Climatology, trends and future tendency of clear air turbulence over Indian airspace

Abstract

Clear-air turbulence (CAT) is a major aviation hazard because it occurs without visible warning and hard to detect, especially over India where atmospheric conditions are highly variable. this study aims to understand where CAT favorable conditions occur, how they are changing over time, and what drives these changes over Indian airspace. To address this, ERA5 reanalysis data from 1970-2024 are analysed using ensemble mean of six turblence diagonostics (VWS, TI3, Brown, NCSU1, Ri, and Dutton) at four cruise relevant pressure levels (200, 225, 275, and 325 hPa). The analysis includes spatial distribution, trend patterns and india averaged temporal trends along with random forest model to assess predictability during winter at 275 hpa on Delhi-Bombay route(DEL-BOM). The results show that CAT favorable conditions are most at 275 hpa (40-50%) particularly over northern India, The Indo-Gangetic plain, and the Himalayan foothills. However, the strongest increasing trends are observed at upper levels (200-225)hpa during winter and pre-monsoon (MAM) period, with increase aof about 0.97% per decade (200hpa) and 0.88% per decade (225hpa). In contrast, CAT favorable conditions decrease during monsoon(JJA)season,with reduction of about 0.89% per decade at 200hpa. The results indicate CAT risk is increasing mainly at upper levels ,during specific seasons, rather than uniformly across all regions. The observed changes are primarily driven by jet streams variability, enhanced vertical wind shear, reduced atmospheric stability, and seasonal shifts in large scale circulation, along with influence of monsoon related convection and terrain induced effects. Overall, the study highlights that CAT over india is becoming more seasonally and vertically structured, with increasing risk during winter at flight relevant altitudes, providing important insights for aviation safety and future turbulence prediction.