Sigma-theta

From Glossary of Meteorology
Revision as of 07:17, 8 May 2018 by imported>Rbrandt (→‎sigma-theta)



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,

sigma-theta-ocean

(Used in meteorology, symbol σθ.) 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 (see Wikipedia 2018). Sigma-theta is used as a proxy to characterize the dispersion capabilities of the lower troposphere with different stability categories. The Yarmartino method is given by:
sigma-theta-atmos

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

Wikipedia, The Free Encyclopedia, 2018: Yarmartino method. Accessed 8 May 2018. Wikipedia, https://en.wikipedia.org/wiki/Yamartino_method.


Term edited 8 May 2018.


Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact permissions@ametsoc.org. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.