Author name code: hundhausen
ADS astronomy entries on 2022-09-14
author:"Hundhausen, Arthur J." OR author:"Hundhausen, Art"
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Title: The mass content of Coronal Mass Ejections
Authors: Burkepile, J. T.; Hundhausen, A. J.; MacQueen, R. M.; deToma,
G.; Darnell, J. A.; Gilbert, H. R.
Bibcode: 2004AAS...204.1806B
Altcode: 2004BAAS...36Q.683B
The total mass content of solar Coronal Mass Ejections (CMEs) can vary
greatly between events. Most CMEs have estimated masses between 10e+14
and 10e+16 grams of material. It is believed that most of the CME
material is coronal in origin (Hildner et al. 1975) but the source of
the mass remains largely unknown. The large fields-of-view of the LASCO
C2 and C3 coronagraphs coupled with observations of the low corona from
the MK4 K-Coronameter at the Mauna Loa Solar Observatory provide the
observations needed to examine CME masses over a wide range of coronal
scale heights. We utilize these observations to estimate both the amount
of material which is ejected from the very low corona and the amount
of mass which is 'swept up' by the CME as it propagates outward. This research is funded by the National Science Foundation.
Title: Role of projection effects on solar coronal mass ejection
properties: 1. A study of CMEs associated with limb activity
Authors: Burkepile, J. T.; Hundhausen, A. J.; Stanger, A. L.; St. Cyr,
O. C.; Seiden, J. A.
Bibcode: 2004JGRA..109.3103B
Altcode:
Many properties of Coronal Mass Ejections (CMEs), such as size,
location and brightness, have been determined from measurements of
white light coronal observations. We expect the average properties
derived from these measurements contain systematic inaccuracies due to
projection effects and suggest that CME properties are most accurately
determined for those events occurring near the plane-of-the-sky
(i.e., over the solar limb as observed from Earth), where projection
effects are minimized. A set of 111 such "limb" events have been
identified in Solar Maximum Mission (SMM) white light observations
through associations with Erupting Prominences at the Limb (EPLs), and
X-ray and limb optical flares. These "limb" CMEs have greater average
speeds (519 ± 46 km/sec) and masses (4.5 ± .5 × 1015
grams) than the average values obtained from all SMM CMEs, consistent
with the expected behavior of projection effects. Only a very small
percentage of "limb" CMEs are centered at high latitudes, suggesting
there are many fewer "true" high latitude CMEs than has previously been
reported. No "limb" CMEs have widths greater than 110°, consistent
with the interpretation that very wide CMEs (i.e., halos) are actually
events of more typical widths originating away from the solar limb
and viewed in projection. Only a small percentage of "limb" CMEs have
measured speeds below 200 km/sec, indicating there may be fewer "true"
subsonic SMM CMEs than previously reported. The correlation detected
between the kinetic energy of the "limb" CMEs and the peak intensity
of the associated GOES X-ray flares, is stronger than was previously
found using a set of CMEs of undetermined limb distances. All these
results provide strong evidence that projection effects systematically
influence the deduced properties of CME events.
Title: The Acceleration of Coronal Mass Ejections
Authors: Burkepile, J. T.; Hundhausen, A. J.; MacQueen, R. M.; Detoma,
G.; Darnell, J. A.; Gilbert, H. R.
Bibcode: 2003AGUFMSH21A..01B
Altcode:
To determine quantitative estimates of the net force acting on a
CME requires knowledge of the CME acceleration as a function of
distance from the solar surface. The CME acceleration is determined
directly from the observed time-height trajectory of the event by two
methods: (a) sucessive differentials and (b) the use of polynomial
and exponential function curve fitting to the trajectory, followed by
successive derivatives. We examine the acceleration of a set of Coronal
Mass Ejections (CMEs) observed over a wide range of coronal scale
heights by combining observations of the low corona from the Mauna
Loa Solar Observatory and the Extreme ultraviolet Imaging Telescope
(EIT) on the Solar and Heliospheric Observatory (SOHO) spacecraft with
observations from the LASCO coronagraphs onboard SOHO. We apply both of
the above techniques to the events and conclude that CME acceleration
is greatest in the low corona despite the strong force of gravity
in that region. (In addition, CME start times determined from outer
coronal (LASCO) observations alone tend to be systematically later
than the actual start times, most likely due to the fact that LASCO
observations cannot observe CME acceleration in the low corona.)
Title: Energy Analysis of Post Mass Ejection Solar Coronal X-ray Loops
Authors: Balch, C. C.; Bagenal, F.; Hundhausen, A. J.
Bibcode: 2001AGUSM..SH32C03B
Altcode:
Solar coronal mass ejections have been shown in the past to be
associated with the enhancement of solar x-ray emission of several
hours duration. Analysis of solar x-ray images has shown that these
long-duration x-ray events are due to an arcade of post mass ejection
loops that form over the magnetic polarity inversion line that lies
underneath the mass ejections. While this has been successfully
described qualitatively in past work, we seek to apply a quantitative
analysis to understand the detailed evolution of energy balance in
the system, including the evolution of heating and cooling mechanisms
We measured a set of intensity-time profiles as a function of height
for particularly well observed arcade events on the solar limb with
relatively simple morphology. We developed a semi-theoretical model,
with the basic premise that at each point in space, the intensity is the
response to an interplay between a source term and a cooling term. This
principle is developed for models with increasingly sophisticated
geometries in order to test the effect of line-of-sight integration of
x-ray emission in the image data. The models for the data are expressed
in terms of a set of free parameters, which are then optimized to
provide the best fit of the model to the data. Our best-fit parameters
enable us to make several inferences about the physical nature of the
system. The region of heating develops early in the event and spans a
surprisingly large vertical dimension. The heating continues throughout
much of the duration of the event. The enhancement of x-ray emission
is primarily due to an enhancement of density of plasma in the loops,
although there is a small increase in temperature. During the early
phase of the event, radiative and conductive cooling are of similar
magnitude, but increase more slowly than heating. Once the cooling
mechanisms surpass heating the event enters the cooling phase. During
this phase, the radiative cooling decreases relatively quickly and
conductive cooling becomes the dominant cooling mechanism. We compare
the energy of the heating with the energies of an approximate model for
the coronal magnetic field to make an estimate of the energy released
by magnetic reconnection.
Title: Examination of geoeffective structures in the solar wind
using ACE and WIND data from 1998-2000.
Authors: Burkepile, J.; Balch, C.; Hundhausen, A.
Bibcode: 2001AGUSM..SH22C09B
Altcode:
Previous correlation studies of solar wind conditions with geomagnetic
activity have shown that long periods (hours) of strong southward
magnetic fields and high solar wind velocities combine to produce major
geomagnetic storms. Magnetic field data from the Advanced Composition
Explorer (ACE) and the WIND satellites confirm the presence of strong
southward components of the interplanetary magnetic field during
all periods of major activity, Ap > 50, between January 1998 and
September 2000. An examination of solar wind data for seven severe
geomagnetic storms in this period reveals that while the interplanetary
signatures of a coronal mass ejection (CME) were present in every event,
the location of the strong southward magnetic field varied. In 6 of the
7 severe storms, strong southward fields were present in the swept up
wind immediately following the shock as well as in the interplanetary
CME. In one of these events, the strong southward magnetic fields
were present only in the wind immediately following the shock and not
in CME itself. In addition to needing information about the magnetic
topology of individual CMEs, improved 3-D models of the interactions of
CMEs and shocks with the ambient solar wind coupled with more accurate
information regarding the CME size, location and trajectory are required
to produce reliable, long term forecasts of geomagnetic activity.
Title: Active and Eruptive Prominences and Their Relationship to
Coronal Mass Ejections
Authors: Gilbert, Holly R.; Holzer, Thomas E.; Burkepile, Joan T.;
Hundhausen, Arthur J.
Bibcode: 2000ApJ...537..503G
Altcode:
In order to understand better the dynamical processes in the
solar atmosphere that are associated with coronal mass ejections
(CMEs), we have carried out a study of prominence activity using Hα
observations obtained at the Mauna Loa Solar Observatory (MLSO). After
developing clear definitions of active prominences (APs) and eruptive
prominences (EPs), we examined 54 Hα events to identify distinguishing
characteristics of APs and EPs and to study the relationship between
prominence activity and CMEs. The principal characteristics we found
to distinguish clearly between APs and EPs are maximum projected radial
height, projected radial velocity, and projected radial acceleration. We
determined CME associations with Hα events by using white-light data
from the Mk III K-Coronameter at MLSO and the LASCO C2 Coronagraph on
SOHO. We found that EPs are more strongly associated with CMEs than
are APs and that the CMEs associated with EPs generally have cores,
while those associated with APs do not. A majority of the EPs in the
study exhibit separation of escaping material from the bulk of the
prominence-the latter initially lifting away from and then returning
toward the solar surface. This separation tends to occur in the height
range from 1.20 to 1.35 R0, and we infer that it involves
the formation of an X-type neutral line in this region, which allows
disconnection of part of the prominence material. This disconnection
view of prominence eruption seems most consistent with flux rope models
of prominence support.
Title: A comparison of ground-based and spacecraft observations of
coronal mass ejections from 1980-1989
Authors: St. Cyr, O. C.; Burkepile, J. T.; Hundhausen, A. J.; Lecinski,
A. R.
Bibcode: 1999JGR...10412493S
Altcode:
We report here an analysis of observations of solar coronal mass
ejections (CMEs) acquired in white light by the Mark III (MK3)
K coronameter at Mauna Loa Solar Observatory between 1980 and
1989. Statistical properties of the locations, sizes, and speeds
of these events are described. These properties are compared to
those in the two other white light CME catalogs from the 1980s,
the CMEs observed by the Solwind and SMM spaceborne coronagraphs,
and relatively good statistical agreement is found between the three
data sets taken over the entire period of observation. A detailed
examination was performed for the 141 MK3 CMEs that were also observed
by SMM. Virtually all (93%) of the CMEs detected low in the corona
by the MK3 instrument were observed to travel out of the SMM field
of view, into interplanetary space. The average width of CMEs in the
MK3 field of view was 12° smaller than that measured in SMM, and we
interpret this statistic as an indication of some increase in size as
CMEs move outward through the corona. For a subset of 55 of those mass
ejections we were able to combine detailed observations from both MK3
and SMM. Using the combined measurements, we were able to detect and to
quantify the initial period of acceleration in a much larger fraction
(61%) of the features than was possible from either MK3 alone (9%)
or SMM alone (21%). The acceleration was positive for 87% of those
features, with an average (median) value of +0.264 kms-2
(+0.044 kms-2). A distinction in terms of association with
other forms of solar activity was also evident in this analysis: 55% of
the CMEs associated with active regions moved with constant speed, but
82% of the features associated with the eruption of solitary prominences
moved with constant acceleration. Also, the average speed for CMEs
associated with active regions was significantly faster than those with
prominence association (955 versus 411 kms-1). The detection
of positive acceleration demonstrates that the forces propelling the
CME continue to dominate these events, at least through the altitudes
covered by the MK3 and SMM fields of view.
Title: A Study of the Prominence/Coronal Mass Ejection Correlation
Authors: Gilbert, H. R.; Burkepile, J. T.; Hundhausen, A. J.; Darnell,
J. A.; Bagenal, F.
Bibcode: 1999AAS...194.1707G
Altcode: 1999BAAS...31..854G
Coronal Mass Ejections (CMEs) are often associated with activity in
the chromosphere and photosphere. H-alpha observations suggest two
different forms of prominence activity. We will label these "active
prominences" and "erupting prominences" for purposes of comparison
with CMEs. A prominence is defined as being "active" when material
moves outward then returns sunward or fades without visibly leaving
the Sun's gravitational field. In contrast, an eruptive prominence has
material that visibly leaves the Sun, often separating from the main,
anchored part of a prominence. The departing material of an eruptive
prominence may fade from H-alpha observations as it travels outward,
or it may remain visible in H-alpha as it leaves the field of view
of the instrument. A study of 54 active and eruptive prominences was
conducted using H-alpha, Helium I, and Coronal White Light data from
the Mauna Loa Solar Observatory in addition to LASCO C2 and C3 data. 94
eruptive prominences and only 46 studied were associated with the
occurrence of a CME in the MKIII or LASCO fields of view. Properties
such as heights, velocities, and accelerations of active prominences
are compared with those of eruptive prominences. Similarly, properties
of prominences associated with the occurrence of a CME are compared
with those that had no associated CME. Using the high cadence H-alpha
limb data, further emphasis is placed on the acceleration profiles of
the eruptive prominences. There is evidence in some events a third
order fit (a least-squares fit of a cubic function) to the observed
trajectory is superior to a second order fit, implying a changing
rather than constant acceleration of the prominence material. Following
prominence material from the low corona out to many solar radii may
help in determining if a third order fit to any trajectories of CME
features is better than the lower order fits.
Title: Measuring Coronal Mass Ejection Masses from the Low through
the Outer Corona
Authors: Burkepile, J. T.; Bagenal, F.; Darnell, J. A.; Elmore, D.;
Holzer, T.; Hundhausen, A. J.; Stanger, A. L.
Bibcode: 1999AAS...194.1702B
Altcode: 1999BAAS...31..853B
Estimates have been made of the masses contained in coronal mass
ejections (CMEs) in the middle and outer corona [Howard et al. (1985),
Howard et al. (1986) and Hundhausen et al. (1994)]. It is our goal to
determine the flow of mass with height as the CME moves outward through
the corona and to distinguish the outflow of material from brightenings
due to deflections and compression created by the CMEs motion through
the ambient coronal material. Coronal mass ejection measurements
in the low corona are made using the Mauna Loa K-Coronameter. The
K-Coronameter has recorded a few hundred CMEs that were also visible
in the Solar Maximum Mission Coronagraph and in the Large Angle and
Spectrometric Coronagraph experiment (LASCO) that image the middle
and outer corona. The mass of each CME is plotted as a function of
height and compared with estimates for the amount of mass swept up
by a CME moving with average speed through a typical coronal helmet
streamer. For those events where the classic loop, cavity structure is
apparent, the masses of the loop front and legs are recorded separately
to better determine the amount of material propagating outward and
the amount of material maintained in the legs following the passage of
the CME. The masses are combined with speeds of the CMEs to determine
the kinetic energy of the CME as a function of height. As an example
we report on a CME which occurred on September 9, 1997 and appeared
over the northwest limb in both the MK3 and LASCO data. The mass of
the CME appeared to increase from 1.5x10(15) grams in the MK3 field to
6.2x10(15) grams in the LASCO field of view. The CME was continuing to
accelerate and the kinetic energy increased by an order of magnitude
from the low corona value of 2.5x10(30) ergs in MK3 to 2.0x10(31) ergs
in the LASCO field of view. References: Howard, R.A., N.R. Sheeley,
Jr., M.J. Koomen, and D.J. Michels, 'Coronal Mass Ejections: 1979-1981',
(1985), J. Geophys. Res., 90, 8173-8191 Howard, R.A., N.R. Sheeley, Jr.,
D.J. Michels, M.J. Koomen, ' The Solar Cycle Dependence of Coronal Mass
Ejections', (1986) in: The Sun and the Heliosphere in Three Dimensions,
Marsden, R.G. (ed)., 1986, p 107-111 Hundhausen, A.J., A.L. Stanger,
and S.A. Serbicki,'Mass and Energy Contents of Coronal Mass Ejections:
SMM Results from 1980 and 1984-1988.', (1994) in: Proc. of the Third
SOHO Workshop, Estes Park Colorado, p 409.
Title: Coronal Mass Ejections
Authors: Hundhausen, A.
Bibcode: 1999mfs..conf..143H
Altcode:
Nature and Structure of Coronal Mass Ejections Specific Examples
Pre-Ejection "Swelling" of the Coronal Helmet Streamer Formation and
Outward Propagation of the Mass Ejection Post-Ejection Depletion of
the Helmet Streamer Region Pre-Eruption Evolution of the Prominence
and Corona The Mass Ejection and Prominence Eruption The Post-Ejection
Corona Summary Some Measured Properties Shape or Geometry Angular Size
Locations The Propagation of Mass Ejections Through the Corona The
Origin of Coronal Mass Ejections Some Essential Facts Large Spatial
Scales Occurrence in (and Disruption of) Closed Magnetic Structures, -
Including Those not Related to Active Regions The Huge Variability in
the Phenomenon Mass Ejections and Prominence Eruptions Mass Ejections
and "Optical" Solar Flares Mass Ejections and Soft X-Ray Flares
Formation (and Acceleration) of a Mass Ejection Within the - SMM Field
of View Formation (and Initial Acceleration) of a Mass Ejection in -
the Low Corona Association with an X-Ray Flare That Rises from a Very
Low - Background Level in the GOES Data A Major Coronal Mass Ejection
with no Detectable X-Ray Flare What, Then, is the Origin of Coronal
Mass Ejection? Summary
Title: Analysis of H-alpha Observations of High Altitude Coronal
Condensations
Authors: Allen, U. A.; Bagenal, F.; Hundhausen, A. J.
Bibcode: 1998ASPC..150..290A
Altcode: 1998IAUCo.167..290A; 1998npsp.conf..290A
No abstract at ADS
Title: The Skew of Polar Crown X-ray Arcades
Authors: McAllister, A. H.; Hundhausen, A. J.; Mackay, D.; Priest, E.
Bibcode: 1998ASPC..150..430M
Altcode: 1998npsp.conf..430M; 1998IAUCo.167..430M
No abstract at ADS
Title: The Skew of Polar Crown X-ray Arcades
Authors: McAllister, A. H.; Mackay, D.; Hundhausen, A. J.; Priest, E.
