explanation blue bibcodes open ADS page with paths to full text
Author name code: brekke
ADS astronomy entries on 2022-09-14
author:"Brekke, Pal"
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Title: Norway's most celebrated scientist
Authors: Southwood, David; Brekke, Pâl
2017A&G....58e5.28S Altcode:
David Southwood and Pål Brekke celebrate the life of Kristian
Birkeland.
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Title: The Total Solar Eclipse on Svalbard 2015
Authors: Sigernes, F.; Ellingsen, P. G.; Holmen, S. E.; Brekke, P.;
Danielsen, A.; Olsen, B.; Syrjäsuo, M.; Chen, X.; Dyrland, M. E.;
Partamies, N.; Baddeley, L. J.; Lorentzen, D. A.; Krogtoft, M. A.;
Dragland, T.; Mortensson, H.; Smistad, L.; Oksavik, K.; Heinselman,
C. J.; Habbal, S. R.
2015AGUFMSH52A..02S Altcode:
This work reports the results from a multi-instrumental campaign
that was planned and executed to record the Total Solar Eclipse that
occurred on Friday 20th of March 2015 in Longyearbyen (78oN, 15oE)
on Svalbard, Norway. Both airborne hyperspectral- and ground-based
camera systems were used to image the event. A novel video accumulation
filter technique is presented that reveals small scale chromospheric
features. The result is fused with a High Dynamic Range (HDR) image
of the Corona taken from the old Auroral Station in Adventdalen. The
Kjell Henriksen Observatory (KHO) was also operative, but did not
detect any dayside auroral signatures. The background sky condition
was too bright during totality for the auroral cameras. The airborne
hyperspectral data is used to cluster and classify active solar regions
with prominences from the background continuum.
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Title: National Report Norway: Arctic Access to Space
Authors: Brekke, P.
2015ESASP.730...43B Altcode:
Norway has long traditions as a space nation, much due to our northern
latitude. Our space science activities are concentrated into relatively
few areas. This concentration is necessary due to limited resources,
both in funding and personnel. The main scientific activities are
within Solar-terrestrial physics and cosmology. The first field has
been a priority since before the space age and is still the major
priority. The usage of the ground infrastructure in Northern Norway and
on Svalbard is essential in studying the middle and upper atmosphere
and the interaction with the Sun. This includes the utilization of
sounding rockets, both small and large, and ground based installations
like radars, lidars and other optical instrumentation. The planned
use of Svalbard as a launch site for large stratospheric balloons may
allow the cosmology community access to our northern infrastructure. The
solar physics community is also heavily involved in the HINODE and IRIS
missions and Norway is supporting downlink of data via the Svalbard
Station for these missions. The sounding rocket program is in close
collaboration with many countries like Germany, USA, France, Canada
and Japan. Two scientific sounding rocket programs are currently
being pursued: The ICI series (from Svalbard) and MaxiDusty (from
Andoya). A series of scientific publications have recently appeared
from the ECOMA campaign a few years ago. A significant improvement of
today's polar and ionospheric research infrastructure in Northern Norway
and Svalbard has recently been put on the ESFRI roadmap for European
research infrastructure through the 5105 and EISCAT 3D initiatives. The
Norwegian government has recently decided to upgrade the VLBI facilities
at Svalbard.
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Title: Variable Cascade Dynamics and Intermittency in the Solar Wind
at 1 AU
Authors: Sigernes, F.; Ellingsen, P. G.; Holmen, S. E.; Brekke, P.;
Danielsen, A.; Olsen, B.; Syrjäsuo, M.; Chen, X.; Dyrland, M. E.;
Partamies, N.; Baddeley, L. J.; Lorentzen, D. A.; Krogtoft, M. A.;
Dragland, T.; Mortensson, H.; Smistad, L.; Oksavik, K.; Heinselman,
C. J.; Habbal, S. R.
2014AGUFMSH52A..02S Altcode:
This work reports the results from a multi-instrumental campaign
that was planned and executed to record the Total Solar Eclipse that
occurred on Friday 20th of March 2015 in Longyearbyen (78oN, 15oE)
on Svalbard, Norway. Both airborne hyperspectral- and ground-based
camera systems were used to image the event. A novel video accumulation
filter technique is presented that reveals small scale chromospheric
features. The result is fused with a High Dynamic Range (HDR) image
of the Corona taken from the old Auroral Station in Adventdalen. The
Kjell Henriksen Observatory (KHO) was also operative, but did not
detect any dayside auroral signatures. The background sky condition
was too bright during totality for the auroral cameras. The airborne
hyperspectral data is used to cluster and classify active solar regions
with prominences from the background continuum.
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Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.;
Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou,
C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman,
C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish,
D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.;
Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons,
R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.;
Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.;
Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.;
Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski,
W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.;
Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.;
Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.;
Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson,
M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu,
K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora,
J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.;
Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N.
2014SoPh..289.2733D Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D
The Interface Region Imaging Spectrograph (IRIS) small explorer
spacecraft provides simultaneous spectra and images of the photosphere,
chromosphere, transition region, and corona with 0.33 - 0.4 arcsec
spatial resolution, two-second temporal resolution, and 1 km
s<SUP>−1</SUP> velocity resolution over a field-of-view of up to
175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous
orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a
19-cm UV telescope that feeds a slit-based dual-bandpass imaging
spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å,
1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines
formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and
transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw
images in four different passbands (C II 1330, Si IV 1400, Mg II k
2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral
rasters that sample regions up to 130 arcsec × 175 arcsec at a variety
of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to
emission from plasma at temperatures between 5000 K and 10 MK and will
advance our understanding of the flow of mass and energy through an
interface region, formed by the chromosphere and transition region,
between the photosphere and corona. This highly structured and dynamic
region not only acts as the conduit of all mass and energy feeding
into the corona and solar wind, it also requires an order of magnitude
more energy to heat than the corona and solar wind combined. The
IRIS investigation includes a strong numerical modeling component
based on advanced radiative-MHD codes to facilitate interpretation of
observations of this complex region. Approximately eight Gbytes of data
(after compression) are acquired by IRIS each day and made available
for unrestricted use within a few days of the observation.
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Title: Secrets of the Northern Lights
Authors: Brekke, Pål
2013S&T...125b..18B Altcode:
No abstract at ADS
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Title: Our Explosive Sun
Authors: Brekke, Pål
2012oes..book.....B Altcode:
No abstract at ADS
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Title: Two methods to forecast auroral displays
Authors: Sigernes, Fred; Dyrland, Margit; Brekke, Pål; Chernouss,
Sergey; Lorentzen, Dag Arne; Oksavik, Kjellmar; Sterling Deehr, Charles
2011JSWSC...1A..03S Altcode:
This work compares the methods by Starkov (1994a) and Zhang &
Paxton (2008), that calculate the size and location of the auroral
ovals as a function of planetary Kp index. The ovals are mapped in
position and time onto a solar illuminated surface model of the
Earth. It displays both the night- and dayside together with the
location of the twilight zone as Earth rotates under the ovals. The
graphical display serves as a tool to forecast auroral activity based
on the predicted value of the Kp index. The forecast is installed as
a service at http://kho.unis.no/. The Zhang & Paxton (2008) ovals
are wider in latitude than the Starkov (1994a) ovals. The nightside
model ovals coincide fairly well in shape for low to normal auroral
conditions. The equatorward border of the diffuse aurora is well
defined by both methods on the nightside for Kp ≤ 7. The dayside
needs further studies in order to conclude.
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Title: Norwegian National Report- Arctic Access to Space
Authors: Brekke, P.
2011ESASP.700...23B Altcode:
No abstract at ADS
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Title: Solar radiation and human health
Authors: Juzeniene, Asta; Brekke, Pål; Dahlback, Arne;
Andersson-Engels, Stefan; Reichrath, Jörg; Moan, Kristin; Holick,
Michael F.; Grant, William B.; Moan, Johan
2011RPPh...74f6701J Altcode:
The Sun has played a major role in the development of life on Earth. In
Western culture, people are warned against Sun exposure because of
its adverse effects: erythema, photoimmunosuppression, photoageing,
photocarcinogenesis, cataracts and photokeratitis. However, Sun exposure
is also beneficial, since moderate doses give beneficial physiological
effects: vitamin D synthesis, reduction of blood pressure and mental
health. Shortage of Sun exposure may be even more dangerous to human
health than excessive exposure. Avoiding Sun exposure leads to vitamin D
deficiency which is associated not only with rickets and osteomalacia,
but also with increased risk of cardiovascular disease, multiple
sclerosis, rheumatoid arthritis, diabetes, influenza, many types of
cancer and adverse pregnancy outcomes. Solar radiation induces nitric
oxide release in tissue and immediate pigment darkening which certainly
play important roles, although these are still unknown. Action spectra
relevant for health are described. We will also review what is known
about spectral and intensity variations of terrestrial solar radiation
as well as its penetration through the atmosphere and into human skin
and tissue.
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Title: International Living With a Star
Authors: Brekke, Pål
2005ESASP.590..623B Altcode: 2005erbp.conf..623B
The response of our space environment to the constantly changing Sun is
known as "Space Weather". Sudden ejections of plasma and magnetic field
structures from the Sun's atmosphere called coronal mass ejections
(CMEs) together with sudden bursts of radiation termed solar flares
all cause space weather effects at the Earth. The International
Living With a Star (ILWS) programme is a space weather focused
and applications driven research programme. Its goal is to develop
the scientific understanding necessary to effectively address those
aspects of the connected Sun-Earth system that directly affects life
and society. Recent large solar storms caused damages to power systems
and satellites and disturbed important navigation and communication
systems. Furthermore, accurate monitoring of the energy output from
the Sun is important for understanding how the Sun contributes to the
observed warming of our planet. The Sun is a variable star we better
learn how to live with.
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Title: Space Weather Effects on SOHO and its Leading Role as a Space
Weather Wãtchdog
Authors: Brekke, P.; Fleck, B.; Haugan, S. V.; van Overbeek, T.;
Schweitzer, H.; Simonin, B.
2005mcsp.conf...83B Altcode:
No abstract at ADS
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Title: Closing remarks on the Sun influence on climate changes.
Authors: Brekke, P.
2005MmSAI..76..913B Altcode:
Numerous attempts have been made over the years to link various aspects
of solar variability to changes in the Earth's climate. Since the Sun's
output of electromagnetic radiation and energetic particles varies, and
since the Sun is the ultimate driver for the climate system, it seems
natural to link the two together and look for the source of climate
variability in the Sun itself. In recent years there has been a growing
concern about the possible anthropogenic forcing of climate change
through the increasing atmospheric content of greenhouse gases. This
has made the connection between solar variability and global climate
change a very controversial research area. This conference brings
together the solar and climate community to present the most recent
results gained on the knowledge of solar variability and the effects
on the Earth's climate system. From the presentations it appears that
the understanding have come a long way, with the Sun driving global
warming in the early part of the last century and anthropogenic effects
taking over in the second half. However, it is also evident that we
need to improve our knowledge about historic solar and temperature
proxy data. Furthermore we need to better understand the atmospheric
response to variations in the ultraviolet and extreme ultraviolet
radiation and the physics of cloud formation.
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Title: The Suns Halloween Scare and the Media Frenzy
Authors: Brekke, P.
2004AGUSMSH32A..01B Altcode:
SOHO appeared to be in everyone's focus this fall as the Sun turned
from an almost spotless orb into an ominously scarred source of
mighty fireworks in just a few days. Over two weeks, it featured three
unusually large sunspot groups (including the largest one of this solar
cycle), 11 X-class flares (including the strongest ever recorded),
numerous halo CMEs (two with near-record speeds) and two significant
proton storms which lasted for a combined five days. Satellites, power
grids, radio communication and navigation systems were significantly
affected in this period. The events caused unprecedented attention
from the media and the public. Images from SOHO as well as quotes from
SOHO scientists appeared in nearly every major news outlet (CNN, BBC,
Associated Press, Reuters, to mention a few). Stories including SOHO
images made the front page of newspapers and were featured prominently
on including USA Today and The Washington Post. NASA estimated that
the story reached "all" US newspapers and 2000 US TV channels. Media
coverage in Europe was also impressive. The attention wiped out all
existing SOHO web traffic records
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Title: The Role of the Sun in Climatic Change
Authors: Kirby, A.; Brekke, P.
2003ESASP.519E...2K Altcode: 2003niyf.conf....2K
No abstract at ADS
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Title: Search for a chromospheric resonator above sunspots
Authors: Brynildsen, N.; Maltby, P.; Brekke, P.; Redvik, T.;
Kjeldseth-Moe, O.
2003AdSpR..32.1097B Altcode:
We have recently observed thirteen sunspots, both with CDS on SOHO
and TRACE. For each sunspot we investigate the oscillations in the
chromosphere, transition region and corona. Above the umbra the
power spectra show one dominant peak corresponding to a period of 3
minutes. The intensity oscillation amplitude increases with increasing
temperature, reaches a maximum for lines emitting close to 1-2 ×
10 <SUP>5</SUP> K, and decreases for higher temperatures. Part of
the wave energy penetrates into the corona, channeled into small
areas that appear to coincide with the endpoints of sunspot coronal
loops. The observations support the hypothesis that the oscillations
are caused by upwardly propagating acoustic waves and show no signs
of the resonances, equally spaced ≈1 mHz in frequency, predicted by
the chromospheric resonator theories.
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Title: UV spectroscopy with SOHO
Authors: Harra, L. K.; Brekke, P.
2003AdSpR..32..965H Altcode:
The UV spectroscopy from SOHO has provided new and exciting results
from a wide range of phenomena observed on the Sun. Determination of
plasma parameters such as velocity, density, temperatures, line widths
and abundances have provided new physical insight into fundamental
problems in solar physics. These include magnetic reconnection, quiet
Sun coronal heating, active region dynamics, flows in solar flares,
formation of the solar wind, determination of coronal mass ejection
onset, characteristics of coronal waves and the twisting of magnetic
structures. This paper will review these results and discuss what can
be achieved with future spectroscopic instrumentation.
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Title: Sunspot Oscillations and Acoustic Wave Propagation
Authors: Brekke, P.; Brynildsen, N.; Maltby, P.; Fredvik, T.;
Kjeldseth-Moe, O.
2003SPD....34.0401B Altcode: 2003BAAS...35..810B
Observations with the Coronal Diagnostic Spectrometer of 3 min
oscillations in sunspot umbrae support the hypothesis that they are
caused by upwardly propagating acoustic waves. This is evident from
the asymmetry of oscillation amplitudes in the red and blue wings of
spectral lines, where the oscillations are decidedly more pronounced
in the blue than in the red line wing. Additional evidence include the
fact that the relation between oscillations in intensity and velocity
agree with that predicted for an acoustic wave with regard to phase
as well as magnitude. Finally, the observed phase difference between
lines formed at different temperatures points to an upward propagating
disturbance, and the value of dominant frequency of the oscillations,
close to 6 mHz, is above the acoustic cutoff frequency in the sunspot
atmosphere. SOHO is a mission of international cooperation between ESA
and NASA. This study was supported by the Research Council of Norway.
