Preprints
https://doi.org/10.5194/gmd-2023-245
https://doi.org/10.5194/gmd-2023-245
Submitted as: development and technical paper
 | 
25 Jan 2024
Submitted as: development and technical paper |  | 25 Jan 2024
Status: this preprint is currently under review for the journal GMD.

Representing effects of surface heterogeneity in a multi-plume eddy diffusivity mass flux boundary layer parameterization

Nathan Patrick Arnold

Abstract. Earth System Models (ESMs) typically represent surface heterogeneity on scales smaller than the atmospheric grid, while land-atmosphere coupling is based on grid mean values. Here we present a general approach allowing subgrid surface heterogeneity to influence the updraft thermodynamic properties in a multi-plume mass flux parameterization. The approach is demonstrated in single column experiments with an Eddy Diffusivity Mass Flux (EDMF) boundary layer scheme. Instead of triggering based on grid mean surface values, updrafts are explicitly assigned to individual surface tiles with positive buoyancy flux. Joint distributions of near-surface vertical velocities and thermodynamic variables are defined over individual surface tiles, and updraft properties are drawn from the positive tails of the distributions. The approach allows updraft properties to covary with surface heterogeneity, and updrafts from different tiles maintain distinct properties to heights of several hundred metres. Mass flux contributions to subgrid variances are increased near the surface, but impacts on mean state variables are relatively small. We suggest that larger impacts might be obtained by adding a specialized plume to represent the effects of secondary circulations.

Nathan Patrick Arnold

Status: open (until 21 Mar 2024)

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  • RC1: 'Comment on gmd-2023-245', Anonymous Referee #1, 22 Feb 2024 reply
  • RC2: 'Comment on gmd-2023-245', Anonymous Referee #2, 01 Mar 2024 reply
Nathan Patrick Arnold

Data sets

SCM files for Representing Effects of Surface Heterogeneity in a Multi-Plume Eddy Diffusivity Mass Flux Boundary Layer Parameterization [Dataset] N. P. Arnold https://doi.org/10.5281/zenodo.10414628

Nathan Patrick Arnold

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Short summary
Earth System Models often represent the land surface at smaller scales than the atmosphere, but surface-atmosphere coupling uses only aggregated surface properties. This study presents a method to allow heterogeneous surface properties to modify boundary layer updrafts. The method is tested in single column experiments. Updraft properties are found to reasonably covary with surface conditions, and simulated boundary layer variability is enhanced over more heterogeneous land surfaces.