Los Alamos National Laboratory, Los Alamos, New Mexico

The fortuitous observations of a magnetic cloud during the ACE/Ulysses radial alignment in March 1998 provide one of the first opportunities to study the same magnetic cloud at two different radial distances. In this paper, we use data from both ACE and Ulysses to examine the expansion of the cloud as well as of the adjacent noncloud solar wind. In particular, we study the evolution 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 moderately 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.

J. Geophys. Res., Vol. 105, No. A12, , 27,269-27,275, 2000