CALMET (currently developed by Exponent, Inc.) is a diagnostic meteorological model which reconstructs the 3D wind and temperature fields starting from meteorological measurements, orography and land use data. Besides the wind and temperature fields, CALMET determines the 2D fields of micro meteorological variables needed to carry out dispersion simulations (mixing height, Monin Obukhov length, friction velocity, convective velocity and others).

The diagnostic wind field module uses a two step approach for the computation of the wind field. In the first step an initial guess wind field is adjusted for kinematic effects of terrain, slope flows, and terrain blocking effects to produce a Step 1 wind field. The second step consists in an objective analysis procedure to introduce observational data into the Step 1 wind field to produce a final wind field. CALMET can optionally use the output of prognostic meteorological models such as WRF or MM5 in three different ways:

  • as a replacement for the initial guess field,
  • as a replacement for the Step 1 field,
  • as pseudo observations in the objective analysis procedure.

The prognostic wind fields in some cases have the advantage to better represent regional flows and certain aspects of sea breeze circulations and slope/valley circulations.

CALMET needs meteorological observations at surface and upper air data. At surface the following variables are needed with hourly resolution: wind speed, wind direction, temperature, cloud cover, ceiling height, surface pressure, relative humidity and precipitation rate. CALMET surface observations can be analyzed by the WindRose PRO3 software, which reads the surf.dat files of versions 5.8 and 6.0. The upper air data, needed at least twice daily, must contain for each vertical level: wind speed, wind direction, temperature, pressure and height.

The output of the CALMET model is directly interfaced with dispersion models such as CALPUFF (Lagrangian puff model), CALGRID (Eulerian photochemical model), KSP (Lagrangian particle model) and LAPMOD (Lagrangian particle model).

Sources: Scire J.S., Robe F.R., Fernau M.E. and Yamartino R.J. (2000) A user's guide for the CALMET meteorological model (Version 5.0).