scholarly journals Pattern Recognition Methods to Separate Forced Responses from Internal Variability in Climate Model Ensembles and Observations

2020 ◽  
Vol 33 (20) ◽  
pp. 8693-8719 ◽  
Author(s):  
Robert C. J. Wills ◽  
David S. Battisti ◽  
Kyle C. Armour ◽  
Tapio Schneider ◽  
Clara Deser
Keyword(s):  
Climate Change ◽  
Pattern Recognition ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Internal Variability ◽  
Forced Response ◽  
Large Ensembles

AbstractEnsembles of climate model simulations are commonly used to separate externally forced climate change from internal variability. However, much of the information gained from running large ensembles is lost in traditional methods of data reduction such as linear trend analysis or large-scale spatial averaging. This paper demonstrates how a pattern recognition method (signal-to-noise-maximizing pattern filtering) extracts patterns of externally forced climate change from large ensembles and identifies the forced climate response with up to 10 times fewer ensemble members than simple ensemble averaging. It is particularly effective at filtering out spatially coherent modes of internal variability (e.g., El Niño, North Atlantic Oscillation), which would otherwise alias into estimates of regional responses to forcing. This method is used to identify forced climate responses within the 40-member Community Earth System Model (CESM) large ensemble, including an El Niño–like response to volcanic eruptions and forced trends in the North Atlantic Oscillation. The ensemble-based estimate of the forced response is used to test statistical methods for isolating the forced response from a single realization (i.e., individual ensemble members). Low-frequency pattern filtering is found to skillfully identify the forced response within individual ensemble members and is applied to the HadCRUT4 reconstruction of observed temperatures, whereby it identifies slow components of observed temperature changes that are consistent with the expected effects of anthropogenic greenhouse gas and aerosol forcing.

Non-linearity in the pathway of El Niño-Southern Oscillation to the tropical North Atlantic

2021 ◽  
pp. 1-54
Author(s):  
Jake W. Casselman ◽  
Andréa S. Taschetto ◽  
Daniela I.V. Domeisen
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Southern Oscillation ◽  
Static Stability ◽  
Reanalysis Data ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Tropical North Atlantic

AbstractEl Niño-Southern Oscillation can influence the Tropical North Atlantic (TNA), leading to anomalous sea surface temperatures (SST) at a lag of several months. Several mechanisms have been proposed to explain this teleconnection. These mechanisms include both tropical and extratropical pathways, contributing to anomalous trade winds and static stability over the TNA region. The TNA SST response to ENSO has been suggested to be nonlinear. Yet the overall linearity of the ENSO-TNA teleconnection via the two pathways remains unclear. Here we use reanalysis data to confirm that the SST anomaly (SSTA) in the TNA is nonlinear with respect to the strength of the SST forcing in the tropical Pacific, as further increases in El Niño magnitudes cease to create further increases of the TNA SSTA. We further show that the tropical pathway is more linear than the extratropical pathway by sub-dividing the inter-basin connection into extratropical and tropical pathways. This is confirmed by a climate model participating in the CMIP5. The extratropical pathway is modulated by the North Atlantic Oscillation (NAO) and the location of the SSTA in the Pacific, but this modulation insufficiently explains the nonlinearity in TNA SSTA. As neither extratropical nor tropical pathways can explain the nonlinearity, this suggests that external factors are at play. Further analysis shows that the TNA SSTA is highly influenced by the preconditioning of the tropical Atlantic SST. This preconditioning is found to be associated with the NAO through SST-tripole patterns.

