Yannick Peings

Response of the wintertime northern hemisphere atmospheric circulation to current and projected arctic sea ice decline: A numerical study with CAM5

AbstractThe wintertime Northern Hemisphere (NH) atmospheric circulation response to current (2007–12) and projected (2080–99) Arctic sea ice decline is examined with the latest version of the Community Atmospheric Model (CAM5). The numerical experiments suggest that the current sea ice conditions force a remote atmospheric response in late winter that favors cold land surface temperatures over midlatitudes, as has been observed in recent years. Anomalous Rossby waves forced by the sea ice anomalies penetrate into the stratosphere in February and weaken the stratospheric polar vortex, resulting in negative anomalies of the northern annular mode (NAM) that propagate downward during the following weeks, especially over the North Pacific. The seasonality of the response is attributed to timing of the phasing between the forced and climatological waves. When sea ice concentration taken from projections of conditions at the end of the twenty-first century is prescribed to the model, negative anomalies of the NA...

Forcing of the wintertime atmospheric circulation by the multidecadal fluctuations of the North Atlantic ocean

The North Atlantic sea surface temperature exhibits fluctuations on the multidecadal time scale, a phenomenon known as the Atlantic Multidecadal Oscillation (AMO). This letter demonstrates that the multidecadal fluctuations of the wintertime North Atlantic Oscillation (NAO) are tied to the AMO, with an opposite-signed relationship between the polarities of the AMO and the NAO. Our statistical analyses suggest that the AMO signal precedes the NAO by 10–15 years with an interesting predictability window for decadal forecasting. The AMO footprint is also detected in the multidecadal variability of the intraseasonal weather regimes of the North Atlantic sector. This observational evidence is robust over the entire 20th century and it is supported by numerical experiments with an atmospheric global climate model. The simulations suggest that the AMO-related SST anomalies induce the atmospheric anomalies by shifting the atmospheric baroclinic zone over the North Atlantic basin. As in observations, the positive phase of the AMO results in more frequent negative NAO—and blocking episodes in winter that promote the occurrence of cold extreme temperatures over the eastern United States and Europe. Thus, it is plausible that the AMO plays a role in the recent resurgence of severe winter weather in these regions and that wintertime cold extremes will be promoted as long as the AMO remains positive.

A Numerical Sensitivity Study of the Influence of Siberian Snow on the Northern Annular Mode

AbstractThe climate version of the general circulation model Action de Recherche Petite Echelle Grande Echelle (ARPEGE-Climat) is used to explore the relationship between the autumn Siberian snow and the subsequent winter northern annular mode by imposing snow anomalies over Siberia. As the model presents some biases in the representation of the polar vortex, a nudging methodology is used to obtain a more realistic but still interactive extratropical stratosphere in the model. Free and nudged sensitivity experiments are compared to discuss the dependence of the results on the northern stratosphere climatology. For each experiment, a positive snow mass anomaly imposed from October to March over Siberia leads to significant impacts on the winter atmospheric circulation in the extratropics. In line with previous studies, the model response resembles the negative phase of the Arctic Oscillation. The well-documented stratospheric pathway between snow and the Arctic Oscillation operates in the nudged experiment...

Wintertime atmospheric response to Atlantic multidecadal variability: effect of stratospheric representation and ocean–atmosphere coupling

The impact of the Atlantic multidecadal variability (AMV) on the wintertime atmosphere circulation is investigated using three different configurations of the Community Atmospheric Model version 5 (CAM5). Realistic SST and sea ice anomalies associated with the AMV in observations are prescribed in CAM5 (low-top model) and WACCM5 (high-top model) to assess the dependence of the results on the representation of the stratosphere. In a third experiment, the role of ocean–atmosphere feedback is investigated by coupling CAM5 to a slab-ocean model in which the AMV forcing is prescribed through oceanic heat flux anomalies. The three experiments give consistent results concerning the response of the NAO in winter, with a negative NAO signal in response to a warming of the North Atlantic ocean. This response is found in early winter when the high-top model is used, and in late winter with the low-top model. With the slab-ocean, the negative NAO response is more persistent in winter and shifted eastward over the continent due to the damping of the atmospheric response over the North Atlantic ocean. Additional experiments suggest that both tropical and extratropical SST anomalies are needed to obtain a significant modulation of the NAO, with small influence of sea ice anomalies. Warm tropical SST anomalies induce a northward shift of the ITCZ and a Rossby-wave response that is reinforced in the mid-latitudes by the extratropical SST anomalies through eddy–mean flow interactions. This modeling study supports that the positive phase of the AMV promotes the negative NAO in winter, while illustrating the impacts of the stratosphere and of the ocean–atmosphere feedbacks in the spatial pattern and timing of this response.

