Excitation mechanism of ionospheric 6-day oscillation during the 2019
September sudden stratospheric warming event
Abstract
A sudden stratospheric warming (SSW) event in the Antarctic region
occurred in September 2019. During the SSW event, the quasi 6–day wave
(Q6DW) was enhanced in the mesosphere, and strong 6–day oscillations
are observed in ionospheric parameters, such as the equatorial
electrojet (EEJ) and electron density. The 6–day variation in the EEJ
has a westward–moving structure with the zonal wavenumber 1, indicating
the influence of the Q6DW. In this study, we investigate the excitation
mechanism of the 6–day variations in the EEJ and electron density using
numerical simulations. The main results are as follows. The 6–day
variations in the ionosphere are not generated by the Q6DW, but
generated by the waves with periods from 10 to 14 hours. The amplitude
of the 10–14 hour waves is modulated with a period of 6 days, due to
the nonlinear interaction between the Q6DW and migrating semidiurnal
tide. This leads to the 6–day variations in the EEJ and electron
density through the E–region dynamo process. At a fixed local time, the
secondary waves generated by the Q6DW-tidal interaction produce
westward-moving ionospheric 6-day variations with zonal wavenumber 1,
which cannot be distinguished from the ionospheric variations by the
Q6DW itself. The interference of secondary waves leads to a longitudinal
asymmetry in the magnitude of the ionospheric 6–day oscillation.