Arctic Oscillation/North Atlantic Oscillation Research Articles

What Leads to Persisting Surface Air Temperature Anomalies from Winter to Following Spring over Mid- to High-Latitude Eurasia?

AbstractSurface air temperature (SAT) anomalies tend to persist from winter to the following spring over the mid- to high latitudes of Eurasia. The present study compares two distinct cases of Eurasian SAT anomaly evolution and investigates the reasons for the persistence of continental-scale mid- to high-latitude Eurasian SAT anomalies from winter to following spring (termed persistent cases). The persisting SAT anomalies are closely associated with the sustenance of large-scale atmospheric circulation anomaly pattern over the North Atlantic and Eurasia, featuring a combination of the North Atlantic Oscillation/Arctic Oscillation (NAO/AO) and the Scandinavian pattern, from winter to spring. The combined circulation anomalies result in SAT warming over most of mid- to high-latitude Eurasia via anomalous wind-induced temperature advection. The sustenance of atmospheric circulation anomaly pattern is related to the maintenance of the North Atlantic triple sea surface temperature (SST) anomaly pattern due to air–sea interaction processes. The Barents Sea ice anomalies, which form in winter and increase in spring, also partly contribute to the sustenance of atmospheric circulation anomalies via modulating thermal state of the lower troposphere. In the cases that notable SAT warming (cooling) in winter is replaced by pronounced SAT cooling (warming) in the subsequent spring—termed reverse cases—the North Atlantic SST anomalies become small and the Greenland Sea ice change is a response to atmospheric change in spring. Without the support of lower boundary forcing, the atmospheric circulation anomaly pattern experiences a reverse in the spatial distribution from winter to spring likely due to internal atmospheric processes.

Temporal variation of dust emissions in dust sources over Central Asia in recent decades and the climate linkages

The temporal variation of dust emissions over Central Asia in recent decades and the linkages with atmospheric factors have not been well documented. This study investigated the annual and interannual variations of dust emissions in the six main dust emission regions (i.e., Sor Mertvyy Kultuk (SMK), Ustyurt Plateau (UP), Southeast of Aralkum (SA), Eastern shore of the southern Caspian (ESC), Central Karakum desert (CK), and Trans-Unguz Karakum desert (TK)), using the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) data from 1980 to 2018. The climate linkages with the variation trend were explored using reanalysis data and the climate indices from NOAA Climate Prediction Center (CPC). The results indicated that, in early spring, dust emissions are distinct in all these sources (except for ESC) due to the cold air intrusions from north, northwest, and northeast directions, and the effect of precipitation was limited by the high evaporation. Whereas in summer and/or early autumn, dust emissions were primarily in SA, ESC, CK, and TK because of the strong northeasterly winds, low vegetation, and dry soils. The overall interannual change of dust emissions in Central Asia showed that relatively larger emissions occurred during 1980–1986 and 1993–2003, especially in April. The dust emissions in SA, ESC, and TK in summer were positively correlated with the pressure gradient between northwestern Kazakhstan and Hindu Kush (NWKHKI), while those in SMK were negatively correlated with Caspian Sea High. The dust emissions in the six dust sources were highly correlated with the maximum wind speeds but showed different sensitivities to drought. The Multivariate El Niño-Southern Oscillation Index (MEI) was related to dust emissions in April over coastal Caspian-Sea areas (SMK and ESC), while those in February over the southern parts (ESC, CK, and TK) were significantly correlated with North Atlantic Oscillation/Arctic Oscillation (NAO/AO). These conclusions could contribute to the meteorology research related to dust emissions and also to the decisions made for environmental protection.

Spatial and temporal pattern of extreme temperature during 1961–2018 in China

AbstractAs extreme climate events in China occur frequently, the characteristics of temperature extremes have changed substantially. Spatial and temporal pattern in the selected temperature extreme indices was analyzed by using the Mann–Kendall method (MK), sliding t-test and standard t-test, and Pearson correlation analysis method. In addition, the relationship between them and AO/NAO (Arctic Oscillation/North Atlantic Oscillation) was investigated during 1961–2018 in mainland China. The results show regional and seasonal pattern in temperature extremes. Both ELTs (extreme low temperatures) and EHTs (extreme high temperatures) show increasing trend in autumn and winter, but decreasing trend in spring and summer. In particular, ELTs in all northern basins have more significant increasing trend, while EHTs in the southern areas show insignificant or even decreasing trend. The AO plays an important role in the change of ELTs in summertime (summer and autumn), while the NAO accounts for it during wintertime (winter and spring). Moreover, the NAO is partly responsible for the change of EHTs.

