| Based on the observed snowfall data from 836 observational stations in China and the Version 3.0 of Daily Surface Climate Variables of China,this paper analyzed the climatic characteristics of snowfall in China during the period of 1961-2012,and focused on the evaluation of the objective criteria method to distinguish the snowfall characteristics in China.According to the difference between the objective criterion method and the observation,the objective criterion method was improved.The main conclusions are as follows:(1)There are obvious regional characteristics of snowfall in China.The large snowfall areas are located in northeastern China,northwestern China and the eastern Tibetan plateau.The snowfall mainly concentrates from October to April of the next year in the four subregions.In terms of long-term changes,the snowfall days in China are generally decreasing,and the snowfall amount in the east of northeastern China,northern Xinjiang and the eastern Tibetan plateau is obviously increasing.In the four subregions,the total snowfall days decreased and the total snowfall amount increased,which was caused by the reduction of light snowfall and the increase of moderate-heavy snowfall.In northeastern China,the snowfall days is characterized by the interdecadal variation of "more-less-more",and there is a 3-4 year interannual oscillation of snowfall amount.In northwestern China,the snowfall days shows the characteristics of "more-less" year alternation,and the snowfall amount increases from less to more.The snowfall days in the eastern Tibetan plateau shows a decadal variation from more to less,with the snowfall amount increasing first and then decreasing.In southeastern China,the snowfall days was more in 1970 and less in 1990 s,and the snowfall amount showed "more-less" annual alternation.(2)Method I-V use daily average temperature less than 0°C,wet bulb temperature less than 0°C,wet bulb temperature dynamic threshold method,0cm ground temperature less than 0°C and 700-850 h Pa thickness less than 1550 m respectively to identify snowfall.Method I-? show the same snowfall large areas with the observation,but the snowfall amount in southeastern China was overestimated.Method IV underestimates the snowfall in the eastern Tibetan plateau.Method V obviously overestimates the snowfall in the middle and lower reaches of the Yangtze River.Methods ?-? can show the general decreasing trend of snowfall days,and the snowfall amount obtained by several objective criteria exhibits the same increaseing trend as the observation in northeastern China,northwestern China and the eastern Tibetan plateau,but the trend of snowfall amount in southeastern China is quite different from the observation.It is reasonable to use method ?-? instead of the observation to study the interannual and decadal changes of snowfall in northeastern China and the interannual changes in northwestern China.When analyzing the snowfall variation in the eastern Tibetan plateau,it is found that the results of method I and II are most close to the observation.(3)When the daily average air temperature is used to distinguish snowfall,the threshold of 0°C is appropriate in northeastern and northwestern China,and the threshold of 0°C is lower in the eastern Tibetan plateau and southeastern China.The threshold of Methods II and III in the four snowfall regions is too large,which makes more rainfall recognized as snowfall.The reasonable threshold value should be greater than 0°C when using 0 cm ground temperature to distinguish snowfall in the four snowfall regions.The reason for the poor effect of method V is due to the selection of the discriminant variable.It is more reasonable to use the wet bulb temperature to distinguish snowfall instead of the air temperature,0cm ground temperature and 700-850 h Pa thickness.The reference threshold of the wet bulb temperature to distinguish snowfall in northeastern China,northwestern China,the eastern Tibetan plateau and southeastern China are-1.5?,-1.5?,-0.4? and-0.3? respectively. |
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