Berrisford, P., Coauthors, 2011: The ERA-interim archive,version 2.0. ERA Report Series, ECMWF, 23 pp.
Chen H. W., Q. Zhang, H. Körnich, and D. Chen, 2013: A robust mode of climate variability in the arctic: The Barents oscillation.Geophys. Res. Lett.,40(11),2856-2861, https://doi.org/10.1002/grl.50551.10.1002/grl.50551cae18578b78b99650ebf430c37a96395http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fgrl.50551%2Ffullhttp://doi.wiley.com/10.1002/grl.50551The 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.
Cohen J. L., J. C. Furtado, M. A. Barlow, V. A. Alexeev, and J. E. Cherry, 2012: Arctic warming,increasing snow cover and widespread boreal winter cooling.Environmental Research Letters,7,014007, https://doi.org/10.1088/1748-9326/7/1/014007.10.1088/1748-9326/7/1/014007577d901c7bfb946e00b6b6dd7d8543fbhttp%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2012ERL.....7a4007Chttp://stacks.iop.org/1748-9326/7/i=1/a=014007?key=crossref.b774aafc53389f43a9e3492e8a36e8b1The most up to date consensus from global climate models predicts warming in the Northern Hemisphere (NH) high latitudes to middle latitudes during boreal winter. However, recent trends in observed NH winter surface temperatures diverge from these projections. For the last two decades, large-scale cooling trends have existed instead across large stretches of eastern North America and northern Eurasia. We argue that this unforeseen trend is probably not due to internal variability alone. Instead, evidence suggests that summer and autumn warming trends are concurrent with increases in high-latitude moisture and an increase in Eurasian snow cover, which dynamically induces large-scale wintertime cooling. Understanding this counterintuitive response to radiative warming of the climate system has the potential for improving climate predictions at seasonal and longer timescales.
Comiso J. C., C. L. Parkinson, R. Gersten, and L. Stock, 2008: Accelerated decline in the Arctic sea ice cover. Geophys. Res. Lett. 35, https://doi.org/10.1029/2007GL031972.10.1029/2007GL031972343feb606e7415f45d25b40e917085b6http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2007GL031972%2Fpdfhttp://onlinelibrary.wiley.com/doi/10.1029/2007GL031972/pdfSatellite data reveal unusually low Arctic sea ice coverage during the summer of 2007, caused in part by anomalously high temperatures and southerly winds. The extent and area of the ice cover reached minima on 14 September 2007 at 4.1 10kmand 3.6 10km, respectively. These are 24% and 27% lower than the previous record lows, both reached on 21 September 2005, and 37% and 38% less than the climatological averages. Acceleration in the decline is evident as the extent and area trends of the entire ice cover (seasonal and perennial ice) have shifted from about -2.2 and -3.0% per decade in 1979-1996 to about -10.1 and -10.7% per decade in the last 10 years. The latter trends are now comparable to the high negative trends of -10.2 and -11.4% per decade for the perennial ice extent and area, 1979-2007.
Compo, G. P., Coauthors, 2011: The twentieth century reanalysis project.Quart. J. Roy. Meteor. Soc.,137,1-28, https://doi.org/10.1002/qj.776.10.1002/qj.77604625428c9538cbba9d0077dab5bb471http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fqj.776%2Fpdfhttp://adsabs.harvard.edu/abs/2009EGUGA..1111820CA potential consequence of climate variability and change is an altered likelihood of weather extremes. To estimate the fidelity of regional projections of these altered risks in the Twenty-first century, daily data is needed to assess the simulations of weather and climate throughout the Twentieth century. Such daily data must have quantified estimates of uncertainty in Twentieth century weather to allow quantitative comparison with simulations. To this end, we have begun the Twentieth Century Reanalysis Project. This Project is an effort to produce a reanalysis dataset spanning the 20th Century assimilating only surface observations of synoptic pressure, monthly sea surface temperature and sea ice distribution. The project uses the recently developed Ensemble Filter data assimilation system which allows direct computation of both the analysis and the uncertainty in that analysis. The dataset will provide the first estimate of global tropospheric and stratospheric variability spanning more than 100 years with 6 hourly resolution. The first version has global coverage spanning 1908-1958 and 2 degree longitude-latitude horizontal resolution. Comparison with independent radiosonde data indicates that the analyses have a high quality, with correlations higher than 0.94 throughout the troposphere. Overall, the quality is similar to that of current 3-day operational numerical weather prediction forecasts, as anticipated from previous studies.