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Title: The 6 mHz Oscillations above Sunspots
Authors: Brekke, P.; Brynildsen, N.; Maltby, P.; Fredvik, T.;
Kjeldseth-Moe, O.
2002AAS...200.8806B Altcode: 2002BAAS...34..790B
Sunspot oscillations in the transition region and corona are observed
simultaneously with CDS on SOHO and TRACE. Results obtained from
investigations of ten sunspots in 2001 and 2002 are presented. We
find that the oscillation amplitude above the umbra increases with
increasing temperature, reaches a maximum for lines emitted close to 200
000 K, and decreases for higher temperatures. Part of the wave energy
penetrates into the corona, channeled into small areas that appear
to coincide with the endpoints of sunspot coronal loops. The observed
power spectra show one dominating peak, near 6 mHz, and not several,
equally spaced resonances as predicted by theories based on the idea
of a chromospheric resonator. We conclude that the observations are
compatible with upwardly propagating acoustic waves.
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Title: Variability and dynamic state of active region loops
Authors: Fredvik, T.; Kjeldseth-Moe, O.; Haugan, S. V. H.; Brekke,
P.; Gurman, J. B.; Wilhelm, K.
2002AdSpR..30..635F Altcode:
A set of 218 consecutive CDS rasters taken at the solar limb on October
26-28 1999 has been used to investigate the variability and plasma
dynamics of active region loops. Each raster contains simultaneous
images in 6 different lines, covering the full temperature range of
CDS, 10 000 K (He I) to 2.7 MK (Fe XVI). Activity is seen to go on
without breaks at temperatures below 1 MK for the full 39 hours of the
series. Transition region loops or extended sections of loops, 50-200
Mm long, appear and disappear in intervals as short as 11 minutes,
the observing cadence. In the corona the emission is less variable,
but significant changes are seen. Measured Doppler shifts correspond
to typical plasma velocities of 20 km s <SUP>-1</SUP> to 100 km
s <SUP>-1</SUP>, at temperatures 10 000 K to 450 000 K, and siphon
flows may occur in some of the loops. High velocities are frequently
seen where the emitted intensities are weak, often on the outer edges
of loops as defined in that particular spectral line. At coronal
temperatures, 1 MK and higher, systematic loop velocities occur only
occasionally. Simultaneous observations with EIT and SUMER were made
during part of the raster series and are compared with the CDS result.
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Title: Space Weather Effects and how Soho has Improved the Warnings
Authors: Brekke, P.
2002stma.conf..385B Altcode:
No abstract at ADS
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Title: Solar eruptions - the effects on the Earth's environment
Authors: Brekke, P.
2002HiA....12..384B Altcode:
The response of our space environment to the constantly changing Sun
is known as "Space Weather". The Solar and Heliospheric Observatory
(SOHO) has obtained significant new information about coronal mass
ejections (CMEs), the source of the most severe disturbances in the
Earth's environment. Most of the time space weather is of little
concern in our everyday lives. However, when the space environment
is disturbed by the variable outputs of the Sun, technologies that
we depend on both in orbit and on the ground can be affected. The
increasing deployment of radiation-, current-, and field-sensitive
technological systems over the last few decades and the increasing
presence of complex systems in space combine to make society more
vulnerable to solar-terrestrial disturbances. Thus, our society is
much more sensitive to space weather activity today compared to the
last solar maximum. By observing the Sun 24 hours per day, SOHO has
proved to be an important "space weather watchdog". The importance of
real-time monitoring of the Sun will be pointed out and a number of
enterprises affected by space weather will be discussed.
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Title: EUV irradiance measurements from SOHO during Cycle 23
Authors: Brekke, P.; Thompson, W.; Pap, J.; McMullin, D.
2002cosp...34E..97B Altcode: 2002cosp.meetE..97B
EUV irradiance variability of the double peak feature of cycle 23 is
presented. EUV irradiance measurements are being made from SOHO on a
regular basis by the Solar Extreme-Ultra-Violet Monitor (SEM) and the
Coronal Diagnostic Spectrometer (CDS). SEM continuously measures the
full solar disk absolute photon flux at the prominent and scientifically
important He II 304 A line, as well as the absolute integral flux
between 1 and 500 A. CDS produces full disk spectra in two bands in
the range 307-380 A and 515-632 A. The "Sun as a Star" spectrum has
been made roughly once a month starting 25 March 1997 to present. As
well as irradiance values, the most recent observations also provide
moderate resolution solar images to help quantify the important sources
of irradiance variability. The EUV irradiance variability is compared
to measurements of total irradiance from VIRGO and other solar cycle
indices such as sunspot number, magnetic field measurements, and the
10.7 radio flux.
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Title: The Sun During The Ulysses Fast Latitude Scan and Northern
Polar Pass As Seen By Soho
Authors: Fleck, B.; Brekke, P.; Haugan, S. V. H.
2002EGSGA..27.3839F Altcode:
In 2001, during the Ulysses fast latitude scan (January - September)
and second north- ern polar pass (September - December), the Sun showed
a remarkable resurgence of solar activity after its rapid drop-off
following the activity maximum in the summer of 2000. In early April
active region 9393, the largest active region of the current cycle,
produced a series of events, among them the biggest X-ray flare on
record. In the fall there were three severe proton storms, one of them
the third largest on record since measurements began in 1976. It is
interesting to note that five out of the eight proton storms with flux
densities greater than 10,000 cm-2 s-1 sr-1 (>10 MeV) since 1976
occurred in cycle 23, and three of these five in 2001. The overall
change in solar ac- tivity in 2001 will be reviewed and some of the
most dramatic events from that year discussed.
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Title: From Solar Min To Solar Max: Half A Solar Cycle of Soho
Observations
Authors: Brekke, P.
2002EGSGA..27.1316B Altcode:
The Solar and Heliospheric Observatory (SOHO) has provided an
unparalleled breadth and depth of information about the Sun, from its
interior, through the hot and dynamic atmosphere, out to the solar
wind. Analysis of the helioseismology data from SOHO has shed new light
on a number of structural and dynamic phenomena in the solar interior,
such as the absence of differential rotation in the radiative zone,
subsur- face zonal and meridional flows, sub-convection-zone mixing,
a possible circumpolar jet, and very slow polar rotation. Evidence for
an upward transfer of magnetic energy from the Sun's surface toward
the corona has been established. The ultraviolet in- struments have
revealed an extremely dynamic solar atmosphere where plasma flows
play an important role. Electrons in coronal holes were found to
be relatively `cool', whereas heavy ions are extremely hot and have
highly anisotropic velocity distribu- tions. The source regions for
the high speed solar wind has been identified and the acceleration
profiles of both the slow and fast solar wind have been measured. This
presentation will summarize some of the findings from the SOHO mission
from the past six years.
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Title: The Solar Inner Corona and Transition Region Observed with SOHO
Authors: Brekke, P.
2002cosp...34E..98B Altcode: 2002cosp.meetE..98B
Recent sophisticated space missions have clearly changed our view
of the solar transition region. In particular the ESA/NASA Solar
and Heliospheric Observatory (SOHO) and NASA's TRACE satellite has
provided a unique opportunity to explore solar atmosphere in detail. The
combination of high spatial, spectral and temporal observations has
made it possible to derive three dimensional images of emission,
velocity and line widths of solar features. Active region loop
structures at transition region temperatures appear to be extremely
time variable and dynamic, a result with profound implications for our
understanding and modeling of the upper solar atmosphere. Large line of
sight Dopplershifts have also been observed in these structures. A 3
minute transition region oscillation has been observed above sunspots
suggesting upward-propagating acoustic waves. Clear evidences of
velocity oscillations in the internetwork regions has also been observed
in both the chromosphere and the transition region. The longstanding
puzzling problem, the apparent net redshift of emission lines in
the transition region has been revisited. The extensive wavelength
coverage of the SOHO spectrometers has made it possible to extend
the measurements to much higher temperatures compared to previous
instruments. The combination of magnetograms, EUV spectral imaging
and the high resolution broad-band images from TRACE has also given us
new insight concerning the structure of the transition region and it's
relation with the photospheric magnetic filed. In this review I will
present some recent results based on SOHO observation with particular
emphasis on the dynamics of active regions loop systems.
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Title: Space Weather Effects on SOHO
Authors: Brekke, P.; Fleck, B.; Haugan, S.; Schweitzer, H.; Chaloupy,
M.
2002cosp...34E2156B Altcode: 2002cosp.meetE2156B
Since its launch on 2 December 1995, the Solar and Heliospheric
Observatory (SOHO) has provided an unparalleled breadth and depth of
information about the Sun, from its interior, through the hot and
dynamic atmosphere, and out to the solar wind. SOHO is in a halo
orbit around L1 Lagrangian point where it views the Sun 24 hours a
day. Thus, it is situated outside the Earth's protective magnetosphere
which shields other satellites from high energy particles from the
Sun. We present a summary of the observed effects on the instruments
and electronics on SOHO throughout the mission. In particular we will
focus on a number of large particle events during the recent years
while the Sun was approaching maximum activity, and how they affected
both the scientific data as well as hardware components.
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Title: Search for a chromospheric resonator above sunspots
Authors: Brynildsen, N.; Maltby, P.; Brekke, P.; Fredvik, T.;
Kjeldseth-Moe, O.
2002cosp...34E.178B Altcode: 2002cosp.meetE.178B
We have recently observed eleven sunspots, both with CDS on SOHO
and TRACE as part of our on-going investigations of the sunspot
atmosphere. For each sunspot we investigate the oscillations in
the chromosphere, transition region and corona. The observed power
spectra show one dominating peak corresponding to a period of 3
minutes. The oscillation amplitude above the umbra increases with
increasing temperature, reaches a maximum for lines emitting close to
200 000 K, and decreases for higher temperatures. Part of the wave
energy penetrates into the corona, channeled into small areas that
appear to coincide with the endpoints of sunspot coronal loops. The
observations support the hypothesis that the oscillations are caused
by upwardly propagating acoustic waves and show no signs of equally
spaced resonances as predicted by theories based on the idea of a
chromospheric resonator.
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Title: The SUMER spectral atlas of solar-disk features
Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi,
B. N.; Schühle, U.; Lemaire, P.
2001AIPC..598...45C Altcode: 2001sgc..conf...45C
A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas
of the Sun between 670 Å and 1609 Å in first order of diffraction
has been derived from observations obtained with the SUMER (Solar
Ultraviolet Measurements of Emitted Radiation) spectrograph on
the spacecraft SOHO (Solar and Heliospheric Observatory) [1]. The
atlas contains spectra of the average quiet Sun, a coronal hole and
a sunspot on disk. Different physical parameters prevalent in the
bright network (BN) and in the cell interior (CI)-contributing in a
distinct manner to the average quiet-Sun emission-have their imprint
on the BN/CI ratio, which is also shown for the entire spectral
range. With a few exceptions, all major lines are given with their
identifications and wavelengths. Lines that appear in second order
are superimposed on the first order spectra, but below 500 Å the
responsivity of the normal-incidence optical system is very low. The
spectra include emissions from atoms and ions in the temperature range
6 10<SUP>3</SUP> K to 2 10<SUP>6</SUP> K, i.e., continua and mission
lines emitted from the lower chromosphere to the corona. This spectral
atlas, with its broad wavelength coverage, provides a rich source
of new diagnostic tools for studying the physical parameters in the
chromosphere, the transition region and the corona. In particular,
the wavelength range below 1100 Å as observed by SUMER represents
a significant improvement over the spectra produced in the past. In
view of the manifold appearance and temporal variation of the solar
atmosphere it is obvious that our atlas can only be a-hopefully
typical-snapshot. The spectral radiances are determined with a
relative uncertainty of 0.15 to 0.30 (1σ), and the wavelength scale
is accurate to typically 10 mÅ, which is the level achievable with
semi-automatic processing. The SUMER solar-disk spectral atlas will
be published in the near future by Curdt et al. [2]. It includes
profiles of the average quiet Sun, an equatorial coronal hole, and
a sunspot. As an example we show in Fig. 1 the spectral range from
1300 Å to 1342 Å with the prominent O I and C II lines. Resolved
emission lines are indicated by a mark, the measured wavelength in
angstrom, and the identification, if available. Marks point to line
lists available in the literature, where additional information about
a specific line can be found [3-7]. New lines or identifications
are indicated. Lines observed in first order and in second-order of
diffraction are distinguished. Only the three least-significant digits
of the wavelength values are given. If available, unidentified lines
are characterized by the temperature classification defined in [3] (a:
T<SUB>e</SUB><3 10<SUP>5</SUP> b: T<SUB>e</SUB>~3 10<SUP>5</SUP> c:
T<SUB>e</SUB>~4 10<SUP>5</SUP> d: 6 10<SUP>5</SUP><T<SUB>e</SUB>
<9 10<SUP>5</SUP> e: T<SUB>e</SUB>~1.4 10<SUP>6</SUP> f:
T<SUB>e</SUB>~1.8 10<SUP>6</SUP>). The vertical axes are scaled
to spectral radiance in units of mW sr<SUP>-1</SUP> m<SUP>-2</SUP>
Å<SUP>-1</SUP> on the left the radiometric calibration for first
order lines is given, on the right for second order lines. Note,
that second order lines are always superimposed on a first order
background. We have taken care of the type of photocathode (bare or KBr)
when applying the radiometric calibration to different sections of the
spectrum. Also displayed in green is the BN/CI ratio in an attempt
to characterize the quiet-Sun chromospheric network structure. A
pre-print of the SUMER spectral atlas and a line list is available at
http://www.linmpi.mpg.de/~curdt. .
