ISSN 1006-9895

CN 11-1768/O4

Characteristics of Atmospheric Stratification and Melting Effect of Heavy Hail Events in Guangdong Province
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Affiliation:

1.School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225;2.National Meteorological Center, Beijing 100081;3.Nanjing University of Information Science and Technology, Nanjing 210044

Fund Project:

National Natural Science Foundation of China Grants 41175048, 41330421National Natural Science Foundation of China (Grants 41175048, 41330421)

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    Abstract:

    Based on conventional L-band soundings, automatic weather station data and ERA-Interim 0.125°×0.125° reanalysis data at 6-hour intervals, we investigate 23 heavy hail events (HHEs, hail diameter ≥20 mm) that occurred in Guangdong province from 2004 to 2017. The 23 hail events are selected according to the Hail Classification Standard in China (GB/T 27957-2011). Characteristics of atmospheric stratification during these events and melting effects of hails are quantitatively analyzed, and a model of physical parameters is established to distinguish heavy hails. The results are as follows. (1) The upper-dry and lower-moist characteristic of vertical stratification is more evident for HHEs than for small hail events (SHEs, hail diameter ≥5 mm and <20 mm), and the convective (potential) instability is more dependent on the upper-dry and lower-moist stratification rather than that of the upper-cold and lower-warm. (2) The ratio of H/H+ (cold cloud/warm cloud) can be used to distinguish HHEs from SHEs, and the ratio above 1.6/1 is one reference criterion for the forecast of heavy hails. (3) Compared with SHEs, the height of maximum thermal buoyancy of HHEs is higher than the isothermal layer of −5℃, which helps the hail embryos to enter efficient growth layer (−10℃-−30℃) and thus drives heavy hail growth. The maximum thermal buoyancy ≥4℃ is a key threshold to distinguish HHEs from SHEs. (4) Thermal conduction and convection transport () play a main role in the melting process of heavy hails, and there is an anti-correlation relationship of with DBZ level (dry bulb zero level) and (average environmental temperature). Impacts of latent heat caused by vaporization and re-condensation of water resulted from hail melting process are reflected in the fact that the smaller the hail diameter over the DBZ level is, the larger the latent heat consume or release, originated from evaporation of water surrounding hail (), and the greater the large hails will melt. The downward extension of the dry layer in the mid-troposphere inhibits the melting of large-size hails. (5) Based on statistical and comparative analyses of this paper, a model of physical parameters is established for prediction of heavy hails. These physical parameters include ΔTd85≥46℃, T−Td≥15℃ at 500 hPa, the minimum T−Td≤2℃ between 700 hPa and 1000 hPa, H/H+≥1.6/1, the intensity of maximum thermal buoyancy≥4℃, and the height of maximum thermal buoyancy higher than the height of −5℃. The above conditions are favorable for the generation of heavy hails.

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History
  • Received:April 23,2018
  • Revised:
  • Adopted:
  • Online: June 04,2019
  • Published: