Campus Units

Geological and Atmospheric Sciences, Environmental Science, Human Computer Interaction

Document Type

Article

Publication Version

Published Version

Publication Date

10-1-2018

Journal or Book Title

Weather and Forecasting

Volume

33

Issue

5

First Page

1109

Last Page

1120

DOI

10.1175/WAF-D-18-0036.1

Abstract

The Great Plains low-level jet (LLJ) is influential in the initiation and evolution of nocturnal convection through the northward advection of heat and moisture, as well as convergence in the region of the LLJ nose. However, accurate numerical model forecasts of LLJs remain a challenge, related to the performance of the planetary boundary layer (PBL) scheme in the stable boundary layer. Evaluated here using a series of LLJ cases from the Plains Elevated Convection at Night (PECAN) program are modifications to a commonly used local PBL scheme, Mellor–Yamada–Nakanishi–Niino (MYNN), available in the Weather Research and Forecasting (WRF) Model. WRF forecast mean absolute error (MAE) and bias are calculated relative to PECAN rawinsonde observations. The first MYNN modification invokes a new set of constants for the scheme closure equations that, in the vicinity of the LLJ, decreases forecast MAEs of wind speed, potential temperature, and specific humidity more than 19%. For comparison, the Yonsei University (YSU) scheme results in wind speed MAEs 22% lower but specific humidity MAEs 17% greater than in the original MYNN scheme. The second MYNN modification, which incorporates the effects of potential kinetic energy and uses a nonzero mixing length in stable conditions as dependent on bulk shear, reduces wind speed MAEs 66% for levels below the LLJ, but increases MAEs at higher levels. Finally, Rapid Refresh analyses, which are often used for forecast verification, are evaluated here and found to exhibit a relatively large average wind speed bias of 3 m s−1in the region below the LLJ, but with relatively small potential temperature and specific humidity biases.

Comments

This article is published as Jahn, David E., and William A. Gallus Jr. "Impacts of modifications to a local planetary boundary layer scheme on forecasts of the Great Plains low-level jet environment." Weather and Forecasting 33, no. 5 (2018): 1109-1120. DOI: 10.1175/WAF-D-18-0036.1. Posted with permission.

Rights

Copyright 2018 AMS https://www.ametsoc.org/ams/index.cfm/publications/authors/journal-and-bams-authors/author-resources/copyright-information/copyright-policy/

Copyright Owner

American Meteorological Society

Language

en

File Format

application/pdf

Share

COinS