scholarly journals A Multimodel Assessment of Future Projections of North Atlantic and European Extratropical Cyclones in the CMIP5 Climate Models*

2013 ◽  
Vol 26 (16) ◽  
pp. 5846-5862 ◽  
Author(s):  
Giuseppe Zappa ◽  
Len C. Shaffrey ◽  
Kevin I. Hodges ◽  
Phil G. Sansom ◽  
David B. Stephenson
Keyword(s):  
Central Europe ◽  
North Atlantic ◽  
Climate Models ◽  
Storm Track ◽  
Coupled Model ◽  
Extratropical Cyclones ◽  
Strong Wind ◽  
Wind Speeds ◽  
High Emission ◽  
Strong Winds

Abstract The response of North Atlantic and European extratropical cyclones to climate change is investigated in the climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5). In contrast to previous multimodel studies, a feature-tracking algorithm is here applied to separately quantify the responses in the number, the wind intensity, and the precipitation intensity of extratropical cyclones. Moreover, a statistical framework is employed to formally assess the uncertainties in the multimodel projections. Under the midrange representative concentration pathway (RCP4.5) emission scenario, the December–February (DJF) response is characterized by a tripolar pattern over Europe, with an increase in the number of cyclones in central Europe and a decreased number in the Norwegian and Mediterranean Seas. The June–August (JJA) response is characterized by a reduction in the number of North Atlantic cyclones along the southern flank of the storm track. The total number of cyclones decreases in both DJF (−4%) and JJA (−2%). Classifying cyclones according to their intensity indicates a slight basinwide reduction in the number of cyclones associated with strong winds, but an increase in those associated with strong precipitation. However, in DJF, a slight increase in the number and intensity of cyclones associated with strong wind speeds is found over the United Kingdom and central Europe. The results are confirmed under the high-emission RCP8.5 scenario, where the signals tend to be larger. The sources of uncertainty in these projections are discussed.

scholarly journals The Ability of CMIP5 Models to Simulate North Atlantic Extratropical Cyclones*

2013 ◽  
Vol 26 (15) ◽  
pp. 5379-5396 ◽  
Author(s):  
Giuseppe Zappa ◽  
Len C. Shaffrey ◽  
Kevin I. Hodges
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Climate Models ◽  
Storm Track ◽  
Coupled Model ◽  
Cmip5 Models ◽  
Extratropical Cyclones ◽  
The North ◽  
Systematic Biases ◽  
The North Atlantic

Abstract The ability of the climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) to simulate North Atlantic extratropical cyclones in winter [December–February (DJF)] and summer [June–August (JJA)] is investigated in detail. Cyclones are identified as maxima in T42 vorticity at 850 hPa and their propagation is tracked using an objective feature-tracking algorithm. By comparing the historical CMIP5 simulations (1976–2005) and the ECMWF Interim Re-Analysis (ERA-Interim; 1979–2008), the authors find that systematic biases affect the number and intensity of North Atlantic cyclones in CMIP5 models. In DJF, the North Atlantic storm track tends to be either too zonal or displaced southward, thus leading to too few and weak cyclones over the Norwegian Sea and too many cyclones in central Europe. In JJA, the position of the North Atlantic storm track is generally well captured but some CMIP5 models underestimate the total number of cyclones. The dynamical intensity of cyclones, as measured by either T42 vorticity at 850 hPa or mean sea level pressure, is too weak in both DJF and JJA. The intensity bias has a hemispheric character, and it cannot be simply attributed to the representation of the North Atlantic large-scale atmospheric state. Despite these biases, the representation of Northern Hemisphere (NH) storm tracks has improved since CMIP3 and some CMIP5 models are able of representing well both the number and the intensity of North Atlantic cyclones. In particular, some of the higher-atmospheric-resolution models tend to have a better representation of the tilt of the North Atlantic storm track and of the intensity of cyclones in DJF.

scholarly journals The response of the Northern Hemisphere storm tracks and jetstreams to climate change in the CMIP3, CMIP5, and CMIP6 climate models

