Collaborative Research: Using Polarimetric Radar Observations, Cloud Modeling, and In Situ Aircraft Measurements for Large Hail Detection and Warning of Impending Hail

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Hail is one of the most dangerous and destructive manifestations of severe weather, resulting in an annual average of more than $10 billion USD in insured property losses around the world. In addition to the strong hail impact on personal and business property, the agricultural and renewable energy sectors also suffer. Advanced polarimetric weather radars are the best instruments to remotely detect hail in the clouds, estimate its size, and produce timely warnings of impending hail if guided by the physical cloud models that predict hail growth and its fallout on the surface. However, existing methodologies for quantifying and forecasting large hail have serious limitations which will be mitigated as a result of the project. This project will capitalize on the unique observations of hail from the armored T-28 research aircraft that penetrated hail-bearing storms during multiple field campaigns in the past. Combining direct hail measurements within the cloud aloft and at the surface with cloud modeling describing its evolution on the way to the ground and the collocated polarimetric radar observations within the full depth of the storm will help to better understand the microphysical processes of hail generation and develop more advanced methodologies for its quantification and prediction / nowcasting.The technical approach will involve utilization of the documented measurements of sizes, number concentrations, and shapes of hailstones aloft to initialize the cloud model. The model involves spectral bin microphysics describing the evolution of hailstones including the change of hail size and kinetic energy with height within the storm as they fall to the surface. The output of the cloud model will be converted into the vertical profiles of polarimetric radar variables which will be compared to the associated measured profiles. This will allow to retrieve size distribution of hail above the melting layer using vertical profiles of radar variables associated with melting hail within the melting layer and beneath and will serve as an observational reference for cloud models’ evaluation and optimization. Novel polarimetric radar predictors in deep convective updrafts signifying large or giant hail at the surface will be identified and explored across a wide range of thermodynamic and climatological regimes and height of the surface relative to sea level using polarimetric radar data collected by the operational WSR-88D radars in a multitude of particularly devastating hailstorms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.