Land / Atmosphere Interactions Background
Motivated by the positive results found using MODIS data to initialize sea-surface temperatures (SSTs) in numerical weather prediction (NWP) models LaCasse et al. (2008), this project seeks to improve the specification of the lower boundary in regional NWP models over land areas as well. In an initial study, SPoRT conducted an assessment of daily regional simulations of the Weather Research and Forecasting (WRF) NWP model initialized with high-resolution land surface data from the NASA Land Information System (LIS) versus a Control configuration that used land surface data from the National Centers for Environmental Prediction (NCEP) Eta model (Case et al. 2008). The goal of this study was to investigate the benefits of using the LIS to improve land surface initialization for regional NWP. The land surface initial conditions for the LISWRF runs came from an offline integration of the Noah land surface model (LSM) within LIS for two years prior to the beginning of the month-long study, on an identical grid domain as the subsequent WRF simulations. Atmospheric variables used to force the offline Noah LSM integration were provided by the North American Land Data Assimilation System and Global Data Assimilation System gridded analyses.
Initial 0-10 cm volumetric soil moisture (%) from 4-km WRF simulations initialized at 0000 UTC 28 March 2007 for (a) Control NSSL WRF interpolating soil moisture off of the 40-km NCEP NAM data, (b) Offline LIS run integrating the Noah land surface model from 1 January 2004 to 28 March 2007 on the exact WRF grid, and (c) Difference between the LIS and Control.
The benefits of running LIS with WRF for regional modeling are numerous:
- LIS provides the capability to conduct long-term offline integrations or "spinups" to allow the surface and soil profiles to reach thermodynamic equilibrium, using bias-adjusted meteorological inputs or "forcings".
- Offline LIS output is generated at the same resolution as the local/regional grids (i.e. for each nest), and is then used directly as input to the WRF simulation, eliminating the need for horizontal spatial interpolation.
- Users can run WRF with the LSMs available in LIS (in the fully-coupled mode), whereas only the Noah, Rapid Update Cycle's LSM, or thermal diffusion scheme can be run within the standard ARW.
- The LIS provides a plug-in framework through which users can introduce new high-resolution land datasets, LSMs, or land surface observations into WRF.
In Case et al. (2008), comparisons between the Control and LISWRF runs suggested that the LIS land surface initial conditions led to an improvement in the timing and evolution of a sea-breeze circulation over portions of northwestern Florida. Surface verification statistics for the entire month indicated that the LISWRF runs produced a more accurate diurnal range in 2-m temperatures compared to the Control runs through a reduction in the nocturnal warm bias combined with a reduction in the daytime cold bias. The positive results of the LISWRF experiments over Florida help to illustrate the importance of initializing regional NWP models with high-quality land surface data generated at the same grid resolution.
Current and future work involve conducting WRF sensitivity experiments using the real-time NSSL WRF configuration for selected severe weather cases from the 2007 and 2008 NSSL/SPC Spring Experiments (and beyond). The sensitivity experiments include examining the impacts of LIS land surface initialization data (see figure above), as well as MODIS SSTs and new physics schemes in WRF developed by NASA Goddard Space Flight Center scientists. Other experiments using LIS will include local modeling applications with National Weather Service forecast offices, examining the impacts of high-resolution land surface LIS data on WRF predictions of summertime convective initiation and precipitation systems over the southeastern U.S.
For more information on LIS, visit the official Land Information System website.