Bibcode: 1997SPD....28.0255M
Altcode: 1997BAAS...29..903M
A one-to-one relationship between the chirality of filament channels
and the skew (relative orientation) of the overlying coronal arcades,
as seen with the Yohkoh Soft X-ray Telescope (SXT) was found by Martin
and McAllister [1997]. The basis of the relationship is a sample of
over 30 mid-and low-latitude filaments during a 6 month period in
early 1992. This relationship can be coupled with the predictions
for the axial component of polar crown filaments based on the work
of Leroy et al. [1983] to predict the skew of polar crown arcades in
the recent cycle 22. Thus the axial component of the filament fields
along the southern polar crown is predicted to point to the west and a
similar component in the corona will lead to right skewed arcades. As
has been pointed out in the past, this orientation is inconsistent
with the action of photospheric differential rotation on an east-west
arcade [Ballegooijen and Martens, 1990]. In this poster we report
on the results of a recent survey of the SXT images over the whole
declining phase of cycle 22 (Oct. 1991 to June 1995). These results
are not in general agreement with those expected based on the past
filament observations. They show highly left skewed polar arcades
rather than the predicted right skew. The observations are, however,
in general agreement with the effects of differential rotation and
with recent numerical simulations of polar crown structures, which we
will also briefly present. This posses an unexpected and challenging
problem and we will discuss some possible ways of reconciling the
different observational results. Leroy, Bommier, and Sahal-Brechot,
The Magnetic Field in Prominences of the Polar Crown, Solar Physics,
83, 135-142, 1983. Martin and McAllister, The Chirality of X-ray
Coronal Arcades Overlying Quiescent Filaments, Astrophys. Journ.,
submitted, 1997. Ballegooijen and Martens, Magnetic Fields in Quiescent
Prominences, ApJ, 361, 283-289, 1990.
Title: Measurement and modelling of soft x-ray loop arcades observed
by YOHKOH SXT
Authors: Balch, Christopher C.; Hundhausen, Arthur J.; Bagenal, Fran
Bibcode: 1997SPD....28.0147B
Altcode: 1997BAAS...29R.887B
Yohkoh soft x-ray telescope (SXT) observations of the high temperature
corona have motivated a measurement program of soft x-ray loops and
systems of such loops that are hypothesized to be a post coronal
mass ejection signature. This presumed connection between CMEs and
expanding loop arcade systems is based on the picture for CMEs proposed
by Kopp & Pneuman (1976) (and other workers as well): specifically
that the loop arcade system forms as magnetic field lines that were
previously opened by the CME reconnect and heat coronal plasma through
the release of magnetic energy at the reconnection point. We make direct
measurements of soft x-ray intensity for a few, well-observed arcade
events on the solar limb. Soft x-ray intensity is measured by defining
a 2-dimensional region on an x-ray image and summing the intensities
from each pixel in the region. This leads to the construction of a
soft x-ray intensity light curve. A series of 'light-curve regions'
of fixed geometric size are defined at successive heights above the
solar limb. Thus we measure soft x-ray intensity from the arcade as
a function of time and height. In order to develop a framework for
physical interpretation of these measurements, we developed a model
based on our hypothesis and investigated whether the model can explain
the data. In particular, we assume that the release of energy is a
function of radial distance (from Sun center), and we examine the
roles and relative importance of line-of-sight geometric effects,
and of finite decay times of individual loops.
Title: Analysis of H-alpha observations of high-altitude coronal
condensations
Authors: Allen, U. A.; Bagenal, F.; Hundhausen, A.
Bibcode: 1997SPD....28.0153A
Altcode: 1997BAAS...29..889A
An analysis of H-alpha observations of relatively long-lived,
high-altitude coronal condensations referred to as "coronal spiders"
is presented. Dimensions of the condensation are typically in the range
10,000km to 50,000km, and the condensation occurs up to approximately a
tenth of a solar radius above the limb. Simple analytical methods yield
an estimate of the mass of the condensation for reasonable ranges of
temperature and electron density. Conditions under which coronal spiders
form, as well as the evolution of the structure, are also studied.
Title: A Study of the Origin and Dynamics of Coronal Mass Ejections
Authors: Burkepile, J. T.; Hundhausen, A. J.; Bagenal, F.; McAllister,
A. H.; MacQueen, R. M.
Bibcode: 1997SPD....28.0125B
Altcode: 1997BAAS...29..883B
Coronal mass ejections (CMEs) are dynamic events that typically
involve the expulsion of 10(15) to 10(16) grams of coronal and
chromospheric plasma into interplanetary space. The relationship
between mass ejections and other forms of solar activity, especially
those evident on the solar disk, remains unclear. In an attempt to
accurately determine CME onset times and origins, we have combined
observations from the Solar Heliospheric Observatory (SOHO) Large
Angle Spectroscopic Coronagraphs (LASCO), the SOHO Extreme Ultraviolet
Imaging, the Mauna Loa Observatory (MLO) white light and chromospheric
instruments and the Yohkoh Soft X-ray Telescope. Mass ejections believed
to have occurred both at or near the limb of the sun and on the solar
disk have been employed in the comparison. When available, the MLO and
LASCO white light observations have been combined to determine material
trajectories, and hence accurate CME onset times. The evolution of
the magnetic fields and associated plasma structures prior to, during
and after mass ejections have been examined by comparing He-I and Hα
chromospheric disk signatures with EUV and X-ray observations.
Title: Multi-Spectral Imaging of Coronal Activity.
Authors: Bagenal, Fran; Darnell, Tony; Burkepile, Joan; Hundhausen,
Art; Alexander, David
Bibcode: 1997SPD....28.0146B
Altcode: 1997BAAS...29Q.887B
By combining white light coronameter, Yohkoh soft x-ray and H-alpha
images from time intervals that encompass coronal mass ejections
(CMEs), we are able to examine the related evolution of structures
in the solar atmosphere. For example, what is the role of prominences
in pre-CME evolution of the corona; how well does the Pneumann &
Kopp model describe post-CME re-formation of coronal loops. On the
west limb, Yohkoh data show the structure of the corona before the CME
while prominences/filaments are revealed by H-alpha images. On the east
limb,the same data show x-ray-emitting loops that brighten and expand
after the CME. We have chosen examples of events from 1994 and 1995
that illustrate the use of such composite images. Composite white light,
Yohkoh and H-alpha images are also shown for the Whole Sun Month and we
discuss the possibilities of adding SOHO data as they become available.
Title: Coronal Mass Ejections
Authors: Hundhausen, A. J.
Bibcode: 1997cwh..conf..259H
Altcode: 2006mslp.conf..259H
No abstract at ADS
Title: A comparison of interplanetary coronal mass ejections at
ULYSSES with YOHKOH soft X-ray coronal events.
Authors: Weiss, L. A.; Gosling, J. T.; McAllister, A. H.; Hundhausen,
A. J.; Burkepile, J. T.; Phillips, J. L.; Strong, K. T.; Forsyth, R. J.
Bibcode: 1996A&A...316..384W
Altcode:
Coronal Mass Ejections (CMEs) observed at several AU by the Ulysses
spacecraft are mapped radially back to the Sun and compared with
Yohkoh Soft X-ray Telescope (SXT) images of the corona in an effort
to identify correlated events. Correlations between the observations
were difficult to make during the ecliptic phase of the Ulysses mission
when the satellite footprint was at low heliographic latitudes and the
Sun was particularly active. During its traversal to high southerly
latitudes (February 1992 - September 1994), however, the correspondence
became clearer for two reasons: 1) the radial velocity profiles of the
high-latitude CMEs were better preserved since they were less likely to
be driving shocks or to have interacted with high-speed streams; and
2) solar activity decreased, making it easier to discern individual
and/or low-intensity events in the SXT images. We describe five
Ulysses-observed CMEs which correlated with spatially and temporally
isolated coronal X-ray events in the Yohkoh SXT images, concentrating
on similarities and differences between their solar wind and coronal
structures. Two of the five events appeared to have been initiated
concurrently with active region (AR) flares; the other three involved
the restructuring of low-intensity, polar crown arcades. Significantly,
however, all five events exhibited an "LDE" signature, though only the
two AR events generated a detectable signal above the GOES integrated
background X-ray flux. The characteristics of the interplanetary
CMEs were not well correlated with their coronal X-ray signatures:
similar-looking coronal events produced very different interplanetary
field structures, and different-looking coronal signatures evolved into
remarkably similar structures at Ulysses. Although we suspect that all
of the events may have had an initially helical field structure, only
three of the events displayed coherent field rotations characteristic
of nearly force-free flux ropes (two of these were associated with
polar crown arcades and one with an AR flare). It appears that the
most important factor in determining the magnetic field evolution of
a CME in interplanetary space is its plasma beta, but that it is very
difficult to predict the interplanetary beta based on the post-eruption
coronal X-ray signature.
Title: Heliospheric Links Explorer (HELIX)
Authors: Rust, David M.; Crooker, N. U.; Golub, Leon; Hundhausen,
A. J.; Lanzerotti, L. J.; Lazarus, Alan J.; Seehafer, Norbert; Zanetti,
Lawrence J.; Zwickl, Ron W.
Bibcode: 1996SPIE.2804...39R
Altcode:
The proposed HELIX mission consists of two spacecraft that will
enable stereoscopic imaging of solar mass ejections, starting with
their origins on the Sun and continuing to 1 AU and beyond. With a
complement of telescopes and plasma detectors, the HELIX spacecraft
will test magnetic helicity conservation and other approaches to
understanding the physics of solar mass ejections. The mission will
help explain how and why solar ejections occur and how they evolve in
interplanetary space. 3D images and velocity maps and in-situ space
plasma and magnetic field measurements will allow identification and
tracking of ejected plasma. Detection of eruptions aimed at Earth will
be an immediate practical benefit of the mission. The HELIX mission
should lead to the development of a reliable storm prediction capability
that will be of significant value to communications systems operators,
electric power networks, NASA operators and others.
Title: The Solar Corona as a Minimum Energy System?
Authors: Charbonneau, P.; Hundhausen, A. J.
Bibcode: 1996SoPh..165..237C
Altcode:
This paper is an exploration of the possibility that the large-scale
equilibrium of plasma and magnetic fields in the solar corona is
a minimum energy state. Support for this conjecture is sought by
considering the simplest form of that equilibrium in a dipole solar
field, as suggested by the observed structure of the corona at times
of minimum solar activity. Approximate, axisymmetric solutions to
the MHD equations are constructed to include both a magnetically
closed, hydrostatic region and a magnetically open region where plasma
flows along field lines in the form of a transonic, thermally-driven
wind. Sequences of such solutions are obtained for various degrees
of magnetic field opening, and the total energy of each solution is
computed, including contributions from both the plasma and magnetic
field. It is shown that along a sequence of increasingly closed coronal
magnetic field, the total energy curve is a non-monotonic function of
the parameter measuring the degree of magnetic field opening, with a
minimum occurring at moderate field opening.
Title: Development of a Coronal Helmet Streamer of 24 January 1992
Authors: Hiei, E.; Hundhausen, A. J.
Bibcode: 1996mpsa.conf..125H
Altcode: 1996IAUCo.153..125H
No abstract at ADS
Title: Formation of an X-Ray Helmet Structure after a Coronal Mass
Ejection
Authors: Hiei, E.; Hundhausen, A. J.; Burkepile, J.
Bibcode: 1996ASPC..111..383H
Altcode: 1997ASPC..111..383H
SXT images, related to coronal mass ejections (CME), are studied, from
the "listing of Mauna Loa Mark-III white light mass ejection during
the Yohkoh period of observations (October 1991 through 1995)." Among
them, two events (30 Apr 1993 and 24 Jan 1992) clearly show a typical
helmet streamer, and one event (16 Jan 1993) shows dimming, which may
be due to coronal mass depletion.
Title: Declining Phase Coronal Evolution: The Statistics of X-ray
Arcades
Authors: McAllister, A. H.; Hundhausen, A. J.; Burkepile, J. T.;
McIntosh, P.; Hiei, E.
Bibcode: 1996mpsa.conf..123M
Altcode: 1996IAUCo.153..123M
No abstract at ADS
Title: The Relation of YOHKOH Coronal Arcades Events to Coronal
Streamers and CMEs
Authors: McAllister, A. H.; Hundhausen, A. J.
Bibcode: 1996ASPC...95..171M
Altcode: 1996sdit.conf..171M
No abstract at ADS
Title: Further thoughts on the solar corona as a minimum energy
system.
Authors: Charbonneau, P.; Hundhausen, A. J.
Bibcode: 1996ASIC..481..249C
Altcode:
The authors conjecture that the global, large-scale structure of the
solar corona represents a form of minimum energy state. They illustrate
this conjecture with the help of an approximate model applicable to
quiet solar minimum conditions. Possible implications and applications
of the conjecture are discussed in the context of coronal mass ejections
and of empirical modeling of the solar corona.
Title: The band of solar wind variability at low heliographic
latitudes near solar activity minimum: Plasma results from the
Ulysses rapid latitude scan
Authors: Gosling, J. T.; Bame, S. J.; Feldman, W. C.; McComas,
D. J.; Phillips, J. L.; Goldstein, B.; Neugebauer, M.; Burkepile,
J.; Hundhausen, A. J.; Acton, L.
Bibcode: 1995GeoRL..22.3329G
Altcode:
Near solar activity minimum large variations in the quiescent solar
wind flow are confined to a narrow latitude band centered near the
heliographic equator. During Ulysses' recent rapid latitude scan this
band was ∼43° wide. Flow parameters poleward of the band in the
opposite solar hemispheres were nearly the same. Main entry into the
band of variable solar wind was via a shock disturbance most likely
associated with over-expansion of a coronal mass ejection event. Wind
variability within the band was associated primarily with longitudinal
structure in the solar corona and solar rotation; high-speed streams
observed there were associated with locations where the polar coronal
holes extended equatorward toward the Ulysses orbit. Observations
indicate that the polar coronal holes at this time occupied only
∼13% of the low corona, yet a nearly uniform high-speed wind (average
speed ∼750 km s-1) filled ∼63% of the heliosphere. This
indicates the holes expanded by a factor of ∼4.8 from the low corona
to interplanetary space. Much of this lateral expansion occurred beyond
1.74 solar radii from Sun center.
Title: Reply
Authors: Gosling, J. T.; Hundhausen, A. J.
Bibcode: 1995SoPh..160...57G
Altcode:
No abstract at ADS
Title: ACOS: HAO's next generation Coronal Observing Facility at
Mauna Loa
Authors: Hassler, D. M.; Elmore, D. F.; Lecinski, A.; Streander,
K.; Burkepile, J.; Stanger, A.; Hundhausen, A. J.; Rottman, G. J.;
MacQueen, R. M.
Bibcode: 1995SPD....26..721H
Altcode: 1995BAAS...27..970H
No abstract at ADS
Title: Declining Phase Coronal Evolution: The Statistics of X-ray
Arcades
Authors: McAllister, A. H.; Hundhausen, A. J.; Burkpile, J. T.;
McIntosh, P.; Hiei, E.
Bibcode: 1995SPD....26..602M
Altcode: 1995BAAS...27Q.961M
No abstract at ADS
Title: Mass and energy contents of coronal mass ejections: SMM
results from 1980 and 1984-1988
Authors: Hundhausen, A. J.; Stanger, A. L.; Serbicki, S. A.
Bibcode: 1994ESASP.373..409H
Altcode: 1994soho....3..409H
No abstract at ADS
Title: A study of GOES X-ray events associated with coronal mass
ejections; 1986
Authors: Burkepile, J. T.; Hundhausen, A. J.; Seiden, J. A.
Bibcode: 1994ESASP.373...57B
Altcode: 1994soho....3...57B
No abstract at ADS
Title: Coronal mass ejections and major solar flares: The great
active center of March 1989
Authors: Feynman, Joan; Hundhausen, Arthur J.
Bibcode: 1994JGR....99.8451F
Altcode:
The solar flare and coronal mass ejection (CME) events associated with
the large and complex March 1989 active region are discussed. This
active region gave us a chance to study the relation of CME with truly
major solar flares. The work concentrates on questions of the relation
of CMEs and flares to one another and to other types of activity on
the Sun. As expected, some major (X-3B class) flares had associated
CMEs. However, an unexpected finding is that others did not. In fact,
there is strong evidence that the X4-4B flare of March 9th had no
CME. This lack of a CME for such an outstanding flare event has
important implications of theories to CME causation. Apparently, not
all major flares cause CMEs or are caused by CMEs. The relations between
CMEs and other types of solar activity are also discussed. No filament
disappearances are reported for major CMEs studied here. Comparing
these results with other studies, CMEs occur in association with
flares and with erupting prominences, but neither are required for
a CME. The relation between solar structures showing flaring without
filament eruptions and structures showing filament eruptions without
flares becomes important. The evolutionary relation between an active
flaring sunspot region and extensive filaments without sunspots is
reviewed, and the concept of an ``evolving magnetic structure'' (EMS)
is introduced. It is suggested that all CMEs arise in EMSs and that
CMEs provide a major path through which azimuthal magnetic fields
escape from the Sun during the solar cycle.
Title: Speeds of coronal mass ejections: SMM observations from 1980
and 1984-1989
Authors: Hundhausen, A. J.; Burkepile, J. T.; St. Cyr, O. C.
Bibcode: 1994JGR....99.6543H
Altcode:
The speeds of 936 features in 673 coronal mass ejections have
been determined from trajectories observed with the Solar Maximum
Mission (SMM) coronagraph in 1980 and 1984-1989. The distribution of
observed speeds has a range (from 5th to 95th percentile) of 35 to
911 kms-1 the average and median speeds are 349 and 285
kms-1. The speed distributions of some selected classes
of mass ejections are significantly different. For example, the
speeds of 331 ``outer loops'' range from 80 to 1042 kms-1
the average and median speeds for this class of ejections are 445
and 372 kms-1. The speed distributions from each year of
SMM observations show significant changes, with the annual average
speeds varying from 157 (1984) to 458 kms-1 (1985). These
variations are not simply related to the solar activity cycle; the
annual averages from years near the sunspot maxima and minimum are
not significantly different. The widths, latitudes, and speeds of
mass ejections determined from the SMM observations are only weakly
correlated. In particular, mass ejection speeds vary only slightly with
the heliographic latitudes of the ejection. High-latitude ejections,
which occur well poleward of the active latitudes, have speeds similar
to active latitude ejections.
Title: Coronal Eruptive Events on April 4, and may 4, 1992
Authors: Sime, D. G.; Hiei, E.; Hundhausen, A. J.
Bibcode: 1994xspy.conf..197S
Altcode:
No abstract at ADS
Title: Reformation of a Coronal Helmet Streamer by Magnetic
Reconnection after a Coronal Mass Ejection
Authors: Hiei, E.; Hundhausen, A. J.; Sime, D. G.
Bibcode: 1994xspy.conf..205H
Altcode:
No abstract at ADS
Title: Reformation of a coronal helmet streamer by magnetic
reconnection after a coronal mass ejection
Authors: Hiei, E.; Hundhausen, A. J.; Sime, D. G.
