scholarly journals Impact of ocean resolution on storms in the North Atlantic region

2021 ◽  
Author(s):  
Johanna Knauf ◽  
Joakim Kjellsson ◽  
Annika Reintges
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Storm Track ◽  
Life Time ◽  
Horizontal Resolution ◽  
Storm Tracks ◽  
Cold Bias ◽  
The North ◽  
Storm Tracking ◽  
The North Atlantic

<p>We study the impact of ocean horizontal resolution on storm tracks over the North Atlantic Ocean using the FOCI-OpenIFS climate model and the TRACK storm-tracking algorithm. We find that increasing ocean resolution from 1/2° to 1/10° reduces a cold bias over the North Atlantic which leads to a northward shift of the storm tracks, in particular in winter and spring seasons.<span> </span></p><p>Most climate models with non-eddying oceans, i.e. horizontal resolutions of 100 km or higher, suffer from a cold SST bias in the North Atlantic. Refining the horizontal resolution from 1/2° to 1/10° allows for a distinct Gulf Stream extension and better representation of the major current systems which reduces this cold bias. The associated warming of the ocean surface with increasing resolution also warms the troposphere and leads to a northward shift in the tropospheric eddy-driven jet. Overall, the increased ocean resolution thus improves the ocean circulation as well as the atmospheric circulation.<span> </span></p><p>We use two metrics to evaluate the storm track activity in the simulations. We calculate 2-8 day bandpass-filtered mean sea-level pressure (MSLP) and eddy heat flux (v’T’) which is an Eulerian metric that shows variability of low- and high-pressure systems as well as their associated heat flux, but says nothing about the genesis, lysis or life time of individual storms. We also use the TRACK storm-tracking algorithm with 12-hourly MSLP data to produce trajectories of individual storms, which allows us to study individual storms.<span> </span></p><p>The Eulerian approach using MSLP variance and eddy heat fluxes clearly shows a northward shift of the storm tracks as the ocean resolution is increased. Overall, the northward shift leads to reduced biases compared to ERA-Interim reanalysis. Storm-track trajectories show higher storm track and storm genesis densities around 60°N with the higher ocean resolution. Interestingly, a higher ocean resolution also results in longer life time of storms. We speculate that this is due to enhanced air-sea interactions where cyclones are fed more energy from the eddy-resolving ocean than from the non-eddying ocean.</p>

scholarly journals The Life Cycle of the North Atlantic Storm Track*

2015 ◽  
Vol 72 (2) ◽  
pp. 821-833 ◽  
Author(s):  
Lenka Novak ◽  
Maarten H. P. Ambaum ◽  
Rémi Tailleux
Keyword(s):  
Heat Flux ◽  
Life Cycle ◽  
North Atlantic ◽  
Storm Track ◽  
High Heat ◽  
High Heat Flux ◽  
Dominant Type ◽  
The North ◽  
Eddy Heat Flux ◽  
The North Atlantic

Abstract The North Atlantic eddy-driven jet exhibits latitudinal variability with evidence of three preferred latitudinal locations: south, middle, and north. Here the authors examine the drivers of this variability and the variability of the associated storm track. The authors investigate the changes in the storm-track characteristics for the three jet locations and propose a mechanism by which enhanced storm-track activity, as measured by upstream heat flux, is responsible for cyclical downstream latitudinal shifts in the jet. This mechanism is based on a nonlinear oscillator relationship between the enhanced meridional temperature gradient (and thus baroclinicity) and the meridional high-frequency (periods of shorter than 10 days) eddy heat flux. Such oscillations in baroclinicity and heat flux induce variability in eddy anisotropy, which is associated with the changes in the dominant type of wave breaking and a different latitudinal deflection of the jet. The authors’ results suggest that high heat flux is conducive to a northward deflection of the jet, whereas low heat flux is conducive to a more zonal jet. This jet-deflecting effect was found to operate most prominently downstream of the storm-track maximum, while the storm track and the jet remain anchored at a fixed latitudinal location at the beginning of the storm track. These cyclical changes in storm-track characteristics can be viewed as different stages of the storm track’s spatiotemporal life cycle.

