Chapter 7
Clouds and the Radiative Heating of
the Earth Surface-Atmosphere System
Rolf Stuhlmann
GKSS Research Center
21502 Geesthacht
Germany
Abstract
The Earth Radiation Budget Experiment (ERBE) and the Scanner for Radiation Budget (ScaRaB), for instance, 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 by clouds. These type of investigations are supplemented by use of imager data taken
by the geostationary satellites (and also the polar orbiters for the more pol ward regions of
the globe) which, with their high spatial and temporal resolution, describe the variability of
the atmosphere and the embedded clouds. The ERB data sets are used to look at the energy
balance at the top of the atmosphere (TOA) to determine the sinks and sources of the Earth
surface-atmosphere circulation system and to extract the TOA cloud radiative forcing, which
represents the net effect of clouds on the total system. But, even in case of a negligible TOA
cloud forcing, there might be a strong effect of clouds on the weather and climate processes,
which is felt through the changes in rediative interaction at the surface and in the atmosphere,
separately. Therefore, it is essential to use the data also to study how the TOA energy balance
is divided up between the surface and the atmosphere. Here, for instance, the Global Energy
and Water Cycle Experiment (GEWEX) Surface Radiation (SRB) Project is retrieving surface radiation fluxes over the globe from the International Satellite Cloud Climatology Project
(ISCCP) data. Doing that, the uncertainty in deriving the cloud base altitudes from satellite
data leads to the largest errors in determining the net longwave fluxes at the surface. But,
despite the problem of retrieving the cloud bottom heights from currently available global satellite data sets. first attempts are also made to study the effects of clouds on the radiative
heating of the atmosphere itself. 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 strenghtens 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
NATO AS] Series. Vol.] 45
Radiation and Water in the Climate System:
Remote Measurements
Edited by Ehrhard Raschke
© Springer-Verlag Berlin Heidelberg 1996
Clouds and the Radiative Heating of
the Earth Surface-Atmosphere System
Rolf Stuhlmann
GKSS Research Center
21502 Geesthacht
Germany
Abstract
The Earth Radiation Budget Experiment (ERBE) and the Scanner for Radiation Budget (ScaRaB), for instance, 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 by clouds. These type of investigations are supplemented by use of imager data taken
by the geostationary satellites (and also the polar orbiters for the more pol ward regions of
the globe) which, with their high spatial and temporal resolution, describe the variability of
the atmosphere and the embedded clouds. The ERB data sets are used to look at the energy
balance at the top of the atmosphere (TOA) to determine the sinks and sources of the Earth
surface-atmosphere circulation system and to extract the TOA cloud radiative forcing, which
represents the net effect of clouds on the total system. But, even in case of a negligible TOA
cloud forcing, there might be a strong effect of clouds on the weather and climate processes,
which is felt through the changes in rediative interaction at the surface and in the atmosphere,
separately. Therefore, it is essential to use the data also to study how the TOA energy balance
is divided up between the surface and the atmosphere. Here, for instance, the Global Energy
and Water Cycle Experiment (GEWEX) Surface Radiation (SRB) Project is retrieving surface radiation fluxes over the globe from the International Satellite Cloud Climatology Project
(ISCCP) data. Doing that, the uncertainty in deriving the cloud base altitudes from satellite
data leads to the largest errors in determining the net longwave fluxes at the surface. But,
despite the problem of retrieving the cloud bottom heights from currently available global satellite data sets. first attempts are also made to study the effects of clouds on the radiative
heating of the atmosphere itself. 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 strenghtens 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
NATO AS] Series. Vol.] 45
Radiation and Water in the Climate System:
Remote Measurements
Edited by Ehrhard Raschke
© Springer-Verlag Berlin Heidelberg 1996