Dee, D. P., Coauthors, 2011: The ERA-Interim reanalysis: Configuration and performance of the data assimilation system.Quart. J. Roy. Meteor. Soc.,137,553-597, https://doi.org/10.1002/qj.828.10.1002/qj.8285b3115ec8b338ee97111270a1831c4b2http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fqj.828%2Fpdfhttp://doi.wiley.com/10.1002/qj.v137.656ERA-Interim is the latest global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The ERA-Interim project was conducted in part to prepare for a new atmospheric reanalysis to replace ERA-40, which will extend back to the early part of the twentieth century. This article describes the forecast model, data assimilation method, and input datasets used to produce ERA-Interim, and discusses the performance of the system. Special emphasis is placed on various difficulties encountered in the production of ERA-40, including the representation of the hydrological cycle, the quality of the stratospheric circulation, and the consistency in time of the reanalysed fields. We provide evidence for substantial improvements in each of these aspects. We also identify areas where further work is needed and describe opportunities and objectives for future reanalysis projects at ECMWF. Copyright 2011 Royal Meteorological Society
Honda M., J. Inoue, and S. Yamane, 2009: Influence of low Arctic sea-ice minima on anomalously cold Eurasian winters. Geophys. Res. Lett. 36, https://doi.org/10.1029/2008GL037079.10.1029/2008GL03707911ff7459b32da24cee92554351efd9cbhttp%3A%2F%2Fwww.cabdirect.org%2Fabstracts%2F20103055291.htmlhttp://www.cabdirect.org/abstracts/20103055291.htmlInfluence of low Arctic sea-ice minima in early autumn on the wintertime climate over Eurasia is investigated. Observational evidence shows that significant cold anomalies over the Far East in early winter and zonally elongated cold anomalies from Europe to Far East in late winter are associated with the decrease of the Arctic sea-ice cover in the preceding summer-to-autumn seasons. Results fro...
Kalnay, E., Coauthors, 1996: The NCEP/NCAR 40-year reanalysis project. Bull. Amer. Meteor. Soc., 77, 437-471, https://doi.org/10.1175/1520-0477(1996)077<0437:TNYRP>2.0,CO;2.10.1175/1520-0477(1996)077<0437:TNYRP>2.0.CO;29bfeacc7ab553b364e43408563ad850bhttp%3A%2F%2Fintl-icb.oxfordjournals.org%2Fexternal-ref%3Faccess_num%3D10.1175%2F1520-0477%281996%290772.0.CO%3B2%26amp%3Blink_type%3DDOIhttp://journals.ametsoc.org/doi/abs/10.1175/1520-0477%281996%29077%3C0437%3ATNYRP%3E2.0.CO%3B2
Kryzhov V. N., O. V. Gorelits, 2015: The Arctic Oscillation and its impact on temperature and precipitation in Northern Eurasia in the 20th Century.Russian Meteorology and Hydrology,40,711-721, 3103/ S1068373915110011.https://doi.org/10.10.3103/S1068373915110011211ae5db2e77a65d7f7ee18f3eeaa083http%3A%2F%2Flink.springer.com%2Farticle%2F10.3103%2FS1068373915110011http://link.springer.com/10.3103/S1068373915110011Presented is the review of the modern knowledge of the Arctic Oscillation (AO). Demonstrated is the relation of air temperature and precipitation in Northern Eurasia to this dominant type of wintertime atmospheric variability at northern extratropical latitudes. It is demonstrated that AO is a result of the coupling between the troposphere and stratosphere. The attention is paid to the long-range forecasting of AO index and to the factors complicating the forecasting. Given are the new results of the authors research. Used is the wintertime AO index computed by the authors from the 20th Century Reanalysis dataset. The high- and low-frequency components of AO index variability and the periods of statistically significant trends are analyzed using the 112-year series (1901-2012). Demonstrated is the key impact of wintertime AO phase on the anomalies of air temperature and precipitation in Northern Eurasia at the time scale of years and decades. This impact is manifested in the northern part of Northern Eurasia in the prevalence of warmer and wetter winters at the positive AO phase and of colder and drier winters at the negative AO phase. The precipitation anomalies of opposite sign prevail in the southern part of Northern Eurasia. It is demonstrated that the winter AO phase affects the terms of the springtime air temperature transition to positive values.
