Study On Climate Feature, Variation Rule And The Forecast Method Of Frost In Ningxia Province

In this paper, by selecting the period between 1961 and 2004 meteorological observational data of 20 stations including frost times (April 15^th to October 15^th ),first frost,last frost.frostless period in Ningxia and using the methods of resultant analysis, tendency analysis, T-test,Departure test,a study of the climate characteristics of frost times in Ningxia was done anew,an analysis of the rule of interannual and decade change ,the abrupt of frost times in Ningxia was conducted first;The absolute variabilities, guarantee rates and the rule of interannual change of the first frost,last frost,frostless period were analyzed anew by dividing area in Ningxia and the rule of decade change, the rule of interannual change of different period , the abrupt of long time of them in Ningxia were conducted first;By selecting the period between 1981 and 2007 ground meteorological observational data of 6 stations including frost date from April 14^th to May 20^th (Xiji station from April 14^th to May 30^th), including the first day before frost date in Ningxia and using the methods of multivariate regressin, F-test , the multivariate regression equations were established first on the minimum temperature of the frost date and ground meteorological observational data of the first day before frost date in Ningxia; The test was done on the regression equations. Wo hope to supply scientific gist to frost forecasting, preventing and reducing disaster and using reasonably the climate resoures in Ningxia. The studies and analysis show that:1. The most of the frost times was in April and October, next was in May and September monthly from 1961-2004 in Ningxia;The most of the frost times was in the middle of April, next was in the later of April, in the middle and front of October and in the front of May by ten days in Ningxia Province. The occurrence frequency was most at the mountain area in Sounth Ningxia Province(except Helan mountain and Liupan mountain), next was in Mahuangshan, Zhongwei, Yanchi, Lingwu and the most of north Yinchuan. The least was in Tongxin, Wuzhong and Qingtongxia. The occurrence times of frost possessed obvious features of annual variation and inter-decadal variation in April, May, June. September, October, spring, autumn and full year in Ningxia Province. Occurrence times of frost presented descendant tendency in above every period in Ningxia Province recently 44 years. The occurrence times of frost had showly descending trend in June and autumn and full year. The occurrence times of frost presented annual variation climate abrupt in above every period (except June) . The abrupt years were 1988, 1982, 1972, 1974, 1984, 1974 and 1984. The frost times reduced obviously after the abrupt years, the reduction range was 36.5%-72.1%.2. The average first frost dates were October 13^th, October 12^th and October 8^th, the average last frost dates were April 21^th, April 27^th and May 8^th, the average frostless periods were 177 days. 169 days and 154 days in Irrigated region, Middle arid region and Guyuan region of Ningxia,the average frostless periods were shortened from North to south.The absolute variability of frostless period was larger than that of the first frost and the last frost in Ningxia Province recently 44 years, the interannual change was bigger; Absolute variability of the last frost was larger than that of the first frost; This showed the first frost was stabler than the last frost and the interannual change was smaller relatively. The probability(43.2%, 45.5%) that the first frost appeared early were smaller than that(47.7%, 50%) of the last frost ended late in Irrigated and Guyuan region.the probability(47.7%) that the first frost appeard early was bigger than that(43.2%) of the last frost ended late in Middle arid region.Therefore the harm of last frost was graver than that of the first frost in Irrigated region and Guyuan region and the harm of the first frost was graver than that of the last frost in Middle arid region.The probabilities were the biggest appearing early and ending late in 0-5 days,6-10 days and 11-15 days in three regions of Ningxia,it appeared one times every 4-6 years averagely;The proportions of the years were 91%-93% that frostless period concentrated on 20 days or so from average. This showed frostless period didn't disperse.3. In 1960s and 1970s, the first frost appeared early and the last frost ended late,the frostless periods were shorten;After 1980s the first frost appeared late and the last frost ended early,it made the frostless period prolong;In eight years from 1997-2004 the first frost appeared late or early and the last frost ended early,it made the frostless period prolong in three regions of Ningxia. The first frost appeared late gradually and the last frost ended early significantly made the frostless period prolong obviously in the past 44 years.But after 1980s the first frost appeared early unobviously, while the last frost ended early unobviously, the frostless period was shortened unobviously in Guyuan region. The first frost appeared early, while the last frost ended late, so that the frostless periods were shortened in Irrigated region and Middle arid region of Ningxia from 1997 to 2004,but the tendency in Guyuan region was on the contrary, the tendencies of the last frost and the frostless period in Middle arid region were significant. The abrupt change of the first date and the ending date of frost occured in Ningxia province in the past 44 years.The first frost leaped from relative earlier stage to relative later in 1972 and 1974. The last frost leaped from relative later stage to relative earlier stage, the frostless period leaped from relative shorter stage to relative longer stage in 1983 and 1984.4. The frost weather possessed the characteristics of high pressure, low humidity , little cloud or fine day and weak wind at 08^th of frost date. When strong cold air entered Ningxia Province, the higher 14^th station pressure was, the lower the 14^th temperature, the minimum temperature and the 14^th relative humidity were, the bigger the 14^th wind velocity was, the closer to north wind the 14^th wind direction was, the easier frost occured on the second day. We analyzed the correlation between the minimum temperature of the frost date and the meteorological station data of the fisrt day before frost date. The correlation was the highest between the frost and the 14^th temperature, next was between the frost and the 14^th station pressure, the minimum temperature, the 14^th wind velocity and the 14^th wind direction, the lowest was between the frost and the 14^th relative humidity of the first day before frost date. We had established six multivariate regression equations of them and tested the equations.The regression equations of meteorological stations were significant. The historical forcast accuracy were higher. The history accuracy rates were 53.5%-85%, The forcast accuracy rates were 55.9%-90.1%. This was higher than that of forecast-man, the forcast accuracy rate of forecast-man was 53.6%. The result was better.