Papers on Northern Hemisphere winters 2009-2010 and 2010-2011

This is a list of papers on Northern Hemisphere winters 2009-2010 and 2010-2011 which were very cold and snowy at some places. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (October 25, 2011): Taws et al. (2011) added.

Re-emerging ocean temperature anomalies in late-2010 associated with a repeat negative NAO – Taws et al. (2011) “Northern Europe was influenced by consecutive episodes of extreme winter weather at the start and end of the 2010 calendar year. A tripole pattern in North Atlantic sea surface temperature anomalies (SSTAs), associated with an exceptionally negative phase of the North Atlantic Oscillation (NAO), characterized both winter periods. This pattern was largely absent at the surface during the 2010 summer season; however equivalent sub-surface temperature anomalies were preserved within the seasonal thermocline throughout the year. Here, we present evidence for the re-emergence of late-winter 2009/10 SSTAs during the following early winter season of 2010/11. The observed re-emergence contributes toward the winter-to-winter persistence of the anomalous tripole pattern. Considering the active influence of the oceans upon leading modes of atmospheric circulation over seasonal timescales, associated with the memory of large-scale sea surface temperature anomaly patterns, the re-emergence of remnant temperature anomalies may have also contributed toward the persistence of a negative winter NAO, and the recurrence of extreme wintry conditions over the initial 2010/11 winter season.” Taws, S. L., R. Marsh, N. C. Wells, and J. Hirschi (2011), Geophys. Res. Lett., 38, L20601, doi:10.1029/2011GL048978.

Recent warm and cold daily winter temperature extremes in the Northern Hemisphere – Guirguis et al. (2011) “The winters of 2009–2010 and 2010–2011 brought frigid temperatures to parts of Europe, Russia, and the U.S. We analyzed regional and Northern Hemispheric (NH) daily temperature extremes for these two consecutive winters in the historical context of the past 63 years. While some parts clearly experienced very cold temperatures, the NH was not anomalously cold. Extreme warm events were much more prevalent in both magnitude and spatial extent. Importantly, the persistent negative state of the North Atlantic Oscillation (NAO) explained the bulk of the observed cold anomalies, however the warm extremes were anomalous even accounting for the NAO and also considering the states of the Pacific Decadal Oscillation (PDO) and El Niño Southern Oscillation (ENSO). These winters’ widespread and intense warm extremes together with a continuing hemispheric decline in cold snap activity was a pattern fully consistent with a continuation of the warming trend observed in recent decades.” Guirguis, K., A. Gershunov, R. Schwartz, and S. Bennett (2011), Geophys. Res. Lett., 38, L17701, doi:10.1029/2011GL048762.

European cold winter 2009–2010: How unusual in the instrumental record and how reproducible in the ARPEGE-Climat model? – Ouzeau et al. (2011) “Boreal winter 2009–2010 made headlines for cold anomalies in many countries of the northern mid-latitudes. Northern Europe was severely hit by this harsh winter in line with a record persistence of the negative phase of the North Atlantic Oscillation (NAO). In the present study, we first provide a wider perspective on how unusual this winter was by using the recent 20th Century Reanalysis. A weather regime analysis shows that the frequency of the negative NAO was unprecedented since winter 1939–1940, which is then used as a dynamical analog of winter 2009–2010 to demonstrate that the latter might have been much colder without the background global warming observed during the twentieth century. We then use an original nudging technique in ensembles of global atmospheric simulations driven by observed sea surface temperature (SST) and radiative forcings to highlight the relevance of the stratosphere for understanding if not predicting such anomalous winter seasons. Our results demonstrate that an improved representation of the lower stratosphere is necessary to reproduce not only the seasonal mean negative NAO signal, but also its intraseasonal distribution and the corresponding increased probability of cold waves over northern Europe.” Ouzeau, G., J. Cattiaux, H. Douville, A. Ribes, and D. Saint-Martin (2011), Geophys. Res. Lett., 38, L11706, doi:10.1029/2011GL047667. [Full text]

Anomalous climatic conditions associated with the El Niño Modoki during boreal winter of 2009 – Ratnam et al. (2011) “The winter months from December 2009 to February 2010 witnessed extreme conditions affecting lives of millions of people around the globe. During this winter, the El Niño Modoki in the tropical Pacific was a dominant climatic mode. In this study, exclusive impacts of the El Niño Modoki are evaluated with an Atmospheric General Circulation Model. Sensitivity experiments are conducted by selectively specifying anomalies of the observed sea surface temperature in the tropical Pacific. Observed data are also used in the diagnostics to trace the source of forced Rossby waves. Both the observational results and the model simulated results show that the heating associated with the El Niño Modoki in the central tropical Pacific accounted for most of the anomalous conditions observed over southern parts of North America, Europe and over most countries in the Southern Hemisphere viz. Uruguay. Unlike those, the model-simulated results suggest that the anomalously high precipitation observed over Australia and Florida might be associated with the narrow eastern Pacific heating observed during the season.” J. V. Ratnam, S. K. Behera, Y. Masumoto, K. Takahashi and T. Yamagata, Climate Dynamics, DOI: 10.1007/s00382-011-1108-z.

