Radial Variation of Solar Wind Electrons Inside a Magnetic Cloud Observed at 1 and 5 AU

R. M. Skoug, W. C. Feldman, J. T. Gosling, D. J. McComas, D. B. Reisenfeld, C. W. Smith, R. P. Lepping, and A. Balogh

Geophysical Research Letters, 105, 27,269--27,275, 2000.

Abstract:

The fortuitous observation of a magnetic cloud during the ACE/Ulysses radial alignment in March, 1998 provides one of the first opportunities to study the same magnetic cloud at two different locations. In this paper, we use data from both ACE and Ulysses to examine the expansion behavior of the cloud, as well as of the adjacent non-cloud solar wind. In particular, we study the behavior of the electrons as the cloud expanded from 1 to 5.4 AU, including the core, halo, and total electron populations. We find that the core and total electron temperatures at either spacecraft are anticorrelated with electron density. However, combined observations from the two spacecraft show that both temperature and density decreased as the cloud expanded, and thus that single point measurements cannot be used to determine a polytropic index describing the expansion of solar wind electrons within the cloud.