34th Solar Physics Division Meeting, June 2003
Session 6 Solar Wind and Heliosphere
Poster, Monday, June 16, 2003, 3:30-5:00pm, Mezzanine

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[6.11] A Study of Extremely Low Density Solar Wind Detected on Three Successive Solar Rotations

L.-H. Wang, R.P. Lin (Space Science Lab. & Department of Physics, UC, Berkeley), D.E. Larson, H.S. Hudson (Space Science Lab., UC, Berkeley)

Three periods of extremely low density solar wind (n < 1 cm-3) were detected by the WIND 3D plasma and Energetic Particle (3DP) instrument on successive solar rotations, July 4, July 31 and Aug 28,1999. The measurements show that the halo electron pitch angle distributions were far narrower than those in normal solar wind. With the increasing distance from the Sun, adiabactic focusing narrows the pitch angle distribution, while Coulomb collisions, which are proportional to the electron number density, widens the pitch angle distribution.In the low density events, fewer Coulomb collisions lead to a more anisotropic halo electron distribution. The observations are compared to numerical results from a 1-dimensional simulation based on the Fokker-Planck equation. We also examine solar observations from SOHO and YOHKOH to search for the source of the low density solar wind.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.