---------------------------------------------------------
Title: The SUMER spectral atlas of solar-disk features
Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi,
B. N.; Schühle, U.; Lemaire, P.
2001A&A...375..591C Altcode:
A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas of
the Sun between 670 Å and 1609 Å in the first order of diffraction
has been derived from observations obtained with the SUMER (Solar
Ultraviolet Measurements of Emitted Radiation) spectrograph on the
spacecraft SOHO (Solar and Heliospheric Observatory). The atlas contains
spectra of the average quiet Sun, a coronal hole and a sunspot on the
disk. Different physical parameters prevalent in the bright network (BN)
and in the cell interior (CI) - contributing in a distinct manner to
the average quiet-Sun emission - have their imprint on the BN/CI ratio,
which is also shown for almost the entire spectral range. With a few
exceptions, all major lines are given with their identifications and
wavelengths. Lines that appear in second order are superimposed on the
first order spectra. These lines are clearly marked in the atlas. The
spectra include emissions from atoms and ions in the temperature range
6*E<SUP>3</SUP> K to 2*E<SUP>6</SUP> K, i.e., continua and emission
lines emitted from the lower chromosphere to the corona. This spectral
atlas, with its broad wavelength coverage, provides a rich source of new
diagnostic tools to study the physical parameters in the chromosphere,
the transition region and the corona. In particular, the wavelength
range below 1100 Å as observed by SUMER represents a significant
improvement over the spectra produced in the past. In view of the
manifold appearance and temporal variation of the solar atmosphere,
it is obvious that our atlas can only be a - hopefully typical -
snapshot. Brief descriptions of the data reduction and calibration
procedures are given. The spectral radiances are determined with a
relative uncertainty of 0.15 to 0.30 (1sigma ) and the wavelength
scale is accurate to typically 10 mÅ. The atlas is also available
in a machine readable form. Table A.1 is only available in electronic
form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/375/591
---------------------------------------------------------
Title: VizieR Online Data Catalog: SUMER Spectral Atlas of Solar
Disk Features (Curdt+, 2001)
Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi,
B. N.; Schuhle, U.; Lemaire, P.
2001yCat..33750591C Altcode:
List of spectral lines in the wavelength range from 668Å to 1611Å
identified in SUMER (Solar Ultraviolet Measurements of Emitted
Radiation, spectrograph on the spacecraft SOHO) spectra of the average
quiet Sun (QS), a coronal hole (CH) and a sunspot on disk (SS). Spectral
lines observed in second order of diffraction which are also given
here, extend the lower wavelength limit to below 500Å. For each entry
we give the observed wavelengths in angstrom, the identification,
the transition, the peak of spectral radiance, L<SUP>peak</SUP>, in
mW/(sr*m<SUP>2</SUP>*Å) (incl. background), and a cross-reference
to other line lists available in the literature (cf., Sect. 5.1). For
second-order lines radiance entries are generally not provided, since
the background separation in both orders of diffraction is a non-trivial
task, which can not be automated. Only a few radiance values of strong
second-order lines with negligible first-order contribution are given,
which are marked by an asterisk (*). (1 data file).
---------------------------------------------------------
Title: From solar min to solar max: half a solar cycle of SOHO
observations
Authors: Brekke, P.; Fleck, B.
2001ICRC...27I..21B Altcode:
The Solar and Heliospheric Observatory (SOHO) has provided an
unparalleled breadth and depth of information about the Sun, from its
interior, through the hot and dynamic atmosphere, out to the solar
wind. Analysis of the helioseismology data from SOHO has shed new light
on a number of structural and dynamic phenomena in the solar interior,
such as the absence of differential rotation in the radiative zone,
subsurface zonal and meridional flows, subconvection-zone mixing, a
possible circumpolar jet, and very slow polar rotation. Evidence for
an upward transfer of magnetic energy from the Sun's surface toward the
corona has been established. The ultraviolet instruments have revealed
an extremely dynamic solar atmosphere where plasma flows play an
important role. Electrons in coronal holes were found to be relatively
`cool', whereas heavy ions are extremely hot and have highly anisotropic
velocity distributions. The source regions for the high speed solar
wind has been identified and the acceleration profiles of both the slow
and fast solar wind have been measured. This paper tries to summarize
some of the findings from the SOHO mission from the past five years.
---------------------------------------------------------
Title: Impact of SOHO, TRACE and Yohkoh on Solar Physics (CD-ROM
Directory: contribs/brekke)
Authors: Brekke, P.
2001ASPC..223..311B Altcode: 2001csss...11..311B
No abstract at ADS
---------------------------------------------------------
Title: Recent insights into the physics of the sun and heliosphere
: highlights from SOHO and other space missions : IAU Symposium
203, proceedings of the 24th General Assembly of the IAU held at
Manchester, United Kingdom, 7-11 August 2000
Authors: Brekke, Pål; Fleck, Bernhard; Gurman, Joseph B.
2001IAUS..203.....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transition Region Flows
Authors: Brekke, P.
2000eaa..bookE2266B Altcode:
Ultraviolet emission lines emitted from the SOLAR TRANSITION REGION are
often shifted from their expected rest wavelengths. Shifts of spectral
lines are due to the so-called DOPPLER EFFECT, where the source of
emission is moving either away from or towards the observer, causing
a change in the apparent wavelength. The shifted emission lines are
most often interpreted as a flow of plasma along ...
---------------------------------------------------------
Title: Solar Spectroscopy: Ultraviolet and Extreme Ultraviolet
Emission
Authors: Brekke, P.
2000eaa..bookE2233B Altcode:
Vacuum ultraviolet (VUV) emission is defined as that electromagnetic
radiation with wavelengths shorter than 2000 Å. Its name comes from
the fact that light shorter than 2000 Å is strongly absorbed by most
gases and, in particular, the atmosphere. VUV is usually divided into
far ultraviolet (FUV) extending from 1200 to 2000 Å and the extreme
ultraviolet (EUV) in the range 300 to 1200 Å. The spec...
---------------------------------------------------------
Title: EUV Full-Sun Imaged Spectral Atlas Using the SOHO Coronal
Diagnostic Spectrometer
Authors: Thompson, William T.; Brekke, Pål
2000SoPh..195...45T Altcode:
The Coronal Diagnostic Spectrometer (CDS) aboard the Solar and
Heliospheric Observatory (SOHO) carries out a regular program
of measuring the full-disk irradiance using the Normal Incidence
Spectrograph (NIS). The full-disk solar spectrum is returned in the
wavelength bands 308-379 Å and 513-633 Å, with a spectral resolution
between 0.3 and 0.6 Å. A recent modification to the CDS on-board
software allows simultaneous moderate resolution monochromatic images
to be made of the stronger lines in these wavelength ranges. We report
on observations made 23 April 1998, 21 May 1998, and 22 June 1998. A
total of 69 monochromatic full-Sun images are extracted from the
spectral line data. For the first time, spectrally resolved images
of the full Sun in He ii 303.8 Å and Si xi 303.3 Å are presented
and compared. Velocity maps of the Sun in singly ionized helium are
presented. Correlations of intensity to velocity over a wide range of
transition region and coronal temperatures are shown. Lines from He i to
Fe xiv show statistical red shifts of 1-7 km s<SUP>−1</SUP> between
active regions and quiet Sun areas. Velocity maps of Mg ix and x are
presented, showing strong upflow and downflow regions associated with
active regions, but not correlated with the brightest emission. Changes
in line width are also presented in He i, with discussion of similar
features in other lines of comparable temperature. Corrections which
need to be applied to CDS/NIS data to extract meaningful velocities
and line widths are presented and discussed. The identifications of
the lines in the CDS spectrum are examined. The spatial and spectral
variation of the background component of the CDS spectrum is examined.
---------------------------------------------------------
Title: The Extreme-Ultraviolet Solar Irradiance Spectrum Observed
with the Coronal Diagnostic Spectrometer (CDS) on SOHO
Authors: Brekke, P.; Thompson, W. T.; Woods, T. N.; Eparvier, F. G.
2000ApJ...536..959B Altcode:
We present a calibrated solar EUV irradiance spectrum in the ranges
307-380 Å and 515-632 Å. The “Sun as a star” spectrum was recorded
by the Coronal Diagnostic Spectrometer (CDS) on SOHO on 1997 May
15 using the normal incidence spectrometer (NIS) with a spectral
resolution between 0.3 and 0.6 Å. The relatively high spectral
resolution allows the separation of blends and the differentiation
of weak emission lines. The full-disk spectrum is compared with
simultaneous well-calibrated EUV irradiance measurements from a
NASA/LASP rocket payload to validate the preflight calibration of
CDS. Significant errors in the preflight calibration were found, and
a new calibration has been established for the CDS/NIS system. The
present spectrum includes emission lines formed in the temperature
range 10<SUP>4</SUP> to over 10<SUP>6</SUP> K. Line fluxes for the
most prominent lines are extracted for the calibration and for the
solar irradiance studies. This measurement should represent well solar
minimum conditions as the daily 10.7 cm radio flux was 73 (units of
10<SUP>-22</SUP> W m<SUP>-2</SUP> Hz<SUP>-1</SUP>). A modest spatial
resolution, constrained by the observing mode used, allows for the
discrimination between quiet and active sun. The calibrated quiet-Sun
irradiance spectrum is compared with previous measurements.
---------------------------------------------------------
Title: Observed Variability and Dynamics of Active Region Loops
Authors: Haugan, S. V. H.; Brekke, P.; Fredvik, T.; Kjeldseth-Moe,
O.; Wilhelm, K.; Gurman, J. B.
2000SPD....31.0205H Altcode: 2000BAAS...32..811H
A series of 218 rasters taken with the Coronal Diagnostic Spectrometer
(CDS) on SOHO demonstrates the strong time variability and
dynamical state of the plasma in active region loops at transition
region temperatures, i.e. 10 000 K to 500 000 K, first reported
by Kjeldseth-Moe and Brekke (1998). The continuous raster series,
which covered 39 hours, show how transition region loops or sections
of loops, 50-200 Mm in length, appear and disappear in intervals as
short as 10 minutes, the observing cadence. At the same temperatures
plasma velocities of 20 km s<SUP>-1</SUP> to 100 km s<SUP>-1</SUP>
are indicated from observed Doppler shifts. Siphon flows may occur in
some of the loops, but in other loops patterns are less obvious. High
velocities are frequently seen where the emitted intensities are weak,
often on the “outside” of the loops as defined by the emission in
that particular spectral line. At coronal temperatures the emission
is less time variable, but significant changes are seen. Systematic
loop velocities occur only occasionally in the corona. Simultaneous
observations with EIT and SUMER were made during part of the raster
series and is compared with the CDS result.
---------------------------------------------------------
Title: EUV irradiance variations measured with the SOHO Coronal
Diagnostic Spectrometer
Authors: Brekke, P.; Thompson, W. T.
2000SPD....3102114B Altcode: 2000BAAS...32S.831B
The Coronal Diagnostic Spectrometer aboard the Solar and Heliospheric
Observatory observes the solar EUV spectrum in two bands between
308--379 { Angstroms} and 513--633 { Angstroms}. The full Sun
irradiance can be measured by rastering the instrument over the solar
disk. Measurements of the solar irradiance have been made starting
25 March 1997 and continuing to the present, ranging from very quiet
to very active Sun. These measurements are the only current EUV
spectral irradiance measurements taken on a regular basis. As well as
irradiance values, the most recent observations also provide moderate
resolution solar images to help quantify the important sources of the
irradiance variability. The dependence of individual spectral lines on
the solar cycle is presented, spanning the temperature range from 3 x
10<SUP>4</SUP> K to 2.7 x 10<SUP>6</SUP> K. The important spectral lines
of He II and Si XI at 304 { Angstroms} are observed in second order
and separated. The high spectral resolution of these measurements,
combined with the coverage of a significant proportion of the solar
cycle, provide a unique dataset for understanding solar variability in
the EUV. In addition, these data are important input for interpreting
data from broadband and lower resolution irradiance monitors, such as
the SOHO SEM and TIMED.
---------------------------------------------------------
Title: Four years of SOHO discoveries - some highlights.
Authors: Fleck, B.; Brekke, P.; Haugan, S.; Duarte, L. S.; Domingo,
V.; Gurman, J. B.; Poland, A. I.
2000ESABu.102...68F Altcode:
Analysis of the helioseismic data from SOHO has shed new light on
solar and heliosheric physics: the structure and dynamics of the
solar interior, the heating and dynamics of the solar corona, and the
acceleration and composition of the solar wind.
---------------------------------------------------------
Title: EUV Irradiance Variations Measured with the SOHO Coronal
Diagnostic Spectrometer
Authors: Thompson, W. T.; Brekke, P.
2000ESASP.463..435T Altcode: 2000sctc.proc..435T
No abstract at ADS
---------------------------------------------------------
Title: Signatures of Magnetic Reconnection and Observed EUV Emission
Line Profiles in An Active Region
Authors: Brekke, P.; Brynildsen, N.; Kjeldseth-Moe, O.; Maltby, P.;
Wilhelm, K.
2000AdSpR..26..457B Altcode:
We report on observations with SUMER on SOHO of high-velocity events,
also called explosive events. The high spatial and spectral resolutions
of SUMER allow simultaneous observations of EUV emission lines formed
at different temperatures within the transition region. Complex
line profiles with three separate line components appear to be
a characteristic feature of many high-velocity events based on a
survey of Si IV λ1393 observations. The present study is based on
551 spectra of the active region NOAA 7995 obtained on 17 November
1996. We find that the complex line profiles of explosive events may be
represented by a composite line profile consisting of three Gaussian
line components. Both positive and negative line-of-sight velocities
are found to be significantly larger at 6.3 ×10<SUP>5</SUP> K than
at 1.5 - 1.7 ×10<SUP>5</SUP> K. We briefly confront the observations
with signatures predicted from magnetic reconnections, disturbances
originating in the corona and flows in an extremely structured
transition region
---------------------------------------------------------
Title: Structure and Dynamics in the Atmosphere Above Sunspot Regions
Authors: Brynildsen, N.; Brekke, P.; Haugan, S. V. H.; Kjeldseth-Moe,
O.; Maltby, P.; Wikstøl, Ø.
2000AdSpR..25.1743B Altcode:
Based on simultaneous observations of 10 EUV emission lines with the
Coronal Diagnostic Spectrometer - CDS on the Solar and Heliospheric
Observatory - SOHO we study the spatial distributions of both line
emission and line-of-sight velocity in the atmosphere above 17
sunspots. We find that both the enhanced EUV line emissions and the
velocities are distributed non-uniformly over the sunspot regions. Areas
with enhanced line emission tend to be red shifted, but they seldom
coincide exactly with areas with enhanced velocity. Bright sunspot
plumes with motion directed away from the observer are observed in
most of the sunspot regions
---------------------------------------------------------
Title: Solar Eruptions-the effects on the Earth's environment
Authors: Brekke, P.
