[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

[PEM12-P19] Assessment of the launch condition of a sounding rocket experiment for the daytime sporadic-E layers

*古城 侑季¹、齊藤 昭則¹、安藤 慧¹、西岡 未知²、江尻 省³ (1.京都大学、2.（独）情報通信研究機構、3.国立極地研究所)

キーワード：スポラディックE層、電離圏、イオノグラム、イオノゾンデ、観測ロケット

A sounding rocket experiment is planned to launch in the summer of 2024 from JAXA Uchinoura Space Center in Kagoshima to investigate the daytime sporadic-E (Es) layers. In advance of the experiment, we statistically examined the density and altitude of Es layers expected to be observed for any given date and time in the summer by analyzing historical data. Ionograms obtained by the ionosonde of NICT Yamagawa Radio Observation Facility, Kagoshima, were used for the analysis. Instead of the published manually and automatically scaled parameters, whose sampling intervals are 1-hour and 15-minute respectively, the altitude and maximum frequency values of Es layers are automatically identified from the ionograms obtained every 5 minutes from 2018 to 2022. The results show that the occurrence rate of a high-density Es layers at Yamagawa is the highest in late May to mid-June and decreases significantly in late August, and the density is higher morning, especially around 1000 LT, than afternoon during the summer months. The occurrence rate of the Es layers whose maximum plasma frequency is above 5 MHz is 98 % at 1000 LT in mid-June. It is 82 % for above 8 MHz criterion. In late August, it is 70 % for above 5 MHz and 34 % for above 8 MHz. At 1500 LT, the rate for above 5 MHz is 80 % in mid-June. Although the highest-density Es layers is expected in late May to mid-June, considering the rocket launch window, the experiment is preferrable to conduct at 1000-1100 LT in early July. The occurrence rate is 86~90 % for above 5 MHz in this time. The altitude of Es layers at 1000 LT is expected around 110 km during the summer months. Seasonal variation of Es layers, however, varied from year to year. Comparison with ionograms obtained at Kokubunji, Tokyo, shows that the variation also varies from place to place. We will also discuss these year and place differences. It is also known from numerical simulations and lidar observations that the Es layers sometimes have a multilayered structure in the vertical direction. According to the simulation, two Es layers are expected in vertical direction at 1000 LT. In ionograms, vertical thickness of echo from multilayered Es is sometimes displayed large. Structure of Es layers can be examined with thickness of Es echo in ionograms. We will discuss features of Es layers expected to be observed in the sounding rocket experiment, based on models and observations with ionosondes and other instruments.