2020 ◽  
Author(s):  
Ben Harvey ◽  
Peter Cook ◽  
Len Shaffrey ◽  
Reinhard Schiemann
Keyword(s):  
Climate Change ◽  
Spatial Pattern ◽  
North Atlantic ◽  
Climate Models ◽  
Climate Model ◽  
Storm Track ◽  
Coupled Model ◽  
Storm Tracks ◽  
Cmip5 Models ◽  
Jet Streams

<p>Understanding and predicting how extratropical cyclones might respond to climate change is essential for assessing future weather risks and informing climate change adaptation strategies. Climate model simulations provide a vital component of this assessment, with the caveat that their representation of the present-day climate is adequate. In this study the representation of the NH storm tracks and jet streams and their responses to climate change are evaluated across the three major phases of the Coupled Model Intercomparison Project: CMIP3 (2007), CMIP5 (2012), and CMIP6 (2019). The aim is to quantity how present-day biases in the NH storm tracks and jet streams have evolved with model developments, and to further our understanding of their responses to climate change.</p><p>The spatial pattern of the present-day biases in CMIP3, CMIP5, and CMIP6 are similar. However, the magnitude of the biases in the CMIP6 models is substantially lower in the DJF North Atlantic storm track and jet stream than in the CMIP3 and CMIP5 models. In summer, the biases in the JJA North Atlantic and North Pacific storm tracks are also much reduced in the CMIP6 models. Despite this, the spatial pattern of the climate change response in the NH storm tracks and jet streams are similar across the CMIP3, CMIP5, and CMIP6 ensembles. The SSP2-4.5 scenario responses in the CMIP6 models are substantially larger than in the corresponding RCP4.5 CMIP5 models, consistent with the larger climate sensitivities of the CMIP6 models compared to CMIP5.</p>

scholarly journals Sting-Jet Windstorms over the North Atlantic: Climatology and Contribution to Extreme Wind Risk

2017 ◽  
Vol 30 (14) ◽  
pp. 5455-5471 ◽  
Author(s):  
Neil C. G. Hart ◽  
Suzanne L. Gray ◽  
Peter A. Clark
Keyword(s):  
North Atlantic ◽  
Storm Track ◽  
Relative Vorticity ◽  
Strong Wind ◽  
Socioeconomic Impacts ◽  
Wind Speeds ◽  
The North ◽  
Extreme Wind ◽  
Strong Surface ◽  
Wind Events

Extratropical cyclones with damaging winds can have large socioeconomic impacts when they make landfall. During the last decade, studies have identified a mesoscale transient jet, the sting jet, that descends from the tip of the hooked cloud head toward the top of the boundary layer in the dry intrusion region as a cause of strong surface winds, and especially gusts, in some cyclones. While many case studies have focused on the dynamics and characteristics of these jets, there have been few studies that assess the climatology of the associated cyclones and their importance for wind risk. Here the climatological characteristics of North Atlantic cyclones are determined in terms of the possibility that they had sting jets using a previously published sting-jet precursor diagnostic applied to ERA-Interim data over 32 extended winter seasons from 1979 to 2012. Of the 5447 cyclones tracked, 32% had the precursor (42% in the 22% of cyclones that developed explosively). Precursor storms have a more southerly and zonal storm track than storms without the precursor, and precursor storms tend to be more intense as defined by 850-hPa relative vorticity. This study also shows that precursor storms are the dominant cause of cyclone-related resolved strong wind events over the British Isles for 850-hPa wind speeds exceeding 30 m s−1. Hence, early detection of a sting-jet storm could give advance warning of enhanced wind risk. However, over continental northwestern Europe, precursor cyclone-related windstorm events occur far less often.

scholarly journals Projected Changes in European and North Atlantic Seasonal Wind Climate Derived from CMIP5 Simulations