Reexamination of Fram Strait sea ice export and its role in recently accelerated Arctic sea ice retreat

Using the high-resolution global ocean-sea ice model MITgcm-ECCO2, variability and changes of Arctic sea ice export through Fram Strait during 1979–2012 are examined. The simulated annual mean ice export is about 3216 km3/year, which is 12.7% of the 34-year averaged Arctic sea ice volume, with the maximum and minimum occurring in 1994/95 and 1984/1985, respectively. Winter (October–March) ice export is much more than summer (April–September) and exhibits a greater interannual variation. This study suggests that a significant regime shift of Fram Strait ice export from high to low value occurs around the mid-1990s. Further analysis shows that the regime shift of the atmospheric circulation from conventional Arctic Oscillation/North Atlantic Oscillation (AO/NAO) to the dipole-structure Arctic Rapid change Pattern (ARP) plays an important role on the regime shift of ice export. This shift of atmospheric circulation pattern dominates the variability of ice motion and changes the main source region of ice outflow. Combined with the decreased ice thickness and the less ice outflow related to the weakened northerly/northeasterly winds near the strait, sea ice export decreased, eventually generating a regime shift around the mid-1990s. The distinct impact of changes in Fram Strait ice export on the Arctic sea ice inside the basin before and after mid-1990s indicates that the recent continuing loss of Arctic sea ice was mainly induced by the accelerated ice melting in the Arctic Ocean, rather than the ice outflow through Fram Strait.

Subseasonal variability and predictability of the Arctic Oscillation/North Atlantic Oscillation in BCC_AGCM2.2

The subseasonal variability and predictability of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO) is evaluated using a full set of hindcasts generated from the Beijing Climate Center Atmospheric General Circulation Model version 2.2 (BCC_AGCM2.2). It is shown that the predictability of the monthly mean AO/NAO index varies seasonally, with the highest predictability during winter (December–March) and the lowest during autumn (August–November), with respect to both observations and BCC_AGCM2.2 results. As compared with the persistence prediction skill of observations, the model skillfully predicts the monthly mean AO/NAO index with a one-pentad lead time during all winter months, and with a lead time of up to two pentads in December and January. During winter, BCC_AGCM2.2 exhibits an acceptable skill in predicting the daily AO/NAO index of ∼9 days, which is higher than the persistence prediction skill of observations of ∼4 days. Further analysis suggests that improvements in the simulation of storm track activity, synoptic eddy feedback, and troposphere–stratosphere coupling in the Northern Hemisphere could help to improve the prediction skill of subseasonal AO/NAO variability by BCC_AGCM2.2 during winter. In particular, BCC_AGCM2.2 underestimates storm track activity intensity but overestimates troposphere–stratosphere coupling, as compared with observations, thus providing a clue to further improvements in model performance.

Atmospheric bridge on orbital time scales

Large-scale atmospheric patterns are examined on orbital timescales using a climate model which explicitly resolves the atmosphere–ocean–sea ice dynamics. It is shown that, in contrast to boreal summer where the climate mainly follows the local radiative forcing, the boreal winter climate is strongly determined by modulation of circulation modes linked to the Arctic Oscillation/North Atlantic Oscillation (AO/NAO) and the Northern/Southern Annular Modes. We find that during a positive phase of the AO/NAO the convection in the tropical Pacific is below normal. The related atmospheric circulation provides an atmospheric bridge for the precessional forcing inducing a non-uniform temperature anomalies with large amplitudes over the continents. We argue that this is important for mechanisms responsible for multi-millennial climate variability and glacial inception.

