Abstract:

Based on conventionally observational data at 89 weather stations in Jiangxi province from 1960 to 2013, characteristics of vertical temperature stratification for 106 freezing rain cases were analyzed in terms of methods of a statistical analysis and a interpolation, from which a prediction method was established. The results indicate that temperature decreases sharply from 1000 hPa to 850 hPa and increases on 700 hPa when freezing rain happens. There is significant inversion layer between 925 hPa and 700 hPa. Warm layer is essential to freezing rain, and it is located in 700 hPa for 87.7 % cases and in 850 hPa for only 9.4 % cases. Temperature threshold standard for freezing rain prediction is defined in Jiangxi province i.e., temperature is <1.0 ℃ at 1000 hPa, <-2.0 ℃ at 925 hPa and 850 hPa, and ≥0.0 ℃ at 700 hPa. However, it should be vigilant when warm layer is located in 850 hPa. The lower ground temperature is, the more favorable formation of freezing rain is. Freezing rain occurs when the minimum temperature is below 0.0 ℃ and average temperature is below 1.0 ℃. Cold and warm air converges continuously over the areas from 27 °N to 28 °N. In addition, the frequency of average temperature below 1.0 ℃ and minimum temperature below 0.0 ℃ in the south of the Poyang Lake to Fuhe River are significantly higher than those in other areas, which makes freezing rain in these areas more often than in others. According to the corresponding relationship of freezing rain with atmospheric inversion temperature stratification and ground air temperature, an automatic diagnostic method is developed based on the data from the model and observational stations.

Key words: Freezing rain, Vertical temperature stratification, Inversion, Ground temperature, Prediction method