The impact of clouds on the radiative heating of the earth surface-atmosphere system determined from satellite data

Abstract

During the last 30 years observations from earth-orbiting and geostationary satellites have greatly improved the quality and detail of information about the global distribution of clouds and their effects on the energy balance of the Earth. Data from the Earth radiation experiments provide excellent data sets to study the diurnal, seasonal, and regional variations of the radiation balance of the climate system and how it is affected by the radiative forcing of clouds. These types of investigations are supplemented by use of the International Satellite Cloud Climatology Project data set which, with its unprecedented spatial and temporal resolution, describes the variability of the atmosphere and the embedded clouds. Cloud radiative forcing at the top of the atmosphere represents the overall effect of clouds on the Earth surface-atmosphere system. But, even if the cloud forcing at the top of the atmosphere is small, there might be a strong effect of clouds on the weather and climate processes which is felt through the changes in radiative interaction at the surface and in the atmosphere separately. Thus, after firstly looking at the energy balance at the top of the atmosphere, the above mentioned data sets are now more used to determine also the energy balance at the surface. For instance, the Global Energy and Water Cycle Experiment Surface Radiation Project is retrieving fluxes of shortwave surface radiation over the globe from the International Satellite Cloud Climatology Project data. The Surface Radiation Project will shortly extend the retrievals to the longwave. The uncertainty in deriving the cloudbase altitudes from the satellite data leads to the largest errors in determining the net longwave fluxes at the surface. Despite the problem of retrieving the cloud bottom heights from currently available global satellite data sets, first attempts are made to study the effects of clouds on the radiative heating of the atmosphere inselt. First results sustain that the effect of clouds in the shortwave spectral domain is primarily a cooling of the surface. In the longwave spectral domain the effect of clouds is primarily on the atmosphere, where the distribution of cloud atmospheric forcing strengthens the meridional temperature gradient. To improve the efforts to determine the atmospheric heating profiles and the net longwave radiation budget at the surface, a global measurement of cloud layering and vertical cloud thickness is urgently needed. A space borne millimeter wave radar will provide the information about the vertical structure of clouds and cloudbase altitude, and, with suitable complementary measurements, is a promising method to provide estimates of water and ice mass.