scholarly journals Investigating Possible Arctic–Midlatitude Teleconnections in a Linear Framework

2016 ◽  
Vol 29 (20) ◽  
pp. 7329-7343 ◽  
Author(s):  
Raymond Sellevold ◽  
Stefan Sobolowski ◽  
Camille Li
Keyword(s):  
Large Scale ◽  
Lower Troposphere ◽  
Internal Variability ◽  
Stationary Wave ◽  
The Arctic ◽  
Stationary Waves ◽  
Arctic Amplification ◽  
Weather Patterns ◽  
Linear Framework ◽  
Circulation Changes

Abstract There is an ongoing debate over whether accelerated Arctic warming [Arctic amplification (AA)] is altering the large-scale circulation responsible for the anomalous weather experienced by midlatitude regions in recent years. Among the proposed mechanisms is the idea that local processes associated with sea ice loss heat the lower troposphere at high latitudes, thus weakening the equator-to-pole temperature gradient and driving changes in quasi-stationary waves, the midlatitude jets, and storm tracks. It is further hypothesized that these circulation changes are conducive to persistent weather patterns. Because of the short observational record and large atmospheric internal variability, it is difficult to identify robust relationships and infer causality. Here, a simplified, linear, steady-state model is used to investigate the direct response of the midlatitude atmospheric circulation to thermal forcing in the Arctic. The results suggest that there is a weak midlatitude circulation response to an idealized, but representative, Arctic heating perturbation. Further, the stationary wave responses are shown to be well within the bounds of internal variability. A midlatitude response is excited if the idealized heating penetrates up to the tropopause. Such deep, persistent heating is not observed on average during the AA period but does suggest a pathway for Arctic–midlatitude linkages under specific conditions. This study adds to the growing body of work suggesting that warming in the lower troposphere associated with Arctic amplification is not currently a direct driver of anomalous midlatitude circulation changes.

Emergent constraints on the large scale atmospheric circulation and regional hydroclimate: do they still work in CMIP6 and how much can they actually constrain the future?

2021 ◽  
pp. 1-62
Author(s):  
Isla R. Simpson ◽  
Karen A. McKinnon ◽  
Frances V. Davenport ◽  
Martin Tingley ◽  
Flavio Lehner ◽  
...  
Keyword(s):  
Large Scale ◽  
Coupled Model ◽  
Internal Variability ◽  
Stationary Wave ◽  
Meridional Wind ◽  
Least Squares Regression ◽  
Enso Teleconnections ◽  
Projected Change ◽  
Out Of Sample ◽  
The Relationship

AbstractAn ‘emergent constraint’ (EC) is a statistical relationship, across a model ensemble, between a measurable aspect of the present day climate (the predictor) and an aspect of future projected climate change (the predictand). If such a relationship is robust and understood, it may provide constrained projections for the real world. Here, Coupled Model Intercomparison Project 6 (CMIP6) models are used to revisit several ECs that were proposed in prior model intercomparisons with two aims: (1) to assess whether these ECs survive the partial out-of-sample test of CMIP6 and (2) to more rigorously quantify the constrained projected change than previous studies. To achieve the latter, methods are proposed whereby uncertainties can be appropriately accounted for, including the influence of internal variability, uncertainty on the linear relationship, and the uncertainty associated with model structural differences, aside from those described by the EC. Both least squares regression and a Bayesian Hierarchical Model are used. Three ECs are assessed: (a) the relationship between Southern Hemisphere jet latitude and projected jet shift, which is found to be a robust and quantitatively useful constraint on future projections; (b) the relationship between stationary wave amplitude in the Pacific-North American sector and meridional wind changes over North America (with extensions to hydroclimate), which is found to be robust but improvements in the predictor in CMIP6 result in it no longer substantially constrains projected change in either circulation or hydroclimate; and (c) the relationship between ENSO teleconnections to California and California precipitation change, which does not appear to be robust when using historical ENSO teleconnections as the predictor.

