Plasma sheet changes caused by sudden enhancements of the solar wind pressure

• Published in: Journal of Geophysical Research: Space Physics Vol. 115; no. A5
• Main Authors: Miyashita, Y., Keika, K., Liou, K., Machida, S., Kamide, Y., Miyoshi, Y., Matsumoto, Y., Shinohara, I., Saito, Y., Mukai, T.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.05.2010; American Geophysical Union
• Subjects: Atmospheric sciences; Earth sciences; Earth, ocean, space; Exact sciences and technology; Magnetism; magnetotail compression; substorm trigger; sudden impulse; Plasma; Magnetic reconnection; magnetic field; density; pressure; expansion; solar wind; entropy; correlation; temperature; Magnetospheric tail; ions; Plasma layer; compression; Triggering
• ISSN: 0148-0227; 2169-9380; 2156-2202; 2169-9402
• DOI: 10.1029/2009JA014617

Using Geotail data, we have studied the response of the plasma sheet in the magnetotail to sudden enhancements of the solar wind pressure. We have selected three events in which there were no indications of substorm expansions around the corresponding sudden impulses (SIs) on the ground. It is shown that the ion number density and temperature, as well as the ion pressure, increase significantly due to the plasma sheet compression. The specific entropy does not significantly change, suggesting that the plasma sheet compression is nearly adiabatic. This plasma behavior is in contrast to the nonadiabatic substorm‐associated processes. Hence examining the correlation between the number density and the temperature, and especially the specific entropy is critical for distinguishing between substorm‐associated and SI‐associated changes of the plasma sheet. The northward magnetic field in the plasma sheet also increases, or at least does not decrease, associated with the compression, implying that the lateral magnetotail compression suppresses the triggering of magnetic reconnection and therefore substorm expansion onsets.