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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American Geophysical Union (AGU)
2021-08-01
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Online Access: | https://doi.org/10.1029/2020MS002437 |
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doaj-b412d4f3dd5a4765b7fde3f9528b67662021-08-27T14:57:23ZengAmerican Geophysical Union (AGU)Journal of Advances in Modeling Earth Systems1942-24662021-08-01138n/an/a10.1029/2020MS002437A Locally Smoothed Terrain‐Following Vertical Coordinate to Improve the Simulation of Fog and Low Stratus in Numerical Weather Prediction ModelsStephanie Westerhuis0Oliver Fuhrer1ETH Zürich Zürich SwitzerlandMeteoSwiss Zürich SwitzerlandAbstract 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.https://doi.org/10.1029/2020MS002437foglow stratusnumerical weather predictionvertical coordinate formulation |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Stephanie Westerhuis Oliver Fuhrer |
spellingShingle |
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 Journal of Advances in Modeling Earth Systems fog low stratus numerical weather prediction vertical coordinate formulation |
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) |
series |
Journal of Advances in Modeling Earth Systems |
issn |
1942-2466 |
publishDate |
2021-08-01 |
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. |
topic |
fog low stratus numerical weather prediction vertical coordinate formulation |
url |
https://doi.org/10.1029/2020MS002437 |
work_keys_str_mv |
AT stephaniewesterhuis alocallysmoothedterrainfollowingverticalcoordinatetoimprovethesimulationoffogandlowstratusinnumericalweatherpredictionmodels AT oliverfuhrer alocallysmoothedterrainfollowingverticalcoordinatetoimprovethesimulationoffogandlowstratusinnumericalweatherpredictionmodels AT stephaniewesterhuis locallysmoothedterrainfollowingverticalcoordinatetoimprovethesimulationoffogandlowstratusinnumericalweatherpredictionmodels AT oliverfuhrer locallysmoothedterrainfollowingverticalcoordinatetoimprovethesimulationoffogandlowstratusinnumericalweatherpredictionmodels |
_version_ |
1721188135541407744 |