C
Altcode:
This paper is concerned with the clarification of the radial
expansion-within 1 AU heliocentric distance-of the extended solar
corona. The work has been stimulated by the recent availability of
solar wind measurements by the Helios 1 solar probe for the period 1974
December-1975 April covering (for the first time) the interplanetary
medium between 1 and 0.3 AU. The first part of the work analyzes these
data from a theoretical point of view. Thus, in order to classify the
plasma states represented by the data, the particle fluxes J =- nvr2
are calculated by using measured proton densities, n (r), and streaming
velocities, v (r), and are correlated with heliocentric distances
as well as with density and streaming velocity fluctuations, An and
AVp, respectively. The quantity J has been chosen as a classifying
criterion because its constancy represents the necessary condition for
the validity of theoretical models assuming steady-state spherically
symmetric flow. The results of these calculations indicate that (i)
the normalized particle flux J = JIJE (E indicates 1 AU heliocentric
distance) varies by a factor of 10 (between 0.5 and 5) over the
interplanetary range explored by Helios 1; (ii) the strong deviations
from the value 1 are found only for states with streaming velocities
below about 500 km s -`, while for the high-speed states J 1; (iii)
the deviations AJ found for low-speed states are strongly correlated
with particle density fluctuations and moderately anticorrelated
with streaming velocity fluctuations; and (iv) time-dependent andlor
additional processes could play a significant role. In the second part
of the work we use all observational data representing high-speed flows
(i.e., satisfying the condition V > 600 km s -`) in conjunction with
the fluid equations for a twocomponent plasma (protons + electrons)
in order to estimate unknown properties of the solar wind. Thus, using
best fits to the observed n (r), v (r), and T (r) values, by the aid
of the momentum equation one obtains the electron temperature profile,
Te(r). Subject heading: Sun: solar wind
Title: Magnetic fields and flows between 1 and 0.3 AU during the
primary mission of Helios 1
Authors: Burlaga, L. F.; Ness, N. F.; Mariani, F.; Bavassano, B.;
Villante, U.; Rosenbauer, H.; Schwenn, R.; Harvey, J.
Bibcode: 1978JGR....83.5167B
Altcode:
Helios 1 moved from 1 AU on December 10, 1974, to 0.31 AU on March
15, 1975, and the sun rotated beneath the spacecraft nearly 4 times
during the interval. Recurrent high-speed streams with uniform magnetic
polarity were observed, and they were associated with coronal holes of
the same polarity. Although they were recurrent, the streams and their
magnetic field patterns were not stationary, because the coronal holes
which produced them changed in shape and latitude from one rotation to
the next. We estimated that the magnetic field intensity of open field
lines in some of these holes was of the order 10-20 G. Recurrent slow
flows were also observed. The magnetic field polarity and intensity in
these flows were irregular, and they changed from one rotation to the
next. Cold magnetic enhancements (CME's) characterized by a twofold
to threefold enhancement of magnetic field intensity and a fivefold to
sevenfold depression of proton temperature relative to conditions ahead
of the CME's were observed in some slow flows. Some of these CME's were
contiguous with interaction regions of streams. At perihelion, Helios
observed a recurrent stream which was associated with a lobe of the
south polar coronal hole. The longitudinal width of the stream was three
times that of the hole. We estimate that the width of the eastern and
western boundaries of the streams at the coronal holes was only 2.5°
+/- 1.5°, and we infer that the width at the northern boundary of the
stream was <~5°. We conclude that between the sun and 0.3 AU there
was a diverging stream surrounded by a thin boundary layer in which
there was a large velocity shear. There is evidence for compression of
the magnetic field in the western boundary layer (interaction region),
presumably due to steepening of the stream within 0.31 AU.
Title: The prediction of fast stream front arrivals at the earth on
the basis of solar wind measurements at smaller solar distances
Authors: Rosenbauer, H.; Schwenn, R.; Bame, S. J.
Bibcode: 1978omap....1R....R
Altcode:
The problems involved in the prediction of the arrival of fast
solar wind streams at the earth on the basis of measurements made by
space probes in the region between 0.3 and 1 AU are discussed. It is
shown that arrival time predictions accurate to within a few hours
that can be made at least as long as the large scale conditions
on the Sun are relatively stationary as observed near the time of
solar minimum. However, the latitudinal extent of the respective
high speed streams is found to be important for making quantitative
predictions. Coronal data sufficient for locating the sources of high
speed streams can improve the precision of these predictions.
Title: Direct observation of the latitudinal extent of a high-speed
stream in the solar wind
Authors: Schwenn, R.; Montgomery, M. D.; Rosenbauer, H.; Miggenrieder,
H.; Muehlhaeuser, K. H.; Bame, S. J.; Feldman, W. C.; Hansen, R. T.
Bibcode: 1978JGR....83.1011S
Altcode:
Solar wind speeds measured from the Helios 1 solar probe between
0.31 and 1 AU and the earth-orbiting Imp 7/8 satellites have been
correlated with coronal holes as determined from K coronal brightness
measurements. In March 1975 during perihelion passage, Helios 1
traversed the range of heliographic latitudes from -6° to +6° in
a period of only 20 days. During that time the space probe crossed
the northern boundary of the high-speed stream associated with an
equatorward extension of the south polar coronal hole. While this same
stream continued to be observed by Imp satellites at -5° latitude, it
was no longer observable from Helios 1 at +5° latitude. The conclusion
is that sharp boundaries separate high-speed flows from the surrounding
solar wind. The thickness of the boundary in latitude appears to be
narrower than about 10°. The local latitudinal gradient in flow speed
is at least 30 kms-1 deg-1. With less confidence
it can be deduced from the Helios 1 data that the actual gradients at
0.31 AU might even exceed 100 kms-1 deg-1.
Title: The prediction of fast stream front arrivals at the earth on
the basis of solar wind measurements at smaller solar distances.
