How is the Two-Regime Stable Boundary Layer Reproduced by the Different Turbulence Parametrizations in the Weather Resea
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How is the Two-Regime Stable Boundary Layer Reproduced by the Different Turbulence Parametrizations in the Weather Research and Forecasting Model? Rafael Maroneze1 · Otávio C. Acevedo2 · Felipe D. Costa1 · Franciano S. Puhales2 · Vagner Anabor2 · Danilo N. Lemes Jr.1 · Luca Mortarini3 Received: 9 March 2020 / Accepted: 23 October 2020 © Springer Nature B.V. 2020
Abstract Five planetary-boundary-layer parametrizations of the Weather Research and Forecasting model are compared with respect to their ability to simulate the very stable and the weakly stable regimes of the stable boundary layer. This is performed for single column models where the large-scale mechanical forcing is represented by geostrophic wind speeds ranging from 0.5 to 12 m s−1 . The performance of the models is assessed by contrasting the relationships they produce between the turbulence velocity scale and the mean wind speed, between potential temperature gradient and the mean wind speed, and between the flux and gradient Richardson numbers. The level-2.5 Mellor–Yamada–Nakanishi–Niino parametrization simulates the very stable regime the best, mainly because its heat eddy diffusivity decreases with respect to the momentum eddy diffusivity as the stability increases, while the same is not true for the other parametrizations considered. Keywords Eddy diffusivity · Regime transition · Stable-boundary-layer regimes · Turbulence parametrizations · Weather Research and Forecasting model
1 Introduction The Weather Research and Forecasting (WRF) model (Skamarock et al. 2008) is currently the most used model for both scientific research and operational numerical weather prediction. The WRF model is also employed to investigate air chemistry, hydrology, wind and solar energy, wildland fires, hurricanes, regional climate, and other phenomena (Powers et al. 2017). Most of these applications demand a correct simulation of both daytime and nighttime periods, specifically at levels near the surface, and within the planetary boundary layer
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Rafael Maroneze [email protected]
1
Universidade Federal do Pampa-Campus Alegrete, Av. Tiaraju, 810 - Ibirapuitã, Alegrete, RS 97546-550, Brazil
2
Departamento de Física, Universidade Federal de Santa Maria, Santa Maria, Brazil
3
Institute of Atmospheric Sciences and Climate - National Research Council, Turin, Italy
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(PBL). The present study addresses a difficulty that affects most PBL parametrizations: the representation of turbulence in very stable conditions. These are typically nocturnal, but they may also occur at daytime over snow-covered surfaces, sea-ice, and during the polar winter. The existence of two distinct regimes in the stable boundary layer (SBL) has been known for many years (André and Mahrt 1982; Mahrt and Gamage 1987). More recently, the two regimes have been classified both observationally and in modelling as weakly stable and very stable (Mahrt 1998; van de Wiel et al. 2002; Sun et al. 2012; Acevedo et al. 2016, among others). In the weakly stable regime, turbulen
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