Geophys. Res. Lett., accepted subject to minor revision 4/09.
Jonathon S. Wright
Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY
Adam H. Sobel
Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences, Columbia University, New York, NY
Gavin A. Schmidt
NASA Goddard Institute for Space Studies, and Center for Climate Systems Research, Columbia University, New York, NY
The direct effect of condensate evaporation on atmospheric water vapor and its isotopic composition is assessed in a climate model. The model contains two parallel hydrologic cycles, an active one which influences the model physics and dynamics and a passive one which does not. Two model simulations are performed, one in which passive cloud and precipitation can evaporate and one in which they cannot. The active hydrologic cycles, and thus the simulated circulations and temperatures, are identical in both simulations. Eliminating passive condensate evaporation reduces the specific humidity in the passive cycle by amounts ranging from near zero to 25% of the control value, depending on location. Zonal mean water vapor in the lower and middle troposphere is enriched in HDO relative to the control case, and is depleted in the upper troposphere.