Morice C. P., J. J. Kennedy, N. A. Rayner, and P. D. Jones, 2012: Quantifying uncertainties in global and regional temperature change using an ensemble of observational estimates: The HadCRUT4 data set. J. Geophys. Res. 117, https://doi.org/10.1029/2011JD017187.10.1029/2011JD0171878b1cc10538405cb9260ddc3ff5fdae8bhttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2011JD017187%2Fabstracthttp://onlinelibrary.wiley.com/doi/10.1029/2011JD017187/abstractRecent developments in observational near-surface air temperature and sea-surface temperature analyses are combined to produce HadCRUT4, a new data set of global and regional temperature evolution from 1850 to the present. This includes the addition of newly digitized measurement data, both over land and sea, new sea-surface temperature bias adjustments and a more comprehensive error model for describing uncertainties in sea-surface temperature measurements. An ensemble approach has been adopted to better describe complex temporal and spatial interdependencies of measurement and bias uncertainties and to allow these correlated uncertainties to be taken into account in studies that are based upon HadCRUT4. Climate diagnostics computed from the gridded data set broadly agree with those of other global near-surface temperature analyses. Fitted linear trends in temperature anomalies are approximately 0.07ºC/decade from 1901 to 2010 and 0.17ºC/decade from 1979 to 2010 globally. Northern/southern hemispheric trends are 0.08/0.07ºC/decade over 1901 to 2010 and 0.24/0.10ºC/decade over 1979 to 2010. Linear trends in other prominent near-surface temperature analyses agree well with the range of trends computed from the HadCRUT4 ensemble members.
Outten S. D., I. Esau, 2012: A link between Arctic sea ice and recent cooling trends over Eurasia.Climatic Change,110,1069-1075, https://doi.org/10.1007/s10584-011-0334-z.10.1007/s10584-011-0334-z9fbb230fa04380926a7eed28b2c0f6bbhttp%3A%2F%2Flink.springer.com%2Farticle%2F10.1007%2Fs10584-011-0334-zhttp://link.springer.com/10.1007/s10584-011-0334-zA band of cooling that extends across mid-latitude Eurasia is identified in the wintertime surface air temperatures of the latest ECMWF reanalysis. This cooling is related to extreme warming around the Kara Sea through changes in the meridional temperature gradient. Surface temperatures in the Arctic have risen faster than those at lower latitudes, and as the Arctic warming increases, this north outh temperature gradient is weakened. This change in the meridional temperature gradient causes a decrease in the westerly winds that help maintain the mild European climate by transporting heat from the Atlantic. Since decreasing sea ice concentrations have been shown to be a driving factor in Arctic amplification, a singular value decomposition analysis is used to confirm the co-variability of the Arctic sea ice, including the Kara Sea, and the temperatures over the mid-latitude Eurasia. These findings suggest that decreasing sea ice concentrations can change the meridional temperature gradient and hence the large-scale atmospheric flow of the Northern Hemisphere.
Outten S., R. Davy, and I. Esau, 2013: Eurasian winter cooling: Intercomparison of reanalyses and CMIP5 Data Sets.Atmospheric and Oceanic Science Letters,6,324-331, https://doi.org/10.3878/j.issn.1674-2834.12.0112.10.3878/j.issn.1674-2834.12.01126f754e444b8d4c1aa339921ab60b455dhttp%3A%2F%2Fd.wanfangdata.com.cn%2FPeriodical_dqhhykxkb201305018.aspxhttp://www.tandfonline.com/doi/full/10.1080/16742834.2013.11447102A cooling trend in wintertime surface air temperature over continental Eurasia has been identified in reanalysis and the Coupled Model Inter-comparison Project phase 5 (CMIP5) ‘historical’ simulations over the period 1989-2009. Here the authors have shown that this cooling trend is related to changes in Arctic sea-ice around the Barents-Kara seas. This study illustrates a consistent spatial and temporal structure of the wintertime temperature variability centered over Asia using state-of-the-art reanalyses and global climate model datasets. Our findings indicate that there is a physical basis for seasonal predictions of near-surface temperatures over continental Asia based on changes to the ice-cover in the Barents-Kara seas.
