Investigating Climate Variability over the Eastern Region of India during the Pre-Monsoon Thunderstorm Season

Abstract

Recent observational and modelling studies indicated increased upper tropospheric warming and lower stratospheric cooling over the past few decades. This shift has significantly impacted complex atmospheric circulation processes, which are closely linked to the rising frequency of intense weather events and pose critical challenges in global climate change. The present study investigates the decadal variability of three thermodynamic parameters, temperature, relative humidity (RH), and vertical wind shear (VWS) across different vertical pressure levels. We utilize radiosonde observations recorded at 00 and 12 UTC from 1987 to 2024 over two tropical stations in eastern India, Kolkata and Bhubaneswar, and spatial variability of weather parameters (e.g., temperature, RH, wind shear) from ERA5 reanalysis datasets for the south-eastern region of India (12–27 ºN, 75–95 ºE) focusing on the pre-monsoon months (March–May). Eastern India receives frequent pre-monsoon thunderstorms every year, and the changing climate may be linked to changes in the intensity and/or frequency of these events. The Mann–Kendall trend test and Sen's slope estimator are employed to quantify the magnitude and statistical significance of the observed tendencies. To understand dynamic changes, we further analyze annual mean values and linear tendencies of vertical wind shear difference derived from upper-level (200 and 500 hPa) and lower-level (surface and 700 hPa) wind shear. The results show a substantial warming trend in both the lower (1000–850 hPa) and upper troposphere (100 hPa). An overall declining trend in RH, except at around 500 hPa, where an increasing trend is observed, along with a relatively stronger decreasing trend in low-level (0–3 km) wind shear compared to deep-layer (0-6 km) wind shear.