Stability Array (STAR)

Stability Array (STAR) are historical tabulations for U.S. stations and a scattering of stations world wide. STAR was born from the work of Pasquill (1951), Turner (1964), and Martin and Tidvart (1968). It provides, at least roughly, the diffusion characteristics for the lowest part of the atmosphere and biosphere. It is an objective method of determining stability from readily available surface meteorological observations utilizing only the variables of ceiling height, total sky cover, and wind direction and speed as input. The methodology employed recognizes that stability near the ground is dependent primarily upon net radiation and wind speed. Wind direction is not a factor in objective determination of stability categories. Without the influence of clouds, insolation (incoming radiation) during the day is dependent mainly upon the solar elevation, which is a function of time of year, time of day, and station location. When clouds exist, their cover and thickness decrease incoming and outgoing radiation. In this system, insolation is estimated by solar elevation and modified for existing conditions of total sky cover and ceiling height. At night, estimates of outgoing radiation are again based on total sky cover and ceiling height. The STABILITY ARRAY consists of frequency and percent frequency tables of wind direction versus wind speed groups for each stability category. This system produces seven categories ranging from extremely unstable (A) to neutral (D) to extremely stable (G) and is summarized on a monthly, seasonal, and annual basis.