Long-term Trend Of Cloud Parameters In East Asia And Its Impact On Regional Radiation Budget

In order to study the long-term trend of cloud parameters and the effect of cloud on radiation budget over East Asia,the MODIS cloud products are statistically analyzed.Spatial and temporal distribution of cloud physical characteristics are calculated.Using BCC_RAD radiation transfer model,sensitivity experiments are firstly carried out to calculate the influence of different cloud parameters on radiation flux.Finally,the actual cloud parameters obtained from satellite data are input into BCC_RAD model,and the influence of cloud parameters on radiation budget and the effect of the change of cloud parameters on radiation over East Asia are calculated.The key findings are as follows:The temporal and spatial variations of cloud cover and cloud top height in East Asia and its typical regions are analyzed.The annual mean of total cloud cover over the East Asian continent is low in the northwest and high in the southeast.The high value area with total cloud cover greater than 0.8 appears over the Sichuan Basin.High cloud cover in East Asia is increasing.The annual variability of mid-cloud amount is on the low side,while the low-cloud amount tends to decrease,with a decrease rate of-0.1%/yr.Cloud top height in East Asia increases at a rate of 0.020±0.010 km/yr.The annual mean of water and ice cloud effective radius over East Asia decreases from ocean to land.The annual variation rate of water and ice cloud effective radius decreases in land and offshore areas,and the variation rate is in the range of-0.1?m/yr⁰?m/yr.The water cloud optical thickness increases by 0.05 yr^-1 in northeastern China and eastern sea areas,while decreases by-0.07 yr^-1 and-0.05 yr^-1 in southern China and southern Japan,respectively.The variation trend in winter is more obvious than that in summer.Based on BCC_RAD radiation transfer model,the sensitivity tests of the effect of different cloud parameters on radiation are calculated.It is found that the net radiation flux at long-wave band increases positively with the cloud amount increasing,while the net radiation flux at short-wave band increases negatively with the cloud amount increasing,and the rate of increase decreases with the increase of cloud amount.Cloud height mainly affects cloud top temperature and cloud bottom temperature.The influence of ice water content on long-wave and short-wave radiation flux and heating rate is larger than that of water cloud content in magnitude.In the long-wave band,the influence of ice cloud effective radius on radiation flux and heating rate is larger than that of water cloud effective radius in magnitude,while in the short-wave band,the influence of ice cloud effective radius on radiation is smaller than that of water cloud effective radius.The annual mean shortwave-,longwave-and net-radiative forcing caused by water cloud changes in East Asia at the top-of-atmosphere?TOA?are-72.4,15.7 and-56.7 W m^-2,respectively.The corresponding forcing caused by ice cloud changes are-88.5,55.7 and-32.7W m^-2,respectively.The effects of water cloud and ice cloud optical thickness long-term changes on radiation budgets in different regions are remarkably different.Both positive cloud radiation effect(e.g.southern China,0⁰.4 W m^-2 per year)and negative cloud radiation effect(e.g.northeastern China,-0.4⁰ W m^-2 per year)occurs,which indicates that the cloud radiation effect due to long-term cloud optical thickness changes are significant and opposite in different areas.