Ionospheric semi‐diurnal lunitidal perturbations during the 2021 Sudden Stratospheric Warming event: Latitudinal and inter‐hemispheric variations in the American, Asian‐Australian, and African‐European sectors

The ionosphere exhibits enhanced semidiurnal lunitidal (M2) perturbations during sudden stratospheric warming (SSW) events, of which the manifestation and mechanism are not well documented and understood. This paper studies the latitudinal and inter-hemispheric variations of the ionospheric M2 perturbations during the 2021 major Arctic SSW with total electron content (TEC) data in the American, Asian-Australian, and African-European sectors. Results show that the M2 perturbations in the three sectors all enhanced during the SSW, with the strongest M2 perturbations in the Northern and Southern Hemispheres at about 10 degrees similar to 15 degrees N and 25 degrees similar to 30 degrees S geomagnetic latitudes, respectively. Also, clear M2 perturbations in the three sectors all extended to middle latitudes during the SSW only in the Southern Hemisphere. Comparatively, the inter-hemispheric asymmetry of the magnitude of the M2 perturbations during the SSW was more complex. The inter-hemispheric asymmetry of the crest locations of the low-latitude M2 perturbations in the three sectors during the SSW was probably due to the F-region meridional wind effect on the diffusion process of the low-latitude plasma fountain. Meanwhile, the longitudinal differences were also obvious. The TEC M2 amplitude in the American sector was obviously larger than those in the Asian-Australian and African-European sectors during the SSW. The M2 characteristics in the southern middle latitude in the American sector were significantly different from those in the other two sectors during the SSW, which may be related to the differences of the combined effects of the local wind and geomagnetic configuration. In addition, a moderate geomagnetic activity occurred during the 2021 SSW, which brings difficulties to the analysis of the SSW-related TEC variation.