A New Method of Calculating Falling Zone of Freezing Rain in Zhejiang
In 2008, the thick icecoating caused by the severe freezing rain covered power transmission line in Zhejiang, leading to enormous damages to Zhejiang power grid. However, only one third of the weather stations observed the glaze with a short duration. In this paper, two severe freezing rain processes which occurred in 2008 and 2013 were analyzed using the global reanalysis data ERAInterim and the disaster records of icecoating on Zhejiang power grid. The results show that there are three layers of coldwarmcold with the warm layer’s temperature above 0℃ during the heavy freezing rain process in Zhejiang Province. In Zhejiang, the liquid water falling from the warm layer would be frozen into ice particles because the temperature in warm layer is lower and the thickness of the bottom ice layer is thicker. Sometimes, the ground temperature is above 0℃, so rain would be observed at weather stations during freezing rain. However, the thickness of bottom ice layer become thinner at high elevation, then tiny liquid water can be frozen into ice particles after it passes through the bottom ice layer. The freezing rain can be found mostly above 400 m elevation of central Zhejiang and above 600 m elevation of southern Zhejiang. According to the freezing rain characteristics in Zhejiang, the falling zone of freezing rain can be calculated based on the global reanalysis data, and the results match the disaster records of icecoating well. In general, this is a new method for freezing rain monitoring and forecasting, especially for some mountainous provinces like Zhejiang.