The July 1995 episode meteorology was simulated on NCSC's T90 Cray supercomputer, using the Pennsyvania State University/National Center for Atmospheric Reseach (PSU/NCAR) Mesoscale Meteorology Model Five (MM5) version 1. This model is a prognostic meteorology model that uses the fundamental equations of motions and atmospheric physics representations to "predict" fields of meteorological variables such as temperature, humidity, solar radiation, wind speeds and directions, clouds, precipitation, and the convective mixing depth just above the earth's surface (called the plantary boundary layer).
The MM5 model uses inputs that describe the terrain and land use; inputs that describe the meteorology in global or hemispheric region; and local observations to describe the domain and boundary conditions for the model.
Figure 1. The supporting data files and operational programs for the MM5.
The MM5 model was operated in a "nested" mode in which a higher spatial resolution simulation was serially performed inside a courser grid domain simulation. This was done so that the larger grid simulation provided the boundary conditions for the smaller grid simulation, allowing more accurate smaller scale simulations. The nesting was 1 to 3, so that a 12-km^2 gridded model was operated inside the 36-km^2 gridded model. The outer most grid was initialized from the US Weather Service's large-scale forecast model predictions.
Figure 2. The 108-km^2, 36-km^2, 12-km^2, and 4-km^2 simulation domains for the 1995 episode.
In the NC modeling simulations, the MM5 model was configured with 26 unequal vertical layers from the surface to the top of the troposphere (over 16 km high). The layers became thicker as the pressure decreased, so that they each represent about the same amount of air mass. The lowest or surface layer was 38 meters thick. A table of layer structure is available. As will be shown later, these 26 layers were aggregated into 16 layers for chemical model simulations. This aggregation was only performed on the highest 14 layers; the lowest 12 layers were identical in the meteorological and chemical models.
Figure 3. The vertial grid structure of the MM5 in the NC modeling simulations.
The MM5 model is "terrain following", that is, the layer structure above is measured above each cell's local earth's surface.
For the July 1995 episode, the model was run for 6.5 days, starting at 00Z July 10, 1995, outputting data at hourly increments. The first 12 hours were regarded as start-up, so the first useable hour was 12Z (07EST, 08EDT) July 10, 1995. Numerous runs and test runs were made before settling on the final model configuration. More detail on these simulations is available at NCSC's technical support web site.