scholarly journals Teleconnection Processes Linking the Intensity of the Atlantic Multidecadal Variability to the Climate Impacts over Europe in Boreal Winter

2020 ◽  
Vol 33 (7) ◽  
pp. 2681-2700 ◽  
Author(s):  
Saïd Qasmi ◽  
Christophe Cassou ◽  
Julien Boé
Keyword(s):  
Large Scale ◽  
Decadal Variability ◽  
Circulation Model ◽  
Climate Impacts ◽  
Boreal Winter ◽  
Global Circulation Model ◽  
Atlantic Multidecadal Variability ◽  
European Continent ◽  
Wave Source ◽  
Multidecadal Variability

AbstractThe response of the European climate to the Atlantic multidecadal variability (AMV) remains difficult to isolate in observations because of the presence of strong internal variability and anthropogenically forced signals. Using model sensitivity experiments proposed within the CMIP6/Decadal Climate Prediction Project Component C (DCPP-C) framework, the wintertime AMV–Europe teleconnection is here investigated in large ensembles of pacemaker-type simulations conducted with the CNRM-CM5 global circulation model. To evaluate the sensitivity of the model response to the AMV amplitude, twin experiments with the AMV forcing pattern multiplied by 2 and 3 (2xAMV and 3xAMV, respectively) are performed in complement to the reference ensemble (1xAMV). Based on a flow analog method, we show that the AMV-forced atmospheric circulation tends to cool down the European continent, whereas the residual signal, mostly including thermodynamical processes, contributes to warming. In 1xAMV, both terms cancel each other, explaining the overall weak AMV-forced atmospheric signal. In 2xAMV and 3xAMV, the thermodynamical contribution overcomes the dynamical cooling and is responsible for milder and wetter conditions found at large scale over Europe. The thermodynamical term includes the advection of warmer and more humid oceanic air penetrating inland and the modification of surface radiative fluxes linked to both altered cloudiness and snow-cover reduction acting as a positive feedback with the AMV amplitude. The dynamical anomalous circulation combines 1) a remote response to enhanced diabatic heating acting as a Rossby wave source in the western tropical Atlantic and 2) a local response associated with warmer SST over the subpolar gyre favoring an anomalous high. The extratropical influence is reinforced by polar amplification due to sea ice melting in all the subarctic seas. The weight between the tropical–extratropical processes and associated feedbacks is speculated to partly explain the nonlinear sensibility of the response to the AMV forcing amplitude, challenging thus the use of the so-called pattern-scaling technique to evaluate teleconnectivity and related impacts associated with decadal variability.

Assessing the Climate Impacts of the Observed Atlantic Multidecadal Variability Using the GFDL CM2.1 and NCAR CESM1 Global Coupled Models

2017 ◽  
Vol 30 (8) ◽  
pp. 2785-2810 ◽  
Author(s):  
Yohan Ruprich-Robert ◽  
Rym Msadek ◽  
Frederic Castruccio ◽  
Stephen Yeager ◽  
Tom Delworth ◽  
...  
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
Walker Circulation ◽  
Climate Impacts ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Atlantic Multidecadal Variability ◽  
Coupled Models ◽  
Multidecadal Variability ◽  
The Pacific

The climate impacts of the observed Atlantic multidecadal variability (AMV) are investigated using the GFDL CM2.1 and the NCAR CESM1 coupled climate models. The model North Atlantic sea surface temperatures are restored to fixed anomalies corresponding to an estimate of the internally driven component of the observed AMV. Both models show that during boreal summer the AMV alters the Walker circulation and generates precipitation anomalies over the whole tropical belt. A warm phase of the AMV yields reduced precipitation over the western United States, drier conditions over the Mediterranean basin, and wetter conditions over northern Europe. During boreal winter, the AMV modulates by a factor of about 2 the frequency of occurrence of El Niño and La Niña events. This response is associated with anomalies over the Pacific that project onto the interdecadal Pacific oscillation pattern (i.e., Pacific decadal oscillation–like anomalies in the Northern Hemisphere and a symmetrical pattern in the Southern Hemisphere). This winter response is a lagged adjustment of the Pacific Ocean to the AMV forcing in summer. Most of the simulated global-scale impacts are driven by the tropical part of the AMV, except for the winter North Atlantic Oscillation–like response over the North Atlantic–European region, which is driven by both the subpolar and tropical parts of the AMV. The teleconnections between the Pacific and Atlantic basins alter the direct North Atlantic local response to the AMV, which highlights the importance of using a global coupled framework to investigate the climate impacts of the AMV. The similarity of the two model responses gives confidence that impacts described in this paper are robust.

scholarly journals Atmospheric dynamics on tidally locked Earth-like planets in the habitable zone of an M dwarf star

2013 ◽  
Vol 8 (S299) ◽  
pp. 376-377 ◽  
Author(s):  
Ludmila Carone ◽  
Rony Keppens ◽  
Leen Decin
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Rotation Period ◽  
Circulation Model ◽  
Return Flow ◽  
Parameter Study ◽  
Global Circulation Model ◽  
Dwarf Star ◽  
Global Circulation ◽  
M Dwarf

