Cloud type climatology over the Tibetan Plateau: A comparison of ISCCP and MODIS/TERRA measurements with surface observations

Abstract

Area averaged seasonal climatology of high, middle and low clouds over the Tibetan Plateau was obtained from the International Satellite Cloud Climatology Project (ISCCP) D2 and the Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra products, and was compared with climatology calculated by using the Carbon Dioxide Information Analysis Center (CDIAC) Cloud Climatology for Land Station Worldwide. From all three data sets, there is a large degree of consistency for the high cloud climatology in terms of amount and occurrence frequency. A great amount of high clouds exists over the Tibetan Plateau and its seasonal cycle is evident with the largest amount and highest frequency in spring and summer. However, compared with the surface observations, both the ISCCP D2 and the MODIS/Terra products largely underestimated low clouds over the Tibetan Plateau. Approximately, the underestimation of cloud amount from the ISCCP D2 is more than 20% and cloud frequency bias from the MODIS/Terra up to 50%; moreover, a quite large discrepancy in the seasonal cycle is shown. For middle clouds, the ISCCP D2 and the MODIS/Terra products overestimate amount and occurrence frequency, and present rather weak seasonal variation compared with the weather station data. When using satellite data to analyze cloud cover the Tibetan Plateau, certain issues about large potential bias must be taken into consideration, and particularly, great caution is needed while using the ISCCP D2 and MODIS data to study middle and low clouds, especially when high and thick clouds exist.