scholarly journals Impact of the Atmospheric Mean State on Tropical Instability Wave Activity

2012 ◽  
Vol 25 (7) ◽  
pp. 2341-2355 ◽  
Author(s):  
Yukiko Imada ◽  
Masahide Kimoto ◽  
Xianyan Chen
Keyword(s):  
High Resolution ◽  
Negative Feedback ◽  
Mean Field ◽  
Surface Current ◽  
Atmospheric Model ◽  
Instability Wave ◽  
Tropical Instability Waves ◽  
Resolution Model ◽  
The Difference ◽  
High Resolution Models

Abstract The features of simulated tropical instability waves (TIWs) in the Pacific Ocean are compared between atmospheric models of two different resolutions coupled with a uniform oceanic model. Results show that TIWs are more active in the high-resolution model, even though it includes atmospheric negative feedback. Such negative feedback is not identified in the low-resolution atmospheric model because of the absence of atmospheric responses. Comparison of the energetics between the two models shows that the large TIW activity in the higher-resolution model is due to the difference in barotropic energy sources near the surface. A high-resolution atmosphere results in a tighter intertropical convergence zone and associated stronger wind curl and shear. This causes a stronger surface current shear between the South Equatorial Current (SEC) and North Equatorial Counter Current (NECC), which is one of the main sources of TIW kinetic energy. These results indicate the important role of the atmospheric mean field on TIW activity and the advantage of using high-resolution models to represent coupling among multiscale phenomena.

scholarly journals Central Mediterranean Sea forecast: effects of high-resolution atmospheric forcings

2006 ◽  
Vol 3 (3) ◽  
pp. 637-669 ◽  
Author(s):  
S. Natale ◽  
R. Sorgente ◽  
S. Gaberšek ◽  
A. Ribotti ◽  
A. Olita
Keyword(s):  
High Resolution ◽  
Ocean Circulation ◽  
Regional Scale ◽  
Circulation Model ◽  
Surface Current ◽  
Ocean Model ◽  
Central Mediterranean ◽  
Resolution Model ◽  
Atmospheric Forcings ◽  
Very High

Abstract. Ocean forecasts over the Central Mediterranean, produced by a near real time regional scale system, have been evaluated in order to assess their predictability. The ocean circulation model has been forced at the surface by a medium, high or very high resolution atmospheric forcing. The simulated ocean parameters have been compared with satellite data and they were found to be generally in good agreement. High and very high resolution atmospheric forcings have been able to form noticeable, although short-lived, surface current structures, due to their ability to detect transient atmospheric disturbances. The existence of the current structures has not been directly assessed due to lack of measurements. The ocean model in the slave mode was not able to develop dynamics different from the driving coarse resolution model which provides the boundary conditions.

Neighborhood-Based Contingency Tables Including Errors Compensation

2019 ◽  
Vol 147 (1) ◽  
pp. 329-344 ◽  
Author(s):  
Joël Stein ◽  
Fabien Stoop
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Contingency Tables ◽  
Global Model ◽  
New Method ◽  
False Alarms ◽  
Scale Models ◽  
Resolution Model ◽  
High Resolution Model ◽  
High Resolution Models

Some specific scores use a neighborhood strategy in order to reduce double penalty effects, which penalize high-resolution models, compared to large-scale models. Contingency tables based on this strategy have already been proposed, but can sometimes display undesirable behavior. A new method of populating contingency tables is proposed: pairs of missed events and false alarms located in the same local neighborhood compensate in order to give pairs of hits and correct rejections. Local tables are summed up so as to provide the final table for the whole verification domain. It keeps track of the bias of the forecast when neighborhoods are taken into account. Moreover, the scores computed from this table depend on the distance between forecast and observed patterns. This method is applied to binary and multicategorical events in a simplified framework so as to present the method and to compare the new tables with previous neighborhood-based contingency tables. The new tables are then used for the verification of two models operational at Météo-France: AROME, a high-resolution model, and ARPEGE, a large-scale global model. The comparison of several contingency scores shows that the importance of the double penalty decreases more for AROME than for ARPEGE when the neighboring size increases. Scores designed for rare events are also applied to these neighborhood-based contingency tables.

scholarly journals The Influence of the Spectral Truncation on the Simulation of Waves in the Tropical Stratosphere