scholarly journals The Role of Synoptic Cyclones for the Formation of Arctic Summer Circulation Patterns as Clustered by Self-Organizing Maps

Atmosphere ◽  
2019 ◽  
Vol 10 (8) ◽  
pp. 474 ◽  
Author(s):  
Min-Hee Lee ◽  
Joo-Hong Kim
Keyword(s):  
Arctic Ocean ◽  
Large Scale ◽  
The Arctic ◽  
Cyclone Activity ◽  
Summer Circulation ◽  
Self Organizing Maps ◽  
Weather Patterns ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Self Organizing

Contribution of extra-tropical synoptic cyclones to the formation of mean summer atmospheric circulation patterns in the Arctic domain (≥60° N) was investigated by clustering dominant Arctic circulation patterns based on daily mean sea-level pressure using self-organizing maps (SOMs). Three SOM patterns were identified; one pattern had prevalent low-pressure anomalies in the Arctic Circle (SOM1), while two exhibited opposite dipoles with primary high-pressure anomalies covering the Arctic Ocean (SOM2 and SOM3). The time series of their occurrence frequencies demonstrated the largest inter-annual variation in SOM1, a slight decreasing trend in SOM2, and the abrupt upswing after 2007 in SOM3. Analyses of synoptic cyclone activity using the cyclone track data confirmed the vital contribution of synoptic cyclones to the formation of large-scale patterns. Arctic cyclone activity was enhanced in the SOM1, which was consistent with the meridional temperature gradient increases over the land–Arctic ocean boundaries co-located with major cyclone pathways. The composite daily synoptic evolution of each SOM revealed that all three SOMs persisted for less than five days on average. These evolutionary short-term weather patterns have substantial variability at inter-annual and longer timescales. Therefore, the synoptic-scale activity is central to forming the seasonal-mean climate of the Arctic.

scholarly journals Late Twenty-First-Century Changes in the Midlatitude Atmospheric Circulation in the CESM Large Ensemble

2017 ◽  
Vol 30 (15) ◽  
pp. 5943-5960 ◽  
Author(s):  
Y. Peings ◽  
J. Cattiaux ◽  
S. Vavrus ◽  
Gudrun Magnusdottir
Keyword(s):  
Atmospheric Circulation ◽  
Extreme Temperature ◽  
Internal Variability ◽  
First Century ◽  
The Arctic ◽  
Arctic Amplification ◽  
Large Ensemble ◽  
Longitudinal Sector ◽  
Twenty First Century ◽  
Projected Changes

Projected changes in the midlatitude atmospheric circulation at the end of the twenty-first century are investigated using coupled ocean–atmosphere simulations from the Community Earth System Model Large Ensemble (CESM-LENS). Different metrics are used to describe the response of the midlatitude atmospheric dynamics in 40 ensemble members covering the 1920–2100 period. Contrasted responses are identified depending on the season and longitudinal sector that are considered. In winter, a slowdown of the zonal flow and an increase in waviness is found over North America, while the European sector exhibits a reinforced westerly flow and decreased waviness. Extreme temperature events in midlatitudes are more sensitive to thermodynamical than dynamical changes, and a general decrease in the intensity of wintertime cold spells is found. Analyses of individual ensemble members reveal a large spread in circulation changes due to internal variability. Causes for this spread are found to be tied to the Arctic amplification in the Pacific–North American sector and to the polar stratosphere in the North Atlantic. A competition mechanism is also discussed between the midlatitude response to polar versus tropical changes. While the upper-tropospheric tropical warming pushes the jet stream poleward, in winter, Arctic amplification and the weaker polar vortex exert an opposite effect. This competition results in a narrowing of the jet path in the midlatitudes, leading to decreased/unchanged waviness/blockings. This interpretation somewhat reconciles conflicting results between the hypothesized effect of Arctic amplification and projected changes in midlatitude flow characteristics. This study also illustrates that further understanding of regional processes is critical for anticipating changes in the midlatitude dynamics.

