scholarly journals Northern Hemisphere Extratropical Cyclones in a Warming Climate in the HiGEM High-Resolution Climate Model

2011 ◽  
Vol 24 (20) ◽  
pp. 5336-5352 ◽  
Author(s):  
Jennifer L. Catto ◽  
Len C. Shaffrey ◽  
Kevin I. Hodges
Keyword(s):  
Northern Hemisphere ◽  
North Atlantic ◽  
Storm Tracks ◽  
Cyclone Intensity ◽  
The North ◽  
Warming Climate ◽  
The Pacific ◽  
The North Atlantic ◽  
Mean Climate ◽  
Enhanced Surface

Abstract Changes to the Northern Hemisphere winter (December–February) extratropical storm tracks and cyclones in a warming climate are investigated. Two idealized climate change experiments with the High Resolution Global Environmental Model version 1.1 (HiGEM1.1), a doubled CO2 and a quadrupled CO2 experiment, are compared against a present-day control run. An objective feature tracking method is used and a focus is given to regional changes. The climatology of extratropical storm tracks from the control run is shown to be in good agreement with the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), while the frequency distribution of cyclone intensity also compares well. In both simulations the mean climate changes are generally consistent with the simulations of the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) models, with strongly enhanced surface warming at the winter pole and reduced lower-tropospheric warming over the North Atlantic Ocean associated with the slowdown of the meridional overturning circulation. The circulation changes in the North Atlantic are different between the two idealized simulations with different CO2 forcings. In the North Atlantic the storm tracks are influenced by the slowdown of the MOC, the enhanced surface polar warming, and the enhanced upper tropical-troposphere warming, giving a northeastward shift of the storm tracks in the 2 × CO2 experiment but no shift in the 4 × CO2 experiment. Over the Pacific, in the 2 × CO2 experiment, changes in the mean climate are associated with local temperature changes, while in the 4 × CO2 experiment the changes in the Pacific are impacted by the weakened tropical circulation. The storm-track changes are consistent with the shifts in the zonal wind. Total cyclone numbers are found to decrease over the Northern Hemisphere with increasing CO2 forcing. Changes in cyclone intensity are found using 850-hPa vorticity, mean sea level pressure, and 850-hPa winds. The intensity of the Northern Hemisphere cyclones is found to decrease relative to the control.

scholarly journals Northern hemisphere winter storm tracks of the Eemian interglacial and the last glacial inception

2007 ◽  
Vol 3 (2) ◽  
pp. 181-192 ◽  
Author(s):  
F. Kaspar ◽  
T. Spangehl ◽  
U. Cubasch
Keyword(s):  
Northern Hemisphere ◽  
North Atlantic ◽  
Storm Track ◽  
Storm Tracks ◽  
Winter Storm ◽  
The North ◽  
The North Atlantic ◽  
Hemisphere Winter ◽  
Eemian Interglacial ◽  
The Last Glacial

Abstract. Climate simulations of the Eemian interglacial and the last glacial inception have been performed by forcing a coupled ocean-atmosphere general circulation model with insolation patterns of these periods. The parameters of the Earth's orbit have been set to conditions of 125 000 and 115 000 years before present (yr BP). Compared to today, these dates represent periods with enhanced and weakened seasonality of insolation in the northern hemisphere. Here we analyse the simulated change in northern hemisphere winter storm tracks. The change in the orbital configuration has a strong impact on the meridional temperature gradients and therefore on strength and location of the storm tracks. The North Atlantic storm track is strengthened, shifted northward and extends further to the east in the simulation for the Eemian at 125 kyr BP. As one consequence, the northern parts of Europe experience an increase in winter precipitation. The frequency of winter storm days increases over large parts of the North Atlantic including the British Isles and the coastal zones of north-western Europe. Opposite but weaker changes in storm track activity are simulated for 115 kyr BP.

On the Role of Atmospheric Teleconnections in Climate

2008 ◽  
Vol 21 (12) ◽  
pp. 2990-3001 ◽  
Author(s):  
Anastasios A. Tsonis ◽  
Kyle L. Swanson ◽  
Geli Wang
Keyword(s):  
Northern Hemisphere ◽  
North Atlantic ◽  
Recent Application ◽  
The North ◽  
The Pacific ◽  
Atmospheric Teleconnections ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
The Tropics

Abstract In a recent application of networks to 500-hPa data, it was found that supernodes in the network correspond to major teleconnection. More specifically, in the Northern Hemisphere a set of supernodes coincides with the North Atlantic Oscillation (NAO) and another set is located in the area where the Pacific–North American (PNA) and the tropical Northern Hemisphere (TNH) patterns are found. It was subsequently suggested that the presence of atmospheric teleconnections make climate more stable and more efficient in transferring information. Here this hypothesis is tested by examining the topology of the complete network as well as of the networks without teleconnections. It is found that indeed without teleconnections the network becomes less stable and less efficient in transferring information. It was also found that the pattern chiefly responsible for this mechanism in the extratropics is the NAO. The other patterns are simply a linear response of the activity in the tropics and their role in this mechanism is inconsequential.