Bibcode: 1993GeoRL..20.2785H
Altcode:
A bright feature observed on Jan. 24-26, 1992 with the soft X-ray
telescope on the YOHKOH spacecraft and with the coronameter at the
Mauna Loa Solar Observatory assumed the appearance of a coronal helmet
streamer as it slowly expanded. Mauna Loa observations from Jan. 22-24
indicate that a prominence eruption and coronal mass ejection occurred
before this feature was seen. We interpret the Jan. 24-26 observations
as evidence for “reformation” of a magnetically closed helmet
structure as a consequence of magnetic reconnection that proceeded
along a vertical magnetic neutral sheet formed by the mass ejection.
Title: Sizes and locations of coronal mass ejections: SMM observations
from 1980 and 1984-1989
Authors: Hundhausen, A. J.
Bibcode: 1993JGR....9813177H
Altcode:
The SMM coronagraph/polarimeter obtained images of the solar corona in
1980 and from 1984 to 1989. Approximately 1300 coronal mass ejections
have been identified in this data set; accurate measurements of
angular widths and apparent central latitudes have been made for
1209 of them. The distribution of observed angular widths is broad
and slightly skewed toward large values; the average width is
47° (in position angle measured around the limb of the Sun), the
median width is 44°. There is no evidence in this data set for any
significant or systematic change in angular widths during the epoch
of SMM observations. The distribution of apparent central latitudes
for all 1209 measurements is roughly symmetric about the heliographic
equator, with a root-mean-square average latitude of 35°. The latitude
distributions for different calendar years show significant changes
in the spread about the equator; mass ejections occurred over a wide
range of latitudes at times of high solar activity but were largely
confined to near-equatorial latitudes at times of low activity. For
example, the root-mean-square average latitude was 41° in 1980,
38° in 1989 (both years near maxima in sunspot number) but only 13°
in 1986 (the year of minimum sunspot number). The changes in the
distribution of mass ejection latitudes do not correspond to those for
solar features or activity related to small-scale magnetic structures
such as sunspots, active regions, or Hα flares; they do resemble
those of features related to large-scale magnetic structures, such as
prominences and bright coronal regions. In 1984, when the ``quiet''
or background corona suggested the presence of a magnetic dipole
structure tilted at ~30° with respect to the solar rotation axis,
mass ejection latitudes were clumped about the tilted ``heliomagnetic
equator'' rather than the heliographic equator. Approximately half of
the mass ejections that occurred during 1984 were preceded by several
days of brightening and spreading of the bright, background corona at
the mass ejection site, and produced a conspicuous disruption of the
preexisting structure. These observations strengthen the arguments
for a close connection between mass ejections and large-scale, closed
magnetic structures in the corona.
Title: Speeds and accelerations of coronal mass ejections.
Authors: St. Cyr, O. Chris; Hundhausen, A. J.; Burkepile, J. T.
Bibcode: 1992ESASP.348..125S
Altcode: 1992cscl.work..125S
More than 1300 coronal mass ejections have been detected in observations
made by the coronagraph aboard SMM during 1980 and 1984-1989. The speed
(projected onto the plane of the sky) for at least one morphoplogical
feature in about half of these mass ejections could be measured. The
average speed of all mass ejection features was about 350 km/s, but
speeds range from a few 10s of km/s to more than 2000 km/s. There also
appear to be significant variations between the speed distributions
for different years. When a mass ejection feature appeared in three or
more sequential images, its acceleration could also be calculated. But,
because of the limited time a mass ejection remained in the SMM field
of view, the ability to detect any given acceleration diminished
with increasing mass ejection speed. In fact, the SMM observations
do not reveal a discernable acceleration for most mass ejections. A
modest yet credible acceleration was detected in 136 cases, while a
deceleration was detected in only 7 cases. The LASCO coronagraph will
have a more extensive field of view than the SMM instrument; hence,
with these new SOHO (Solar and Heliospheric Observatory) observations,
some of the challenging questions concerning mass ejection dynamics
can be addressed. How far away from the Sun does the material in a
mass ejection continue being accelerated? At what radial distance
is the motion of the mass ejection dominated by deceleration as it
interacts with the ambient interplanetary material?
Title: The Magnetic Topology of Solar Coronal Structures Following
Mass Ejections
Authors: Kahler, S. W.; Hundhausen, A. J.
Bibcode: 1992JGR....97.1619K
Altcode:
The bright radial structures observed in the solar corona for 1-2
days following a coronal mass ejection (CME) have traditionally been
interpreted as unidirectional magnetic fields, commonly known as
``legs,'' at the sides of the ejections. We examine in detail the
bright structures following 16 CMEs observed with the coronagraph
on the Solar Maximum Mission (SMM) spacecraft and find that these
structures can form anywhere within the lateral span of a CME, not
only at the sides. We suggest that a more plausible interpretation is
that the bright radial structures are the tops of coronal streamers
containing magnetic neutral sheets across which the magnetic fields
reverse direction. The observational support for this view is that:
(1) the bright features left behind at CME sides, when a CME has left
the field of view of this instrument, last <10 hours; (2) some
bright radial structures form at the sites of preexisting streamers;
(3) some such structures have the broad bases characteristic of helmet
streamers; and (4) in several cases, narrow radial structures form
over Hα prominences. A reexamination of the structures observed in the
Skylab era, including the well-studied CME of August 10, 1973, reveals
that they are also consistent with the streamer interpretation. This
interpretation avoids several difficulties encountered with the ``leg''
interpretation: (1) the systematic brightening of legs ~1 day after
the CME; (2) the origin of the energetic electrons characteristic of
stationary type IV bursts if they are associated with high-density,
unidirectional-field structures unfavorable for particle acceleration;
and (3) the lack of strong evidence of magnetic reconnection in the
coronagraph data following CMEs.
Title: Disconnection of open coronal magnetic structures
Authors: McComas, D. J.; Phillips, J. L.; Hundhausen, A. J.; Burkepile,
J. T.
Bibcode: 1992sws..coll..225M
Altcode:
We have examined the Solar Maximum Mission coronagraph/polarimeter
observations for evidence of magnetic disconnection of previously
open magnetic structures and a number of likely examples have been
found. Probable coronal disconnections typically appear as pinching off
of helmet streamers followed by the release and outward acceleration
of a large U or V-shaped structure. The observed sequence of events
is consistent with reconnection across the heliospheric current sheet
between previously open magnetic field regions, and the creation of a
detached magnetic structure which is open to interplanetary space at
both ends. Sunward of the reconnection point, coronal disconnection
events would return previously open magnetic flux to the Sun as
closed field arches. Here we (1) describe one clear disconnection
event (1 June 1989); (2) examine the results of a limited survey of
disconnection events; and (3) discuss the potential importance of
coronal disconnections for maintaining flux in interplanetary space.
Title: Concerning solar sources for Cycle 22 solar wind activity in
the heliosphere
Authors: Mihalov, J. D.; Barnes, A.; McDonald, F. B.; Burkepile,
J. T.; Hundhausen, A. J.
Bibcode: 1992sws..coll..229M
Altcode:
Beginning in 1989, the active phase of the present solar cycle became
manifest in the outer heliosphere as large disturbances in solar wind
velocity as observed by the Ames plasma analyzers aboard Pioneer 10
(46-50 AU heliocentric distance) and Pioneer 11 (about 28 AU). Inner
heliospheric baseline plasma observations from the Pioneer Venus
Orbiter (0.7 AU) and IMP 8 (1 AU) are useful for attempts to correlate
solar events with the outer heliospheric disturbances. With regard to
the onset of activity at Pioneer 11, Pioneer Venus observations are
pertinent, and some of these in turn correspond with CMEs (coronal mass
ejections) observed in SMM coronagraph data. In particular, enhanced
solar wind speeds observed at Pioneer Venus during December 1988 to
February 1989 are associated with seven large solar wind shocks (or
shock candidates); corresponding CMEs may be identified. Two of these
seven shocks were identified as candidates for a precursor to the
onset of the disturbances at Pioneer 11. At Pioneer 10 the disturbed
period includes two large disturbances, associated with the passage
of shocks. There are several candidate CMEs in the SMM observations,
one of which may be associated with the second Pioneer 10 shock.
Title: SMM's Long, Hard Look at the Solar Corona
Authors: Hundhausen, A. J.
Bibcode: 1991BAAS...23..934H
Altcode:
No abstract at ADS
Title: Observations of disconnection of open magnetic structures
Authors: McComas, D. J.; Phillips, J. L.; Hundhausen, A. J.; Burkepile,
J. T.
Bibcode: 1991GeoRL..18...73M
Altcode:
We have surveyed the Solar Maximum Mission coronagraph/polarimeter
observations for evidence of magnetic disconnection of previously open
magnetic structures and have identified several sequences of images
consistent with this interpretation. Such disconnection occurs when open
field lines above helmet streamers reconnect, in contrast to previously
suggested disconnections of CMEs into closed plasmoids. In this paper
a clear example of open field disconnection is shown in detail. The
event, on June 27, 1988, is preceded by compression of a preexisting
helmet streamer and the open coronal field around it. The compressed
helmet streamer and surrounding open field region detach in a large
U-shaped structure which subsequently accelerates outward from the
Sun. The observed sequence of events is consistent with reconnection
across the heliospheric current sheet and the creation of a detached
U-shaped magnetic structure. Unlike CMEs, which may open new magnetic
flux into interplanetary space, this process could serve to close off
previously open flux, perhaps helping to maintain the roughly constant
amount of open magnetic flux observed in interplanetary space.
Title: Coronal mass ejection shock fronts containing the two types
of intermediate shocks
Authors: Steinolfson, R. S.; Hundhausen, A. J.
Bibcode: 1990JGR....9520693S
Altcode:
Shock configurations in two dimensions are examined along with the
types of MHD shocks they contain for various shock front speeds
using physical conditions characteristic of those in coronal mass
ejections (CMEs). MHD shock jump solutions are used, along with known
restrictions on the allowable shock solutions, at special points in
the flowfield where the shock velocity and the upstream ambient field
become aligned. Numerical solutions are used to confirm the analytically
determined configurations. It is shown how, with an ambient magnetic
configuration more representative of that in a streamer, the main
features of the analytic configuration can be obtained. The simulation
supports the possible existence of intermediate shocks near the leading
edge of the concave-upward region of some CMEs. THe CME speed can be
readily found with a fair degree of accuracy, and a reasonable estimate
can be made of the ambient sound speed and the coronal density.
Title: The Effect of Solar Activity on Sungrazing Comets
Authors: St. Cyr, O. C.; Hundhausen, A. J.; MacQueen, R. M.
Bibcode: 1990BAAS...22.1323S
Altcode:
No abstract at ADS
Title: Concave-outward slow shocks in coronal mass ejections
Authors: Steinolfson, R. S.; Hundhausen, A. J.
Bibcode: 1990JGR....9515251S
Altcode:
We consider the formation of slow shocks in a simplified model corona
consisting of closed magnetic field lines near the coronal base with
overlying open magnetic field lines. An increase in the magnetic field
strength in the closed region is used to drive the corona outward,
resulting in the generation of slow shocks for a suitable choice of
parameters. The nature of the initial corona and the driver cause the
field to be deflected around the expanding driver region and thereby
produce a slow shock with a geometry that is concave upward (away from
the Sun). The fastest-moving response generated in the corona occurs
across nonlinear, fast-mode simple waves that are expansive over the
driver region and compressive at the flanks. A nonlinear intermediate
wave forms between the preceding fast wave and the following slow
shock. This study not only demonstrates that concave-upward slow shocks
can be formed in a magnetic environment, such as our simple model of
the solar corona; it also provides the first evidence that nonlinear
manifestations of all three wave modes may occur as the corona adjusts
from ambient conditions to those produced by the driver.
Title: Solar wind and coronal structure near sunspot minimum:
Pioneer and SMM observations from 1985-1987
Authors: Mihalov, J. D.; Barnes, A.; Hundhausen, A. J.; Smith, E. J.
Bibcode: 1990JGR....95.8231M
Altcode:
The solar wind speeds observed in the outer heliosphere (20 to 40 AU
heliocentric distance, approximately) by Pioneers 10 and 11, and at a
heliocentric distance of 0.7 AU by the Pioneer Venus spacecraft, reveal
a complex set of changes in the years near the recent sunspot minimum,
1985-1987. The pattern of recurrent solar wind streams, the long-term
average speed, and the sector polarity of the interplanetary magnetic
field all changed in a manner suggesting both a temporal variation,
and a changing dependence on heliographic latitude. Coronal observation
made from the Solar Maximum Mission spacecraft during this same epoch
show a systematic variation in coronal structure and (by implication)
the magnetic structure imposed on the expanding solar wind. These
observations suggest interpretation of the solar wind speed variations
in terms of the familiar model where the speed increases with distance
from a nearly flat interplanetary current sheet (or with ``heliomagneitc
latitude''), and where this current sheet becomes aligned with the
solar equatorial planet as sunspot minimum approaches, but deviates
rapidly from that orientation after minimum. We confirm here that
this basic organization of the solar wind speed persists in the outer
heliosphere with an orientation of the neutral sheet consistent with
the inferred at a heliocentric distance of a few solar radii, from
the coronal observations.
Title: MHD intermediate shocks in coronal mass ejections
Authors: Steinolfson, R. S.; Hundhausen, A. J.
Bibcode: 1990JGR....95.6389S
Altcode:
We consider a simplified model of coronal mass ejections in which
at least a portion of the interaction with the background corona
involves a shock wave and examine the allowable shock solutions and
their compressive signatures. The MHD shock-jump equations have a
maximum of three possible types of solutions with an entropy rise
for fixed values of the physical variables (slow, intermediate,
and fast shocks). However, one of the three solution classes (the
intermediate shock) is widely believed to not occur in nature and is
regarded as nonevolutionary or extraneous. Without the intermediate
shock, there is no multiplicity of solutions in that only one shock
(or none) can occur for given physical values. We consider all three
potential shock types and show, solely on the basis of the shock-jump
equations, that intermediate shocks must exist along some segment
of the shock front for certain parametric regimes and for conditions
that probably occur in some coronal mass ejections. Intermediate
shocks arise as a result of cross-flow interactions in our study;
that is, allowable shock solutions at certain locations in the flow
field dictate that intermediate shocks occur in adjacent (perpendicular
to the flow velocity) regions. Consequently, the flow must be treated
as, at least, a two-dimensional problem. Numerical simulations of the
nonlinear, time-dependent MHD equations in two dimensions verify the
formation of intermediate shocks as predicted from arguments based on
analytic theory.
Title: Slow shocks in an open magnetic field near the sun
Authors: Hu, You-Qiu; Zhu, Zhong-Wei; Hundhausen, A. J.; Holzer,
T. E.; Low, B. C.
Bibcode: 1990SCSMP..33..332H
Altcode:
A numerical study on the formation of the slow shock in an open
magnetic field due to the motion of a coronal mass ejection driven by
a magnetic flux eruption from below the corona is presented. The slow
shock obtained in the numerical model is characterized by a limited
latitudinal extent and a slightly flattened shape. It is determined
that a fast-mode wave always coexists and interacts with the medium
ahead of the slow shock and deflects the background magnetic field
to create a rarefaction ahead of the slow shock and a compression in
the flank. Thus, these effects have a significant influence on the
geometry and features of the slow shock.
Title: The launch of solar coronal mass ejections: Results from the
coronal mass ejection onset program
Authors: Harrison, R. A.; Hildner, E.; Hundhausen, A. J.; Sime, D. G.;
Simnett, G. M.
Bibcode: 1990JGR....95..917H
Altcode:
We describe a set of solar coronal mass ejection (CME) events where
coincident data sets from both X ray and white light instruments have
been made available through deliberate planning. Using these we have
been able to put tight limits on possible descriptions of the typical
sequence of events, and these we relate to interpretations of models
involving flares and CMEs. Our findings confirm recent suggestions
that CME onsets precede any related flare activity and that the
associated flaring commonly lies to one side of the CME span. The CME
launch appears to be associated with minor X ray (flare precursor)
activity. Although this scenario has been previously discussed (see
Harrison, 1986, and references therein), the abundance of flare and
CME models which are not compatible with this picture demands that
confirmation be sought using programs such as this.
Title: Solar Coronal Mass Ejections
Authors: Hundhausen, A. J.; Sime, D. G.; Low, B. C.
Bibcode: 1990IAUS..140...16H
Altcode:
No abstract at ADS
Title: SMM Observations of Sungrazing Comets
Authors: MacQueen, R. M.; St. Cyr, O. C.; Hundhausen, A. J.
Bibcode: 1989BAAS...21.1144M
Altcode:
No abstract at ADS
Title: Coronal Mass Ejections (Public Lecture to be given at end
of session)
Authors: Hundhausen, A. J.
Bibcode: 1989BAAS...21..856H
Altcode:
No abstract at ADS
Title: Waves in Low-β plasmas: Slow shocks
Authors: Steinolfson, R. S.; Hundhausen, A. J.
Bibcode: 1989JGR....94.1222S
Altcode:
The response of a conducting fluid containing an embedded magnetic field
(with β<1) to the sudden injection of material along the field
lines is investigating using results from wave theory and numerical
simulations of the nonlinear magnetohydrodynamic equations. A primary
interest is the possible generation of, and the role played by,
slow shocks in the medium response to the ejecta. We show that slow
shock preceding an impermeable ejecta, the slow shock configuration
deduced in the present computations is concave toward the ejecta
``driver.'' Fast-mode waves, which have not steepened into shocks,
precede the slow shock and significantly alter the ambient medium
(provided β is not too low). The slow waves are shown to play an
important role in accommodating the driven ejecta. At low β the fast
mode becomes primarily a transverse wave for parallel propagation,
whereas the slow wave approaches a longitudinal, or sound, wave. The
compressive effects of the motion then are principally transmitted
by the slow shock, while the fast wave primarily just reorients the
magnetic field.
Title: Density and white light brightness in looplike coronal mass
ejections: Temporal evolution
Authors: Steinolfson, R. S.; Hundhausen, A. J.