2019 ◽  
Vol 32 (19) ◽  
pp. 6467-6490 ◽  
Author(s):  
Kimmo Ruosteenoja ◽  
Timo Vihma ◽  
Ari Venäläinen
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
Global Climate ◽  
Arctic Sea Ice ◽  
Global Climate Models ◽  
Near Surface ◽  
Wind Speeds ◽  
The North ◽  
Seasonal Wind ◽  
Projected Changes

Abstract Future changes in geostrophic winds over Europe and the North Atlantic region were studied utilizing output data from 21 CMIP5 global climate models (GCMs). Changes in temporal means, extremes, and the joint distribution of speed and direction were considered. In concordance with previous research, the time mean and extreme scalar wind speeds do not change pronouncedly in response to the projected climate change; some degree of weakening occurs in the majority of the domain. Nevertheless, substantial changes in high wind speeds are identified when studying the geostrophic winds from different directions separately. In particular, in northern Europe in autumn and in parts of northwestern Europe in winter, the frequency of strong westerly winds is projected to increase by up to 50%. Concurrently, easterly winds become less common. In addition, we evaluated the potential of the GCMs to simulate changes in the near-surface true wind speeds. In ocean areas, changes in the true and geostrophic winds are mainly consistent and the emerging differences can be explained (e.g., by the retreat of Arctic sea ice). Conversely, in several GCMs the continental wind speed response proved to be predominantly determined by fairly arbitrary changes in the surface properties rather than by changes in the atmospheric circulation. Accordingly, true wind projections derived directly from the model output should be treated with caution since they do not necessarily reflect the actual atmospheric response to global warming.

scholarly journals Tendency Bias Correction in Coupled and Uncoupled Global Climate Models with a Focus on Impacts over North America

2019 ◽  
Vol 32 (2) ◽  
pp. 639-661 ◽  
Author(s):  
Y. Chang ◽  
S. D. Schubert ◽  
R. D. Koster ◽  
A. M. Molod ◽  
H. Wang
Keyword(s):  
North America ◽  
Bias Correction ◽  
Climate Models ◽  
Global Climate ◽  
Storm Track ◽  
Coupled Model ◽  
Global Climate Models ◽  
Forecast Skill ◽  
Boreal Summer ◽  
Transient Wave

Abstract We revisit the bias correction problem in current climate models, taking advantage of state-of-the-art atmospheric reanalysis data and new data assimilation tools that simplify the estimation of short-term (6 hourly) atmospheric tendency errors. The focus is on the extent to which correcting biases in atmospheric tendencies improves the model’s climatology, variability, and ultimately forecast skill at subseasonal and seasonal time scales. Results are presented for the NASA GMAO GEOS model in both uncoupled (atmosphere only) and coupled (atmosphere–ocean) modes. For the uncoupled model, the focus is on correcting a stunted North Pacific jet and a dry bias over the central United States during boreal summer—long-standing errors that are indeed common to many current AGCMs. The results show that the tendency bias correction (TBC) eliminates the jet bias and substantially increases the precipitation over the Great Plains. These changes are accompanied by much improved (increased) storm-track activity throughout the northern midlatitudes. For the coupled model, the atmospheric TBCs produce substantial improvements in the simulated mean climate and its variability, including a much reduced SST warm bias, more realistic ENSO-related SST variability and teleconnections, and much improved subtropical jets and related submonthly transient wave activity. Despite these improvements, the improvement in subseasonal and seasonal forecast skill over North America is only modest at best. The reasons for this, which are presumably relevant to any forecast system, involve the competing influences of predictability loss with time and the time it takes for climate drift to first have a significant impact on forecast skill.

scholarly journals Projections of Cold Air Outbreaks In CMIP6 Earth System Models

2021 ◽  
Author(s):  
Erik T. Smith ◽  
Scott Sheridan
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
Coupled Model ◽  
Meridional Overturning Circulation ◽  
Cold Air ◽  
Complex Processes ◽  
The North ◽  
Meridional Overturning ◽  
Earth System Models ◽  
Cold Air Outbreaks

