THE PSU/NCAR MM5

The Fifth Generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (PSU/NCAR MM5) is a non-hydrostatic, three-dimensional, limited-area atmospheric numerical model with multiple options to parameterize convection, radiation, explicit microphysics, the surface, and the boundary layer. The vertical coordinate is the terrain-following sigma. The model domain is configurable and interactive nesting is available.

The 'MM5 Modeling System' includes the model and several 'pre-processors' that define the model domain, terrestrial characteristics (i.e. topography, vegetation, soil conditions), and prepare initial and lateral boundary conditions (Grell et. al. 1994.) The assimilation of observations, to improve the initial condition, is also available. The MM5 System is available in the form of public domain computer software from the National Center for Atmospheric Research (NCAR) in Boulder Colorado.

THE PSU/NCAR MM5 AT WFO CRP

At the National Weather Service (NWS) Forecast Office in Corpus Christi Texas (WFO CRP), the MM5 has been running operationally since June 2001. The purpose for running the MM5 system at WFO CRP is to improve the forecasting of weather phenomena on the mesoscale. The current WFO CRP configuration of the model domain and physics is as follows:

1. Nested Domain with Two-Way Interaction

Domain 1: 75 and 75 points in the horizontal (grid spacing of 30-km), centered at WFO CRP. Twenty three (23) vertical sigma levels.

Domain 2 (inner nest): 46 and 43 points in the horizontal (grid spacing of 10-km) and 23 sigma levels. This smaller domain zooms on the region for which WFO CRP issues meteorological and hydrological short-fused (i.e. Severe Thunderstorm Warnings) and long-fused (i.e. Zone Forecasts) products.

2. A new version of the original Kain and Fritsch (1993) convective parameterization scheme

3. MRF Boundary Layer scheme (Hong and Pan, 1996)

4. Mixed-Phase Explicit Microphysics (Reisner et. al. 1998)

5. RRTM (Rapid Radiative Transfer Model) longwave radiation scheme (Mlawer et al. 1997) and Dudhia shortwave scheme

6. OSU/Eta Land Surface Model (Chen and Dudhia, 2001)

Initial values must be provided to the MM5 domain before numerical integration commences. This process is referred to as 'data initialization'. The accuracy/quality of initial condition data directly affects the accuracy of the numerical model output. At WFO CRP, the three-dimensional initial values for the MM5 are provided by initial condition data from the Eta-12 numerical model (originating from the NWS National Centers for Environmental Prediction.) The MM5 system requires initial sea surface temperature (SST) data. At WFO CRP, a high-resolution (10-km) SST analysis (updated daily) is utilized. Non-meteorological accelerations generated at the beginning of the forecast, which could degrade the quality of the forecast, should be minimized. They are minimized by balancing mass and momentum during data initialization. At WFO CRP, balancing is achieved via a form of �dynamic initialization' known as Four Dimensional Data Assimilation or FDDA. During this process, the model is run during a 12-hr �pre-forecast' period (from t-12 to t, where t is the initial time, in hours, of the actual forecast) wherein the model output is relaxed or nudged to several Eta-12 analyses. This process results in an initial condition (t) that is in dynamic balance with respect to the MM5 equations. After the 12-hr period, FDDA is turned off and the model equations are integrated for 24-hrs (the forecast.)

Since the model domain, as configured at WFO CRP, is of limited area (the model domain does not cover the globe), a lateral boundary condition is necessary wherein the four lateral boundaries of the MM5 domain need values for various atmospheric parameters to be specified at the initial time and during the model run. These boundary values are obtained from the Eta-12 model initial analysis and forecasts (mapped to AWIPS grid 212 which has a 40-km grid spacing.) Within the MM5 domain, the MM5 is nudged toward the Eta-12 output wherein the strength of the nudging decreases toward the center of the MM5 domain.

The basic MM5 System software from NCAR is setup to run manually. A Unix shell script was written in order to run the model in operational mode. The model is run twice daily (the 00 and 12 UTC runs.)

The forecast output from Domain 2, in 1-hr increments out to 24 hrs, is available to WFO CRP forecasters via AWIPS (Advanced Weather Interactive Processing System)

Please direct any questions or comments regarding the MM5-related information contained on this site in an e-mail to Waylon.Collins@noaa.gov.

Selected MM5 output

The output from the forecast is displayed in 3-hr increments out to 24-hrs. The output from the MM5 run beginning at 00 UTC should be available by 07 UTC (200 AM CDT.) each day. For the model run beginning at 12 UTC, the output should be available by 19 UTC (200 PM CDT.) The computer software used to generate these images is called RIP (Read/Interpolate/Plot) (Stoelinga, 2000)

Click on the following desired link to view MM5 output from Domain 1.

Domain 1: Mean Sea Level Pressure, Surface wind, and Precipitation Totals

Domain 1: Column Integrated Cloud Mixing Ratio (Clouds)

Domain 1: Surface Air Temperature

References

Chen, F., and J. Dudhia, 2001: Coupling an advanced land-surface/hydrology model with the Penn State/NCAR MM5 modelling system. Part I: Model Implementation and sensitivity. Mon. Wea.Rev., 129, 569-585

Hong, S.Y., and H.L. Pan, 1996: Nonlocal boundary layer vertical diffusion in a medium-range forecast model. Mon. Wea. Rev., 124, 2322-2339.

Kain, J. S., and J. M. Fritsch, 1993: Convective parameterization for mesoscale models: The Kain-Fritsch scheme. The representation of cumulus convection in numerical models, K. A. Emanuel and D. J. Raymond, Eds., Amer. Meteor. Soc., 246 pp.

Mlawer, E. J., S. J. Taubman, P.D. Brown, M. J. Iacono, 1997: Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave. J. Geophys. Res. Vol. 102, 16663-16682.