Characterization of storm events along the Gulf of Cadiz (eastern central Atlantic Ocean)

The present work deals with the characterization and classification of storm events affecting Cadiz Gulf, i.e. the coast including Southern Portugal, SW Spain and Northern Morocco. The general morphology of the gulf and its location determine the exposition and trajectory of storms affecting the zone, producing significant energy gradients alongshore. This study focuses on the frequency and distribution of the different types of storms, in order to estimate their probability of occurrence. Storm classification was obtained by using wave data records from the HIPOCAS (Hindcast of dynamic Processes of the Ocean and Coastal Areas of Europe) network. The Storm Power Index was used to classify coastal storms. The investigated data sets covered 44 years, between 1958 and 2001. A significant gradient in energy (Storm Power and storm class frequency), approaching direction and storm duration was observed along the gulf, from the most exposed points (Cape San Vicente–Portimao) to the inner, more sheltered ones (Faro–Huelva–Cadiz) and to the southern moderately exposed ones (Bolonia–Tangier). The monthly distribution of number of storms, duration and sum of Storm Power were compared by means of multiple and independent regression analysis with values of different climatic and meteorological indexes. Multiple linear regression analysis between storminess indices and the teleconnection patterns points out that 45% of the change in monthly storminess indices calculated along the Cadiz Gulf are related to changes in the teleconnection patterns, especially North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and East Atlantic (EA). Negative NAO and AO phases and positive EA phases correlate with storminess in the zone. Furthermore, when neutral to strong negative NAO–AO and positive EA phases occurred at the same time and/or when an abrupt change of theses indices occurred, then a greater number of storms with longer duration and higher Storm Power Index were recorded.

Causes of Greenland temperature variability over the past 4000 yr: implications for northern hemispheric temperature changes

Abstract. Precise understanding of Greenland temperature variability is important in two ways. First, Greenland ice sheet melting associated with rising temperature is a major global sea level forcing, potentially affecting large populations in coming centuries. Second, Greenland temperatures are highly affected by North Atlantic Oscillation/Arctic Oscillation (NAO/AO) and Atlantic multidecadal oscillation (AMO). In our earlier study, we found that Greenland temperature deviated negatively (positively) from northern hemispheric (NH) temperature trend during stronger (weaker) solar activity owing to changes in atmospheric/oceanic changes (e.g. NAO/AO) over the past 800 yr (Kobashi et al., 2013). Therefore, a precise Greenland temperature record can provide important constraints on the past atmospheric/oceanic circulation in the region and beyond. Here, we investigated Greenland temperature variability over the past 4000 yr reconstructed from argon and nitrogen isotopes from trapped air in a GISP2 ice core, using a one-dimensional energy balance model with orbital, solar, volcanic, greenhouse gas, and aerosol forcings. The modelled northern Northern Hemisphere (NH) temperature exhibits a cooling trend over the past 4000 yr as observed for the reconstructed Greenland temperature through decreasing annual average insolation. With consideration of the negative influence of solar variability, the modelled and observed Greenland temperatures agree with correlation coefficients of r = 0.34–0.36 (p = 0.1–0.04) in 21 yr running means (RMs) and r = 0.38–0.45 (p = 0.1–0.05) on a centennial timescale (101 yr RMs). Thus, the model can explain 14 to 20% of variance of the observed Greenland temperature in multidecadal to centennial timescales with a 90–96% confidence interval, suggesting that a weak but persistent negative solar influence on Greenland temperature continued over the past 4000 yr. Then, we estimated the distribution of multidecadal NH and northern high-latitude temperatures over the past 4000 yr constrained by the climate model and Greenland temperatures. Estimated northern NH temperature and NH average temperature from the model and the Greenland temperature agree with published multi-proxy temperature records with r = 0.35–0.60 in a 92–99% confidence interval over the past 2000 yr. We found that greenhouse gases played two important roles over the past 4000 yr for the rapid warming during the 20th century and slightly cooler temperature during the early period of the past 4000 yr. Lastly, our analysis indicated that the current average temperature (1990–2010) or higher temperatures occurred at a frequency of 1.3 times per 1000 yr for northern high latitudes and 0.36 times per 4000 yr for NH temperatures, respectively, indicating that the current multidecadal NH temperature (1990–2010) is more likely unprecedented than not (p = 0.36) for the past 4000 yr.

