Rayleigh‐Taylor Instability Observed at the Dayside Magnetopause Under Northward Interplanetary Magnetic Field

Abstract

AbstractUnder northward interplanetary magnetic field, periodical fluctuations with the period of 85 s have been observed by one of the Time History of Events and Macroscale Interactions during Substorms spacecraft at the dayside magnetopause when the solar wind dynamic pressure suddenly dropped. The observed magnetic field distortions, characterized by the compression of the main component as well as the flapping of the perpendicular components, are in line with the theoretical predictions of the Rayleigh‐Taylor (R‐T) instability excited at the magnetopause. With the convective electric field and the mean electric field removed, the perturbations in the electric field are identified as typical two sinusoidal signals with a 90° phase difference, consistent with previous prediction of the attendant electrostatic field arising from the R‐T instability. The transverse motions of the plasmas resulting from the electric drifting driven by the electrostatic field are observed both in pitch‐angle distributions and in distribution functions. The growth rate of the R‐T instability is about 43 s, implying that the instability has time to grow during the disturbances. Using the Gauss theorem, the calculated net charge density based on the electric field observation is one part of 27 compared to the totally observed plasma density, indicating that only a tiny fraction of the charge separates to set up the electrostatic field, which is due to a collective effect in the plasma.