Ionospheric Signatures of Secondary Waves From Quasi‐6‐Day Wave and Tide Interactions

Y Yamazaki,Y Miyoshi

doi:10.1029/2020ja028360

Abstract

AbstractA sudden stratospheric waring occurred in the southern hemisphere during September 2019, accompanied by an exceptionally strong quasi‐6‐day wave (Q6DW). We examine the ionospheric response using global total electron content (TEC) maps, with a focus on the short‐period variability (5–48 h). A Fourier analysis of the TEC data reveals ionospheric variations associated with the secondary waves due to the non‐linear interaction between the Q6DW and atmospheric tides. The largest signatures among them are related to the ∼29‐h standing oscillation, which is attributable to the Q6DW interaction with the migrating diurnal tide, with the maximum amplitude ∼8% of the zonal mean. Also detected are the signatures associated with the westward‐propagating ∼13‐h oscillation with the zonal wavenumber 1 (∼4%) and westward‐propagating ∼11‐h oscillation with the zonal wavenumber 3 (∼3%), both of which can be attributed to the Q6DW interaction with the migrating semidiurnal tide. The signatures related to the Q6DW interaction with the migrating terdiurnal tide and some non‐migrating tides are also observed. This is the first time that secondary wave signatures of the Q6DW‐tidal interaction are identified in ionospheric observations with predicted zonal wavenumbers and periods. The oscillations are symmetric about the magnetic equator with amplitude peaks at ±20° magnetic latitudes, suggesting that the oscillations are generated by the modulation of the equatorial plasma fountain.

Highlights

The state of the ionosphere significantly changes from day to day
The present study examined ionospheric signatures of short-period (5–48 h) waves during the September 2019 Antarctic stratospheric warmings (SSWs), which was accompanied by an exceptionally strong quasi-6-day wave (Q6DW) in the mesosphere and lower thermosphere (MLT) region (Figure 1)
A Fourier analysis was performed on global total electron content (TEC) maps to derive spectra for different zonal wavenumbers (Figure 2)

Summary

Introduction

The state of the ionosphere significantly changes from day to day. The ionospheric weather is controlled by forcing from above (e.g., solar radiation and energy deposition from the magnetosphere) and by forcing from below, through upward-propagating waves, such as planetary waves, tides, and gravity waves (e.g., Liu, 2016). Sudden stratospheric warmings (SSWs) are extreme meteorological events that disturb the whole atmosphere (e.g., Chau et al, 2012; Pedatella et al, 2018) and provide opportunities to study vertical atmospheric coupling processes including their influences on the ionosphere. Most previous studies on the ionospheric response to SSWs focused on northern hemisphere events (e.g., Goncharenko et al, 2010, 2013; Oberheide et al, 2020). The September 2002 SSW was the only “major” warming event recorded in the southern hemisphere, according to the SSW classification developed for northern hemisphere events (Krüger et al, 2005). Identifying ionospheric effects of the September 2002 SSW was, difficult because of geomagnetic storms that took place around the same time (Olson et al, 2013)

Objectives

Results

Conclusion