2015 ◽  
Vol 72 (10) ◽  
pp. 3819-3828 ◽  
Author(s):  
T. R. Krismer ◽  
M. A. Giorgetta ◽  
J. S. von Storch ◽  
I. Fast
Keyword(s):  
High Resolution ◽  
Lower Stratosphere ◽  
Wave Spectrum ◽  
Atmospheric Model ◽  
Quasi Biennial Oscillation ◽  
Highly Active ◽  
Main Driver ◽  
Resolution Model ◽  
Diffusion Scheme ◽  
Tropical Wave

Abstract Convectively triggered waves are the main driver of the tropical stratospheric circulation. In atmospheric models, the model’s resolution limits the length of the simulated wave spectrum. In this study, the authors compare the tropical tropospheric wave sources, their projection on the wave field in the lower stratosphere, and the circumstances of their upward propagation in the atmospheric model ECHAM6 with three spectral truncations of T63, T127, and T255. The model internally generates the quasi-biennial oscillation (QBO), which dominates the variability in the tropical stratosphere. This analysis focuses on two opposite phases of the QBO to account for the influence of the background wind field on the wave filtering. It is shown that, compared to the high-resolution model versions, the T63 version has less convective variability and less wave momentum in the lower stratosphere at wavenumbers larger than 20, well below the version’s truncation limit. In the low-resolution version, the upward propagation of the waves is further hindered by the highly active (relative to the high-resolution versions) horizontal diffusion scheme. However, even in the T255 version of ECHAM6, the convective variability is too small compared to TRMM observations at periods shorter than 2 days and wavelengths shorter than 1000 km. Hence, to model a realistic tropical wave activity, the convective parameterization of the model has to improve to increase the day-to-day precipitation variability.

scholarly journals Multimodel Prediction Skills of the Somali and Maritime Continent Cross-Equatorial Flows

2018 ◽  
Vol 31 (6) ◽  
pp. 2445-2464 ◽  
Author(s):  
Chen Li ◽  
Jing-Jia Luo ◽  
Shuanglin Li ◽  
Harry Hendon ◽  
Oscar Alves ◽  
...  
Keyword(s):  
High Resolution ◽  
Walker Circulation ◽  
Seasonal Prediction ◽  
Atmospheric Model ◽  
Precipitation Anomaly ◽  
Boreal Summer ◽  
Maritime Continent ◽  
Anomaly Correlation Coefficient ◽  
The Difference ◽  
The Individual

Predictive skills of the Somali cross-equatorial flow (CEF) and the Maritime Continent (MC) CEF during boreal summer are assessed using three ensemble seasonal forecasting systems, including the coarse-resolution Predictive Ocean Atmospheric Model for Australia (POAMA, version 2), the intermediate-resolution Scale Interaction Experiment–Frontier Research Center for Global Change (SINTEX-F), and the high-resolution seasonal prediction version of the Australian Community Climate and Earth System Simulator (ACCESS-S1) model. Retrospective prediction results suggest that prediction of the Somali CEF is more challenging than that of the MC CEF. While both the individual models and the multimodel ensemble (MME) mean show useful skill (with the anomaly correlation coefficient being above 0.5) in predicting the MC CEF up to 5-month lead, only ACCESS-S1 and the MME can skillfully predict the Somali CEF up to 2-month lead. Encouragingly, the CEF seesaw index (defined as the difference of the two CEFs as a measure of the negative phase relation between them) can be skillfully predicted up to 4–5 months ahead by SINTEX-F, ACCESS-S1, and the MME. Among the three models, the high-resolution ACCESS-S1 model generally shows the highest skill in predicting the individual CEFs, the CEF seesaw, as well as the CEF seesaw index–related precipitation anomaly pattern in Asia and northern Australia. Consistent with the strong influence of ENSO on the CEFs, the skill in predicting the CEFs depends on the model’s ability in predicting not only the eastern Pacific SST anomaly but also the anomalous Walker circulation that brings ENSO’s influence to bear on the CEFs.

scholarly journals Towards Direct Simulation of Future Tropical Cyclone Statistics in a High-Resolution Global Atmospheric Model

2010 ◽  
Vol 2010 ◽  
pp. 1-13 ◽  
Author(s):  
Michael F. Wehner ◽  
G. Bala ◽  
Phillip Duffy ◽  
Arthur A. Mirin ◽  
Raquel Romano
Keyword(s):  
High Resolution ◽  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Tropical Storm ◽  
Model Studies ◽  
The North ◽  
Resolution Model ◽  
High Resolution Model

