Understanding Water, Energy and Climate: a GEWEX Global Water and Energy Budget Pathfinder Data Set

Principal Investigator: Dr. Dubayah

The Land Data Assimilation System (LDAS) is an ongoing activity jointly sponsored by NOAA and NASA, designed to provide better initialization of soil moisture for weather forecasting models. A difficulty in the application of current-generation land surface schemes in numerical weather prediction models is specification of the soil moisture at the beginning of the forecast period. The Land Data Assimilation System (LDAS) avoids the problem of accumulated errors in initial soil moisture, and other surface properties, by using observed surface focings for a suitable period (typically months to years) prior to the forecast time. The system has been developed, and testing is underway, for the continental U.S. in connection with the NWS Eta model. In parallel with the development of the real-time LDAS system is a retrospective analysis pathway, which is producing long-term simulations of land surface variables using the LDAS land surface schemes. The Variable Infiltration Capacity (VIC) model, in particular, has been run using LDAS surface forcings for the period 1988-97, at the LDAS 1/8: resolution over the continental U.S. The analysis period will shortly be extended backward to 1950. These retrospective simulations facilitate estimation of parameters of the land surface scheme, and also provide historical benchmarks for assessing the magnitude of excursions in surface variables, especially soil moisture.