17:15 〜 19:15
[PEM12-P18] Possible generation mechanism of plasma bubbles during a geomagnetic storm in April 2023 based on satellite observations and simulations
キーワード：磁気嵐、全球測位衛星システム、あらせ衛星、プラズマバブル、電場、シミュレーション
Equatorial Plasma bubbles (EPBs) are sometimes expanded from the equator to mid-latitudes during geomagnetic storms. A background eastward electric field is one of the most important factors for generating EPBs through the Rayleigh-Taylor instability. The large-scale evolution of EPBs was extensively studied using ground and satellite observations. However, the development mechanism of storm-time EPBs to mid-latitudes is still unknown. In this study, we clarify a possible generation mechanism of EPBs expanding to the mid-latitudes during a geomagnetic storm in April 2023 by analyzing global navigation satellite system-total electron content (TEC), rate of TEC index (ROTI), Arase satellite data, Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) model, and three-dimensional high-resolution bubble model.
The EPBs in the African-European longitudinal sector indicated by the ROTI enhancement expanded northward to mid-latitudes of ~40° N in geomagnetic latitude and they tilted westward with increasing latitude during the main phase of the geomagnetic storm. The Arase satellite passed through the EPBs and observed electron density depletions at 20–21.5 h MLT around 15° N in geomagnetic latitude at an altitude of 450–700 km. Some density depletions correspond to the enhanced ROTI regions related to the EPBs. An electric field enhancement was also observed by the Arase satellite when it passed through one of the density depletion regions at ~20.5 h MLT. The maximum amplitude of the upward velocity to the ground was ~675.1 m/s. The ionospheric virtual height (h’F) at El Arenosillo (37.1° N, 353.3° E) showed an increase from 250 km at 19:15 UT to 310 km at 19:50 UT. The timing when the h’F increased (19:15 UT) corresponded to that of an increase in the solar wind dynamic pressure from 10 nPa to 20 nPa, while the IMF Bz already directed southward around 17:30 UT. The background eastward electric field was estimated to be 1.39 mV/m during the geomagnetic storm on the basis of the ionosonde data at El Arenosillo.
On the other hand, we use the three-dimensional high-resolution bubble model to clarify how the storm-time EPBs expand from the magnetic equator to the mid-latitudes. The ionospheric electric field data over the magnetic equator were needed for the three-dimensional high-resolution bubble model, but the observational data of the ionospheric electric field over the magnetic equator were not available in this event. In this analysis, we also use the GAIA model to reproduce the latitudinal profile of the eastward electric field at the European–African longitudinal sector during the geomagnetic storm. The eastward electric field in the European–African longitudinal sector calculated by the GAIA model showed the enhancement at all latitudes after 19:15 UT. The result was consistent with the observation result obtained by the ionosonde. The amplitude of the calculated eastward electric field during the geomagnetic storm was ~7–8 mV/m near the magnetic equator at 19:45 UT.
The analysis results described above strongly suggests that the eastward electric field enhancement in this event could be caused by the enhancement of the penetration electric field due to the increase of the dynamic pressure under the southward IMF condition. We will discuss in detail the possible generation mechanism of the storm-time EPBs extending to the mid-latitudes based on the simulation results.
The EPBs in the African-European longitudinal sector indicated by the ROTI enhancement expanded northward to mid-latitudes of ~40° N in geomagnetic latitude and they tilted westward with increasing latitude during the main phase of the geomagnetic storm. The Arase satellite passed through the EPBs and observed electron density depletions at 20–21.5 h MLT around 15° N in geomagnetic latitude at an altitude of 450–700 km. Some density depletions correspond to the enhanced ROTI regions related to the EPBs. An electric field enhancement was also observed by the Arase satellite when it passed through one of the density depletion regions at ~20.5 h MLT. The maximum amplitude of the upward velocity to the ground was ~675.1 m/s. The ionospheric virtual height (h’F) at El Arenosillo (37.1° N, 353.3° E) showed an increase from 250 km at 19:15 UT to 310 km at 19:50 UT. The timing when the h’F increased (19:15 UT) corresponded to that of an increase in the solar wind dynamic pressure from 10 nPa to 20 nPa, while the IMF Bz already directed southward around 17:30 UT. The background eastward electric field was estimated to be 1.39 mV/m during the geomagnetic storm on the basis of the ionosonde data at El Arenosillo.
On the other hand, we use the three-dimensional high-resolution bubble model to clarify how the storm-time EPBs expand from the magnetic equator to the mid-latitudes. The ionospheric electric field data over the magnetic equator were needed for the three-dimensional high-resolution bubble model, but the observational data of the ionospheric electric field over the magnetic equator were not available in this event. In this analysis, we also use the GAIA model to reproduce the latitudinal profile of the eastward electric field at the European–African longitudinal sector during the geomagnetic storm. The eastward electric field in the European–African longitudinal sector calculated by the GAIA model showed the enhancement at all latitudes after 19:15 UT. The result was consistent with the observation result obtained by the ionosonde. The amplitude of the calculated eastward electric field during the geomagnetic storm was ~7–8 mV/m near the magnetic equator at 19:45 UT.
The analysis results described above strongly suggests that the eastward electric field enhancement in this event could be caused by the enhancement of the penetration electric field due to the increase of the dynamic pressure under the southward IMF condition. We will discuss in detail the possible generation mechanism of the storm-time EPBs extending to the mid-latitudes based on the simulation results.