Poster Summaries
601
than 80% of the clear sky value for identical cloud types. The difficulty is further illustrated by
Doutriaux and Yu who show that simply validating the results of a GCM against ISCCP C1
cloud climatologies can lead to significant biases owing to sampling ambiguities in the satellite
retrieval algorithms. When validating GCM results in this way, the GCM cloud predictions
must be carefully procesed so that the resulting modeled cloud prediction matches the sampling characteristics of the satellite platform. Beyond this, simply determing the proper vertical
distribution of parameterized cloudiness is shown to be a significant difficulty, especially with
low level clouds.
The influence of clouds on the current climate was sucessfully demonstrated by the Earth
Radiation Budget Experiment (ERBE) where clouds were shown, on average, to lead to a
slight cooling of the earth system. SCARAB, the follow-on to the ERBE, was launched in
1993 and collected one year of radiation budget data. Before these data can be analyzed, the
sensors must be carefully calibrated. Raison finds that it is possible to calibrate the short wave
channel of the SCARAB with a geophysical technique and that biases in the data arising from
a thermal leak associated with the silica filter can be corrected using statistical methods. After
this calibration is implemented, TOA radiation budgets will be calculated and comparison to
the ERBE can be conducted.
Not only do tropospheric clouds influence the earths climate, but condensed water in the polar
stratosphere has been shown to influence the chemistry of this atmospheric region leading to
significant decreases in ozone concentrations. The Japanese Space Agency will launch ADEOS
in 1996 and attempt to quantify the aerosol concentrations in the stratosphere. However,
before this can be accomplished, the retrieval of aerosol characteristics from the data must be
understood theoretically. Okamato et al., therefore, consider this important procedure and
show that it will be possible to infer the chemical composition of stratospheric aerosol particles,
as well as their size distribution and shape from the ADEOS data.
Determination of cirrus cloud radiative and microphysical characteristics is a primary goal of
much of the cloud research currently being conducted. The global coverage of cirrus, the nonsphericity of the ice particles and their remoteness in the upper troposphere make understanding
their influence on climate very difficult. Using data from EUCREX 94, Chepfer and Brogniez
illustrate both the strengths and weaknesses of multi-aircraft cirrus observational experiments.
By carefully coordinating aircraft flight tracks, visible and infrared optical depths associated
with an extensive cirrus layer are considered and meso gamma scale variability in the cirrus
radiative properties are clearly demonstrated. However, side-by-side flights of the three aircraft
involved in the experiment revealed nontrivial biases in the flux radiometer measurements making quantitative interpretation of these data a significant challenge. As a special case of the
cirrus cloud-climate problem, Drummond et aI. examine cirrus modification by jet aircraft
condensation trails. They show that the ice particles generated in the aircraft effluent are likely composed of high concentrations of radiatively active particles with characteristic effective
radii of less than 10 microns. Their data also suggest modification of the ambient cirrus by
interaction of the condensation trail with the natural cirrus generation process.
In summary, these results represent significant progress in understanding the physical mechanisms that make clouds an important component of the earth's atmosphere. However, these
results clearly demonstrate that considerable research in all aspects of cloud-climate coupling
must be conducted before adequate characterization of clouds in GCMs can be accomplished.
Chepfer H, Brogniez G: First analysis of radiative measurements for cirrus clouds during
EUCREX94
Doutriaux M, Yu W: Validation of cloud cover simulated by a GCM using ISCCP C1 cloud
climatology
601
than 80% of the clear sky value for identical cloud types. The difficulty is further illustrated by
Doutriaux and Yu who show that simply validating the results of a GCM against ISCCP C1
cloud climatologies can lead to significant biases owing to sampling ambiguities in the satellite
retrieval algorithms. When validating GCM results in this way, the GCM cloud predictions
must be carefully procesed so that the resulting modeled cloud prediction matches the sampling characteristics of the satellite platform. Beyond this, simply determing the proper vertical
distribution of parameterized cloudiness is shown to be a significant difficulty, especially with
low level clouds.
The influence of clouds on the current climate was sucessfully demonstrated by the Earth
Radiation Budget Experiment (ERBE) where clouds were shown, on average, to lead to a
slight cooling of the earth system. SCARAB, the follow-on to the ERBE, was launched in
1993 and collected one year of radiation budget data. Before these data can be analyzed, the
sensors must be carefully calibrated. Raison finds that it is possible to calibrate the short wave
channel of the SCARAB with a geophysical technique and that biases in the data arising from
a thermal leak associated with the silica filter can be corrected using statistical methods. After
this calibration is implemented, TOA radiation budgets will be calculated and comparison to
the ERBE can be conducted.
Not only do tropospheric clouds influence the earths climate, but condensed water in the polar
stratosphere has been shown to influence the chemistry of this atmospheric region leading to
significant decreases in ozone concentrations. The Japanese Space Agency will launch ADEOS
in 1996 and attempt to quantify the aerosol concentrations in the stratosphere. However,
before this can be accomplished, the retrieval of aerosol characteristics from the data must be
understood theoretically. Okamato et al., therefore, consider this important procedure and
show that it will be possible to infer the chemical composition of stratospheric aerosol particles,
as well as their size distribution and shape from the ADEOS data.
Determination of cirrus cloud radiative and microphysical characteristics is a primary goal of
much of the cloud research currently being conducted. The global coverage of cirrus, the nonsphericity of the ice particles and their remoteness in the upper troposphere make understanding
their influence on climate very difficult. Using data from EUCREX 94, Chepfer and Brogniez
illustrate both the strengths and weaknesses of multi-aircraft cirrus observational experiments.
By carefully coordinating aircraft flight tracks, visible and infrared optical depths associated
with an extensive cirrus layer are considered and meso gamma scale variability in the cirrus
radiative properties are clearly demonstrated. However, side-by-side flights of the three aircraft
involved in the experiment revealed nontrivial biases in the flux radiometer measurements making quantitative interpretation of these data a significant challenge. As a special case of the
cirrus cloud-climate problem, Drummond et aI. examine cirrus modification by jet aircraft
condensation trails. They show that the ice particles generated in the aircraft effluent are likely composed of high concentrations of radiatively active particles with characteristic effective
radii of less than 10 microns. Their data also suggest modification of the ambient cirrus by
interaction of the condensation trail with the natural cirrus generation process.
In summary, these results represent significant progress in understanding the physical mechanisms that make clouds an important component of the earth's atmosphere. However, these
results clearly demonstrate that considerable research in all aspects of cloud-climate coupling
must be conducted before adequate characterization of clouds in GCMs can be accomplished.
Chepfer H, Brogniez G: First analysis of radiative measurements for cirrus clouds during
EUCREX94
Doutriaux M, Yu W: Validation of cloud cover simulated by a GCM using ISCCP C1 cloud
climatology