Projected northern rocky mountain annual streamflow for 2000-2099 under the B1, A1B and A2 SRES emissions scenarios

THE B1, A1B AND A2 SRES EMISSIONS SCENARIOS Jeannine-Marie St. Jacques1*, Suzan Lapp1*, Yang Zhao2, Elaine M. Barrow1 and David J. Sauchyn1; 1Prairie Adaptation Research Collaborative (P.A.R.C.), Room 120, 2 Research Drive, Regina, SK, Canada, S4S 7H9; 2Department of Mathematics and Statistics, University of Regina, Regina, Saskatchewan, Canada, S4S 0A2; *Corresponding authors’ e-mail: stjacqje@uregina.ca, lapp200s@uregina.ca. ABSTRACT The 20th century hydroclimatology of the northern Rocky Mountains is heavily influenced by recurring large-scale climate patterns: the Pacific Decadal Oscillation (PDO), the El NinoSouthern Oscillation (ENSO), and the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). Hence, northern Rocky Mountain river discharge variability can be successfully modeled by regression techniques using these climate indices as predictors. Generalized least squares (GLS) regression addresses residual autocorrelation and allows reliable significance testing of any predictor coefficients, and hence, is highly suitable for hydrological modeling. We developed GLS regression equations which captured a major portion of streamflow variability for ten centennial-length northern Rocky Mountain annual discharge records. Both unregulated and paired regulated and naturalized flows were examined. Using archived global climate model runs from the Coupled Model Intercomparison Project Phase 3 (CMIP3), we projected the PDO, ENSO and NAO for the 21st century for the B1, A1B and A2 SRES emission scenarios. These projected climate indices were used as inputs into the GLS equations, giving projected northern Rocky Mountain river discharges for the 21st century. These projections showed generally declining trends in surface water availability for 20002099. Researchers have projected increases in summer warmth and typically decreasing summer precipitation, and increases in winter precipitation and temperature for this region under greenhouse forcing. Our results suggest that in the competition between these two opposing effects on surface water availability, the former will dominate.

A robust mode of climate variability in the Arctic: The Barents Oscillation

The Barents Oscillation (BO) is an anomalous wintertime atmospheric circulation pattern in the Northern Hemisphere that has been linked to the meridional flow over the Nordic Seas. There are speculations that the BO has important implications for the Arctic climate; however, it has also been suggested that the pattern is an artifact of Empirical Orthogonal Function (EOF) analysis due to an eastward shift of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). In this study, EOF analyses are performed to show that a robust pattern resembling the BO can be found during different time periods, even when the AO/NAO is relatively stationary. This “BO” has a high and stable temporal correlation with the geostrophic zonal wind over the Barents Sea, while the contribution from the AO/NAO is small. The surface air temperature anomalies over the Barents Sea are closely associated with this mode of climate variability.

On the origin of multidecadal to centennial Greenland temperature anomalies over the past 800 yr

Abstract. The surface temperature of the Greenland ice sheet is among the most important climate variables for assessing how climate change may impact human societies due to its association with sea level rise. However, the causes of multidecadal-to-centennial temperature changes in Greenland temperatures are not well understood, largely owing to short observational records. To examine these, we calculated the Greenland temperature anomalies (GTA[G-NH]) over the past 800 yr by subtracting the standardized northern hemispheric (NH) temperature from the standardized Greenland temperature. This decomposes the Greenland temperature variation into background climate (NH); polar amplification; and regional variability (GTA[G-NH]). The central Greenland polar amplification factor as expressed by the variance ratio Greenland/NH is 2.6 over the past 161 yr, and 3.3–4.2 over the past 800 yr. The GTA[G-NH] explains 31–35% of the variation of Greenland temperature in the multidecadal-to-centennial time scale over the past 800 yr. We found that the GTA[G-NH] has been influenced by solar-induced changes in atmospheric circulation patterns such as those produced by the North Atlantic Oscillation/Arctic Oscillation (NAO/AO). Climate modeling and proxy temperature records indicate that the anomaly is also likely linked to solar-paced changes in the Atlantic meridional overturning circulation (AMOC) and associated changes in northward oceanic heat transport.

Twenty-first century central Rocky Mountain river discharge scenarios under greenhouse forcing

The present-day hydroclimatology of the central Rocky Mountains is heavily influenced by recurring large-scale climate patterns: the Pacific Decadal Oscillation (PDO), the El Niño-Southern Oscillation (ENSO), and the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). Hence, low frequency central Rocky Mountain river discharge variability can be successfully modeled by regression techniques using these climate indices as predictors. Generalized Least Squares (GLS) regression equations captured a large portion of streamflow variability at the hydrological apex of North America. Using archived runs from global climate models from the IPCC Fourth Assessment Report (AR4) (Phase 3 of the Coupled Model Intercomparison Project – CMIP3), the PDO, ENSO and the NAO were projected for the 21st century for the B1, A1B and A2 Special Report on Emission Scenarios (SRES). These projected climate indices were used as inputs into the GLS regression equations, giving projected central Rocky Mountains river discharges. These projections showed generally declining trends in central Rocky Mountains surface water availability for 2006–2050 and 2006–2096. This study's novel result is that projection distribution functions show a shift in the variance of the flows, from a relatively symmetric equal probability of low versus high flows about the mode and mean in 2006, to a broader, left-skewed flow pattern with a higher probability of low flows in general, and extreme low flows in particular, by 2096.

