Validity of the hydrostatic approximation at convection-resolving scales: Diagnostic analysis and model intercomparison

2020 ◽  
Author(s):  
Christian Zeman ◽  
Nikolina Ban ◽  
Nils Wedi ◽  
Christoph Schär
Keyword(s):  
Climate Models ◽  
Horizontal Resolution ◽  
Vertical Wind ◽  
Small Scale ◽  
Reconstruction Technique ◽  
Cosmo Model ◽  
Operational Forecasts ◽  
Scale Modelling ◽  
Hydrostatic Approximation ◽  
Vertical Accelerations

<div>The increasing availability of computing power allows the use of kilometer-scale convection-resolving weather and climate models for operational forecasts. One of the open questions at these scales concerns the validity of the hydrostatic approximation, which assumes that vertical accelerations are small compared to the balancing forces of gravity and the vertical pressure gradient. This assumption is valid as long as the ratio of vertical to horizontal length scales of motion is small. Results from previous studies suggest that the horizontal resolution at which the hydrostatic approximation becomes invalid is highly dependent on the particular model, model configuration, and case setup.</div><div> </div><div>While most of the previous studies have been conducted with an idealized setup, this work will concentrate on a real-world case. To this end, a few summer days with strong convection over complex terrain in Europe are simulated with the nonhydrostatic regional Consortium for Small-scale Modelling (COSMO) model with horizontal resolutions ranging from 12 km to 275 m. To assess the validity of the hydrostatic approximation, we developed a hydrostatic reconstruction technique and diagnose the vertical wind using the hydrostatic set of equations. The diagnosed values are then compared to the actual nonhydrostatic up- and downdrafts with a statistical analysis of vertical wind speed frequencies for the different resolutions.</div><div> </div><div>Results suggest that the diagnosed hydrostatic vertical velocities are very similar to the nonhydrostatic vertical velocities up to horizontal resolutions of 1 km and thus the use of the hydrostatic approximations at these scales still seems to be a valid option.</div><div> </div><div> <div>Furthermore, the study contains an intercomparison of precipitation and vertical winds produced by the nonhydrostatic COSMO model and the hydrostatic Integrated Forecast System (IFS) from ECMWF for the same case. The intercomparison supports the previous findings that at resolutions of ∼2 km and ∼4 km the effect of the hydrostatic approximation is negligible. The results also show that a small enough timestep size is essential in order to properly resolve the high vertical velocities associated with convection.</div> </div>

scholarly journals Atmospheric Blocking and Mean Biases in Climate Models

2010 ◽  
Vol 23 (23) ◽  
pp. 6143-6152 ◽  
Author(s):  
Adam A. Scaife ◽  
Tim Woollings ◽  
Jeff Knight ◽  
Gill Martin ◽  
Tim Hinton
Keyword(s):  
Climate Change ◽  
Climate Models ◽  
Climate Model ◽  
Horizontal Resolution ◽  
Small Scale ◽  
Model Data ◽  
Atmospheric Blocking ◽  
Intergovernmental Panel ◽  
Weather And Climate ◽  
Main Culprit

Abstract Models often underestimate blocking in the Atlantic and Pacific basins and this can lead to errors in both weather and climate predictions. Horizontal resolution is often cited as the main culprit for blocking errors due to poorly resolved small-scale variability, the upscale effects of which help to maintain blocks. Although these processes are important for blocking, the authors show that much of the blocking error diagnosed using common methods of analysis and current climate models is directly attributable to the climatological bias of the model. This explains a large proportion of diagnosed blocking error in models used in the recent Intergovernmental Panel for Climate Change report. Furthermore, greatly improved statistics are obtained by diagnosing blocking using climate model data corrected to account for mean model biases. To the extent that mean biases may be corrected in low-resolution models, this suggests that such models may be able to generate greatly improved levels of atmospheric blocking.

scholarly journals Sensitivity experiments of a severe rainfall event in north-western Italy: 17 August 2006

2008 ◽  
Vol 2 (1) ◽  
pp. 133-138 ◽  
Author(s):  
M. Milelli ◽  
E. Oberto ◽  
A. Parodi
Keyword(s):  
Weather Prediction ◽  
Numerical Weather Prediction Model ◽  
Precipitation Forecast ◽  
Small Scale ◽  
Moist Convection ◽  
Cosmo Model ◽  
Quantitative Precipitation Forecast ◽  
Scale Modelling ◽  
North Western ◽  
Priority Project

