Chanabasanagouda Sanganagouda Patil

The onset of the Southwest Monsoon (SWM) over Karnataka marks a critical transition from hot, dry pre-monsoon conditions to a period of high convective activity, bringing thunderstorms along with heavy rainfall and strong gusty winds. The study investigates the characteristics of thunderstorms and associated key synoptic and thermodynamic factors during the onset of monsoon for the year of 2024. The monsoon advanced over Karnataka on 1st June 2024 and covered the entire state by 6th June 2024. Thunderstorm activities were observed in the entire Karnataka region with isolated extremely heavy rainfall at a few locations (e.g., rainfall ~11 cm in Bengaluru on 3rd June). Synoptic analysis revealed a persistent shear zone along 8°N over South Peninsular India (3.1– 4.5 km altitude) and cyclonic circulations over the Arabian Sea, enhancing the moisture transport over the region. A low-pressure system over the Bay of Bengal and mid-tropospheric circulations over coastal Karnataka further intensified convective instability during the study period. Based on the upper air sounding data, the thermodynamic indices indicated that strong moisture convergence, high Convective Available Potential Energy (CAPE) ~2501 J/Kg and vertical wind shear are fostering thunderstorm genesis. The study highlights the complex interplay of large-scale dynamics and localized processes in thunderstorm formation during monsoon onset of 2024. Improved understanding of these mechanisms can enhance predictive accuracy, disaster preparedness and mitigate the socio-economic impacts in the Karnataka region.

The study examines the long-term (2011-2023) analysis of thunderstorm and lightning activities and their impacts on local meteorology and air pollutants over Bengaluru. The diurnal thunderstorm events occur mainly in the late evening hours (1900–2100 IST) and on monthly maximum in May while minimum in January. Annually, Bengaluru experiences an average of 41 thunderstorms and 157 lightning strikes, both of which have shown a statistically significant upward trend at a 95% confidence level. The rate of increase is 3.41% per year for thunderstorms and 3.3% per year for lightning events. Local temperatures coupled with abundant moisture supply from the southwest/northeast monsoon creates a favourable condition for the initiation of thunderstorms over the region. This study also focused on the trend analysis of meteorological parameters and atmospheric compositions, a rising trend were found in rainfall (1.44 mm year–1), RH (0.74% year–1) & pressure (0.03 hPa year–1) whereas a slight declining trends in temperature (0.06 0C year-1) & wind speed (-0.02 ms-1 year–1). As the availability of heat and humidity are two main prerequisites for the occurrence of thunderstorm and hence the probability of severe thunderstorms may increase in future. The AOD, NO2 & O3 showed a significant increasing trend while no trend for SO2. The Pearson correlations showed the AOD, NO2 & SO2 concentrations are significant negatively correlated with wind speed but positively correlated with atmospheric pressure. A further study indicated a significant impact of thunderstorm on the air pollutants has also been quantified and it was observed that PM2.5 concentration gradually decreases after the commencement of thunderstorm while quick increase response (less than 1 hour) was observed in O3 and delay response (after 2:30 hours) in NO2 which may linked to lightning activities. The results reveal that thunderstorms can affect both the local meteorology as well as atmospheric pollutants and vice-versa from regional to global.