Meteorological Simulations

 In developing MIST, mesoscale (regional) meteorological modeling was conducted for approximately 20 cities to estimate the impact of mitigation strategies on local meteorology – near surface air temperature, in particular. In some cases multiple cities were modeled using a single large domain with multiple nests (a nest is a subregion of the modeling domain for which the meteorological model calculates atmospheric conditions using finer resolution grid cells). In all cases the domain structure used 3 nest levels with the finest domain having horizontal resolution of 2 km. The outer domains had grid cell resolutions of 6km and 18km. The simulations used a standardized (streamlined) approach which did not allow for location-specific tuning of model parameters. This standardization allows for more straight-forward comparison of heat island mitigation across cities. The cost, however, is a slight increase in the level of uncertainty of the model results in general.

The primary weather patterns responsible for poor air quality in each modeling domain were identified and multiple modeling episodes were selected to correspond to conditions of poor air quality and oppressive urban air temperatures, in general. The two or three weather patterns most responsible for elevated levels of ambient ozone were selected for detailed modeling. These typically corresponded to days on which the average temperature was high and the relative humidity was low. Under such conditions biogenic and anthropogenic emissions are high, pollutant removal by vegetation is low, and the atmospheric conditions favor formation of ozone.

The mesoscale atmospheric model used in all of these simulations is version 3.4 of the MM5 model from the National Center for Atmospheric Research. Details of this model can be found at http://www.mmm.ucar.edu/mm5/mm5-home.html and in the numerous publications referenced by this site. The MM5 model consists of 4 preprocessor steps, a model integration (forecast) step, and post-processing analyses. The mm5 model and its preprocessors each have control files that specify a large number of simulation options.

 

Advanced users seeking more detailed information on this and other topics related to the scientific and modeling underpinnings of the MIST software tool should read the detailed model description document that can be downloaded from the MIST website.