Tracking and Characterization of Convective Storms Through Their Lifecycle in the Monsoon Core Zone Using Polarimetric Radar Observations

Deep convective clouds range from isolated storm to organized mesoscale systems and play a vital role in Earth's energy and water cycles by transporting heat, moisture, and momentum from the boundary layer to the upper troposphere. During the Indian monsoon season, deep moist convection significantly influences the spatial and temporal distribution of rainfall. Observing convective storms/cells and their evolution with time is key for quantifying their behaviour and its dependence on the large-scale environment. One of the challenges in studying convective storm properties is observing the quick evolution of individual storms. Prior studies of deep convection in India have mostly used satellite data to describe the storm structure. However, studies on convective modes, their lifecycle, microphysics, and link to large-scale are lacking, which motivates this work. 

Against this background, we identified and tracked storms using high-resolution C-band polarimetric (CPol) radar data (6 min, 0.5 km) obtained at IITM's Atmospheric Research Testbed (ART) facility at Silkheda in the monsoon core zone. The storms are identified based on the horizontal radar reflectivity texture. This Lagrangian tracking resulted in a storm lifecycle of over 63,000 tracks from June-September 2023, providing unique information on individual storm initiation and growth, location, area, and depth. Results show that about 80% of storms have a short life span of < 1 hr. and cover a small area of < 50 km², while 16% of storms survive up to 2 hrs. and acquire larger areas up to 100 km². During monsoon onset (June) and active (July) periods, storms are wider, more intense, and deeper compared to August and the withdrawal month (September). Diurnal cycle shows that between the noon and early evening hours, storms gradually deepen, intensify, and expand in area. Upon matching the radar tracked storms with large-scale data, it is seen that low-level humidity and CAPE have a major impact on the evolution of convective storm properties. Furthermore, using polarimetric variables, this work investigates the internal vertical microphysical structure of tracked convective cells. The high reflectivity values and greater specific differential phase up to 7 km at the cell initiation provide further evidence of the favorable moist low-level conditions. The radar derived statistics of convective storm lifecycles and interaction between storms described here have the potential to increase our understanding of factors controlling convective evolution and their representation in models.