Seasonal forecasting of the Atlantic Niño

2020 ◽  
Author(s):  
Chloé Prodhomme ◽  
Javier García-Serrano ◽  
Noel Keenlyside ◽  
Eleftheria Exarchou ◽  
Ingo Richter ◽  
...  
Keyword(s):  
Large Scale ◽  
Circulation Pattern ◽  
Large Set ◽  
Equatorial Atlantic ◽  
Start Date ◽  
The North ◽  
Mature Phase ◽  
Anomaly Correlation Coefficient ◽  
Sst Bias ◽  
June July

<p>The Atlantic Niño is the leading mode of interannual variability in the Tropical Atlantic, which has impacts not only on the African monsoon but also in remote regions. In the present study, we investigate the predictability of the Atlantic Niño's mature phase (June-July) at seasonal time-scale, as well as its conditioning. We analyze a large set of state-of-the art forecasts systems from the North American Multi-Model Ensemble (NMME) and Copernicus Climate Change Service (C3S) multi-models. The prediction skill of the ATL3 index has considerably improved as compared to previous forecast quality assessments, with Anomaly Correlation Coefficient (ACC) reaching up to 0.8 for the May start date. Most of the models achieve skillful prediction of the Atlantic Niño from the May start-date, and some outperform persistence. For the start-dates of April, March and February, most of the models perform better than persistence and some achieve significant correlation skill for ATL3. While there has been improvement in forecasting capability, overall the warm SST bias and associated drift remain large in the equatorial Atlantic in most of the systems. Our results suggests that the skill in predicting the Atlantic Niño in summer is weakly related to the local SST drift during the first month of the forecast, but not to the magnitude of the SST bias during the peak. In addition, we find evidence that the skill in the equatorial Atlantic is related to the ability of the models to properly represent the large-scale atmospheric circulation pattern in the South Atlantic (i.e. St. Helena high).</p>

Energetics of the Western Hemisphere Circulation Pattern

2019 ◽  
Vol 32 (22) ◽  
pp. 7857-7870 ◽  
Author(s):  
Xin Tan ◽  
Ming Bao ◽  
Xuejuan Ren
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Low Frequency ◽  
Lower Troposphere ◽  
Circulation Pattern ◽  
Western Hemisphere ◽  
Self Organizing Maps ◽  
Atlantic Sector ◽  
The North ◽  
Energy Maintenance

Abstract The Western Hemisphere (WH) circulation pattern, identified by self-organizing maps cluster analysis, is a low-frequency atmospheric regime that influences the fluctuations of large-scale circulation over the North Pacific–North American–North Atlantic areas. The reanalysis datasets from ECMWF are used to estimate the energetics of the WH pattern in this study. The composite results based on monthly WH events reveal that the kinetic energy (KE) associated with the WH pattern is maintained through the barotropic conversion from the climatological-mean westerlies, mainly in the Atlantic jet exit regions. The KE could also be gained through the barotropic feedback forcing from transient eddies. The corresponding baroclinic conversion of available potential energy (APE) from the climatological-mean state, which contributes most efficiently to the energy maintenance of the WH pattern, is obvious in the middle and lower troposphere, owing to the thermal contrast of the colder continent and warmer ocean over the North America–North Atlantic sector. The baroclinic conversion associated with the heat flux on the climatological temperature gradient is consistent with the southwestward-tilting height anomalies from 850 to 500 hPa. The baroclinic feedback from transient eddies contributes negatively to the energy conversion and destroys the maintenance of the WH pattern.

scholarly journals A Diagnosis of Thickness Fluxes in an Eddy-Resolving Model

2007 ◽  
Vol 37 (3) ◽  
pp. 727-742 ◽  
Author(s):  
Carsten Eden ◽  
Richard J. Greatbatch ◽  
Jürgen Willebrand
Keyword(s):  
Large Scale ◽  
North Atlantic Ocean ◽  
A Priori ◽  
Baroclinic Instability ◽  
Optimization Technique ◽  
Subtropical Gyre ◽  
Equatorial Atlantic ◽  
The North ◽  
Eddy Fluxes ◽  
The Mean

