1959—2017年开平市日照时数的变化特征及其成因初探

Variation Characteristics of Sunshine Duration in Kaiping City from 1959 to 2017 and a Preliminary Study of the Causation

利用开平市国家一般气象站1959—2017年逐月日照时数和1959—2012年逐年总云量、低云量、雨日、降水量、平均风速、相对湿度等资料,通过数理统计、线性倾向估计、小波分析、Mann-Kendall检验等方法,分析了开平市日照时数的变化特征及影响因子。结果表明:1)1959—2017年开平市年日照时数呈显著下降趋势,趋势系数为-7.36h/年,其中1993年为突变年,1993年后下降趋势明显;2)日照时数在4个季节均呈减少趋势,减少幅度从大到小分别为秋季、春季、冬季和夏季,月日照时数平均值为152.3h,其中7月最高为221.6h,3月最低为78.8h;3)日照时数存在3~5、7~8年的短期振荡周期,1980年以前存在准14年的振荡周期,1975年以后存在21~23年的中期振荡周期;4)影响日照时数变化的最主要因子是云量,云量增多,特别是低云量增多,会导致日照时数减少,次要因子是降水,平均风速也是影响因子之一。

Using the data of monthly sunshine duration taken from national observation stations in Kaiping for 1959-2017 and the data of annual total cloud amount, low cloud amount, rain days, precipitation amount, mean wind speed and relative humidity, this work studies the variation characteristics of sunshine duration in the city and governing factors by means of mathematical statistics, linear tendency estimation, wavelet analysis and Mann-Kendal test. The results are shown as follows. 1) The annual sunshine duration shows a significantly decreasing trend over the period from 1959 to 2017, with a trend coefficient of-7.36 h/a. There was an abrupt change in 1993, after which the decreasing trend was much more obvious. 2) The duration of sunshine shows a declining trend in all four seasons, with the largest amplitude in autumn, followed by spring, winter and summer. The average of monthly sunshine duration is 152.3 h, with July having the maximum(221.6 h) and March the minimum(78.8 h). 3) The sunshine duration oscillates at periods of 3 to 5 and 7 to 8 years, a quasi-14-year oscillatory period existed before 1980 and a medium-range oscillatory period of 21 to 23 years was found after 1975. 4) A primary factor affecting the variation of sunshine duration is cloudiness;when it increases, especially at the low level, the sunshine duration decreases. The secondary factor is the precipitation and mean wind speed is also one of the governing factors.