Overland, J. E., M. Y. Wang, 2010: Large-scale atmospheric circulation changes are associated with the recent loss of Arctic sea ice,Tellus A,62,1-9, http://dx.doi.org/10.1111/j.1600-0870.2009.00421.x.10.1111/j.1600-0870.2009.00421.xb0ed8ee2685a605c97c5df18b284831chttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1111%2Fj.1600-0870.2009.00421.x%2Fcitedbyhttp://onlinelibrary.wiley.com/doi/10.1111/j.1600-0870.2009.00421.x/citedbyRecent loss of summer sea ice in the Arctic is directly connected to shifts in northern wind patterns in the following autumn, which has the potential of altering the heat budget at the cold end of the global heat engine. With continuing loss of summer sea ice to less than 20% of its climatological mean over the next decades, we anticipate increased modification of atmospheric circulation patterns. While a shift to a more meridional atmospheric climate pattern, the Arctic Dipole (AD), over the last decade contributed to recent reductions in summer Arctic sea ice extent, the increase in late summer open water area is, in turn, directly contributing to a modification of large scale atmospheric circulation patterns through the additional heat stored in the Arctic Ocean and released to the atmosphere during the autumn season. Extensive regions in the Arctic during late autumn beginning in 2002 have surface air temperature anomalies of greater than 3 ºC and temperature anomalies above 850 hPa of 1 ºC. These temperatures contribute to an increase in the 1000�500 hPa thickness field in every recent year with reduced sea ice cover. While gradients in this thickness field can be considered a baroclinic contribution to the flow field from loss of sea ice, atmospheric circulation also has a more variable barotropic contribution. Thus, reduction in sea ice has a direct connection to increased thickness fields in every year, but not necessarily to the sea level pressure (SLP) fields. Compositing wind fields for late autumn 2002�2008 helps to highlight the baroclinic contribution; for the years with diminished sea ice cover there were composite anomalous tropospheric easterly winds of 651.4 m s�1, relative to climatological easterly winds near the surface and upper tropospheric westerlies of 653 m s�1. Loss of summer sea ice is supported by decadal shifts in atmospheric climate patterns. A persistent positive Arctic Oscillation pattern in late autumn (OND) during 1988�1994 and in winter (JFM) during 1989�1997 shifted to more interannual variability in the following years. An anomalous meridional wind pattern with high SLP on the North American side of the Arctiche AD pattern, shifted from primarily small interannual variability to a persistent phase during spring (AMJ) beginning in 1997 (except for 2006) and extending to summer (JAS) beginning in 2005.
Petoukhov V., V. A. Semenov, 2010: A link between reduced Barents-Kara sea ice and cold winter extremes over northern continents. J. Geophys. Res. 115, https://doi.org/10.1029/2009JD013568.10.1029/2009JD013568dc1ac9e62c94b87f316ae99122829c96http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2009JD013568%2Fpdfhttp://onlinelibrary.wiley.com/doi/10.1029/2009JD013568/pdfThe recent overall Northern Hemisphere warming was accompanied by several severe northern continental winters, as for example, extremely cold winter 2005-2006 in Europe and northern Asia. Here we show that anomalous decrease of wintertime sea ice concentration in the Barents-Kara (B-K) seas could bring about extreme cold events like winter 2005-2006. Our simulations with the ECHAM5 general circulation model demonstrate that lower-troposphere heating over the B-K seas in the Eastern Arctic caused by the sea ice reduction may result in strong anticyclonic anomaly over the Polar Ocean and anomalous easterly advection over northern continents. This causes a continental-scale winter cooling reaching -1.5ºC, with more than 3 times increased probability of cold winter extremes over large areas including Europe. Our results imply that several recent severe winters do not conflict the global warming picture but rather supplement it, being in qualitative agreement with the simulated large-scale atmospheric circulation realignment. Furthermore, our results suggest that high-latitude atmospheric circulation response to the B-K sea ice decrease is highly nonlinear and characterized by transition from anomalous cyclonic circulation to anticyclonic one and then back again to cyclonic type of circulation as the B-K sea ice concentration gradually reduces from 100% to ice free conditions. We present a conceptual model that may explain the nonlinear local atmospheric response in the B-K seas region by counter play between convection over the surface heat source and baroclinic effect due to modified temperature gradients in the vicinity of the heating area.
Poli, P., Coauthors, 2013: The data assimilation system and initial performance evaluation of the ECMWF pilot reanalysis of the 20th-century assimilating surface observations only (ERA-20C). ERA Report Series,59 pp.ffb0e0849f3f8e6fdf25cf7bb40e8622http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F306168220_The_data_assimilation_system_and_initial_performance_evaluation_of_the_ECMWF_pilot_reanalysis_of_the_20th-century_assimilating_surface_observations_only_ERA-20Chttp://www.researchgate.net/publication/306168220_The_data_assimilation_system_and_initial_performance_evaluation_of_the_ECMWF_pilot_reanalysis_of_the_20th-century_assimilating_surface_observations_only_ERA-20Creact-text: 522 Passive microwave and infrared nadir sounders such as the Advanced Microwave Sounding Unit A (AMSU-A) and the Atmospheric InfraRed Sounder (AIRS), both flying on NASA s EOS Aqua satellite, provide information about vertical temperature and humidity structure that is used in data assimilation systems for numerical weather prediction and climate applications. These instruments scan cross track... /react-text react-text: 523 /react-text [Show full abstract]http://www.researchgate.net/publication/306168220_The_data_assimilation_system_and_initial_performance_evaluation_of_the_ECMWF_pilot_reanalysis_of_the_20th-century_assimilating_surface_observations_only_ERA-20C
Skeie P., 2000: Meridional flow variability over the Nordic Seas in the Arctic oscillation framework.Geophys. Res. Lett.,27(16),2569-2572, https://doi.org/10.1029/2000GL011529.10.1029/2000GL011529505295e71d1919af468de20348135fc9http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2000GL011529%2Ffullhttp://doi.wiley.com/10.1029/2000GL011529An anomalous recurring atmospheric circulation pattern of high relevance for the climate of the Nordic Seas and Siberia is identified. It is found as the second Empirical Orthogonal Function (EOF) of monthly winter sea level pressure (SLP) anomalies poleward of 30°N where the leading EOF is the Arctic Oscillation (AO). The most prominent centre of action of the circulation pattern is located over the Barents Region. This “Barents Oscillation” (BO) is shown to have a high temporal correlation with the sensible heat loss of the Nordic Seas (r=0.76). The BO also correlates to Eurasian surface air temperature (SAT) anomalies with r=0.72 after the AO related SAT variations are removed by means of a linear regression. Two sets of SLP composites are constructed where one is based on low and high Nordic Seas heat loss months and the other is based on warm and cold Eurasian months. Patterns reminiscent of the BO emerge in the two composites when AO related variability is removed.