Extreme winter precipitation in the Iberian Peninsula in 2010: anomalies, driving mechanisms and future projections – Vicente-Serrano et al. (2011) “This work provides a first assessment of the outstanding characteristics of the anomalous precipitation occurrence in the winter of 2010 over the Iberian Peninsula, as well as on the associated atmospheric driving mechanisms. Large areas of Iberia, those located in the western and southern sectors, registered a new historical maximum in winter precipitation values. Simultaneously, the most extreme, negative North Atlantic Oscillation (NAO) index for winter was recorded in 2010. The anomalous pressure gradient in the North Atlantic region steered a large number of low pressure systems via an unusually southern path, directly influencing Iberia and northern Africa. Storms were frequent, and a high number of days occurred with weather types prone to cause precipitation. In addition, the most extreme daily precipitation episodes were recorded during the period with the strongest negative NAO index. Global climate models for the entire 21st century show that strong negative NAO winters, similar to that which occurred in 2010, may be expected in the future.” Vicente-Serrano SM, Trigo RM, López-Moreno JI, Liberato MLR and others (2011), Clim Res 46:51-65. [Full text]

Origin and predictability of the extreme negative NAO winter of 2009/10 – Jung et al. (2011) “The winter of 2009/2010 was one of the most negative winters of the North Atlantic Oscillation (NAO) during the last 150 years. While most operational extended-range forecasting systems had difficulties in predicting the onset of the negative NAO phase, once established, extended-range forecasts were relatively skilful in predicting its persistence. Here, the origin and predictability of the unusual winter of 2009/10 are explored through numerical experimentation with the ECMWF Monthly forecasting system. More specifically, the role of anomalies in sea surface temperature (SST) and sea ice, the tropical atmospheric circulation, the stratospheric polar vortex, solar insolation and near surface temperature (proxy for snow cover) are examined. None of these anomalies is capable of producing the observed NAO anomaly, especially in terms of its magnitude. The results of this study support the hypothesis that internal atmospheric dynamical processes were responsible for the onset and persistence of the negative NAO phase during the 2009/10 winter.” Jung, T., F. Vitart, L. Ferranti, and J.-J. Morcrette (2011), Geophys. Res. Lett., 38, L07701, doi:10.1029/2011GL046786.

Sea ice response to an extreme negative phase of the Arctic Oscillation during winter 2009/2010 – Stroeve et al. (2011) “Based on relationships established in previous studies, the extreme negative phase of the Arctic Oscillation (AO) that characterized winter of 2009/2010 should have favored retention of Arctic sea ice through the 2010 summer melt season. The September 2010 sea ice extent nevertheless ended up as third lowest in the satellite record, behind 2007 and barely above 2008, reinforcing the long-term downward trend. This reflects pronounced differences in atmospheric circulation during winter of 2009/2010 compared to the mean anomaly pattern based on past negative AO winters, low ice volume at the start of the melt season, and summer melt of much of the multiyear ice that had been transported into the warm southerly reaches of the Beaufort and Chukchi seas.” Stroeve, J. C., J. Maslanik, M. C. Serreze, I. Rigor, W. Meier, and C. Fowler (2011), Geophys. Res. Lett., 38, L02502, doi:10.1029/2010GL045662. [Full text]

The UK winter of 2009/2010 compared with severe winters of the last 100 years – Prior & Kendon (2011) No abstract. John Prior, Mike Kendon, Weather, Volume 66, Issue 1, pages 4–10, January 2011, DOI: 10.1002/wea.735. [Full text]

Winter 2010 in Europe: A cold extreme in a warming climate – Cattiaux et al. (2010) “The winter of 2009/2010 was characterized by record persistence of the negative phase of the North-Atlantic Oscillation (NAO) which caused several severe cold spells over Northern and Western Europe. This somehow unusual winter with respect to the most recent ones arose concurrently with public debate on climate change, during and after the Copenhagen climate negotiations. We show however that the cold European temperature anomaly of winter 2010 was (i) not extreme relative to winters of the past six decades, and (ii) warmer than expected from its record-breaking seasonal circulation indices such as NAO or blocking frequency. Daily flow-analogues of winter 2010, taken in past winters, were associated with much colder temperatures. The winter 2010 thus provides a consistent picture of a regional cold event mitigated by long-term climate warming.” Cattiaux, J., R. Vautard, C. Cassou, P. Yiou, V. Masson-Delmotte, and F. Codron (2010), Geophys. Res. Lett., 37, L20704, doi:10.1029/2010GL044613. [Full text]

