Influence of Clouds on the Radiation Budget

Clouds and the Radiation Budget

The interaction of clouds with solar radiation is an important topic of the radiation budget of the earth. To better understand this interaction in the remote sensing departement we investigate the uncertainties of the solar cloud radiative effect at the surface and at the top of the atmosphere (using satellite data).

Clouds do have a great contribution on the energy and the water budget of the earth. Furthermore, clouds do have an influence on the temperature at the surface, since they reduce the heating during daytime or they reduce the cooling at nighttime. Therefore it is important to investigate cloud behaviour and their global distribution. 

Measurements

We use measurements from ground stations and measurement from satellites. These methods show different sources of uncertainty due to assumptions required for retrieving the cloud coverage and radiation fluxes. 

At the top of the atmosphere we apply satellite observations for quantification of cloudy scenes. We investigate the solar reflection of those scenes. The algorithm is able to only deviate cloud or non-cloudy pixels, but can't give information about the degree of cloud coverage. This results in many scenes with broken clouds not being detected as such and are assumed to be either cloudy or contain no clouds at all. The influence of this assumption on the radiation fluxes at the top of atmosphere is one focus of investigations.

At the surface the cloud radiative effect is a function of cloud type and coverage. Furthermore, it depends on the observation geometry between clouds, sun and observer. The cloud type may consist of more than one type in different levels. Especially in this case the attribution of the effect on one cloud is problematic. But nevertheless is important for climate-relevant statements. A method was developed to determine the radiative effect of a observed cloud independently from the cloud coverage. Thereby it is possible to attach a cloud with its radiative effect. This makes the comparison with radiative fluxes from a radiative transfer model much easier.

Another focus is the validation of cloud properties and radiative parameters from satellite observations. We use ship measurements - often the only available ground observations over oceans. The German research vessel Polarstern measures atmospheric variables sind 2007 regularly on the Atlantic Ocean.