Bibcode: 1988JGR....9314269S
Altcode:
The preceding paper (Steinolfson, this issue) describes three ambient
coronal models suitable for the study of time-dependent phenomena: (1)
a static corona with a dipole magnetic field, (2) a steady polytropic
corona with an equatorial coronal streamer, and (3) a heated corona
with an equatorial coronal streamer. We now consider the propagation
of coronal mass ejections initiated in each atmosphere by an identical
energy source. A localized thermal energy input at the base of closed
field regions produces mass ejections that are simulated by numerical
integration of the MHD equations. We show that the computed ejection
in the first atmosphere listed above does not adequately represent
the general characteristics of observed looplike mass ejections. The
simulated ejection in a polytropic corona with a streamer does simulate
some of the observed features. It is only when a heating term is
added to the initial atmosphere with a streamer that all of these are
reproduced. A detailed comparison between a computed mass ejection and
a representative observation demonstrates that the simulation can also
duplicate some of the quantitative properties (e.g., brightness level)
of individual looplike ejections.
Title: Moving Radio Loop Structure During a Fast CME
Authors: Gopalswamy, N.; Kundu, M. R.; Hundhausen, A.
Bibcode: 1988BAAS...20Q.682G
Altcode:
No abstract at ADS
Title: Do slow shocks precede some coronal mass ejections?
Authors: Hundhausen, A. J.; Holzer, T. E.; Low, B. C.
Bibcode: 1987JGR....9211173H
Altcode:
The observed speeds of coronal mass ejections are often below the
estimated Alfvén speed but above the sound speed for the background
solar corona. This suggets that slow magnetohydrodynamic shocks may form
as mass ejections sweep through the corona. We argue on the basis of
the Rankine-Hugoniot relations and the propagation of small-amplitude
slow mode waves that the shape of a slow shock front would be flattened
(with respect to a sun-centered sphere) or perhaps even concave outward
(from the sun) and thus present a very different appearance from the
fast coronal shock waves that have been commonly modeled as wrapping
around a mass ejection. The region behind a slow shock front standing
just off the top of a coronal mass ejection would extend well out
beyond the visible flanks of the ejection. The deflections of coronal
structures that are commonly observed well outside of these flanks
(and which are inconsistent with a fast shock wrapped around the mass
ejection) are consistent with the presence of the slow shock, whether
they lie in the enlarged postshock region or in a region still further
beyond. Although the flattering of the tops of some mass ejections
suggests our proposed slow shock configuration, a true test of its
existence awaits formulation of quantitative models and detailed
comparison with observations.
Title: Activity Associated with the Solar Origin of Coronal Mass
Ejections
Authors: Webb, D. F.; Hundhausen, A. J.
Bibcode: 1987SoPh..108..383W
Altcode:
Solar coronal mass ejections (CMEs) observed in 1980 with the HAO
Coronagraph/Polarimeter on the Solar Maximum Mission (SMM) satellite are
compared with other forms of solar activity that might be physically
related to the ejections. The solar phenomena checked and the method
of association used were intentionally patterned after those of Munro
et al.'s (1979) analysis of mass ejections observed with the Skylab
coronagraph to facilitate comparison of the two epochs. Comparison of
the results reveals that the types and degree of CME associations are
similar near solar activity minimum and at maximum. For both epochs,
most CMEs with associations had associated eruptive prominences and the
proportions of association of all types of activity were similar. We
also found a high percentage of association between SMM CMEs and X-ray
long duration events (LDEs), in agreement with Skylab results. We
conclude that most CMEs are the result of the destabilization and
eruption of a prominence and its overlying coronal structure, or of
a magnetic structure capable of supporting a prominence.
Title: The Coronal Transient of 1986 October 15: A New Look at
"Post Flare Loops"
Authors: Hundhausen, A. J.; Sime, D. G.
Bibcode: 1987BAAS...19..938H
Altcode:
No abstract at ADS
Title: The velocity field of a coronal mass ejection: The event of
September 1, 1980
Authors: Low, B. C.; Hundhausen, A. J.
Bibcode: 1987JGR....92.2221L
Altcode:
A coronal mass ejection with the appearance of two sets of overlapping
loops occurred at about 0600 UT on September 1, 1980, over the
northwest limb of the sun. It was one of the fastest events observed
by the Solar Maximum Mission coronagraph during the 1980 epoch, with
apparent radial velocity components or several features approaching
1000 km s-1. A study of the slow evolution of Hα
prominence filaments and coronal structures in the northwest solar
sector suggests that the mass ejection resulted from the disruption of
a helmet streamer in association with, possibly, two filaments to give
rise to the double-loop structure. This event is well covered by 10
coronagraph images of good quality so that the complex velocity field,
defined by the apparent motions of many different parts of the mass
ejection, can be mapped out as a function of space and time. The results
of such an analysis are presented and related to current concerns
in the theoretical understanding of mass ejections. In particular,
it is concluded that a self-similar description of the velocity field
is a gross oversimplification and that although some evidence of wave
propagation can be found, the bright features in this mass ejection are
plasma structures moving (presumably) with frozen-in magnetic fields,
rather than waves propagating through plasmas and magnetic fields.
Title: The coronal mass ejection of July 6, 1980: A candidate for
interpretation as a coronal shock wave
Authors: Sime, D. G.; Hundhausen, A. J.
Bibcode: 1987JGR....92.1049S
Altcode:
Sime et al. (1984, 1985) have argued that two common characteristics of
looplike coronal mass ejections are inconsistent with interpretation
of such loops as shock waves moving through the corona. These are the
cessation of lateral motions of the loop sides to form nearly radial,
stationary bright columns or ``legs'' in the late stages of many mass
ejections and the pushing aside or bending of pre-existing coronal
features well outside the loop sides. Both are contrary to the notion
of a propagating wave with a shock at its front and in disagreement
with quantitative models of shock propagation in the corona. We
report here Solar Maximum Mission (SMM) coronagraph observations
of a looplike coronal mass ejection that occurred on July 6, 1980,
and that was atypical in the two characteristics mentioned above. The
sides of the loop moved laterally while they were visible and did not
stop to form stationary ``legs.'' A group of raylike features initially
outside the mass ejection loop were not pushed aside or bent until the
laterally moving loop sides passed over them. We thus propose the July
6, 1980, mass ejection as a candidate for identification as a shock
wave. Quantitative analysis of the motion of the bright loop is also
consistent with such an identification. The loop top moves outward
with an apparent radial speed of ~1000 kms-1,
faster than all but one other mass ejection observed by SMM in 1980
and probably faster than the Alfvén speed in the corona. The loop
sides move laterally at a speed of ~800 kms-1
and show no evidence for a significant deceleration. The excess mass
in the bright loop is estimated at <=2×1014
g, comparable to the expected error in its measurement and well below
the value found to be typical of coronal mass ejections.
Title: The Origin and Propagation of Coronal Mass Ejections (R)
Authors: Hundhausen, A. J.
Bibcode: 1987sowi.conf..181H
Altcode:
No abstract at ADS
Title: On the Interpretation of "Halo" Coronal Mass Ejections
Authors: St. Cyr, O. C.; Hundhausen, A. J.
Bibcode: 1987sowi.conf..235S
Altcode:
No abstract at ADS
Title: Disruption of a coronal streamer by an eruptive prominence
and coronal mass ejection
Authors: Illing, R. M. E.; Hundhausen, A. J.
Bibcode: 1986JGR....9110951I
Altcode:
We describe and analyze in detail the coronal mass ejection of 18
August 1980, using images from the coronagraph on the Solar Maximum
Mission (SMM) satellite. The event occurred at the site of a large
coronal helmet streamer and evolved into the three-part structure of a
bright frontal shell, followed by a relatively dark space surrounding
a bright filamentary core as seen in many mass ejections of the SMM
epoch. The bright core can be identified as material from a prominence
whose eruption was observed from the ground; this identification is
based on (1) the looplike and filamented appearance of the core,
(2) its motion along a trajectory that is a good extrapolation of
the motion deduced from ground-based observations of the prominence
eruption, and (3) direct observations of Hα emission when the core
is in the coronagraph field of view. The mass of the frontal shell
is equal to that of the coronal helmet streamer (to the ~30% accuracy
with which mass estimates can be made), indicating that the shell is
the coronal material previously in the helmet streamer, displaced
and set into motion by the erupting prominence and surrounding
cavity. The mass ejected in the bright core (or prominence) is
estimated to be ~50% larger than the ``coronal'' material in the
frontal loop. The total mass of 2.5×1015 g and
energy of 5×1031 ergs estimated for this mass
ejection are both greater than in typical ejections of the Skylab era
but are comparable to the average mass and energy in an interplanetary
shock wave.
Title: The propagation of coronal mass ejection transients
Authors: MacQueen, R. M.; Hundhausen, A. J.; Conover, C. W.
Bibcode: 1986JGR....91...31M
Altcode:
Measurements of the direction of propagation of 29 coronal mass
ejection events observed during the Skylab epoch (1973-1974) and 19
events observed during the SMM epoch (1980) reveal that the former
undergo an average 2.2° equatorward deflection, while the latter do not
deviate signficantly from radial motion. No differences between eruptive
prominence-associated or flare-associated events can be detected for
either epoch. The results suggest that coronal mass ejection events
are influenced by the background coronal magnetic and flow patterns;
the nonradial forces affecting the Skylab epoch mass ejections arise
from the large-scale dipolar magnetic field and flow configuration
present at that time.
Title: Reply
Authors: Sime, D. G.; MacQueen, R. M.; Hundhausen, A. J.
Bibcode: 1985JGR....90..563S
Altcode:
No abstract at ADS
Title: Observation of a coronal transient from 1.2 to 6 solar radii
Authors: Illing, R. M. E.; Hundhausen, A. J.
Bibcode: 1985JGR....90..275I
Altcode:
We describe in detail the eruptive prominence associated coronal
mass ejection of August 5, 1980, as seen in both the Solar Maximum
Mission (SMM) coronagraph polarimeter and the Mauna Loa Observatory
(MLO) K coronameter and prominence monitor. This event gives us the
first detailed look at the propagation of a ``depletion'' transient
into the outer corona. The event begins in the MLO K coronameter as a
rising depletion of material, but appears later in the SMM coronagraph
as an ordinary coronal mass ejection with a three-part structure: a
bright core within a dark lunette surrounded by a bright featureless
``loop.'' A joint time-height plot of the major structures of the
eruption seen by both instruments suggests that we can associate the
three-part structure in the outer corona with features in the low corona
(prominence, prominence cavity, outer bright front). We argue from its
observed mass that the leading loop in the SMM field of view is probably
material that was in the background corona before the event. We suggest
that this material has been displaced and set into motion by the rising
``cavity.'' One ``leg'' of the transient as seen by the SMM instrument
is strongly bowed away from the bright core or prominence; this is in
contrast to the straight, radial legs seen after Skylab mass ejections.
Title: Some macroscopic properties of shock waves in the heliosphere
Authors: Hundhausen, A. J.
Bibcode: 1985GMS....34...37H
Altcode:
In situ plasma and magnetic field observations demonstrate the existence
of collisionless shocks associated with spatial inhomogeneities or
temporal variations in the solar wind and with solar wind-planetary
interactions. Remote observations suggest that similar shocks
occur in association with solar activity in the solar corona. This
tutorial will be focused on the formation and propagation of such
shock waves in the heliospheric plasma. Simple theoretical models
(both analytic and numerical) of these phenomena to illuminate the
basic physical processes controlling shock formation and propagation
in the interplanetary medium will be drawn upon.
Title: Analysis of HI Balmer-alpha Emission from an Eruptive
Prominence above 3 Solar Radii
Authors: Illing, R. M. E.; Athay, R. G.; Hundhausen, A. J.
Bibcode: 1985BAAS...17..514I
Altcode:
No abstract at ADS
Title: K-Coronameter observations and potential field model comparison
in 1976 and 1977
Authors: Bruno, R.; Burlaga, L. F.; Hundhausen, A. J.
Bibcode: 1984JGR....89.5381B
Altcode:
Results of determining the shape and location of the heliospheric
current sheet from a potential field model and from K-coronameter
observations are compared. Interplanetary magnetic field polarities
as observed by IMP 8, Helios 1 and 2, and Voyager 2 spacecraft were
used to test the two methods over the period May 1976 to August 1977
throughout 18 Carrington rotations. The computed heliospheric current
sheets from both methods had a quasi-stationary four-sector structure
and very similar shapes. Agreement between interplanetary magnetic field
polarity and the results from the potential field model was found on 79%
of the days, while agreement between the interplanetary field polarity
and the polarities derived from the K-coronameter data was found on 87%
of the days.
Title: Coronal mass ejections observed during the solar maximum
mission: Latitude distribution and rate of occurrence
Authors: Hundhausen, A. J.; Sawyer, C. B.; House, L.; Illing, R. M. E.;
Wagner, W. J.
Bibcode: 1984JGR....89.2639H
Altcode:
Sixty-five coronal mass ejections have been identified in a systematic
examination of white-light coronal images obtained between March and
September 1980 by the coronagraph/polarimeter flown on the solar maximum
mission spacecraft. These ejections were more uniformly distributed
in position angle (or ``projected'' solar latitude) than the similar
events observed during the Skylab mission in 1973-1974 27% of the solar
maximum mission mass ejections were centered at positions more than 45°
from the solar equator. The average rate of occurrence of the observed
mass ejections for the entire solar maximum mission epoch, based on the
assumption that one coronagraph image per spacecraft orbit is sufficient
for detection, was 0.9+/-0.15 per 24-hour day. Application of the same
sampling assumption to the Skylab data set leads to a rate of 0.75
per 24-hour day and thus a change in this rate from the Skylab era
(on the declining phase of sunspot cycle 20) to solar maximum mission
(near the maximum of sunspot cycle 21) of only ~20%.
Title: Density distribution in looplike coronal transients: A
comparison of observations and a theoretical model
Authors: Sime, D. G.; MacQueen, R. M.; Hundhausen, A. J.
Bibcode: 1984JGR....89.2113S
Altcode:
Examination of the intensity changes in five outer coronal ``looplike''
transients observed by the Skylab coronagraph shows general tendencies
(1) greatest concentration of material at the flanks rather than at
the tops of the bright loops that characterize these transients, (2)
presence of a large region of depleted density within these loops, and
(3) developement of bright legs that contain most of the material in
the transient and that display very little lateral motion as the top of
the bright loop moves radially outward through the outer corona. These
properties of looplike coronal transients provide useful constraints on
theoretical models of this phenomenon. In particular, direct comparison
of the observed density distributions with those predicted by models
of compressional waves initiated by an impulsive energy release in
the low corona are a necessary test of these models. These models
predict a maximum enhancement at the top of the loop, rather than at
the flanks and ``legs'' that move laterally with a significant fraction
of the propagation speed of the loop top, in conflict with the observed
tendencies. If the observed loops are taken to have the geometry assumed
in the compressive wave models (``toroidal symmetry'' about a rotation
axis passing through the center of the sun), the predicted density
enhancements are several times larger than those inferred from the
observations. Agreement cannot be achieved without use of a geometry
which conflicts with that used for the model calculations.
Title: Description of a Coronal Helmet Streamer by an Eruptive
Prominence-Associated Mass Ejection
Authors: Illing, R. M. E.; Hundhausen, A. J.
Bibcode: 1984BAAS...16..454I
Altcode:
No abstract at ADS
Title: Coronal transients and their interplanetary effects.
Authors: Hundhausen, A. J.; Burlaga, L. F.; Feldman, W. C.; Gosling,
J. T.; Hildner, E.; House, L. L.; Howard, R. A.; Krieger, A. S.;
Kundu, M. R.; Low, B. C.; Sheeley, N. R., Jr.; Steinolfson, R. S.;
Stewart, R. T.; Stone, R. G.; Wu, S. T.
Bibcode: 1984NASRP1120....6H
Altcode:
Contents: 1. Introduction. 2. Background material: Ancient history -
solar flares and geomagnetic storms. Modern history - interplanetary
shock waves. Coronal transients or mass ejections. 3. The present:
Theoretical models. New observations of coronal mass ejections. 4. The
future: Solar origins. Interplanetary effects.
Title: Possible observation of a disconnected magnetic structure in
a coronal transient
Authors: Illing, R. M. E.; Hundhausen, A. J.
Bibcode: 1983JGR....8810210I
Altcode:
We present SMM coronograph/polarimeter observations of the
coronal transient of March 15-16, 1980, which show a bright front
convex toward the sun propagating out through the corona at 175 km
s-1. A fan-shaped bright region connecting this
front to the inner corona collapses into a narrow bright ray over the
next few hours. We interrupt these observations as resulting from the
disconnection of magnetic loops from the underlying prominencelike
loop structures seen rising earlier in the event. Other similar
``inverted arches'' exist in the C/P data but are usually seen with
poorer temporal resolution.
Title: The solar wind ionization state as a coronal temperature
diagnostic
Authors: Owocki, S. P.; Holzer, T. E.; Hundhausen, A. J.
Bibcode: 1983ApJ...275..354O
Altcode:
The 'frozen' solar wind ionization state within a few solar radii
of the photosphere suggests that ion measurements at 1 AU may yield
information on the electron temperature conditions at the base of
the coronal expansion. The freezing-in process is examined in light
of traditional assumptions as to coronal expansion, where electron
temperature decreases monotonically with height, the bulk flow of all
charge states of a given ion species are equal to the proton speed,
and the ion outflow is spherically symmetric. The consequences of
the relaxation of these assumptions include the underestimation of
the magnitude of a temperature maximum occurring near the freezing-in
radius. Because it is associated with high speed, low density flow,
an areal divergence that is faster than that in a spherical outflow
lowers the ionization state freezing-in level relative to that which
is typical in spherically symmetric expansion.
Title: The effect of a coronal shock wave on the solar wind ionization
state
Authors: Owocki, S. P.; Hundhausen, A. J.
Bibcode: 1983ApJ...274..414O
Altcode:
In connection with studies of solar wind ionization state freezing, it
is shown that, by using a Lagrangian approach of following individual
fluid parcels, the techniques used previously for calculating
ionization state variations in a steady state case can be extended
straightforwardly to time-varying flows. The specific ionization
state calculations presented are for a relatively simple picture
of time-dependent coronal flow, based on a well-known model of a
self-similar shock wave propagating through the corona. Time-dependent
ionization effects for the sudden transition between two otherwise
steady flows are likely to be limited to a narrow range of gas
parcels which, having been shocked within the coronal freezing-in
radius, pass a fixed interplanetary observer in an interval of a
few tens of minutes. The amplitude of any rise in interplanetary
ionization temperature associated with the coronal shock is likely
to be considerably smaller than the jump in electron temperature that
actually occurs in the corona.
