Sunward propagating Alfvén waves in association with sunward drifting proton beams in the solar wind


The group of Solar and Heliospheric Physics published a paper on ApJ, reporting an observation of sunward proton beam drift in association with the sunward propagating Alfven waves. The sunward propagation is found to be in the pristine solar wind disconnected from the Earth bow shock. Although several possibilities are discussed in the end of this paper, it still remains a mystery on how to generate the sunward waves and associated proton beams.

For details please refer to: doi:10.1088/0004-637X/805/2/176, 2015

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Imprints of impulse-excited hydromagnetic waves on electrons in the Van Allen radiation belts


Drift-resonance resonance between electrons and ultralow frequency waves are characterized by energy-dependent phase differences between electron flux and electromagnetic oscillations. In the initial wave cycles, however, such characteristic differs from observations. The differences are found to be imprints of impulse-excited waves before they transform into more typical standing waves. Our identification of such imprints provides a new understanding of how energy couples in the inner magnetosphere, and a new diagnostic for the generation of hydromagnetic waves

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On the generation of magnetic dips ahead of advancing dipolarization fronts


Dipolarization fronts (DFs) in the magnetotail are typically asymmetric with a small Bz dip followed by a sharp Bz enhancement. Using THEMIS observations of hundreds of DFs, we find that the depth of the Bz dip as a function of the front azimuth depends on DF propagation speed and ambient plasma density. These statistical signatures support the hypothesis that the Bz dip is caused by ion reflection and suggest that secondary currents carried by these reflected ions can reshape the front significantly.

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