Investigating the Linear and Nonlinear Stationary Wave Response to Anomalous North American Snow Cover

2011 ◽  
Vol 68 (4) ◽  
pp. 904-917 ◽  
Author(s):  
Stefan Sobolowski ◽  
Gavin Gong ◽  
Mingfang Ting
Keyword(s):  
Snow Cover ◽  
North American ◽  
Land Surface ◽  
Large Scale ◽  
Wave Model ◽  
Stationary Wave ◽  
Response Analysis ◽  
Stationary Waves ◽  
Continental Scale ◽  
Wave Response

Abstract Continental-scale snow cover represents a broad thermal forcing on monthly-to-intraseasonal time scales, with the potential to modify local and remote atmospheric circulation. A previous GCM study reported robust transient-eddy responses to prescribed anomalous North American (NA) snow cover. The same set of experiments also indicated a robust upper-level stationary wave response during spring, but the nature of this response was not investigated until now. Here, the authors diagnose a deep, snow-induced, tropospheric cooling over NA and hypothesize that this may represent a pathway linking snow to the stationary wave response. A nonlinear stationary wave model is shown to reproduce the GCM stationary wave response to snow more accurately than a linear model, and results confirm that diabatic cooling is the primary driver of the stationary wave response. In particular, the total nonlinear effects due to cooling, and its interactions with transient eddies and orography, are shown to be essential for faithful reproduction of the GCM response. The nonlinear model results confirm that direct effects due to transients and orography are modest. However, with interactions between forcings included, the total effects due to these terms make important contributions to the total response. Analysis of observed NA snow cover and stationary waves is qualitatively similar to the patterns generated by the GCM and linear/nonlinear stationary wave models, indicating that the snow-induced signal is not simply a modeling artifact. The diagnosis and description of a snow–stationary wave relationship adds to the understanding of stationary waves and their forcing mechanisms, and this relationship suggests that large-scale changes in the land surface state may exert considerable influence on the atmosphere over hemispheric scales and thereby contribute to climate variability.

scholarly journals Influence of Arctic Wetlands on Arctic Atmospheric Circulation

2007 ◽  
Vol 20 (16) ◽  
pp. 4243-4254 ◽  
Author(s):  
William J. Gutowski ◽  
Helin Wei ◽  
Charles J. Vörösmarty ◽  
Balázs M. Fekete
Keyword(s):  
Boundary Conditions ◽  
Atmospheric Circulation ◽  
Land Surface ◽  
Lower Boundary ◽  
Internal Variability ◽  
Surface Fluxes ◽  
Arctic Climate ◽  
The Arctic ◽  
Energy And Momentum ◽  
Circulation Changes

Abstract The Arctic’s land surface has large areas of wetlands that exchange moisture, energy, and momentum with the atmosphere. The authors use a mesoscale, pan-Arctic model simulating the summer of 1986 to examine links between the wetlands and arctic atmospheric dynamics and water cycling. Simulations with and without wetlands are compared to simulations using perturbed initial and lateral boundary conditions to delineate when and where the wetlands influence rises above nonlinear internal variability. The perturbation runs expose the temporal variability of the circulation’s sensitivity to changes in lower boundary conditions. For the wetlands cases examined here, the period of the most significant influence is approximately two weeks, and the wetlands do not introduce new circulation changes but rather appear to reinforce and modify existing circulation responses to perturbations. The largest circulation sensitivity, and thus the largest wetlands influence, occurs in central Siberia. The circulation changes induced by adding the wetlands appear as a propagating, equivalent barotropic wave. The wetlands anomaly circulation spreads alterations of surface fluxes to other locations, which undermines the potential for the wetlands to present a distinctive, spatially fixed forcing to atmospheric circulation. Using the climatology of artic synoptic-storm occurrence to indicate when the arctic circulation is most sensitive to altered forcing, the results suggest that the circulation is susceptible to the direct influence of wetlands for a limited time period extending from spring thaw of wetlands until synoptic-storm occurrence diminishes in midsummer. Sensitivities in arctic circulation uncovered through this work occur during a period of substantial transition from a fundamentally frozen to thawed state, a period of major concern for impacts of greenhouse warming on pan-Arctic climate. Changing arctic climate could alter the behavior revealed here.