Title: Comparison of heliospheric current sheet structure obtained
from potential magnetic field computation and from observed maximum
coronal brightness.
Authors: Wilcox, J. M.; Hundhausen, A. J.
Bibcode: 1983NASCP2280..565W
Altcode:
No abstract at ADS
Title: Comparison of heliospheric current sheet structure obtained
from potential magnetic field computations and from observed
polarization coronal brightness
Authors: Wilcox, J. M.; Hundhausen, A. J.
Bibcode: 1983JGR....88.8095W
Altcode:
A comparison is conducted of the structure of the heliospheric
current sheet early in sunspot cycle 21 as computed from the observed
photospheric magnetic field with a potential field approximation and
as inferred from synoptic maps of the observed coronal polarization
brightness. On most of the solar rotations compared, the two methods
give essentially the same results; the basic shape of the warped current
sheet and the amplitude (in solar latitude) of the displacements of the
sheet from the solar equator are similar. On one rotation the current
sheet computed with the potential field approximation appears to be
distorted by a large photospheric region of unbalanced magnetic flux.
Title: A comparison of coronal and interplanetary current sheet
inclinations
Authors: Behannon, K. W.; Burlaga, L. F.; Hundhausen, A. J.
Bibcode: 1983JGR....88.7837B
Altcode:
HAO white-light K-coronameter observations show that the inclination of
the heliospheric current sheet at the base of the corona can be both
large (nearly vertical with respect to the solar equator) or small
during Carrington rotations 1660-1666 and even on a single solar
rotation. We discuss Voyager 1 an 2 magnetic field observations of
crossings of the heliospheric current sheet at distances from the
sun of 1.4 and 2.8 AU. Two cases are considered: one in which the
corresponding coronameter data indicate a nearly vertical (north-south)
current sheet and another in which a nearly horizontal near-equatorial
current sheet is indicated. For the crossings of the vertical current
sheet a variance analysis based on hour averages of the magnetic
field data gave a minimum variance direction consistent with a steep
inclination. The horizontal current sheet was observed by Voyager as a
region of mixed polarity and low speeds lasting several days, consistent
with multiple crossings of a horizontal but irregular and fluctuating
current sheet at 1.4 AU. However, variance analysis of individual
current sheet crossings in this interval, using 1.92-s averages, did not
give minimum variance directions consistent with a horizontal current
sheet. We conclude that one cannot assume that the minimum variance
direction with be the same as the normal to the current sheet when the
analysis results are likely to be influenced by small-scale variations
or curvatures within or near the sheet proper. This influence may be
more pronounced when the sheet is locally nearly horizontal.
Title: Nonlinear periodic solutions for the isothermal magnetostatic
atmosphere
Authors: Low, B. C.; Hundhausen, A. J.; Zweibel, E. G.
Bibcode: 1983PhFl...26.2731L
Altcode:
Zweibel and Hundhausen (1982) have obtained analytically a family
of isothermal, horizontally periodic, magnetostatic atmospheres
in a uniform gravitational field. The present investigation is
concerned with another set of period analytic solutions, taking into
account the equilibrium configuration of plasma condensations in an
otherwise everywhere uniform field. The physics of the support of
the condensations by the embedded magnetic field is of interest to
the study of solar prominences and interstellar clouds. Attention is
given to the nonlinear problem, the general results, models for plasma
condensations, and questions of stability.
Title: A comparison of coronal and interplanetary current sheet
inclinations
Authors: Behannon, K. W.; Burlaga, L. F.; Hundhausen, A. J.
Bibcode: 1983STIN...8331566B
Altcode:
The HAO white light K-coronameter observations show that the inclination
of the heliospheric current sheet at the base of the corona can be both
large (nearly vertical with respect to the solar equator) or small
during Cararington rotations 1660 - 1666 and even on a single solar
rotation. Voyager 1 and 2 magnetic field observations of crossing
of the heliospheric current sheet at distances from the Sun of 1.4
and 2.8 AU. Two cases are considered, one in which the corresponding
coronameter data indicate a nearly vertical (north-south) current
sheet and another in which a nearly horizontal, near equatorial current
sheet is indicated. For the crossings of the vertical current sheet, a
variance analysis based on hour averages of the magnetic field data gave
a minimum variance direction consistent with a steep inclination. The
horizontal current sheet was observed by Voyager as a region of mixed
polarity and low speeds lasting several days, consistent with multiple
crossings of a horizontal but irregular and fluctuating current sheet at
1.4 AU. However, variance analysis of individual current sheet crossings
in this interval using 1.92 see averages did not give minimum variance
directions consistent with a horizontal current sheet.
Title: Temporal Evolution of the Solar Corona
Authors: Seagraves, P.; Fisher, R.; Hundhausen, A.
Bibcode: 1983BAAS...15Q.704S
Altcode:
No abstract at ADS
Title: Density Distribution in Loop-Like Coronal Transients: A
Comparison of Observations and a Theoretical Model
Authors: Sime, D. G.; MacQueen, R. M.; Hundhausen, A. J.
Bibcode: 1983BAAS...15..707S
Altcode:
No abstract at ADS
Title: Spatial structure of solar wind in 1976
Authors: Zhao, X. -P.; Hundhausen, A. J.
Bibcode: 1983JGR....88..451Z
Altcode:
Interplanetary scintillation measurements of the solar wind speed
from 1976 show the expected trends toward high speed at either high
heliographic latitudes or at large angular displacements from an
interplanetary neutral sheet deduced from coronal observations. However,
detailed examinations of the speed measurements when the neutral
sheet is displaced from the solar equator reveals a lack of equatorial
symmetry and suggests a minimum speed near the neutral sheet. For this
epoch, the average solar wind speed u varies with angular displacement
λ from the neutral sheet as u=350 km s-1+800
sin2 λ km s-1 for ||λ||<=35°
and is approximately constant at 600 km s-1
for ||λ||>35°.
Title: Quadrupole distortions of the heliospheric current sheet in
1976 and 1977
Authors: Bruno, R.; Burlaga, L. F.; Hundhausen, A. J.
Bibcode: 1982JGR....8710339B
Altcode:
Latitudinal variations in the position of the heliospheric current
sheet were investigated using interplanetary measurements from Helios
A. Helios B. IMP8, and white light corona measurements in the period
May 1976 to May 1977. The latitude of the heliospheric current sheet
between 0.3 AU and IAU is consistent with that of the maximum brightness
curve of white light polarization brightness at 1.75 solar radii within
approximately +/-7°. The combined data sets show that the four-sector
magnetic sector pattern observed in the ecliptic plane for most of
this epoch could be attributed to a warped current sheet whose shape
near the sun resembles a saddle surface that is nearly symmetrical
about the equatorial plane. The latitudinal extent of the current
sheet is on the average 8° and the maximum extent is 15° (except
on one rotation, when it is 20°). These results can be interpreted
as a consequence of the solar magnetic field, the dominant components
of the field being due to a dipole nearly aligned with the sun's spin
axis and a quadrupole component whose strength is ~17% of the dipole.
Title: Magnetostatic Atmospheres - a Family of Isothermal Solutions
Authors: Zweibel, E. G.; Hundhausen, A. J.
Bibcode: 1982SoPh...76..261Z
Altcode:
Most models of large scale solar magnetic fields assume either that
the fields are potential or that they are force free. We present a
new, analytic, two parameter family of magnetic fields in equilibrium
with isothermal plasma in a gravitational field. We discuss these
models from the viewpoint of the insight into the balance of magnetic
pressure gradient, and gravitational forces that they provide. We show
that substantial deviations from the potential field configuration are
obtained for plasma β of order unity, and we emphasize the variety
of possible relationships between isobars and magnetic fieldlines.
Title: Magnetostatic atmospheres in a spherical geometry and their
application to the solar corona
Authors: Rohrer Hundhausen, J.; Hundhausen, A. J.; Zweibel, Ellen G.
Bibcode: 1981JGR....8611117R
Altcode:
No abstract at ADS
Title: The coronal and interplanetary current sheet in early 1976
Authors: Burlaga, L. F.; Hundhausen, A. J.; Zhao, X. -P.
Bibcode: 1981JGR....86.8893B
Altcode:
A comparison of Helios 1 and 2 observations of the interplanetary
sector pattern in early 1976 with the maximum brightness curves in the
K coronameter data at 1.5 RS shows that the latter may be
identified with the footprints of the sector boundary surface to an
accuracy of ~10°. The neutral line computed by Wilcox et al (1980)
from a potential field model, using Mt. Wilson photospheric magnetic
field measurements and a source surface at 2.6 RS, is similar
in shape to the K coronameter maximum brightness curves but extends
to higher latitudes. The Helios observations give better agreement
with the K coronameter curves for the one solar rotation on which a
test of the latitude extent of the neutral line was possible. The K
coronameter results and the Helios data show that the sector boundary
surface probably extended to ~15° in the northern hemisphere and
to ~30° in the southern hemisphere, with little change between 1.5
RS and 1 AU. The surface was warped appreciably from a
single tilted plane (a dipole configuration) suggesting a significant
magnetic quadrupole contribution.
Title: Organization of solar wind plasma properties in a tilted,
heliomagnetic coordinate system
Authors: Zhao, X. -P.; Hundhausen, A. J.
Bibcode: 1981JGR....86.5423Z
Altcode:
We have used a superposed epoch analysis to examine the variation in
solar wind properties observed in 1974 in a 'heliomagnetic' coordinate
system tilted with respect to the solar equator. A tilt of 30°+/-10°
was found to produce the best 'organization' of these properties
in such a coordinate system. The solar wind speed increased with
heliomagnetic latitude, while the proton density and the proton flux
density decreased. These variations are qualitatively consistent with
those inferred from coronal hole and other interplanetary observations.
Title: Solar cycle modulation of galactic cosmic rays: Speculation
on the role of coronal transients
Authors: Newkirk, G., Jr.; Hundhausen, A. J.; Pizzo, V.
Bibcode: 1981JGR....86.5387N
Altcode:
Coronal transients are believed to involve the expulsion of magnetic
'bubbles' or loops into interplanetary space. The close relationship
of coronal transients with other forms of solar activity suggests a
variation in their frequency of occurrence by a factor of 3-10 over the
solar cycle. As magnetic 'inclusions' in the interplanetary magnetic
field, transients should then lead to a solar cycle dependent scattering
of cosmic rays entering the inner solar system. The power spectrum of
a model of the transverse magnetic fluctuations and its solar cycle
dependence is compared to the observed power spectra. Coronal transients
are tentatively identified as the solar origin of the low-frequency
power in the interplanetary field and, as such, an important factor
in cosmic ray modulation.
Title: Coronal evolution during the sunspot cycle: Coronal holes
observed with the Mauna Loa K-coronameters
Authors: Hundhausen, A. J.; Hansen, R. T.; Hansen, S. F.
Bibcode: 1981JGR....86.2079H
Altcode:
The white-light corona was observed regularly at the Mauna Loa
Observatory during the years 1965-1967 and 1969-1978. Display of the
measured polarization brightness in the form of synoptic maps permits
the identification of large coronal holes and the study of their
slow evolution during the sunspot cycle. The polar coronal holes were
clearly seen to shrink in size during the ascending phase of cycle 20
(1965-1967), to be absent during a two-year period (1969-1970) just
after sunspot maximum, to reappear near the end of 1970, and to remain
as prominent features of the corona for the years 1971-1978. During
the sunspot maximum epoch the corona was dominated by 'mid-latitude'
holes, elongated in the direction parallel to the solar equator. Large
equatorial holes or equatorward extensions of the polar holes were
observed during the ascending, maximum, and descending phases of cycle
20 and appear to be sources of solar wind streams with maximum speeds
over 600 km s-1 at all of these epochs. The lifetimes of
these holes and streams were greatest during the descending phase of
the cycle, or in 1974-1975.
Title: Time-Dependent Solar Wind Ionization
Authors: Owocki, S. P.; Hundhausen, A. J.
Bibcode: 1981BAAS...13..812O
Altcode:
No abstract at ADS
Title: Large-Scale Solar Magnetic Fields, Coronal Holes and High-Speed
Solar Wind Streams
Authors: Hundhausen, A. J.; Holzer, T. E.
Bibcode: 1980RSPTA.297..521H
Altcode: 1980RSLPT.297..521H
The connection between geomagnetic disturbances recurring with
the 27 day synodic solar rotation period and streams of plasma
emitted from particular regions on the Sun (so-called M-regions)
has been one of the long-standing problems of solar-terrestrial
physics. The 'plasma streams' have been identified with long-lived
streams of fast solar wind, imbedded in unipolar magnetic 'sectors',
for more than a decade. The solar sources of these streams have been
identified unequivocally only within the past few years as large-scale
coronal regions of open, diverging magnetic fields and abnormally
low particle densities, observed as 'coronal holes'. The temporal
evolution of holes and streams seems to reflect the evolution of
the large-scale solar magnetic fields; the observed spatial pattern
of holes suggests a grand three-dimensional structure of solar wind
flow and interplanetary magnetic fields organized by a near-equatorial
neutral sheet. The conclusion that much of the solar wind comes from
coronal holes implies several important modifications of our ideas
regarding the physical origins of the solar wind and any theoretical
models of solar wind formation.
Title: Polar Coronal Holes and Cosmic-Ray Modulation
Authors: Hundhausen, A. J.; Sime, D. G.; Hansen, R. T.; Hansen, S. F.
Bibcode: 1980Sci...207..761H
Altcode:
A comparison of the size of polar coronal holes with the cosmic-ray
intensity observed during the most recent sunspot cycle shows
close correspondence. This lends support to recent suggestions
that the well-known sunspot-cycle modulation of cosmic rays is a
three-dimensional effect, probably related to the global character of
the interplanetary magnetic field.
Title: Problems of Large Scale Solar Magnetic Fields, the Corona, and
the Heliosphere as Related to the Solar Cycle and the Role of SCADM
Authors: Hundhausen, A.
Bibcode: 1980NASCP2098..195H
Altcode: 1980sscs.nasa..195H
No abstract at ADS
Title: Solar activity and the solar wind.
Authors: Hundhausen, A. J.
Bibcode: 1979RvGSP..17.2034H
Altcode: 1979RvGeo..17.2034H
The availability of in situ solar wind observations from the complete
sunspot cycle 20 (1964-1976) suggests an examination of the changes
in the character of the solar wind related to the solar cycle and
comparison of these observed changes with those expected from earlier
studies of solar-terrestrial physics. In many ways the observations
correspond to these expectations; flare-associated shock waves were
probably most important near sunspot maximum, while long-lived streams
of high-speed wind, now known to originate in coronal holes, were
clearly most important in the declining years of the cycle. However,
one important pattern of deviation from the expected behavior must
be emphasized. The largest elevations of solar wind speed and the
highest level of geomagnetic activity, associated with coronal holes
and long-lived streams occurred very late in the cycle rather than
near sunspot maximum. The implications of this 'anomalous' behavior
are not well understood.
Title: Solar wind and related coronal variations
Authors: Hundhausen, A. J.
Bibcode: 1979LPICo.390...56H
Altcode:
No abstract at ADS
Title: A broad look at solar physics adapted from the solar physics
study of August 1975
Authors: Parker, E.; Timothy, A.; Beckers, J.; Hundhausen, A.; Kundu,
M. R.; Leith, C. E.; Lin, R.; Linsky, J.; MacDonald, F. B.; Noyes, R.
Bibcode: 1979sswp.book....3P
Altcode: 1979sswp.book....3B
The current status of our knowledge of the basic mechanisms involved
in fundamental solar phenomena is reviewed. These include mechanisms
responsible for heating the corona, the generation of the solar
wind, the particle acceleration in flares, and the dissipation of
magnetic energy in field reversal regions, known as current sheets. The
discussion covers solar flares and high-energy phenomena, solar active
regions; solar interior, convection, and activity; the structure and
energetics of the quiet solar atmosphere; the structure of the corona;
the solar composition; and solar terrestrial interactions. It also
covers a program of solar research, including the special observational
requirements for spectral and angular resolution, sensitivity, time
resolution, and duration of the techniques employed.
Title: Solar wind spatial structure: The meaning of latitude gradients
in observations averaged over solar longitude
Authors: Hundhausen, A. J.
Bibcode: 1978JGR....83.4186H
Altcode:
The three-dimensional structure of the solar wind is often studied by
searching for solar latitude variations in observed physical properties
that have been averaged over solar longitude. The effects of longitude
averaging are examined here by using general qualitative arguments
and quantitative calculations for a simple class of assumed spatial
variations in the solar wind speed. We show that unless the solar
wind spatial structure is simply organized about the solar equator,
its presence is extremely difficult to infer from longitude averages
unless the observations extend to very high solar latitudes. Thus
the absence of semiannual variations in ecliptic observations or the
absence of large latitude gradients in radio scintillation or comet
tail results do not constitute evidence agaist the presence of strong
spatial variations (or large spatial gradients) in the solar wind.
Title: Streams, Sectors, and Solar Magnetism
Authors: Hundhausen, Arthur J.
Bibcode: 1978nsp..conf...59H
Altcode:
Introduction and Background Coronal Holes, Solar Wind Stream, and
Interplanetary Sectors During - the Skylab Epoch Coronal and
Solar Wind Conditions, 1972-1976 The Polar Regions of the Sun as
Sources of Solar Wind Streams The General Relationship Among Holes,
Streams and Sectors The Large-Scale Coronal and Interplanetary
Structure Related to Coronal - Holes Formulation of a
Phenomenological Description Some Specific Applications of the
Phenomenological Model Some Comments on the Phenomenological
Descriptions Variations in Coronal and Interplanetary Structure
During the Solar - Activity Cycle The Evolution of Solar
Magnetic Fields in 1972 and 1973 Physical Implications and Problems
The Magnetic Geometry Associated with Coronal Holes Magnetic
Fluxes in the Corona and Solar Wind Particle and Energy Fluxes
in the Corona and Solar Wind Some Specific Implications with
Respect to Quantitative Models Summary Acknowledgements
References
Title: Waves in the solar wind.
Authors: Gosling, J. T.; Hundhausen, A. J.
Bibcode: 1978UsFiN.124..685G
Altcode:
No abstract at ADS
Title: Waves in the solar wind.