We present a set of high-resolution global atmospheric general circulation model (AGCM) simulations focusing on the model's ability to represent tropical storms and their statistics. We find that the model produces storms of hurricane strength with realistic dynamical features. We also find that tropical storm statistics are reasonable, both globally and in the north Atlantic, when compared to recent observations. The sensitivity of simulated tropical storm statistics to increases in sea surface temperature (SST) is also investigated, revealing that a credible late 21st century SST increase produced increases in simulated tropical storm numbers and intensities in all ocean basins. While this paper supports previous high-resolution model and theoretical findings that the frequency of very intense storms will increase in a warmer climate, it differs notably from previous medium and high-resolution model studies that show a global reduction in total tropical storm frequency. However, we are quick to point out that this particular model finding remains speculative due to a lack of radiative forcing changes in our time-slice experiments as well as a focus on the Northern hemisphere tropical storm seasons.

scholarly journals The importance of model resolution on simulated precipitation in Europe – from global to regional model

2020 ◽  
Author(s):  
Gustav Strandberg ◽  
Petter Lind
Keyword(s):  
High Resolution ◽  
Extreme Precipitation ◽  
Climate Models ◽  
Climate Model ◽  
Horizontal Resolution ◽  
Model Resolution ◽  
Simulated Precipitation ◽  
The Difference ◽  
Model Ensembles ◽  
High Resolution Models

Abstract. Precipitation, and especially extreme precipitation, is a key climate variable as it effects large parts of society. It is difficult to simulate in a climate model because of its large variability in time and space. This study investigates the importance of model resolution on the simulated precipitation in Europe for a wide range of climate model ensembles: from global climate models (GCM) at horizontal resolution of around 300 km to regional climate models (RCM) at horizontal resolution of 12.5 km. The aim is to investigate the differences between models and model ensembles, but also to evaluate their performance compared to gridded observations from E-OBS. Model resolution has a clear effect on precipitation. Generally, extreme precipitation is more intense and more frequent in high-resolution models compared to low-resolution models. Models of low resolution tend to underestimate intense precipitation. This is improved in high-resolution simulations, but there is a risk that high resolution models overestimate precipitation. This effect is seen in all ensembles, and GCMs and RCMs of similar resolution give similar results. The number of precipitation days, which is more governed by large-scale atmospheric flow, is not dependent on model resolution, while the number of days with heavy precipitation is. The difference between different models is often larger than between the low- and high-resolution versions of the same model, which makes it difficult to quantify the improvement. In this sense the quality of an ensemble is depending more on the models it consists of rather than the average resolution of the ensemble. Furthermore, the difference in simulated precipitation between an RCM and the driving GCM depend more on the choice of RCM and less on the down-scaling itself; as different RCMs driven by the same GCM may give different results. The results presented here are in line with previous similar studies but this is the first time an analysis like this is done across such relatively large model ensembles of different resolutions, and with a method studying all parts of the precipitation distribution.

scholarly journals Overview of spatial verification methods and their application to ensemble forecasting

2021 ◽  
Vol 4 ◽  
pp. 30-49
Author(s):  
A.Yu. Bundel ◽  
◽  
A.V. Muraviev ◽  
E.D. Olkhovaya ◽  
◽  
...  
Keyword(s):  
High Resolution ◽  
Ensemble Forecasting ◽  
Object Based ◽  
Verification Methods ◽  
International Projects ◽  
Resolution Model ◽  
High Gradients ◽  
High Resolution Models ◽  
High Degree ◽  
Spatial Verification

State-of-the-art high-resolution NWP models simulate mesoscale systems with a high degree of detail, with large amplitudes and high gradients of fields of weather variables. Higher resolution leads to the spatial and temporal error growth and to a well-known double penalty problem. To solve this problem, the spatial verification methods have been developed over the last two decades, which ignore moderate errors (especially in the position), but can still evaluate the useful skill of a high-resolution model. The paper refers to the updated classification of spatial verification methods, briefly describes the main methods, and gives an overview of the international projects for intercomparison of the methods. Special attention is given to the application of the spatial approach to ensemble forecasting. Popular software packages are considered. The Russian translation is proposed for the relevant English terms. Keywords: high-resolution models, verification, double penalty, spatial methods, ensemble forecasting, object-based methods

scholarly journals Resolution Dependence of Regional Hydro-Climatic Projection: A Case-Study for the Johor River Basin, Malaysia