scholarly journals Internal Variability in Projections of Twenty-First-Century Arctic Sea Ice Loss: Role of the Large-Scale Atmospheric Circulation

2014 ◽  
Vol 27 (2) ◽  
pp. 527-550 ◽  
Author(s):  
Justin J. Wettstein ◽  
Clara Deser
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Wave Train ◽  
Internal Variability ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Arctic Sea ◽  
Rossby Wave Train ◽  
Arctic Sea Ice Loss

Abstract Internal variability in twenty-first-century summer Arctic sea ice loss and its relationship to the large-scale atmospheric circulation is investigated in a 39-member Community Climate System Model, version 3 (CCSM3) ensemble for the period 2000–61. Each member is subject to an identical greenhouse gas emissions scenario and differs only in the atmospheric model component's initial condition. September Arctic sea ice extent trends during 2020–59 range from −2.0 × 106 to −5.7 × 106 km2 across the 39 ensemble members, indicating a substantial role for internal variability in future Arctic sea ice loss projections. A similar nearly threefold range (from −7.0 × 103 to −19 × 103 km3) is found for summer sea ice volume trends. Higher rates of summer Arctic sea ice loss in CCSM3 are associated with enhanced transpolar drift and Fram Strait ice export driven by surface wind and sea level pressure patterns. Over the Arctic, the covarying atmospheric circulation patterns resemble the so-called Arctic dipole, with maximum amplitude between April and July. Outside the Arctic, an atmospheric Rossby wave train over the Pacific sector is associated with internal ice loss variability. Interannual covariability patterns between sea ice and atmospheric circulation are similar to those based on trends, suggesting that similar processes govern internal variability over a broad range of time scales. Interannual patterns of CCSM3 ice–atmosphere covariability compare well with those in nature and in the newer CCSM4 version of the model, lending confidence to the results. Atmospheric teleconnection patterns in CCSM3 suggest that the tropical Pacific modulates Arctic sea ice variability via the aforementioned Rossby wave train. Large ensembles with other coupled models are needed to corroborate these CCSM3-based findings.

scholarly journals Decadal changes of wintertime poleward heat and moisture transport associated with the amplified Arctic warming

2021 ◽  
Author(s):  
Xiaozhuo Sang ◽  
Xiu-Qun Yang ◽  
Lingfeng Tao ◽  
Jiabei Fang ◽  
Xuguang Sun
Keyword(s):  
Heat Transport ◽  
Moisture Transport ◽  
Stationary Wave ◽  
The Arctic ◽  
Stationary Waves ◽  
High Latitudes ◽  
Arctic Warming ◽  
Poleward Heat Transport ◽  
Heat And Moisture ◽  
Moisture Transports

Abstract The Arctic warming, especially during winter, has been almost twice as large as the global average since the late 1990s, which is known as the Arctic amplification. Yet linkage between the amplified Arctic warming and the midlatitude change is still under debate. This study examines the decadal changes of wintertime poleward heat and moisture transports between two 18-yr epochs (1999–2016 and 1981–1998) with five atmospheric reanalyses. It is found that the wintertime Arctic warming induces an amplification of the high latitude stationary wave component of zonal wavenumber one but a weakening of the wavenumber two. These stationary wave changes enhance poleward heat and moisture transports, which are conducive to further Arctic warming and moistening, acting as a positive feedback onto the Arctic warming. Meanwhile, the Arctic warming reduces atmospheric baroclinicity and thus weakens synoptic eddy activities in the high latitudes. The decreased transient eddy activities reduce poleward heat and moisture transports, which decrease the Arctic temperature and moisture, acting as a negative feedback onto the Arctic warming. The total poleward heat transport contributes little to the Arctic warming, since the increased poleward heat transport by stationary waves is nearly canceled by the decreased transport by transient eddies. However, the total poleward moisture transport increases over most areas of the high latitudes that is dominated by the increased transport by stationary waves, which provides a significant net positive feedback onto the Arctic warming and moistening. Such a poleward moisture transport feedback may be particularly crucial to the amplified Arctic warming during winter when the ice-albedo feedback vanishes.

