准径向行星际磁场的磁层顶展开：THEMIS和Geotail观测
Magnetopause expansions for quasi-radial interplanetary magnetic field: THEMIS and Geotail observations
摘要：
我们报告了THEMIS和Geotail观测结果，在准径向行星际磁场（IMF）和几乎恒定的太阳风动压的长时间间隔内，磁层顶（MP）的长期膨胀。膨胀是全球性的：磁层顶分别位于其标称向阳面和磁尾位置之外3 RE和~7 RE。扩展状态持续了几个小时，就像准径向IMF条件一样长，表明稳态情况。当观测到的太阳风气压为1.1-1.3 nPa时，新的日下MP平衡位置位于14.5 RE，远远超出了它的预期位置。平衡位置受地磁活动的影响。磁层顶的膨胀是由于高β磁鞘的总压力显著降低，我们称之为低压磁鞘（LPM）模式。在上游条件下，当IMF锥角小于20 ~ 25 grad，高马赫数，质子等离子体β <1.3时，观察到一个显著的LPM模态。THEMIS在磁层顶附近的磁鞘中观测到的总压力最小值为0.16 nPa，因此施加到磁层顶的太阳风压力的比例为0.2，非常小。磁层顶的平衡位置在很宽的时间和空间尺度上被一种近似连续的波动所调制。
英文摘要：
We report 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 RE and ~7 RE 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 ~1.1-1.3 nPa, the new equilibrium subsolar MP position lay at ~14.5 RE, 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 ~ 25 grad, 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.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
