Zonal average cloud characteristics for global atmospheric chemistry modeling

The zonal average cloud distribution for the lower (approximately six km) troposphere is studied. It is derived from surface observations of cloud occurrence and the average vertical extent of clouds. Assessments of updraft velocities through convective clouds and lifetime estimates of stratiform clouds are used to calculate the average time that air spends in clouds and the time between successive cloud encounters, as a function of latitude and altitude. The inferred cloud data and satellite observations are compared. Data derived from calculations with a general circulation model and satellite observations do not show a good fit. The results lead to the conclusion that for such models an effort must be devoted to develop cloud parameterizations in order to produce cloud distributions as needed for global atmospheric chemistry modeling.