Abstract Output from an eddy-resolving model of the North Atlantic Ocean is used to estimate values for the thickness diffusivity κ appropriate to the Gent and McWilliams parameterization. The effect of different choices of rotational eddy fluxes on the estimated κ is discussed. Using the raw fluxes (no rotational flux removed), large negative values (exceeding −5000 m2 s−1) of κ are diagnosed locally, particularly in the Gulf Stream region and in the equatorial Atlantic. Removing a rotational flux based either on the suggestion of Marshall and Shutts or the more general theory of Medvedev and Greatbatch leads to a reduction of the negative values, but they are still present. The regions where κ < 0 correspond to regions where eddies are acting to increase, rather than decrease (as in baroclinic instability) the mean available potential energy. In the subtropical gyre, κ ranges between 500 and 2000 m2 s−1, rapidly decreasing to zero below the thermocline in all cases. Rotational fluxes and κ are also estimated using an optimization technique. In this case, |κ| can be reduced or increased by construction, but the regions where κ < 0 are still present and the optimized rotational fluxes also remain similar to a priori values given by the theoretical considerations. A previously neglected component (ν) of the bolus velocity is associated with the horizontal flux of buoyancy along, rather than across, the mean buoyancy contours. The ν component of the bolus velocity is interpreted as a streamfunction for eddy-induced advection, rather than diffusion, of mean isopycnal layer thickness, showing up when the lateral eddy fluxes cannot be described by isotropic diffusion only. All estimates show a similar large-scale pattern for ν, implying westward advection of isopycnal thickness over much of the subtropical gyre. Comparing ν with a mean streamfunction shows that it is about 10% of the mean in midlatitudes and even larger than the mean in the Tropics.

scholarly journals Weak upstream westerly wind attracts western north pacific typhoon tracks to west

2021 ◽  
Author(s):  
Jun-Hyeok Son ◽  
Jae-Il Kwon ◽  
Ki-Young Heo
Keyword(s):  
Tibetan Plateau ◽  
Rossby Wave ◽  
Large Scale ◽  
Rossby Waves ◽  
Circulation Pattern ◽  
The Tibetan Plateau ◽  
Circulation Anomaly ◽  
North East ◽  
The North ◽  
Typhoon Tracks

Abstract The steering flow of the large-scale circulation patterns over the Western North Pacific and North East Asia, constrains typhoon tracks. Westerly winds impinging on the Tibetan Plateau, and the resulting flow uplift along the slope of the mountain, induce atmospheric vortex flow and generate stationary barotropic Rossby waves downstream. The downstream Rossby wave zonal phase is determined by the upstream zonal wind speed impinging on the Tibetan Plateau. Positive anomaly of westerly wind forcing tends to induce an eastward shift of the large-scale Rossby wave circulation pattern, forming a cyclonic circulation anomaly over North East Asia. In this study, we show that the Tibetan Plateau dynamically impacts the tracks of western Pacific typhoons via modulation of downstream Rossby waves. Using the topographically forced stationary Rossby wave theory, the dynamical mechanisms for the formation of the North East Asian cyclonic anomaly and its impact on the typhoon tracks are analyzed. The eastward shift of typhoon tracks, caused by the southwesterly wind anomaly located to the southeast of the North East Asian cyclonic circulation anomaly, is robust in June and September, but it is not statistically significant in July–August. The physical understanding of the large-scale circulation pattern affecting typhoon trajectories has large implications not only at the seasonal prediction of the high impact weather phenomena, but also at the right understanding of the long-term climate change.

scholarly journals Relationship between winter orographic precipitation with synoptic and large-scale atmospheric circulation: The case of mount Olympus, Greece

2018 ◽  
Vol 52 (1) ◽  
pp. 45 ◽  
Author(s):  
Michael Nikolaos Styllas ◽  
Dimitrios Kaskaoutis
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Rainfall Variability ◽  
Circulation Pattern ◽  
Western Mediterranean ◽  
The Arctic ◽  
Central Mediterranean ◽  
Winter Rainfall ◽  
Atmospheric Circulation Patterns ◽  
The North

The relationship between the winter (DJFM) precipitation and the atmospheric circulation patterns is examined around Mount Olympus, Greece in order to assess the effects of orography and atmospheric dynamics over a small (less than 100 x 100 km) spatial domain. Winter accumulated rainfall datasets from 8 stations spread along the eastern (marine) and western (continental) sides of the Mount Olympus at elevations between 30 m and 1150 m are used during the period 1981 to 2000. Synoptic scale conditions of mean sea-level pressure and geopotential heights at 850 hPa and 500 hPa, were used to explain the multiyear rainfall variability. High pressure systems dominated over the central Mediterranean and most parts of central Europe during the late 1980’s and early 1990’s, are associated with minimum winter rainfall along both sides of Mount Olympus. The winter of 1996 was associated with peak in rainfall along the marine side of the mountain and was characterized by enhancement of upper level trough over the western Mediterranean and increased low tropospheric depressions over the southern Adriatic and the Ionian Seas. This atmospheric circulation pattern facilitated a southeasterly air flow that affected more (less) the marine (continental) sides of the mountain. In contrast, dominance of low pressure systems with cores over the Gulf of Genoa and the Central Mediterranean affect the study area mostly from west/southwest revealing higher correlations with the precipitation in the continental side of the mountain (r= -0.80; Elassona station) and considerably lower correlations with the marine side (r = -0.67; Katerini station). This highlights the orographic barrier of the Mount Olympus revealing large differences between the upward and leeward sides. Large scale atmospheric patterns like the North Atlantic Oscillation and the Arctic Oscillation seem to influence the winter rainfall in the lowlands along the continental side of the mountain.

