Convective Meteorology (Mesoscale Dynamics)

Mechanism of hail formation and hail-Zdr column relationship as seen from simulations with cloud model with spectral bin microphysics

Professor Alexander Khain
Hebrew University of Jerusalem

10 September 2014, 2:00 PM

National Weather Center, Room 1350
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

A mid-latitude storm typical of Oklahoma is simulated using a high resolution cloud model with spectral bin microphysics. It is shown that in polluted atmosphere typical for continents, large hail growth occurs as a result of re-circulation of raindrops in the updraft and accretion of supercooled water. In the case of low aerosol concentration, the amount of supercooled water is lower and hail size is substantially smaller.

A relationship between the parameters of the Zdr columns detected by dual-polarization radars and hail intensity and size is investigated.

In polluted air, Zdr columns arise in cloud updrafts due to the presence of lofted supercooled raindrops. These raindrops serve as embryos of large hail. Therefore hail amount and its size closely correlate with the parameters of the Zdr columns. In the case of low aerosol concentration, the structure of Zdr columns is very different from that in polluted environment. The Zdr columns are either absent or very short.

The conclusion is that both atmospheric instability and aerosol concentration determine formation of hail and Zdr columns.

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