2000IAUJD...7E...9B Altcode:
The response of our space environment to the constantly changing Sun
is known as "Space Weather". The Solar and Heliospheric Observatory
(SOHO) has obtained significant new information about coronal mass
ejections (CME's), the source to the most severe disturbances in
the Earth's environment. Most of the time space weather is of little
concern in our everyday lives. However, when the space environment
is disturbed by the variable outputs of the Sun, technologies that
we depend on both in orbit and on the ground can be affected. The
increasing deployment of radiation-, current-, and field-sensitive
technological systems over the last few decades and the increasing
presence of complex systems in space combine to make society more
vulnerable to solar-terrestrial disturbances. Thus, our society is
much more sensitive to space weather activity today compared to the
last solar maximum. By observing the Sun 24 hours per day SOHO has
proved to be an important “space weather watchdog”. The importance
of real-time monitoring of the Sun will be pointed out and a number
of enterprises affected by space weather will be discussed.
---------------------------------------------------------
Title: Observations of Transition Region Plasma
Authors: Brekke, Pâl
1999SoPh..190..379B Altcode:
Recent space missions have changed our view of the solar transition
region. In particular the ESA/NASA Solar and Heliospheric Observatory
(SOHO) and NASA's TRACE satellite have provided a unique opportunity
to explore the solar atmosphere in detail. The combination of high
spatial, spectral and temporal observations has made it possible to
derive three dimensional images of the emission and velocity structures
of solar features. Active region loop structures at transition region
temperatures appear to be extremely time variable and dynamic, a result
with profound implications for our understanding and modeling of the
upper solar atmosphere. Large Dopplershifts have also been observed
in these structures. A 3-minute transition region oscillation has
been observed above sunspots suggesting upward-propagating acoustic
waves. Clear evidence of velocity oscillations in the internetwork
regions has also been observed in both the chromosphere and the
transition region. The longstanding and puzzling problem of the
apparent net red shift of emission lines from the transition region
has been revisited. The extensive wavelength coverage of the SOHO
spectrometers has made it possible to extend the measurements to much
higher temperatures compared to previous instruments. The combination
of magnetograms, EUV spectral imaging and the high resolution broad-band
images from TRACE has also given us new insight concerning the structure
of the transition region and its relation with the photospheric
magnetic field.
---------------------------------------------------------
Title: The SUMER EUV Atlas in the Spectral Range 670 A - 1498 A
Authors: Curdt, W.; Brekke, P.; Schühle, U.; Wilhelm, K.; Dwivedi,
B. N.
1999ESASP.446..251C Altcode: 1999soho....8..251C
An extreme ultraviolet spectral atlas between 660 and 1600 A (first
order) of a quiet Sun, a coronal hole, and a Sun spot region has
been derived from observations with the SUMER (Solar Ultraviolet
Measurements of Emitted Radiation) instrument on SOHO. More than 1000
emission lines are given with the best available identification. The
spectra are radiometrically calibrated. Lines in second order are
superimposed on this spectrum. The spectral scans include emissions
from atoms and ions in the temperature range from 6 000 to 2000 000 K,
i.e., continua and emission lines emitted from the lower chromosphere
to the corona. This broad wavelength coverage provides an important
new diagnostic tool for studying the essential physical parameters
throughout the upper solar atmosphere. In particular, the wavelength
range shortward of 1100 A as observed by SUMER represents a significant
improvement over the spectra produced in the past. A brief description
of the data reduction and calibration procedures is given. The absolute
intensities are determined with an uncertainty of better than +- 15%
in most of the range presented, and the wavelength scale is accurate
to better than 0.01 A. The atlas will also be available in machine
readable form.
---------------------------------------------------------
Title: The Time Variable Solar Atmosphere - Dynamical and Variable
Active Region Loops Observed with CDS on SOHO.
Authors: Kjeldseth-Moe, O.; Brekke, P.
1999ASPC..184..286K Altcode:
The Coronal Diagnostic Spectrometer, CDS, on SOHO has detected an
upper solar atmosphere that is much more dynamic and time variable than
previously expected. Loops in active regions, particularly in emission
lines formed at temperatures 10<SUP>5</SUP> K to 1 MK, traditionally
thought of as the transition region, are seen to change significantly
over an hour. Loops appear or disappear, the emission along their
length change, or they change shape or expand outward, all on time
scales of 10-20 minutes. The structural variability is accompanied by
high Doppler shifts, especially in the 2-5x10<SUP>5</SUP> K temperature
range. Velocities corresponding to the shifts typically amount to +/-
50-100 km<SUP>-1</SUP>. We find that existing theoretical models for
loops cannot explain the observations. However, models with extreme
fine structure, combined with episodic heating and magneto-acoustic
wave disturbances propagating in the loop legs seem promising. The
rapidly changing conditions that we observe give a new conception of
loop systems that has never before been seriously considered.
---------------------------------------------------------
Title: EUV Observations of Sunspot Regions with CDS on SOHO
Authors: Brynildsen, N.; Brekke, P.; Haugan, S. V. H.; Kjeldseth-Moe,
O.; Maltby, P.
1999ASPC..184..266B Altcode:
The spatial distributions of line emission and line-of-sight velocity in
seventeen different sunspot regions are studied, based on observations
with the Coronal Diagnostic Spectrometer - CDS on SOHO. Ten EUV emission
lines, formed in the chromosphere, transition region, and corona are
observed. Enhanced EUV line emissions in the transition region are
distributed non-uniformly over the active regions and are located both
inside and outside sunspots. Most sunspot regions show strongly enhanced
transition region line emission above the spot, i.e. sunspot plumes
are reinvented. From wavelength shifts we derive the line-of-sight
velocity, relative to the average velocity in the rastered area, 120"
x 120". In sunspot plumes we find that the motion is directed away from
the observer and increases with increasing line formation temperature,
T, reaches a maximum up to 40 km s<SUP>-1</SUP> close to log T ≅ 5.5,
then decreases abruptly. The spatial extent of both emission features
and flow regions increase with increasing temperature within the
transition region. The observations show a marked difference between
the transition region and the low corona, both regarding the spatial
distributions of line emission and line-of-sight velocity.
---------------------------------------------------------
Title: A Transition Region Eruption Observed with CDS, TRACE and EIT
Authors: Brekke, P.; Kjeldseth-Moe, O.; Fredvik, T.; Haugan, S. V. H.;
Tarbell, T. D.; Gurman, J. B.
1999AAS...194.5905B Altcode: 1999BAAS...31..918B
An ejection of plasma on the west limb has been observed with CDS,
TRACE and EIT on 19 May 1998. The start of the eruption coincided
with a weak flare observed with GOES. Erupting material rose to 120
Mm above the solar surface in 17 min, and then fell back to the solar
surface. Vertical velocities of 200 km s(-1) are estimated from a series
of TRACE images in the C(+3) resonance lines at 155 nm and from EIT
images in the 19.5 nm band, while Doppler shifts of the transition
region lines observed with CDS yield maximum horizontal velocities
of 300 km s(-1) at the top of the plasma trajectories. The similar
appearance and time variation of the eruption as seen with all three
instruments indicate the presence of a multi-temperature plasma in
spatial regions less than 1-2 arc seconds, with temperatures ranging
from 10(5) K to 1.5 MK. The material did not have the momentum to break
loose from the Sun and was not associated with any CME observed with
LASCO. However, we may speculate that CMEs are similar to the eruption
observed, with even higher speeds involved.
---------------------------------------------------------
Title: Time Variation of Active Region Loops Observed with CDS on SOHO
Authors: Fredvik, T.; Kjeldseth-Moe, O.; Brekke, P.; Haugan, S. V. H.
1999AAS...194.5904F Altcode: 1999BAAS...31R.918F
The emission from plasma filled loops, 10(4) K < T <1.5 MK,
above active regions are much more time variable than previously
considered. These loops, which define the solar atmosphere above active
regions in this temperature range, appear or disappear, the emission
along their length change, or they change shape or expand outward,
all on time scales of 10-20 minutes. In this paper we report on an
investigation with CDS on SOHO of 20 loop systems observed on the solar
limb between September 1997 and May 1998. We describe the apparent
isothermal appearance of many loops and discuss to what extent loops
radiating in different emission lines, i.e. at different temperatures,
are co-located within their recorded widths. Finally, we demonstrate
the time variability of loop systems at different temperatures, and
show how the rapidly changing conditions require a new conception of
loop systems that has never before been seriously considered.
---------------------------------------------------------
Title: Multi-wavelength observations of the onset phase of a coronal
mass ejection
Authors: Innes, D. E.; Inhester, B.; Srivastava, N.; Brekke, P.;
Harrison, R. A.; Matthews, S. A.; Noëns, J. C.; Schmieder, B.;
Thompson, B. J.
1999SoPh..186..337I Altcode:
The structure and dynamics of the initial phases of a coronal mass
ejection (CME) seen in soft X-ray, extreme ultraviolet and optical
emission are described. The event occurred on the SW limb of the Sun in
active region AR 8026 on 9 April 1997. Just prior to the CME there was
a class C1.5 flare. Images taken with the Extreme Ultraviolet Imaging
Telescope (EIT) reveal the emergence of a candle-flame shaped extreme
ultraviolet (EUV) cavity at the time of the flare. Yohkoh images,
taken about 15 min later, show that this cavity is filled with hot
X-ray emitting gas. It is most likely that this is the site of the
flare. Almost simultaneous to the flare, an Hα surge or small filament
eruption occurs about 50 arc sec northwards along the limb from the EUV
cavity. At both the site of the core of the hot, EUV cavity and the
filament ejection are X-ray jets. These jets seem to be connected by
hot loops near their bases. Both jets disappear within a few minutes
of one another.
---------------------------------------------------------
Title: SOHO Observations of the Structure and Dynamics of Sunspot
Region Atmospheres
Authors: Brynildsen, N.; Maltby, P.; Brekke, P.; Haugan, S. V. H.;
Kjeldseth-Moe, O.
1999SoPh..186..141B Altcode:
We present results from a study of the spatial distributions of line
emission and relative line-of-sight velocity in the atmosphere above
17 sunspot regions, from the chromosphere, through the transition
region and into the corona, based on simultaneous observations of ten
EUV emission lines with the Coronal Diagnostic Spectrometer - CDS on
SOHO. We find that the spatial distributions are nonuniform over the
sunspot region and introduce the notation 'sunspot loop' to describe an
enhanced transition region emission feature that looks like a magnetic
loop, extending from inside the sunspot to the surrounding regions. We
find little evidence for the siphon flow. Attention is given to the time
variations since we observe both a rapid variation with a characteristic
time of a few to several minutes and a slow variation with a time
constant of several hours to ≈ 1 day. The most prominent features
in the transition region intensity maps are the sunspot plumes. We
introduce an updated criterion for the presence of plumes and find
that 15 out of 17 sunspots contain a plume in the temperature range
logT≈5.2-5.6. The relative line-of-sight velocity in sunspot plumes
is high and directed into the Sun in the transition region. Almost
all the sunspot regions contain one or a few prominent, strongly
redshifted velocity channels, several of the channels extend from the
sunspot plume to considerable distances from the sunspot. The flow
appears to be maintained by plasmas at transition region temperatures,
moving from regions located at a greater height outside the sunspots
and towards the sunspot. The spatial correlation is high to moderate
between emission lines formed in the transition region lines, but
low between the transition region lines and the coronal lines. From
detailed comparisons of intensity and velocity maps we find transition
region emission features without any sign of coronal emission in the
vicinity. A possible explanation is that the emission originates in
magnetic flux tubes that are too cold to emit coronal emission. The
comparisons suggest that gas at transition region temperature occur in
loops different from loops with coronal temperature. However, we cannot
exclude the presence of transition region temperatures close to the
footpoints of flux tubes emitting at coronal temperatures. Regions with
enhanced transition region line emission tend to be redshifted, but the
correlation between line emission and relative line-of-sight velocity
is weak. We extend our conditional probability studies and confirm
that there is a tendency for line profiles with large intensities and
red shifts (blue shifts) above the average to constitute an increasing
(decreasing) fraction of the profiles as the wavelength shift increases.
---------------------------------------------------------
Title: EUV Full Sun Imaged Spectral Atlas Using the SOHO Coronal
Diagnostic Spectrometer
Authors: Thompson, W. T.; Brekke, P.
1999AAS...194.1607T Altcode: 1999BAAS...31R.850T
The Coronal Diagnostic Spectrometer (CDS) aboard the Solar and
Heliospheric Observatory (SOHO) carries out a regular program
of measuring the full-disk irradiance using the Normal Incidence
Spectrograph (NIS). The full-disk solar spectrum is returned in
the wavelength bands 308-379 { Angstroms} and 513-633 { Angstroms},
with a spectral resolution between 0.3 and 0.6 { Angstroms}. A recent
modification to the CDS on-board software allows simultaneous moderate
resolution monochromatic images to be made of the stronger lines in
these wavelength ranges. We report on observations made 23 April
1998, 21 May 1998, and 22 June 1998. A total of 69 monochromatic
full-sun images are extracted from the spectral line data. For the
first time, spectrally resolved images of the full Sun in He II
303.8 { Angstroms} and Si XI 303.3 { Angstroms} are presented and
compared. Velocity maps of the Sun in neutral and singly ionized helium
are presented. Correlations of intensity to velocity over a wide range
of transition region and coronal temperatures are shown. Velocity maps
of Mg IX and X are presented.
---------------------------------------------------------
Title: Solar Wind Outflow and the Chromospheric Magnetic Network
Authors: Hassler, Donald M.; Dammasch, Ingolf E.; Lemaire, Philippe;
Brekke, Pal; Curdt, Werner; Mason, Helen E.; Vial, Jean-Claude;
Wilhelm, Klaus
1999Sci...283..810H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An eruption in the transition region observed with CDS and
TRACE, on May 19, 1998.
Authors: Brekke, P.; Kjeldseth-Moe, O.; Tarbell, T.
1999joso.proc..170B Altcode:
The authors present simultaneous CDS and TRACE observations in the EUV
of an eruption of May 19, 1998. A large ejection of plasma was seen
on the west limb and could be followed in EUV rasters in transition
region lines with CDS and in high cadence images in the C<SUP>+3</SUP>
155 nm line from TRACE. The onset of the eruption coincided with a
weak flare observed with GOES. The eruption extended to 120000 km
above the solar surface after 17 min and then fell back to the solar
surface. At the leading edge of the eruption CDS observed Doppler
shifts of 300 km s<SUP>-1</SUP> away from the observer (i.e. parallel
to the solar surface) in the O<SUP>+4</SUP> line at 62.9 nm. High
cadence observations with TRACE indicate that the plasma velocities
perpendicular to the line of sight (i.e. along the solar vertical)
reached similar values, i.e. 200 km s<SUP>-1</SUP>. Perhaps this was a
"coronal mass ejection" that did not make it?
---------------------------------------------------------
Title: Jets and Eruptions in the Transition Region Observed with CDS,
EIT and TRACE
Authors: Brekke, P.; Kjeldseth-Moe, O.; Tarbell, T.; Gurman, J.