Interannual variations of the blocking high over the Ural Mountains and its association with the AO/NAO in boreal winter

This paper analyzes interannual variations of the blocking high over the Ural Mountains in the boreal winter and their association with the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). In January, the relationship between the Ural blocking high (UR) and the AO index is statistically significant. The UR tends to occur more frequently and with greater strength during negative AO periods. Some strong URs also occur during positive AO phases (positive UR-AO events), as in January 2008. This paper discusses the characteristics of atmospheric circulation in the cases of positive UR-AO events and contrast cases (negative UR-AO events). The eastward extending of the Icelandic Low (IL) center and the associated NAO dipole anomaly pattern in the upstream region may play a more important role for the UR-AO events. When the center of the IL shifts eastward to 30°W, the amplitude of zonal wavenumber 2 (wavenumber 3) is intensified in the positive (negative) UR-AO events, which favors positive (negative) height anomalies over the Urals. Further analyses indicate that the intensified zonal wind in high latitudes and weakened zonal wind in midlatitudes over the North Atlantic Ocean render the eastward shift of the IL and the NAO dipole anomaly pattern. The Ural blocking in January 2008 bears similar characteristics to the positive UR-AO events.

GCM projections for the Pacific Decadal Oscillation under greenhouse forcing for the early 21st century

AbstractThe climatology and hydrology of western North America display strong periodic cycles which are correlated with the low‐frequency Pacific Decadal Oscillation (PDO). The PDO's signature is seen throughout the entire North Pacific region, with related significant associations to hydrology and ecology in western North America and northeastern Asia. Therefore, the status of the PDO in a warmer world caused by anthropogenic climate change is of great interest. We developed early 21st‐century projections of the PDO, using data from archived runs of the most recent high‐resolution global climate models from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (Phase 3 of the Coupled Model Intercomparison Project). Because of the geographical adjacency and hypothesized interactions between the PDO and the El Niño‐Southern Oscillation (ENSO), and between the PDO and the North Atlantic Oscillation/Arctic Oscillation (NAO/AO), we also developed concurrent projections of ENSO and the NAO and examined their relationships with the projected PDO. For the B1, A1B and A2 Special Report on Emissions Scenarios (SRES) emission scenarios, the PDO projections for 2000–2050 showed a weak multi‐model mean shift towards more occurrences of the negative phase PDO, which becomes statistically significant for the time period 2000–2099. However, not all the models showed a consistent shift to negative PDO conditions. Copyright © 2011 Royal Meteorological Society

Observed Influences of Autumn–Early Winter Eurasian Snow Cover Anomalies on the Hemispheric PNA-like Variability in Winter

Abstract The impact of the Eurasian snow cover extent on the Northern Hemisphere (NH) circulation is investigated by applying a lagged maximum covariance analysis (MCA) to monthly satellite-derived snow cover and NCEP reanalysis data. Wintertime atmospheric signals significantly correlated with persistently autumn–early winter snow cover anomalies are found in the leading two MCA modes. The first MCA mode indicates the effect of Eurasian snow cover anomalies on the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). The second MCA mode corresponds with the forcing of Eurasian snow cover anomalies on the hemispheric Pacific–North America (PNA)-like atmospheric variations. This snow–atmosphere relationship may present a significant potential for wintertime predictability.

