Remote-sensing-based estimates of the fundamental global water cycle: Annual cycle

Abstract

The average annual cycle of the atmospheric branch of the fundamental global water cycle (FGWC) was studied with remote-sensing-based precipitation estimates from the Global Precipitation Climatology Project (GPCP; blended microwave-infrared-rain gauge) Version 2 and the Goddard Profiling algorithm (GPROF; passive microwave) Version 6 data sets and overocean evaporation estimates from the Goddard Satellite Surface Turbulent Fluxes Version 2 (passive microwave) data set from 1988 to 2000. Overland evaporation was estimated from the remote-sensing-based precipitation estimates combined with a global evaporation minus precipitation (EmP) data set produced by the Climate Analysis Section of the National Center for Atmospheric Research. Results show that 75% to 85% of the total global evaporation and approximately 70% of the total global precipitation occur over the oceans in each season. In the GPCP-based FGWC estimate, there is a remarkable balance in the interhemispheric import-export of atmospheric moisture in December-January-February and June-July-August. The dominant cross-equatorial atmospheric moisture transports in the atmospheric branch of the FGWC supply a significant amount of moisture to precipitation regions and are from the Northern Hemisphere to the Southern Hemisphere in December-January-February and the Southern Hemisphere to the Northern Hemisphere in June-July-August, with approximately 3 × 10 6 m 3 s -1 net annual transport from the Southern Hemisphere to the Northern Hemisphere in the GPCP-based FGWC estimate. In the GPROF-based FGWC estimate, there are substantial imbalances in interhemispheric moisture transports that may be attributable to missing data over snow- or ice-covered surfaces, inadequate diurnal sampling, and uncertainties in precipitation estimates especially over land. A quantitative evaluation of these results and comparisons with previous FGWC estimates is not possible without quantitative error estimates on precipitation, evaporation, and EmP estimates. These results show that evaporation, precipitation, and atmospheric moisture transport over the oceans play a very important role in the FGWC and that they should be a significant component in the Global Energy and Water Cycle Experiment and other national and international research programs on the global water cycle. Copyright 2005 by the American Geophysical Union.