scholarly journals Impact of Freshwater Release in the North Atlantic under Different Climate Conditions in an OAGCM

2009 ◽  
Vol 22 (23) ◽  
pp. 6377-6403 ◽  
Author(s):  
Didier Swingedouw ◽  
Juliette Mignot ◽  
Pascale Braconnot ◽  
Eloi Mosquet ◽  
Masa Kageyama ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
North Atlantic ◽  
Freshwater Input ◽  
Climatic Response ◽  
Last Glacial ◽  
The North ◽  
The Mean ◽  
The North Atlantic ◽  
Mean Climate ◽  
Freshwater Release

Abstract The response of climate to freshwater input in the North Atlantic (NA) has raised a lot of concern about the issue of climate stability since the discovery of abrupt coolings during the last glacial period. Such coolings have usually been related to a weakening of the Atlantic meridional overturning circulation (AMOC), probably associated with massive iceberg surges or meltwater pulses. Additionally, the recent increase in greenhouse gases in the atmosphere has also raised the possibility of a melting of the Greenland ice sheet, which may impact the future AMOC, and thereby the climate. In this study, the extent to which the mean climate influences the freshwater release linked to ice sheet melting in the NA and the associated climatic response is explored. For this purpose the simulations of several climatic states [last interglacial, Last Glacial Maximum, mid-Holocene, preindustrial, and future (2 × CO2)] are considered, and the climatic response to a freshwater input computed interactively according to a surface heat flux budget over the ice sheets is analyzed. It is shown that the AMOC response is not linear with the freshwater input and depends on the mean climate state. The climatic responses to these different AMOC changes share qualitative similarities for the general picture, notably a cooling in the Northern Hemisphere and a southward shift of the intertropical convergence zone (ITCZ) in the Atlantic and across the Panama Isthmus. The cooling in the Northern Hemisphere is related to the sea ice cover response, which strongly depends on the responses of the atmospheric circulation, the local oceanic heat transport, and the density threshold of the oceanic convection sites. These feedbacks and the magnitude of temperature and precipitation changes outside the North Atlantic depend on the mean climate.

scholarly journals Further Investigation of the Impact of Idealized Continents and SST Distributions on the Northern Hemisphere Storm Tracks

2012 ◽  
Vol 69 (3) ◽  
pp. 840-856 ◽  
Author(s):  
Jérôme Saulière ◽  
David James Brayshaw ◽  
Brian Hoskins ◽  
Michael Blackburn
Keyword(s):  
Boundary Conditions ◽  
North Atlantic ◽  
North Pacific ◽  
Rossby Waves ◽  
Storm Track ◽  
Storm Tracks ◽  
The North ◽  
The Pacific ◽  
The North Atlantic ◽  
The Impact

Abstract Building on previous studies of the basic ingredients of the North Atlantic storm track (examining land–sea contrast, orography, and SST), this article investigates the impact of Eurasian topography and Pacific SST anomalies on North Pacific and Atlantic storm tracks through a hierarchy of atmospheric GCM simulations using idealized boundary conditions in the Hadley Centre HadGAM1 atmospheric circulation model. The Himalaya–Tibet mountain complex is found to play a crucial role in shaping the North Pacific storm track. The northward deflection of the westerly flow around northern Tibet generates an extensive pool of very cold air in the northeastern tip of the Asian continent, which strengthens the meridional temperature gradient and favors baroclinic growth in the western Pacific. The Kuroshio SST front is also instrumental in strengthening the Pacific storm track through its impact on near-surface baroclinicity, while the warm waters around Indonesia tend to weaken it through the impact on baroclinicity of stationary Rossby waves propagating poleward from the convective heating regions. Three mechanisms by which the Atlantic storm track may be affected by changes in the boundary conditions upstream of the Rockies are discussed. In the model configuration used here, stationary Rossby waves emanating from Tibet appear to weaken the North Atlantic storm track substantially, whereas those generated over the cold waters off Peru appear to strengthen it. Changes in eddy-driven surface winds over the Pacific generally appear to modify the flow over the Rocky Mountains, leading to consistent modifications in the Atlantic storm track. The evidence for each of these mechanisms is, however, ultimately equivocal in these simulations.

scholarly journals North Atlantic warming over six decades drives decreases in krill abundance with no associated range shift

