Magnetopause expansions for quasi-radial interplanetary magnetic field: THEMIS and Geotail observations

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Title:	Magnetopause expansions for quasi-radial interplanetary magnetic field: THEMIS and Geotail observations
Authors:	Suvorova,AV;Shue,JH;Dmitriev,AV;Sibeck,DG;McFadden,JP;Hasegawa,H;Ackerson,K;Jelinek,K;Safrankova,J;Nemecek,Z
Contributors:	太空科學研究所
Keywords:	UPSTREAM PRESSURE VARIATIONS;SOLAR-WIND CONDITIONS;BOW SHOCK;MAGNETOSHEATH;PLASMA;MAGNETOSPHERE;PARALLEL;FORESHOCK;MOTION;FLOW
Date:	2010
Issue Date:	2012-03-27 17:30:33 (UTC+8)
Publisher:	國立中央大學
Abstract:	We report Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Geotail observations of prolonged magnetopause (MP) expansions during long-lasting intervals of quasi-radial interplanetary magnetic field (IMF) and nearly constant solar wind dynamic pressure. The expansions were global: The magnetopause was located more than 3 R(E) and similar to 7 R(E) outside its nominal dayside and magnetotail locations, respectively. The expanded states persisted several hours, just as long as the quasi-radial IMF conditions, indicating steady state situations. For an observed solar wind pressure of similar to 1.1-1.3 nPa, the new equilibrium subsolar MP position lay at similar to 14.5 R(E), far beyond its expected location. The equilibrium position was affected by geomagnetic activity. The magnetopause expansions result from significant decreases in the total pressure of the high-beta magnetosheath, which we term the low-pressure magnetosheath (LPM) mode. A prominent LPM mode was observed for upstream conditions characterized by IMF cone angles less than 20 degrees-25 degrees, high Mach numbers and proton plasma beta <= 1.3. The minimum value for the total pressure observed by THEMIS in the magnetosheath adjacent to the magnetopause was 0.16 nPa and the fraction of the solar wind pressure applied to the magnetopause was therefore 0.2, extremely small. The equilibrium location of the magnetopause was modulated by a nearly continuous wavy motion over a wide range of time and space scales.
Relation:	JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
Appears in Collections:	[Graduate Institute of Space Science] journal & Dissertation

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