We had also recognized that future coordination with MM4 (to be used in Phase 2) modeling

grid definition may have been desirable, although differences in mapping projections between

the two models would have to be addressed.

Figure 3-1 displays the final meteorological domain selected for the Phase 1 demonstration.

By specifying a grid size of 20 km, an array of 35 by 50 grid points covers the recommended

1000 km by 700 km domain within the 100 by 100 grid limit currently set in MESOPAC and

MESOPUFF II. We had estimated in the protocol that the resulting five years of hourly

meteorological data generated on this grid would require about 3.3 gigabytes of storage.

Computational Domain

All sources and receptors to be modeled must be contained within the computational domain.

Puffs are not tracked after they leave this grid. Overall size of this domain can be set equal to

the full dimensions of the meteorological domain, or specified to occupy a subset of the grid.

All sources and receptors should be at least 20-50 km from the boundaries of this grid to avoid

underestimating concentrations by immediately losing puffs from near-boundary sources

and/or missing short-term recirculation events at near-boundary receptors. The size of the

computational domain does not affect the volume of output produced, but does affect the CPU

requirements of the modeling. Grid spacing must be the same as the meteorological domain.

For the demonstration study, sources were to be located as far as 200 km from SNP.

Provision for a 4 grid (80 km) buffer zone on all sides of this source region yielded a

computational domain of 30 by 30 grid points (Figure 3-1; dotted inset). We proposed using

this smaller computational grid, rather than the entire meteorological domain, to minimize

computing requirements while still giving an adequate representation of the sources to be

studied. Future studies that include different source regions can use the same meteorological

fields, but specify a computational domain appropriate to the application.

Sampling Domain

MESOPUFF II allows output concentrations and fluxes to be reported for both gridded and

non-gridded receptors. Gridded receptors consist of all grid points within a user specified

sampling domain. Non-gridded receptors can be located anywhere within the computational

domain. Gridded receptor concentrations and fluxes can be used to produce spatial isopleth

maps; as such, specification of a sampling grid is useful for general characterizations of an

area.

The sampling domain may be specified as a subset of the computational domain, with a

maximum of 40 by 40 grid points. Grid spacing may be smaller than on the meteorological

and computational grids. This is accomplished by specifying an integral number of divisions

of the computational grid spacing (usually 2). Note that an increase

 

 

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