Authors: Rosenbauer, H.; Schwenn, R.; Bame, S. J.
Bibcode: 1978omap.conf...32R
Altcode:
No abstract at ADS
Title: A survey on initial results of the HELIOS plasma experiment
Authors: Rosenbauer, H.; Schwenn, R.; Marsch, E.; Meyer, B.;
Miggenrieder, H.; Montgomery, M. D.; Muehlhaeuser, K. H.; Pilipp,
W.; Voges, W.; Zink, S. M.
Bibcode: 1977JGZG...42..561R
Altcode:
The reported results are mainly based on data obtained during the
first part of the Helios-1 mission. The sun was very quiet during
the considered period. The data are, therefore, representative
for comparatively stationary conditions in the solar corona. Data
obtained concerning the protons were evaluated by means of a special
computer routine. The significance of the data is discussed, taking
into account the status of the corona and the interplanetary plasma
during the considered part of the Helios-1 mission, fast stream
structures in the region between 0.3 and 1 AU, radial gradients
of fast and slow solar wind, and the separation of proton double
streams and alpha-particles. Attention is also given to the 'strahl'
in the electron distribution, differences between fast streams and
slow plasma on the basis of the observed electron distributions,
and radial gradients in the case of solar wind electron parameters.
Title: Preliminary results of the Helios plasma measurements.
Authors: Rosenbauer, H.; Miggenrieder, H.; Montgomery, M.; Schwenn, R.
Bibcode: 1976pspe.proc..319R
Altcode: 1976pspe.conf..319R
The instrumentation aboard the sun-probes Helios A/B is described. The
quiet interplanetary 'weather' during the first year of the Helios
mission permitted the study of the development of fast stream
characteristics with respect to the radial distance from the Sun. The
changes of plasma velocity with solar longitude were found to be more
abrupt not only at the trailing edges but also at the front sides of
fast streams at smaller distances from the sun. A pronounced narrow
'beam' of fast electrons traveling outward from the sun along the
magnetic field lines was detected. The meaning of this newly discovered
part of the distribution function and its relation to the 'core' and
'halo' regions are discussed.
Title: Preliminary results of the Helios plasma experiment.
Authors: Schwenn, R.; Rosenbauer, H.; Miggenrieder, H.; Meyer, B.
Bibcode: 1976spre.conf..671S
Altcode: 1976spre.proc..671S
The instruments used in the plasma experiment aboard the Helios
space probe are described, and some preliminary results from the
solar-wind ion instruments are presented. Proton bulk velocities and
proton temperatures are plotted as functions of solar longitude with
respect to the probe. It is shown that the first three solar rotations
monitored by Helios were characterized by two high-speed solar-wind
streams with a velocity rise time of about 2 days, a constant velocity
of about 700 to 800 km/s for some days, and a slow decrease for several
other days. Only the temperatures seemed to increase slightly during
the third rotation. Helios passed perihelion during the fourth rotation
and observed significant changes in stream structure, with decreased
velocities and temperatures increased to as high as 1 million K. It is
suggested that there may be rather sharp transitions between different
regions in the solar-wind plasma, implying very sharply separated
sources of different streams in the corona, or that the abrupt changes
in solar-wind parameters might be due to time variations.
Title: Das Plasmaexperiment auf Helios (E1).
Authors: Schwenn, R.; Rosenbauer, H.; Miggenrieder, H.
Bibcode: 1975RF.....19..226S
Altcode:
The solar probe Helios carries four independent instruments designed
for solar wind measurements. Three instruments analyze the positive
component (protons and heavier ions) of the solar wind. One instrument
measures electrons in the energy range from 0.5 to 1660 eV with a
one-dimensional angular resolution. With these instruments the velocity
distribution functions of the various particles can be measured. Onboard
data processing techniques and the High-Data-Mode measurement program
are discussed.
Title: Preliminary Results of the Helios Plasma Experiment. (Abstract)
Authors: Rosenbauer, H.; Meyer, B.; Miggenrieder, H.; Montgomery,
M.; Schwenn, R.
Bibcode: 1975ICRC....5.1857R
Altcode: 1975ICRC...14.1857R
No abstract at ADS
Title: Radial gradients in solar wind plasma
Authors: Schwenn, R.
Bibcode: 1974hsde.rept...30S
Altcode:
The Helios experiment 1 is described, and possible applications to
radial solar wind velocity gradient measurements are indicated. This
experiment measures ion and electron velocity spectra of the solar
wind plasma. The usefulness of line-up of other active interplanetary
spacecraft with intact plasma instruments for correlation purposes is
discussed. It should be possible to determine the radial gradient of
the solar wind azimuthal velocity, the corotation of the solar wind,
since the ratio between the bulk velocity and the azimuthal velocity
is lower than at the earth's orbit.