The UAF MM5 realtime modeling system is centered around the Fifth-Generation Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) Mesoscale Model (MM5). This is a regional-scale atmospheric model designed to simulate the atmospheric circulation over a sub-continental sized area at resolutions of several to tens of kilometers.
Models of this type simulate atmospheric dynamics via computations carried out on one or a set of horizontal grids, which span a specified geographic region (domain) and have a given grid resolution. Above each point on the horizontal grid sits a column of additional points, the set of which define a three-dimensional computational space. The model performs calculations at each of the points in this space based on physical relationships which govern atmospheric behavior. At any given time, the future properties of a particular point are governed by the combination of its current properties and those of the surrounding points. Calculations are performed based on equations which relate these properties, which tells the model what the properties of the point will be at a future time (the next time step). Through repetition of this process, the model moves the state of the atmosphere forward in time, producing a weather forecast.
MM5 uses a terrain-following vertical coordinate system and has the capability to run with several horizontally nested domains (grids). This allows the model to run at a relatively high resolution over a specific area of interest, while maintaining a low resolution over the surrounding areas. This flexibility means that high-resolution forecasts can be produced for a smaller region in a much shorter time than would be possible if the entire large domain had to run at the fine grid spacing (because more points mean more computation time), while still allowing the model to simulate the larger-scale circulation.
For our particular application, we run the model with five domains. The largest, coarsest grid has a resolution of 45 km (27.9 mi) and extends over the entire state of Alaska, along with western Canada and the northeastern corner of Russia. A second, finer grid with a spacing of 15 km (9.3 mi) is nested within the coarse grid and covers most of Interior Alaska, along with the northern and southern coasts. The third and fourth grids are located within the 15 km grid and are centered over Fairbanks and Anchorage, each with a resolution of just 5 km (3.1 mi). The fifth and final domain has 9 km (5.6 mi) spacing and is nested within the coarse grid, comprising the entire Alaskan panhandle.
Our model is initialized and nudged from output of the ETA model, a larger-scale model run by the National Centers for Environmental Predicition (NCEP), along with surface observations incorporated in the initialization. We produce thrice-daily forecasts with initialization times of 06, 12, and 18Z (9 p.m., 3 a.m., and 9 a.m. Alaska Standard Time), which are usually up on the webpage within 6 - 6.5 hours of initialization time. The forecasts are run out to 48 hours for the large grid, from 4 - 33 hours for the second domain, from 9 - 24 hours for the fine grids over Fairbanks and Anchorage, and for 3 - 24 hours for the panhandle domain.
See below for the specifics of our current model configuration:
Grid Structure:
Physics Options:
More detailed information about MM5 and available physics options can be found on the MM5 homepage .
