9:45 AM - 10:00 AM
[PEM12-22] Horizontal structures and movements of sporadic E layers observed with ionosonde receiver network
Keywords:Sporadic E layer, Ionosphere, Ionosonde
The sporadic-E (Es) layers are high plasma density layers that appear suddenly in the E region of the ionosphere, around 90 – 130 km altitude. It is considered that metal ions converge at the nodes of the vertical shear of zonal winds, and the Es layer is formed. The neutral winds play a major role in the formation and movement of the Es layer. Since the wind velocity varies with local time and altitude, it is necessary to consider temporal variations of the Es altitude to elucidate the mechanism of horizontal movement of the Es layer. Although the dependence of the horizontal movement of the Es layer on local time has been investigated by several observations, there are few observations that investigate the dependence of the horizontal movement on altitude. To enable both altimetric and horizontal observations, we performed a network observation with ionosonde receivers, which the altitude can be measured. The horizontal scale of the new network is about 100 km, with which the Es horizontal movements can be observed.
Ionosonde receivers were installed at Aso and Miyazaki in June 2023. They receive HF radio waves transmitted from ionosonde and measure the electron density and altitude of the Es above the midpoint between the ionosonde and receivers. We performed a tristatic observation by using the ionosonde vertical observation at Yamagawa and oblique observations between Yamagawa and Aso/Miyazaki. The distances are 190 km between Yamagawa and Aso, 100 km between Yamagawa and Miyazaki, and 125 km between Aso and Miyazaki. In this tristatic observation, the velocity and direction of Es horizontal movement were estimated from the time lag in temporal variation of Es density observed at each site. In this study, we statistically analyzed the observed Es horizontal movements. Es layers migrated isotropically at high altitudes (≧ 115 km), while they tended to migrate westward in the zonal direction at low altitudes (< 115 km). At low altitudes, daytime Es tended to move both of northward and southward, while nighttime Es tended to move mainly southward in the meridional direction. The direction of Es layer movements rotated clockwise from southeast at 20 LT to west at 3 LT. This temporal variation of Es movement is the same as that of the neutral wind direction in the E-region at mid-latitude. During the daytime, the direction of Es movement varied from day to day, and that of the neutral wind likewise varied from day to day at low altitude according to the GAIA model. The temporal changes in the direction of Es movements were roughly consistent with the neutral wind of GAIA. We suggest that the Es layers are considered to be out of the zonal wind node and transported by the background neutral winds at low altitude. Based on these results, we will discuss the physical process of horizontal movement of Es layers in the presentation.
Ionosonde receivers were installed at Aso and Miyazaki in June 2023. They receive HF radio waves transmitted from ionosonde and measure the electron density and altitude of the Es above the midpoint between the ionosonde and receivers. We performed a tristatic observation by using the ionosonde vertical observation at Yamagawa and oblique observations between Yamagawa and Aso/Miyazaki. The distances are 190 km between Yamagawa and Aso, 100 km between Yamagawa and Miyazaki, and 125 km between Aso and Miyazaki. In this tristatic observation, the velocity and direction of Es horizontal movement were estimated from the time lag in temporal variation of Es density observed at each site. In this study, we statistically analyzed the observed Es horizontal movements. Es layers migrated isotropically at high altitudes (≧ 115 km), while they tended to migrate westward in the zonal direction at low altitudes (< 115 km). At low altitudes, daytime Es tended to move both of northward and southward, while nighttime Es tended to move mainly southward in the meridional direction. The direction of Es layer movements rotated clockwise from southeast at 20 LT to west at 3 LT. This temporal variation of Es movement is the same as that of the neutral wind direction in the E-region at mid-latitude. During the daytime, the direction of Es movement varied from day to day, and that of the neutral wind likewise varied from day to day at low altitude according to the GAIA model. The temporal changes in the direction of Es movements were roughly consistent with the neutral wind of GAIA. We suggest that the Es layers are considered to be out of the zonal wind node and transported by the background neutral winds at low altitude. Based on these results, we will discuss the physical process of horizontal movement of Es layers in the presentation.