Diurnal variation of 340 nm Lambertian equivalent reflectivity due to clouds and aerosols over land and oceans

Abstract

Thirty years of satellite measurements of Lambert equivalent reflectivity (LER) at 340 nm have been analyzed to show the changes in diurnal LER that are associated with cloud and aerosol amounts. Five degree zonal mean diurnal variations of LER are obtained from multiple NASA and NOAA satellites making 340 nm LER measurements from 0600 to 1800 local solar time. These zonal means were calculated separately over water and land. The results show different behavior of clouds over oceans with LER peaking in the morning compared to LER over land, which peaks in the afternoon. Over the oceans the cloud amount increases as a function of latitude in both hemispheres, with the exception of the midtropics (10–20°). Over land, the amount of cloudiness significantly decreases by almost a factor of 2 from the equator to ∼25° and then, in the Northern Hemisphere, increases as a function of latitude. The zonal means represent measured cloud amounts, and thus a quantification of energy reflected back into space as a function of time of day. Cloud fraction measurements made by Aqua and Terra Moderate Resolution Imaging Spectroradiometer show a signature that is similar to the measured ratios of LER in morning to afternoon. The similarity in pattern demonstrates that the LER is measuring a quantity directly related to cloud fraction.