Evaluation of ABL parametrization schemes in the COSMO, a regional non-hydrostatic atmospheric model over an inhomogeneous environment

The correct simulation of the atmospheric boundary layer (ABL) is crucial for reliable weather forecasts in truly complex terrain. However, common assumptions for model parametrizations are only valid for horizontally homogeneous and flat terrain. Here, we evaluate the turbulence parametrization of the numerical weather prediction model COSMO with a horizontal grid spacing of for the Inn Valley, Austria. The long-term, high-resolution turbulence measurements of the i-Box measurement sites provide a useful data pool of the ABL structure in the valley and on slopes. We focus on days and nights when ABL processes dominate and a thermally-driven circulation is present. Simulations are performed for case studies with both a one-dimensional turbulence parametrization, which only considers the vertical turbulent exchange, and a hybrid turbulence parametrization, also including horizontal shear production and advection in the budget of turbulence kinetic energy (TKE). We find a general underestimation of TKE by the model with the one-dimensional turbulence parametrization. In the simulations with the hybrid turbulence parametrization, the modelled TKE has a more realistic structure, especially in situations when the TKE production is dominated by shear related to the afternoon up-valley flow, and during nights, when a stable ABL is present. The model performance also improves for stations on the slopes. An estimation of the horizontal shear production from the observation network suggests that three-dimensional effects are a relevant part of TKE production in the valley.

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“… 2010 ; Buzzi et al. 2011 ), and parametrization testing (Anurose and Subrahamanyam 2015 ; Panosetti et al. 2016 ).…”

Section: Methodsmentioning

confidence: 99%

The Impact of Three-Dimensional Effects on the Simulation of Turbulence Kinetic Energy in a Major Alpine Valley

Goger

Rotach

Gohm

et al. 2018

Boundary-Layer Meteorol

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“…The lowest vertical level of the model is placed at 10 m above the local topography and a generalized terrain following height co-ordinate system is adopted for the definition of vertical grid points above. The prognostic variables in this model include temperature, specific humidity, horizontal and vertical Cartesian wind components, pressure perturbation, cloud water content, cloud ice content, turbulent kinetic energy, specific water content of rain, snow and graupel [18]. The COSMO model includes parameterization for radiative transfer, cloud micro-physics, sub-grid scale turbulence, and convection.…”

Section: About the Cosmo Modelmentioning

confidence: 99%

“…This version of the model was released in April 2018. More details on the functioning of COSMO are accessible on the model's website and other published literature [13,[15][16][17][18].…”

Section: About the Cosmo Modelmentioning

confidence: 99%

An assessment of a very severe cyclonic storm in the Arabian sea using the COSMO model

et al. 2020

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Accurate and reliable representation of convective processes is one of the major sources of uncertainty in numerical weather prediction (NWP) models, especially for those operating in the grey zone resolutions. The performance of NWP models become more sensitive to their grid resolutions, when they are used for simulation of severe weather events, such as a cyclonic storm. In this paper, we present a detailed assessment of an intense convective episode with heavy precipitation associated with the passage of a very severe cyclonic storm "OCKHI" using the Consortium for Small-scale Modelling (COSMO). A set of distinct numerical simulations are carried out using COSMO to address the impact of grid resolution and the treatment of explicit and implicit convection. Results obtained from the present investigation indicate that explicit treatment of convection in the COSMO model led to improved prediction of the cyclonic event in terms of sea level pressure, maximum sustained surface wind speeds and the accumulated rainfall, but reduction of the spatial grid resolution from 7 to 3 km did not show appreciable differences in the forecast fields. Conclusively, the current study recommends switching off the convection parameterization scheme at a grid resolution of 7 km for improved predictability of tropical cyclones.

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“…The COSMO model is one of the regional NWP models designed for both operational weather forecasting and research mode scientific applications on the meso-β and meso-γ scale (Baldauf et al 2011;Anurose and Subrahamanyam 2015;Schattler et al 2016;Roshny et al 2018;Subrahamanyam et al 2019). The governing equations of the atmosphere in the COSMO model are based on the primitive hydro-thermodynamical equations describing compressible non-hydrostatic flow in a moist atmosphere.…”

Section: About the Cosmo Modelmentioning

confidence: 99%

Impact of a very severe cyclonic storm ‘OCKHI’ on the vertical structure of marine atmospheric boundary layer over the Arabian Sea

Subrahamanyam

Roshny

Paul

et al. 2020

Bull. of Atmos. Sci.& Technol.

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Although considerable progress has been made in improving the early predictability of the tropical cyclones, our knowledge of the vertical structure of the marine atmospheric boundary layer (MABL) over a cyclone-affected ocean remains limited. Here, we investigate the impact of a very severe cyclonic storm 'OCKHI' on the MABL parameters over the Arabian Sea by using a regional numerical weather prediction model, namely Consortium for Small-scale Modelling (COSMO). Time-series meteograms of the surface-layer and upper-air meteorological parameters are examined for six distinct locations on the trajectory of OCKHI. Equivalent day analysis on the surface-layer turbulent fluxes over these locations reveals a substantial rise in the magnitude of sensible and latent heat fluxes during the passage of the storm. Surface-layer parameters within the MABL exhibit large diurnal variability during the passage of the storm compared with the normal days. Profiles of thermodynamic parameters indicate a significant dip in the mixed layer heights near the eye of the storm due to the formation of deep convective precipitating clouds. A decline in the mixed layer height during the propagation of the storm was a persistent feature. The present study also provides a conserved variable analysis of the equivalent potential temperature (θ e ) and specific humidity (q) for a diagnostic investigation on the MABL processes and the movement of an air parcel. Keywords Air-sea interface fluxes • Conserved variable analysis • COSMO • Equivalent potential temperature • Marine atmospheric boundary layer • OCKHI • Tropical cyclones Bala Subrahamanyam D.

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Evaluation of ABL parametrization schemes in the COSMO, a regional non-hydrostatic atmospheric model over an inhomogeneous environment

Cited by 10 publications

References 43 publications

The Impact of Three-Dimensional Effects on the Simulation of Turbulence Kinetic Energy in a Major Alpine Valley

The Impact of Three-Dimensional Effects on the Simulation of Turbulence Kinetic Energy in a Major Alpine Valley

An assessment of a very severe cyclonic storm in the Arabian sea using the COSMO model

Impact of a very severe cyclonic storm ‘OCKHI’ on the vertical structure of marine atmospheric boundary layer over the Arabian Sea

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