A Comparison of the Propagated Solar Wind with Near-Earth Solar Wind Observations

Abstract:

Magneotospheric dynamics are primarily controlled by the solar wind and its interplanetary magnetic field (IMF). Majority of the magnetospheric studies relied on observation of the solar wind frequently taken as far away as the L1 Lagrange point approximately 230 R_E upstream. The quality of the empirical or theoretical modeling depends on how accurately the solar wind observation at L1 can be propagated to the magnetosphere and drives the magnetospheric dynamics.

It has been more than two decades that researchers seek to determine the structures and evolution of the solar wind observationally in order to characterize the propagated solar wind parcels that interact with the Earth. Russell et al. [1980] used solar wind data at the Earth and L1 without considering the type of solar wind structures and found that the Bz correlations varied from 0.0 to 1.0. Although the most probable correlation was 0.85, half of the time the correlation was less than 0.5. The scale of IMF correlations was reexamined by Collier et al. [1998] using data from Wind and IMP 8. It should be noted that Collier et al. [1998] examined data during solar minimum and Russell et al. [1980] examined data during solar maximum. The scales of solar wind plasma and magnetic field were further examined by Richardson and Paularena [2001]. The found that the transverse scale for a decrease in density correlation by 0.1 is 120 Re and for velocity about 70 Re. In contrast the transverse scales for the components of the IMF are about 50 Re. Using ISEE 2 and IMP8 from 1978 to 1985, Hsu and McPherron [2009] found that a small transvers IMF structure of about 15 R_e can occur only about 5%~13% .

Most of the recent studies examining Sun-Earth coupling using OMNI solar data which is propagated to the Earth-Sun line by a method based upon minimum variance analysis [Weimer et al., 2003; Bargatze et al., 2005]. The important question of how often a near-earth IMF structure is absent from the propagated solar wind and vice versa is critical for the magnetospheric studies. In this study we use the Themis solar wind observations in the year 2008 to compare with the OMNI solar wind data to examine how often the propagated solar wind is matched with the near-Earth solar wind observations and its implication for magnetospheric studies.