ULF Fluctuation of Low‐Latitude Ionospheric Electric Fields During Sudden Commencements

Abstract

AbstractWe use the C/NOFS satellite observations to provide the direct evidence for ultra‐low‐frequency (ULF) fluctuations in the low‐latitude ionospheric electric field during the sudden commencement (SC) on 8 March 2012. The meridional plasma drift shows a sudden downward motion with a large amplitude after SC onset. This initial westward electric field signature is followed by ULF fluctuations with periods of 28–100 s. Further, C/NOFS observations show that the ionospheric zonal electric field and compressional component of geomagnetic field present the similar ULF fluctuations with a ∼90° phase difference, indicating the existence of a standing compressional mode wave. The fluctuations in the ionospheric electric field and horizontal component of the geomagnetic field on the ground also exhibit a high correlation and the frequency of the ground‐based geomagnetic field shows no dependence with latitudes. These results suggest that the ULF waves in the ionospheric electric field may be associated with a cavity mode. We also show the ULF waves in ionospheric electric fields in other cases. The ULF wave electric fields provide important information on the ionospheric studies and ionosphere‐magnetosphere coupling in low latitudes.