Atmospheric Model Variants
i.e., these are the ways models differ from one another
Varying Model Characteristic Typical Assumption or Value

Description of Characteristic, Comments
Basic Assumptions Varies highly   The model is required to satisfy the basic assumptions
Neq 6 to 8   Number of differential equations used in modeling
Δt 5 minutes   Time step used in numerical integration
Δx and Δy 50 to 350 km (30 to 220 mi)   East-west and north-south separation between model grid points (points of
        numerical evaluation)
nh 18   Number of vertical levels at which model parameters are evaluated
tmax Several days   The maximum time into the future to which the model extends

          The models generally use differential equations to evaluate various dependent variables at certain preselected values of four
 independent variables.  The independent variables are time (t), east-west position (x), north-south position (y) and vertical position (z).  The
 dependent variables may ordinarily include (1) temperature (T), (2) pressure (P), (3) dew point (Tdew), or its equivalent, relative humidity (RH)
 or specific humidity, (4) wind speed, (v), (5) wind direction (θ), (7) cloud cover, (8) precipitation type and intensity and (9) visibility.  Other
 variables which are sometimes modeled, if there is need, include (10) concentration of various pollutants, (11) concentration of pollen, (12)
 inversion depth, (13) tendency of pollutants to disperse, (14) amount and intensity of sunlight, etc.