Upper Tropospheric Humidity over the Atlantic:

Seasonal and Inter-annual Variations Observed from MOZAIC-Aircraft

Dr. Herman G.J. Smit,

Institute of Chemistry and Dynamics of the Geosphere: Troposphere (ICG-II)

Research Centre Juelich GmbH

Germany

Although upper tropospheric humidity (UTH) plays a crucial role in our Earth’s climate, very little is known about the spatial and temporal distribution of UTH content and the processes controlling it. A comprehensive climatology of the UTH distribution over the Atlantic obtained from MOZAIC (Measurement of Ozone and Water Vapor by Airbus In Service Aircraft) measurements will be presented and discussed. UTH reveals a strong spatial and temporal variability on different scales whereby a significant portion of the observations show ice supersaturation. Very pronounced are the seasonal cycle and inter-annual variability of UTH in the mid-latitudes related to large scale transport. In the tropics and sub-tropics UTH show a clearly bi-modal distribution with a wet (ice supersaturated) and a dry branch which are strongly linked to the tropical dynamics of deep convection and subsidence.