Investigations of relative humidity in the upper troposphere with ACE and OSIRIS

In the future, contrail clouds may contribute several per cent of the anthropogenic contribution to the radiative forcing of global warming. There is uncertainty as to the relative humidity required to form persistent contrails from jet wakes; this bears on the mechanism used in models of contrail formation. It is important to map the geographical regions of super saturation where contrails may persist or transform into cirrus cloud decks. These were investigated by mapping the relative humidity with respect to ice and the relative humidity with respect to water. These quantities have been derived from the water vapor and temperature data from the ACE satellite in the altitude regime from 8 km to 20 km. High level cirrus were obtained from the OSIRIS data. The results of our preliminary evaluation of satellite investigations of RHi using ACE data will be reported. A comparison with the OSIRIS data for thin cirrus clouds was conducted. Comparisons with AIRS relative humidity were conducted as well. Comparisons of the OSIRIS cirrus with CloudSat cirrus maps will also be presented. In general there is good agreement between the datasets used in this investigation. .