Energy and Water Cycles in the Climate System ...
15
systematic uncertainties to values of about 5 to 10 Wm- 2 for daily averages (e.g.: Dieckmann
and Smith, 1989).
Fig. 1.8 shows purposely as an example results which had already been derived from the measurements of the very early Nimbus satellites (from Raschke et al., 1973) instead of the many
very recent results which are discussed by Stuhlmann (this volume). The geographical distribution and also amounts of the annual net radiation, resulting from the incident radiation and
the global cloud and temperature distributions, and surface albedoes as well, show the same
patterns as observed now with radiative surplus areas between about 40° northern and southern
latitude and the known deficit regions poleward. However, at the first time, these data revealed
also regional deficits over the subtropical bright and hot deserts over both hemispheres, which
enforce compensating circulations (see their discussions by Sohn and Smith, 1992).
NIM8U S 3
1969 - 1970
RADIATION BALANCE
(cal cm-2 min- 1 )
Figure 1.8: Global distribution of the annual net-radiation budget at the top of the atmosphere,
derived from the measurements of the satellite Nimbus 3, made in 1969 and 1970 (from Raschke
et al., 1973).
The energy transports which will be required to balance the deficits in the planetary radiation
budget have frequently been estimated. Fig. 1.9 (from Sohn and Smith, 1992) shows an annual
average, based on the ERB data derived from Nimbus 7 wide field-of-view measurements. It
clarly indicates the dominating "source" over the tropical Pacific and "sinks" over the Sahara
and central South America.
Various analyses of such data demonstrated also the magnitude and sign of the effect of clouds
(often called "cloud forcing": see Stuhlmann, in this volume) on the outgoing radiation fields.
In such estimates, in principle monthly averages of the albedo or longwave emission to space
are subtracted from "clear-sky values" measured over each area during the same month but
in many cases only during one or two days. These estimates bear many error sources. They
however revealed, that high-level cirrus - when no other lower clouds are present - may slightly
increase the radiative energy gain of the planet ("heating" it) while in the average all clouds
reduce the net gain of radiative energy by about 20 to 25 Wm- 2 • Thus, in general, clouds
"cool" the planet Earth. Such cloud-effect analyses are also an excellent tool to validate model
15
systematic uncertainties to values of about 5 to 10 Wm- 2 for daily averages (e.g.: Dieckmann
and Smith, 1989).
Fig. 1.8 shows purposely as an example results which had already been derived from the measurements of the very early Nimbus satellites (from Raschke et al., 1973) instead of the many
very recent results which are discussed by Stuhlmann (this volume). The geographical distribution and also amounts of the annual net radiation, resulting from the incident radiation and
the global cloud and temperature distributions, and surface albedoes as well, show the same
patterns as observed now with radiative surplus areas between about 40° northern and southern
latitude and the known deficit regions poleward. However, at the first time, these data revealed
also regional deficits over the subtropical bright and hot deserts over both hemispheres, which
enforce compensating circulations (see their discussions by Sohn and Smith, 1992).
NIM8U S 3
1969 - 1970
RADIATION BALANCE
(cal cm-2 min- 1 )
Figure 1.8: Global distribution of the annual net-radiation budget at the top of the atmosphere,
derived from the measurements of the satellite Nimbus 3, made in 1969 and 1970 (from Raschke
et al., 1973).
The energy transports which will be required to balance the deficits in the planetary radiation
budget have frequently been estimated. Fig. 1.9 (from Sohn and Smith, 1992) shows an annual
average, based on the ERB data derived from Nimbus 7 wide field-of-view measurements. It
clarly indicates the dominating "source" over the tropical Pacific and "sinks" over the Sahara
and central South America.
Various analyses of such data demonstrated also the magnitude and sign of the effect of clouds
(often called "cloud forcing": see Stuhlmann, in this volume) on the outgoing radiation fields.
In such estimates, in principle monthly averages of the albedo or longwave emission to space
are subtracted from "clear-sky values" measured over each area during the same month but
in many cases only during one or two days. These estimates bear many error sources. They
however revealed, that high-level cirrus - when no other lower clouds are present - may slightly
increase the radiative energy gain of the planet ("heating" it) while in the average all clouds
reduce the net gain of radiative energy by about 20 to 25 Wm- 2 • Thus, in general, clouds
"cool" the planet Earth. Such cloud-effect analyses are also an excellent tool to validate model