5:15 PM - 6:45 PM
[PEM10-P04] Mid-latitude ionospheric and thermospheric responses to the strong substorm that occurred on October 24, 2003
The causes of ionospheric and thermospheric variations at mid-latitudes can be attributed to the ionospheric electric field that promptly penetrates from the polar regions to the equator associated with storms and substorms, and to the thermospheric waves that originate from atmospheric heating in the polar regions and propagate to lower latitudes. In the former case, when the Region 1 field-aligned currents dominate as the substorm current wedge, westward electric fields penetrate to the mid-low latitudes on the night side. The oblique downward ExB drift associated with the westward electric fields causes O+ in the ionosphere to penetrate to lower altitudes, interacting with higher O2 densities, resulting in 630-nm airglow enhancement. So far, we have reported 7 events of a simultaneous 630-nm airglow enhancement at two or more stations using data obtained by all-sky cameras installed at three mid-latitude stations in Japan: Rikubetsu (43.5oN, 143.8oE), Shigaraki (34.9oN, 136.1oE), and Sata (31.0oN, 130.7oE). In this study, we elucidate the mid-latitude ionospheric and thermospheric responses for an extremely strong substorm on October 24, 2003 by analyzing ground magnetic field, GNSS-TEC, airglow imagers, ionosonde, and a Fabry-Perot interferometer.
According to the substorm list by Newell and Gjerloev [2011], the substorm started at 15:25 UT on October 24, 2003. The 630-nm airglow enhancement started at almost the same time at the three stations mentioned above. In addition, the airglow intensity was rapidly decreased after 16:00 UT, about 30 minutes after the airglow enhancement onset. A downward motion of the ionosphere was observed after the substorm onset by ionosondes in Japan and Australia, coincident with the onset of the 630-nm airglow enhancement. Subsequently, a rapid upward motion of the ionosphere was observed with a decrease in the airglow intensity. These results indicate that there is a good correlation between the variation of 630-nm airglow intensity and the change in ionospheric virtual height, and that this airglow variation was caused not by a change in the electron density but by a change in the product of O+ and O2 densities associated with the ionospheric height variation. A Fabry-Perot interferometer installed at Shigaraki showed no neutral wind fluctuations associated with the substorm onset. This result suggests that the downward motion of the ionosphere after the substorm onset is due to the westward electric field penetration. The upward motion of the ionosphere during the substorm was also not associated with significant neutral wind variations. The eastward electric field associated with overshielding is considered to occur ~15-20 minutes after substorm onset (Ebihara et al., JGR, 2014) and may have contributed to the upward motion of the ionosphere ~30 minutes after the onset. Using TEC data obtained by the GNSS receiver network installed in Japan, we also investigated the deviation from the 1-hour moving average of the total electron content (TEC) obtained between the satellites and the receivers. The results showed that the TEC simultaneously increased by ~0.1 TECU in the 30-45oN after the substorm onset, similar to the airglow enhancement. This is possibly caused by the plasma supply from the plasmasphere. In order to clarify the connection between the polar regions and middle latitudes and the cause of the electric fields, we have a plan to compare these results with TIEGCM simulations and other models.
According to the substorm list by Newell and Gjerloev [2011], the substorm started at 15:25 UT on October 24, 2003. The 630-nm airglow enhancement started at almost the same time at the three stations mentioned above. In addition, the airglow intensity was rapidly decreased after 16:00 UT, about 30 minutes after the airglow enhancement onset. A downward motion of the ionosphere was observed after the substorm onset by ionosondes in Japan and Australia, coincident with the onset of the 630-nm airglow enhancement. Subsequently, a rapid upward motion of the ionosphere was observed with a decrease in the airglow intensity. These results indicate that there is a good correlation between the variation of 630-nm airglow intensity and the change in ionospheric virtual height, and that this airglow variation was caused not by a change in the electron density but by a change in the product of O+ and O2 densities associated with the ionospheric height variation. A Fabry-Perot interferometer installed at Shigaraki showed no neutral wind fluctuations associated with the substorm onset. This result suggests that the downward motion of the ionosphere after the substorm onset is due to the westward electric field penetration. The upward motion of the ionosphere during the substorm was also not associated with significant neutral wind variations. The eastward electric field associated with overshielding is considered to occur ~15-20 minutes after substorm onset (Ebihara et al., JGR, 2014) and may have contributed to the upward motion of the ionosphere ~30 minutes after the onset. Using TEC data obtained by the GNSS receiver network installed in Japan, we also investigated the deviation from the 1-hour moving average of the total electron content (TEC) obtained between the satellites and the receivers. The results showed that the TEC simultaneously increased by ~0.1 TECU in the 30-45oN after the substorm onset, similar to the airglow enhancement. This is possibly caused by the plasma supply from the plasmasphere. In order to clarify the connection between the polar regions and middle latitudes and the cause of the electric fields, we have a plan to compare these results with TIEGCM simulations and other models.