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Analysis of Climate Change and Circulation Features of Frost Days in Hunan Province, China in Recent 67 Years

This paper provides a basis for crop structure adjustment and selection of suitable growth period varieties in Hunan Province of China, and improves the predictive capacity of Hunan’s abnormal frost disasters to defend against frost disasters effectively. Using the frost date data of 97 meteorological monitoring stations in Hunan Province from 1951 to 2017, statistical analysis was carried out on the variable characteristics of frost days, initial and final frost days and frost-free periods. The NCEP/NCAR data were used to study the circulation characteristics of the province’s frosty weather by linear and polynomial fitting methods to show that: 1) The frost days decrease −0.1 d/a from December to January. 2) The inter-annual rate of change in the initial and final frost days and frost-free period is large, and the average first frost day showed a delayed trend (0.13 d/a). The average final frost day showed an early change trend (−0.12 d/a), and the average frost-free period showed an extended trend (0.22 d/a). 3) The frosty weather in Hunan Province has obvious geographical distribution characteristics. The first frost day showed distribution characteristics of “early in the east and later in the west”, and the final frost day showed the distribution characteristics of “early in the south and later in the north”. The frost-free period showed the distribution pattern of “long in the south and short in the north”. 4) The circulation characteristic values of the frosty days are as follows: 500 hPa East Asian trough is stable, and the temperature field has a cold tongue of −40°C. The −12°C line is located in south part of Hunan and the 0°C line of 850 hPa is stretched to Hubei. Meanwhile, the ground has cold high pressure, and the center pressure is greater than 1025 hPa. These findings could be used for adjusting crop structure, select suitable varieties for growth in Hunan and predicted abnormal frost disasters for effective prevention.