Cloud and Aerosol Amounts as a Function of Time of Day as Measured by TOMS, SeaWiFS and SBUV Instruments

Daily cloud and aerosol UV reflectivity values have been measured since 1979 from the Total Ozone Mapping Spectrometer (TOMS) and Solar Backscatter UltraViolet (SBUV) series of instruments. The reflectivities are calculated as Lambert Equivalent Reflectivity (LER) at 340 nm for TOMS and SBUV and at 412nm for the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The UV region of the spectrum is particularly useful to measure cloud amounts due to the fact that the surface reflectivities of snow/ice free land & water are relatively small and the measurements are almost unaffected by vegetation or sea color changes. The NOAA SBUV series of instruments had slowly precessing orbits that provided useful LER data from ~6:30AM to ~5:30PM local time, while the TOMS and SeaWiFS instruments were primarily in stable, noon-time orbits. By analyzing the calculated LER as a function of time of day, it is possible to observe significant cloud changes as the day progresses. In addition, the changes in cloud cover over land surfaces are significantly different than those over water. We will present time of day LER results in 5 degree zonal means from 60 North to 60 South for both land and water.