Abstract. This study is embedded into a wider project named "Tackle deficiencies in Quantitative Precipitation Forecast (QPF)'' in the framework of the COSMO (COnsortium for Small-scale MOdelling) community. In fact QPF is an important purpose of a numerical weather prediction model, for forecasters and customers. Unfortunately, precipitation is also a very difficult parameter to forecast quantitatively. This priority project aims at looking into the COSMO Model deficiencies concerning QPF by running different numerical simulations of various events not correctly predicted by the model. In particular, this work refers to a severe event (moist convection) happened in Piemonte region during summer 2006. On one side the results suggest that details in orography representation have a strong influence on accuracy of QPF. On the other side COSMO Model exhibits a poor sensitivity on changes in numerical and physical settings when measured in terms of QPF improvements. The conclusions, although not too general, give some hint towards the behaviour of the COSMO Model in a typical convective situation.

scholarly journals Glacial Inception on Baffin Island: The Role of Insolation, Meteorology, and Topography

2017 ◽  
Vol 30 (11) ◽  
pp. 4047-4064 ◽  
Author(s):  
Leah Birch ◽  
Timothy Cronin ◽  
Eli Tziperman
Keyword(s):  
Mass Balance ◽  
Snow Cover ◽  
Climate Models ◽  
Global Climate ◽  
Horizontal Resolution ◽  
Global Climate Models ◽  
Orbital Parameter ◽  
Small Scale ◽  
Baffin Island ◽  
Realistic Topography

Abstract Geologic evidence suggests that the last glacial inception (115 kya) occurred within the mountains of Baffin Island. Global climate models (GCMs) have difficulty simulating this climate transition, likely because of their coarse horizontal resolution that smooths topography and necessitates the use of cumulus parameterizations. A regional configuration of the Weather Research and Forecasting (WRF) Model is used to simulate the small-scale topographic and cloud processes neglected by GCMs, and the sensitivity of the region to Milankovitch forcing, topography, and meteorology is tested. It is found that ice growth is possible with 115-kya insolation, realistic topography, and slightly colder-than-average meteorology, represented by specific years within the past three decades. The simulation with low GCM-like topography shows a negative surface mass balance, even with the relevant orbital parameter configuration, demonstrating the criticality of realistic topography. The downslope growth of the ice sheets is studied by looking at the sensitivity of the mass balance to initial snow cover prescribed beyond that of the present day. It is found that the snow-albedo feedback, via its effects on the mass balance, allows such larger snow cover to persist. Implications for GCM studies of glacial inception are discussed.

scholarly journals Model intercomparison of COSMO 5.0 and IFS 45r1 at kilometer-scale grid spacing

2021 ◽  
Author(s):  
Christian Zeman ◽  
Nils P. Wedi ◽  
Peter D. Dueben ◽  
Nikolina Ban ◽  
Christoph Schär
Keyword(s):  
Diurnal Cycle ◽  
Climate Models ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Model Intercomparison ◽  
Grid Spacing ◽  
Convective Processes ◽  
Hydrostatic Approximation ◽  
Velocity Spectra ◽  
Convective Cells

Abstract. The increase in computing power and recent model developments allow the use of global kilometer-scale weather and climate models for routine forecasts. At these scales, deep convective processes can be partially resolved explicitly by the model dynamics. Next to horizontal resolution, other aspects such as the applied numerical methods, the use of the hydrostatic approximation, and timestep size are factors that might influence a model's ability of resolving deep convective processes. In order to improve our understanding of the role of these factors, a model intercomparison between the nonhydrostatic COSMO model and the hydrostatic Integrated Forecast System (IFS) from ECMWF has been conducted. Both models have been run with different spatial and temporal resolutions in order to simulate two summer days over Europe with strong convection. The results are analyzed with focus on vertical wind speed and precipitation. Results show that even at around 3 km horizontal grid spacing the effect of the hydrostatic approximation seems to be negligible. However, timestep proves to be an important factor for deep convective processes, with a reduced timestep generally allowing for higher updraft velocities and thus more energy in vertical velocity spectra, in particular for smaller wavelengths. A shorter timestep is also causing an earlier onset and peak of the diurnal cycle. Furthermore, the amount of horizontal diffusion plays a crucial role for deep convection with more diffusion generally leading to larger convective cells and higher precipitation intensities. The study also shows that for both models the parameterization of deep convection leads to lower updraft and precipitation intensities and biases in the diurnal cycle with a precipitation peak which is too early.

