A Method for Simulating Wind Conditions During Atmospheric Stagnation Periods

Abstract

A method is presented whereby meteorological conditions encountered during air pollution episodes may be simulated. Meteorological conditions are expressed in terms of atmospheric stability, mixing depth, surface temperature, present wind direction, present wind speed, and wind direction and speed variability. Realistic conditions are obtained by varying stability, mixing depth and surface temperature diurnally in accordance with patterns observed during past episodes. Wind direction and speed are determined by using a digital computer to generate values from empirical frequency distributions and random number generator routines. Once an initial wind direction and speed are selected, subsequent directions are obtained by generating wind direction changes from wind direction variability frequency distributions and adding them changes to former values. Wind speeds are generated from conditional frequency distributions appropriate for each wind direction. Comparison of computer generated and observed wind directions and speeds failed to reveal any significant statistical differences. Generating wind conditions stochastically from empirical frequency distributions provides one with greater flexibility in testing the effectiveness of hypothetical all pollution control strategies during emergencies. Repeated simulators of wind conditions in this manner, when used as meteorological input to a dispersion model, may provide aid in evaluating different control strategies.