Flow-following, finite-volume Icosahedral Model: Difference between revisions

Revision as of 07:40, 19 February 2015

Revision as of 08:00, 19 February 2015

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{{unreferenced|date=February 2015}}

The '''Flow-following, finite-volume Icosahedral Model''' (FIM) is a [[numerical weather prediction]] model currently{{when|date=February 2015}} under development at the [[Earth System Research Laboratory]] in the United States.

The FIM is being developed as a candidate to eventually supplant the [[Global Forecast System]], the United States's current medium-range forecast model. The FIM was originally slated to become operational some time in 2014 (as of spring 2014 the model is still testing); the GFS will continue to be run and maintained for several years afterward, much in the same way the GFS and its predecessor, the [[Nested Grid Model]], ran concurrently for several years. The model currently produces similar results to the GFS, but runs slower on the NWS's operational computers. Its three-part name derives from its key features: "flow-following" indicates that its vertical coordinates are based on both terrain and [[potential temperature]] (isentropic [[sigma coordinates]], previously used in the now-discontinued [[rapid update cycle]] model), and "finite-volume" describes the method used for calculating horizontal transport. The "icosahedral" portion describes the model's most uncommon feature: whereas most grid-based forecast models have historically used rectangular grid points (a less than ideal arrangement for a planet that is a slightly [[oblate spheroid]]), the FIM instead fits Earth to a [[truncated icosahedron]], with twelve evenly spaced pentagons (including two at the poles) anchoring a grid of hexagons.