Formation of the Earth's Low-Latitude Boundary Layer


Shen-Wu Chang
Center for Space Plasma and Aeronomic Research
University of Alabama in Huntsville
NSSTC/Space Science Branch/XD12
Huntsville, Alabama

Friday, 24 June 2005
Socialization : 10:15 a.m.
Presentation : 10:30 a.m.

A boundary layer around the Earth's equatorial magnetopause is often filled with solar wind and magnetospheric plasma. This layer which is termed low-latitude boundary layer (LLBL) has a thickness of ~1000 km to a few Earth radii. In-situ measurements from satellites show that LLBL is on closed magnetic field lines. There are several models of LLBL involving different physical processes at the magnetopause. For example, when the interplanetary magnetic field (IMF) is southward, magnetic reconnection near the subsolar region yields open magnetic field lines in the LLBL. LLBL field lines convect tailward and become cusp field lines. Solar wind plasmas directly enter these regions along field lines. For northward IMF, reconnection takes place at high-latitude poleward from the cusp. Field lines convect sunward sweeping through the cusp and then reconnect with geomagnetic field lines in the other hemisphere to form a closed LLBL. In this dual reconnection model, solar wind plasma that previously entered the cusp becomes trapped in the LLBL. An alternative view suggests that solar wind plasma enters the LLBL via diffusion due to wave-particle interaction at the magnetopause. Field lines in LLBL convect sunward instead of tailward in the dual reconnection model. Recent satellite auroral images and plasma measurements and radar data during northward IMF and large solar wind dynamic pressure conditions appear to be consistent with the diffusion model but not the dual-reconnection model.

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