“…Joint frequency atmospheric dispersion data consists of a 3-dimensional matrix of windspeed r class, stability class, and wind direction. In order to istimate national average atmospheric conditions for use in the RISKIND computer code (Yuan et al 1995), joint frequency data from 177 sites was averaged and normalized. In performing this averaging and normalization, the directional component of the joint frequency data was condensed to yield a 2-dimensional matrix of stability class and windspeed class, which is the format used by RISKIND.…”