Abstract: The Arctic region serves as a sensitive zone for global climate change. Understanding its atmospheric vertical structure is crucial for elucidating the Arctic amplification effect. However, our understanding of atmospheric characteristics over the central Arctic Ocean is constrained by the scarcity of radiosonde observation data in this area. Based on radiosonde observations collected during the 13th Chinese National Arctic Research Expedition in summer 2023, this study systematically analyzed atmospheric vertical structure characteristics over the Arctic Ocean region (75.5°N—90°N). The observations are compared with historical data and combined with ERA5 reanalysis data to explore the influence mechanisms of typical weather processes. Results indicate: (1) Inversion phenomena, characterized by a temperature increase with altitude rather than the typical decrease, are widespread in the atmospheric boundary layer. The temperature lapse rate in the lower inversion layer is 0.36 ℃·100 m^–1, with a median inversion base height of 250 m, a median inversion thickness of 210 m, and a median inversion strength of 3.2 ℃. (2) In our study, between altitudes of 1 to 10 km, the average temperature lapse rate is 5.44℃·km^–1, and the cold-point tropopause is typically found at an altitude of 9.98 km with a corresponding temperature of –48.6 ℃. (3) Near-surface high humidity (relative humidity >90%) and inverted humidity structures lead to frequent sea fog, with 90% of water vapor is concentrated below 5.5 km. (4) Although no distinct regional patterns emerge, frequent low-level jets occur with core heights between 2 and 4 km. (5) Inversion layers and humidity inversions characteristics are particularly pronounced near the North Pole, with an average inversion thickness of 405 m and an average inversion strength of 6.47 ℃. While the strength is significantly higher than at historical drifting stations. Weather-scale analysis indicates that the formation of the warm center and strong inversion at 660 m on September 6 in the North Pole region was closely associated with radiative cooling under the control of a low-level cold high-pressure system and the superposition of warm advection at the 925 hPa level. This study fills a gap in radiosonde observations over the North Pole region in China, providing crucial observational evidence for improving polar numerical models and deepening our understanding of sea-ice-atmosphere coupling mechanisms in the Arctic amplification effect.

Key words: boundary layer inversion, low-level jet, moisture inversion, Arctic amplification effect, Arctic research expedition, North Pole