1999ASPC..183..357B Altcode: 1999hrsp.conf..357B
No abstract at ADS
---------------------------------------------------------
Title: The evolution of solar bipolar jets observed in the UV by
SUMER on SOHO.
Authors: Mendoza-Torres, J. E.; Wilhelm, K.; Innes, D. E.; Curd, W.;
Kliem, B.; Brekke, P.
1998larm.confE..17M Altcode:
Observations of bipolar jets made in the UV by SUMER onboard SOHO
are presented. The observations were carried out in the interval
74.9-79.0 nm which contains some chromospheric and transition region
lines. The theory predicts that under the conditions of the solar
chromosphere the reconnection of magnetic lines accelerates plasma
into two oppositely directed jets. In the chromosphere, as well as in
other solar layers, different phenomena, where plasma acceleration
take place, are observed. Of them the UV jets, observed by SUMER,
represent one of the most clear evidences of the link between magnetic
reconnection and plasma acceleration. The jets are clearly revealed
by a considerably intensity increase and large doppler shifts of the
line wings. It should be noted that the enhancement of only one wing
also occurs and that the central component of the line also undergoes
velocity shifts and amplitude enhancement. The behavior of the wings
found in this work is consistent with results obtained for other events
(Innes et al. 1997) namely: 1)The wings are observed during few minutes
2) The doppler velocities of the line wings (red and blue) are similar
to each other and typical values are of the order of 100 km/sec, 3) In
general, the blue component is more long-lived than the red one, 4)the
red component is, in general, more intense than the blue one. In this
work, an analysis of the velocities of the three spectral components
(the central and the wings) as a function of the location on the slit,
used for the observations, is also done. The ratios of two OV (density
sensitive) and two OIV (temperature sensitive) lines, whose wavelengths
are in the observed range, are also analyzed. An important result is
that these parameters show gradients along the slit. An analysis of
the spatial distributions and the correlations between them is done. A
discussion of these results, in relation with the appearance and the
evolution of the jets, will be done.
---------------------------------------------------------
Title: Time Variability of Active Region Loops Observed with the
Coronal Diagnostic Spectrometer (Cds) on SOHO
Authors: Kjeldseth-Moe, O.; Brekke, P.
1998SoPh..182...73K Altcode:
Monochromatic images from the Coronal Diagnostic Spectrometer (CDS)
of loops above active regions show clear evidence of rapid time
variability. The rapidly changing conditions that we observe give a
new conception of loop systems that has never before been seriously
considered. Loop systems, particularly in emission lines formed at
temperatures in the 1-5 × 10<SUP>5</SUP> K range, traditionally thought
of as transition region temperatures, are seen to change significantly
over a period of 1 hour. Loops may appear or disappear in certain
emission lines, may show rapid variations in the distribution of the
emission along their lengths, or may change shape or expand outward,
all on time scales of 10-20 min. At other temperatures below 1.5 MK
the variability appears less striking, but is still pronounced. At
high temperatures, i.e., T ≥ 1.5 MK, conditions are normally much
more stable. Examples exist, however, of loop systems showing violent
changes in images at all temperatures up to Fe xvi formed at 2.7
MK. The structural variability is accompanied by high Doppler shifts,
especially in the O v line. Corresponding velocities typically amount to
50-100 km s<SUP>-1</SUP>, but values as high as 300 km s<SUP>-1</SUP>
have been recorded. Animations with illustrative examples of loop
variability have been prepared and are found on the enclosed CD-ROM. In
addition we briefly discuss other structural and dynamical properties
of active region loops, particularly those with temperatures below 1.5
MK. Theoretical models of loops cannot explain the present observations,
but models that combine extreme fine structure, episodic heating and
magneto-acoustic wave disturbances propagating in the loop legs seem
promissing.
---------------------------------------------------------
Title: Flows in Sunspot Plumes Detected with SOHO
Authors: Brynildsen, N.; Maltby, P.; Brekke, P.; Fredvik, T.; Haugan,
S. V. H.; Kjeldseth-Moe, O.; Wikstol, O.
1998ApJ...504L.135B Altcode: 1998astro.ph..5249B
In the Letter, “Flows in Sunspot Plumes Detected with the Solar and
Heliospheric Observatory” by N. Brynildsen, P. Maltby, P. Brekke,
T. Fredvik, S. V. H. Haugan, O. Kjeldseth-Moe, and Ø. Wikstøl (ApJ,
502, L85 [1998]), the following correction should be made: <P />In
the last line on page L86, which reads “peak line intensity I>=5
are located (1) above the umbra or, ” an “Ī” should be inserted so
that the revised line reads “peak line intensity I>=5Ī are located
(1) above the umbra or.”
---------------------------------------------------------
Title: Flows in Sunspot Plumes Detected with the Solar and
Heliospheric Observatory
Authors: Brynildsen, N.; Maltby, P.; Brekke, P.; Fredvik, T.; Haugan,
S. V. H.; Kjeldseth-Moe, O.; Wikstøl, Ø.
1998ApJ...502L..85B Altcode:
Bright extreme-UV sunspot plumes have been observed in eight out of
11 different sunspot regions with the Coronal Diagnostic Spectrometer
on Solar and Heliospheric Observatory. From wavelength shifts, we
derive the line-of-sight velocity relative to the average velocity
in the rastered area, 120<SUP>”</SUP>×120<SUP>”</SUP>. In sunspot
plumes, we find that the motion is directed away from the observer
and increases with increasing line formation temperature, reaches a
maximum between 15 and 41 km s<SUP>-1</SUP> close to log logT~5.5,
then decreases abruptly. The flow field in the corona is not well
correlated with the flow in the transition region, and we discuss
briefly the implication of this finding.
---------------------------------------------------------
Title: SOHO Observations of the Connection Between Line Profile
Parameters in Active and Quiet Regions and the Net Red Shift in EUV
Emission Lines
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Wilhelm, K.
1998SoPh..181...23B Altcode:
We present high spatial and spectral resolution observations of
one active and one quiet-Sun region, obtained with CDS and SUMER on
SOHO. The connections between the line profile parameters are studied
and a systematic wavelength shift towards the red with increasing peak
line intensity (line broadening) is detected. The large scatter in
the data calls for another approach. We apply conditional probability
analysis to a series of EUV emission lines and find significant
correlations between line profile parameters. For a given interval in
wavelength shift we find that: (1) line profiles with large intensities
(line widths) and red shifts above the average constitute an increasing
fraction of the profiles as the relative wavelength shift increases,
(2) line profiles with large intensities (line widths) and blue
shifts compared to the average, on the other hand, constitute a
decreasing fraction of the profiles as the relative wavelength shift
increases. These results extend the findings of an earlier quiet-Sun
study from one to several emission lines and expand the validity to
include the active region. Interestingly, the active region observations
show correlations between peak line intensity and wavelength shift in
the coronal lines.
---------------------------------------------------------
Title: EUV Spectroscopy of the Sunspot Region NOAA 7981 Using SOHO -
II. Velocities and Line Profiles
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele,
T.; Thompson, W. T.; Wilhelm, K.
1998SoPh..179..279B Altcode:
We have studied the dynamics in the sunspot transition region between
the chromosphere and the corona and investigated the extension of
the flow field into the corona. Based on EUV spectra of a medium size
sunspot and its surroundings, NOAA 7981, observed with CDS and SUMER
on SOHO, we derive line-of-sight velocities and study the line profiles
for a series of emission lines.
---------------------------------------------------------
Title: Extreme-Ultraviolet Sunspot Plumes Observed with SOHO
Authors: Maltby, P.; Brynildsen, N.; Brekke, P.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Wikstøl, Ø.; Rimmele, T.
1998ApJ...496L.117M Altcode: 1998astro.ph..1144M
Bright EUV sunspot plumes have been observed in five out of nine sunspot
regions with the Coronal Diagnostic Spectrometer on the Solar and
Heliospheric Observatory. In the other four regions, the brightest line
emissions may appear inside the sunspot but are mainly concentrated in
small regions outside the sunspot areas. These results are in contrast
to those obtained during the Solar Maximum Mission but are compatible
with the Skylab mission results. The present observations show that
sunspot plumes are formed in the upper part of the transition region,
occur in both magnetic unipolar and bipolar regions, and may extend
from the umbra into the penumbra.
---------------------------------------------------------
Title: EUV Spectroscopy of the Sunspot Region NOAA 7981 Using SOHO -
I. Line Emission and Time Dependence
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele,
T.; Thompson, W. T.; Wilhelm, K.
1998SoPh..179...43B Altcode:
EUV spectra of a medium-size sunspot and its surroundings, NOAA 7981,
were obtained on 2 August 1996 with the Coronal Diagnostic Spectrometer
(CDS) and the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) on the Solar and Heliospheric Observatory (SOHO). The spectral
lines formed in the transition region and corona show considerable
structure and large deviations from a uniform spatial distribution over
the active region. Enhanced EUV emissions in transition region lines
are concentrated in small regions outside the umbra of the sunspot
throughout most of the observing sequence. Only during a short,
active period do we find an enhanced line emission that reaches into
the umbra. Preliminary values for the umbral intensity are given.
---------------------------------------------------------
Title: Plasma jets in the solar atmosphere observed in EUV emission
lines by SUMER on SOHO
Authors: Wilhelm, K.; Innes, E. E.; Curdt, W.; Kliem, B.; Brekke, P.
1998ESASP.421..103W Altcode: 1998sjcp.conf..103W
No abstract at ADS
---------------------------------------------------------
Title: Three Dimensional EUV Imaging of Sunspot Regions Observed
with SOHO
Authors: Brynildsen, N.; Brekke, P.; Haugan, S. V. H.; Kjeldseth-Moe,
O.; Maltby, P.; Harrison, R. A.; Rimmele, T.; Wilhelm, K.
1998ASPC..155..171B Altcode: 1998sasp.conf..171B
No abstract at ADS
---------------------------------------------------------
Title: Active Region Structures and Dynamics in the Transition Region
and Corona (Invited review)
Authors: Brekke, P.
1998ASPC..155..150B Altcode: 1998sasp.conf..150B
No abstract at ADS
---------------------------------------------------------
Title: Inconstancy of the Transition Region - Variable and Dynamic
Active Region Loops
Authors: Kjeldseth-Moe, O.; Brekke, P.; Haugan, S. V. H.
1998ESASP.417..153K Altcode: 1998cesh.conf..153K
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric and Photospheric Activity of the Sun as a Star
Using SOLSTICE Data
Authors: Catalano, S.; Lanza, A. F.; Brekke, P.; Rottman, Gary J.;
Hoyng, P.
1998ASPC..154..584C Altcode: 1998csss...10..584C
The distribution of photospheric and chromospheric active regions
(spots and plages) on the surface of stars is mainly recovered from
the deconvolution of light or line flux curves. Here we check the
reliability of the maximum entropy technique to derive surface maps from
the rotational modulation of the continuum and line fluxes observed
in active stars. We compare the solar chromospheric map obtained from
the deconvolution of daily average of the C 2 line flux at 133.5 nm
measured by SOLSTICE, and solar Hα images contemporaneously obtained
at Catania observatory. Hα plages may not exactly overlay C 2 plages,
however the agreement between the reconstructed and the direct images
is strikingly good. Only small (<20<SUP>circ</SUP>-30<SUP>circ</SUP>
in diameter) or low contrast (Delta I/I < 0.3) structures are not
recovered. We use also the Wolf sunspot number to study the longitude
distribution of the active regions in photosphere and chromosphere,
contrasting the solar behaviour with that of other active stars.
---------------------------------------------------------
Title: Velocity Fields of a Filament Region Observed with Ground-Based
Telescopes and from SOHO
Authors: Mein, P.; Schmieder, B.; Malherbe, J. -M.; Wiik, J. E.;
Engvold, O.; Brekke, P.; Zirker, J. B.; Poland, A. I.; Delaboudiniere,
J. -P.; Staiger, J.
1998ASPC..150..135M Altcode: 1998npsp.conf..135M; 1998IAUCo.167..135M
No abstract at ADS
---------------------------------------------------------
Title: Active Regions Observed in Extreme Ultraviolet Light by the
Coronal Diagnostic Spectrometer on SOHO
Authors: Fludra, A.; Brekke, P.; Harrison, R. A.; Mason, H. E.; Pike,
C. D.; Thompson, W. T.; Young, P. R.
1997SoPh..175..487F Altcode:
We present observations of five active regions made by the Coronal
Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory
(SOHO). CDS observes the Sun in the extreme ultraviolet range 150-780
Å. Examples of active region loops seen in spectral lines emitted at
various temperatures are shown. Several classes of loops are identified:
those that are seen in all temperatures up to 2 x 10<SUP>6</SUP> K;
loops seen at 10<SUP>6</SUP> K but not reaching 1.6 x 10<SUP>6</SUP>
K; those at temperatures 2- 4 x 10<SUP>-5</SUP> K and occasionally at
6 x 10<SUP>-5</SUP> K but not reaching 10<SUP>6</SUP> K. An increasing
loop size with temperature and the relationship between the cool and
hot structures is discussed. CDS observations reveal the existence of
loops and other unresolved structures in active regions, at temperatures
between 1.5- 4 x 10<SUP>-5</SUP> K, which do not have counterparts in
lines emitted above 8 x 10<SUP>-5</SUP> K. Bright compact sources only
seen in the transition region lines are investigated. These sources can
have lifetimes of up to several days and are located in the vicinity
of sunspots. We study the variability of active region sources on time
scales from 30 sec to several days. We find oscillatory behaviour of Hei
and Ov line intensities in an active region on time scales of 5-10 min.
---------------------------------------------------------
Title: Doppler Shifts in the Quiet-Sun Transition Region and Corona
Observed with SUMER on SOHO
Authors: Brekke, P.; Hassler, D. M.; Wilhelm, K.
1997SoPh..175..349B Altcode:
New observations of systematic red shifts of transition region and
coronal lines obtained with SUMER (Solar Ultraviolet Measurements of
Emitted Radiation) on SOHO (the Solar and Heliospheric Observatory)
are presented. With the extensive wavelength coverage of SUMER it is
possible to extend the measurements of the red shifts to much higher
temperatures compared to previous instruments. We find lines formed in
the upper transition region (e.g. Ov, Sv, and Svi) to be red-shifted
similar to lower temperature lines (T ≤ 1.8 x 10<SUP>-5</SUP>
K). Even hotter lines such as Ovi, Neviii and Mgx show systematic red
shifts on the order of 5 km s<SUP>-1</SUP> in the quiet Sun. This is
a new and significant result since previous measurements of the red
shifts were less well constrained.
---------------------------------------------------------
Title: High-Velocity Flows in an Active Region Loop System Observed
with the Coronal Diagnostic Spectrometer (Cds) on SOHO
Authors: Brekke, P.; Kjeldseth-Moe, O.; Harrison, R. A.
