# Closure assumptions

From Glossary of Meteorology

## closure assumptions

Approximations made to the Reynolds-averaged equations of turbulence to allow solutions for flow and turbulence variables.

The Reynolds-averaged equations contain statistical correlations such as the variance or covariance between dependent variables such as velocity or temperature. The equations that forecast lower-order correlations often contain unknowns of higher statistical order, a difficulty known as the closure problem. When the higher-order terms are approximated as empirical functions of lower-order terms and of known independent variables, the resulting approximate equations can then be solved. These approximations, known as closure assumptions, must satisfy parameterization rules.

Stull, R. B. 1988. An Introduction to Boundary Layer Meteorology. 666 pp.

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.