scholarly journals The Emergence and Transient Nature of Arctic Amplification in Coupled Climate Models

2021 ◽  
Vol 9 ◽  
Author(s):  
Marika M. Holland ◽  
Laura Landrum
Keyword(s):  
Sea Ice ◽  
21St Century ◽  
Climate Models ◽  
Internal Variability ◽  
The Arctic ◽  
Arctic Amplification ◽  
Arctic Warming ◽  
Transient Nature ◽  
Coupled Climate Models ◽  
Large Ensembles

Under rising atmospheric greenhouse gas concentrations, the Arctic exhibits amplified warming relative to the globe. This Arctic amplification is a defining feature of global warming. However, the Arctic is also home to large internal variability, which can make the detection of a forced climate response difficult. Here we use results from seven model large ensembles, which have different rates of Arctic warming and sea ice loss, to assess the time of emergence of anthropogenically-forced Arctic amplification. We find that this time of emergence occurs at the turn of the century in all models, ranging across the models by a decade from 1994–2005. We also assess transient changes in this amplified signal across the 21st century and beyond. Over the 21st century, the projections indicate that the maximum Arctic warming will transition from fall to winter due to sea ice reductions that extend further into the fall. Additionally, the magnitude of the annual amplification signal declines over the 21st century associated in part with a weakening albedo feedback strength. In a simulation that extends to the 23rd century, we find that as sea ice cover is completely lost, there is little further reduction in the surface albedo and Arctic amplification saturates at a level that is reduced from its 21st century value.

scholarly journals The Role of Stationary Waves in the Maintenance of the Northern Annular Mode as Deduced from Model Experiments

2006 ◽  
Vol 63 (11) ◽  
pp. 2931-2947 ◽  
Author(s):  
Heiner Körnich ◽  
Gerhard Schmitz ◽  
Erich Becker
Keyword(s):  
Lower Troposphere ◽  
Circulation Model ◽  
Stationary Wave ◽  
Stationary Waves ◽  
Mean Flow ◽  
Thermal Forcing ◽  
Annular Mode ◽  
Model Experiments ◽  
Wave Forcing ◽  
Orographic Forcing

Abstract The influence of stationary waves on the maintenance of the tropospheric annular mode (AM) is examined in a simple global circulation model with perpetual January conditions. The presented model experiments vary in the configurations of stationary wave forcing by orography and land–sea heating contrasts. All simulations display an AM-like pattern in the lower troposphere. The zonal momentum budget shows that the feedback between eddies with periods less than 10 days and the zonal-mean zonal wind is generally the dominating process that maintains the AM. The kinetic energy of the high-frequency eddies depends on the stationary wave forcing, where orographic forcing reduces and thermal forcing enhances it. The AMs in the model experiments differ in the superposed anomalous stationary waves and in the strength of the zonally symmetric component. If only orographic stationary wave forcing is taken into account, the mountain torque decelerates the barotropic wind anomaly, and thus acts to weaken the AM. However, the combined forcing of orography and land–sea heating contrasts produces a feedback between the anomalous stationary waves and the AM that compensates for the mountain torque. The different behavior of the model experiments results from the fact that only the thermal forcing changes the character of the anomalous stationary waves from external Rossby waves for orographic forcing alone to vertically propagating waves that enable the feedback process through wave–mean flow interaction. Only with this feedback, which is shown to be due to linear zonal–eddy coupling, does the model display a strong AM with centers of action over the oceans. The main conclusions are that this process is necessary to simulate a realistic northern AM, and that it distinguishes the northern from the southern AM.

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