One-and-a-half order closure

From Glossary of Meteorology

one-and-a-half order closure

A higher-order closure for turbulence where forecast equations are retained for mean variables (e.g., first-order
or first moment mean values of potential temperature and wind components), and for variance of selected variables (e.g., selected second statistical moments such as turbulence kinetic energy or potential temperature variance).

It is not second-order closure because forecast equations are not retained for covariances, which are also second moments statistically. Any other higher-order statistics remaining in the equations are approximated by the mean and variance values. One type of one-and-a-half-order closure is k-ε closure.
Compare first-order closure, K-theory, second-order closure, nonlocal closure, Reynolds averaging, closure assumptions.

Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact [email protected]. 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.