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


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 aurorae1. 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 magnetopause2. But the plasma content in the outer magnetosphere increases during northward solar-wind magnetic field conditions3,4, 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 instability5. This can supply plasma sources for various space weather phenomena.

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Figure 1: Three-dimensional (3D) cutaway view of Earth's magnetosphere, showing signatures of Kelvin–Helmholtz instability (KHI).
Figure 2: Detection by Cluster of rolled-up plasma vortices on 20 November 2001 (20:26–20:42 ut).
Figure 3: The ion energy spectra and velocity distributions observed by C1, showing the coexistence of the solar-wind (cold) and magnetospheric (hot) populations.


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We are indebted to the Cluster team for the design and successful operation of the Cluster II mission. Part of this work was done while H.H. visited UC Berkeley.

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Correspondence to H. Hasegawa.

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Supplementary information

Supplementary Figure

Relation between the x components of the ion bulk velocity and of the local Alfvén velocity during the observation of the vortices, indicating the absence of local reconnection near the vortices. (DOC 73 kb)

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Hasegawa, H., Fujimoto, M., Phan, TD. et al. Transport of solar wind into Earth's magnetosphere through rolled-up Kelvin–Helmholtz vortices. Nature 430, 755–758 (2004).

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