1997SoPh..175..511B Altcode:
EUV spectra of coronal loops above an active region show clear evidence
of strong dynamical activity. We present an example where the Ov
629 Å line, formed at 240 000 K, is shifted from its reference
position corresponding to line-of-sight velocities greater than 50
km s<SUP>-1</SUP> with the shift extending over a large fraction
of a loop. The observations were made with the Coronal Diagnostic
Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO),
and are from active region NOAA 7981 on the east solar limb on 27
July 1996. An animation has been prepared showing the variation of the
shift or flow velocity along the loop. This animation is to be found
on the enclosed CD-ROM and gives a clear impression of the dynamical
condition present in the loop. The appearance of the loop system in
different lines formed over a range in temperature as well as the
observed dynamics indicates that loops at different temperatures are
not closely co-located. Finally, the results are discussed and related
to mechanisms that may cause line shifts.
---------------------------------------------------------
Title: Bursts of Explosive Events in the Solar Network
Authors: Innes, D. E.; Brekke, P.; Germerott, D.; Wilhelm, K.
1997SoPh..175..341I Altcode:
Observations of the quiet-Sun network in the UV emission line Siiv 1393
Å over a time period of two hours are presented. Bursts of explosive
events, highly Doppler-shifted emission, seem to be sporadically emitted
from the brighter regions of the network lanes. Individual events have
typical lifetimes of ≈ 1-6 min and come in bursts of up to 30 min. The
most spectacular burst in this dataset, shown in the accompanying movie,
lasts ≈ 30 min and shows a wide variety of line profiles with both
red and blue shifts ≈180 km s<SUP>1</SUP>. There appears to be no
characteristic form or evolutionary pattern to the line profiles in
either the individual events or series of events. There are about
twice as many blue shifts as red shifts.
---------------------------------------------------------
Title: Eruptive prominence and associated CME observed with SUMER,
CDS and LASCO (SOHO)
Authors: Wiik, J. E.; Schmieder, B.; Kucera, T.; Poland, A.; Brekke,
P.; Simnett, G.
1997SoPh..175..411W Altcode:
Observations of an eruptive prominence were obtained on 1 May 1996,
with the SUMER and CDS instruments aboard SOHO during the preparatory
phase of the Joint Observing Programme JOP12. A coronal mass ejection
observed with LASCO is associated temporally and spatially with this
prominence. The main objective of JOP12 is to study the dynamics of
prominences and the prominence-corona interface. By analysing the
spectra of Oiv and Siiv lines observed with SUMER and the spectra of
15 lines with CDS, Doppler shifts, temperatures and electron densities
(ratio of Oiv 1401 to 1399Å) were derived in different structures of
the prominence. The eruptive part of the prominence consists of a bubble
(plasmoid) of material already at transition region temperatures with
red shifts up to 100 km s<SUP>-1</SUP> and an electron density of the
order of 10<SUP>10</SUP>cm<SUP>-3</SUP>. The whole prominence was very
active. It developed both a large helical loop and several smaller loops
consisting of twisted threads or multiple ropes. These may be studied
in the SUMER movie (movie 2). The profiles of the SUMER lines show a
large dispersion of velocities (±50 km s<SUP>-1</SUP>) and the ratio
of the Oiv lines indicates a large dispersion in electron density (3 x
10<SUP>9</SUP>cm<SUP>-3</SUP> to 3x 10<SUP>11</SUP>cm<SUP>-3</SUP>). The
CME observed by LASCO left the corona some tens of minutes before the
prominence erupted. This is evidence that the prominence eruptions are
probably the result of the removal of the restraining coronal magnetic
fields which are in part responsible for the original stability of
the prominence.
---------------------------------------------------------
Title: Initial Comparison of MDI Photospheric Magnetic Movies and
CDS Transition Region Movies in Quiet Sun
Authors: Tarbell, T.; Brekke, P.; Fludra, A.; Deforest, C.; Saba,
J.; Covington, J.
1997SPD....28.0111T Altcode: 1997BAAS...29..881T
We present simultaneous, coaligned movies of photospheric magnetic
fields and transition region (TR) intensities in very quiet sun near
disk center obtained by SOHO in January, 1997. For example, the 22 Jan
1997 CDS movies show He I 584 (2x10(4) K) and O V 630 (2.4 x 10(5) K)
from 16:51 to 19:54 UT, with a 310 x 240 arcsecond field of view, 105
second cadence, and 1.7 arcsecond pixels. MDI photospheric longitudinal
magnetograms, with 60 second cadence and 0.6 arcsecond pixels, have been
coaligned with these. Bright TR emission correlates more strongly with
close bipoles in the photospheric magnetic field than with magnetic
flux alone. Some strong photospheric flux tubes are barely visible
in the TR emission, appearing only occasionally in connections with
nearby weak opposite polarity fields. Bright transient emissions in
the TR are located at places of cancelling opposite polarities in
photospheric magnetic fields. The flux cancellation continues for tens
of minutes or hours in the magnetic movies. Searches for more rapid
magnetic counterparts to these TR transients and for emerging magnetic
flux regions in the movies are under way. This work was supported by
NASA grant NAG5-3077 at Stanford and Lockheed Martin.
---------------------------------------------------------
Title: The Non-Uniformity in the Sunspot Transition Region
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Rimmele, T.;
Wilhelm, K.
1997ESASP.404..257B Altcode: 1997cswn.conf..257B
No abstract at ADS
---------------------------------------------------------
Title: Transition Region Velocities and Line Profiles in the Sunspot
Region 7981
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele,
T. Thompson, W. T.; Wilhelm, K.
1997ESASP.404..251B Altcode: 1997cswn.conf..251B
No abstract at ADS
---------------------------------------------------------
Title: CDS Observations of the Connection Between Line Intensity
and Doppler Shift in the Active Region NOAA 7981
Authors: Fredvik, T.; Brynildsen, N.; Maltby, P.; Kjeldseth-Moe, O.;
Brekke, P.; Haugen, S. V. H.; Harrison, R. A.
1997ESASP.404..391F Altcode: 1997cswn.conf..391F
No abstract at ADS
---------------------------------------------------------
Title: Flows with High Velocities in an Active Region Loop Observed
with the Coronal Diagnostic Spectrometer
Authors: Kjeldseth-Moe, O.; Brekke, P.; Harrison, R. A.
1997ESASP.404..457K Altcode: 1997cswn.conf..457K
No abstract at ADS
---------------------------------------------------------
Title: First Results from SOHO on Waves Near the Solar Transition
Region
Authors: Steffens, S.; Deubner, F. -L.; Fleck, B.; Wilhelm, K.;
Schuhle, U.; Curdt, W.; Harrison, R.; Gurman, J.; Thompson, B. J.;
Brekke, P.; Delaboudiniere, J. -P.; Lemaire, P.; Hessel, B.; Rutten,
R. J.
1997ASPC..118..284S Altcode: 1997fasp.conf..284S
We present first results from simultaneous observations with the
CDS, EIT and SUMER instruments {please see Solar Physics 162 (1995)
for a description of the instruments} onboard SOHO and the VTT at
Tenerife. Our aim is to study the wave propagation, shock formation,
and transmission properties of the upper chromosphere and transition
region. The preliminary results presented here include the variation
of velocity power spectra with height, difference in power between
internetwork and network regions, and variations in mean flows displayed
by different spectral lines.
---------------------------------------------------------
Title: The Net Redshifts in EUV Emission Lines and the Connection
Between Intensity and Doppler Shift
Authors: Brynildsen, N.; Fredvik, T.; Maltby, P.; Kjeldseth-Moe, O.;
Brekke, P.; Haugan, S. V. H.; Harrison, R. A.; Wilhelm, K.
1997ESASP.404..263B Altcode: 1997cswn.conf..263B
No abstract at ADS
---------------------------------------------------------
Title: EUV Line Emission and Time Dependence in the Sunspot Region
NOAA 7981
Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.;
Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele,
T.; Thompson, W. T.; Wilhelm, K.
1997ESASP.404..245B Altcode: 1997cswn.conf..245B
No abstract at ADS
---------------------------------------------------------
Title: First Results of the SUMER Telescope and Spectrometer on SOHO -
I. Spectra and Spectroradiometry
Authors: Wilhelm, K.; Lemaire, P.; Curdt, W.; Schühle, U.; Marsch, E.;
Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Huber,
M. C. E.; Vial, J. -C.; Kühne, M.; Siegmund, O. H. W.; Gabriel, A.;
Timothy, J. G.; Grewing, M.; Feldman, U.; Hollandt, J.; Brekke, P.
1997SoPh..170...75W Altcode:
SUMER - the Solar Ultraviolet Measurements of the Emitted Radiation
instrument on the Solar and Heliospheric Observatory (SOHO) - observed
its first light on January 24, 1996, and subsequently obtained a
detailed spectrum with detector B in the wavelength range from 660
to 1490 Å (in first order) inside and above the limb in the north
polar coronal hole. Using detector A of the instrument, this range
was later extended to 1610 Å. The second-order spectra of detectors
A and B cover 330 to 805 Å and are superimposed on the first-order
spectra. Many more features and areas of the Sun and their spectra
have been observed since, including coronal holes, polar plumes and
active regions. The atoms and ions emitting this radiation exist at
temperatures below 2 × 10<SUP>6</SUP> K and are thus ideally suited
to investigate the solar transition region where the temperature
increases from chromospheric to coronal values. SUMER can also be
operated in a manner such that it makes images or spectroheliograms
of different sizes in selected spectral lines. A detailed line profile
with spectral resolution elements between 22 and 45 mÅ is produced for
each line at each spatial location along the slit. From the line width,
intensity and wavelength position we are able to deduce temperature,
density, and velocity of the emitting atoms and ions for each emission
line and spatial element in the spectroheliogram. Because of the high
spectral resolution and low noise of SUMER, we have been able to detect
faint lines not previously observed and, in addition, to determine
their spectral profiles. SUMER has already recorded over 2000 extreme
ultraviolet emission lines and many identifications have been made on
the disk and in the corona.
---------------------------------------------------------
Title: SOHO observations of the north polar solar wind
Authors: Peres, G.; Ciaravella, A.; Betta, R.; Orlando, S.; Reale,
F.; Kohl, J.; Noci, G.; Fineschi, S.; Romoli, M.; Brekke, P.; Fludra,
A.; Gurman, J. B.; Lemaire, P.; Schuhle, U.
1997ESASP.404..587P Altcode: 1997cswn.conf..587P
No abstract at ADS
---------------------------------------------------------
Title: Systematic Redshifts in the Quiet Sun Transition Region and
Corona Observed with SUMER on SOHO
Authors: Brekke, P.; Hassler, D. M.; Wilhelm, K.
1997ESASP.404..229B Altcode: 1997cswn.conf..229B
No abstract at ADS
---------------------------------------------------------
Title: Flows and Dynamics in the Corona Observed with the Coronal
Diagnostic Spectrometer (cds)
Authors: Brekke, P.; Kjeldseth-Moe, O.; Brynildsen, N.; Maltby, P.;
Haugan, S. V. H.; Harrison, R. A.; Thompson, W. T.; Pike, C. D.
1997SoPh..170..163B Altcode:
EUV spectra obtained with the Coronal Diagnostic Spectrometer (CDS)
on the Solar and Heliospheric Observatory (SOHO) show significant flows
of plasma in active region loops, both at coronal and transition region
temperatures. Wavelength shifts in the coronal lines Mgix 368 Å and
Mgx 624 Å corresponding to upflows in the plasma reaching velocities
of 50 km s<SUP>-1</SUP> have been observed in an active region. Smaller
velocities are detected in the coronal lines Fexvi 360 Å and Sixii
520 Å. Flows reaching 100 km s<SUP>-1</SUP> are observed in spectral
lines formed at transition region temperatures, i.e., Ov 629 Å and
Oiii 599 Å, demonstrating that both the transition region and the
corona are clearly dynamic in nature. Some high velocity events show
even higher velocities with line profiles corresponding to a velocity
dispersion of 300-400 km s<SUP>-1</SUP>. Even in the quiet Sun there
are velocity fluctuations of 20 km s<SUP>-1</SUP> in transition region
lines. Velocities of the magnitude presented in this paper have never
previously been observed in coronal lines except in explosive events
and flares. Thus, the preliminary results from the CDS spectrometer
promise to put constraints on existing models of the flows and energy
balance in the solar atmosphere. The present results are compared to
previous attempts to observe flows in the corona.
---------------------------------------------------------
Title: The EUV Solar Irradiance Spectrum Observed with the Coronal
Diagnostic Spectrometer (CDS) on SOHO
Authors: Brekke, P.; Thompson, W. T.
1997ESASP.404..235B Altcode: 1997cswn.conf..235B
No abstract at ADS
---------------------------------------------------------
Title: The Ultraviolet Spectrum of a 3B Class Flare Observed with
SOLSTICE
Authors: Brekke, P.; Rottman, G. J.; Fontenla, J.; Judge, P. G.
1996ApJ...468..418B Altcode:
An observation of the ultraviolet spectrum (1200-1800 Å) during the
impulsive phase of a very extended 3B-X3 class solar flare on 1992
February 27 was obtained with the Solar-Stellar Irradiance Comparison
Experiment (SOLSTICE). This observation is combined with ground-based
Hα, magnetogram, and microwave data as well as hard X-ray measurements
from the Ulysses spacecraft. This flare shows a dramatic enhancement of
lines formed in the solar transition region. The irradiance (emitted
flux density from the entire solar disk) of the resonance lines of
C iv and Si iv increased by a factor of 12-13 during the impulsive
phase of the flare. These irradiance enhancements are comparable
with those measured during stellar flares. By taking into account the
emitting flare area we infer that the radiance (specific intensity)
of the flaring plasma was at least a factor of 15,000 brighter than the
average solar disk radiance just prior to the event. Assuming the flare
site's initial radiance was that of a typical active region, it then
must have brightened by a factor of at least 3400. Such enhancement
far exceeds previous published values (e.g., OSO 8, Skylab, and SMM)
and indicates that many observations were affected by limited dynamic
range. Thus, the SOLSTICE observation may be the first measurement of
the true UV enhancement during the impulsive phase of very bright solar
flares. <P />The Si III multiplet near 1295 Å also shows remarkable
enhancement, but other allowed lines of C II, Si III (1206 Å), N V,
and He II show more moderate enhancements, the weakest being H I Lyα,
the irradiance of which increases only 6%. Some of the differences
between the various enhancements are certainly caused by the timing of
the observations since the scanning spectrometer observed different
spectral features over periods of 4 minutes. Other differences due
to line formation processes are being investigated but are consistent
with density effects in the line emission coefficients. The inferred
Lyα radiance enhancement is consistent with current post-impulsive
phase flare models. However, the formation of the C IV and Si IV lines,
formed during the impulsive phase of the flare, remains unknown. During
the impulsive phase of the flare the strong transition region lines
are systematically redshifted by 50 km s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Intercombinations and Allowed Transitions in O IV
Authors: Brage, Tomas; Judge, P. G.; Brekke, P.
