Total Cloud Amount Difference Between ISCCP Product and Ground Observation over China

ISCCP (International Satellite Cloud Climatology Project) is an international authorized objective climatology project on cloud study. It has provided valuable data to studying the budget of global cloud and radiation, the distribution of cloud and water since 1983. The spatial and temporal total cloud amount differences are investigated using ISCCP D2 product and cloud dataset of ground observation over China during 1984—2006, based upon the analysis on the differences of cloud amount observation between the satellite platform and the ground observation. Due to the difference between the detection method and ability, observation coverage and time, inconstancy of cloud top/base, cloud height, cloud thickness, and cloud vertical distribution, the total cloud amount from satellite platform are different from that of surface dataset value. The quantitative analysis results show, although the two datasets show the consistent characteristics of total cloud amount distribution and climatology variation, regional differences are still remarkable. Based on the total cloud amount data from 568 surface stations, a new total cloud amount gird data series is formed with the reference of ISCCP D2 girds. Total cloud amount from satellite data is 8.46% higher than that given by surface data in the comparable 145 satellite-surface grids over China on average. The total cloud amount difference is smaller in the southern region, and larger in the northeastern region. It is closely related with the difference of detection method, cloud properties in different regions and the natural geography factors. With the 172 ISCCP D2 grids and 568 ground stations, the climate change trend is compared and analyzed. The annual variation of total cloud amount derived from the ISCCP D2 product and ground observation is accordant in the 5 regions (the northwest region, Tibetan Plateau region, the northeast region, the north of China and the south of China) during the period of 1984—2006. The total cloud amount decreases over China in the recent 23 years, the trend from ISCCP D2 product 0.015% per year is less than that from the ground observation, 0.063%per year. The total cloud amount increases slowly in the northeastern region, while decreases in Tibetan Plateau region and the northwestern region. With integral anomaly method, it shows the total cloud amount decreases in 1984—2001 and increases rapidly in 2002—2006 using satellite and surface data. The causes that total cloud amount from the two datasets (ISCCP D2 product and ground observation) over China have difference, and the quantitative results on spatial-distribution difference of total cloud amount and the trend of climate change, are helpful to further study on the cloud amount, radiation balance, and the promotion of climate models' performances.