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

[PEM12-P24] Statistical characteristics of mid-latitude plasma bubbles based on GNSS observations at the American longitudinal sector

*Sota Kato¹, Yuichi Otsuka¹, Satonori Nozawa¹, Atsuki Shinbori¹, Takuya Sori¹, Michi Nishioka², Septi Perwitasari² (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.National Institute of Information and Communications Technology)

Radio waves used in Global Positioning System (GPS) and satellite broadcasting and communications pass through the Earth's upper atmosphere called the ionosphere, which is partially ionized by solar radiation. The phenomenon called "plasma bubble" that occurs in the equatorial ionosphere is one of the most severe disturbances in the ionosphere, and it causes interference to radio waves passing through itself. Until now, plasma bubbles have been regarded as an equatorial phenomenon and have been studied extensively. However, recent GPS observations have revealed the existence of a small number of plasma bubbles that reach mid-latitudes and high latitudes, but the cause of the development of plasma bubbles in mid-latitudes and high latitudes has not been clarified. Therefore, the purpose of this study is to clarify the cause of plasma bubbles that reach mid-latitudes by comparing plasma bubbles that reach only low latitudes and plasma bubbles that reach mid-latitudes and high latitudes.
In this study, the Rate of TEC index (ROTI), an index representing ionospheric electron density disturbances obtained from Global Navigation Satellite System - Total Electron Content (GNSS-TEC) data, was used for analysis. In the U.S. region (230° to 330° longitude), where GNSS receivers are widely installed from the equator to high latitudes, the highest arrival magnetic latitude of the enhanced ROTI region (0.5 TECU/min (1 TECU=10¹⁶ m^-2)) was examined in 5° increments for cases where the enhanced ROTI region extends from near the magnetic equator to 15° or more magnetic latitude during the year 2021. During the year 2021, the enhanced ROTI region reached its highest magnetic latitude of 25-30 degrees, with eight cases observed. These eight cases occurred from October to December, and the Kp index at sunset was less than 3+ when the enhanced ROTI region occurred. The seasonal variation in the frequency of the enhanced ROTI region extending over 15° magnetic latitude was also examined, and the occurrence frequency increased around equinox and December. On the other hand, no enhanced ROTI region was observed from May to August. This seasonal variation is consistent with the seasonal variation in the occurrence frequency of plasma bubble by Burke et al. [2004].
In the future, we will also examine the arrival magnetic latitudes from the 2011 to 2022 data and report a summary of the discussion on the characteristics of plasma bubbles extending to mid-latitudes.