Rapid Refresh: NCEP operational upgrade and work toward version 3 and the North American Rapid Refresh Ensemble (NARRE)
For RAPv2, the most significant improvement within the data assimilation module was the upgrade from a traditional 3DVAR technique to a hybrid ensemble technique, using covariance information from the 80-member global ensemble data assimilation system. This change, enabled by global assimilation developments and facilitated by use of the community-based Gridpoint Statistical Interpolation (GSI) analysis package, has resulted in significant forecast improvement for most upper-air variables and forecast lengths. Additional assimilation enhancements include improved cloud analysis and soil temperature and moisture adjustment procedures. Within the WRF-ARW model component, the most significant enhancements include switching from the MYJ planetary boundary layer (PBL) to a specially adapted MYNN PBL scheme, an upgrade from a 6-layer to a new 9-layer version of the Smirnova (RUC) land surface model formulation (LSM), and a modified roughness length specification. There are also smaller upgrades to other model components, including the Thompson microphysics and the radiation schemes.
A number of model and assimilation upgrades have been made for RAPv3 and additional refinements are being evaluated. These include upgrades to the new Grell-Freitas cumulus parameterization, upgrade to a new Thompson scheme that incorporates aerosols, enhancements to the satellite radiance assimilation (cycled bias correction and more satellite data types assimilated), and improvements to the hybrid-ensemble assimilation parameters. Development work is also underway toward the North American Rapid Refresh Ensemble (NARRE) forecasting system, planned for NCEP implementation in 2017. This 6-member system will include 3 members each from the ARW and 3 NMMB dynamic cores and a common ensemble-based data assimilation system.
In the presentation, RAPv2 and RAPv3 enhancements and the associated forecast improvements will be described, with a brief discussion of the preliminary work toward the NARRE.