A Locally Smoothed Terrain‐Following Vertical Coordinate to Improve the Simulation of Fog and Low Stratus in Numerical Weather Prediction Models

Abstract The correct simulation of fog and low stratus (FLS) is a difficult task for numerical weather prediction (NWP) models. The Swiss Plateau experiences many days with FLS in winter. Most NWP models employ terrain‐following vertical coordinates. As a consequence, the typically flat cloud top is...

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Autores principales:	Stephanie Westerhuis, Oliver Fuhrer
Formato:	article
Lenguaje:	EN
Publicado:	American Geophysical Union (AGU) 2021
Materias:	fog low stratus numerical weather prediction vertical coordinate formulation Physical geography GB3-5030 Oceanography GC1-1581
Acceso en línea:	https://doaj.org/article/b412d4f3dd5a4765b7fde3f9528b6766
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spelling	oai:doaj.org-article:b412d4f3dd5a4765b7fde3f9528b67662021-11-12T07:13:23ZA Locally Smoothed Terrain‐Following Vertical Coordinate to Improve the Simulation of Fog and Low Stratus in Numerical Weather Prediction Models1942-246610.1029/2020MS002437https://doaj.org/article/b412d4f3dd5a4765b7fde3f9528b67662021-08-01T00:00:00Zhttps://doi.org/10.1029/2020MS002437https://doaj.org/toc/1942-2466Abstract The correct simulation of fog and low stratus (FLS) is a difficult task for numerical weather prediction (NWP) models. The Swiss Plateau experiences many days with FLS in winter. Most NWP models employ terrain‐following vertical coordinates. As a consequence, the typically flat cloud top is intersected by sloping coordinate surfaces above hilly terrain such as the Swiss Plateau. Horizontal advection across the sloping coordinate surfaces leads to spurious numerical diffusion which promotes erroneous FLS dissipation. To address this problem, we propose a new vertical coordinate formulation which features a local smoothing of the model levels. We demonstrate the positive impact of the new vertical coordinate formulation on a case study in detail and for a full month using the COSMO model. The improved vertical coordinate formulation is not yet sufficient to obtain perfect FLS forecasts, it is however a crucial aspect to consider on the way thereto.Stephanie WesterhuisOliver FuhrerAmerican Geophysical Union (AGU)articlefoglow stratusnumerical weather predictionvertical coordinate formulationPhysical geographyGB3-5030OceanographyGC1-1581ENJournal of Advances in Modeling Earth Systems, Vol 13, Iss 8, Pp n/a-n/a (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	fog low stratus numerical weather prediction vertical coordinate formulation Physical geography GB3-5030 Oceanography GC1-1581
spellingShingle	fog low stratus numerical weather prediction vertical coordinate formulation Physical geography GB3-5030 Oceanography GC1-1581 Stephanie Westerhuis Oliver Fuhrer A Locally Smoothed Terrain‐Following Vertical Coordinate to Improve the Simulation of Fog and Low Stratus in Numerical Weather Prediction Models
description	Abstract The correct simulation of fog and low stratus (FLS) is a difficult task for numerical weather prediction (NWP) models. The Swiss Plateau experiences many days with FLS in winter. Most NWP models employ terrain‐following vertical coordinates. As a consequence, the typically flat cloud top is intersected by sloping coordinate surfaces above hilly terrain such as the Swiss Plateau. Horizontal advection across the sloping coordinate surfaces leads to spurious numerical diffusion which promotes erroneous FLS dissipation. To address this problem, we propose a new vertical coordinate formulation which features a local smoothing of the model levels. We demonstrate the positive impact of the new vertical coordinate formulation on a case study in detail and for a full month using the COSMO model. The improved vertical coordinate formulation is not yet sufficient to obtain perfect FLS forecasts, it is however a crucial aspect to consider on the way thereto.
format	article
author	Stephanie Westerhuis Oliver Fuhrer
author_facet	Stephanie Westerhuis Oliver Fuhrer
author_sort	Stephanie Westerhuis
title	A Locally Smoothed Terrain‐Following Vertical Coordinate to Improve the Simulation of Fog and Low Stratus in Numerical Weather Prediction Models
title_short	A Locally Smoothed Terrain‐Following Vertical Coordinate to Improve the Simulation of Fog and Low Stratus in Numerical Weather Prediction Models
title_full	A Locally Smoothed Terrain‐Following Vertical Coordinate to Improve the Simulation of Fog and Low Stratus in Numerical Weather Prediction Models
title_fullStr	A Locally Smoothed Terrain‐Following Vertical Coordinate to Improve the Simulation of Fog and Low Stratus in Numerical Weather Prediction Models
title_full_unstemmed	A Locally Smoothed Terrain‐Following Vertical Coordinate to Improve the Simulation of Fog and Low Stratus in Numerical Weather Prediction Models
title_sort	locally smoothed terrain‐following vertical coordinate to improve the simulation of fog and low stratus in numerical weather prediction models
publisher	American Geophysical Union (AGU)
publishDate	2021
url	https://doaj.org/article/b412d4f3dd5a4765b7fde3f9528b6766
work_keys_str_mv	AT stephaniewesterhuis alocallysmoothedterrainfollowingverticalcoordinatetoimprovethesimulationoffogandlowstratusinnumericalweatherpredictionmodels AT oliverfuhrer alocallysmoothedterrainfollowingverticalcoordinatetoimprovethesimulationoffogandlowstratusinnumericalweatherpredictionmodels AT stephaniewesterhuis locallysmoothedterrainfollowingverticalcoordinatetoimprovethesimulationoffogandlowstratusinnumericalweatherpredictionmodels AT oliverfuhrer locallysmoothedterrainfollowingverticalcoordinatetoimprovethesimulationoffogandlowstratusinnumericalweatherpredictionmodels
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A Locally Smoothed Terrain‐Following Vertical Coordinate to Improve the Simulation of Fog and Low Stratus in Numerical Weather Prediction Models

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