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.

scholarly journals The Basic Ingredients of the North Atlantic Storm Track. Part I: Land–Sea Contrast and Orography

2009 ◽  
Vol 66 (9) ◽  
pp. 2539-2558 ◽  
Author(s):  
David James Brayshaw ◽  
Brian Hoskins ◽  
Michael Blackburn
Keyword(s):  
North Atlantic ◽  
Rocky Mountains ◽  
Large Scale ◽  
Storm Track ◽  
Storm Tracks ◽  
Cold Pool ◽  
North American Continent ◽  
The North ◽  
The North Atlantic ◽  
The Impact

Abstract Understanding and predicting changes in storm tracks over longer time scales is a challenging problem, particularly in the North Atlantic. This is due in part to the complex range of forcings (land–sea contrast, orography, sea surface temperatures, etc.) that combine to produce the structure of the storm track. The impact of land–sea contrast and midlatitude orography on the North Atlantic storm track is investigated through a hierarchy of GCM simulations using idealized and “semirealistic” boundary conditions in a high-resolution version of the Hadley Centre atmosphere model (HadAM3). This framework captures the large-scale essence of features such as the North and South American continents, Eurasia, and the Rocky Mountains, enabling the results to be applied more directly to realistic modeling situations than was possible with previous idealized studies. The physical processes by which the forcing mechanisms impact the large-scale flow and the midlatitude storm tracks are discussed. The characteristics of the North American continent are found to be very important in generating the structure of the North Atlantic storm track. In particular, the southwest–northeast tilt in the upper tropospheric jet produced by southward deflection of the westerly flow incident on the Rocky Mountains leads to enhanced storm development along an axis close to that of the continent’s eastern coastline. The approximately triangular shape of North America also enables a cold pool of air to develop in the northeast, intensifying the surface temperature contrast across the eastern coastline, consistent with further enhancements of baroclinicity and storm growth along the same axis.

scholarly journals The North Atlantic variability structure, storm tracks, and precipitation depending on the polar vortex strength

2004 ◽  
Vol 4 (5) ◽  
pp. 6127-6148 ◽  
Author(s):  
K. Walter ◽  
H.-F. Graf
Keyword(s):  
North Atlantic ◽  
Storm Track ◽  
Polar Vortex ◽  
The State ◽  
Storm Tracks ◽  
The Arctic ◽  
Ample Evidence ◽  
Vortex Strength ◽  
The North ◽  
The North Atlantic

Abstract. There is ample evidence that the state of the northern polar stratospheric vortex in boreal winter influences tropospheric variability. Therefore, the main teleconnection patterns over the North Atlantic are defined separately for winter episodes in which the zonal mean wind at 50 hPa and 65° N is above or below the critical Rossby velocity for zonal planetary wave one. It turns out that the teleconnection structure in the middle and upper troposphere differs considerably between the two regimes of the polar vortex, while this is not the case at sea level. If the "polar vortex is strong", there exists "one" meridional dipole structure of geopotential height in the upper and middle troposphere, which is situated in the central North Atlantic. If the "polar vortex is weak", there exist "two" such dipoles, one over the western and one over the eastern North Atlantic. Storm tracks (and precipitation related with these) are determined by mid and upper tropospheric conditions and we find significant differences of these parameters between the stratospheric regimes. For the strong polar vortex regime, in case of a negative upper tropospheric "NAO" index we find a blocking height situation over the Northeast Atlantic and the strongest storm track of all. It is reaching far north into the Arctic Ocean and has a secondary maximum over the Denmark Strait. Such storm track is not found in composites based on a classic NAO defined by surface pressure differences between the Icelandic Low and the Azores High. Our results show that it is essential to include the state of the upper dynamic boundary conditions (the polar vortex strength) in any study of the variability over the North Atlantic. Climate forecast based solely on the forecast of a "classic NAO" and further statistical downscaling may lead to the wrong conclusions if the state of the polar vortex is not considered as well.

