Statistical characteristics of temperature inversions in Istanbul, Türkiye

This study presents a detailed characterization of temperature inversions (TIs) and their subgroups occurring in Istanbul between 2013 and 2022. A total of 7246 sounding reports were analyzed, and TIs were divided into four subgroups based on their bottom heights: surface-based inversions (SBIs), elevated inversions (EIs), lower-troposphere inversions (LTIs), and boundary layer inversions (BLIs). The occurrence frequencies of TIs were examined on a monthly and yearly basis for both 0000 UTC and 1200 UTC. It was found that TIs were more frequently observed at night due to the dominance of radiation inversions. The highest frequency of TIs occurred in September at 0000 UTC and in July at 1200 UTC. Seasonally, TI frequencies were highest in spring and autumn. The majority of TIs occurred within the first 3000 m of the atmosphere, with the highest frequency at the first level (0–1000 m). TIs above 5000 m were rare. The average depth of TIs was 183.3 m, with the highest depth observed in February and the lowest in June. The average inversion strength was 1.16 °C/100 m, with higher strengths observed in winter. The analysis showed that inversion depths and strengths varied both temporally and spatially. The frequencies of TIs varied among the subgroups, with the highest frequency observed in the subgroup starting from or above the ground but with a maximum base height of 1000 m. The frequencies were generally higher at 0000 UTC compared to 1200 UTC.