Climate Variability in the Context of Climate Change: El Niño and Other Oscillations

2008 ◽  
Author(s):  
Cynthia Rosenzweig ◽  
Daniel Hillel
Keyword(s):  
Climate Change ◽  
Climate Variability ◽  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Global Climate ◽  
Climate System ◽  
The Arctic ◽  
The Pacific ◽  
Earth’S Climate

The climate system envelops our planet, with swirling fluxes of mass, momentum, and energy through air, water, and land. Its processes are partly regular and partly chaotic. The regularity of diurnal and seasonal fluctuations in these processes is well understood. Recently, there has been significant progress in understanding some of the mechanisms that induce deviations from that regularity in many parts of the globe. These mechanisms include a set of combined oceanic–atmospheric phenomena with quasi-regular manifestations. The largest of these is centered in the Pacific Ocean and is known as the El Niño–Southern Oscillation. The term “oscillation” refers to a shifting pattern of atmospheric pressure gradients that has distinct manifestations in its alternating phases. In the Arctic and North Atlantic regions, the occurrence of somewhat analogous but less regular interactions known as the Arctic Oscillation and its offshoot, the North Atlantic Oscillation, are also being studied. These and other major oscillations influence climate patterns in many parts of the globe. Examples of other large-scale interactive ocean–atmosphere– land processes are the Pacific Decadal Oscillation, the Madden-Julian Oscillation, the Pacific/North American pattern, the Tropical Atlantic Variability, the West Pacific pattern, the Quasi-Biennial Oscillation, and the Indian Ocean Dipole. In this chapter we review the earth’s climate system in general, define climate variability, and describe the processes related to ENSO and the other major systems and their interactions. We then consider the possible connections of the major climate variability systems to anthropogenic global climate change. The climate system consists of a series of fluxes and transformations of energy (radiation, sensible and latent heat, and momentum), as well as transports and changes in the state of matter (air, water, solid matter, and biota) as conveyed and influenced by the atmosphere, the ocean, and the land masses. Acting like a giant engine, this dynamic system is driven by the infusion, transformation, and redistribution of energy.

scholarly journals Simulated coordinated impacts of the previous autumn North Atlantic Oscillation (NAO) and winter El Niño on winter aerosol concentrations over eastern China

2019 ◽  
Vol 19 (16) ◽  
pp. 10787-10800 ◽  
Author(s):  
Juan Feng ◽  
Jianping Li ◽  
Hong Liao ◽  
Jianlei Zhu
Keyword(s):  
North Atlantic Oscillation ◽  
South China ◽  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Eastern China ◽  
Central China ◽  
Boreal Winter ◽  
The Impact ◽  
Previous Autumn

Abstract. The high aerosol concentration (AC) over eastern China has attracted attention from both science and society. Based on the simulations of a chemical transport model using a fixed emissions level, the possible impact of the previous autumn North Atlantic Oscillation (NAO) combined with the simultaneous El Niño–Southern Oscillation (ENSO) on the boreal winter AC over eastern China is investigated. We find that the NAO only manifests its negative impacts on the AC during its negative phase over central China, and a significant positive influence on the distribution of AC is observed over south China only during the warm events of ENSO. The impact of the previous NAO on the AC occurs via an anomalous sea surface temperature tripole pattern by which a teleconnection wave train is induced that results in anomalous convergence over central China. In contrast, the occurrence of ENSO events may induce an anomalous shift in the western Pacific subtropical high and result in anomalous southwesterlies over south China. The anomalous circulations associated with a negative NAO and El Niño are not favorable for the transport of AC and correspond to worsening air conditions over central and south China. The results highlight the fact that the combined effects of tropical and extratropical systems play a considerable role in affecting the boreal winter AC over eastern China.

scholarly journals Impact of internal variability on climate change for the upcoming decades: analysis of the CanESM2-LE and CESM-LE large ensembles

2019 ◽  
Vol 156 (3) ◽  
pp. 299-314 ◽  
Author(s):  
Gabriel Rondeau-Genesse ◽  
Marco Braun
Keyword(s):  
Climate Change ◽  
Climate Models ◽  
Climate Model ◽  
Ghg Emissions ◽  
Internal Variability ◽  
Mean Annual Temperature ◽  
Large Ensemble ◽  
Climate Change Effects ◽  
Large Ensembles ◽  
The Mean

