Land Surface Modeling
Figure 1. Schematic showing the structure of the WRF model with urban-canopy parameterization. Application of the WRF/Noah/Urban coupled modeling system over Salt Lake City and surrounding complex terrain.
RAL scientists work to understand, through theoretical and observational studies, the complex biophysical, hydrological, and bio-geochemical interactions between the land-surface and the atmosphere at micro- and mesoscales. The ultimate goal is to integrate such knowledge into numerical mesoscale weather prediction and regional climate models to improve prediction of the impacts of land-surface processes on regional weather, climate, and hydrology. Land surface modeling efforts were funded in FY06 by NSF, the Air Force Weather Agency (AFWA), NOAA, NASA, and the CFD Research Corporation.
FY06 Accomplishments
The unified Noah land surface model (LSM) has been implemented in the official release WRF V2.0 since May 2004. Currently an advanced single-layer urban canopy model is being tested in WRF, together with a more-detailed urban land-use classification, and this new WRF urban-modeling capability is expected to be released later in 2006. The WRF/Noah-urban coupled modeling system, with 0.5-km grid spacing, and WRF forecast fields was used to drive a computational fluid dynamics (CFD)-model-based transport and dispersion model for a case study during the Urban 2000 field experiment conducted in Salt Lake City (Fig. 1). Verification results indicate that the use of the WRF forecasts by the quasi-steady CFD-Urban model has resulted in a significant improvement (by four or five times) in the accuracy of transport and dispersion calculations.
Although the important role of soil moisture in the development of deep-convection has been recognized, it remains the most difficult variable to obtain because there is no routine high-resolution observation of soil moisture at the continental scale. Thus, a High-Resolution Land Data Assimilation System (HRLDAS) has been developed to support the WRF/Noah coupled land surface modeling system and ATEC range forecasts. It uses observed hourly precipitation, solar radiation derived from satellite, and analyzed surface wind and temperature to force a land-surface model to simulate the evolution of soil moisture. In this system, the NCEP/NOAA hourly 4-km rainfall analysis, based on NEXRAD and rain-gauge observations, is used so that errors in soil moisture caused by precipitation and radiation bias in coupled modeling systems can be avoided. Long-term HRLDAS simulations were conducted over the U.S. Southern Great Plains region to support RAL land-atmospheric interaction studies for IHOP 2002 (Fig. 2). The evaluation of HRLDAS using IHOP data was completed in FY06.
Figure 2. Soil moisture defined by HRLDAS for an IHOP 2002 period. Nested grids used for the HRLDAS IHOP-2002 experiment. (a) 12-km outer grid and 4-km inner grid; (b) HRLDAS surface volumetric soil moisture (contours in 0.02 m3 m-3 intervals starting from 0.02 m3 m-3) valid at 1200 UTC 29 May 2002.
FY07 Plans:
Work to improve the canopy resistance scheme in the coupled WRF/Noah system will continue. The NCEP/NCAR Unified Noah LSM will be released. Enhancements to the coupled WRF/urban modeling system will be made, and an exploration of a possible two-way coupling between WRF/urban and CFD models will be conducted. Development of an urbanized HRLDAS will also begin.