Papers on ENSO effects in Europe

This is a list of papers on the El Niño-Southern Oscillation (ENSO) effects in Europe. Also papers on North-Atlantic (and NAO) link to ENSO are included. 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 (December 5, 2010): Brönnimann et al. (2004) added, thanks to Lars Rosenberg for pointing it out, see the comment section below.

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]

An Atmospheric Teleconnection Linking ENSO and Southwestern European Precipitation – Shaman & Tziperman (2010) “Numerous studies have demonstrated statistical associations between the El Niño-Southern Oscillation (ENSO) and precipitation in the Mediterranean basin. The dynamical bases for these teleconnections have yet to be fully identified. Here we use observational analyses and model simulations to show how ENSO variability affects rainfall over southwestern Europe (Iberia, Southern France and Italy). We define a precipitation index for the region, named southwestern European Precipitation (SWEP). Observational analyses show that ENSO modulates SWEP during the September–December wet season. These precipitation anomalies are associated with changes in large-scale atmospheric fields to the west of Iberia that alter low-level westerly winds and onshore moisture advection from the Atlantic. The vorticity anomalies associated with SWEP variability are linked to ENSO through a stationary barotropic Rossby wave train that emanates from the eastern equatorial Pacific and propagates eastward to the Atlantic and Mediterranean. Solutions of the linearized barotropic vorticity equation produce such eastward propagating Rossby waves with trajectories that traverse the region of observed ENSO-related anomalies. In addition, these linearized barotropic vorticity equation solutions produce a dipole of positive and negative vorticity anomalies to the west of Iberia that matches observations and is consistent with the onshore advection of moisture. Thus, interannual variability of fall and early winter precipitation over southwestern Europe is linked to ENSO variability in the eastern Pacific via an eastward propagating atmospheric stationary barotropic Rossby wave train.” Jeffrey Shaman, Eli Tziperman, Journal of Climate 2010, doi: 10.1175/2010JCLI3590.1.

A 600 k.y. record of El Niño–Southern Oscillation (ENSO): Evidence for persisting teleconnections during the Middle Eocene greenhouse climate of Central Europe – Lenz et al. (2010) “The El Niño–Southern Oscillation (ENSO) is a globally important factor in today’s climate dynamics. Annually laminated oil shales from the maar lake of Messel (Germany) provide high-resolution sedimentological and paleoenvironmental data of a time interval of ∼600 k.y. during the Eocene greenhouse phase. Individual laminae consist of a light spring and summer algal layer (Tetraedron minimum layer) and a dark winter layer composed of terrigenous background sediment. Four sections were selected from the core of the Messel 2001 well in order to count varves and to measure total varve thickness and the thickess of light and dark laminae. Spectral analyses were done in order to detect possible cyclic fluctuations in varve thickness. Fluctuations are significant in the quasi-biennial (2.1–2.5 yr) and low-frequency band (2.8–3.5 yr, 4.9–5.6 yr), thus showing that algal growth as well as the background sedimentation were controlled by ENSO effects at least over a time interval of 600 k.y. This confirms the existence of a previously postulated robust Eocene ENSO. Significant peaks within a quasi-decadal (10–11 yr), interdecadal (17–26 yr), and multidecadal band (∼52 yr, ∼82 yr) show either the enduring influence of more or less cyclic instabilities or the influence of solar cycles.” Olaf K. Lenz, Volker Wilde, Walter Riegel, and Franz-Jürgen Harms, Geology, v. 38 no. 7 p. 627-630, doi: 10.1130/G30889.1.

