Atlantic multi-centennial variability in IPSL-CM6A-LR climate model

2021 ◽  
Author(s):  
Weimin Jiang ◽  
Guillaume Gastineau ◽  
Francis Codron
Keyword(s):  
Sea Ice ◽  
Climate Model ◽  
Barents Sea ◽  
Deep Convection ◽  
Coupled Model ◽  
Lower Troposphere ◽  
Arctic Sea Ice ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Surface Salinity

<p>A pronounced multi-centennial variability of the Atlantic meridional overturning circulation (AMOC) is found to be regulated by the salinity exchanges between the Atlantic and Arctic ocean in the IPSL-CM6A-LR atmosphere-ocean coupled model. The AMOC variations are preceded by salinity-driven density anomalies in the main deep convection sites in the Labrador and Greenland seas. Associated with a strong AMOC, the Arctic sea ice export through the Fram Strait reduces due to the decreased sea ice volume and anomalous northward currents. Anomalous freshwater hence accumulates at the surface in the Central Arctic. Meanwhile, the enhanced Atlantic inflow enters the Arctic through the Barents Sea and leads to a positive salinity in the Eastern Arctic subsurface. The surface freshwater anomalies last for 4 to 5 decades before they eventually reach the Lincoln Sea north of Greenland. The associated oceanic currents around Greenland reorganize, favoring the anomalous Arctic freshwater export to the North Atlantic and intensifying the stratification in deep convection sites. The AMOC then weakens, and the Central Arctic presents a positive surface salinity anomaly in turn. The oscillation switches to the opposite phase. These AMOC and sea ice fluctuations modulate climate worldwide, with a strong AMOC leading to a warming of 0.4°C in the northern extratropics, reaching up to 1°C in the Arctic lower troposphere during winter. In all seasons, a northward displacement of the intertropical convergence zone is also simulated.</p>

Centennial variability driven by salinity exchanges between the Atlantic and Arctic in a coupled climate model

2020 ◽  
Author(s):  
Weimin Jiang ◽  
Guillaume Gastineau ◽  
Francis Codron
Keyword(s):  
Sea Ice ◽  
Climate Model ◽  
Barents Sea ◽  
Coupled Model ◽  
Arctic Sea Ice ◽  
Meridional Overturning Circulation ◽  
Salt Transport ◽  
The Arctic ◽  
Surface Salinity ◽  
Sea Ice Extent

<p>The centennial to multi-centennial variability of the Atlantic Meridional Overturning Circulation (AMOC) is studied in a 1200-yr pre-industrial control simulation of the IPSL-CM6-LR atmosphere-ocean coupled model. In this run, a spectrum analysis finds a periodicity of the low-frequency variability of AMOC, with a period of about 200-year. This variability alters the Northern Hemisphere climate over the land and modulates the Arctic sea ice extent and volume. The associated density variations show large positive (negative) salinity-driven density anomalies in the Nordic Seas and subpolar gyre associated with a strong (week) AMOC state. The positive salinity anomalies in the Greenland Sea are found to be generated by anomalous southward salinity transport in the Fram Straits. The gradual AMOC increase and the associated oceanic northward heat transport melt the sea ice in the Arctic and build shallow negative salinity anomalies in the central Arctic. In parallel, the AMOC is also associated with a northward salt transport into the Eastern Arctic, by an inflow of Atlantic water from the Barents Sea to the East Siberian Ocean. The accumulated surface freshwater in the central Arctic is ultimately exported into the Atlantic mainly through the Fram Strait via intensified East Greenland Current, lowering the upper ocean density and enhancing the stratification at the regions where the cold deep limb of AMOC is formed. The positive salinity anomalies at subsurface then slowly reach the surface though diffusion, increasing the surface salinity. The oscillation then turns into the opposite phase.</p>

scholarly journals The Mechanisms of the Atlantic Meridional Overturning Circulation Slowdown Induced by Arctic Sea Ice Decline

2019 ◽  
Vol 32 (4) ◽  
pp. 977-996 ◽  
Author(s):  
Wei Liu ◽  
Alexey Fedorov ◽  
Florian Sévellec
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Deep Convection ◽  
Arctic Sea Ice ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
The North ◽  
Arctic Sea ◽  
Meridional Overturning ◽  
The North Atlantic