AbstractWe investigated the large scale atmospheric circulation of Gl581g, a potentially habitable planet around an M dwarf star, using an idealized dry global circulation model (GCM) with simplified thermal forcing as a first step towards a systematic extended parameter study. The results are compared with the work of Joshi et al. (1997) who investigated a tidally-locked habitable Earth analogue with less than half the rotation period of Gl581g. The extent, form and strength of the atmospheric circulation in each model generally agree with each other, even though the models differ in key parameters such as planetary radius, surface gravity, forcing scheme and rotation period. The substellar point is associated with an uprising direct circulation-branch of a Hadley-like cell with return flow over the poles. It is compelling to assume that the substellar point of a tidally locked terrestrial exoplanet behaves dynamically like the Earth's tropic associated with clouds and precipitation, making it an ideal target for habitability.

Downscaling of GCM forecasts to streamflow over Scandinavia

2008 ◽  
Vol 39 (1) ◽  
pp. 17-26 ◽  
Author(s):  
Patrik Nilsson ◽  
Cintia B. Uvo ◽  
Willem A. Landman ◽  
Tinh D. Nguyen
Keyword(s):  
Large Scale ◽  
Circulation Model ◽  
Model Output ◽  
Northern Sweden ◽  
Global Circulation Model ◽  
Global Circulation ◽  
Principal Source ◽  
Streamflow Forecasts ◽  
Linear Neural Network ◽  
Model Output Statistics

A seasonal forecasting technique to produce probabilistic and deterministic streamflow forecasts for 23 basins in Norway and northern Sweden is developed in this work. Large scale circulation and moisture fields, forecasted by the ECHAM4.5 model 4 months in advance, are used to forecast spring flows. The technique includes model output statistics (MOS) based on a non-linear Neural Network (NN) approach. Results show that streamflow forecasts from Global Circulation Model (GCM) predictions, for the Scandinavia region are viable and highest skill values were found for basins located in south-western Norway. The physical interpretation of the forecasting skill is that stations close to the Norwegian coast are directly exposed to prevailing winds from the Atlantic Ocean, which constitute the principal source of predictive information from the atmosphere on the seasonal timescale.

scholarly journals Statistical downscaling and scenario construction of precipitation in Scania, southern Sweden

2004 ◽  
Vol 35 (3) ◽  
pp. 261-278 ◽  
Author(s):  
Maj-Lena Linderson ◽  
Christine Achberger ◽  
Deliang Chen
Keyword(s):  
Atmospheric Circulation ◽  
Statistical Downscaling ◽  
Large Scale ◽  
Circulation Model ◽  
Summer Precipitation ◽  
Atmospheric Composition ◽  
Global Circulation Model ◽  
Southern Sweden ◽  
Monthly Basis ◽  
Projected Changes

Statistical downscaling models for precipitation in Scania, southern Sweden, have been developed and applied to calculate the changes in the future Scanian precipitation climate due to projected changes in the atmospheric composition. The models are based on multiple linear regression, linking large-scale predictors at monthly time resolution to regional statistics of daily precipitation on a monthly basis. To account for spatial precipitation variability within the area, the precipitation statistics were derived for different regions in Scania. The final downscaling models, developed for different regions and seasons, use atmospheric circulation, large-scale humidity and precipitation as predictors. Among the precipitation statistics examined, only the models for estimating the mean precipitation and the frequency of wet days were skilful. Based on the Canadian Global Circulation Model 1 (CGCM1), a future scenario of these two statistics was created. The downscaled scenario shows a significant increase of the annual mean precipitation by about 10% and a slight decrease in the frequency of wet days, indicating an increase in the precipitation amounts as well as in the precipitation intensity. The main increase of precipitation amounts and intensity occur during winter, while the summer precipitation amounts decrease slightly. The seasonal changes found in precipitation are likely attributed to changes in the westerly flow of the atmospheric circulation.

scholarly journals Atlantic Multidecadal Variability and the U.K. ACSIS Program

2018 ◽  
Vol 99 (2) ◽  
pp. 415-425 ◽  
Author(s):  
R. T. Sutton ◽  
G. D. McCarthy ◽  
J. Robson ◽  
B. Sinha ◽  
A. T. Archibald ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Heat Content ◽  
Climate Impacts ◽  
Environmental Research ◽  
Atlantic Multidecadal Variability ◽  
Multidecadal Variability ◽  
The North ◽  
Holistic Understanding ◽  
The North Atlantic