Influences of Arctic Oscillation and Madden-Julian Oscillation on cold surges and heavy snowfalls over Korea: A case study for the winter of 2009–2010 – Park et al. (2010) “In the winter of 2009–2010, frequent and long-lasting cold weather affected Korea. Four major cold surges and several heavy snowfall events were observed, including a record-breaking event on 4 January 2010. These four cold surges had distinct properties with regard to their relationships to the phases of the Arctic Oscillation (AO) and the Madden-Julian Oscillation (MJO), suggesting the possible influences of the AO and MJO on the cold surges and heavy snowfalls. The four cold surges were of two distinct types: the wave train type and the blocking type, which were differentiated by their mechanisms. With regard to the relationships of the cold surges to the AO, three cold surges occurred during a strongly negative AO period, which lasted for more than 1 month. The Siberian High expanded from the Arctic high-pressure region to East Asia during the negative AO period. A cold surge occurred during a positive AO, with the expansion of the Siberian High across the Eurasian continent. An MJO-induced circulation, corresponding to strong tropical convection over the tropical Indian Ocean, seems to have reinforced the cold surges over East Asia. In addition, the active local Hadley circulation modulated by a convection center over the Indian Ocean tends to enhance midlatitude synoptic disturbances across East Asia and provides favorable conditions for upward motion over the region. In short, the effects of the AO and MJO, along with the existing low-level moisture supply, contributed to heavy snowfalls associated with strong cold surges over Korea during the winter of 2009–2010.” Park, T.-W., C.-H. Ho, S. Yang, and J.-H. Jeong (2010), J. Geophys. Res., 115, D23122, doi:10.1029/2010JD014794.

Winter 2009–2010: A case study of an extreme Arctic Oscillation event – Cohen et al. (2010) “Winter 2009–2010 made headlines for extreme cold and snow in most of the major population centers of the industrialized countries of the Northern Hemisphere (NH). The major teleconnection patterns of the Northern Hemisphere, El Niño/Southern Oscillation (ENSO) and the Arctic Oscillation (AO) were of moderate to strong amplitude, making both potentially key players during the winter of 2009–2010. The dominant NH winter circulation pattern can be shown to have originated with a two-way stratosphere-troposphere interaction forced by Eurasian land surface and lower tropospheric atmospheric conditions during autumn. This cycle occurred twice in relatively quick succession contributing to the record low values of the AO observed. Using a skillful winter temperature forecast, it is shown that the AO explained a greater variance of the observed temperature pattern across the extratropical landmasses of the NH than did ENSO.” Cohen, J., J. Foster, M. Barlow, K. Saito, and J. Jones (2010), Geophys. Res. Lett., 37, L17707, doi:10.1029/2010GL044256. [Full text]

Northern Hemisphere winter snow anomalies: ENSO, NAO and the winter of 2009/10 – Seager et al. (2010) “Winter 2009/10 had anomalously large snowfall in the central parts of the United States and in northwestern Europe. Connections between seasonal snow anomalies and the large scale atmospheric circulation are explored. An El Niño state is associated with positive snowfall anomalies in the southern and central United States and along the eastern seaboard and negative anomalies to the north. A negative NAO causes positive snow anomalies across eastern North America and in northern Europe. It is argued that increased snowfall in the southern U.S. is contributed to by a southward displaced storm track but further north, in the eastern U.S. and northern Europe, positive snow anomalies arise from the cold temperature anomalies of a negative NAO. These relations are used with observed values of NINO3 and the NAO to conclude that the negative NAO and El Niño event were responsible for the northern hemisphere snow anomalies of winter 2009/10.” Seager, R., Y. Kushnir, J. Nakamura, M. Ting, and N. Naik (2010), Geophys. Res. Lett., 37, L14703, doi:10.1029/2010GL043830. [Full text]

The record-breaking cold temperatures during the winter of 2009/2010 in the Northern Hemisphere – Wang et al. (2010) “In this study, we show that the record-breaking cold temperatures from North America to Europe and Asia during the period of 28 December 2009 to 13 January 2010 are associated with extremely negative values of the North Atlantic Oscillation (NAO) index, which produce northerly surface wind anomalies and cause the southward advection of the cold Arctic air. Corresponded to longer-term variations of Pacific and Atlantic Sea Surface Temperatures (SSTs), the downward trend of the NAO has occurred since the early 1990s. It is speculated that if the downward trend of the NAO continues, more frequent cold outbreaks and heavy snow are likely in the coming years.” Dr Chunzai Wang, Hailong Liu, Sang-Ki Lee, Atmospheric Science Letters, Volume 11, Issue 3, pages 161–168, July/September 2010, DOI: 10.1002/asl.278. [Full text]