scholarly journals Resolution dependence of CO2-induced Tropical Atlantic sector climate changes

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
W. Park ◽  
M. Latif
Keyword(s):  
Large Scale ◽  
Climate Changes ◽  
Climate Models ◽  
Climate Model ◽  
Equatorial Region ◽  
Atmospheric Response ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
Atlantic Sector ◽  
Sst Bias

Abstract A long-standing problem in state-of-the-art climate models is the Tropical Atlantic (TA) warm sea surface temperature (SST) bias, which goes along with major biases in large-scale atmospheric circulation. Here we show that TA-sector climate changes forced by increasing atmospheric carbon dioxide (CO2) levels are sensitive to model resolution. Two versions of a climate model employing greatly varying atmospheric resolution and exhibiting very different warm bias strength are compared. The version with high atmospheric resolution features a small SST bias and simulates an eastward amplified SST warming over the equatorial Atlantic, in line with the observed SST trends since the mid-20th century. On the contrary, the version with coarse atmospheric resolution exhibits a large SST bias and projects relatively uniform SST changes across the equatorial Atlantic. In both model versions, the warming pattern resembles the pattern of interannual SST variability simulated under present-day conditions. Atmospheric changes also vastly differ among the two climate model versions. In the version with small SST bias, a deep atmospheric response is simulated with a major change in the Walker circulation and strongly enhanced rainfall over the equatorial region, whereas the atmospheric response is much weaker and of rather different character in the model with large SST bias. This study suggests that higher atmospheric resolution in climate models may enhance global warming projections over the TA sector.

scholarly journals Large-scale climate signals of a European oxygen isotope network from tree rings

2021 ◽  
Vol 17 (3) ◽  
pp. 1005-1023
Author(s):  
Daniel F. Balting ◽  
Monica Ionita ◽  
Martin Wegmann ◽  
Gerhard Helle ◽  
Gerhard H. Schleser ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Tree Ring ◽  
Tree Rings ◽  
Large Scale ◽  
Southern Oscillation ◽  
Circulation Pattern ◽  
Isotopic Signature ◽  
Atmospheric Circulation Patterns ◽  
The North ◽  
Instrumental Records

Abstract. We investigate the climate signature of δ18O tree-ring records from sites distributed all over Europe covering the last 400 years. An empirical orthogonal function (EOF) analysis reveals two distinct modes of variability on the basis of the existing δ18O tree-ring records. The first mode is associated with anomaly patterns projecting onto the El Niño–Southern Oscillation (ENSO) and reflects a multi-seasonal climatic signal. The ENSO link is pronounced for the last 130 years, but it is found to be weak over the period from 1600 to 1850, suggesting that the relationship between ENSO and the European climate may not be stable over time. The second mode of δ18O variability, which captures a north–south dipole in the European δ18O tree-ring records, is related to a regional summer atmospheric circulation pattern, revealing a pronounced centre over the North Sea. Locally, the δ18O anomalies associated with this mode show the same (opposite) sign with temperature (precipitation). Based on the oxygen isotopic signature derived from tree rings, we argue that the prevailing large-scale atmospheric circulation patterns and the related teleconnections can be analysed beyond instrumental records.

scholarly journals Seasonal extrema of sea surface temperature in CMIP6 models

2021 ◽  
Author(s):  
Yanxin Wang ◽  
Karen J. Heywood ◽  
David P. Stevens ◽  
Gillian M. Damerell
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
World Ocean ◽  
Model Performance ◽  
Ocean Model ◽  
Sea Surface ◽  
Polar Regions ◽  
Equatorial Atlantic ◽  
The North ◽  
Sst Bias

Abstract. CMIP6 model sea surface temperature (SST) seasonal extrema averaged over 1981–2010 are assessed against the World Ocean Atlas (WOA18) observational climatology. We propose a mask to identify and exclude regions of large differences between three commonly-used climatologies. The biases in SST seasonal extrema are largely consistent with the annual mean SST biases. However, the amplitude and spatial pattern of SST bias vary seasonally in the 20 CMIP6 models assessed. Large seasonal variations in the SST bias occur in eastern boundary upwelling regions, polar regions, the North Pacific and eastern equatorial Atlantic. These results demonstrate the importance of evaluating model performance not simply against annual mean properties. Models with greater vertical resolution in their ocean component typically demonstrate better representation of SST extrema, particularly seasonal maximum SST. No significant relationship with horizontal ocean model resolution is found.

Why Has There Been No People’s Power Rebellion in North Korea?