Multidecadal fluctuations of the North Atlantic Ocean and feedback on the winter climate in CMIP5 control simulations

PUBLICATIONS Journal of Geophysical Research: Atmospheres RESEARCH ARTICLE 10.1002/2015JD024107 Key Points: • Although large uncertainties in observations, the CMIP5 models seem to lack internally generated AMV • Multiannual persistence of the wintertime NAO is a driver of the AMV, but no consistent feedback of the AMV onto the atmosphere is found • A lagged NAO signal is identified in the two models that exhibit a large AMV Supporting Information: • Figures S1–S9 Correspondence to: Y. Peings, ypeings@uci.edu Citation: Peings, Y., G. Simpkins, and G. Magnusdottir (2016), Multidecadal fluctuations of the North Atlantic Ocean and feedback on the winter climate in CMIP5 control simulations, J. Geophys. Res. Atmos., 120, doi:10.1002/2015JD024107. Received 18 AUG 2015 Accepted 24 FEB 2016 Accepted article online 29 FEB 2016 ©2016. American Geophysical Union. All Rights Reserved. PEINGS ET AL. Multidecadal fluctuations of the North Atlantic Ocean and feedback on the winter climate in CMIP5 control simulations Yannick Peings 1 , Graham Simpkins 1 , and Gudrun Magnusdottir 1 Department of Earth System Science, University of California, Irvine, California, USA Abstract This study examines the relationship between the Atlantic Multidecadal Variability (AMV) and the wintertime atmospheric circulation of the North Atlantic in simulations of the fifth Coupled Model Intercomparison Project (CMIP5). Comparisons of internal (using preindustrial control simulations) and externally forced (using historical and Representative Concentration Pathways 8.5 simulations) simulated AMV with observations suggest that the CMIP5 models lack internally generated AMV, except for two models (GFDL-ESM2G and HadGEM2-ES). A long-term influence of the winter North Atlantic Oscillation (NAO) on the AMV is identified, but no consistent feedback of the AMV onto the atmospheric circulation is found among the models. However, GFDL-ESM2G and HadGEM2-ES show a small lagged NAO signal that suggests a driving role of the ocean on decadal fluctuations of the atmosphere, with two different potential mechanisms. HadGEM2-ES exhibits a latitudinal shift of the Atlantic Intertropical Convergence Zone that can modulate the NAO through a Rossby wave train emanating from the tropics. In GFDL-ESM2G, the AMV is associated with a decrease in storm track activity and a shift of the intraseasonal weather regimes toward the negative NAO regime. These results raise hope that some long-term predictability of the winter climate over the North Atlantic and surrounding continents could be extracted from long-term oceanic fluctuations of the North Atlantic Ocean, provided that the AMV is correctly represented in coupled ocean-atmosphere models. 1. Introduction Climate variability occurs on all time scales, driven by either internal fluctuations of the climate system [e.g., DelSole et al., 2011] or by external forcings such as volcanoes, variations in solar insolation, and greenhouse gas/aerosol concentrations [e.g., Lean and Rind, 2008]. North Atlantic sea surface temperature (SST) exhibits large multidecadal variability known as Atlantic Multidecadal Variability (AMV) [e.g., Ting et al., 2011] or the Atlantic Multidecadal Oscillation [Kerr, 2000; Enfield et al., 2001; Knight et al., 2005]. From the late nineteenth century to present, North Atlantic SST has oscillated between a warm and a cold state with a period of about 60–70 years. The AMV is also present in paleoclimatic reconstructions, suggesting that the AMV is not a true oscillation but rather the manifestation of some persistence in the North Atlantic SST anomalies at the multi- decadal time scale [e.g., Gray et al., 2004; Knudsen et al., 2011]. The causes of AMV remain unclear but have been related to both internal variability of the climate system as well as to natural and anthropogenic external forcings [e.g., Ting et al., 2009; Ottera et al., 2010; Booth et al., 2012; Terray, 2012; Knudsen et al., 2014; Tandon and Kushner, 2015]. Preindustrial climate simulations from general circulation models (GCMs) support the view that the AMV is generated by internal variations of the ocean [Delworth and Mann, 2000; Knight et al., 2005; Ting et al., 2014]. GCMs suggest that the AMV is tied to the Atlantic Meridional Overturning Circulation (AMOC) [e.g., Delworth et al., 1993; Muir and Fedorov, 2015], although the observational record of the AMOC is too short to examine its long-term variability [Cunningham et al., 2007]. The AMOC is the Atlantic component of the global thermohaline circulation, which is driven by temperature and salinity gradients in the ocean that modulate deep convection in high latitudes [e.g., Kuhlbrodt et al., 2007]. Some climate simulations have suggested that the strength of the AMOC is modulated by low-frequency stochastic atmospheric variability and associated surface wind stress. In parti- cular, a reinforcement of the AMOC is generally preceded by a persistent positive North Atlantic Oscillation (NAO) in winter [e.g., Eden and Willebrand, 2001; Medhaug et al., 2012; Barrier et al., 2014]. The NAO is the first mode of atmospheric variability in the Atlantic region in winter [Hurrell and van Loon, 1997]. Persistent anomalies in the NAO force some wind stress and heat flux anomalies that amplify or weaken the formation of the North Atlantic Deep Water masses [e.g., Bersch, 2002], which in turn leads to a reinforcement or AMV FEEDBACK ON ATMOSPHERE IN CMIP5

Changes in North American Atmospheric Circulation and Extreme Weather: Influence of Arctic Amplification and Northern Hemisphere Snow Cover

