Water vapor tracers as diagnostics for the regional hydrologic cycle

Understanding of the local and remote sources of water vapor can be a valuable diagnostic of the regional atmospheric hydrologic cycle and the interactions between the land and atmosphere, especially in North America where moisture transport and local evaporation are important sources of water for precipitation. In the present study, we have implemented passive tracers as prognostic variables to follow water vapor evaporated in predetermined regions until the water tracer precipitates. All evaporative sources of water are accounted for by tracers, and the water vapor variable provides the validation of the tracer water and the formulation of the sources and sinks. The GEOS GCM is used to simulate several summer periods to determine the source regions of precipitation for the United States. Using this methodology, a detailed analysis of the recycling of water, interannual variability of the surface sources of water and links to the Great Plains low-level jet and North American monsoon will be presented. Potential uses in GCM sensitivity studies, predictability studies and data assimilation especially regarding the North American monsoon and GEWEX America Prediction Project (GAPP) will be discussed.