| Based on the observation data of Huashan meteorological observing station in Shaanxi province from 1981 to 2015 and NCEP daily reanalysis,characteristics and variation of the weather landscape happening over Huashan are analyzed by statistics method.Annual,seasonal and monthly variation characteristics of cloud sea,snowfall,rime and glaze are also studied,.On the first part of paper,the relationship between the variation of Huashan cloud sea and meteorological elements are analyzed.On the basis of meteorological data from 1985 to 2014 at Huashan,the relation between the change of cloud sea and elements such as rainfall,relative humidity and wind speed are studied.The results show :(1)The annual average day of cloud sea is 26.27 d,and the maximum is 72 d,the minimum is 3d;Particularly,as the area of cloud sea smaller than 200 square kilometer(sq.km)is concerened specially,t,the annual average days is 2.87 d,the peak value is 20d(1985?1994)and the minimum value is 2d(1997).In addition,there is no cloud sea larger than 200 sq.km since 1997.(2)Generally speaking,the trend of occurrence of cloud sea is descending and the difference among years from 1985-2014 is obvious.The most days of cloud sea occruance is fall(8.13d)and it is hard to be found in winter(4.60d);meanwhile,it is interesting to note that cloud sea larger than 200 sq.km often occurred in winter and rarely in summer.(3)As monthly analysis,could sea is easly observed in August and rarely in May;and the one with area larger than 200 sq.km mostly occurred in November which is followed by March and December,and the least May.(4)As cloud sea with area larger than 200 sq.km is focused,that occurring day or the day before,it usually rained and the probability reaches approximately 84.30%;And when the averaged relative humidity mounts to 70%,cloud sea is easy to formulate with a breeze on the speed of less 10.0m/s that is favorable to the maintenace of cloud sea.Synoptic analysis is employed on a case study,which demonstrates a cloud sea occurring and vanishing from 20 th to 27 th,November 1994.the dynamic and vapor condition for a continual meteorological variation of the daily NCEP global reanalysis data from 10 th to 30 th,November 1994,which based on 17 standard pressure levels(1000hPa ?925hPa? 850 hPa ?700hPa?600hPa?500hPa?400hPa?300hPa?250hPa?200hPa?150hPa?100hPa?70hPa?50hPa?30hPa?20hPa?10hPa).Four analysis time(00,06,12,18)and the horizontal resolution is 1.0°x1.0°.The author laid stress on general atmospheric circulation and the evolution features of physical elements.The study indicates that(1)the air-current,at 500 hPa height,was straight and had many short wave trough activities in this period,and under the irregular disturbance under the stable atmospheric pressure provided imperative dynamic and cold air for the formation of cloud sea.(2)Shaanxi province was influenced by two cold high where is located in the weak uniform pressure field those cold highs back.Accompanied with cold high moved twice southward,there was a fluctuation from decreasing temperature to increasing temperature,which is corresponding to the formation process of cloud sea from setting up,weakening,expanding to evanishing.(3)With respect to the main cause of this cloud sea,the moisture came from the lower layers of troposphere,transmitted by south wind.Besides,the specific humidity was influenced by the wind direction.(4)Nevertheless,at the height of 800hPa(near to the station's height),air-current was on the rise at the speed of smaller than o.1m/s,it was just accorded with the typical ascending velocity in steady atmosphere when the sheet cloud is formulated.On the 27 th,the cloud sea dissipated with the impact of the sinking activity of atmosphere.The introduction of the temporal change characteristics of snowfall,glaze and rime is displayed in the third part,and with the analysis of the strength of them with the date of snow depth,sedimentation diameter and the weight,then the Meteorological elements of temperature and winddirection which influence drimeand glaze are analyzed on their changing relationship.The result shows that the respective annual average days of snowfall is 51.3,snowfall occurrence is the most reaching 82 days in 1984,and the least in 2013 only 20 days;there spective annual meandays of glaze is 4.35,and glaze occurred most frequently in 1982(11days)and the least in 1995,2005,2007-2010 and 2015(just 1 day);the spective annual average days of rime is 23.6,as for the rime,the maximum is 35 days in the year of 1989 and the minimum is 10 days in the year of 2013.About the specific month,snowfall and rime happened most in February taking up 391 days and 188 days,while apiece and glaze is in March(35 days).On the contrary,all of these sceneries rarely occurred in May and snowfall shared the same month changing trend with rime.Meanwhile,the result still shows that the average first day(15th,October)of snowfall is the earliest and final day(27th,April)is the latest among the three climatic sceneries.And the first snowfall day(15th,September)is earlier than snow cover and glaciation on electric wire,while the final day(22th,May)is much later then the latter.During 1981-2015,the total snowing days accounted for 1797 days At the wind direction of W~WNW,it most favorable for rime and glaze happening,while in the maintenace stage,the temperature of rime is lower than glaze at the static of-9.13 to-3.48?. |
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