Potential linkage between the atmospheric summer circulation over Eurasia and preceding sea ice anomalies southwest of Greenland

2020 ◽  
Author(s):  
Jerome Sauer ◽  
Johanna Baehr ◽  
Nedjeljka Žagar
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Vertical Velocity ◽  
Wave Train ◽  
Labrador Sea ◽  
Momentum Exchange ◽  
Near Surface ◽  
June July ◽  
Sst Anomalies

<p>Sea ice alters the surface albedo and modulates the heat, moisture and momentum exchange between the ocean and the atmosphere. Various studies suggest an influence of the sea ice on the atmospheric circulation, whereby the focus is often on simultaneous connections and Arctic-wide sea ice conditions. Sea ice has a strong memory and we thus hypothesize a potential feedback on the atmosphere also at higher lags. Using ERA5 reanalysis data between 1983 and 2017, the present work investigates a potential connection of the summer atmospheric circulation over Eurasia to winter sea ice anomalies southwest of Greenland. Composites of the June-July geopotential height pattern show a wave-train structure throughout the troposphere and the resulting circulation anomalies are found to influence the two metre temperatures over northeastern Europe and northern Russia. These anomalies are significantly correlated with December-January sea ice anomalies. Persistent sea surface temperature (SST) anomalies associated with the strong ice memory indicates that the winter signal is partly stored in the Labrador Sea. The observations indicate a response in the June-July 500 hPa vertical velocity in proximity of the strongest SST anomalies that is dynamically consistent with the lower-level and upper-level divergence pattern. The result suggests that the vertical velocity potentially connects a vorticity forcing in the upper troposphere to near-surface conditions over the Labrador Sea that originate from the preceeding winter. <br>A further analysis shows a particularly pronounced wave-train signal when the December-January ice anomalies appear in phase with a strong North Atlantic Oscillation (NAO) index. Those years are characterized by extensive and persistent SST anomalies in the North Atlantic bearing similarities with the tripole pattern that is known to be associated with the NAO. The SST signal is accompanied by widespread heat flux anomalies hinting at a further influence coming from the central North Atlantic. The study provides a first analysis of two possible factors that potentially contribute to the linkage between winter sea ice and the summer atmospheric circulation.</p>

Teleconnections between Tropical Pacific SST Anomalies and Extratropical Southern Hemisphere Climate

2014 ◽  
Vol 28 (1) ◽  
pp. 56-65 ◽  
Author(s):  
Laura M. Ciasto ◽  
Graham R. Simpkins ◽  
Matthew H. England
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Rossby Wave ◽  
Wave Train ◽  
Cold Season ◽  
Tropical Pacific ◽  
Central Pacific ◽  
Sst Variability ◽  
Sst Anomalies

Abstract Teleconnections from tropical Pacific sea surface temperature (SST) anomalies to the high-latitude Southern Hemisphere (SH) are examined using observations and reanalysis. Analysis of tropical Pacific SST anomalies is conducted separately for the central Pacific (CP) and eastern Pacific (EP) regions. During the austral cold season, extratropical SH atmospheric Rossby wave train patterns are observed in association with both EP and CP SST variability. The primary difference between the patterns is the westward displacement of the CP-related atmospheric anomalies, consistent with the westward elongation of CP-related convective SST required for upper-level divergence and Rossby wave generation. Consequently, CP-related patterns of SH SST, Antarctic sea ice, and temperature anomalies also exhibit a westward displacement, but otherwise, the cold season extratropical SH teleconnections are largely similar. During the warm season, however, extratropical SH teleconnections associated with tropical CP and EP SST anomalies differ substantially. EP SST variability is linked to largely zonally symmetric structures in the extratropical atmospheric circulation, which projects onto the southern annular mode (SAM), and is strongly related to the SH temperature and sea ice fields. In contrast, CP SST variability is only weakly related to the SH atmospheric circulation, temperature, or sea ice fields and no longer exhibits any clear association with the SAM. One hypothesized mechanism suggests that the relatively weak CP-related SST anomalies are not able to substantially impact the background flow of the subtropical jet and its subsequent interaction with equatorward-propagating waves associated with variability in the SAM. However, there is currently no widely established mechanism that links tropical Pacific SST anomalies to the SAM.

Why Does a Colder (Warmer) Winter Tend to Be Followed by a Warmer (Cooler) Summer over Northeast Eurasia?