AbstractThis study tests the hypothesis that Arctic amplification (AA) of global warming remotely affects midlatitudes by promoting a weaker, wavier atmospheric circulation conducive to extreme weather. The investigation is based on the late twenty-first century over greater North America (20°–90°N, 50°–160°W) using 40 simulations from the Community Earth System Model Large Ensemble, spanning 1920–2100. AA is found to promote regionally varying ridging aloft (500 hPa) with strong seasonal differences reflecting the location of the strongest surface thermal forcing. During winter, maximum increases in future geopotential heights are centered over the Arctic Ocean, in conjunction with sea ice loss, but minimum height increases (troughing) occur to the south, over the continental United States. During summer the location of maximum height inflation shifts equatorward, forming an annular band across mid-to-high latitudes of the entire Northern Hemisphere. This band spans the continents, whose enhanced surface...

Daily States of the March–April East Pacific ITCZ in Three Decades of High-Resolution Satellite Data

AbstractZonally elongated areas of cloudiness that make up the east Pacific intertropical convergence zone (ITCZ) can take on several configurations in instantaneous observations. A novel statistical model is used to automatically assess the daily state of the east Pacific ITCZ using infrared satellite images from 1980 to 2012. Four ITCZ states are defined based on ITCZ location relative to the equator: north (nITCZ) and south (sITCZ) of the equator, simultaneously north and south of the equator (dITCZ, for double ITCZ), and over the equator (eITCZ). A fifth ITCZ state is used to classify days when no zonally elongated area of cloudiness is present (aITCZ, for absent ITCZ). The ITCZ states can occur throughout the year (except for the eITCZ, which is not present during June–October), with the nITCZ state dominating in terms of frequency of occurrence. Interannual variability of the state distribution is large.The most striking variability in ITCZ states is observed in spring. During March–April, the dITCZ...

Late Twenty-First-Century Changes in the Midlatitude Atmospheric Circulation in the CESM Large Ensemble

AbstractProjected changes in the midlatitude atmospheric circulation at the end of the twenty-first century are investigated using coupled ocean–atmosphere simulations from the Community Earth System Model Large Ensemble (CESM-LENS). Different metrics are used to describe the response of the midlatitude atmospheric dynamics in 40 ensemble members covering the 1920–2100 period. Contrasted responses are identified depending on the season and longitudinal sector that are considered. In winter, a slowdown of the zonal flow and an increase in waviness is found over North America, while the European sector exhibits a reinforced westerly flow and decreased waviness. Extreme temperature events in midlatitudes are more sensitive to thermodynamical than dynamical changes, and a general decrease in the intensity of wintertime cold spells is found. Analyses of individual ensemble members reveal a large spread in circulation changes due to internal variability. Causes for this spread are found to be tied to the Arctic...

Snow‐(N)AO relationship revisited over the whole twentieth century

Several studies suggest that the Siberian snow cover in fall is a source of predictability of the Arctic Oscillation (AO) in winter. Although a plausible dynamical mechanism was proposed, the robustness of this relationship was recently challenged. Here we use two atmospheric reanalyses to revisit the snow-AO relationship and its modulation across the whole twentieth century. While our results support a stratospheric pathway mechanism, they show that the snow-AO relationship has only emerged in the 1970s and should be rather analyzed as a contrasted multidecadal behavior of the North Atlantic Oscillation (NAO) and Pacific North America pattern. They confirm that the quasi-biennial oscillation is a plausible candidate for the modulation of the snow-(N)AO relationship across the twentieth century, but they further show that this modulation might be a purely stochastic effect. Therefore, they emphasize the limitations of any empirical prediction of the (N)AO only based on snow and/or sea ice predictors.

Changes in Greenland’s peripheral glaciers linked to the North Atlantic Oscillation

Glaciers and ice caps peripheral to the main Greenland Ice Sheet contribute markedly to sea-level rise1–3. Their changes and variability, however, have been difficult to quantify on multi-decadal timescales due to an absence of long-term data4. Here, using historical aerial surveys, expedition photographs, spy satellite imagery and new remote-sensing products, we map glacier length fluctuations of approximately 350 peripheral glaciers and ice caps in East and West Greenland since 1890. Peripheral glaciers are found to have recently undergone a widespread and significant retreat at rates of 12.2 m per year and 16.6 m per year in East and West Greenland, respectively; these changes are exceeded in severity only by the early twentieth century post-Little-Ice-Age retreat. Regional changes in ice volume, as reflected by glacier length, are further shown to be related to changes in precipitation associated with the North Atlantic Oscillation (NAO), with a distinct east–west asymmetry; positive phases of the NAO increase accumulation, and thereby glacier growth, in the eastern periphery, whereas opposite effects are observed in the western periphery. Thus, with projected trends towards positive NAO in the future5,6, eastern peripheral glaciers may remain relatively stable, while western peripheral glaciers will continue to diminish.Combining historical aerial surveys, expedition photographs, and both spy and modern satellite imagery reveals a pronounced retreat of peripheral glaciers in east and west Greenland, linked to changes in precipitation associated with the NAO.