We explore the mechanisms by which Arctic sea ice decline affects the Atlantic meridional overturning circulation (AMOC) in a suite of numerical experiments perturbing the Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next ~100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in anomalous positive heat and salinity fluxes in the subpolar North Atlantic, inducing positive temperature and salinity anomalies over the regions of oceanic deep convection. At first, these anomalies largely compensate one another, leading to a minimal change in upper ocean density and deep convection in the North Atlantic. Over the following years, however, more anomalous warm water accumulates in the Arctic and spreads to the North Atlantic. At the same time, freshwater that accumulates from seasonal sea ice melting over most of the upper Arctic Ocean also spreads southward, reaching as far as south of Iceland. These warm and fresh anomalies reduce upper ocean density and suppress oceanic deep convection. The thermal and haline contributions to these buoyancy anomalies, and therefore to the AMOC slowdown during this period, are found to have similar magnitudes. We also find that the related changes in horizontal wind-driven circulation could potentially push freshwater away from the deep convection areas and hence strengthen the AMOC, but this effect is overwhelmed by mean advection.

scholarly journals Mechanisms causing reduced Arctic sea ice loss in a coupled climate model

2013 ◽  
Vol 7 (2) ◽  
pp. 555-567 ◽  
Author(s):  
A. E. West ◽  
A. B. Keen ◽  
H. T. Hewitt
Keyword(s):  
Sea Ice ◽  
Climate Model ◽  
Historical Record ◽  
Arctic Sea Ice ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Slight Reduction ◽  
Coupled Climate Model ◽  
Ice Melt ◽  
Arctic Sea

Abstract. The fully coupled climate model HadGEM1 produces one of the most accurate simulations of the historical record of Arctic sea ice seen in the IPCC AR4 multi-model ensemble. In this study, we examine projections of sea ice decline out to 2030, produced by two ensembles of HadGEM1 with natural and anthropogenic forcings included. These ensembles project a significant slowing of the rate of ice loss to occur after 2010, with some integrations even simulating a small increase in ice area. We use an energy budget of the Arctic to examine the causes of this slowdown. A negative feedback effect by which rapid reductions in ice thickness north of Greenland reduce ice export is found to play a major role. A slight reduction in ocean-to-ice heat flux in the relevant period, caused by changes in the meridional overturning circulation (MOC) and subpolar gyre in some integrations, as well as freshening of the mixed layer driven by causes other than ice melt, is also found to play a part. Finally, we assess the likelihood of a slowdown occurring in the real world due to these causes.

scholarly journals Investigating future changes in the volume budget of the Arctic sea ice in a coupled climate model

2017 ◽  
Author(s):  
Ann Keen ◽  
Ed Blockley
Keyword(s):  
Sea Ice ◽  
21St Century ◽  
Climate Model ◽  
Coupled Model ◽  
Ice Cover ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Ice Melt ◽  
Arctic Sea ◽  
Projected Changes

Abstract. We consider the volume budget of the Arctic sea ice in the CMIP5 global coupled model HadGEM2-ES, and evaluate how the budget components evolve during the 21st century under a range of different forcing scenarios. As the climate warms and the ice cover declines, the Arctic sea ice processes that change the most in HadGEM2-ES are summer melting at the top surface of the ice, and basal melting due to extra heat from the warming ocean. However, the declining ice cover affects how much impact these changes have on the ice volume budget, where the biggest contribution to Arctic ice decline is the reduction in the total amount of basal ice formation during the autumn and early winter. This highlights the importance of taking the declining ice area into account when evaluating projected changes in the sea ice budget, especially if comparing models with very different rates of decline. Changes in the volume budget during the 21st century have a distinctive seasonal cycle, with processes contributing to ice decline occurring in May/June and September to November. During July and August the total amount of sea ice melt decreases, due to the reducing ice cover. The choice of forcing scenario affects the rate of ice decline and the timing and magnitude of changes in the volume budget components, but for the HadGEM2-ES model and for the range of scenarios considered for CMIP5, the mean changes in the volume budget depend on the evolving ice area, and are independent of the speed at which the ice cover declines.

The Transient and Equilibrium Response of the AMOC to Arctic sea decline in a coupled model.

2021 ◽  
Author(s):  
Amelie Simon ◽  
Brady Ferster ◽  
Alexey Fedorov ◽  
Juliette Mignot ◽  
Eric Guilyardi
Keyword(s):  
Climate Change ◽  
Sea Ice ◽  
General Circulation ◽  
Initial Conditions ◽  
Coupled Model ◽  
Arctic Sea Ice ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Arctic Sea ◽  
The Impact

