Alternative small scale meteorology input to a chemical transport ...

2.6. Current meteorological data input to the CMAQ system in MODELS-3
Meteorological data input to air quality studies is the scope of this research.
Meteorological data are important in many of the processes simulated in the CMAQ system
included in MODELS-3. The meteorology model that has been selected and evaluated with
CMAQ is the Fifth-Generation Pennsylvania State University / National Center for Atmospheric
Research (NCAR) Mesoscale Model (MM5). MM5 is based on primitive physical equations
of momentum, thermodynamics and moisture for the variables temperature, specific humidity,
wind components, and pressure. MM5 can be run either as a hydrostatic or non-hydrostatic
model. In the hydrostatic model, the variables are explicitly predicted. In the non-hydrostatic
model, pressure, temperature and density are defined in terms of a reference state and
perturbations from the reference state. MM5 is non-mass conserving in the non-hydrostatic
mode (Otte, 1999). The vertical (sigma_p) coordinate is defined as a function of pressure. The
model’s prognostic equations are thoroughly discussed in Grell et al. (1994) and Dudhia et al.
(1998). MM5 is designed for forecasts at different spatial scales - grid dimensions from
hundreds of kilometers down to 4 km. or even less. Different physical processes are important
at different scales and MM5 users are allowed to choose from alternative schemes for them.
MM5 users are also allowed to use a four-dimensional data assimilation (FDDA) throughout the
simulations where artificial (non-physical) forcing functions are added to the model’s prognostic
equations to nudge the solutions towards either a verifying analysis or observations. MM5
documentation, along with other publications, is also available at
http://www.mmm.ucar.edu/mm5/mm5-home.html.
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