2018 ◽  
pp. 1-34
Author(s):  
Andrew Jackson
Keyword(s):  
Rural Areas ◽  
North Korea ◽  
Large Scale ◽  
Political Elite ◽  
Information Control ◽  
Al Jazeera ◽  
The North ◽  
New Information ◽  
Effective System ◽  
The Right

One scenario put forward by researchers, political commentators and journalists for the collapse of North Korea has been a People’s Power (or popular) rebellion. This paper analyses why no popular rebellion has occurred in the DPRK under Kim Jong Un. It challenges the assumption that popular rebellion would happen because of widespread anger caused by a greater awareness of superior economic conditions outside the DPRK. Using Jack Goldstone’s theoretical expla-nations for the outbreak of popular rebellion, and comparisons with the 1989 Romanian and 2010–11 Tunisian transitions, this paper argues that marketi-zation has led to a loosening of state ideological control and to an influx of infor-mation about conditions in the outside world. However, unlike the Tunisian transitions—in which a new information context shaped by social media, the Al-Jazeera network and an experience of protest helped create a sense of pan-Arab solidarity amongst Tunisians resisting their government—there has been no similar ideology unifying North Koreans against their regime. There is evidence of discontent in market unrest in the DPRK, although protests between 2011 and the present have mostly been in defense of the right of people to support themselves through private trade. North Koreans believe this right has been guaranteed, or at least tacitly condoned, by the Kim Jong Un government. There has not been any large-scale explosion of popular anger because the state has not attempted to crush market activities outright under Kim Jong Un. There are other reasons why no popular rebellion has occurred in the North. Unlike Tunisia, the DPRK lacks a dissident political elite capable of leading an opposition movement, and unlike Romania, the DPRK authorities have shown some flexibility in their anti-dissent strategies, taking a more tolerant approach to protests against economic issues. Reduced levels of violence during periods of unrest and an effective system of information control may have helped restrict the expansion of unrest beyond rural areas.

Information And Map-Made Control With The Functions Of Business Analytics For Urban Management

2019 ◽  
pp. 72-78
Keyword(s):  
Large Scale ◽  
Information Support ◽  
Urban Management ◽  
Business Analytics ◽  
Administrative District ◽  
The North ◽  
Model Of Management ◽  
Complex Development ◽  
Coordination System ◽  
Key Aspects

The key aspects of the process of designing and developing an information and cartographic control tool with business analytics functions for the municipal level of urban management are considered. The review of functionality of the developed tool is given. Examples of its use for the analysis and monitoring of implementation of the program of complex development of territories are given. The importance of application of information support of management and coordination at all levels of management as an integral part of the basic model of management and coordination system of large-scale urban projects of dispersed construction is proved. Information and map-made tool with business intelligence functions was used and was highly appreciated in the preparation of information-analytical and presentation materials of the North-Eastern Administrative District of Moscow. Its use made it possible to significantly optimize the list of activities of the program of integrated development of territories, their priority and timing.

Adsorption Isotherm Predictions for Multiple Molecules in MOFs Using the Same Deep Learning Model

2019 ◽  
Author(s):  
Ryther Anderson ◽  
Achay Biong ◽  
Diego Gómez-Gualdrón
Keyword(s):  
Neural Network ◽  
Machine Learning ◽  
Molecular Simulation ◽  
Large Scale ◽  
Learning Model ◽  
Operating Conditions ◽  
Small Subset ◽  
Screening Methods ◽  
Large Set ◽  
Metal Organic

<div>Tailoring the structure and chemistry of metal-organic frameworks (MOFs) enables the manipulation of their adsorption properties to suit specific energy and environmental applications. As there are millions of possible MOFs (with tens of thousands already synthesized), molecular simulation, such as grand canonical Monte Carlo (GCMC), has frequently been used to rapidly evaluate the adsorption performance of a large set of MOFs. This allows subsequent experiments to focus only on a small subset of the most promising MOFs. In many instances, however, even molecular simulation becomes prohibitively time consuming, underscoring the need for alternative screening methods, such as machine learning, to precede molecular simulation efforts. In this study, as a proof of concept, we trained a neural network as the first example of a machine learning model capable of predicting full adsorption isotherms of different molecules not included in the training of the model. To achieve this, we trained our neural network only on alchemical species, represented only by their geometry and force field parameters, and used this neural network to predict the loadings of real adsorbates. We focused on predicting room temperature adsorption of small (one- and two-atom) molecules relevant to chemical separations. Namely, argon, krypton, xenon, methane, ethane, and nitrogen. However, we also observed surprisingly promising predictions for more complex molecules, whose properties are outside the range spanned by the alchemical adsorbates. Prediction accuracies suitable for large-scale screening were achieved using simple MOF (e.g. geometric properties and chemical moieties), and adsorbate (e.g. forcefield parameters and geometry) descriptors. Our results illustrate a new philosophy of training that opens the path towards development of machine learning models that can predict the adsorption loading of any new adsorbate at any new operating conditions in any new MOF.</div>

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