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Scale Awareness, Resolved Circulations, and Practical Limits In The MYNN–EDMF Boundary Layer and Shallow Cumulus Scheme

Abstract

Proper behavior of physics parameterizations in numerical models at grid sizes of order 1 km is a topic of current research. Modifications to parameterization schemes to accommodate varying grid sizes are termed “scale aware.” The general problem of grids on which a physical process is partially resolved is called the “gray zone” or “terra incognita.” Here we examine features of the Mellor–Yamada–Nakanishi–Niino (MYNN) boundary layer scheme with eddy diffusivity and mass flux (EDMF) that were intended to provide scale awareness, as implemented in WRF, version 4.1. Scale awareness is provided by reducing the intensity of nonlocal components of the vertical mixing in the scheme as the grid size decreases. However, we find that the scale-aware features cause poorer performance in our tests on a 600-m grid. The resolved circulations on the 600-m grid have different temporal and spatial scales than are found in large-eddy simulations of the same cases, for reasons that are well understood theoretically and are described in the literature. The circulations [model convectively induced secondary circulations (M-CISCs)] depend on the grid size and on details of the model numerics. We conclude that scale awareness should be based on effective resolution, and not on grid size, and that the gray-zone problem for boundary layer turbulence and shallow cumulus cannot be solved simply by reducing the intensity of the parameterization. Parameterizations with different characteristics may lead to different conclusions.

Article / Publication Data
Active/Online
YES
Status
FINAL PRINT PUBLICATION
Volume
148
Available Metadata
Accepted On
September 10, 2020
DOI ↗
Fiscal Year
NOAA IR URL ↗
Peer Reviewed
YES
Publication Name
Monthly Weather Review
Published On
November 01, 2020
Final Online Publication On
November 11, 2020
Final Print Publication On
November 01, 2020
Publisher Name
American Meteorological Society
Print Volume
148
Print Number
11
Page Range
4629–4639
Issue
11
Submitted On
February 25, 2020
Project Type
LAB SUPPORTED
URL ↗

Authors

Authors who have authored or contributed to this publication.

  • Wayne M. Angevine - lead Csl
    Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder
    NOAA/Global Systems Laboratory
  • Joseph B. Olson - second Gsl
    Federal
  • Jake J. Gristey - third Csl
    Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder
    NOAA/Global Systems Laboratory
  • Ian Glenn - fourth Csl
    Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder
    NOAA/Global Systems Laboratory
  • Graham Feingold - fifth Csl
    Federal
  • David (Dave) D. Turner - sixth Gsl
    Federal