An evaluation of neutral and convective planetary boundary-layer parameterizations relative to large eddy simulations

Abstract

This paper compares a number of one-dimensional closure models for the planetary boundary layer (PBL) that are currently in use in large-scale atmospheric models. Using the results of a large-eddy simulation (LES) model as the standardof comparison, the PBL models are evaluatedover a range of stratifications from free convective to neutral and a range of surface shear stresses. Capping inversion strengths for the convective cases range from weakly to strongly capped. Six prototypical PBL models are evaluated in this study, which focuses on the accuracy of the boundary-layer fluxes of momentum, heat, and two passive scalars. One scalar mimics humidity and the other is a top-down scalar entrained into the boundary layer from above. A set of measures based on the layer-averaged differences of these fluxes from the LES solutions is developed. In addition to the methodological framework and suite of LES solutions, the main result of the evaluation is the recognition that all of the examined PBL parameterizations have difficulty reproducing the entrainment at the top of the PBL, as given by the LES, in most parameter regimes. Some of the PBL models are relatively accurate in their entrainment flux in a subset of parameter regimes. The sensitivity of the PBL models to vertical resolution is explored, and substantive differences are observed in the performance of the PBL models, relative to LES, at low resolution typical of large scale atmospheric models.

Evaluation of Three Planetary Boundary Layer Schemes in the WRF Model

“…Insufficient entrainment flux under convective conditions by the Mellor-Yamada level 2.5 scheme and other local closure schemes has been found in some onedimensional tests (Holtslag et al 1995;Ayotte et al 1996;Pagowski 2004). Simulated PBL growth and structure have been shown to be sensitive to the entrainment flux by Ayotte et al (1996), Betts et al (1997), andNoh et al (2003).…”

“…Simulated PBL growth and structure have been shown to be sensitive to the entrainment flux by Ayotte et al (1996), Betts et al (1997), andNoh et al (2003). The nonlocal ACM2 and YSU schemes both were designed for their entrainment flux to better match results from large-eddy simulations.…”

Columnar modelling of nucleation burst evolution in the convective boundary layer – first results from a feasibility study Part I: Modelling approach

“…Nevertheless, even most of state-of-the-art non-local mixing schemes have difficulties to represent the entrainment processes at the top of even the cloudless boundary layer (Ayotte et al, 1996;Siebesma and Holtslag, 1996;McFarlane, 1997, 1999;Mironov et al, 1999).…”

Characterizing moisture exchange between the Hawaiian convective boundary layer and free troposphere using stable isotopes in water

“…Since these mechanisms regulate the vertical transport of energy, moisture, trace gases, and pollutants, they play a significant role in climate. Yet while numerous laboratory [Deardorff et al, 1980], observational [Nelson et al, 1989;Lenschow et al, 1999;Bretherton et al, 1995;Faloona et al, 2005;Träumner et al, 2011], and modeling [Sullivan et al, 1998;Brooks and Fowler, 2012] studies have investigated shallow convection and entrainment and their role in transporting material vertically, simulated climates remain sensitive to the choice of model parameterization [Ayotte et al, 1996;Stevens, 2002;Hu et al, 2010]. Such sensitivities suggest bulk features of vertical moisture exchange are still not fully understood.…”