Abstract Historical and future simulated temperature data from five climate models in the Coupled Model Intercomparing Project Phase 6 (CMIP6) are used to understand how climate change might alter cold air outbreaks (CAOs) in the future. Three different Shared Socioeconomic Pathways (SSPs), SSP 1 – 2.6, SSP 2 – 4.5, and SSP 5 – 8.5 are examined to identify potential fluctuations in CAOs across the globe between 2015 and 2054. Though CAOs may remain persistent or even increase in some regions through 2040, all five climate models show CAOs disappearing by 2054 based on current climate percentiles. Climate models were able to accurately simulate the spatial distribution and trends of historical CAOs, but there were large errors in the simulated interannual frequency of CAOs in the North Atlantic and North Pacific. Fluctuations in complex processes, such as Atlantic Meridional Overturning Circulation, may be contributing to each model’s inability to simulate historical CAOs in these regions.

Sources and transport pathways of precipitating waters in cold-season deep North Atlantic cyclones

2021 ◽  
Author(s):  
Lukas Papritz ◽  
Franziska Aemisegger ◽  
Heini Wernli
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Water Cycle ◽  
Storm Track ◽  
Cold Season ◽  
Surface Fluxes ◽  
Extratropical Cyclones ◽  
Transport Pathways ◽  
The North ◽  
Cyclone Tracking

AbstractExtratropical cyclones are responsible for a large share of precipitation at mid-latitudes and they profoundly impact the characteristics of the water cycle. In this study, we use the ERA5 reanalysis and a cyclone tracking scheme combined with a Lagrangian diagnostic to identify the sources of moisture precipitating close to the center of 676 deep North Atlantic cyclones in winters 1979 to 2018. Moisture uptakes occur pre-dominantly in originally cold and dry air heated over the North Atlantic, in particular, over the warm waters of the Gulf Stream, whereas more remote sources from land or the subtropics are less important. Analysing the dynamical environment of moisture uptakes, we find that moisture precipitating during the cyclone intensification phase originates in the pre-cyclone environment in the cold sectors of preceding cyclones and the cyclone-anticyclone interaction zone. These moisture sources are linked to the cyclone’s ascent regions via the so-called feeder airstream, a north-easterly cyclone-relative flow that arises due to the cyclone propagation exceeding the advection by the low-level background flow. During the decay phase more and more of the moisture originates in the cyclone’s own cold sector. Consequently, the residence time of precipitating waters in cyclones is short (median of ≈ 2 days) and transport distances are typically less than the distance travelled by the cyclone itself. These findings emphasize the importance of pre-conditioning by surface fluxes in the pre-cyclone environment for the formation of precipitation in cyclones, and suggest an important role for the hand-over of moisture from one cyclone to the next within a storm track.

scholarly journals CMIP5 Projections of Arctic Amplification, of the North American/North Atlantic Circulation, and of Their Relationship

2015 ◽  
Vol 28 (13) ◽  
pp. 5254-5271 ◽  
Author(s):  
Elizabeth A. Barnes ◽  
Lorenzo M. Polvani
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
Coupled Model ◽  
Arctic Region ◽  
The Arctic ◽  
Cmip5 Models ◽  
Arctic Amplification ◽  
Arctic Warming ◽  
The North ◽  
Sequence Of Events

Abstract Recent studies have hypothesized that Arctic amplification, the enhanced warming of the Arctic region compared to the rest of the globe, will cause changes in midlatitude weather over the twenty-first century. This study exploits the recently completed phase 5 of the Coupled Model Intercomparison Project (CMIP5) and examines 27 state-of-the-art climate models to determine if their projected changes in the midlatitude circulation are consistent with the hypothesized impact of Arctic amplification over North America and the North Atlantic. Under the largest future greenhouse forcing (RCP8.5), it is found that every model, in every season, exhibits Arctic amplification by 2100. At the same time, the projected circulation responses are either opposite in sign to those hypothesized or too widely spread among the models to discern any robust change. However, in a few seasons and for some of the circulation metrics examined, correlations are found between the model spread in Arctic amplification and the model spread in the projected circulation changes. Therefore, while the CMIP5 models offer some evidence that future Arctic warming may be able to modulate some aspects of the midlatitude circulation response in some seasons, the analysis herein leads to the conclusion that the net circulation response in the future is unlikely to be determined solely—or even primarily—by Arctic warming according to the sequence of events recently hypothesized.