Authors: Gosling, J. T.; Hundhausen, A. J.
Bibcode: 1977SciAm.236c..36G
Altcode: 1977SciAm.236...36G
The formation and evolution of velocity waves in the solar wind are
discussed on the basis of spacecraft observations of the solar-wind
stream structure. Variations in solar-wind speed are explained in
terms of the expansion of different portions of the corona at different
rates, the evolution of a velocity wave near earth is described, and
the case of a single parcel of gas halfway up the leading edge of a
solar-wind velocity wave is considered in detail. It is shown that a
solar-wind wave will gradually be damped out if its peak speed is such
that the speed of the gas converging on the parcel is less than the
speed of sound and that a pair of shock waves will form if the speed
of the converging gas exceeds the speed of sound. The predictions of
a one-dimensional quantitative model of how solar-wind waves steepen
are compared with observations by Pioneers 10 and 11 and IMP 7. The
overall pattern of the solar wind in the plane of earth's orbit as it
might appear to a stationary observer situated far above the north pole
of the sun is deduced from the Pioneer 10 and IMP 7 data with the aid
of a theoretical model. It is concluded that the concept of steepening
velocity waves seems to explain the observed changes in solar-wind
structure between 1 AU and about 5 AU and that the structure can be
extended theoretically out to still more distant reaches of the solar
system (beyond 20 AU, where the spiral pattern will begin to close
back on itself).
Title: An interplanetary view of coronal holes.
Authors: Hundhausen, A. J.
Bibcode: 1977chhs.conf..225H
Altcode:
No abstract at ADS
Title: Plasma Flow from the Sun
Authors: Hundhausen, Arthur
Bibcode: 1977soiv.conf...36H
Altcode:
No abstract at ADS
Title: Solar wind stream evolution at large heliocentric distances:
Experimental demonstration and the test of a model
Authors: Gosling, J. T.; Hundhausen, A. J.; Bame, S. J.
Bibcode: 1976JGR....81.2111G
Altcode:
A detailed comparison is made of the speed-time profiles of six
solar wind streams observed between June 1 and October 1, 1973, by
instruments aboard Imp 7 at 1.0 AU and Pioneer 10 at 4.5 AU. This period
includes a short interval when Pioneer 10 was coaligned with Imp 7 and
the sun. The comparison provides several vivid illustrations of the
phenomena of stream steepening in the solar wind with the attendant
formation of forward-reverse shock pairs and the gradual decay of
stream amplitudes with increasing heliocentric distance. In some
respects the interplanetary medium appears to act like a ‘low-pass
filter’ large-amplitude short-wavelength speed structures present
at 1 AU are generally subdued or absent at 4.5 AU. A simple fluid
model of stream propagation which neglects all dissipation effects
except those occurring at shock interfaces is employed to predict
quantitatively the radial evolution of the stream structure observed
at 1 AU. In most cases the model provides an adequate description of
the large-scale features of the stream structure observed near 4.5
AU by Pioneer 10, including the amplitude of the speed fluctuations,
the presence of abrupt jumps in speed at the leading edges of streams,
the time of arrival at 4.5 AU, the filtering out of short-wavelength
structures, and the overall shape of speed-time profiles. The model does
less well in predicting the detailed structure at the leading edges of
streams, e.g., the amplitude of the abrupt speed jumps. In the case of
coalignment of Pioneer 10 with Imp 7 and the sun this lack of detailed
agreement undoubtedly arises from the model's assumption of adiabatic
flow (except at shocks) and its neglect of magnetic forces and nonradial
flow. For other times, the above reasons plus the nonstationary nature
of solar wind streams contribute to the lack of detailed agreement.
Title: Solar wind structure at large heliocentric distances: An
interpretation of Pioneer 10 observations
Authors: Hundhausen, A. J.; Gosling, J. T.
Bibcode: 1976JGR....81.1436H
Altcode:
Examination of hourly values of the solar wind speed observed by the
Pioneer 10 spacecraft beyond a heliocentric distance of 4 AU reveals
(1) a prevalent ‘sawtoothlike’ speed-time profile, most speed
fluctuations displaying a rapid rise and a much slower decline, and
(2) the nearly universal appearance of abrupt (on the 1-hour time
resolution of these data) changes in the speed on the rising portions of
the speed fluctuations. These previously unreported characteristics,
as well as the rate of decay of stream amplitudes derived earlier
by Collard and Wolfe, are in general agreement with the predictions
of stream propagation models that neglect any conversion of kinetic
energy to thermal energy outside of shock fronts. Thus the Pioneer 10
observations give the first confirmation of the general concept of solar
wind stream evolution employed in these models, i.e., that solar wind
speed inhomogeneities appear to steepen to form shock waves and that
the ‘wave amplitudes’ decay slowly as the shock waves propagate
outward from the sun.
Title: Solar activity (Activité solaire).
Authors: Newkirk, G.; Dunn, R. B.; Mehltretter, P.; MacQueen, R.;
Bonnet, R. M.; White, O. R.; Fokker, A. D.; Zwaan, C.; Bruzek, A.;
Durrant, C.; Grossmann-Doerth, U.; Mehltretter, J. P.; Svestka, Z.;
de Feiter, L. D.; Tandberg-Hanssen, E.; Howard, R.; Stix, M.; Pneuman,
G. W.; Hundhausen, A. J.; Sawyer, C.; Simon, P.
Bibcode: 1976IAUTA..16b..13N
Altcode:
No abstract at ADS
Title: Coronal expansion and solar wind.
Authors: Hundhausen, A.
Bibcode: 1976cesw.book.....H
Altcode:
No abstract at ADS
Title: Solar Activity and the Solar Wind: I. Eleven-Year Cycles
Authors: Hundhausen, A. J.
Bibcode: 1975CoASP...6...63H
Altcode: 1975ComAp...6...63H
The paper examines the apparently absent or weak correlation
between variations in solar-wind properties and the 11-year period
of the sunspot cycle. The discovery of the 11-year sunspot cycle is
reviewed, its relationship with geomagnetic activity is illustrated,
and previously proposed relationships between solar-wind velocity
and solar-activity cycle (i.e., variations in the intensity of solar
corpuscular radiation) are discussed. Results of spacecraft observations
are summarized which indicate that large systematic changes in the
parameters describing the basic flow of solar wind have not been
detected during the rising portion of the present solar cycle. It is
concluded that the modulation in magnetospheric energy dissipation
inferred from large changes in geomagnetic activity during the solar
cycle cannot be explained as a direct response to changes in solar-wind
energy flux.
Title: INVITED - Solar and Stellar Winds.
Authors: Hundhausen, A.
Bibcode: 1975BAAS....7..410H
Altcode:
No abstract at ADS
Title: Latitude-dependent nonlinear high-speed solar wind streams
Authors: Suess, S. T.; Hundhausen, A. J.; Pizzo, V.
Bibcode: 1975JGR....80.2023S
Altcode:
The theory of the nonlinear interaction between high- and low-speed
solar wind streams has been limited either to small amplitudes or to
the equatorial plane. It is shown how both of these restrictions can
be removed for flow more than a few solar radii away from the sun
by employing a quasi-radial approximation to develop a perturbation
expansion of the equations of motion. The lowest-order equations
describe the radial flow in large-amplitude latitude-dependent
streams. Higher-order equations describe the nonradial flow
associated with the streams and can be used to test the validity of the
quasi-radial approximation for any given set of boundary conditions.As
an example, the theory is used to model a set of interplanetary
scintillation observations indicating the disappearance, above 40°N
latitude, of the scintillation associated with a specific set of
streams. The analysis illustrates the relative nonlinear steepening
and displacement in phase of the density and velocity peaks as a
function of latitude and time. Results are given in terms of the range
of possible latitudinal variations at the sun and 1 AU allowed by the
observations. It is concluded that a disappearance of the streams above
40°N is not necessary to explain a weakening of stream interactions
and thus the disappearance of scintillations at high solar latitudes.
Title: A model for the origin of solar wind stream interfaces
Authors: Hundhausen, A. J.; Burlaga, L. F.
Bibcode: 1975JGR....80.1845H
Altcode:
The basic variations in solar wind properties that have been observed
at ‘stream interfaces’ near 1 AU are explained by a gas dynamic
model in which a radially propagating stream, produced by a temperature
variation in the solar envelope, steepens nonlinearly while moving
through interplanetary space. The region thus identified with the stream
interface separates the ambient solar wind from the fresh hot material
originally in the stream. However, the interface regions given by the
present model are thicker than most stream interfaces observed in the
solar wind, a fact suggesting that some additional physical process may
be important in determining that thickness. Variations in the density,
speed, or Alfvén pressure alone appear not to produce streams with
such an interface.
Title: REVIEWS : Coronal expansion and solar wind
Authors: Hundhausen, A. J.
Bibcode: 1974JPlPh..11..173H
Altcode:
No abstract at ADS
Title: Shock Waves and Plasma Ejection: Corpuscular and Interplanetary
Evidence (presented by G. Newkirk)
Authors: Hundhausen, A. J.
Bibcode: 1974IAUS...57..361H
Altcode:
No abstract at ADS
Title: The Speed, Density, and Flux Variations in Large-Scale Solar
Wind Disturbances
Authors: Hundhausen, A. J.
Bibcode: 1974ASSL...44...73H
Altcode: 1974mgph.proc...73H; 1974maph.conf...73H
No abstract at ADS
Title: The expansion of a low-density solar corona: A one-fluid
model with magnetically modified thermal conductivity
Authors: Durney, B. R.; Hundhausen, A. J.
Bibcode: 1974JGR....79.3711D
Altcode:
A one-fluid model of the coronal expansion, including the reduction in
radial heat conduction produced by a spiral interplanetary magnetic
field, is extended to the low coronal densities that may occur in
the regions of open diverging magnetic field lines, or ‘coronal
holes,’ that are regarded as probable sources of the solar wind. At
such densities, the ‘cutoff’ in heat conduction at very large
heliocentric distances (where the magnetic field becomes nearly
azimuthal) has a profound effect on the nature of the expansion. The
corona becomes nearly isothermal out to the distance where the flow
of plasma dominates the transport of energy. This outward extension
of high coronal temperatures leads to large solar wind speeds,
approaching those given by Parker's original isothermal model as the
coronal density becomes vanishingly small. The model predicts expansion
speeds as high as 500 km s-1, with densities in agreement
with those observed near the orbit of earth, for a reasonable set of
coronal densities and temperatures (e.g., with coronal temperatures
no higher than 2.1×106 °K). However, the temperatures
(or pressures) predicted at the orbit of earth are substantially higher
than those observed; this deficiency of the model could only be removed
by incorporation of additional physical effects or processes.
Title: Interplanetary Gas. XVIII. The Mean Free Path of Protons at
i Astronomical Unit
Authors: Brandt, John C.; Nichols Thayer, Nina; Wolff, Charles L.;
Hundhausen, A. J.
Bibcode: 1973ApJ...183.1037B
Altcode:
Velocity distribution functions of solar-wind protons obtained by
the Vela 3 satellites have been analyzed to obtain a microscopic
determination of the momentum flux along magnetic field lines with
respect to a reference frame moving at the bulk speed. The determination
from macroscopic parameters allows the calculation of an effective
mean free path for protons at 1 a.u. which averages 0.06 a.u. and is
relatively independent of solar-wind velocity w. For quiet times when
300 km 1 < w < 400 km s ', the experimental mean free path is
2 to 3 times smaller than the value from plasma theory. For w >
400 km s', the experimental value is 10 to 100 times smaller than the
theoretical value. The shorter mean free path for quiet times has been
incorporated into the model by Wolff, Brandt, and Southwick by use
of a coefficient of viscosity reduced by a factor of 3 at Earth. The
resulting model is in better agreement with the values of the quiet
solar wind at Earth suggested by Hundhausen than is the model with
full viscosity. Subject headings: interplanetary medium - solar wind
Title: Nonlinear model of high-speed solar wind streams
Authors: Hundhausen, A. J.
Bibcode: 1973JGR....78.1528H
Altcode:
A hydrodynamic model describing the generation and propagation of
high-speed plasma streams in the solar wind is presented. The model is
based upon numerical integrations of the conservation equations for a
time-dependent, spherically symmetric, radial flow of interplanetary
plasma. The nearly radial nature of the solar wind flow justifies
the use of the model to approximate ‘corotating streams,’
e.g., nonspherically symmetric flows that are steady in a frame of
reference rotating with the sun. The predicted variations in solar
wind properties are in good agreement with those observed at 1 AU
for a reasonable choice of parameters characterizing a ‘coronal
disturbance’ at the heliocentric distance of 28 Rs. This
choice must include a perturbation of the coronal temperature but need
not include perturbations of the coronal density or mass efflux. The
streams produced by such a disturbance ‘steepen’ in transit to
the orbit of the earth, with formation of a pair of shocks predicted
at slightly larger heliocentric distances. The average dependencies
of density and temperature upon the solar wind speed deduced from
the model resemble those inferred from solar wind observations. This
suggests that the major density changes associated with high-speed
streams are the products of interplanetary compression and rarefaction
within the evolving stream structure. The same processes explain the
deviations of proton temperature from their average dependence on
solar wind speed; however, that basic dependence appears to reflect
the temperature changes imposed on the plasma in the corona.
Title: Solar wind stream interactions and interplanetary heat
conduction
Authors: Hundhausen, A. J.
Bibcode: 1973JGR....78.7996H
Altcode:
The compression of plasma in solar wind stream interaction regions
(where a fast-moving stream overtakes slower-moving material) implies
the existence of a heat source for solar wind electrons. The resulting
electron thermal structure is largely determined by a balance between
the rate of compressive heating in this ‘interaction region’ source
and the rate of thermal conduction away from the region. Two different
quantitative models of the thermal structure are derived under the
common simplifying assumptions of a steady state, a negligible
spatial extent for the heat source, and a radial magnetic field
line geometry. The models employ contrasting assumptions about the
heat conduction process; one is based upon a ‘classical’ thermal
conductivity, and the other uses a ‘saturated’ heat conduction flux
density. The predicted dependence of electron temperature increase on
the characteristics of the stream interaction region is significantly
different for the two cases. It is thus suggested that observations
of electron temperatures in such regions could be used to examine the
nature of the interplanetary heat conduction process.
Title: Evolution of large-scale solar wind structures beyond 1 AU
Authors: Hundhausen, A. J.
Bibcode: 1973JGR....78.2035H
Altcode:
The evolution of solar wind speed fluctuations beyond 1 AU is considered
under the assumption that turbulent dissipation is negligible (except
at shock fronts). Both a dimensional argument, giving the distance
scale on which a shell of high-speed solar wind is ‘smoothed’ into
the ambient, and numerical solutions of the nonlinear fluid equations
indicate that the solar wind structures observed near 1 AU persist to
well beyond 5-10 AU. In fact, the shock fronts associated with such
structures under this set of assumptions are found to strengthen with
increasing heliocentric distance. The comparison of these predictions
with future solar wind observations should reveal the importance of
large-scale turbulent processes in the interplanetary plasma.
Title: Large-scale dynamical effects upon the solar wind flow
parameters
Authors: Pizzo, V.; Gosling, J. T.; Hundhausen, A. J.; Bame, S. J.
Bibcode: 1973JGR....78.6469P
Altcode:
The Vela 3 proton data have been examined to determine the extent
to which interplanetary compressions and rarefactions affect the
large-scale nonshock statistics of the solar wind temperature T and
density n. Considered as a joint function of velocity V and velocity
gradient ΔV/Δt, the temperature is found to be much more strongly
related to the velocity. The density shows significant V dependence,
but ΔV/Δt appears to be more important. Simple analytic functions
are derived from flow parameter values obtained during times of little
velocity change (|ΔV/Δt| ≤ 1 km sec-1 hr-1) to
describe the average T-V and n-V dependencies. Fluctuations about these
norms in both n and T are demonstrated to be positively correlated with
ΔV/Δt on a time scale of 9-12 hours. However, more rapid (≤6-hour)
variations in T during periods of high V, low n, and negative ΔV/Δt
(corresponding to the rarefaction phase of interacting stream events)
lack this association. The large-scale compressional perturbation of n
and T is not limited in importance to the relatively infrequent large
interacting streams, but should be regarded as a fundamental and widely
occurring solar wind process. The implication is that much, perhaps
most, nonshock solar wind activity can be viewed as a steady succession
of interacting streams of varying intensities. This circumstance limits
the usefulness of the average relations in identifying the physical
processes dominating the flow in the acceleration region of the corona.
Title: Simulation of driven flare-associated disturbances in the
solar wind
Authors: De Young, D. S.; Hundhausen, A. J.
Bibcode: 1973JGR....78.3633D
Altcode:
The dynamics of nonspherical flare-associated disturbances are
considered when the outflow of energetic material at 0.1 AU, which
gives rise to the disturbance, is maintained for an arbitrary period
of time. The propagation of such disturbances into the interplanetary
medium is examined under conditions of different total disturbance
energies, energy flux densities, and sizes of the disturbance region
at 0.1 AU. The development of these disturbances is followed by using
numerical solutions of time dependent two-dimensional hydrodynamic flow
in spherical coordinates. Decreasing the total disturbance energy by
reducing its duration produces an increase in transit time to 1 AU,
ranging from ∼37 hours for Etot = 2.9 × 1032
ergs to 58 hours for Etot = 2.8 × 1030 ergs,
all for disturbances contained initially in a cone of a half angle
equal to 15°. Variation of energy flux density at 0.1 AU shows that
disturbances of constant total energy propagate to 1 AU more slowly
as the flux density at 0.1 AU decreases. Disturbances that differ
only in the area that contains the outflow at 0.1 AU reflect this
condition in the shock front shapes at larger heliocentric distances,
smaller initial areas resulting in shock fronts with a smaller radius
of curvature at 1 AU.
Title: Compressions and rarefactions in the solar wind: Vela 3
Authors: Gosling, J. T.; Hundhausen, A. J.; Pizzo, V.; Asbridge, J. R.
