Clouds and the Radiative Heating ...
171
If the cloud properties, which have to be used within the radiative transfer calculations to
determine radiation fluxes MtW/LW(P) and MSW/LW(p) at the corresponding pressure levels,
are directly retrieved from spatially high resolution (1-5 km) satellite data, there still exists
the problem of deriving the correct cloud parameters for scattered inhomogeneous cloudiness.
This problem of beam filling leads to an uncertainty in optical thickness and corresponding
cloud cover of the detected cloud within a pixel and thus will lead to a systematic error in
the parameterization of the vertical cloud extension (Stuhlmann, 1993). These uncertainties
again will cause the largest errors for the CGRH(p) profiles and somewhat smaller errors ifthe
profiles are integrated over the troposphere.
The problem how to parameterize the clouds' vertical extension or the corresponding cloud
bottom altitudes for the radiative flux divergence calculations requires more work in the future.
Nevertheless, the uncertainties related to this problem are small enough for a preliminary and
a more general discussion of cloud radiative effects on the Earth surface-atmosphere system
as it was done here. In the future, it will be urgently needed to have a global measurement
of cloud layering, vertical cloud thickness, and an understanding how much water exists in
the cloud in the form of liquid and solid. This information coupled with knowledge about the
cloud microphysics strongly dictates how much radiation is absorbed and reflected as well as
governing the interchange of substances between different phases. Here, the science community
together with the space agencies develop plans to study the feasibility of an international multisensor cloud-radiation satellite mission. Such a mission has to fill the gap of data necessary
for determining the distribution of clouds, understanding of this distribution in relation to
the governing processes, and quantifying the links between clouds, radiation and the water
budget. Such a mission may include a millimeter wave cloud profiling radar (IGPO, 1994), a
backscatter lidar, a sub-millimeter-wave radiometer, and a ERB-type instrument. A selection
of such instruments would provide three-dimensional profiles of clouds fields, major aerosol
layers together with a characterization of cirrus cloud extinction, ice mass and crystal size, and
the related TOA ERB field.
7.7 References
Alberta TL, Charlock TP, Whitlock CH, Rose FG, DiPasquale R, Pinker R, Staylor WF, Gupta SK (1994) Climate observations with GEWEX Surface Radiation Budget
Project data. Proceedings of the 8th Conference on Atmospheric Radiation, AMS, January
1994, Nashville, Tennessee, 22-24
Barkstrom BR, Smith GL (1986) The Earth Radiation Budget experiment: Science and
implementation. Rev Geophys 24: 379-390
Bishop JKB, Rossow WB (1991) Spatial and temporal variability of global surface solar
irradiance. J Geophys Res 96: 16.839-16.858
Brooks DR, Minnis P (1984) Simulation of the Earth's monthly average regional radiation
balance derived from satellite measurements. J Climate Appl Meteor 23: 392-403
Cess RD (1976) Climate change, an appraisal of atmospheric feedback mechanisms employing
zonal climatology. J Atmos Sci 33: 1831-1848
Cess RD, Briegleb BP, Lian MS (1982) Low-latitude cloudiness and climate feedback:
comparative estimates from satellite data. J Atmos Sci 39: 53-59
Cess RD et al. (1989) Interpretation of cloud-climate feedback as produced by 14 atmospheric
general circulation models. Science 245: 513-516
171
If the cloud properties, which have to be used within the radiative transfer calculations to
determine radiation fluxes MtW/LW(P) and MSW/LW(p) at the corresponding pressure levels,
are directly retrieved from spatially high resolution (1-5 km) satellite data, there still exists
the problem of deriving the correct cloud parameters for scattered inhomogeneous cloudiness.
This problem of beam filling leads to an uncertainty in optical thickness and corresponding
cloud cover of the detected cloud within a pixel and thus will lead to a systematic error in
the parameterization of the vertical cloud extension (Stuhlmann, 1993). These uncertainties
again will cause the largest errors for the CGRH(p) profiles and somewhat smaller errors ifthe
profiles are integrated over the troposphere.
The problem how to parameterize the clouds' vertical extension or the corresponding cloud
bottom altitudes for the radiative flux divergence calculations requires more work in the future.
Nevertheless, the uncertainties related to this problem are small enough for a preliminary and
a more general discussion of cloud radiative effects on the Earth surface-atmosphere system
as it was done here. In the future, it will be urgently needed to have a global measurement
of cloud layering, vertical cloud thickness, and an understanding how much water exists in
the cloud in the form of liquid and solid. This information coupled with knowledge about the
cloud microphysics strongly dictates how much radiation is absorbed and reflected as well as
governing the interchange of substances between different phases. Here, the science community
together with the space agencies develop plans to study the feasibility of an international multisensor cloud-radiation satellite mission. Such a mission has to fill the gap of data necessary
for determining the distribution of clouds, understanding of this distribution in relation to
the governing processes, and quantifying the links between clouds, radiation and the water
budget. Such a mission may include a millimeter wave cloud profiling radar (IGPO, 1994), a
backscatter lidar, a sub-millimeter-wave radiometer, and a ERB-type instrument. A selection
of such instruments would provide three-dimensional profiles of clouds fields, major aerosol
layers together with a characterization of cirrus cloud extinction, ice mass and crystal size, and
the related TOA ERB field.
7.7 References
Alberta TL, Charlock TP, Whitlock CH, Rose FG, DiPasquale R, Pinker R, Staylor WF, Gupta SK (1994) Climate observations with GEWEX Surface Radiation Budget
Project data. Proceedings of the 8th Conference on Atmospheric Radiation, AMS, January
1994, Nashville, Tennessee, 22-24
Barkstrom BR, Smith GL (1986) The Earth Radiation Budget experiment: Science and
implementation. Rev Geophys 24: 379-390
Bishop JKB, Rossow WB (1991) Spatial and temporal variability of global surface solar
irradiance. J Geophys Res 96: 16.839-16.858
Brooks DR, Minnis P (1984) Simulation of the Earth's monthly average regional radiation
balance derived from satellite measurements. J Climate Appl Meteor 23: 392-403
Cess RD (1976) Climate change, an appraisal of atmospheric feedback mechanisms employing
zonal climatology. J Atmos Sci 33: 1831-1848
Cess RD, Briegleb BP, Lian MS (1982) Low-latitude cloudiness and climate feedback:
comparative estimates from satellite data. J Atmos Sci 39: 53-59
Cess RD et al. (1989) Interpretation of cloud-climate feedback as produced by 14 atmospheric
general circulation models. Science 245: 513-516