A Statistical Study of the Decreased TEC Region During Summer at Northern High Latitudes

• Published in: Geophysical research letters Vol. 52; no. 8
• Main Authors: Wang, Jian‐ping, Zhang, Bei‐chen, Zhang, Qing‐yu, Zhang, Shun‐rong, Zhang, Qing‐he, Wang, Guo‐jun, Liu, Jian‐jun
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.04.2025; Wiley
• Subjects: Depletion; F region; Global navigation satellite system; Ionization; Ionosphere; Latitude; Navigation; Navigation satellites; Navigation systems; Navigational satellites; Northern Hemisphere; Plasma density; Polar caps; Polar ionosphere; Satellite observation; Satellites; Solar activity; Spatial distribution; Summer; Total Electron Content; Troughs
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2025GL114676

Based on the vertical Total Electron Content (TEC) data observed by the Global Navigation Satellite System in the northern hemisphere, a large area of low plasma density during summer at high latitudes, termed decreased TEC region, was investigated statistically between 2014 and 2024. Compared with the classical depleted structures that usually occur in the nighttime F region at high latitudes during winter, decreased TEC region is usually found in the sunlit polar cap ionosphere during summer. The decreased TEC region is predominantly located in regions above 70° magnetic latitude for moderate and high solar activity. The lower‐TEC region is biased towards the dawn and midnight sectors. Along the 18:25–06:25 Magnetic Local Time meridian, the depth of the decreased TEC region reached 7.6TECu in 2014. The decreased TEC region is deeper for higher Kp (Kp > 2) than for low Kp (Kp ≤ 2). Plain Language Summary The polar ionosphere is filled with non‐uniform plasma densities. In addition to higher plasma density regions, many depleted structures, such as ionization troughs, polar holes, and auroral cavities, are observed at the F‐region of the polar ionosphere. In the summer hemisphere, most of the high‐latitude ionosphere is under the sunlit ionization. However, large area with decreased total electron content (TEC) is found in the summer hemisphere. Based on an 11‐year Global Navigation Satellite System TEC data, for the first time, we investigated the spatial distribution of the polar ionospheric TEC at high latitudes in the northern hemisphere. This decreased TEC region occurs mainly in regions above 70° magnetic latitude for moderate and high solar activity. The lower‐TEC region is predominantly located in the dawn and midnight sectors. The depth of the decreased TEC region is deeper for higher Kp than for low Kp. The result is expected for further understanding of the summer polar ionosphere. Key Points A large area of low Total Electron Content (TEC) during summer, “decreased TEC region,” differing from the classical depleted structures Decreased TEC region is usually observed under moderate and high solar activities The decreased TEC region depends on Kp