Investigation of clear‐sky occurrence rate estimated from CALIOP and MODIS observations

We derived the global distribution of the clear‐sky occurrence rate during the daytime using Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) and Moderate‐resolution Imaging Spectrometer (MODIS) data. Our goal was to estimate the frequency of likely successful CO2 and CH4 column concentration retrievals by the Greenhouse gases Observing Satellite (GOSAT). Clear‐sky regions over land were frequently found around desert regions throughout the year, and at northern mid‐latitudes in the winter hemisphere. Overall, clear‐sky regions covered approximately 11% of the globe annually, on average. From a comparison of the CALIOP and MODIS cloud data for June 2007, we found that MODIS overestimated the clear‐sky ratio by approximately 5%, except for in the tropics.