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Comparison of individually matched analyses of high-level cloudiness from the High-Resolution Infrared Sounder (HIRS) CO2-slicing analysis and the International Satellite Cloud Climatology Project (ISCCP) analysis of satellite data for 4 months shows that the former reports about 0.12 more high-level clouds than the latter. Almost all of the difference in high-level cloud amounts occurs as differences of thin cirrus, defined by infrared emissivity ε 3.6) high-level clouds appear to be more frequently associated with each other than with cirrus. Notable concentrations of cirrus in the Tropics mark regions of frequent deep convective activity. However, there are also prominent features associated with the subtropical jet streams. In midlatitudes, cirrus concentrations occur in the oceanic cyclone tracks, but they are even larger over major mountain complexes. Although the quantitative uncertainties of both datasets are large in the polar regions, the agreements and disagreements between them can be explained by the presence of large amounts of cirrus over both polar regions.
Jin et al. (Fri,) studied this question.