Statistical Behavior of Large‐Scale Ionospheric Disturbances From High Latitudes to Mid‐Latitudes During Geomagnetic Storms Using 20‐yr GNSS‐TEC Data: Dependence on Season and Storm Intensity

Abstract

To establish the statistical behavior of ionospheric TEC variations from high latitudes to mid‐latitudes during the main and recovery phases of geomagnetic storms, we conducted a superposed epoch analysis of interplanetary magnetic field, solar wind, geomagnetic indices (AE and SYM‐H), and global navigation satellite system (GNSS)‐total electron content (TEC) data for 20 yr (2000–2019). In this study, we identify 663 geomagnetic storm events with the minimum SYM‐H value of less than −40 nT and investigate the characteristics of the TEC variations for the weak (−60 ≤ SYM‐Hmin < −40 nT), moderate (−100 ≤ SYM‐Hmin < −60 nT), and strong (−150 ≤ SYM‐Hmin < −100 nT) geomagnetic storms. The main results obtained from the present study are as follows: (a) The TEC enhancements related to the tongue of ionization (TOI), auroral oval, and storm‐enhanced density (SED) plume are more dominant in winter than in summer during the main phase of geomagnetic storms. (b) The structure of the mid‐latitude trough in the nighttime sector becomes unclear in winter. (c) The TEC depletion at auroral and mid‐latitudes (40°–70° GMLAT: geomagnetic latitude) starts to appear in the morning sector (8–10 hr GMLT: geomagnetic local time) during the main phase of geomagnetic storms and the decreased region extends in the lower latitude and GMLT directions with time. The negative storm activity tends to be enhanced significantly as the storm intensity becomes larger. The activity of the TEC depletion is dominant in summer than in winter, which is agreement with the classical ionospheric storm scenario.

Periodic oscillations in the high-latitude ionosphere driven by ultralow frequency waves: simultaneous measurements using SuperDARN radars and GNSS-TEC technique

“…2b, rTEC enhancement began at MLATs > 74° after 01:30 UT, and it further increased abruptly after 01:50 UT. This rTEC variation likely occurred because of enhanced electron precipitation from the magnetosphere associated with auroral activity (Shinbori et al, 2021b). Below the equatorward edge of the enhanced rTEC, we observed rTEC depletion with a value of less than − 0.3, corresponding to a mid-latitude trough.…”

“…Figure 2 shows the magnetic latitude (MLAT)-time plot of the LOS plasma ow velocity and the ratio of the TEC difference (rTEC) along the beam-11 direction of the PGR radar from 00:00-04:00 UT on 23 November, 2022. The rTEC is de ned as the normalized difference between instantaneous TEC values and their averages over 10 geomagnetically quiet days divided by quiet-day averages (Shinbori et al, 2020;2021b). In Fig.…”

Observation of the ionosphere by ionosondes in the Southern and Northern hemispheres during geospace events in October 2021

“…These intervals of V SW increase are notable for enhancements in solar wind proton density (N SW ) and increase in the amplitude of the interplanetary magnetic field (IMF) B z component (-6 < B z < 6 nT). The minimum SYM/H geomagnetic index was -60 nT, indicating a moderate geomagnetic storm (Gonzalez et al, 1994;Shinbori et al, 2022).…”

Observational evidence of thermospheric wind and composition changes and the resulting ionospheric disturbances in the European sector during extreme geomagnetic storms

“…Consequently, the O/N 2 ratio is reduced, and the loss process of ionospheric plasma in the polar region dominates. Therefore, at high latitudes, the ionosphere statistically produces negative ionospheric storms during geomagnetic storms (Shinbori et al, 2022). Furthermore, expansion due to heating in the thermosphere is not limited to altitude but extends in the latitudinal direction as well.…”