Bibcode: 1972JGR....77.5442G
Altcode:
Large non-shock-associated proton density enhancements in the
solar wind observed by the Vela 3 satellites have been studied by a
superposed epoch analysis. The enhancements typically represent a
threefold increase above the nominal average density of 7 protons
cm-3, are short lived (of ∼1-day duration), and are
followed by an extended period (∼4 days) of depressed densities
(≈5 protons cm-3). Associated with the 25 enhancements
studied are large positive velocity and proton temperature gradients
arising from low-speed (≈335 km sec-1) cool (∼4
× 104 °K) flows. At times there is also a very sharp
shift in the flow direction associated with the density enhancement,
the flow swinging briefly several degrees to the east ahead of the
enhancement and then several degrees to the west on its trailing
edge. The total average event, i.e., compression and rarefaction,
represents a net proton particle flux increase of about 24% over the
nominal average value of 2.5 × 108 protons cm-2
sec-1. Of the 25 events studied, 17 occur within 1
day of the passage of an interplanetary field sector boundary. The
space-time profiles of these events compare favorably with nonlinear
models of a hot fast solar-wind stream simultaneously overtaking a
cold slow-moving stream ahead while outrunning slower-moving plasma
behind. The heating associated with the compression at the leading edge
of the high-speed stream appears to account for about one-half of the
temperature rise found there. Although there is some evidence for a
small coronal density signal associated with these events, the major
density variations can best be interpreted as the result of a spatial
rearrangement of material within the solar wind in transit from the
sun to the earth. The measurements are consistent with the viewpoint
that low solar-wind speeds frequently originate above the coronal
magnetic loops joining photospheric regions of opposite polarity and
high speeds originate in the diverging-field interstreamer regions.
Title: Energy and mass content of high-speed solar-wind streams
Authors: Montgomery, Michael D.; Bame, S. J.; Hundhausen, A. J.
Bibcode: 1972JGR....77.5432M
Altcode:
The mass and energy flux densities of the solar wind measured by the
Vela 3, Vela 4, and Explorer 34 satellites between July 1965 and October
1969 have been examined. Three-hour averages were used to study the
properties of large-scale high-speed streams, and 27-day averages were
employed in an attempt to identify long-term trends during the rising
part of the current 11-year solar cycle. If the cross-sectional area
of a stream is estimated by assuming that its extent in heliocentric
latitude is the same as its extent in longitude, the total energy
(at 1 AU) and mass flux can be calculated by integrating the excess
mass and energy flux density above the predisturbance level during
corotation of the stream past the observing satellite. The average
energy and mass fluxes for dominant high-speed streams are found
to be 9 × 1025 erg/sec and 8 × 109 g/sec,
respectively. The total mass and energy output of all streams emanating
from the sun over a typical 27-day interval, assuming that all last
for the entire 27 days, is estimated to be less than 10% (∼7%) of the
total solar-wind output from the same range of heliocentric latitudes
(generally ±15°). Both large-scale streams and interplanetary shocks
are found to contribute relatively little to 27-day average values
of either mass or energy flux density. Thus, even though the amount
of mass or energy or both per disturbance appeared to increase with
increasing solar activity, the solar-wind energy and mass flux density
averaged over a solar rotation remained remarkably constant.
Title: Interplanetary Shock Waves and the Structure of Solar Wind
Disturbances
Authors: Hundhausen, A. J.
Bibcode: 1972NASSP.308..393H
Altcode: 1972sowi.conf..393H
No abstract at ADS
Title: Coronal Expansion and Solar Wind
Authors: Hundhausen, A. J.
Bibcode: 1972cesw.book.....H
Altcode: 1972PCS.....5.....H
No abstract at ADS
Title: Composition and dynamics of the solar wind plasma.
Authors: Hundhausen, A. J.
Bibcode: 1972ipm..conf....1H
Altcode:
No abstract at ADS
Title: Evidence for an Angular Momentum Flux in the Solar Wind -
Introduction
Authors: Hundhausen, A. J.
Bibcode: 1972NASSP.308..261H
Altcode: 1972sowi.conf..261H
No abstract at ADS
Title: Dynamics of the Outer Solar Atmosphere
Authors: Hundhausen, A. J.
Bibcode: 1972NASSP.300...89H
Altcode: 1972pss..conf...89H; 1972poss.conf...89H
No abstract at ADS
Title: The interplanetary medium: Part II of solar-terrestrial
physics/1970. Proceedings of the international symposium on
solar-terrestrial physics held in Leningrad, U.S.S.R., 12 - 19
May 1970.
Authors: Dyer, E. R.; Roederer, J. G.; Hundhausen, A. J.
Bibcode: 1972ipm..conf.....D
Altcode: 1972sun..confR....D
No abstract at ADS
Title: Two-dimensional simulation of flare-associated disturbances
in the solar wind
Authors: De Young, D. S.; Hundhausen, A. J.
Bibcode: 1971JGR....76.2245D
Altcode:
The propagation of flare-associated disturbances through the
interplanetary medium is examined by using numerical solutions
of time-dependent two-dimensional hydrodynamic flow in spherical
coordinates. The study is limited to blast wave phenomena, and
the dependence on initial disturbance energy and angular extent is
examined. For constant energy disturbances initially occupying cones
of half angle up to ∼15° at 0.1 AU, the angular dependence of the
transmit time to 1 AU and of the shock shape at 1 AU is very small. For
disturbance energies at 0.1 AU of a few times 1030 ergs,
transit times to 1 AU are ∼65 hours. The calculated disturbance shapes
at 1 AU and the transit times are found to be in good agreement with
the observational data.
Title: Variations of solar-wind plasma properties: Vela observations
of a possible heliographic latitude-dependence
Authors: Hundhausen, A. J.; Bame, S. J.; Montgomery, Michael D.
Bibcode: 1971JGR....76.5145H
Altcode:
Twenty-seven-day averages of the solar-wind density and flow speed,
observed by Vela 3 and 4 spacecraft between July 1965 and July 1968,
are found to vary with the heliographic latitude of observation. High
average densities and low average flow speeds were measured near the
solar equator; low average densities and high average flow speeds
were measured near the northern and southern extremes of the earth's
heliographic latitude excursion. Possible instrumental and statistical
explanations of this pattern of variations are discussed and found to
be unlikely. The variations can be reasonably interpreted in terms
of a latitude-dependence in the structure of high-speed solar-wind
streams related to solar activity.
Title: Observations of the interplanetary medium: Vela 3 and Imp
3, 1965-1967
Authors: Ness, N. F.; Hundhausen, A. J.; Bame, S. J.
Bibcode: 1971JGR....76.6643N
Altcode:
Simultaneous observations were made of the interplanetary plasma by
the Vela 3 satellites and of the interplanetary magnetic field by
the Imp 3 satellite from July 1965 to July 1967. Certain derived
plasma properties are computed and statistically summarized. The
quiet solar wind, defined by the velocity range 300≤V≤350 km/sec,
is found to be represented by an average field strength of 4.7 γ at
ϕSE=137° (317°), θSE=-3.2°, but having
significant temporal departures from these averages. The ratio of
plasma ion thermal energy density to magnetic-field energy density
averages 1.2, with an average βp of 0.78. The average
Alfvén speed is derived to be 36 km/sec, which yields a Mach number
flow for the solar wind of 10.7. The solar-wind plasma most often is
stable with respect to the firehose mode of instability. A nonstationary
sector pattern does not destroy the sequence of correlated variations
of plasma and field parameters observed within the sectors, although
the distortion of sectors by propagating shock waves is suggested.
Title: Heat conduction and nonsteady phenomena in the solar wind
Authors: Hundhausen, A. J.; Montgomery, Michael D.
Bibcode: 1971JGR....76.2236H
Altcode:
The role of heat conduction in the solar wind is assessed by a
dimensional analysis of the electron energy equation. The relaxation
time for transient perturbations of electron temperature is shown to
be ∼4×104 sec for reasonable solar wind parameters. For
phenomena requiring longer times to propagate or develop (e.g.,
disturbances propagating near the solar wind speed) the electron
energy equation can be approximated as time independent. Two such
specific classes of solar wind variations, namely overtaking streams
and shock waves, are considered as sources of electron temperature
perturbations. In both cases heat conduction is found to be so efficient
as to ‘smooth out’ the electron temperature, thus causing any
increase to be much smaller than would be observed for protons. The few
available pertinent observations of electron temperature are consistent
with this analysis. A few effects of electron heat conduction on
small-scale phenomena (e.g., the modification of the Rankine-Hugoniot
relations applicable to interplanetary shocks) are briefly discussed.
Title: Book reviews
Authors: de Graaf, T.; Houziauk, L.; de Pater, A. D.; de Feiter,
L. D.; Hundhausen, A. J.; Veldkamp, J.; Axford, W. Ian
Bibcode: 1970SSRv...11..593D
Altcode:
No abstract at ADS
Title: Dynamics of the Outer Solar Atmosphere
Authors: Hundhausen, A. J.
Bibcode: 1970pss..conf...93H
Altcode:
No abstract at ADS
Title: Helium in the solar wind
Authors: Robbins, D. E.; Hundhausen, A. J.; Bame, S. J.
Bibcode: 1970JGR....75.1178R
Altcode:
Data obtained from electrostatic analyzers on the Vela 3A and 3B
satellites from July 1965 to July 1967 have been analyzed to obtain
relative helium abundances and plasma properties. Ninety percent of the
10,314 spectra used from this period gave helium to hydrogen density
ratios from 0.01 to 0.08. The long term average was 0.037, which is
lower than the recently reported solar-surface ratio of approximately
0.063. For the time period covered in this analysis, only 10% of
the spectra yielded helium to hydrogen density ratios greater than
0.063. Large variations in the helium to hydrogen density ratio were
observed even when averaged over a solar rotation. Sudden increases
in the solar wind helium content followed simultaneous occurrences
of Forbush decreases and sudden-commencement geomagnetic storms. The
magnitude of the helium to hydrogen density ratio, however, was not
correlated to the magnitude of the geomagnetic storm, as measured
by the Kp index. The ratio of the helium to hydrogen velocities was
strongly peaked around 1.0, as might be expected. The distribution
of the helium to hydrogen temperature ratios had a full width at half
maximum of approximately 2.5 and a mean of approximately 4.0.
Title: An Observation of the February 26, 1969 Interplanetary
Shock Wave
Authors: Hundhausen, A. J.; Bame, S. J.; Montgomery, M. D.
Bibcode: 1970ASSL...19..567H
Altcode: 1970iso..conf..567H
No abstract at ADS
Title: Solar wind properties and the state of the magnetosphere.
Authors: Hundhausen, A. J.
Bibcode: 1970AnG....26..427H
Altcode:
No abstract at ADS
Title: Solar wind proton properties: Vela 3 observations from July
1965 to June 1967
Authors: Hundhausen, A. J.; Bame, S. J.; Asbridge, J. R.; Sydoriak,
S. J.
Bibcode: 1970JGR....75.4643H
Altcode:
Observations of the solar wind proton component made between July 1965
and June 1967 on the twin Vela 3 satellites are analyzed to give a
statistical description of solar wind properties. Distributions of the
observed proton density, flow speed, flow direction, thermal anisotropy
magnitude, and anisotropy orientation are displayed; average values,
standard deviations from the averages, median values, and ranges are
given for this set of measured properties. Relationships among the solar
wind properties are discussed. The distributions of the logarithm of
the proton temperature, at differing flow speeds, are nearly normal,
with a constant standard deviation from an average that increases
with increasing flow speed. Statistical description of several basic
plasma parameters and the measured solar wind properties under ‘quiet
conditions’ are also presented.
Title: Solar wind ions: 56Fe+8 to
56Fe+12, 28Si+7,
28Si+8, 28Si+9, and
16O+6
Authors: Bame, S. J.; Asbridge, J. R.; Hundhausen, A. J.; Montgomery,
Michael D.
Bibcode: 1970JGR....75.6360B
Altcode:
Summary Ion species of 56Fe are unambiguously
resolved in the near earth solar wind of July 6, 1969, using an
electrostatic heavy ion analyzer on the Vela 5A satellite. Five
separate groups are identified as 56Fe+8
to 56Fe+12 and their relative abundance
suggests that the ion state was ‘frozen in’ over a narrow
range of heliocentric distance and coronal temperature. The mean
temperature inferred depends on the choice of ionization state
calculations that give about 1.5×106 °K in one case
and 1.26×106 °K in another. Other resolved groups can be
identified as 28Si+7,28Si+8,
and 28Si+9 but may contain small amounts
of nearby sulfur ions. The 16O+6 species,
previously identified in the solar wind with Vela 3 measurements,
is also well resolved in the Vela 5A data. The relative abundances of
oxygen, silicon, and iron ions at this time were 1.00, 0.21, and 0.17,
remarkably similar to the coronal abundances reported by Pottasch and
unlike the solar system, photospheric and solar cosmic ray abundances.
Title: Large-scale characteristics of flare-associated solar wind
disturbances
Authors: Hundhausen, A. J.; Bame, S. J.; Montgomery, M. D.
Bibcode: 1970JGR....75.4631H
Altcode:
The large-scale properties of 19 flare-associated solar wind
disturbances observed by Vela 3 and Vela 4 satellites between August
1965 and June 1967 have been examined. It is generally found that
the solar wind flow speed rises above the value measured immediately
after the shock at the leading edge of such disturbances and remains
elevated for at least 1 day. The mass and energy fluxes may either rise
or fall after the discontinuous change at the shock. Integration of the
excess of these fluxes above the preshock or ambient level gives the
total mass and energy in the interplanetary disturbance. The average
mass is found to be 3×1016 g; the average energy (at 1
AU) is 5×1031 ergs. Both the mass and energy are smaller
for disturbances in which the energy flux falls after the shock than
for disturbances in which it rises. Both quantities are larger for
disturbances observed in early 1967 than for those observed in late
1965, thus suggesting that the mass and energy deposited in the solar
wind by individual flares increased with the rise in solar activity
during the period under discussion. The energy released by the flare
(obtained by correcting for the solar gravitational potential at
1 solar radius) is found to be proportional to the mass released,
despite variation of more than an order of magnitude in both quantities.
Title: Observation of a solar flare induced interplanetary shock
and helium-enriched driver gas
Authors: Hirshberg, J.; Alksne, A.; Colburn, D. S.; Bame, S. J.;
Hundhausen, A. J.
Bibcode: 1970JGR....75....1H
Altcode:
On February 13, 1967, a class 3B solar flare occurred at 20°N,
10°W. The resultant disturbance in the solar wind was observed by
the Los Alamos plasma probe on Vela 3A and the Ames Research Center
magnetometer on Explorer 33. The initial discontinuity in the solar
wind was identified as a shock. The normal to the shock made an angle
of 60° with the plane of the ecliptic. This extreme angle of tipping
indicates that the shock from this flare did not propagate spherically
from the sun as described by simple theory. Nine hours after the
shock passed, plasma containing 22% helium was observed. Since the
solar wind normally contains 4% helium, this observation adds to the
increasing body of evidence that flares occur in regions relatively
rich in helium. The velocity of the solar wind continued to increase
after the helium plasma passed, i.e., at 1 AU the helium-enriched
material was still being propelled from behind. This observation is
evidence that the plasma continued to be accelerated at the sun for
an extended period of time after the flash phase of the flare.
Title: Plasma Measurements Across the Bow Shock and in the
Magnetosheath
Authors: Hundhausen, A. J.
Bibcode: 1970ASSL...19..155H
Altcode: 1970iso..conf..155H
No abstract at ADS
Title: Shock Waves in the Solar Wind
Authors: Hundhausen, A. J.
Bibcode: 1970ASSL...17...79H
Altcode: 1970pfm..conf...79H
No abstract at ADS
Title: Solar Wind Disturbances Associated with Solar Activity
Authors: Hundhausen, A. J.
Bibcode: 1970ASSL...19..111H
Altcode: 1970iso..conf..111H
No abstract at ADS
Title: Composition and dynamics of the solar wind plasma.
Authors: Hundhausen, A. J.
Bibcode: 1970RvGSP...8..729H
Altcode: 1970RvGeo...8..729H
No abstract at ADS
Title: A Solar Flare Disturbance as Observed in the Interplanetary
Medium
Authors: Hirshberg, J.; Bame, S. J.; Hundhausen, A. J.
Bibcode: 1969BAAS....1R.279H
Altcode:
No abstract at ADS
Title: Numerical simulation of flare-generated disturbances in the
solar wind
Authors: Hundhausen, A. J.; Gentry, R. A.
Bibcode: 1969JGR....74.2908H
Altcode:
The propagation of flare-generated shock waves through the solar wind
is examined using numerical solutions of the time-dependent hydrodynamic
equations. These solutions are valid for all shock strengths, including
the intermediate values that have been observed in the solar wind,
and take into account the variation of the properties of the ambient
solar wind. The entire range of time scales for energy deposition in the
disturbance, from impulsive (producing ‘blast waves’) to continuous
deposition, is considered. For the former class of disturbances the
solutions approach a limiting form dependent only on the total energy
in the wave. Relationships among the energy, shock strength at 1 AU, and
transit time to 1 AU are found in the blast wave limit. For disturbances
with energies near 1031 ergs, the wave propagates from the
sun to 1 AU in ∼60 hours, and is preceded by an intermediate strength
shock at the latter distance. Both the transit time and shock strength
are in good agreement with directly observed values.
Title: Nonthermal heating in the quiet solar wind
Authors: Hundhausen, A. J.
Bibcode: 1969JGR....74.5810H
Altcode:
No abstract at ADS
Title: Plasma flow pattern in the Earth's magnetosheath
Authors: Hundhausen, A. J.; Bame, S. J.; Asbridge, J. R.
Bibcode: 1969JGR....74.2799H
Altcode:
Positive-ion observations made on the twin Vela 3 satellites are used to
study the plasma flow pattern in the ‘twilight’ regions (near 90°
from the subsolar point) of the earth's magnetosheath. Observations
from January to May 1967 reveal a persistent deviation from symmetry
about the sun-earth line. Both simultaneous measurements by satellites
on opposite sides of the magnetosheath and long-term averages indicate
a flow pattern whose line of symmetry makes an angle of 8° ± 1°
with the sun-earth line, and ∼6° with the direction of the incident
solar wind. This tilting of the flow pattern is in good agreement with
Walters' 1964 prediction of the effect of the interplanetary magnetic
field on the post-bow shock flow pattern.
Title: Effects of solar flare duration on a double shock pair at 1 AU
Authors: Hundhausen, A. J.; Gentry, R. A.