2020 ◽  
Vol 33 (17) ◽  
pp. 7255-7274
Author(s):  
Shangfeng Chen ◽  
Renguang Wu ◽  
Wen Chen ◽  
Kai Li
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Wave Train ◽  
The Arctic ◽  
The North ◽  
Atmospheric Wave ◽  
Anomaly Pattern ◽  
Sst Anomaly ◽  
The North Atlantic ◽  
Sst Anomalies

AbstractThis study reveals a pronounced out-of-phase relationship between surface air temperature (SAT) anomalies over northeast Eurasia in boreal winter and the following summer during 1980–2017. A colder (warmer) winter over northeast Eurasia tends to be followed by a warmer (cooler) summer of next year. The processes for the out-of-phase relation of winter and summer SAT involve the Arctic Oscillation (AO), the air–sea interaction in the North Atlantic Ocean, and a Eurasian anomalous atmospheric circulation pattern induced by the North Atlantic sea surface temperature (SST) anomalies. Winter negative AO/North Atlantic Oscillation (NAO)-like atmospheric circulation anomalies lead to continental cooling over Eurasia via anomalous advection and a tripolar SST anomaly pattern in the North Atlantic. The North Atlantic SST anomaly pattern switches to a dipolar pattern in the following summer via air–sea interaction processes and associated surface heat flux changes. The summer North Atlantic dipolar SST anomaly pattern induces a downstream atmospheric wave train, including large-scale positive geopotential height anomalies over northeast Eurasia, which contributes to positive SAT anomalies there via enhancement of downward surface shortwave radiation and anomalous advection. Barotropic model experiments verify the role of the summer North Atlantic SST anomalies in triggering the atmospheric wave train over Eurasia. Through the above processes, a colder winter is followed by a warmer summer over northeast Eurasia. The above processes apply to the years when warmer winters are followed by cooler summers except for opposite signs of SAT, atmospheric circulation, and SST anomalies.

scholarly journals Anomalous blocking over Greenland preceded the 2013 extreme early melt of local sea ice

2017 ◽  
Vol 59 (76pt2) ◽  
pp. 181-190 ◽  
Author(s):  
Thomas J. Ballinger ◽  
Edward Hanna ◽  
Richard J. Hall ◽  
Thomas E. Cropper ◽  
Jeffrey Miller ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Regional Climate ◽  
Regional Climate Change ◽  
Circulation Pattern ◽  
The Arctic ◽  
Labrador Sea ◽  
First Year ◽  
Tropospheric Circulation ◽  
Blocking Index

ABSTRACTThe Arctic marine environment is undergoing a transition from thick multi-year to first-year sea-ice cover with coincident lengthening of the melt season. Such changes are evident in the Baffin Bay-Davis Strait-Labrador Sea (BDL) region where melt onset has occurred ~8 days decade−1 earlier from 1979 to 2015. A series of anomalously early events has occurred since the mid-1990s, overlapping a period of increased upper-air ridging across Greenland and the northwestern North Atlantic. We investigate an extreme early melt event observed in spring 2013. (~6σ below the 1981–2010 melt climatology), with respect to preceding sub-seasonal mid-tropospheric circulation conditions as described by a daily Greenland Blocking Index (GBI). The 40-days prior to the 2013 BDL melt onset are characterized by a persistent, strong 500 hPa anticyclone over the region (GBI >+1 on >75% of days). This circulation pattern advected warm air from northeastern Canada and the northwestern Atlantic poleward onto the thin, first-year sea ice and caused melt ~50 days earlier than normal. The episodic increase in the ridging atmospheric pattern near western Greenland as in 2013, exemplified by large positive GBI values, is an important recent process impacting the atmospheric circulation over a North Atlantic cryosphere undergoing accelerated regional climate change.

scholarly journals Response of the Atlantic Thermohaline Circulation to Increased Atmospheric CO2 in a Coupled Model

2004 ◽  
Vol 17 (21) ◽  
pp. 4267-4279 ◽  
Author(s):  
Aixue Hu ◽  
Gerald A. Meehl ◽  
Warren M. Washington ◽  
Aiguo Dai
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
North Atlantic ◽  
Thermohaline Circulation ◽  
Climate Model ◽  
Coupled Model ◽  
The Arctic ◽  
Labrador Sea ◽  
Upper Ocean ◽  
Gin Seas

