Investigations of Relative Humidity and Cirrus Formation with CloudSat, OSIRIS and ACE

The problem of cirrus formation is key to evaluating the contribution of aviation to global warming. Contrail cirrus cloud and cirrus generated from contrails is the most important component of the radiative forcing contribution of aircraft. Cirrus clouds are measured with the CloudSat and Calipso satellites. Subvisual cirrus is measured with OSIRIS instrument on ODIN. Relative humidity is measured with the ACE satellite FTS from water vapor combined with GPS temperatures. Preliminary data from these satellites is used to demonstrate the type of results expected from this investigation.

Cloud presence plots of the frequency of occurrence of cirrus cloud versus relative humidity will be used to investigate cirrus formation and in particular the thermodynamic relationships and mechanisms. This data can be applied to determine the formation areas of cirrus for aviation climate change studies. The satellite cloud presence plots agree with similar plots from aircraft missions.

Cirrus formation models from GCMs will be applied to simulate these plots. Cloud presence plots will be calculated from the CCCMA GCM model and compared with the observed cloud presence plots.

A set of cloud presence formation plots will be derived from our global data maps. The formation plot equations will then be used to compute global cirrus maps from relative humidity maps. This information will be extremely valuable for use with future relative humidity mapping satellites and for use in global warming models to quantify the future aircraft contribution to global warming.