Marine Ecosystem Dynamics Modeling Laboratory

The Meso-Scale Meteorological Model (MM5)

The Meso-Scale Meteorological Model (MM5)

The fifth-generation mesoscale meteorological model (called MM5) is a state of the art regional non-hydrostatic, terrain-following, sigma-coordinate weather model developed jointly by the National Center for Atmospheric Research (NCAR) and the Pennsylvania State University (PSU). The methods used to estimate surface sensible and latent heat fluxes in MM5 were modified to meet ocean and estuarine conditions by Chen et al. (2003). The following presentation applies the modified MM5 to Georgia’s estuaries.

The MM5 for Georgia’s estuaries is configured with 3 numerical domains having horizontal resolutions of 27, 9 and 3 km, respectively (see figure on this page).

mm5 domains

Domain center: 31.4oN, 81.5oW

Domain 01: Large domain:
Number of Grids: 65×65; Grid size: 27 km;

Domain 02: Regional domain:
Number of Grids: 133×133; Grid size: 9 km;

Domain 03: Local domain:
Number of Grids: 85×97; Grid size: 3 km;

Click the image to view larger image

It is driven by the NCAR-ETA weather model through a nested numerical approach. A data nudging assimilation method is used to merge the predicted and the observed surface wind stresses. The assimilation data includes wind speed and direction measured by NOAA’s coastal ocean buoys and weather stations. The original MM5 suffers from a deficiency when applied to the ocean because of an unrealistic simplification of the air-water temperature difference and an incorrect representation of marine boundary layer thermodynamics over the water’s surface (Dudhia et al.,2003). MM5 tends to overestimate the sensible and latent heat fluxes at the water’s surface. To make MM5 useful for our purposes, we have replaced the current heat flux equations with the bulk flux algorithms proposed by Fairall et al (1996). The modified MM5 presents an accurate estimation of the near-surface transfer process and air-water temperature difference under various stable or unstable thermal structure conditions in the near sea-level atmospheric boundary (Chen et al., 2003). The modified MM5 shows excellent agreement with long-term wind and heat flux data measured by the US GLOBEC buoy located on the southern flank of GB (Georges Bank) in 1995.

The wind stress, surface pressure, surface heat flux and precipitation/evaporation output from the MM5 are used to drive the Ogeechee River Estuary model. Since MM5 is capable of providing a 3-5 day forecast of local weather conditions, it was used to develop water and current condition forecast systems for the Ogeechee River Estuary.

An animated example comparing model-predicted and observed wind velocities over the South Atlantic Bight may be viewed here.

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