In this project the PI will analyze and diagnose upper-tropospheric humidity over the tropical Atlantic Ocean. Relative and specific humidity data from the Measurement of Ozone and Water Vapour by Airbus In-Service Aircraft project exist for 10 years since September 1994. Measurements have been made on frequent flights, mostly twice weekly, from Central Europe to locations in South America at levels within the dominant outflow layer of deep convection over the tropical Atlantic Ocean. The data, nearly continuous over 10 years, will be used for the analysis of tropical upper tropospheric water vapor over the Atlantic Intertropical Convergence Zone and the adjacent subtropics. Specific attention will be given to the dominant modes of variability of humidity on time scales varying from less than a week to inter-annual and beyond, up to 10 years. Flight level moisture fluxes, using co-measured wind velocities, will be computed and, together with the humidity information, compared with reanalysis products. The temporal and spatial variability of upper-tropospheric humidity will also be related to that of the underlying sea surface temperature. Diagnostic studies will be undertaken to test specific hypotheses concerning upper tropospheric humidity over the tropical Atlantic and measurements of ozone, a quasi-conservative tracer on the time scale of convective transport, will be used to deduce sources of water vapor. Specifically, the following hypotheses will be tested: that high values of observed upper-tropospheric humidity over the equatorial trough zone are directly related to local vertical transport by deep convection, that the water vapor distributions over the subtropical Atlantic are predominantly controlled by large-scale vertical motion, and that the observed intra-seasonal variability in the upper-tropospheric humidity over the tropical Atlantic is directly linked to the Madden-Julian Oscillation. A post-doctoral research associate will be involved in the research.