Abstract Atlantic multidecadal variability (AMV) is the term used to describe the pattern of variability in North Atlantic sea surface temperatures (SSTs) that is characterized by decades of basinwide warm or cool anomalies, relative to the global mean. AMV has been associated with numerous climate impacts in many regions of the world including decadal variations in temperature and rainfall patterns, hurricane activity, and sea level changes. Given its importance, understanding the physical processes that drive AMV and the extent to which its evolution is predictable is a key challenge in climate science. A leading hypothesis is that natural variations in ocean circulation control changes in ocean heat content and consequently AMV phases. However, this view has been challenged recently by claims that changing natural and anthropogenic radiative forcings are critical drivers of AMV. Others have argued that changes in ocean circulation are not required. Here, we review the leading hypotheses and mechanisms for AMV and discuss the key debates. In particular, we highlight the need for a holistic understanding of AMV. This perspective is a key motivation for a major new U.K. research program: the North Atlantic Climate System Integrated Study (ACSIS), which brings together seven of the United Kingdom’s leading environmental research institutes to enable a broad spectrum approach to the challenges of AMV. ACSIS will deliver the first fully integrated assessment of recent decadal changes in the North Atlantic, will investigate the attribution of these changes to their proximal and ultimate causes, and will assess the potential to predict future changes.

scholarly journals Using the UM dynamical cores to reproduce idealised 3-D flows

2014 ◽  
Vol 7 (6) ◽  
pp. 3059-3087 ◽  
Author(s):  
N. J. Mayne ◽  
I. Baraffe ◽  
D. M. Acreman ◽  
C. Smith ◽  
N. Wood ◽  
...  
Keyword(s):  
Large Scale ◽  
Circulation Model ◽  
Simplified Model ◽  
Global Circulation Model ◽  
Dynamical Equations ◽  
Present Evidence ◽  
Global Circulation ◽  
The Uk ◽  
Tidally Locked Earth

Abstract. We demonstrate that both the current (New Dynamics), and next generation (ENDGame) dynamical cores of the UK Met Office global circulation model, the UM, reproduce consistently, the long-term, large-scale flows found in several published idealised tests. The cases presented are the Held–Suarez test, a simplified model of Earth (including a stratosphere), and a hypothetical tidally locked Earth. Furthermore, we show that using simplifications to the dynamical equations, which are expected to be justified for the physical domains and flow regimes we have studied, and which are supported by the ENDGame dynamical core, also produces matching long-term, large-scale flows. Finally, we present evidence for differences in the detail of the planetary flows and circulations resulting from improvements in the ENDGame formulation over New Dynamics.

Examining the respective roles of greenhouse-gas and aerosol forcing for modes of multi-decadal variability

2020 ◽  
Author(s):  
Andrea Dittus ◽  
Ed Hawkins ◽  
Laura Wilcox ◽  
Dan Hodson ◽  
Jon Robson ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Large Scale ◽  
Climate Model ◽  
Decadal Variability ◽  
Climate Projections ◽  
Anthropogenic Aerosol ◽  
Multidecadal Variability ◽  
Aerosol Forcing ◽  
Early Results ◽  
Wide Range

<p>The respective roles of aerosol and greenhouse-gas forcing in modulating the phasing and amplitude of large-scale modes of multi-decadal variability remain poorly understood, despite the attention that has been devoted to trying to separate the influence of forcing from internal variability in modes such as the Atlantic Multidecadal Variability and the Pacific Decadal Oscillation, for instance. However, understanding what drives multidecadal variability in these basins is imperative for improving near-term climate projections.</p><p>Here, we show how aerosol and greenhouse-gas forcing interact with internal climate variability to generate indices of multi-decadal variability in the Atlantic, using a large ensemble of historical simulations with HadGEM3-GC3.1 for the period 1850-2014, where anthropogenic aerosol emissions are scaled to sample a wide range in historical aerosol forcing. These results are complemented by early results from new stabilised warming simulations with the same climate model and analysis of future projections from models partaking in the Sixth Phase of the Coupled Model Intercomparison Project (CMIP6).</p>

scholarly journals Using the UM dynamical cores to reproduce idealised 3-D flows

2013 ◽  
Vol 6 (3) ◽  
pp. 3681-3741 ◽  
Author(s):  
N. J. Mayne ◽  
I. Baraffe ◽  
D. M. Acreman ◽  
C. Smith ◽  
N. Wood ◽  
...  
Keyword(s):  
Large Scale ◽  
Circulation Model ◽  
Test Case ◽  
Global Circulation Model ◽  
Dynamical Equations ◽  
Present Evidence ◽  
Global Circulation ◽  
The Uk ◽  
Tidally Locked Earth

Abstract. We demonstrate that both the current (New Dynamics), and next generation (ENDGame) dynamical cores of the UK Met Office global circulation model, the UM, reproduce consistently, the long-term, large-scale flows found in several published idealised tests. The cases presented are the Held–Suarez test, a simplified model of Earth (including a stratosphere), and a model of a hypothetical Tidally Locked Earth (TLE). Furthermore, we show that using simplifications to the dynamical equations, which are expected to be justified for the physical domains and flow regimes we have studied, and which are supported by the ENDGame dynamical core, also produces matching long-term, large-scale flows. Finally, we present evidence for differences in the detail of the planetary (meridional) flows and circulations resulting from improvements in the ENDGame formulation over New Dynamics. Specifically, we find greater symmetry in the meridional circulations of the Tidally Locked Earth test case using the ENDGame formulation, which is a better match to our physical expectations of the flow for such a slowly rotating Earth-like system.

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