scholarly journals Objective Calibration of Numerical Weather Prediction Model: Application on Fine Resolution COSMO Model over Switzerland

Atmosphere ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1358
Author(s):  
Antigoni Voudouri ◽  
Euripides Avgoustoglou ◽  
Izthak Carmona ◽  
Yoav Levi ◽  
Edoardo Bucchignani ◽  
...  
Keyword(s):  
Numerical Weather Prediction ◽  
Climate Models ◽  
Optimal Parameter ◽  
Weather Prediction ◽  
Model Performance ◽  
Horizontal Resolution ◽  
Small Scale ◽  
Surface Exchange ◽  
Numerical Weather ◽  
The Impact

The objective calibration method originally performed on regional climate models is applied to a fine horizontal resolution Numerical Weather Prediction (NWP) model over a mainly continental domain covering the Alpine Arc. The method was implemented on the MeteoSwiss COSMO (consortium for a small-scale modeling) model with a resolution of 0.01° (approximately 1 km). For the model calibration, five tuning parameters of the parameterization schemes affecting turbulence, soil-surface exchange and radiation were chosen. A full year was simulated, with the history of the soil included (hindcast) to find the optimal parameter value. A different year has been used to give an independent assessment of the impact of the optimization process. Although the operational MeteoSwiss model is already a well-tuned configuration, the results showed that a slight model performance gain is obtained by using the Calibration of COSMO (CALMO) methodology.

scholarly journals Towards European-scale convection-resolving climate simulations with GPUs: a study with COSMO 4.19

2016 ◽  
Vol 9 (9) ◽  
pp. 3393-3412 ◽  
Author(s):  
David Leutwyler ◽  
Oliver Fuhrer ◽  
Xavier Lapillonne ◽  
Daniel Lüthi ◽  
Christoph Schär
Keyword(s):  
Graphics Processing Units ◽  
Climate Models ◽  
Climate Model ◽  
Deep Convection ◽  
Regional Climate ◽  
Small Scale ◽  
Moist Convection ◽  
Cosmo Model ◽  
Climate Simulations ◽  
Weather And Climate

Abstract. The representation of moist convection in climate models represents a major challenge, due to the small scales involved. Using horizontal grid spacings of O(1km), convection-resolving weather and climate models allows one to explicitly resolve deep convection. However, due to their extremely demanding computational requirements, they have so far been limited to short simulations and/or small computational domains. Innovations in supercomputing have led to new hybrid node designs, mixing conventional multi-core hardware and accelerators such as graphics processing units (GPUs). One of the first atmospheric models that has been fully ported to these architectures is the COSMO (Consortium for Small-scale Modeling) model.Here we present the convection-resolving COSMO model on continental scales using a version of the model capable of using GPU accelerators. The verification of a week-long simulation containing winter storm Kyrill shows that, for this case, convection-parameterizing simulations and convection-resolving simulations agree well. Furthermore, we demonstrate the applicability of the approach to longer simulations by conducting a 3-month-long simulation of the summer season 2006. Its results corroborate the findings found on smaller domains such as more credible representation of the diurnal cycle of precipitation in convection-resolving models and a tendency to produce more intensive hourly precipitation events. Both simulations also show how the approach allows for the representation of interactions between synoptic-scale and meso-scale atmospheric circulations at scales ranging from 1000 to 10 km. This includes the formation of sharp cold frontal structures, convection embedded in fronts and small eddies, or the formation and organization of propagating cold pools. Finally, we assess the performance gain from using heterogeneous hardware equipped with GPUs relative to multi-core hardware. With the COSMO model, we now use a weather and climate model that has all the necessary modules required for real-case convection-resolving regional climate simulations on GPUs.

scholarly journals Effect of the Assimilation Frequency of Radar Reflectivity on Rain Storm Prediction by Using WRF-3DVAR