<p>Since the mid-20th century, the Arctic has experienced two major impacts of climate change: a warming at a faster rate than the global mean surface temperature and a reduction of both winter and summer sea ice cover. However, the impact of the Arctic sea ice loss on global climate remains under debate, in particular the impact on the Atlantic meridional overturning circulation (AMOC). Specifically, some studies find that in response to Arctic sea ice decline, the AMOC weakens on multi-decadal timescales, reaching a new equilibrium state with a significantly reduced AMOC, while others studies see a weak AMOC reduction followed by a partial or full recovery. To further investigate the impact of sea ice loss on the climate, ensemble simulations are performed with the coupled atmosphere-ocean general circulation model CM5A2 from the Insitut Pierre Simon Laplace (IPSL-CM5A2). To induce the change in sea ice, the Arctic sea ice albedo is reduced by about 23%, previously shown to be consistent with the sea ice changes expected to occur by approximately the year 2040. The experimental design compares the response to sea ice loss starting from AMOC minimum and neutral phases, respectively. The objective of our experiment is to further investigate the AMOC-sea ice relationship in the transient and equilibrium responses to decreased sea ice and the robustness within a coupled model. The initial 30-year response results in similar spatial patterns in sea ice volume and 500mb potential height responses (inducing a negative NAO-like pattern) for both types of initial conditions. In both cases, the AMOC reduces by 0.5 to 1.5Sv Sv (about 15% of the model mean AMOC) during the first ~100 years of the experiment. Yet, there are differences in the response depending on the AMOC initial state, for example, in the magnitude and timing of the AMOC reduction. The AMOC eventually recover towards years 151-200. Our results give insight into the importance of decadal variability for anticipating the response of the next decades to climate change, as well as improves the understanding of the long-term transient and equilibrium responses between AMOC and Arctic sea ice.</p>

scholarly journals Simulation of observed climate changes in 1850–2014 with climate model INM-CM5

2018 ◽  
Author(s):  
Evgeny Volodin ◽  
Andrey Gritsun
Keyword(s):  
Sea Ice ◽  
Surface Temperature ◽  
Climate Changes ◽  
Climate Model ◽  
Coupled Model ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Arctic Sea ◽  
Arctic Sea Ice Loss ◽  
Global Mean

Abstract. Climate changes observed in 1850-2014 are modeled and studied on the basis of seven historical runs with the climate model INM-CM5 under the scenario proposed for Coupled Model Intercomparison Project, Phase 6 (CMIP6). In all runs global mean surface temperature rises by 0.8 K at the end of the experiment (2014) in agreement with the observations. Periods of fast warming in 1920–1940 and 1980–2000 as well as its slowdown in 1950–1975 and 2000–2014 are correctly reproduced by the ensemble mean. The notable change here with respect to the CMIP5 results is correct reproduction of the slowdown of global warming in 2000–2014 that we attribute to more accurate description of the Solar constant in CMIP6 protocol. The model is able to reproduce correct behavior of global mean temperature in 1980–2014 despite incorrect phases of the Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation indices in the majority of experiments. The Arctic sea ice loss in recent decades is reasonably close to the observations just in one model run; the model underestimates Arctic sea ice loss by the factor 2.5. Spatial pattern of model mean surface temperature trend during the last 30 years looks close the one for the ERA Interim reanalysis. Model correctly estimates the magnitude of stratospheric cooling.

scholarly journals Observation-based selection of climate models projects Arctic ice-free summers around 2035

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
David Docquier ◽  
Torben Koenigk
Keyword(s):  
Model Selection ◽  
Sea Ice ◽  
Climate Models ◽  
Global Climate ◽  
Coupled Model ◽  
Arctic Sea Ice ◽  
Global Climate Models ◽  
The Arctic ◽  
Arctic Sea ◽  
Area And Volume

AbstractArctic sea ice has been retreating at an accelerating pace over the past decades. Model projections show that the Arctic Ocean could be almost ice free in summer by the middle of this century. However, the uncertainties related to these projections are relatively large. Here we use 33 global climate models from the Coupled Model Intercomparison Project 6 (CMIP6) and select models that best capture the observed Arctic sea-ice area and volume and northward ocean heat transport to refine model projections of Arctic sea ice. This model selection leads to lower Arctic sea-ice area and volume relative to the multi-model mean without model selection and summer ice-free conditions could occur as early as around 2035. These results highlight a potential underestimation of future Arctic sea-ice loss when including all CMIP6 models.

scholarly journals Polar cod in jeopardy under the retreating Arctic sea ice

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Mats Brockstedt Olsen Huserbråten ◽  
Elena Eriksen ◽  
Harald Gjøsæter ◽  
Frode Vikebø
Keyword(s):  
Sea Ice ◽  
Barents Sea ◽  
Keystone Species ◽  
Ice Cover ◽  
Arctic Sea Ice ◽  
Biophysical Model ◽  
The Arctic ◽  
Polar Cod ◽  
Arctic Sea ◽  
Shelf Sea

