《Nature》：太阳风与磁重接

        引起如磁暴和极光等“太空风”现象的带电粒子来源于太阳风。人们通常认为，将太阳风等离子体引进地球磁气圈的主要力量是磁重接，这是一个涉及不同方向磁场线的合并的过程。科学家从来自Cluster四体一组飞船的新的观测结果中，发现了将太阳风等离子体引进磁气圈的另一种方式。令人吃惊的是，当重接变得效率低下时，磁气圈中的等离子体含量会增加；Cluster飞船的数据显示，在这样的条件下，太阳风会进入地球，这是由于在磁气圈由尘埃构成的侧翼存在由 Kelvin-Helmholtz不稳定性或“水上风”不稳定性形成的大型等离子体旋涡。

Transport of solar wind into Earth's magnetosphere through rolled-up Kelvin–Helmholtz vortices

H. HASEGAWA¹, M. FUJIMOTO², T.-D. PHAN³, H. RÈME⁴, A. BALOGH⁵, M. W. DUNLOP⁶, C. HASHIMOTO² & R. TANDOKORO²

¹ Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755-8000, USA
² Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
³ Space Sciences Laboratory, University of California, Berkeley, California 94720-7540, USA
⁴ Centre d'Etude Spatiale des Rayonnements, BP 4346, Toulouse 31029, France
⁵ Space and Atmospheric Physics Group, Imperial College, London SW7 2BZ, UK
⁶ Space Sciences Division, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK

Correspondence and requests for materials should be addressed to H.H. (hiroshi.hasegawa@dartmouth.edu).

Establishing the mechanisms by which the solar wind enters Earth's magnetosphere is one of the biggest goals of magnetospheric physics, as it forms the basis of space weather phenomena such as magnetic storms and aurorae. It is generally believed that magnetic reconnection is the dominant process, especially during southward solar-wind magnetic field conditions when the solar-wind and geomagnetic fields are antiparallel at the low-latitude magnetopause. But the plasma content in the outer magnetosphere increases during northward solar-wind magnetic field conditions, contrary to expectation if reconnection is dominant. Here we show that during northward solar-wind magnetic field conditions—in the absence of active reconnection at low latitudes—there is a solar-wind transport mechanism associated with the nonlinear phase of the Kelvin–Helmholtz instability. This can supply plasma sources for various space weather phenomena.

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