Kavosi Shiva, Raeder Joachim
Department of Physics and Space Science Center, University of New Hampshire, 8 College Road, Durham, New Hampshire 03824, USA.
Nat Commun. 2015 May 11;6:7019. doi: 10.1038/ncomms8019.
Magnetic reconnection is believed to be the dominant process by which solar wind plasma enters the magnetosphere. However, for periods of northward interplanetary magnetic field (IMF) reconnection is less likely at the dayside magnetopause, and Kelvin-Helmholtz waves (KHWs) may be important agents for plasma entry and for the excitation of ultra-low-frequency (ULF) waves. The relative importance of KHWs is controversial because no statistical data on their occurrence frequency exist. Here we survey 7 years of in situ data from the NASA THEMIS (Time History of Events and Macro scale Interactions during Substorms) mission and find that KHWs occur at the magnetopause ∼19% of the time. The rate increases with solar wind speed, Alfven Mach number and number density, but is mostly independent of IMF magnitude. KHWs may thus be more important for plasma transport across the magnetopause than previously thought, and frequently drive magnetospheric ULF waves.
磁重联被认为是太阳风等离子体进入磁层的主要过程。然而，在行星际磁场（IMF）向北的时期，日侧磁层顶发生磁重联的可能性较小，而开尔文 - 亥姆霍兹波（KHWs）可能是等离子体进入以及激发超低频（ULF）波的重要因素。KHWs的相对重要性存在争议，因为目前尚无关于其出现频率的统计数据。在此，我们对美国国家航空航天局（NASA）的THEMIS（亚暴期间事件和宏观尺度相互作用的时间历史）任务的7年现场数据进行了调查，发现KHWs在磁层顶出现的时间约占19%。其发生率随太阳风速度、阿尔文马赫数和数密度的增加而升高，但大多与IMF强度无关。因此，KHWs对于等离子体穿越磁层顶的传输可能比之前认为的更为重要，并且经常驱动磁层ULF波。