Abstract The pace of climate change can have a direct impact on the efforts required to adapt. For short timescales, however, this pace can be masked by internal variability (IV). Over a few decades, this can cause climate change effects to exceed what would be expected from the greenhouse gas (GHG) emissions alone or, to the contrary, cause slowdowns or even hiatuses. This phenomenon is difficult to explore using ensembles such as CMIP5, which are composed of multiple climate models and thus combine both IV and inter-model differences. This study instead uses CanESM2-LE and CESM-LE, two state-of-the-art large ensembles (LE) that comprise multiple realizations from a single climate model and a single GHG emission scenario, to quantify the relationship between IV and climate change over the next decades in Canada and the USA. The mean annual temperature and the 3-day maximum and minimum temperatures are assessed. Results indicate that under the RCP8.5, temperatures within most of the individual large ensemble members will increase in a roughly linear manner between 2021 and 2060. However, members of the large ensembles in which a slowdown of warming is found during the 2021–2040 period are two to five times more likely to experience a period of very fast warming in the following decades. The opposite scenario, where the changes expected by 2050 would occur early because of IV, remains fairly uncommon for the mean annual temperature, but occurs in 5 to 15% of the large ensemble members for the temperature extremes.

scholarly journals Association between stroke occurrence and changes in atmospheric circulation

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Jone Vencloviene ◽  
Ricardas Radisauskas ◽  
Daina Kranciukaite-Butylkiniene ◽  
Abdonas Tamosiunas ◽  
Vidmantas Vaiciulis ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
El Niño ◽  
Arctic Oscillation ◽  
El Nino ◽  
Teleconnection Pattern ◽  
East Atlantic ◽  
Negatively Associated ◽  
The Impact

Abstract Background The impact of weather on morbidity from stroke has been analysed in previous studies. As the risk of stroke was mostly associated with changing weather, the changes in the daily stroke occurrence may be associated with changes in atmospheric circulation. The aim of our study was to detect and evaluate the association between daily numbers of ischaemic strokes (ISs) and haemorrhagic strokes (HSs) and the teleconnection pattern. Methods The study was performed in Kaunas, Lithuania, from 2000 to 2010. The daily numbers of ISs, subarachnoid haemorrhages (SAHs), and intracerebral haemorrhages (ICHs) were obtained from the Kaunas Stroke Register. We evaluated the association between these types of stroke and the teleconnection pattern by applying Poisson regression and adjusting for the linear trend, month, and other weather variables. Results During the study period, we analysed 4038 cases (2226 men and 1812 women) of stroke. Of these, 3245 (80.4%) cases were ISs, 533 (13.2%) cases were ICHs, and 260 (6.4%) cases were SAHs. An increased risk of SAH was associated with a change in mean daily atmospheric pressure over 3.9 hPa (RR = 1.49, 95% CI 1.14–1.96), and a stronger El Niño event had a protective effect against SAHs (RR = 0.34, 95% CI 0.16–0.69). The risk of HS was positively associated with East Atlantic/West Russia indices (RR = 1.13, 95% CI 1.04–1.23). The risk of IS was negatively associated with the Arctic Oscillation index on the same day and on the previous day (RR = 0.97, p < 0.033). During November–March, the risk of HS was associated with a positive North Atlantic Oscillation (NAO) (RR = 1.29, 95% CI 1.03–1.62), and the risk of IS was negatively associated with the NAO index (RR = 0.92, 95% CI 0.85–0.99). Conclusions The results of our study provide new evidence that the North Atlantic Oscillation, Arctic Oscillation, East Atlantic/West Russia, and El Niño-Southern Oscillation pattern may affect the risk of stroke. The impact of these teleconnections is not identical for various types of stroke. Emergency services should be aware that specific weather conditions are more likely to prompt calls for more severe strokes.

Sign in / Sign up

Export Citation Format

Share Document