1996ApJ...464.1030B Altcode:
We report on large-scale ab initio multiconfiguration Hartree-Fock
calculations for important multiplets including the UV 0.01
multiplet, 2s<SUP>2</SUP>2p<SUP>2</SUP>P<SUB>J</SUB>-2s2p<SUP>2</SUP>
<SUP>4</SUP>P<SUB>j'</SUB>, in O IV. The resulting transition
probabilities should be accurate to ±5%-10% for intersystem lines and
1% or better for permitted lines. <P />We present new calculations
of line emission coefficients using these transition probabilities
and collisional rate coefficients published by Zhang, Graziani, &
Pradhan in 1994. We readdress the use of these lines as diagnostics
of electron densities, paying particular attention to uncertainties
in density determinations. We find (1) the absolute uncertainties in
derived densities are difficult to assess, but are at least ±40%
controlled by uncertainties in collision strengths; (2) our new
calculations bring observed and computed line ratios into better
agreement (earlier papers yielding systematically different densities
make the agreement worse); (3) there is additional evidence for strong
blends in the 1404.8 emission feature, as argued by other authors,
and/or evidence for inaccurate laboratory wavelengths; and (4) the
computed branching ratios are in good agreement with observed ratios to
within observational uncertainties of ±7%. <P />We determine electron
densities in a variety of solar features from HRTS data from the first
and second flights of this instrument. The derived electron densities
vary remarkably little between quiet Sun network and active regions,
but resonance line intensities vary dramatically, and we discuss reasons
for this. Finally, we discuss how new high-quality data from the SUMER
instrument to be flown on Solar and Heliosphereic Observatory (SO HO)
could be used to address outstanding problems concerning blends and
heating of the solar transition region.
---------------------------------------------------------
Title: High Velocity Event Observed with CDS on SOHO
Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Harrison, R. A.
1996AAS...188.3714K Altcode: 1996BAAS...28..880K
The Coronal Diagnostic Spectrometer, CDS, on SOHO has observed its
first strong High Velocity Event. The event occurred on 22 March
1996 at approximately 13.36 UT and was located in the leg of an
active region loop. The spectral signature is extremely wide emission
lines corresponding to a velocity dispersion of approximately 300-450
km/s. As measured in the 386 A line from Mg IX, the emission also seems
shifted in wavelength with a redshift corresponding to 65 km/s. The
intensity contrast in the line is a factor 2 compared to the surrounding
areas. The spatial extent is small, less than or corresponding to the
angular resolution of CDS of 4". The event occur in all available lines
from He I to Fe XV, i.e. over a temperature range from 10 000 K to
2.2 MK. This is a new result which has not been reported before. The
relation of this type of event to the well studied explosive events
is discussed.
---------------------------------------------------------
Title: A Solar EUV Spectral Atlas Observed with SUMER
Authors: Brekke, P.; Wilhelm, K.; Lemaire, P.; Curdt, W.; Schuhle,
U.; Poland, A.; Kucera, T.; Hassler, D. M.; Siegmund, O. H. W.
1996AAS...188.3713B Altcode: 1996BAAS...28..879B
We present the first solar EUV spectral atlas in the wavelength range
500 -- 1600 { Angstroms}. The spectra were recorded with the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) which is part
of the ESA/NASA Solar and Heliospheric Observatory (SOHO). The solar
spectrum below 1200 { Angstroms} is not very well known. Thus, the
present spectral atlas, and SUMER observations in general, represents
a new important diagnostic tool to study essential physical parameters
of the solar atmosphere. It includes emission from atoms and ions in
the temperature range 10(4) to 2 x 10(6) K. Thus, emission lines and
continua emitted from the lower chromosphere to the lower corona
can be studied. The atlas is also useful as a planning tool for
SUMER studies to determine useful dwell times, possible blends, and
to select proper data extraction windows. The angular resolution of
SUMER is close to 1 arcsec, but the atlas presented here represents an
average along part of the 1-arcsec wide slit, typically 30 arcsec. The
spectral resolving power of the instrument is lambda /Delta lambda =
17770-38300. For more details about the SUMER instrument we refer to
Wilhelm et al. (Solar Physics, 162, 189, 1995). The spectral data in
this atlas were obtained with the spectrometer slit positioned at the
center of the solar disk with a dwell time of 300 s to bring up weak
lines and continua. The full spectral range was put together from
a number of exposures each covering approximately 20 { Angstroms}
in 1st order on the coated, and therefore most sensitive, part (KrB)
of the detector. 1st and 2nd order spectra are superimposed. The
spectral atlas is available in a computer readable format together
with a IDL program to read and display the data using a widget
interface. The atlas and the programs can be obtained via the World
Wide Web (http://hydra.mpae.gwdg.de/mpae_projects/SUMER/sumer.html)
or by contacting one of the authors.
---------------------------------------------------------
Title: Ultraviolet (1200 to 1800 Angstroms) Emission during the
Impulsive Phase of a Class 3B-X3 Solar Flare Observed with SOLSTICE
Authors: Brekke, P.; Rottman, C. J.; Fontenla, J.; Judge, P. G.
1996mpsa.conf..213B Altcode: 1996IAUCo.153..213B
No abstract at ADS
---------------------------------------------------------
Title: The UV "sun as a star" flare spectrum observed with SOLSTICE
Authors: Brekke, P.; Rottman, G. J.; Fontenla, J.; Judge, P. G.
1996ASPC..109..111B Altcode: 1996csss....9..111B
No abstract at ADS
---------------------------------------------------------
Title: On the Failure of Standard Emission Measure Analysis for
Solar Extreme-Ultraviolet and Ultraviolet Irradiance Spectra
Authors: Judge, P. G.; Woods, T. N.; Brekke, P.; Rottman, G. J.
1995ApJ...455L..85J Altcode:
We perform emission measure analysis of new and accurate UV ( lambda
> 1200 A) and extreme-ultraviolet (EUV) ( lambda <= 1200 A)
irradiance ("Sun-as-a-star") emission-line spectra of the Sun. Our
data consist of (1) daily averaged UV irradiances from the SOLSTICE on
the UARS spacecraft and (2) EUV irradiances obtained on the same date
from a \frac {1}{4} m spectrograph flown on a sounding rocket. Both
instruments have a spectral resolution of roughly 1 A. The absolute
uncertainties in these data are at most +/-15% (+/-2 sigma ), one
of the highest photometric accuracies yet achieved. We find large,
highly significant and systematic discrepancies in the emission measure
analysis of transition region lines which can only be accounted for by
a breakdown of one or more standard assumptions. All strong lines above
1000 A, which are from the Li and Na isoelectronic sequences, are too
strong by factors of between 2.5 and 7 compared with their counterparts
in the EUV region. Previous studies were tantalizingly close to finding
these discrepancies, but those data lacked the wavelength coverage and
relative photometric precision necessary for definitive conclusions. We
argue that either dynamical effects, inaccurate treatments of atomic
processes, and/or Lyman continuum absorption are the culprits. However,
we favor the former explanation. In any event, this study should have
implications for models of the solar transition region, for observing
programs with the CDS and SUMER instruments on SOHO, and for analysis of
UV spectra for stars across the cool half of the H-R diagram. Finally,
the discrepancy is not seen for the "coronal" Li-like ions.
---------------------------------------------------------
Title: The Coronal Diagnostic Spectrometer for the Solar and
Heliospheric Observatory
Authors: Harrison, R. A.; Sawyer, E. C.; Carter, M. K.; Cruise,
A. M.; Cutler, R. M.; Fludra, A.; Hayes, R. W.; Kent, B. J.; Lang,
J.; Parker, D. J.; Payne, J.; Pike, C. D.; Peskett, S. C.; Richards,
A. G.; Gulhane, J. L.; Norman, K.; Breeveld, A. A.; Breeveld, E. R.; Al
Janabi, K. F.; Mccalden, A. J.; Parkinson, J. H.; Self, D. G.; Thomas,
P. D.; Poland, A. I.; Thomas, R. J.; Thompson, W. T.; Kjeldseth-Moe,
O.; Brekke, P.; Karud, J.; Maltby, P.; Aschenbach, B.; Bräuninger,
H.; Kühne, M.; Hollandt, J.; Siegmund, O. H. W.; Huber, M. C. E.;
Gabriel, A. H.; Mason, H. E.; Bromage, B. J. I.
1995SoPh..162..233H Altcode:
The Coronal Diagnostic Spectrometer is designed to probe the solar
atmosphere through the detection of spectral emission lines in the
extreme ultraviolet wavelength range 150 - 800 å. By observing
the intensities of selected lines and line profiles, we may derive
temperature, density, flow and abundance information for the plasmas
in the solar atmosphere. Spatial and temporal resolutions of down to
a few arcseconds and seconds, respectively, allow such studies to be
made within the fine-scale structure of the solar corona. Futhermore,
coverage of large wavelength bands provides the capability for
simultaneously observing the properties of plasmas across the wide
temperature ranges of the solar atmosphere.
---------------------------------------------------------
Title: Observed Redshifts in the Solar Transition Region above Active
and Quiet Regions
Authors: Achour, H.; Brekke, P.; Kjeldseth-Moe, O.; Maltby, P.
1995ApJ...453..945A Altcode:
Solar UV spectral observations show a redshifted emission at
temperatures between the chromosphere and the corona. We have measured
the magnitude of the redshift as a function of the temperature using
solar spectrograms from the High Resolution Telescope and Spectrograph
HRTS. The velocity derived from the average redshift is found to
increase up to a temperature T ≍ 1.35 x 10<SUP>5</SUP> K in both
quiet and active regions, then decrease with increasing temperature,
with the rate of decrease depending critically on the laboratory
wavelengths adopted for the transition region lines. This result
illustrates the need for improved laboratory measurements. <P />We
find that the differential re shift between an active region and the
surroundings increases smoothly with temperature, reaches a maximum
velocity difference of 7 km s 1 at 1.35 × 10<SUP>5</SUP> K and
falls abruptly to zero at 2.3 × 10<SUP>5</SUP> K. This observation
is independent of the laboratory wavelengths. Suggestions regarding
the origin of the redshift are confronted with the results.
---------------------------------------------------------
Title: The OV 1371.29A/1218.35A emission-line ratio in solar and
stellar spectra
Authors: Keenan, F. P.; Brekke, P.; Byrne, P. B.; Greer, C. J.
1995MNRAS.276..915K Altcode:
New calculations of the theoretical electron-density-sensitive
emission-line ratio R=I(2s2p ^1P-2p^2 ^1D)/I(2s^2 ^1S-2s2p
^3P_1)=I(1371.29A)/I(1218.35A) in OV are presented, which are
significantly different from those deduced previously, principally
due to the adoption of improved atomic data in the present
analysis. Electron densities estimated from the current diagnostics,
in conjunction with observed values of R measured from solar spectra
obtained by the S082B spectrograph on board Skylab and by the High
Resolution Telescope and Spectrograph (HRTS) on board a sounding rocket
flight, are found to be in good agreement with densities determined from
line ratios in species formed at similar electron temperatures to OV,
such as OIV and NIV. These results provide experimental support for
the accuracy of the diagnostic calculations presented in this paper,
and hence the atomic data used in their derivation. The observed value
of R for the M0Ve flare star AU Mic, determined from observations made
by the Goddard High Resolution Spectrometer on board the Hubble Space
Telescope, is within 4 per cent of the expected low-density limit,
implying that logN_e<=10.4 for the OV emitting region of the AU
Mic atmosphere. This is similar to density estimates made for AU Mic
using other methods.
---------------------------------------------------------
Title: Needs for Improved Laboratory Wavelength Measurements in
the EUV
Authors: Brekke, P.; Hassler, D. M.
1995ASPC...81..589B Altcode: 1995lahr.conf..589B
No abstract at ADS
---------------------------------------------------------
Title: An Ultraviolet Spectral Atlas of the Sun 1190 - 1730 A
Authors: Brekke, P.
1995ASPC...81..102B Altcode: 1995lahr.conf..102B
No abstract at ADS
---------------------------------------------------------
Title: CDS quicklook display software
Authors: Brekke, P.; Haugan, S. V. H.; Brynildsen, Nils
1994ESASP.373..437B Altcode: 1994soho....3..437B
No abstract at ADS
---------------------------------------------------------
Title: Observed redshifts of transition region/Corona lines
Authors: Brekke, P.
1994SSRv...70...97B Altcode:
Solar UV observations reveal a redshifted emission at transition region
temperatures, commonly interpreted as a net downflow of plasma. In
earlier investigations the magnitude of the redshift has been found to
increase with temperature, reaching a maximum at T=10<SUP>5</SUP> K,
and then to decrease towards higher temperatures. These observations,
mostly from Skylab, suggested no significant shift of the O V line at
1218 Å formed at 2.4×10<SUP>5</SUP> K. The variation of the downflow
velocity with temperature is, however, uncertain since there are few
reliable observations of lines formed at higher temperatures. Using
spectrograms from the High Resolution Telescope and Spectrograph
— HRTS we find an average net redshift of the O V lines at 1218
Å and 1371 Å at all locations extending from disk center to solar
limb. A discrepancy between the observed flow velocity in the two
lines is probably caused by uncertainty in the available laboratory
wavelength of the intercombination line at 1218 Å (2s<SUP>2</SUP>
<SUP>1</SUP>S<SUB>0</SUB>-2s2p<SUP>3</SUP>P<SUB>1</SUB>). The observed
shift in O V is compared with corresponding measurements of lines formed
at other temperatures (Si IV, C IV, N IV, O IV, and Fe XII). Large
variations in the shift are found along the instrument slit. Thus,
blueshifts are also observed with the sites of the largest upflow
located in the sunspot umbrae and in a quiet region close to an
active region.
---------------------------------------------------------
Title: Fine structure and the emission filling factor
Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Maltby, P.
1994SSRv...70...89K Altcode:
There is observational evidence for an extreme fine structure in
the solar transition region, much smaller than 1″ in size (Dereet
al., 1987, 1988) Corresponding to this extreme fine structure there
appear to be an equally complex dynamical structure. We review the
evidence for such dynamical extreme fine structure as demonstrated
by the frequent appearance of multiple velocities, i.e. distinctly
different velocities in the transition region occurring within the
angular resolution element. Multiple velocities are prominent in active
regions and particularly near sunspots, where velocity components
may be supersonic. However, multiple velocities are frequent also in
quiet regions. The consequences of such fine structure for modeling
the transition region will be outlined. Finally the appropriate CDS and
SUMER observations needed to extend our knowledge of a finely structured
transition region and corona, spatially or in time, are discussed.