2021 ◽  
Vol 13 (11) ◽  
pp. 2103
Author(s):  
Yuchen Liu ◽  
Jia Liu ◽  
Chuanzhe Li ◽  
Fuliang Yu ◽  
Wei Wang
Keyword(s):  
Data Assimilation ◽  
Northern China ◽  
Horizontal Resolution ◽  
Radar Reflectivity ◽  
Small Scale ◽  
Time Interval ◽  
Outer Domain ◽  
Storm Prediction ◽  
The Impact ◽  
Assimilation Time

An attempt was made to evaluate the impact of assimilating Doppler Weather Radar (DWR) reflectivity together with Global Telecommunication System (GTS) data in the three-dimensional variational data assimilation (3DVAR) system of the Weather Research Forecast (WRF) model on rain storm prediction in Daqinghe basin of northern China. The aim of this study was to explore the potential effects of data assimilation frequency and to evaluate the outputs from different domain resolutions in improving the meso-scale NWP rainfall products. In this study, four numerical experiments (no assimilation, 1 and 6 h assimilation time interval with DWR and GTS at 1 km horizontal resolution, 6 h assimilation time interval with radar reflectivity, and GTS data at 3 km horizontal resolution) are carried out to evaluate the impact of data assimilation on prediction of convective rain storms. The results show that the assimilation of radar reflectivity and GTS data collectively enhanced the performance of the WRF-3DVAR system over the Beijing-Tianjin-Hebei region of northern China. It is indicated by the experimental results that the rapid update assimilation has a positive impact on the prediction of the location, tendency, and development of rain storms associated with the study area. In order to explore the influence of data assimilation in the outer domain on the output of the inner domain, the rainfall outputs of 3 and 1 km resolution are compared. The results show that the data assimilation in the outer domain has a positive effect on the output of the inner domain. Since the 3DVAR system is able to analyze certain small-scale and convective-scale features through the incorporation of radar observations, hourly assimilation time interval does not always significantly improve precipitation forecasts because of the inaccurate radar reflectivity observations. Therefore, before data assimilation, the validity of assimilation data should be judged as far as possible in advance, which can not only improve the prediction accuracy, but also improve the assimilation efficiency.

scholarly journals A new world natural vegetation map for global change studies

2008 ◽  
Vol 80 (2) ◽  
pp. 397-408 ◽  
Author(s):  
David M. Lapola ◽  
Marcos D. Oyama ◽  
Carlos A. Nobre ◽  
Gilvan Sampaio
Keyword(s):  
Large Scale ◽  
New World ◽  
Climate Models ◽  
Global Climate ◽  
Horizontal Resolution ◽  
Vegetation Classification ◽  
Natural Vegetation ◽  
Global Climate Models ◽  
Vegetation Map ◽  
Vegetation Maps

We developed a new world natural vegetation map at 1 degree horizontal resolution for use in global climate models. We used the Dorman and Sellers vegetation classification with inclusion of a new biome: tropical seasonal forest, which refers to both deciduous and semi-deciduous tropical forests. SSiB biogeophysical parameters values for this new biome type are presented. Under this new vegetation classification we obtained a consensus map between two global natural vegetation maps widely used in climate studies. We found that these two maps assign different biomes in ca. 1/3 of the continental grid points. To obtain a new global natural vegetation map, non-consensus areas were filled according to regional consensus based on more than 100 regional maps available on the internet. To minimize the risk of using poor quality information, the regional maps were obtained from reliable internet sources, and the filling procedure was based on the consensus among several regional maps obtained from independent sources. The new map was designed to reproduce accurately both the large-scale distribution of the main vegetation types (as it builds on two reliable global natural vegetation maps) and the regional details (as it is based on the consensus of regional maps).

scholarly journals Evaluation of the Added Value of Regional Ensemble Forecasts on Global Ensemble Forecasts

2012 ◽  
Vol 27 (4) ◽  
pp. 972-987 ◽  
Author(s):  
Yong Wang ◽  
Simona Tascu ◽  
Florian Weidle ◽  
Karin Schmeisser
Keyword(s):  
Horizontal Resolution ◽  
Added Value ◽  
Ensemble Prediction ◽  
Small Scale ◽  
Initial Condition ◽  
Weather Variables ◽  
Single Model ◽  
Ensemble Forecasts ◽  
Model Based ◽  
Surface Weather