Abstract Changes in the thermohaline circulation (THC) due to increased CO2 are important in future climate regimes. Using a coupled climate model, the Parallel Climate Model (PCM), regional responses of the THC in the North Atlantic to increased CO2 and the underlying physical processes are studied here. The Atlantic THC shows a 20-yr cycle in the control run, qualitatively agreeing with other modeling results. Compared with the control run, the simulated maximum of the Atlantic THC weakens by about 5 Sv (1 Sv ≡ 106 m3 s−1) or 14% in an ensemble of transient experiments with a 1% CO2 increase per year at the time of CO2 doubling. The weakening of the THC is accompanied by reduced poleward heat transport in the midlatitude North Atlantic. Analyses show that oceanic deep convective activity strengthens significantly in the Greenland–Iceland–Norway (GIN) Seas owing to a saltier (denser) upper ocean, but weakens in the Labrador Sea due to a fresher (lighter) upper ocean and in the south of the Denmark Strait region (SDSR) because of surface warming. The saltiness of the GIN Seas are mainly caused by an increased salty North Atlantic inflow, and reduced sea ice volume fluxes from the Arctic into this region. The warmer SDSR is induced by a reduced heat loss to the atmosphere, and a reduced sea ice flux into this region, resulting in less heat being used to melt ice. Thus, sea ice–related salinity effects appear to be more important in the GIN Seas, but sea ice–melt-related thermal effects seem to be more important in the SDSR region. On the other hand, the fresher Labrador Sea is mainly attributed to increased precipitation. These regional changes produce the overall weakening of the THC in the Labrador Sea and SDSR, and more vigorous ocean overturning in the GIN Seas. The northward heat transport south of 60°N is reduced with increased CO2, but increased north of 60°N due to the increased flow of North Atlantic water across this latitude.

scholarly journals Impacts of large-scale atmospheric circulation changes due to winter sea-ice retreat on Black Carbon transport and deposition to the Arctic

2016 ◽  
Author(s):  
Luca Pozzoli ◽  
Srdan Dobricic ◽  
Simone Russo ◽  
Elisabetta Vignati
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Large Scale ◽  
Southern Oscillation ◽  
The Arctic ◽  
The North ◽  
Ice Retreat ◽  
The North Atlantic Oscillation ◽  
Sea Ice Retreat

Abstract. Winter warming and sea ice retreat observed in the Arctic in the last decades determine changes of large scale atmospheric circulation pattern that may impact as well the transport of black carbon (BC) to the Arctic and its deposition on the sea ice, with possible feedbacks on the regional and global climate forcing. In this study we developed and applied a new statistical algorithm, based on the Maximum Likelihood Estimate approach, to determine how the changes of three large scale weather patterns (the North Atlantic Oscillation, the Scandinavian Blocking, and the El Nino-Southern Oscillation), associated with winter increasing temperatures and sea ice retreat in the Arctic, impact the transport of BC to the Arctic and its deposition. We found that the three atmospheric patterns together determine a decreasing winter deposition trend of BC between 1980 and 2015 in the Eastern Arctic while they increase BC deposition in the Western Arctic. The increasing trend is mainly due to the more frequent occurrences of stable high pressure systems (atmospheric blocking) near Scandinavia favouring the transport in the lower troposphere of BC from Europe and North Atlantic directly into to the Arctic. The North Atlantic Oscillation has a smaller impact on BC deposition in the Arctic, but determines an increasing BC atmospheric load over the entire Arctic Ocean with increasing BC concentrations in the upper troposphere. The El Nino-Southern Oscillation does not influence significantly the transport and deposition of BC to the Arctic. The results show that changes in atmospheric circulation due to polar atmospheric warming and reduced winter sea ice significantly impacted BC transport and deposition. The anthropogenic emission reductions applied in the last decades were, therefore, crucial to counterbalance the most likely trend of increasing BC pollution in the Arctic.

scholarly journals The Impact of Regional Arctic Sea Ice Loss on Atmospheric Circulation and the NAO

2016 ◽  
Vol 29 (2) ◽  
pp. 889-902 ◽  
Author(s):  
Rasmus A. Pedersen ◽  
Ivana Cvijanovic ◽  
Peter L. Langen ◽  
Bo M. Vinther
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
General Circulation ◽  
Ice Cover ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Near Surface ◽  
Arctic Sea ◽  
The Impact ◽  
Sea Ice Reduction

