China Electric Power Research Institute
National Key Research and Development Project (Grants 2018YFC0809400 and 2018YFA0606004), the State Grid Co., Ltd. Science and Technology Project (Grant 5200-202016243A-0-0-00, Research on Multi-temporal and Spatial Scale Power Meteorological Disaster Forecast and Warning Technology), the Joint Research Fund in Smart Grid (Grant U1966601) under cooperative agreement between the National Natural Science Foundation of China (NSFC) and State Grid Corporation of China(SGCC).
The spatio-temporal distribution information of freezing rain has high practical value for the electric power, transportation, communications, agriculture and forestry sectors. Previous research was mostly based on observational data, limited by the short length of the data, uneven distribution and partial lack, there may be insufficient understanding. The new-generation ERA5 reanalysis data contains freezing rain data not provided by other reanalysis data, which provides the possibility to further understand the spatio-temporal distribution in China. This paper uses ERA5 freezing rain data to analyze the annual average and interdecadal characteristics of China’s annual freezing rain days and annual freezing rainfall from 1979 to 2020. The spatio-temporal distribution characteristics of the EOF modes are also studied. The results show that China’s annual average freezing rain days and annual average freezing rainfall are most concentrated in Guizhou, Hunan, et al., directly affecting 7 ‘West-to-East’ ultra-high voltage (UHV) direct-current (DC) transmission lines, with a total length of about 4900 kilometers; The number of annual freezing rain days and annual freezing rainfall in concentrated areas are decreasing; As for EOF mode 1 (variance contribution 36.96%) of the number of freezing rain days, it is mainly distributed to the east of the Heihe-Tengchong line, and the overall trend is decreasing, and with the Qinling-Huaihe line as the boundary, there is a north-south reverse distribution; EOF mode 2 (variance contribution 11.56%) of the number of freezing rain days reflects two anti-phase regions in the southern freezing rain concentrated area, and the phase alternate period is 2 to 4 years; The EOF mode distribution of the annual freezing rainfall are similar to the annual number of freezing rain days.