Abstract The regional single-model-based Aire Limitée Adaptation Dynamique Développement International–Limited Area Ensemble Forecasting (ALADIN-LAEF) ensemble prediction system (EPS) is evaluated and compared with the global ECMWF-EPS to investigate the added value of regional to global EPS models. ALADIN-LAEF consists of 16 perturbed members at 18-km horizontal resolution, while ECMWF-EPS includes 50 perturbed members at 50-km horizontal resolution. In ALADIN-LAEF, the atmospheric initial condition uncertainty is quantified by using blending, which combines large-scale uncertainty generated by the ECMWF-EPS singular-vector approach with small-scale perturbations resolved by the ALADIN breeding technique. The surface initial condition perturbations are generated by use of the noncycling surface breeding (NCSB) technique, and different physics schemes are employed for different forecast members to account for model uncertainties. The verification and comparison have been carried out for a 2-month period during summer 2007 over central Europe. The results show a quite favorable level of performance for ALADIN-LAEF compared to ECMWF-EPS for surface weather variables. ALADIN-LAEF adds more value to precipitation forecasts and has greater skill for 10-m wind and mean sea level pressure results than does ECMWF-EPS. For 2-m temperature, ALADIN-LAEF forecasts have larger spread, are statistically more consistent, but also have less skill than ECMWF-EPS due to the strong cold bias in the ALADIN forecasts. For the upper-air weather parameters, the forecast of ALADIN-LAEF has a larger spread, but the forecast skill of ALADIN-LAEF is from neutral to slightly inferior compared to ECMWF-EPS. It may be concluded that a regional single-model-based EPS with fewer ensemble members could provide more added value in terms of greater skill for near-surface weather variables than the global EPS with larger ensemble size, whereas it may have limitations when applied to upper-air weather variables.

Sediment transport modifications induced by submerged artificial reef systems: a case study for the Gulf of Venice

2014 ◽  
Vol 43 (1) ◽  
Author(s):  
Davide Bonaldo ◽  
Alvise Benetazzo ◽  
Andrea Bergamasco ◽  
Francesco Falcieri ◽  
Sandro Carniel ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Coastal Zone Management ◽  
Artificial Reef ◽  
Sediment Concentration ◽  
Quantitative Information ◽  
Small Scale ◽  
Zone Management ◽  
Basin Scale ◽  
Scale Modelling ◽  
Maritime Spatial Planning

AbstractThe shallow, gently sloping, sandy-silty seabed of the Venetian coast (Italy) is studded by a number of outcropping rocky systems of different size encouraging the development of peculiar zoobenthic biocenoses with considerably higher biodiversity indexes compared to neighbouring areas. In order to protect and enhance the growth of settling communities, artificial monolithic reefs were deployed close to the most important formations, providing further nesting sites and mechanical hindrance to illegal trawl fishing.In this framework, a multi-step and multi-scale numerical modelling activity was carried out to predict the perturbations induced by the presence of artificial structures on sediment transport over the outcroppings and their implications on turbidity and water quality. After having characterized wave and current circulation climate at the sub-basin scale over a reference year, a set of small scale simulations was carried out to describe the effects of a single monolith under different geometries and hydrodynamic forcings, encompassing the conditions likely occurring at the study sites. A dedicated tool was then developed to compose the information contained in the small-scale database into realistic deployment configurations, and applied in four protected outcroppings identified as test sites. With reference to these cases, under current meteomarine climate the application highlighted a small and localised increase in suspended sediment concentration, suggesting that the implemented deployment strategy is not likely to produce harmful effects on turbidity close to the outcroppings.In a broader context, the activity is oriented at the tuning of a flexible instrument for supporting the decision-making process in benthic environments of outstanding environmental relevance, especially in the Integrated Coastal Zone Management or Maritime Spatial Planning applications. The dissemination of sub-basin scale modelling results via the THREDDS Data Server, together with an user-friendly software for composing single-monolith runs and a graphical interface for exploring the available data, significantly improves the quantitative information collection and sharing among scientists, stakeholders and policy-makers.

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