Abstract Reduction of the Arctic sea ice cover can affect the atmospheric circulation and thus impact the climate beyond the Arctic. The atmospheric response may, however, vary with the geographical location of sea ice loss. The atmospheric sensitivity to the location of sea ice loss is studied using a general circulation model in a configuration that allows combination of a prescribed sea ice cover and an active mixed layer ocean. This hybrid setup makes it possible to simulate the isolated impact of sea ice loss and provides a more complete response compared to experiments with fixed sea surface temperatures. Three investigated sea ice scenarios with ice loss in different regions all exhibit substantial near-surface warming, which peaks over the area of ice loss. The maximum warming is found during winter, delayed compared to the maximum sea ice reduction. The wintertime response of the midlatitude atmospheric circulation shows a nonuniform sensitivity to the location of sea ice reduction. While all three scenarios exhibit decreased zonal winds related to high-latitude geopotential height increases, the magnitudes and locations of the anomalies vary between the simulations. Investigation of the North Atlantic Oscillation reveals a high sensitivity to the location of the ice loss. The northern center of action exhibits clear shifts in response to the different sea ice reductions. Sea ice loss in the Atlantic and Pacific sectors of the Arctic cause westward and eastward shifts, respectively.

Global Monsoon Responses to Decadal Sea Surface Temperature Variations during the Twentieth Century: Evidence from AGCM Simulations

2019 ◽  
Vol 32 (22) ◽  
pp. 7675-7695 ◽  
Author(s):  
Jie Jiang ◽  
Tianjun Zhou
Keyword(s):  
Twentieth Century ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Sea Surface ◽  
Monsoon Precipitation ◽  
The North ◽  
The North Atlantic ◽  
Sst Anomalies

Abstract Multidecadal variations in the global land monsoon were observed during the twentieth century, with an overall increasing trend from 1901 to 1955 that was followed by a decreasing trend up to 1990, but the mechanisms governing the above changes remain inconclusive. Based on the outputs of two atmospheric general circulation models (AGCMs) forced by historical sea surface temperature (SST) covering the twentieth century, supplemented with AGCM simulations forced by idealized SST anomalies representing different conditions of the North Atlantic and tropical Pacific, evidence shows that the observed changes can be partly reproduced, particularly over the Northern Hemisphere summer monsoon (NHSM) domain, demonstrating the modulation of decadal SST changes on the long-term variations in monsoon precipitation. Moisture budget analysis is performed to understand the interdecadal changes in monsoon precipitation, and the dynamic term associated with atmospheric circulation changes is found to be prominent, while the contribution of the thermodynamic term associated with humidity changes can lead to coincident wetting over the NHSM domain. The increase (decrease) in NHSM land precipitation during 1901–55 (1956–90) is associated with the strengthening (weakening) of NHSM circulation and Walker circulation. The multidecadal scale changes in atmospheric circulation are driven by SST anomalies over the North Atlantic and the Pacific. A warmer North Atlantic together with a colder eastern tropical Pacific and a warmer western subtropical Pacific can lead to a strengthened meridional gradient in mid-to-upper-tropospheric thickness and strengthened trade winds, which transport more water vapor into monsoon regions, leading to an increase in monsoon precipitation.

scholarly journals A Pilot Climate Sensitivity Study Using the CEN Coupled Adjoint Model (CESAM)

2018 ◽  
Vol 31 (5) ◽  
pp. 2031-2056 ◽  
Author(s):  
D. Stammer ◽  
A. Köhl ◽  
A. Vlasenko ◽  
I. Matei ◽  
F. Lunkeit ◽  
...  
Keyword(s):  
Sea Ice ◽  
Surface Temperature ◽  
Climate Sensitivity ◽  
North Atlantic ◽  
Sensitivity Study ◽  
Northern Europe ◽  
Surface Salinity ◽  
Near Surface ◽  
Temperature Anomalies ◽  
Northern European

A pilot coupled climate sensitivity study is presented based on the newly developed adjoint coupled climate model, Centrum für Erdsystemforschung und Nachhaltigkeit (CEN) Earth System Assimilation Model (CESAM). To this end the components of the coupled forward model are summarized, and the generation of the adjoint code out of the model forward code through the application of the Transformation of Algorithms in FORTRAN (TAF) adjoint compiler is discussed. It is shown that simulations of the intermediate-complexity CESAM are comparable in quality to CMIP-type coupled climate models, justifying the usage of the model to compute adjoint sensitivities of the northern Europe near-surface temperature to anomalies in surface temperature, sea surface salinity, and sea ice over the North Atlantic and the Arctic on time scales of up to one month. Results confirm that on a time scale of up to a few days surface temperatures over northern Europe are influenced by Atlantic temperature anomalies just upstream of the target location. With increasingly longer time lapse, however, it is the influence of SSTs over the central and western North Atlantic on the overlying atmosphere and the associated changes in storm-track pattern that dominate the evolution of the surface European temperature. Influences of surface salinity and sea ice on the northern European temperature appear to have similar sensitivity mechanisms, invoked indirectly through their influence on near-surface temperature anomalies. The adjoint study thus confirms that the SST’s impact on the atmospheric dynamics, notably storm tracks, is the primary cause for the influence of northern European temperature changes.