---------------------------------------------------------
Title: New Radiometric Values of the Solar Ultraviolet Continuum
Radiation from 1500 to 1700 Angstrom
Authors: Brekke, P.; Kjeldseth-Moe, O.
1994ApJ...431L..55B Altcode:
A high-resolution stigmatic spectrometer, the High Resolution Telescope
and Spectrograph (HRTS), has been calibrated against broad-band
irradiance measurements of the Sun with the Solar Ultraviolet Irradiance
Monitor (SUSIM) and the Solar-Stellar Irradiance Comparison Experiment
(SOLSTICE), resulting in a new value for the radiance of the solar
UV continuum from 1500 to 1700 A. Previous HRTS results were based
on a comparison with the Skylab SO82B calibration rocket, CALROC, and
agreed, within the stated accuracy of +/- 25%, with other independently
calibrated UV radiance measurements over the last 20 years. The new
calibration increases the derived radiance in this wavelength range
by a factor of 1.35-1.5 over previous measurements. The difference
is systematic over the wavelength range and cannot be explained by
contributions to the irradiance from spectral lines or enhanced emission
in active regions. The new radiance values are significant for solar
atmospheric models as well as for related studies of stellar models,
since the radiance at these wavelengths reflects the value of the
minimum temperature at the top of the photosphere.
---------------------------------------------------------
Title: The solar UV continuum 1440-1680 Å and its center-to-limb
variation
Authors: Brekke, P.; Kjeldseth-Moe, O.
1994SoPh..150...19B Altcode:
The solar UV continuum has been derived from intensity-calibrated
observations with the High-Resolution Telescope and Spectrograph - HRTS
- on its second rocket flight in 1978. A database has been constructed
using the spatially-resolved solar spectrum 1180-1700 å along a slit
extending from near disk center to the solar limb and crossing a sunspot
and two active regions. The angular resolution is approximately 1.8″.
---------------------------------------------------------
Title: Observed Redshift of O V and Downflows in the Transition Region
Authors: Brekke, P.
1994emsp.conf...57B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The HRTS Spectral Database in Oslo
Authors: Brekke, P.
1994emsp.conf..209B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Ultraviolet Spectral Atlas of the Sun between 1190 and
1730 Angstrom
Authors: Brekke, P.
1993ApJS...87..443B Altcode:
An ultraviolet spectral atlas of different solar regions in the
wavelength region 1190-1730 A is presented. The data were obtained with
the High Resolution Telescope and Spectrograph during a rocket flight
in 1978. The spectral resolution of the instrument was 0.05 A while a
spatial resolution of approximately 1.8 arcsec was achieved. The atlas
contains spectra of three different quiet regions including pointings
at disk center and the extreme limb. Data from an active region close
to the solar limb and a prominence have also been included together
with an atlas of a so-called explosive event. The selected areas are
averaged over several arcsec, ranging from 3.5 to 220 arcsec. The
absolute intensities are determined with an accuracy of +/- 30 percent
except for the strongest emission lines that are synthesized from
spectra with different exposure times. The atlas is available in a
machine-readable form together with an IDL program to interactively
measure line widths, total intensities, and solar wavelengths.
---------------------------------------------------------
Title: Multiple Flows and the Fine Structure of the Transition Region
around Sunspots
Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Maltby, P.;
Brueckner, G. E.
1993SoPh..145..257K Altcode:
The fine structure in the flow field in the transition region above
and surrounding a sunspot is determined fromCIV 1548 å line profiles,
observed with the High Resolution Telescope and Spectrograph (HRTS)
during the Spacelab 2 mission. The observed line profiles show one, two,
or three distinct velocity components within the resolution element of
1″ × 1″. Supersonic flows occur in small regions where the line
profile has two or three components. The line component that shows
supersonic speed often is weaker than the subsonic line component,
which may explain why some observers have been unable to detect the
supersonic flow component. The broadening of individual line components
shows non-thermal velocities close to 20 km s<SUP>−1</SUP>. This
suggests that turbulence is less important than usually considered.
---------------------------------------------------------
Title: Observed Redshifts in O V and Downflows in the Solar Transition
Region
Authors: Brekke, P.
1993ApJ...408..735B Altcode:
Spectrograms from HRTS are used to find an average net redshift of
the O V lines at 1218 and 1371 A at all locations extending from
disk center to solar limb. The observed shift in O V is compared
with measurements of the O IV line at 1401 A and the Si IV line at
1402 A. Large variations in the shift are found along the instrument
slit. Blueshifts are also observed with the sites of the largest upflow
located in the sunspot umbrae and in a quiet region close to an active
region. The present result could put new constraints on numerical
models of flows in the solar transition region and will also be of
importance for modeling stellar atmospheres. The spatial variation of
line-of-sight velocities in the O V line at 1371A and the SI IV line
at 1402 A is illustrated.
---------------------------------------------------------
Title: Multiple flows in the solar transition region.
Authors: Brekke, P.; Brynildsen, N.; Kjeldseth-Moe, O.; Maltby, P.;
Brueckner, G. E.
1992ESASP.346..211B Altcode: 1992ssts.rept..211B
The solar transition region between the chromosphere and the corona
shows clear evidence of a fine scale structure that is much smaller
than the best available instrumental resolution in the UV of 1×1
arcsec. Previous studies have suggested filling factors of 0.01
- 0.001, with the solar gas being restricted to thin, extended
fibrills. New evidence of the fine scale structure is found from
its dynamical characteristics, the presence of multiple flows. In
multiple flows the solar gas in small volumes show several distinct
velocities, resulting in line profiles with more than one velocity
component within the spatial resolution element. Multiple velocities
are particularly prominent above sunspots, but by no means restricted
to these regions. Instead they are clearly a general feature in the
solar transition region, occurring in quiet as well as active regions.
---------------------------------------------------------
Title: Observed structure and dynamics of the solar chromosphere and
transition region based on high resolution ultraviolet spectrograms
Authors: Brekke, Pål Ording Lie
1992PhDT.......306B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Data reduction of HRTS spectral images.
Authors: Wahlstrøm, C.; Brekke, P.
1992lest.rept...31W Altcode:
A description of the data reduction of the spectral images from High
Resolution Telescope and Spectrograph (HRTS) is given.
---------------------------------------------------------
Title: An Ultraviolet Spectral Atlas of a Sunspot and an Active
Region 1190--1730 Angstrom
Authors: Brekke, P.; Kjeldseth-Moe, O.; Bartoe, J. -D. F.; Brueckner,
G. E.
1991ApJS...75.1337B Altcode:
An ultraviolet spectral atlas of a sunspot with high spectral
and spatial resolution in the wavelength region 1190-1730 A is
presented. The atlas contains spectra of three different areas in the
sunspot and also of an active region and a quiet region. The selected
areas are averaged over several arcsec, ranging from 3.5 arcsec in the
sunspot to 18 arcsec in the quiet region. Brief descriptions of the data
reduction and calibration procedures are given. The absolute intensities
are determined with an accuracy of + or - 30 percent and the wavelength
scale is accurate to better than 0.01 A. The transition region lines
show the most extreme example known of downflowing gas above a sunspot,
a phenomenon which seems to be commonly connected to sunspots.
---------------------------------------------------------
Title: The Solar UV Continuum 1440 - 1680 Å
Authors: Kjeldseth-Moe, O.; Brekke, P.; Bartoe, J. -D. F.; Brueckner,
G. E.
1991BAAS...23.1060K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dynamical Evidence of Fine Structure in the Solar Transition
Region
Authors: Brekke, P.; Kjeldseth-Moe, O.; Bartoe, J. -D. F.; Brueckner,
G. E.
1991BAAS...23.1060B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dynamics in the solar transition region.
Authors: Brekke, P.; Brynildsen, N.
1991cwlt.conf...71B Altcode:
The authors present an analysis of the dynamical evidence for extreme
fine structure in the transition region using the Si IV line at
1402 Å. Gas velocities, line widths and intensities are measured
from the line profiles by fitting the profiles to a set of Gaussian
components using a least squares method. Both quiet and active regions
are studied. The relation of the observed supersonic flow velocities
to possible shocks in the flow is briefly discussed.
---------------------------------------------------------
Title: Multiple flow velocities in the transition region
Authors: Brekke, P.; Brynildsen, N.; Kjeldseth-Moe, O.; Maltby, P.;
Bartoe, J. -D. F.; Brueckner, G. E.
1991AdSpR..11e.251B Altcode: 1991AdSpR..11..251B
Observations with the High Resolution Telescope and Spectrograph (HRTS)
of the C IV lines at 1550 Å above sunspots reveal the co-existence
of several distinct high velocity gas components within the instrument
resolution element of 1 × 1 arc second. A further investigation of the
HRTS material demonstrates that such multiple gas velocities are not
restricted to the temperature region around 10<SUP>5</SUP> K, where the
C IV lines are formed, but that the gas flows with essentially unchanged
speed through all temperature layers from 2.5 × 10<SUP>5</SUP> K
to 10<SUP>4</SUP> K. Furthermore the phenomenon is not restricted to
sunspots, but occurs also in other solar regions, often most easily
distinguished in active regions. We describe the characteristics of the
velocity fields, analyze the mass fluxes and discuss the requirements
they place on the resolving power of future space instruments.
---------------------------------------------------------
Title: Multiple downflow velocities above sunspotss
Authors: Brekke, P.; Kjeldseth-Moe, O.; Brueckner, G. E.
1990Ap&SS.170..135B Altcode:
Supersonic transition zone downflow appears to be commonly occurring
above sunspots. The downflow has been observed in 29 emission lines
in the ultra-violet spectrum with the High Resolution Telescope and
Spectrograph (HRTS) on two rocket flights and on 5 consecutive days
during the Spacelab-2 mission. Spectra from the second rocket flight,
contain the most extreme example of downflow, showing speeds up to 180
km s<SUP>-1</SUP> and extending over 60 are sec along the slit. The
observations demonstrate the existence of several different distinctive
flow speeds within the 1 arc sec resolution element throughout the
temperature range 7000 240 000 K.
---------------------------------------------------------
Title: An Ultraviolet Spectral Atlas of a Sunspot and an Active
Region 1190-1730Å
Authors: Brekke, P.; Kjeldseth-Moe, O.; Bartoe, J. -D. F.; Brueckner,
G. E.
1990BAAS...22..793B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observed Line Profiles and Mass Fluxes in the Transition
Region above Sunspots
Authors: Maltby, P.; Brekke, P.; Brynildsen, N.; Kjeldseth-Moe, O.;
Bartoe, J. -D. F.; Brueckner, G. E.
1990PDHO....7..244M Altcode: 1990dysu.conf..244M; 1990ESPM....6..244M
Spectrograms obtained with the HRTS show strong mass flows through
the transition zone that are particularly prominent above sunspot
regions. Most characteristic for the flow associated with sunspots
are regions with supersonic downflows, but upward flowing gas is
also observed with generally smaller velocities. The flow pattern
changes from one day to the next and even within a time span of
minutes. An apparent lack of balance between up- and downflowing
massfluxes is found. Generally the net massflux appears to be directed
downward. Possible reasons for this result are briefly discussed in
terms of observability and line emission area filling factor.
---------------------------------------------------------
Title: Transition Region Massflows Associated with Sunspots
Authors: Kjeldseth-Moe, O.; Brekke, P.; Brynildsen, N.; Maltby, P.;
Brueckner, G. E.; Bartoe, J. -D. F.
1989BAAS...21.1178K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Bildebehandling av solspektra fra romfergen.
Authors: Brekke, P.; Brynildsen, N.
1989ATi....22...49B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Gas Flows in the Transition Region above Sunspots
Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Engvold, O.;
Maltby, P.; Bartoe, J. -D. F.; Brueckner, G. E.; Cook, J. W.; Dere,
K. P.; Socker, D. G.
1988ApJ...334.1066K Altcode:
Strong downflows and moderate upflows in the transition region over
a sunspot have been observed with the HRTS on Spacelab 2 in 1985. The
flows are persistent in the sense that they are seen in the same spot
for 5 days. The downflows are prominent in regions of limited extent
(4arcsec - 6arcsec), and flow velocities are in the range 40 - 80 km
s<SUP>-1</SUP> and are thus supersonic. Upward flows have smaller
velocities, 5 - 20 km s<SUP>-1</SUP>, but may extend over a larger
area. In the downflowing regions there is always an appreciable amount
of gas at rest in the line of sight. Flow speeds derived from the
profiles of different lines formed in the transition region between
30,000 and 230,000K are very similar implying constant downflow in
this temperature range.
---------------------------------------------------------
Title: Ultraviolet Rocket-Spectra of a Sunspot
Authors: Brekke, P.; Kjeldseth-Moe, O.; Bartoe, J. -D. F.; Brueckner,
G. E.
1987ESASP.270..341B Altcode: 1987erbp.symp..341B
Downflows in the transition zone above a sunspot were observed with
a high resolution telescope and spectrograph on a rocket. The rocket
spectra on photographic film were digitized. Noise caused by film grains
was removed by Fourier filtering. The spectral images were corrected
for geometrical distortions and calibrated to give the solar intensity
as a function of wavelength. Maximum speeds of 200 km/sec are reached
in the flows which extend over 60 arc-sec along the slit. Components
with distinct, but lower velocities also appear. The variations with
temperature of the characteristic flow speeds are studied.
---------------------------------------------------------
Title: Gasflows in the transition region above sunspots.
Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Bartoe,
J. -D. F.; Brueckner, G. E.
1987ESASP.275...27K Altcode: 1987sspp.symp...27K
Gas flows in the transition region in and above sunspots were observed
with the High Resolution Telescope and Spectrograph on two rocket
flights and during the Spacelab 2 mission. Supersonic downflows of
mass from the corona appear to be generally occurring in sunspots. The
downflows are often concentrated in regions with typical diameters of
4000 km on the Sun, suggesting a flow in a looplike structure. However,
the total flow pattern often has an elongated sheetlike structure
of much larger extent. Flow speeds are typically 80 km/sec and show
small variation with the temperature of the radiating gas. Much higher
flow-speeds (180 km/sec) also occur. Studies of the areas surrounding
the sunspot in the Spacelab material reveal the presence of upflows over
extended regions with flow-speeds of 10 to 30 km/sec. It is not clear
whether the amount of upward flowing gas is sufficient to compensate
for the mass flux in the downflows.