Impact Assessments of Aerosol Optical Depth and Lightning on Thunderstorm Over the Region of Uttarakhand, India

This study delves into the temporal and spatial dynamics of various atmospheric parameters and lightning activity in Uttarakhand, India. Between January and May, there was a notable surge in aerosol optical depth (AOD) attributed to an inflow of aerosols from the Thar Desert and arid regions. AOD peaks in May and subsequently diminishes due to the removal of aerosols from the atmosphere. The month of May exhibits the highest lightning activity, accompanied by noteworthy events in March, April, June, July, August, and September. However, the peak flash rate in May (0.065 flashes/km²/day) is high in comparison to reported values (6.5 flashes/km²/day) over the monsoon zone of India. Convective Available Potential Energy (CAPE) values exhibit an ascending trend from January onwards, reaching their highest values in May, July, and August, driven by rising surface temperatures. Conversely, surface cooling in June leads to a reduction in lightning activity. Lower Outgoing Longwave Radiation (OLR) values observed in June and July suggest the presence of clouds, resulting in substantial rainfall, particularly in Uttarakhand (10975.79 mm and 9640.69 mm). This pattern bears resemblance to findings in the Indian monsoon zone reported previously. Spatially, Uttarakhand experiences distinct seasonal variations in lightning activity, with the lowest in the summer foothills and the highest in the southeastern region from July to September, primarily driven by summer and monsoon convection. Principal component analysis (PCA) reveals robust correlations between flash count, CAPE, and temperature, primarily influenced by land surface heating during the pre-monsoon and monsoon seasons. The flash count also demonstrates a significant positive correlation with AOD, suggesting an impact of aerosols on lightning. OLR shows a negative correlation with flash count in the monsoon zone. Based on seasonal variation, AOD dominance during the pre-monsoon and monsoon seasons, increased lightning activity, reduced OLR values, and a positive correlation between AOD and lightning frequency under clean conditions.