Observed changes in snow depth and number of snow days in the eastern and central Tibetan Plateau

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 46:171-183 (2011) - DOI: https://doi.org/10.3354/cr00985 Observed changes in snow depth and number of snow days in the eastern and central Tibetan Plateau Qinglong You1,2,3,4, Shichang Kang1,5,*, Guoyu Ren2, Klaus Fraedrich3, Nick Pepin6, Yuping Yan2, Lijuan Ma2 1Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), Beijing 100085, China 2Laboratory for Climate Studies, National Climate Center, China Meteorological Administration (CMA), Beijing 100081, China 3Meteorological Institute, KlimaCampus, University of Hamburg, Hamburg 21044, Germany 4Graduate University of Chinese Academy of Sciences, Beijing 100049, China 5State Key Laboratory of Cryospheric Science, CAS, Lanzhou 730000, China 6Department of Geography, University of Portsmouth, Portsmouth PO1 3HE, UK *Corresponding author. Email: shichang.kang@itpcas.ac.cn ABSTRACT: The Tibetan Plateau (TP) has the largest area of snow in the mid-latitude regions, and is strongly affected by the climate change. We examine the temporal variability of winter snow depth and number of days of snow cover at 69 Chinese Meteorological Administration stations above 2000 m a.s.l. in the eastern and central TP during 1961–2005. Snow depth is positively correlated with the number of snow days (R = 0.89, p < 0.0001). Regional mean winter (DJF) depth and days of snow cover increase at rates of 0.32 mm decade–1 and 0.40 d decade–1 from 1961 to 1990, but at rates of –1.80 mm decade–1 and –1.59 d decade–1 (i.e. decrease) between 1991 and 2005. The long term trends are weakly positive, but unrepresentative of shorter time periods. Thus snow depth and cover change depends on the timescale examined and cannot be attributed solely to increased greenhouse gas forcing. The decreasing snow depth in recent years will influence hydrological processes and water resources on the plateau and downstream. Both snow depth and duration have positive correlations with the winter Arctic Oscillation/North Atlantic Oscillation (AO/NAO) index and Niño-3 region (5°N–5°S, 150°W–90°W) sea surface temperature (SST). During high AO/NAO index years, both a deeper India–Burma trough and an intensified cyclonic circulation near Lake Baikal bring more snowfall to the TP, consistent with a higher water vapor flux. The opposite is true in low AO/NAO years. Thus secular changes of snow depth and duration in the TP are not independent of changes in the macro-scale atmospheric circulation. KEY WORDS: Snow depth · Snow days · Tibetan Plateau · Arctic Oscillation · North Atlantic Oscillation Full text in pdf format PreviousNextCite this article as: You Q, Kang S, Ren G, Fraedrich K, Pepin N, Yan Y, Ma L (2011) Observed changes in snow depth and number of snow days in the eastern and central Tibetan Plateau. Clim Res 46:171-183. https://doi.org/10.3354/cr00985 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 46, No. 2. Online publication date: March 08, 2011 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2011 Inter-Research.

Present-Day Arctic Sea Ice Variability in the Coupled ECHAM5/MPI-OM Model

Abstract As a contribution to a detailed evaluation of Intergovernmental Panel on Climate Change (IPCC)-type coupled climate models against observations, this study analyzes Arctic sea ice parameters simulated by the Max-Planck-Institute for Meteorology (MPI-M) fully coupled climate model ECHAM5/Max-Planck-Institute for Meteorology Hamburg Primitive Equation Ocean Model (MPI-OM) for the period from 1980 to 1999 and compares them with observations collected during field programs and by satellites. Results of the coupled run forced by twentieth-century CO2 concentrations show significant discrepancies during summer months with respect to observations of the spatial distribution of the ice concentration and ice thickness. Equally important, the coupled run lacks interannual variability in all ice and Arctic Ocean parameters. Causes for such big discrepancies arise from errors in the ECHAM5/MPI-OM atmosphere and associated errors in surface forcing fields (especially wind stress). This includes mean bias pattern caused by an artificial circulation around the geometric North Pole in its atmosphere, as well as insufficient atmospheric variability in the ECHAM5/MPI-OM model, for example, associated with Arctic Oscillation/North Atlantic Oscillation (AO/NAO). In contrast, the identical coupled ocean–ice model, when driven by NCEP–NCAR reanalysis fields, shows much increased skill in its ice and ocean circulation parameters. However, common to both model runs is too strong an ice export through the Fram Strait and a substantially biased heat content in the interior of the Arctic Ocean, both of which may affect sea ice budgets in centennial projections of the Arctic climate system.

