Editorial Type:
Article
Article Type:
Research Article

Simple Inclusion of z-less Turbulence within and above the Modeled Nocturnal Boundary Layer

Kyung-Ja Ha Department of Atmospheric Sciences, Pusan National University, Pusan, South Korea

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L. Mahrt College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon

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Print Publication:
01 Aug 2001
DOI:
https://doi.org/10.1175/1520-0493(2001)129<2136:SIOZLT>2.0.CO;2
Page(s):
2136–2143
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Abstract

In simple models, the nocturnal boundary layer is generally formulated in terms of eddy diffusivities, which are functions of height above ground and boundary layer depth. This approach is modified in this study to include “z-less” turbulence, which is formulated in terms of a stability-dependent mixing length and a Prandtl number, which are not tied to the existence of a boundary layer depth. These modifications have been guided by analysis of nocturnal boundary layer data from the Cooperative Atmospheric-Surface Exchange Study–1999.

The modeled turbulence sometimes exhibits an upside-down structure with turbulence generated by shear associated with nocturnal flow acceleration at higher levels. The modified model produces a more realistic smoother wind speed maximum (nocturnal jet) and generates layers of turbulence above the boundary layer. Remaining shortcomings of the new model are discussed.

Corresponding author address: Dr. Larry Mahrt, College of Oceanic and Atmospheric Sciences, Ocean Admin Bldg 104, Oregon State University, Corvallis, OR 97331-5503. Email: mahrt@oce.orst.edu

Abstract

In simple models, the nocturnal boundary layer is generally formulated in terms of eddy diffusivities, which are functions of height above ground and boundary layer depth. This approach is modified in this study to include “z-less” turbulence, which is formulated in terms of a stability-dependent mixing length and a Prandtl number, which are not tied to the existence of a boundary layer depth. These modifications have been guided by analysis of nocturnal boundary layer data from the Cooperative Atmospheric-Surface Exchange Study–1999.

The modeled turbulence sometimes exhibits an upside-down structure with turbulence generated by shear associated with nocturnal flow acceleration at higher levels. The modified model produces a more realistic smoother wind speed maximum (nocturnal jet) and generates layers of turbulence above the boundary layer. Remaining shortcomings of the new model are discussed.

Corresponding author address: Dr. Larry Mahrt, College of Oceanic and Atmospheric Sciences, Ocean Admin Bldg 104, Oregon State University, Corvallis, OR 97331-5503. Email: mahrt@oce.orst.edu

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