Water ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3158
Author(s):  
Mou Leong Tan ◽  
Ju Liang ◽  
Matthew Hawcroft ◽  
James M. Haywood ◽  
Fei Zhang ◽  
...  
Keyword(s):  
High Resolution ◽  
River Basin ◽  
Surface Runoff ◽  
Horizontal Resolution ◽  
Peninsular Malaysia ◽  
Maximum Temperature ◽  
Monthly Precipitation ◽  
Tropical Regions ◽  
Resolution Model ◽  
High Resolution Models

High resolution models from the High-Resolution Model Intercomparison Project (HighResMIP), part of CMIP6, have the capacity to allow a better representation of the climate system in tropical regions, but how different model resolutions affect hydrological outputs remains unclear. This research aims to evaluate projections of hydro-climatic change of the Johor River Basin (JRB) in southern Peninsular Malaysia between 1985 to 2015 and 2021 to 2050, focusing on uncertainty quantification of hydrological outputs from low (>1°), medium (0.5° to 1°) and high (≤0.5°) horizontal resolution models. These projections show future increases in annual precipitation of 0.4 to 3.1%, minimum and maximum temperature increases of 0.8 to 0.9 °C and 0.9 to 1.1 °C, respectively. These projected climate changes lead to increases in annual mean streamflow of 0.9% to 7.0% and surface runoff of 7.0% to 20.6% in the JRB. These annual mean changes are consistent with those during the wet period (November to December), e.g., streamflow increases of 4.9% to 10.8% and surface runoff of 28.8 to 39.9% in December. Disagreement in the direction of change is found during the dry seasons, (February to March and May to September), where high resolution models project a decrease in future monthly precipitation and streamflow, whilst increases are projected by the medium- and low-resolution models.

scholarly journals iGen: a program for the automated generation of models and parameterisations

2011 ◽  
Vol 4 (2) ◽  
pp. 843-868 ◽  
Author(s):  
D. F. Tang ◽  
S. Dobbie
Keyword(s):  
High Resolution ◽  
Source Code ◽  
Model Development ◽  
New Approach ◽  
Physical Systems ◽  
Automated Generation ◽  
Resolution Model ◽  
High Resolution Model ◽  
High Resolution Models ◽  
Very High

Abstract. Complex physical systems can often be simulated using very high-resolution models but this is not always practical because of computational restrictions. In this case the model must be simplified or parameterised, but this is a notoriously difficult process that often requires the introduction of "model assumptions" that are hard or impossible to justify. Here we introduce a new approach to parameterising models. The approach makes use of a newly developed computer program, which we call iGen, that analyses the source code of a high-resolution model and formally derives a much faster parameterised model that closely approximates the original, reporting bounds on the error introduced by any approximations. These error bounds can be used to formally justify use of the parameterised model in subsequent numerical experiments. Using increasingly complex physical systems as examples we illustrate that iGen has the ability to produce parameterisations that run typically orders of magnitude faster than the underlying, high-resolution models from which they are derived and show that iGen has the potential to become an important tool in model development.

scholarly journals iGen 0.1: a program for the automated generation of models and parameterisations

2011 ◽  
Vol 4 (3) ◽  
pp. 785-795 ◽  
Author(s):  
D. F. Tang ◽  
S. Dobbie
Keyword(s):  
High Resolution ◽  
Physical System ◽  
Ad Hoc ◽  
New Approach ◽  
Physical Systems ◽  
Automated Generation ◽  
Resolution Model ◽  
Bounded Error ◽  
High Resolution Model ◽  
High Resolution Models

Abstract. Complex physical systems can often be simulated using very high resolution models but this is not always practical because of computational restrictions. In this case the model must be simplified or parameterised in order to make it computationally tractable. A parameterised model is created using an ad-hoc selection of techniques which range from the formal to the purely intuitive, and as a result it is very difficult to objectively quantify the fidelity of the model to the physical system. It is rare that a parameterised model can be formally shown to simulate a physical system to within some bounded error. Here we introduce a new approach to parameterising models which allows error to be formally bounded. The approach makes use of a newly developed computer program, which we call iGen, that analyses the source code of a high-resolution model and formally derives a much faster, parameterised model that closely approximates the original, reporting bounds on the error introduced by any approximations. These error bounds can be used to formally justify conclusions about a physical system based on observations of the model's behaviour. Using increasingly complex physical systems as examples we illustrate that iGen has the ability to produce parameterisations that run typically orders of magnitude faster than the underlying, high-resolution models from which they are derived.

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