A modeling study on the role of aerosols in modulating the lightning flash rates over two different climatological regions of India

Over the last few decades, lightning has been one of the fatal extreme weather phenomena in the Indian subcontinent. Aerosols which act as cloud condensation nuclei (CCN) and ice nuclei (IN) can modify the cloud properties and alter the thermodynamic processes within the deep convective clouds in a way that eventually affects the lightning flash rates associated with thunderstorms. Long-term satellite observations suggest that a maximum number of lightning strikes (40-45 flashes/km²) occur during the pre-monsoon (March-May) and monsoon (June-September) seasons over the Indian subcontinent. We analyzed the lightning data available from satellite observations over two distinctly different climatological regions namely, northeast India and western India. In this study, we evaluate the performance of a numerical weather research and forecasting model (WRF) in reproducing the lighting characteristics over these two regions and further try to understand the sensitivity of simulated lightning flash rates to aerosol characteristics and aerosol-cloud interactions considered in the model.

Two severe lightning episodes which occurred on 5-6 May 2013 and 16 April 2019 over northeast India and western India respectively are chosen as case studies for our model sensitivity experiments. We used Morrison, NSSL & SBM microphysics schemes to understand the capability of bulk and bin schemes in simulating these events. Our results show that SBM (bin) scheme affects lightning flash events more accurately than the other two bulk schemes. Increasing aerosol concentrations, increases the cloud droplet number concentrations, thus influences the collision-coalescence processes thereby increase lightning activity over both regions. To further understand the influence of aerosol size, we used a spectral bin microphysics method with a dry radius range of (0.7nm-12µm), which modified the cloud microphysical features. Changing the number concentration and default size of aerosols also influenced the meteorology and hence the deep convection and thunderstorms occurring over the two selected case study regions. More results with greater details will be presented.