scholarly journals Two types of North American droughts related to different atmospheric circulation patterns

2019 ◽  
Vol 15 (6) ◽  
pp. 2053-2065 ◽  
Author(s):  
Angela-Maria Burgdorf ◽  
Stefan Brönnimann ◽  
Jörg Franke
Keyword(s):  
Atmospheric Circulation ◽  
Great Plains ◽  
North Atlantic ◽  
North American ◽  
Wave Train ◽  
Boreal Summer ◽  
Drought Indices ◽  
Dust Bowl ◽  
Summer Drought ◽  
The Pacific

Abstract. Proxy-based studies suggest that the southwestern USA is affected by two types of summer drought, often termed Dust Bowl-type droughts and 1950s-type droughts. The spatial drought patterns of the two types are distinct. It has been suggested that they are related to different circulation characteristics, but a lack of observation-based data has precluded further studies. In this paper, we analyze multi-annual summer droughts in North America back to 1600 in tree-ring-based drought reconstructions and in a global, monthly three-dimensional reconstruction of the atmosphere. Using cluster analysis of drought indices, we confirm the two main drought types and find a similar catalog of events as previous studies. These two main types of droughts are then analyzed with respect to 2 m temperatures (T2m), sea-level pressure (SLP), and 500 hPa geopotential height (GPH) in boreal summer. 1950s-type droughts are related to a stronger wave train over the Pacific–North American sector than Dust Bowl-type droughts, whereas the latter show the imprint of a poleward-shifted jet and establishment of a Great Plains ridge. The 500 hPa GPH patterns of the two types differ significantly not only over the contiguous United States and Canada but also over the extratropical North Atlantic and the Pacific. Dust Bowl-type droughts are associated with positive GPH anomalies, while 1950s-type droughts exhibit strong negative GPH anomalies. In comparison with 1950s-type droughts, the Dust Bowl-type droughts are characterized by higher sea-surface temperatures (SSTs) in the northern North Atlantic. Results suggest that atmospheric circulation and SST characteristics not only over the Pacific but also over the extratropical North Atlantic affect the spatial pattern of North American droughts.

scholarly journals Effect of a Variable Eddy Transfer Coefficient in an Eddy-Permitting Model of the Subpolar North Atlantic Ocean

2005 ◽  
Vol 35 (3) ◽  
pp. 289-307 ◽  
Author(s):  
Daniel Deacu ◽  
Paul G. Myers
Keyword(s):  
Atlantic Ocean ◽  
Transfer Coefficient ◽  
North Atlantic ◽  
General Circulation ◽  
North Atlantic Ocean ◽  
Negative Impact ◽  
Labrador Sea ◽  
Western Boundary ◽  
Near Surface ◽  
Eastern North Atlantic

Abstract The effect of using a variable eddy transfer coefficient for the Gent–McWilliams (GM) parameterization in a (1/3)°-resolution ocean model of the subpolar North Atlantic Ocean is investigated. Results from four experiments with different implementations of this coefficient are compared among themselves as well as with two control experiments. A series of improvements have been obtained in all of the experiments that use a low level of explicit horizontal tracer diffusion. These include a better representation of the overflow waters originating from the Nordic seas, leading to a more realistic deep western boundary current and to increased eddy activity in the deep ocean in the eastern North Atlantic. In the same experiments, the GM velocities “help” the Labrador Sea Water to spread from the deep convection region to the currents that surround it without incurring significant spurious diapycnal mixing. Thus, two classical pathways for the spreading of this water are established. Moreover, the simulated Labrador Current and the near-surface circulation in the eastern North Atlantic are in better agreement with flow patterns inferred from observations. The increased release of available potential energy obtained in the experiments with variable eddy transfer coefficients is responsible for the simulation of a flow that varies less in time. An overly strong countercurrent still occurs in the Labrador Sea in these experiments, and it has a negative impact on the pathway of the North Atlantic Current in the “Northwest Corner” and on the hydrography of the Labrador Sea. Nonetheless and overall, the use of the variable eddy transfer coefficient has led to better representations of the general circulation and hydrography in the subpolar North Atlantic.

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