Bibcode: 1969JGR....74.6229H
Altcode:
Numerical solutions of the time-dependent equations of motion for
spherically symmetric flow are obtained to study the propagation and
modification of the forward-reverse shock pair in the region between
the sun and 1 AU. For cases where the duration of the disturbance is
long compared to T, the shock transit time to 1 AU, a double shock
pair that resembles those predicted by similarity theory occurs at
1 AU. In cases where the duration of the solar disturbance is less
than about 0.45T, the shock pair structure is appreciably altered by
a rarefaction, initiated at the end of the solar disturbance, which
has caught up with the shock pair. In cases where the duration is less
than about 0.1T, the rarefaction completely destroys the reverse shock,
leaving a single shock. This analysis indicates that a forward-reverse
shock pair will not be observed at 1 AU unless the time duration of the
solar disturbance is greater than about 5 hours. Since solar flares
that last this long are quite rare, it is concluded that observation
of a flare-associated forward-reverse shock pair at 1 AU is unlikely.
Title: Direct Observations of Solar-Wind Particles
Authors: Hundhausen, A. J.
Bibcode: 1968SSRv....8..690H
Altcode:
Direct observations of solar-wind particles are discussed in detail. A
well-defined ‘quiet state’ of the solar wind is indicated by
observations made from 1962 to 1967. The plasma properties in this
quiet state are compared with those predicted by hydrodynamic models
of the coronal expansion. While the basic flow parameters are predicted
with reasonable accuracy by these models, the thermal properties of the
solar-wind particles remain largely unexplained. As the interplanetary
plasma is not in thermodynamic equilibrium, the thermal properties
are determined by the specific energy-transfer mechanisms operative
in the plasma. The observed magnitude of the magnetic-field-aligned
anisotropy of proton random motions is interpreted as evidence for the
presence of instability-generated waves; the effect of these waves on
the thermal properties is examined. The observed chemical compositon
of the solar wind is discussed and related to the solar origin of the
inter-planetary material. Finally, the spatial and temporal structure
of the medium is investigated through consideration of patterns of
variation in the plasma properties.
Title: Solar wind and magnetosheath observations during the January
13-14, 1967, geomagnetic storm
Authors: Bame, S. J.; Asbridge, J. R.; Hundhausen, A. J.; Strong, I. B.
Bibcode: 1968JGR....73.5761B
Altcode:
The interplanetary, magnetosheath, and magnetotail plasmas were observed
with electrostatic analyzers on the Vela 3A and 3B satellites at ∼18
RE during the January 13-14, 1967, geomagnetic storm. Various
parts of the storm phenomenology were observed. The sudden commencement
at 1202 UT on January 13 was caused by an interplanetary shock
that passed the earth with a speed of ∼463 km sec-1,
considerably lower than the probable average propagation speed from the
sun of ∼720 km sec-1. During the initial phase and main
phase development the magnetotail was either compressed or tilted up,
or both. Just before the inward movement of the magnetopause observed
with ATS 1 the solar wind velocity decreased and suddenly increased
again by ∼55 km sec-1. During the main phase development
the solar wind plasma population as observed by the Vela satellites
was distinctly different from the initial phase population, as shown
by the arrival of plasma with substantially increased density and
alpha particle abundance. Near the peak of the main phase and later,
magnetopause crossings showed that the magnetosphere was inflated.
Title: Interplanetary neutral hydrogen and the radius of the
heliosphere
Authors: Hundhausen, A. J.
Bibcode: 1968P&SS...16..783H
Altcode:
The supersonic flow of the solar wind is believed to terminate in
a shock transition to subsonic flow somewhere in the outer part of
the solar system. The radius of the roughly spherical region (the
heliosphere) bounded by this standing shock wave has been estimated as
~20 A.U. as the result of a theoretical study by Patterson, Johnson,
and Hanson of the distribution of interplanetary neutral hydrogen. The
present paper describes a model of particle densities in the region
beyond the heliosphere. It is shown on the basis of this model that most
of the neutral hydrogen in the vicinity of the Earth does not originate
(in charge exchanges between solar wind protons and interstellar
neutral hydrogen) near the shock boundary of the heliosphere, as
assumed by Patterson, Johnson, and Hanson, but in a Shell far beyond
the shock. The neutral hydrogen density near the Earth can then be
maintained only if the shock is near 5 A.U. This reduced value for
the radius of the heliosphere implies an interstellar magnetic field
larger by an order of magnitude than that conventionally accepted. It
is, however, in good agreement with recent estimates of the size of
this region based on the solar modulation of galactic cosmic rays.
Title: The State of Ionization of Oxygen in the Solar Wind
Authors: Hundhausen, A. J.; Gilbert, H. E.; Bame, S. J.
Bibcode: 1968ApJ...152L...3H
Altcode:
No abstract at ADS
Title: Solar Wind Ion Composition
Authors: Bame, S. J.; Hundhausen, A. J.; Asbridge, J. R.; Strong, I. B.
Bibcode: 1968PhRvL..20..393B
Altcode:
In addition to the two ion species previously observed in the solar
wind, 1H+ and 4He++,
Vela satellite measurements reveal the presence of ions of
3He++, 4He+, various ion
species of 16O, and other unidentified heavy ions. From
the number ratios of the O+7, O+6, and
O+5 ion species measured near earth, it may be inferred
that the ionization state ratios are established deep within the solar
corona at million-degree temperatures.
Title: Satellite observations of interplanetary shock waves
Authors: Gosling, J. T.; Asbridge, J. R.; Bame, S. J.; Hundhausen,
A. J.; Strong, I. B.
Bibcode: 1968JGR....73...43G
Altcode:
Interplanetary shock waves propagating through the solar wind have
been observed with hemispherical plate electrostatic analyzers
aboard the twin Vela 3 satellites. From the consideration of mass
flux continuity, the shock velocities have been calculated; the shock
velocities determined from the data in this manner are consistent with
the observed temperature changes across the shocks. These velocities
are significantly less than the mean transit velocities of the shocks
from the sun to the earth derived from the delay times between the
initiating flares and shock arrival. This result is interpreted to
mean that interplanetary shock waves are decelerated as they expand
and propagate through the quiescent solar plasma.
Title: Satellite Measurements of Interplanetary Shock Waves.
Authors: Gosling, J. T.; Ashbridge, J. R.; Bame, S. J.; Hundhausen,
A. J.; Strong, I. B.
Bibcode: 1968AJS....73...62G
Altcode:
Extended ground measurements of the delay time from large solar flares
until the onset of geomagnetic sudden commencements have established
that the typical delay time is of the order of 1-3 days. Such short
delay times have led many to believe that extremely fast (>1000 km
sec-1) shock waves propagating through the solar winds are a relatively
common occurrence at 1 a.u. However, satellite measurements suggest
that such high speed shock waves are probably rare at 1 a.u.; no direct
experimental evidence for a high speed shock wave in the solar wind at 1
a.u. has yet been reported despite more or less continuous measurements
of the solar wind since 1962. Two interplanetary shock waves observed
with hemispherical plate electrostatic analyzers aboard the twin Vela
3 satellites will be discussed in some detail. Both of these shocks
apparently experienced a significant deceleration as they traveled out
from the sun. It is suggested that most interplanetary shock waves
are similarly decelerated as they expand through and interact with
the quiescent solar wind.
Title: Solar wind electrons: Vela 4 measurements
Authors: Montgomery, Michael D.; Bame, S. J.; Hundhausen, A. J.
Bibcode: 1968JGR....73.4999M
Altcode:
No abstract at ADS
Title: Ion Composition of the Solar Wind.
Authors: Bame, S. J.; Hundhausen, A. J.; Asbridge, J. R.; Strong, I. B.
Bibcode: 1968AJS....73Q..55B
Altcode:
During this decade satellite measurements have established the existence
of the solar wind and have shown that it is mainly composed of `H+ and
4He++ ions expanding from the sun with the same bulk velocities. The
number density ratio of these species is highly variable; ratios of ~2'%
to >15% have been observed with electrostatic plasma analyzers on the
Vela satellites. in view of the solar abundances it seems possible that
other ionized components should be found in the solar wind. Measurements
made with the launch 3 Vela analyzers reveal for the first time that
heavy ions are indeed normally present. Various ionic species of oxygen,
carbon, and nitrogen have been observed; oxygen ions, with densities
in the range of a few percent of the helium densities, are the most
abundant and tend to obscure the other heavy ions. From a limited
number of examples it appears that Q6+ is the most prevalent heavy
ion, consistent with an interpretation that the ion species ratios are
established deep within the corona at temperatures near 1 X 1060K. Other
examples show O~+ to have a comparable or higher abundance, suggesting
formation temperatures near 2 X 106 0K at those times. Although the
singly ionized species 4He+ is ordinarily not discernible in the
Vela data, it has been observed at times with an abundance 3 X 10-~
that of the 4He++ species. The solar abundance of the isotope 3He,
presently not known, is important for determining the origin of the
solar material and its subsequent history. The natural width of the
measured energy per charge spectra of the solar wind protons generally
makes an observation of 3He++ impossible, but one observation made at
the time of a very low temperature wind gives a 3He/4He ratio of 10-~.
Title: The Propagation of Blast Waves in the Solar Wind.
Authors: Hundhausen, A. J.; Gentry, R. A.
Bibcode: 1968AJS....73S..64H
Altcode:
J. Geophys. Res.,Jan. 1968) show that solar-flare-associated
interplanetary shock waves observed at 1 a.u. are weak (low Mach number)
shocks. The observed speeds of the shock fronts are significantly
less than the average velocity implied by the time interval between
the associated solar flares and the arrival of the observed shocks at
1 a.u. These observations have led to the suggestion that the shocks
are slowed by the acceleration and heating of the interplanetary
material swept up in transit. A one-dimensional time-dependent
Eulerian formulation of the hydrodynamic equations has been used to
quantitatively study spherical blast waves in the solar wind. For
constant boundary conditions, the solutions of these equations (the
familiar steady-state models of the coronal expansion) are first
obtained numerically. The conditions at the inner boundary are then
varied with time to represent a coronal disturbance, and the propagation
of the disturbance followed throughout interplanetary space. Using
this technique, the propagation of the blast waves resulting from
impulsive coronal disturbances has been examined. Two steady state
models, one assuming an adiabatic expansion, the other including heat
conduction, have been considered. The computer blast waves are slowed
in passage through interplanetary space, and become weak shocks at
1 a.u. Quantitative comparisons of the computed and observed transit
times and shock properties will be presented.
Title: Correlated magnetic field and plasma observations of the
Earth's bow shock
Authors: Greenstadt, E. W.; Green, I. M.; Inouye, G. T.; Hundhausen,
A. J.; Bame, S. J.; Strong, I. B.
Bibcode: 1968JGR....73...51G
Altcode:
Ion spectrums and magnetograms obtained simultaneously when the Vela
3A satellite crossed the earth's bow shock have been correlated. An
intermediate form of ion spectrum, representing neither solar wind
nor magnetosheath, but characterized by an irregular envelope and
occasional large flux peaks, is found to correspond to the appearance
of large-amplitude (10-25 γ), irregular magnetic oscillations of
4-to 30-sec period. The large spectral flux peaks of the shock seem to
result from localized transient accelerations and decelerations of the
bulk of the solar wind protons. Smaller amplitude (<5 γ), longer
period (20-60 seconds), generally more regular magnetic oscillations
are seen in the solar wind outside the shock where the direction of
flow of ion flux peaks is found to oscillate in close correlation with
magnetic waves.
Title: Solar Wind Thermal Anisotropies: Vela 3 and IMP 3
Authors: Hundhausen, A. J.; Bame, S. J.; Ness, N. F.
Bibcode: 1967JGR....72.5265H
Altcode:
Solar wind proton velocity distribution functions derived from Vela 3
satellite observations made during July and August 1965 are usually
anisotropic in a frame of reference moving with the bulk velocity
of the medium. The orientations of these anisotropic distributions
are here compared with the directions of the interplanetary magnetic
field measured on the IMP 3 satellite. On August 3, 4, and 5, 1965,
under relatively quiet conditions, the direction of maximum proton
temperature was aligned with that of the magnetic field lines. The
detailed temporal behavior of the anisotropy and field directions
followed the same pattern during periods of slow changes and during the
passage of a `magnetic filament' past both satellites. The alignment
of the anisotropic distributions and the field lines is shown to hold
for the 33-day period for which these data have been compared. Some
consequences of the possible plasma instabilities implied by this
situation are suggested.
Title: Measurements of the Interplanetary Solar Wind during the
Large Geomagnetic Storm of April 17-18, 1965
Authors: Gosling, J. T.; Asbridge, J. R.; Bame, S. J.; Hundhausen,
A. J.; Strong, I. B.
Bibcode: 1967JGR....72.1813G
Altcode:
During the large geomagnetic storm of April 17-18, 1965, measurements
of the solar wind were made with electrostatic analyzers on the Vela 2
satellites. A number of the observed solar wind changes can be related
to worldwide geomagnetic changes; the most impressive event occurred
after the main phase development when a fivefold increase in the solar
wind density resulted in a sudden geomagnetic impulse. During the
initial phase of the storm the plasma measurements were not complete,
but the evidence indicates that the wind pressure increased at the
time of the sudden commencement, and other features of the initial
phase seem to have been related to solar wind changes. However,
the main phase of the storm developed during a period when the solar
wind remained relatively steady; further, there was nothing abnormal
about the magnitude of the velocity, temperature, or proton density
at that time. The α-particle flux during this period was higher than
usual. The storm recovery was characterized by a period of rising
solar wind velocity and temperature.
Title: Vela Satellite Observations of Solar Wind Ions
Authors: Hundhausen, A. J.; Asbridge, J. R.; Bame, S. J.; Strong, I. B.
Bibcode: 1967JGR....72.1979H
Altcode:
Observations of solar wind ions have been made with the electrostatic
analyzers of the Vela 2 and Vela 3 satellites. Analysis of data
obtained between July 1964 and July 1965 by the two Vela 2 satellites
leads to the following generalizations concerning the properties of the
solar wind. The solar wind velocity varies in magnitude between 280 km
sec-1 and 750 km sec-1; during quiet conditions
it is usually near 320 km sec-1. The variation in direction
is over ∼15°. For periods as long as an hour the deviation from
radial flow may be as large as 10°. When averaged over the year of
observation, the flow is from ∼1½° east of the sun. The proton
temperatures in a direction transverse to the bulk velocity range from
8 × 105°K down to 6 × 10³°K. The lowest temperatures
measured approach the limit set by instrumental resolution; these
extreme values are rarely observed. Low temperatures (typically a few
times 104°K) are observed when the solar wind velocity is
near the low end of its range, high temperatures when the velocity is
high. On the Vela 3 satellites, measurements are made at more energy
steps; hence the data contain more detailed information on the plasma
properties. Two-dimensional mappings of the ion distribution functions
in velocity space are obtained. These mappings reveal significant
anisotropies in the random motions of the ions. A `tail' of nonthermal
particles is usually present; the mean random energy (or temperature)
of the ions is higher in the direction of this tail than in all other
directions. The average direction of this tail of particles is close
to the average direction of the interplanetary magnetic field.
Title: Observations of Solar Wind Plasma Changes across the Bow Shock
Authors: Argo, H. V.; Asbridge, J. R.; Bame, S. J.; Hundhausen, A. J.;
Strong, J. B.
Bibcode: 1967JGR....72.1989A
Altcode:
The Vela 3 satellites are in nearly circular orbits tilted at 60°
to the ecliptic plane at geocentric distances of approximately 18.5
RE (earth radii). Thus the solar wind plasma can be sampled
on both sides of the `bow shock,' on both the dawn and dusk sides of
the earth-sun line, and at positions both in the ecliptic plane and
far above and below it. An analysis of 13 crossings of the bow shock
during July and August 1965, selected on both the dawn and dusk sides
of the magnetosphere and with widely variable ecliptic latitudes show
the solar wind bulk velocity to fall by ∼30% as the magnetosheath
is entered. The density jumps by a factor of 2-5 typically, and the
proton `temperature' by a factor of ∼20. Multiple crossings of the
shock front are common, and each crossing is easily recognized by
the distinctly different characteristics of the solar wind plasma and
magnetosheath plasma. For this time period typical average values of
the bulk velocity and proton temperature near the shock front in the
magnetosheath were 275 km/sec and 106°K. Thus the bulk
velocity is larger than the mean thermal velocity, showing that most
of the proton energy is associated with the ordered flow of the plasma
around the magnetosphere.
Title: Satellite Observations of the General Characteristics and
Filamentary Structure of the Solar Wind
Authors: Strong, I. B.; Asbridge, J. R.; Bame, S. J.; Hundhausen, A.
Bibcode: 1967NASSP.150..365S
Altcode:
No abstract at ADS
Title: Vela 3 Satellite Observations of Solar Wind Ions: A Preliminary
Report
Authors: Hundhausen, A. J.; Asbridge, J. R.; Bame, S. J.; Gilbert,
H. E.; Strong, I. B.
Bibcode: 1967JGR....72...87H
Altcode:
The electrostatic analyzers on the Vela 3 satellites measure the ion
flux with high resolution in both energy and direction. From the
measured fluxes are computed values of the velocity distribution
function at points on a plane in velocity space. The function is
extended over the whole plane by interpolation and displayed by
a contour mapping in this plane. From this mapping the properties
of the function can be visualized, and parameters characterizing
the ion component of the plasma can be computed. The distribution
functions of solar wind protons observed during the first month the
satellites were in orbit are found to be significantly anisotropic in
a frame of reference moving with the local plasma bulk velocity. A
‘tail’ of protons with high random energies is usually present;
evidence is presented that suggests that this tail is aligned with
the interplanetary magnetic field lines, more often pointing away from
the sun (along the lines) than toward the sun. The mean random energy
or temperature of the protons is highest in this direction. The ratio
of the maximum temperature to the average over-all directions ranges
from 1.0 to about 2.5, with a value of 1.4 being most common. The
existence of this anisotropy can be explained by the invariance of
υ⊥²/B as the plasma expands from the sun. Similar
anisotropic distribution functions are found for the He++
or α-particle component of the plasma. The ratio of number densities
of the α's and protons is found to vary from 0.00 to 0.15, with a
mean value of 0.042 during this period.
Title: Measurements of Proton Temperatures in the Solar Wind
Authors: Strong, I. B.; Asbridge, J. R.; Bame, S. J.; Heckman, H. H.;
Hundhausen, A. J.
Bibcode: 1966PhRvL..16..631S
Altcode:
No abstract at ADS