Issue 10 Volume 41 May 16, 2003

92
SOLAR PHYSICS
Includes solar activity, solar flares, solar radiation and sunspots. For related information see 93 Space Radiation.
20030032419 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Three-Dimensional MHD Modeling of The Solar Corona and Solar Wind: Comparison with The Wang-Sheeley Model
Usmanov, A. V.; Goldstein, M. L.; [2003]; 4 pp.; In English; EGS/AGU Spring Meeting; No Copyright; Avail: Other Sources;
Abstract Only
We present simulation results from a tilted-dipole steady-state MHD model of the solar corona and solar wind and
compare the output from our model with the Wang-Sheeley model which relates the divergence rate of magnetic flux tubes
near the Sun (inferred from solar magnetograms) to the solar wind speed observed near Earth and at Ulysses. The boundary
conditions in our model specified at the coronal base and our simulation region extends out to 10 AU. We assumed that a flux
of Alfven waves with amplitude of 35 km per second emanates from the Sun and provides additional heating and acceleration
for the coronal outflow in the open field regions. The waves are treated in the WKB approximation. The incorporation of wave
acceleration allows us to reproduce the fast wind measurements obtained by Ulysses, while preserving reasonable agreement
with plasma densities typically found at the coronal base. We find that our simulation results agree well with Wang and
Sheeley’s empirical model.
Author
Astronomical Models; Three Dimensional Models; Solar Corona; Solar Wind; Computerized Simulation; Solar Wind Velocity
20030032939 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Solar Energetic Particle Variations
Reames, D. V.; [2003]; 11 pp.; In English; COSPAR Proceedings; Original contains black and white illustrations
Report No.(s): COSPAR-D2.3-E3.3-0032-02; No Copyright; Avail: CASI; A03, Hardcopy
In the largest solar energetic-particle (SEP) events, acceleration occurs at shock waves driven out from the Sun by coronal
mass ejections (CMEs). In fact, the highest proton intensities directly measured near Earth at energies up to approximately
1 GeV occur at the time of passage of shocks, which arrive about a day after the CMEs leave the Sun. CME-driven shocks
expanding across magnetic fields can fill over half of the heliosphere with SEPs. Proton-generated Alfven waves trap particles
near the shock for efficient acceleration but also throttle the intensities at Earth to the streaming limit early in the events. At
high energies, particles begin to leak from the shock and the spectrum rolls downward to form an energy-spectral ‘knee’ that
can vary in energy from approximately 1 MeV to approximately 1 GeV in different events. All of these factors affect the
radiation dose as a function of depth and latitude in the Earth’s atmosphere and the risk to astronauts and equipment in space.
SEP ionization of the polar atmosphere produces nitrates that precipitate to become trapped in the polar ice. Observations of
nitrate deposits in ice cores reveal individual large SEP events and extend back approximately 400 years. Unlike sunspots, SEP
events follow the approximately 80-100-year Gleissberg cycle rather faithfully and are now at a minimum in that cycle. The
largest SEP event in the last 400 years appears to be related to the flare observed by Carrington in 1859, but the probability
of SEP events with such large fluences falls off sharply because of the streaming limit.
Author
Shock Waves; Particle Acceleration; Wave-Particle Interactions; Solar Corpuscular Radiation; Solar Terrestrial Interactions;
Coronal Mass Ejection; Spectral Energy Distribution
20030032979 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Comparison of Total Solar Irradiance with NASA/NSO Spectromagnetograph Data in Solar Cycles 22 and 23
Jones, Harrison P.; Branston, Detrick D.; Jones, Patricia B.; Popescu, Miruna D.; [2002]; 22 pp.; In English
Contract(s)/Grant(s): RTOP 344-12-52-14; RTOP 344-12-52-19; Copyright; Avail: CASI; A03, Hardcopy
An earlier study compared NASA/NSO Spectromagnetograph (SPM) data with spacecraft measurements of total solar
irradiance (TSI) variations over a 1.5 year period in the declining phase of solar cycle 22. This paper extends the analysis to
an eight-year period which also spans the rising and early maximum phases of cycle 23. The conclusions of the earlier work
appear to be robust: three factors (sunspots, strong unipolar regions, and strong mixed polarity regions) describe most of the
variation in the SPM record, but only the first two are associated with TSI. Additionally, the residuals of a linear multiple
regression of TSI against SPM observations over the entire eight-year period show an unexplained, increasing, linear time
variation with a rate of about 0.05 W m(exp -2) per year. Separate regressions for the periods before and after 1996 January
01 show no unexplained trends but differ substantially in regression parameters. This behavior may reflect a solar source of
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