An Unusual Heliospheric Plasma Sheet Crossing at 1 AU 

Chin-Chun Wu1, Kan Liou2, Angelos Vourlidas1,2, Ronald P Lepping3, Yi-Ming Wang4, Simon P Plunkett1, Dennis G Socker5 and Shi Tsan Wu6, (1)Naval Research Lab DC, Washington, DC, United States, (2)JHU/Applied Physics Lab, Laurel, MD, United States, (3)NASA Goddard Space Flight Center, Emeritus, Greenbelt, MD, United States, (4)US Naval Research Laboratory, Washington, United States, (5)US Naval Research Laboratory, Washington, DC, United States, (6)University of Alabama in Huntsville, Huntsville, AL, United States
Abstract:
At 11:46UT on September 9, 2011, the Wind spacecraft encountered an interplanetary (IP) fast forward shock. The shock was followed almost immediately (~5 minutes) by a short duration (~35 minutes), extremely large density pulse with a density peak of ~100 cm-3. While a sharp increase in the solar wind density is typical of an IP shock downstream, the unusual large density increase prompts a further investigation. After a close examination of other in situ data from Wind, we find the density pulse was associated with (1) a spike in the plasma beta (ratio of thermal to magnetic pressure), (2) multiple sign changes in the azimuthal angle of magnetic field, (3) depressed magnetic field, (4) a small radial component of magnetic field, and (5) a large (>90 degrees) pitch-angle change in suprathermal electrons (>200 eV) across the density pulse. We conclude that the density pulse is the heliospheric plasma sheet and the estimated thickness is ~820,000km. The unusually large density pulse is likely to be a result of the shock compression from behind. This view is supported by our 3D magnetohydrodynamic simulation. The detailed result and implications will be discussed.

*This work is supported partially by ONR 6.1 program

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