Analysis on Changes of Cloud Coverage in the Maqu Area of the Upper Reaches of Yellow River in the Recent 40 Years

Using the data of total cloud coverage and low cloud coverage from the national basic meteorological stations in Maqu during 1971-2010, with a linear trend analysis and wavelet analysis methods, characteristics of monthly, quarterly, annual, inter-decadal and peridical change of the total cloud coverage and low cloud in recent 40 years were analyzed. The studies have shown that over the past 40 years, the average total cloud amount anomaly is between-0.1% ~0.1%,maintaining a good stability, the average low cloud coverage increases at the rate of 4.0%/10 a; low cloud coverage in spring, summer and autumn show varying degrees of increase trends, obviously up to 7.3%/10 a in the summer; the periodic changes of mean total cloud coverage are not obvious; the average cycle of low cloud coverage is clear which is 6 ~7 a; in the Maqu region the total cloud amount remains stable increasing while the low cloud coverage increases, particularly during the summer with the main feature, the cumulonimbus clouds, indicating a response mechanism of climate change which reflected the convective weather occurs frequently in the context of climate warming in the Maqu grassland.