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Martin Edwards ◽  
Pierre Hélaouët ◽  
Eric Goberville ◽  
Alistair Lindley ◽  
Geraint A. Tarling ◽  
...  
Keyword(s):  
North Atlantic ◽  
Range Shift ◽  
The Core ◽  
Krill Abundance ◽  
The North ◽  
Living Space ◽  
Warming Climate ◽  
Two Temperatures ◽  
The North Atlantic

AbstractIn the North Atlantic, euphausiids (krill) form a major link between primary production and predators including commercially exploited fish. This basin is warming very rapidly, with species expected to shift northwards following their thermal tolerances. Here we show, however, that there has been a 50% decline in surface krill abundance over the last 60 years that occurred in situ, with no associated range shift. While we relate these changes to the warming climate, our study is the first to document an in situ squeeze on living space within this system. The warmer isotherms are shifting measurably northwards but cooler isotherms have remained relatively static, stalled by the subpolar fronts in the NW Atlantic. Consequently the two temperatures defining the core of krill distribution (7–13 °C) were 8° of latitude apart 60 years ago but are presently only 4° apart. Over the 60 year period the core latitudinal distribution of euphausiids has remained relatively stable so a ‘habitat squeeze’, with loss of 4° of latitude in living space, could explain the decline in krill. This highlights that, as the temperature warms, not all species can track isotherms and shift northward at the same rate with both losers and winners emerging under the ‘Atlantification’ of the sub-Arctic.

The North Atlantic anchor: Canada and the Pacific Century

2018 ◽  
Vol 73 (3) ◽  
pp. 364-378 ◽  
Author(s):  
Kim Richard Nossal
Keyword(s):  
North Atlantic ◽  
Policy Making ◽  
International Order ◽  
Asia Pacific ◽  
The North ◽  
The Pacific ◽  
Defence Policy ◽  
Key Driver ◽  
The North Atlantic ◽  
Strategic Perspective

This paper surveys Canada’s ambivalence towards the Asia Pacific, and seeks to put that ambivalence into the broader context of the dominant strategic perspective in Canada that has privileged, and continues to privilege, a North Atlantic focus for Canadian foreign and defence policy. It argues that Canada’s laggardly approach to Asia Pacific diplomacy can be best explained by the widespread perception among Canadians—and their government—that the North Atlantic alliance should remain the key driver of Canadian foreign and defence policy. Indeed, this geostrategic outlook has actually intensified with the election of Donald J. Trump and his unorthodox approach to the transatlantic alliance and the liberal international order. I argue that this North Atlantic outlook, so dominant for so much of Canada’s history, will continue to anchor Canadian foreign and defence policy, making Canada’s engagement in the Asia Pacific more problematic.

scholarly journals Understanding Bjerknes Compensation in Meridional Heat Transports and the Role of Freshwater in a Warming Climate

2018 ◽  
Vol 31 (12) ◽  
pp. 4791-4806 ◽  
Author(s):  
Qianzi Yang ◽  
Yingying Zhao ◽  
Qin Wen ◽  
Jie Yao ◽  
Haijun Yang
Keyword(s):  
Global Warming ◽  
North Atlantic ◽  
Coupled Model ◽  
Phase Changes ◽  
Box Model ◽  
Freshwater Flux ◽  
The North ◽  
Warming Climate ◽  
Transient Period ◽  
The North Atlantic

The Bjerknes compensation (BJC) under global warming is studied using a simple box model and a coupled Earth system model. The BJC states the out-of-phase changes in the meridional atmosphere and ocean heat transports. Results suggest that the BJC can occur during the transient period of global warming. During the transient period, the sea ice melting in the high latitudes can cause a significant weakening of the Atlantic meridional overturning circulation (AMOC), resulting in a cooling in the North Atlantic. The meridional contrast of sea surface temperature would be enhanced, and this can eventually enhance the Hadley cell and storm-track activities in the Northern Hemisphere. Accompanied by changes in both ocean and atmosphere circulations, the northward ocean heat transport in the Atlantic is decreased while the northward atmosphere heat transport is increased, and the BJC occurs in the Northern Hemisphere. Once the freshwater influx into the North Atlantic Ocean stops, or the ocean even loses freshwater because of strong heating in the high latitudes, the AMOC would recover. Both the atmosphere and ocean heat transports would be enhanced, and they can eventually recover to the state of the control run, leading to the BJC to become invalid. The above processes are clearly demonstrated in the coupled model CO2 experiment. Since it is difficult to separate the freshwater effect from the heating effect in the coupled model, a simple box model is used to understand the BJC mechanism and freshwater’s role under global warming. In a warming climate, the freshwater flux into the ocean can cool the global surface temperature, mitigating the temperature rise. Box model experiments indicate clearly that it is the freshwater flux into the North Atlantic that causes out-of-phase changes in the atmosphere and ocean heat transports, which eventually plays a stabilizing role in global climate change.

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