Thompson D. W. J., J. M. Wallace, 1998: The Arctic oscillation signature in the wintertime geopotential height and temperature fields.Geophys. Res. Lett.,25,1297-1300, https://doi.org/10.1029/98GL00950.10.1029/98GL00950adf244c1165dc0c5b3e8ecc1d4c5e7fehttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F98GL00950%2Fpdfhttp://doi.wiley.com/10.1029/98GL00950The leading empirical orthogonal function of the wintertime sea-level pressure field is more strongly coupled to surface air temperature fluctuations over the Eurasian continent than the North Atlantic Oscillation (NAO). It resembles the NAO in many respects; but its primary center of action covers more of the Arctic, giving it a more zonally symmetric appearance. Coupled to strong fluctuations at the 50-hPa level on the intraseasonal, interannual, and interdecadal time scales, this rctic Oscillation (AO) can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft. It is proposed that the zonally asymmetric surface air temperature and mid-tropospheric circulation anomalies observed in association with the AO may be secondary baroclinic features induced by the land-sea contrasts. The same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature, sea-level pressure, and 50-hPa height over the past 30 years: parts of Eurasia have warmed by as much as several K, sea-level pressure over parts of the Arctic has fallen by 4 hPa, and the core of the lower stratospheric polar vortex has cooled by several K. These trends can be interpreted as the development of a systematic bias in one of the atmosphere's dominant, naturally occurring modes of variability.
Wu B. Y., D. Hand orf, K. Dethloff, A. Rinke, and A. X. Hu, 2013: Winter weather patterns over Northern Eurasia and Arctic sea ice loss.Mon. Wea. Rev.,141,3786-3800, https://doi.org/10.1175/MWR-D-13-00046.1.10.1175/MWR-D-13-00046.18d1b497a4f4ba7b05b32ce57fb1fbb60http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2013MWRv..141.3786Whttp://journals.ametsoc.org/doi/abs/10.1175/MWR-D-13-00046.1Using NCEP-NCAR reanalysis and Japanese 25-yr Reanalysis (JRA-25) winter daily (1 December-28 February) data for the period 1979-2012, this paper reveals the leading pattern of winter daily 850-hPa wind variability over northern Eurasia from a dynamic perspective. The results show that the leading pattern accounts for 18% of the total anomalous kinetic energy and consists of two subpatterns: the dipole and the tripole wind patterns. The dipole wind pattern does not exhibit any apparent trend. The tripole wind pattern, however, has displayed significant trends since the late 1980s. The negative phase of the tripole wind pattern corresponds to an anomalous anticyclone over northern Eurasia during winter, as well as two anomalous cyclones occurring over southern Europe and in the mid- to high latitudes of East Asia. These anomalous cyclones in turn lead to enhanced winter precipitation in these two regions, as well as negative surface temperature anomalies over the mid- to high latitudes of Asia. The intensity of the tripole wind pattern and the frequency of its extreme negative phase are significantly correlated with autumn Arctic sea ice anomalies. Simulation experiments further demonstrate that the winter atmospheric response to Arctic sea ice decrease is dynamically consistent with the observed trend in the tripole wind pattern over the past 24 winters, which is one of the causes of the observed declining winter surface air temperature trend over Central and East Asia. The results of this study also imply that East Asia may experience more frequent and/or intense winter extreme weather events in association with the loss of Arctic sea ice.