Trends and characteristics of winter storms in CMIP6

2021 ◽  
Author(s):  
Mareike Schuster ◽  
Uwe Ulbrich
Keyword(s):  
Climate Change ◽  
North Atlantic ◽  
Life Time ◽  
Storm Tracks ◽  
The Arctic ◽  
Cmip5 Models ◽  
Atlantic Basin ◽  
North Atlantic Basin ◽  
The North ◽  
The North Atlantic

<p>Windstorms are considered the most devastating natural peril in many regions around the globe. For insurance associations in Europe for example, the damages generated by windstorms make up to about 90% of the claims in the category of natural hazards. The interannual variability of windstorms can be quite strong and thus research has recently focused on this topic.</p><p>However, storm risk and its changes under anthropogenically induced climate change are so far rather little discussed in literature. Thus, there are still large uncertainties about how climate change will affect the extratropical circulation. CMIP5 models showed at times opposing signals regarding number and strength of windstorm generating cyclones and storm tracks. In more detail, the latest IPCC AR5 states that substantial uncertainty and low confidence remains in projecting changes in NH storm tracks, especially for the North Atlantic basin.</p><p>With the lately released CMIP6 simulations, providing model output of increased spatial and temporal resolution, there is potential for new insights and enhanced confidence regarding future trends of storminess.</p><p>In our study, we assess characteristics and trends of windstorm diagnostics in an ensemble of the latest CMIP6 climate scenario simulations, with a focus to the North Atlantic basin and winterstorms affecting Europe.</p><p>In the CMIP6 model ensemble the trends of winter windstorm frequencies appear to be overall weaker in an anthropogenically changed climate than in the preceding CMIP5 scenarios; yet, first results indicate that they are somewhat more consistent amongst models. All CMIP6 models exhibit a windstorm frequency increase locally confined over the Arctic, while in the mid and high latitudes a wide-ranging decrease of windstorm activity is simulated. In our study we will also assess what this entails for characteristics like life time, intensity and size.</p>

scholarly journals The North Atlantic variability structure, storm tracks, and precipitation depending on the polar vortex strength

2005 ◽  
Vol 5 (1) ◽  
pp. 239-248 ◽  
Author(s):  
K. Walter ◽  
H.-F. Graf
Keyword(s):  
North Atlantic ◽  
Storm Track ◽  
Polar Vortex ◽  
The State ◽  
Storm Tracks ◽  
The Arctic ◽  
Boreal Winter ◽  
Vortex Strength ◽  
The North ◽  
The North Atlantic

Abstract. Motivated by the strong evidence that the state of the northern hemisphere vortex in boreal winter influences tropospheric variability, teleconnection patterns over the North Atlantic are defined separately for winter episodes where the zonal wind at 50hPa and 65° N is above or below the critical velocity for vertical propagation of zonal planetary wave 1. We argue that the teleconnection structure in the middle and upper troposphere differs considerably between the two regimes of the polar vortex, while this is not the case at sea level. If the polar vortex is strong, there exists one meridional dipole structure of geopotential height in the upper and middle troposphere, which is situated in the central North Atlantic. If the polar vortex is weak, there exist two such dipoles, one over the western and one over the eastern North Atlantic. Storm tracks (and precipitation related with these) are determined by mid and upper tropospheric conditions and we find significant differences of these parameters between the stratospheric regimes. For the strong polar vortex regime, in case of a negative upper tropospheric "NAO" index we find a blocking height situation over the Northeast Atlantic and the strongest storm track of all. It is reaching far north into the Arctic Ocean and has a secondary maximum over the Denmark Strait. Such storm track is not found in composites based on a classic NAO defined by surface pressure differences between the Icelandic Low and the Azores High. Our results suggest that it is important to include the state of the polar vortex strength in any study of the variability over the North Atlantic.

scholarly journals Changes in Northern Hemisphere Winter Storm Tracks under the Background of Arctic Amplification

