Sigma-theta
From Glossary of Meteorology
sigma-theta
(Used in physical oceanography, symbol σθ.) The density ρ (<1000 kg m−3) that a parcel of water of salinity S and temperature T would have if it were raised adiabatically to the sea surface, where its temperature would change from T to potential temperature θ due to adiabatic decompression. In symbols,
(Used in meteorology, symbol θσ.) The standard deviation of horizontal wind direction used primarily in air pollution applications. Sigma-theta can either be computed directly from measured wind direction or with the Yamartino method. Sigma-theta is used as a proxy to characterize the dispersion capabilities of the lower troposphere in the Pasquill-Gifford categories. The Yarmartino method is given by:
where sa = (1/n)Σisinθi and ca = (1/n)Σicosθi are computed from a sequence of n wind angle (θi) measurements.
Term edited 9 April 2018.
