华山云海的变化特征以及与气象要素的关系

Change characteristics of the sea of clouds in Huashan Mountain and the relationship with meteorological elements

用华山气象站1985—2014年气象要素资料,分析近30 a华山云海的变化及云海与降水、相对湿度、风速的关系。结果表明,华山年平均云海日为26.27 d,最多年份72 d,最少年份仅3 d;面积<200 km 2云海年平均日数24.23 d;面积≥200 km 2云海平均日数2.87 d,最多有20 d(1985、1994年),最少有2 d(1997年),1997年后再没有面积≥200 km 2的云海出现。云海的出现呈逐年下降的趋势,年际差异明显。秋季云海出现日数最多(平均云海日数8.13 d),冬季最少(平均4.60 d);各月的云海日数8月最多,5月最少。面积≥200 km 2云海冬季出现日数最多,夏季最少;11月出现最多,3、12月次之,5月最少。面积≥200 km 2云海出现的前一天或当天一般都有降水,两天中至少有一天出现降水的几率是84.30%;平均相对湿度≥70%时,较易形成云海;云海日出现时常伴有风,但总体风速不大,通常≤10.0 m·s-1,利于云海的形成保持。

Based on the data from Huashan Meteorological Station during 1985—2014,this paper analyzed the changes of clouds in Huashan Mountain in the past 30 years and the related weather elements like precipitation,relative humidity and wind speed.It turned out that the annual mean days with the sea of clouds was 26.27 d,the maximum days with the sea of clouds was 72 d,and the minimum was 3 d.In particular,the annual mean days with the area of the sea of clouds≤200 km 2 was 24.23 d while the days with area≥200 km 2 was 2.87 d on average,with a maximum of 20 d(in 1985 and 1994)and a minimum of 2 d(in 1997).While no sea of clouds with an area≥200 km 2 has appeared since 1997.Generally speaking,the occurrence of the sea of clouds shows a descending trend with obvious interannual differences.Days with the sea of clouds tend to occur most in autumn(with average number of 8.13 d)but least in winter(with average number of 4.60 d);specifically,we can see that the number of days with the sea of clouds is the highest in August and the lowest in May.It is interesting to note that the sea of clouds with area≥200 km 2 appears most in winter but least in summer.Such events appear the most in November,followed by March and December,and the least in May.On the very day or the day before the appearance of the sea of clouds with the area≥200 km 2,it always tends to rain and the probability is about 84.30%.When the relative humidity is≥70%,it is inclined to form the sea of clouds,and,at that time,the winds blow usually at the speed≤10.0 m·s-1,which is beneficial to the developing and maintaining of the sea of clouds.