NASA Scientific and Technical Aerospace Reports

in the W we use the SOHO/SUMER spectrograph to take a time series of exposures from a single pointing position, providing
a measurement of spectral line properties as a function of time and position along the slit. temperatures from 80,000 - 1.6
million K. These measurements are combined with TRACE movies in transition region and coronal temperature bands to
obtain more complete information concerning prominence structure and motions. The resulting observations allow us to
analyze the thermal and kinetic energy of the moving prominence sources as functions of time.
Author
Coronas; Line Spectra; Plasmas (Physics); Solar Prominences; Thermal Energy; Thermodynamic Properties
20040070946 NASA Marshall Space Flight Center, Huntsville, AL, USA
Modern Solar Mysteries
Hathaway, David H.; [2004]; 1 pp.; In English; No Copyright; Avail: Other Sources; Abstract Only
100 years ago we thought that the Sun and stars shone as a result of slow gravitational contraction over a few tens of
millions of years - putting astronomers at odds with geologists who claimed that the Earth was much, much older. That
mystery was solved in the 1920s and 30s with the discovery of nuclear energy (proving that the geologists had it right all
along). Other scientific mysteries concerning the Sun have come and gone but three major mysteries remain: 1) How does the
Sun produce sunspots with an 11-year cycle? 2) What produces the huge explosions that result in solar flares, prominence
eruptions, and coronal mass ejections? and 3) Why is the Sun’s outer atmosphere, the corona, so darned hot? Recent progress
in solar astronomy reveals a single key to understanding all three of these mysteries.
Author
Sun; Astronomy; Solar Atmosphere; Solar Physics
20040071040 NASA Marshall Space Flight Center, Huntsville, AL, USA
Recent Progress in Understanding the Sun’s Magnetic Dynamo
Hathaway, David. H.; 2004; 1 pp.; In English; No Copyright; Avail: Other Sources; Abstract Only
100 years ago we thought that the Sun and stars shone as a result of slow gravitational contraction over a few tens of
millions of years - putting astronomers at odds with geologists who claimed that the Earth was much, much older. That
mystery was solved in the 1920s and 30s with the discovery of nuclear energy (proving that the geologists had it right all
along). Other scientific mysteries concerning the Sun have come and gone but three major mysteries remain: 1) How does the
Sun produce sunspots with an 11-year cycle? 2) What produces the huge explosions that result in solar flares, prominence
eruptions, and coronal mass ejections? and 3) Why is the Sun’s outer atmosphere, the corona, so darned hot? Recent progress
in solar astronomy reveals a single key to understanding all three of these mysteries.The 11-year time scale for the sunspot
cycle indicates the presence of a magnetic dynamo within the Sun. For decades this dynamo was though to operate within the
Sun’s convection zone - the outmost 30% of the Sun where convective currents transport heat and advect magnetic lines of
force. The two leading theories for the dynamo had very different models for the dynamics of the convection zone. Actual
measurements of the dynamics using the techniques of helioseismology showed that both of these models had to be wrong
some 20 years ago. A thin layer of strongly sheared flow at the base of the convection zone (now called the tachocline) was
then taken to be the seat of the dynamo. Over the last 10 years it has become apparent that a weak meridional circulation within
the convection zone also plays a key role in the dynamo. This meridional circulation has plasma rising up from the tachocline
in the equatorial regions, spreading out toward the poles at a top speed of about 10-20 m/s at the surface, sinking back down
to the tachocline in the polar regions, and then flowing back toward the equator at a top speed of about 1-2 m/s in the tachocline
itself. Recent dynamo models that include this meridional flow now appear to have some power for predicting the size of
future sunspot cycles.
Author
Coronas; Sun; Sunspots; Solar Magnetic Field
20040073450 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Thermal and Nonthermal Contributions to the Solar Flare X-Ray Flux
Dennis, Brian R.; Phillips, K. J. H.; Sylwester, Janusz; Sylwester, Barbara; Schwartz, Richard A.; Tolbert, A. Kimberley, et
al.; [2004]; 1 pp.; In English; COSPAR (Committee on Space Research), 16 Jul. - 1 Aug. 2004, Paris, France; No Copyright;
Avail: Other Sources; Abstract Only
The relative thermal and nonthermal contributions to the total energy budget of a solar flare are being determined through
analysis of RHESSI X-ray imaging and spectral observations in the energy range from approx. 5 to approx. 50 keV. The classic
ways of differentiating between the thermal and nonthermal components - exponential vs. sources - can now be combined for
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