利用中国西北地区135个测站1961—2007年1—12月日照时数资料,采用EOF、REOF、趋势分析、Mann-Kendall分析、相关分析等方法,分析了47 a来西北地区日照时数的时空分布特征及其变化规律。结果表明:西北地区的日照时数从东南向西北减少,甘青新交界区是西北地区日照的高值区。冬季日照最少,夏季最多,春季多于秋季。西北地区大部分地方日照时数显著减少,全区平均减少速率为19.92 h/10 a,1980年发生突变。新疆西南部和青海南部日照时灵敏有明显增多趋势,甘南—陇中—宁南—陇东—陕中日照时数不显著增多。将西北地区日照时数分为7个不同类型区域:即西北地区东部区、新疆中北部区 、新疆西南区、海西北高原区、祁连山区、青南高原和河西走廊区。西北地区东部和新疆中北部的日照时数为单峰型,河西走廊、祁连山区、新疆西南部的日照时数呈双峰型分布,青海高原的日照时数呈三峰型分布。在气候变暖的背景下,西北地区相对湿度增加,云量增多,是造成大部分地方日照减少的主要原因。

With EOF, REOF,Mann-Kendall, trend analysis and correlation analysis method, the spatial distribution features and time evolution rule of sunshine duration in the last 47 years in Northwest China are analyzed based on the monthly mean data for the period 1961 to 2007 collected from 135 observational stations. It is shown that sunshine duration of the region decreases from the southeast to the northwest, the value on both sides is low and the center is high. The border area of Gansu, Qinghai and Xinjiang is the high value region in sunshine duration of northwest. The winter sunshine duration is the least, summer is the most, and the spring's is more than the autumn's. Northwest sunshine duration in most part of northwest reduces remarkably, the average reduction rate of the entire region is 19.92 h/10 a; it has a sudden change in 1980. Southwest Xinjiang and southern Qinghai present an obvious increasing tendency, but in Gannan-Central Gansu-southern Ningxia-east Gansu-Central Shaanxi the increase in sunshine duration is not obvious. Using the REOF method we detailedly divide the region into seven subregions, i.e.,the eastern part of northwest, mid-northern Xinjiang, southwest Xinjiang, northwest Qinghai Plateau, Qilian mountainous area, southern Qinghai Plateau and Gansu Corridor. The sunshine duration is a single peak in eastern part and mid-northern Xinjiang, while it is a double peak pattern in Gansu Corridor, Qilian mountainous area and southwest Xinjiang, and a triple peak pattern in Qinghai plateau. Under background of the climate warming the relative humidity increases and the cloud cover increases in Northweat China, a primary cause for the reduction of sunshine duration in most part of the region.