2017 ◽  
Vol 30 (10) ◽  
pp. 3705-3724 ◽  
Author(s):  
Jiabao Wang ◽  
Hye-Mi Kim ◽  
Edmund K. M. Chang
Keyword(s):  
North America ◽  
North Atlantic ◽  
North Pacific ◽  
Storm Track ◽  
Storm Tracks ◽  
Arctic Amplification ◽  
Northeastern North America ◽  
The North ◽  
The North Atlantic ◽  
The North Pacific

Abstract An interdecadal weakening in the North Atlantic storm track (NAST) and a poleward shift of the North Pacific storm track (NPST) are found during October–March for the period 1979–2015. A significant warming of surface air temperature (Ts) over northeastern North America and a La Niña–like change in the North Pacific under the background of Arctic amplification are found to be the contributors to the observed changes in the NAST and the NPST, respectively, via modulation of local baroclinicity. The interdecadal change in baroclinic energy conversion is consistent with changes in storm tracks with an energy loss from eddies to mean flow over the North Atlantic and an energy gain over the North Pacific. The analysis of simulations from the Community Earth System Model Large Ensemble project, although with some biases in storm-track and Ts simulations, supports the observed relationship between the NAST and Ts over northeastern North America, as well as the link between the NPST and El Niño–Southern Oscillation. The near-future projections of Ts and storm tracks are characterized by a warmer planet under the influence of increasing greenhouse gases and a significant weakening of both the NAST and the NPST. The potential role of the NAST in redistributing changes in Ts over the surrounding regions is also examined. The anomalous equatorward moisture flux associated with the weakening trend of the NAST would enhance the warming over its upstream region and hinder the warming over its downstream region via modulation of the downward infrared radiation.

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.

Some physical drivers of changes in the winter storm tracks over the North Atlantic and Mediterranean during the Holocene

2010 ◽  
Vol 368 (1931) ◽  
pp. 5185-5223 ◽  
Author(s):  
David James Brayshaw ◽  
Brian Hoskins ◽  
Emily Black
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Storm Track ◽  
Storm Tracks ◽  
The Holocene ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
The Impact ◽  
Holocene Period

The winter climate of Europe and the Mediterranean is dominated by the weather systems of the mid-latitude storm tracks. The behaviour of the storm tracks is highly variable, particularly in the eastern North Atlantic, and has a profound impact on the hydroclimate of the Mediterranean region. A deeper understanding of the storm tracks and the factors that drive them is therefore crucial for interpreting past changes in Mediterranean climate and the civilizations it has supported over the last 12 000 years (broadly the Holocene period). This paper presents a discussion of how changes in climate forcing (e.g. orbital variations, greenhouse gases, ice sheet cover) may have impacted on the ‘basic ingredients’ controlling the mid-latitude storm tracks over the North Atlantic and the Mediterranean on intermillennial time scales. Idealized simulations using the HadAM3 atmospheric general circulation model (GCM) are used to explore the basic processes, while a series of timeslice simulations from a similar atmospheric GCM coupled to a thermodynamic slab ocean (HadSM3) are examined to identify the impact these drivers have on the storm track during the Holocene. The results suggest that the North Atlantic storm track has moved northward and strengthened with time since the Early to Mid-Holocene. In contrast, the Mediterranean storm track may have weakened over the same period. It is, however, emphasized that much remains still to be understood about the evolution of the North Atlantic and Mediterranean storm tracks during the Holocene period.

scholarly journals Simulated northern hemispheric storm tracks of the Eemian interglacial and the last glacial inception

2006 ◽  
Vol 2 (6) ◽  
pp. 1249-1276
Author(s):  
F. Kaspar ◽  
T. Spangehl ◽  
U. Cubasch
Keyword(s):  
North Atlantic ◽  
Storm Track ◽  
Storm Tracks ◽  
Strong Impact ◽  
Winter Storm ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
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 on the northern hemisphere. Here we analyze the simulated change in 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 strenghtened, 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. Opposite but weaker changes in storm track activity are simulated for 115 kyr BP.

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