Global evolution and propagation of electric fields associated with Sudden Commencements observed by multi­ple magnetospheric satellites and ionospheric radars

Abstract:

Sudden commencements (SCs) are triggered by a compression of the dayside magnetosphere, leading to fast mode wave propagation in the equatorial plane. In contrast, the compression induces Alfven waves that propagate toward the dayside polar ionosphere along field lines, and then ionospheric electric fields propagate toward low-latitude ionosphere at speed of light. Several direct observations have provided evidence of the fast mode or Alfven wave propagation, but spatial and temporal evolutions of these propagations are not well known. Moreover, a previous study shows that upward Poynting fluxes transport electromagnetic energy toward the nightside magnetosphere. However, whether such upward Poynting fluxes are launched from the ionosphere or converted from fast mode waves has not been confirmed yet. In this study, we investigate evolution of the electric field in the magnetosphere-ionosphere coupled system using THEMIS, Van Allen Probes, GOES 13 and 15, SuperDARN, and HF Doppler radars. We find 70 SC events occurred from January 2013 to December 2014. The result of event studies shows the time delay of the onsets between dayside and nightside magnetospheric electric fields, which can be explained by the fast mode wave propagation. However, we also find that the SC onset of the nightside electric field (~21 h LT) is 15 s later than that of the midnight one although they are detected in the same L-value, which may suggest a dawn-dusk asymmetry of the electromagnetic energy propagation time in the inner magnetosphere. In the ionosphere, both SuperDARN and HF Doppler radars detect a northward velocity at ~15 h LT about 1 min after that of the dayside magnetospheric electric field, which is consistent with the Alfven velocity from the dayside magnetosphere to the polar ionosphere. We will evaluate the possible propagation path of the electromagnetic energy associated with SCs.