The Control of Polar Haloclines by Along-Isopycnal Diffusion in Climate Models

2009 ◽  
Vol 22 (3) ◽  
pp. 486-498 ◽  
Author(s):  
Willem P. Sijp ◽  
Matthew H. England
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Multiple Equilibria ◽  
Climate Models ◽  
Coupled Model ◽  
Surface Salinity ◽  
The North ◽  
Winter Convection ◽  
Anomalous Surface ◽  
Strong Control

Abstract Increasing the value of along-isopycnal diffusivity in a coupled model is shown to lead to enhanced stability of North Atlantic Deep Water (NADW) formation with respect to freshwater (FW) perturbations. This is because the North Atlantic (NA) surface salinity budget is dominated by upward salt fluxes resulting from winter convection for low values of along-isopycnal diffusivity, whereas along-isopycnal diffusion exerts a strong control on NA surface salinity at higher diffusivity values. Shutdown of wintertime convection in response to a FW pulse allows the development of a halocline responsible for the suppression of deep sinking. In contrast to convection, isopycnal salt diffusion proves a more robust mechanism for preventing the formation of a halocline, as surface freshening leads only to a flattening of isopycnals, leaving at least some diffusive removal of anomalous surface FW in place. As a result, multiple equilibria are altogether absent for sufficiently high values of isopycnal diffusivity. Furthermore, the surface salinity budget of the North Pacific is also dominated by along-isopycnal diffusion when diffusivity values are sufficiently high, leading to a breakdown of the permanent halocline there and the associated onset of deep-water formation.

Can Isopycnal Mixing Control the Stability of the Thermohaline Circulation in Ocean Climate Models?

2006 ◽  
Vol 19 (21) ◽  
pp. 5637-5651 ◽  
Author(s):  
Willem P. Sijp ◽  
Michael Bates ◽  
Matthew H. England
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Climate Models ◽  
Thermohaline Circulation ◽  
Vertical Component ◽  
Coupled Model ◽  
General Circulation Models ◽  
Tracer Transport ◽  
Horizontal Diffusion ◽  
The Stability

Abstract Convective overturning arising from static instability during winter is thought to play a crucial role in the formation of North Atlantic Deep Water (NADW). In ocean general circulation models (OGCMs), a strong reduction in convective penetration depth arises when horizontal diffusion (HD) is replaced by Gent and McWilliams (GM) mixing to model the effect of mesoscale eddies on tracer advection. In areas of sinking, the role of vertical tracer transport due to convection is largely replaced by the vertical component of isopycnal diffusion along sloping isopycnals. Here, the effect of this change in tracer transport physics on the stability of NADW formation under freshwater (FW) perturbations of the North Atlantic (NA) in a coupled model is examined. It is found that there is a significantly increased stability of NADW to FW input when GM is used in spite of GM experiments exhibiting consistently weaker NADW formation rates in unperturbed steady states. It is also found that there is a significant increase in NADW stability upon the introduction of isopycnal diffusion in the absence of GM. This indicates that isopycnal diffusion of tracer rather than isopycnal thickness diffusion is responsible for the increased NADW stability observed in the GM run. This result is robust with respect to the choice of isopycnal diffusion coefficient. Also, the NADW behavior in the isopycnal run, which includes a fixed background horizontal diffusivity, demonstrates that HD is not responsible in itself for reducing NADW stability when simple horizontal diffusion is used. Our results suggest that care should be taken when interpreting the results of coarse grid models with regard to NADW sensitivity to FW anomalies, regardless of the choice of mixing scheme.

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