Abstract The Arctic amplification of global warming is causing the Arctic-Atlantic ice edge to retreat at unprecedented rates. Here we show how variability and change in sea ice cover in the Barents Sea, the largest shelf sea of the Arctic, affect the population dynamics of a keystone species of the ice-associated food web, the polar cod (Boreogadus saida). The data-driven biophysical model of polar cod early life stages assembled here predicts a strong mechanistic link between survival and variation in ice cover and temperature, suggesting imminent recruitment collapse should the observed ice-reduction and heating continue. Backtracking of drifting eggs and larvae from observations also demonstrates a northward retreat of one of two clearly defined spawning assemblages, possibly in response to warming. With annual to decadal ice-predictions under development the mechanistic physical-biological links presented here represent a powerful tool for making long-term predictions for the propagation of polar cod stocks.

Subpolar Gyre – AMOC – Atmosphere Interactions on Multidecadal Timescales in a Version of the Kiel Climate Model

2021 ◽  
Author(s):  
Jing Sun ◽  
Mojib Latif ◽  
Wonsun Park
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Deep Convection ◽  
Meridional Overturning Circulation ◽  
Subpolar Gyre ◽  
Surface Salinity ◽  
The North ◽  
Ocean Coupling ◽  
Meridional Overturning ◽  
The North Atlantic

<p>There is a controversy about the nature of multidecadal climate variability in the North Atlantic (NA) region, concerning the roles of ocean circulation and atmosphere-ocean coupling. Here we describe NA multidecadal variability from a version of the Kiel Climate Model, in which both subpolar gyre (SPG)-Atlantic Meridional Overturning Circulation (AMOC) and atmosphere-ocean coupling are essential. The oceanic barotropic streamfuntions, meridional overturning streamfunctions, and sea level pressure are jointly analyzed to derive the leading mode of Atlantic variability. This mode accounting for about 23.7 % of the total combined variance is oscillatory with an irregular periodicity of 25-50 years and an e-folding time of about a decade. SPG and AMOC mutually influence each other and together provide the delayed negative feedback necessary for maintaining the oscillation. An anomalously strong SPG, for example, drives higher surface salinity and density in the NA’s sinking region. In response, oceanic deep convection and AMOC intensify, which, with a time delay of about a decade, reduces SPG strength by enhancing upper-ocean heat content. The weaker gyre circulation leads to lower surface salinity and density in the sinking region, which eventually reduces deep convection and AMOC strength. There is a positive ocean-atmosphere feedback between the sea surface temperature and low-level atmospheric circulation over the Southern Greenland area, with related wind stress changes reinforcing SPG changes, thereby maintaining the (damped) multidecadal oscillation against dissipation. Stochastic surface heat-flux forcing associated with the North Atlantic Oscillation drives the eigenmode.</p>

Mechanisms for and Predictability of a Drastic Reduction in the Arctic Sea Ice: APPOSITE Data with Climate Model MIROC

2019 ◽  
Vol 32 (5) ◽  
pp. 1361-1380 ◽  
Author(s):  
J. Ono ◽  
H. Tatebe ◽  
Y. Komuro
Keyword(s):  
Sea Ice ◽  
Climate Model ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Ensemble Prediction ◽  
Forecast Errors ◽  
Drastic Reduction ◽  
Sea Ice Concentration ◽  
Sea Ice Extent ◽  
Arctic Sea

Abstract The mechanisms for and predictability of a drastic reduction in the Arctic sea ice extent (SIE) are investigated using the Model for Interdisciplinary Research on Climate (MIROC) version 5.2. Here, a control (CTRL) with forcing fixed at year 2000 levels and perfect-model ensemble prediction (PRED) experiments are conducted. In CTRL, three (model years 51, 56, and 57) drastic SIE reductions occur during a 200-yr-long integration. In year 56, the sea ice moves offshore in association with a positive phase of the summer Arctic dipole anomaly (ADA) index and melts due to heat input through the increased open water area, and the SIE drastically decreases. This provides the preconditioning for the lowest SIE in year 57 when the Arctic Ocean interior is in a warm state and the spring sea ice volume has a large negative anomaly due to drastic ice reduction in the previous year. Although the ADA is one of the key mechanisms behind sea ice reduction, it does not always cause a drastic reduction. Our analysis suggests that wind direction favoring offshore ice motion is a more important factor for drastic ice reduction events. In years experiencing drastic ice reduction events, the September SIE can be skillfully predicted in PRED started from July, but not from April. This is because the forecast errors for the July sea level pressure and those for the sea ice concentration and sea ice thickness along the ice edge are large in PRED started from April.

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