From Glossary of Meteorology
Revision as of 10:18, 9 April 2018 by imported>Rbrandt (→‎sigma-theta)


  1. (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,


  1. (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/nisinθi and ca = (1/nicosθi are computed from a sequence of n wind angle (θi) measurements.

Term edited 9 April 2018.

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