The Atmospheric Boundary Layer and the “Gray Zone” of Turbulence: A Critical Review

Rachel Honnert (1) , Georgios A Efstathiou (2) , Robert J Beare (2) , Junshi Ito (3) , Adrian Lock (4) , Roel Neggers (5) , Robert S Plant (6) , Hyeyum Hailey Shin (7) , Lorenzo Tomassini (4) , Bowen Zhou (8)

1 CNRM - Centre national de recherches météorologiques
2 University of Exeter
3 Department of Geophysics, Graduate School of Science, Tohoku University, Japan
4 UK METOFFICE EXETER GBR
5 University of Cologne
6 Department of Meteorology, University of Reading, Reading, UK
7 NCAR - National Center for Atmospheric Research [Boulder]
8 Laboratory for Mesoscale Severe Weather/MOE and School of Atmospheric Sciences, Nanjing University, Nanjing, China

Recent increases in computing power mean that atmospheric models for numerical weather prediction are now able to operate at grid spacings of the order of a few hundred meters, comparable to the dominant turbulence length scales in the atmospheric boundary layer. As a result, models are starting to partially resolve the coherent overturning structures in the boundary layer. In this resolution regime, the so-called boundary layer “gray zone,” neither the techniques of high-resolution atmospheric modeling (a few tens of meters resolution) nor those of traditional meteorological models (a few kilometers resolution) are appropriate because fundamental assumptions behind the parameterizations are violated. Nonetheless, model simulations in this regime may remain highly useful. In this paper, a newly formed gray zone boundary layer community lays the basis for parameterizing gray zone turbulence, identifies the challenges in high-resolution atmospheric modeling and presents different gray zone boundary layer models. We discuss both the successful applications and the limitations of current parameterization approaches, and consider various issues in extending promising research approaches into use for numerical weather prediction. The ultimate goal of the research is the development of unified boundary layer parameterizations valid across all scales. The horizontal grid resolution of atmospheric models has become fine enough that models are able to partially resolve turbulent motions in the atmospheric boundary layer. This resolution regime comprises the "gray zone" of turbulence. The traditional parameterization methods for the representation of turbulence are no longer valid in the turbulence "gray zone". Due to the gray-zone problem, it is no longer the case that increases to the model resolution will necessarily improve the quality and usefulness of simulation results. We review the current efforts by modelers to overcome the gray-zone problems in order to provide useful simulations at high resolutions. We conclude that the task is far from being hopeless, and propose that extensions to the approaches being developed for this field may also prove valuable for other geophysical modeling problems.

Domaines: Physique [physics]

Rachel Honnert, Georgios A Efstathiou, Robert J Beare, Junshi Ito, Adrian Lock, et al.. The Atmospheric Boundary Layer and the “Gray Zone” of Turbulence: A Critical Review. Journal of Geophysical Research: Atmospheres, 2020, 125 (13), ⟨10.1029/2019JD030317⟩. ⟨meteo-03357873⟩