Mediterranean climate variability documented in oxygen isotope records from northern Red Sea corals—A review

Annually banded reef corals from the northern Red Sea provide a high-resolution archive of past climate variations at the southeastern rim of the Mediterranean basin. Subseasonally resolved oxygen isotope records derived from the carbonate skeletons of these massive colonies robustly document seasonality and interannual to decadal climate variability. These proxy records of climate, supported by analyses of instrumental data and model simulations, reveal the prominent role of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO) in controlling eastern Mediterranean/Middle East climate on seasonal, interannual to decadal and orbital timescales, most pronounced during winter. Variability at interannual periods of 5–6 yr evident in the coral records is indicative of AO/NAO-like atmospheric variability over the Northern Hemisphere and its influence on eastern Mediterranean/Middle East climate during the last centuries, the late Holocene and the last interglacial period. The coral oxygen isotope records, which are recording temperature and surface evaporation in the northern Red Sea, are linked via AO/NAO-controlled atmospheric circulation changes to variations in temperature and precipitation throughout the Mediterranean and Middle East region. Whereas the entire eastern Mediterranean/Middle East region experiences colder winters during the high-index state of the AO/NAO, the resulting changes in hydrologic balance have a more complex spatial pattern. More arid conditions in the northern Red Sea are accompanied by drier winters in the northeastern Mediterranean but by wetter winters along the southeastern rim of the Mediterranean Sea. This observation may raise difficulties for proxy-based reconstructions of eastern Mediterranean precipitation from the Levant, which is located in the transition zone between positive and negative precipitation anomalies. Compared to the AO/NAO, the atmospheric teleconnections of the El Niño-Southern Oscillation (ENSO) on eastern Mediterranean/Middle East climate, which are modulated by higher-latitude atmospheric circulation over the North Pacific-North Atlantic region, are weaker and non-stationary.

Increasing influence of ENSO and decreasing influence of AO/NAO in the recent decades over northwest India winter precipitation

The interannual variability of northwest India winter precipitation (NWIWP) is examined in association with the variability of surface temperature, mean sea level pressure, tropospheric geopotential height, and wind patterns over the globe to study the changes in the large‐scale circulation features associated with NWIWP. The data for the study have been considered from 1950 to 2008 (for a period of 59 years). The analysis is based on correlations and composites performed using India Meteorological Department records based on station data. We find that the interannual variability of NWIWP is influenced by Arctic Oscillation/North Atlantic Oscillation (AO/NAO) and El Niño–Southern Oscillation (ENSO) phenomena. Above‐normal NWIWP is associated with the positive phase of AO/NAO and the warm phase of ENSO, but showing strong secular variations. During the recent decades, the influence of ENSO over NWIWP has increased while the influence of AO/NAO has decreased. This conclusion is supported by a consistency across the different observation data sets employed in the study. A physical mechanism for such effect is proposed, by which western disturbances are intensified over NW India by the intensification of Asian westerly jet stream over Middle East during positive phase of AO/NAO and shift and intensification of Asian jet to the lower latitudes during the warm phase of ENSO.

Unprecedented low twentieth century winter sea ice extent in the Western Nordic Seas since A.D. 1200

We reconstructed decadal to centennial vari- ability of maximum sea ice extent in the Western Nordic Seas for A.D. 1200-1997 using a combination of a regional tree-ring chronology from the timberline area in Fennoscandia and d 18 O from the Lomonosovfonna ice core in Svalbard. The reconstruction successfully explained 59% of the variance in sea ice extent based on the calibration period 1864-1997. The significance of the reconstruction statistics (reduction of error, coefficient of efficiency) is computed for the first time against a realistic noise background. The twentieth century sustained the lowest sea ice extent values since A.D. 1200: low sea ice extent also occurred before (mid-seventeenth and mid- eighteenth centuries, early fifteenth and late thirteenth centuries), but these periods were in no case as persistent as in the twentieth century. Largest sea ice extent values occurred from the seventeenth to the nineteenth centuries, during the Little Ice Age (LIA), with relatively smaller sea ice-covered area during the sixteenth century. Mod- erate sea ice extent occurred during thirteenth-fifteenth centuries. Reconstructed sea ice extent variability is dominated by decadal oscillations, frequently associated with decadal components of the North Atlantic Oscilla- tion/Arctic Oscillation (NAO/AO), and multi-decadal lower frequency oscillations operating at *50-120 year. Sea ice extent and NAO showed a non-stationary rela- tionship during the observational period. The present low sea ice extent is unique over the last 800 years, and results from a decline started in late-nineteenth century after the LIA.