Real-time testing and description of the FIM global model

The Flow-following finite-volume Icosahedral Model (FIM) has been developed at NOAA/ESRL over the last few years, and began real-time testing in February 2008. The FIM has 3 key unique numerical aspects: use of an isentropic-hybrid (e.g., “flow-following) vertical coordinate, finite-volume numerics, and an icosahedral horizontal grid. These characteristics make the FIM very promising for global numerical weather prediction and even climate prediction, with improved transport (isentropic, finite volume) and absence of polar singularity issues.

Currently, the FIM is configured with the GFS physics suite, and efforts are now underway to incorporate WRF physics options and WRF/Chem inline chemistry. NOAA/ESRL and NCEP plan to use the FIM model at least as an alternative dynamic core component to the future NCEP global ensemble forecast system.

In this paper, the FIM model will be described, including overall performance of the FIM compared to the GFS model for 5-7-day forecasts at 30km resolution (FIM nearly equal to GFS as of Feb 2009). Results from 15-km tests will also be included, as well as results from 50-level (ptop=10 hPa) and 64-level (ptop=0.5 hPa) versions. This paper will introduce companion papers on FIM tropical cyclone performance (Fiorino et al.) and FIM case studies (Szoke et al.)