Impact of the Stratosphere on the Winter Tropospheric Teleconnections between ENSO and the North Atlantic and European Region – Cagnazzo & Manzini (2009) “The possible role of stratospheric variability on the tropospheric teleconnection between El Niño–Southern Oscillation (ENSO) and the North Atlantic and European (NAE) region is addressed by comparing results from two ensembles of simulations performed with an atmosphere general circulation model fully resolving the stratosphere (with the top at 0.01 hPa) and its low-top version (with the top at 10 hPa). Both ensembles of simulations consist of nine members, covering the 1980–99 period and are forced with prescribed observed sea surface temperatures. It is found that both models capture the sensitivity of the averaged polar winter lower stratosphere to ENSO in the Northern Hemisphere, although with a reduced amplitude for the low-top model. In late winter and spring, the ENSO response at the surface is instead different in the two models. A large-scale coherent pattern in sea level pressure, with high pressures over the Arctic and low pressures over western and central Europe and the North Pacific, is found in the February–March mean of the high-top model. In the low-top model, the Arctic high pressure and the western and central Europe low pressure are very much reduced. The high-top minus low-top model difference in the ENSO temperature and precipitation anomalies is that North Europe is colder and the Northern Atlantic storm track is shifted southward in the high-top model. In addition, it has been found that major sudden stratospheric warming events are virtually lacking in the low-top model, while their frequency of occurrence is broadly realistic in the high-top model. Given that this is a major difference in the dynamical behavior of the stratosphere of the two models and that these events are favored by ENSO, it is concluded that the occurrence of sudden stratospheric warming events affects the reported differences in the tropospheric ENSO–NAE teleconnection. Given that the essence of the high-top minus low-top model difference is a more annular (or zonal) pattern of the anomaly in sea level pressure, relatively larger over the Arctic and the NAE regions, this interpretation is consistent with the observational evidence that sudden stratospheric warmings play a role in giving rise to persistent Arctic Oscillation anomalies at the surface.” Cagnazzo, Chiara, Elisa Manzini, 2009, J. Climate, 22, 1223–1238.

The role of the stratosphere in the European climate response to El Niño – Ineson & Scaife (2009) “El Niño/Southern Oscillation (ENSO) is the largest natural interannual climate signal in the tropics; oscillations between warm El Niño and cold La Niña phases occur every few years. The effects are felt not only in the centre of action, the tropical Pacific region, but around the globe. Observational studies show a clear response in European climate to ENSO in late winter. However, the underlying mechanisms of the link are not yet understood. Here we use a general circulation model of the atmosphere, that has been extended into the upper atmospheric layers, to provide end-to-end evidence for a global teleconnection pathway from the Pacific region to Europe via the stratosphere. We present evidence for an active stratospheric role in the transition to cold conditions in northern Europe and mild conditions in southern Europe in late winter during El Niño years. In our experiments, this mechanism is restricted to years when stratospheric sudden warmings occur. The response in European surface climate to the El Niño signal is large enough to be useful for seasonal forecasting.” S. Ineson & A. A. Scaife, Nature Geoscience 2, 32 – 36 (2009), doi:10.1038/ngeo381.

On ENSO impacts on European wintertime rainfalls and their modulation by the NAO and the Pacific multi-decadal variability described through the PDO index – Zanchettin et al. (2008) “While strong relationships have previously been established between the El Niño/Southern Oscillation (ENSO) and climate variability in many parts of the world, previous analyses of ENSO impacts on European rainfalls have been variable and inconclusive. In this paper, the role and apparent interactions of a range of known teleconnections are assessed. It is shown that ENSO events do indeed appear to impact European rainfalls and that these impacts are likely to also depend on the concurrent state of the North Atlantic Oscillation (NAO) and the Pacific Decadal Oscillation (PDO). In particular, it is demonstrated that ENSO impacts most significantly on European wintertime rainfalls during positive (warm) phases of the PDO.” Davide Zanchettin, Stewart W. Franks, Pietro Traverso, Mario Tomasino, International Journal of Climatology, Volume 28, Issue 8, pages 995–1006, 30 June 2008.

ENSO influence on Europe during the last centuries – Brönnimann et al. (2007) “El Niño/Southern Oscillation (ENSO) affects climate not only in the Pacific region and the tropics, but also in the North Atlantic-European area. Studies based on twentieth-century data have found that El Niño events tend to be accompanied in late winter by a negative North Atlantic Oscillation index, low temperatures in northeastern Europe and a change in precipitation patterns. However, many questions are open, for example, concerning the stationarity of this relation. Here we study the relation between ENSO and European climate during the past 500 years based on statistically reconstructed ENSO indices, early instrumental station series, and reconstructed fields of surface air temperature, sea-level pressure, precipitation, and 500 hPa geopotential height. After removing years following tropical volcanic eruptions (which systematically mask the ENSO signal), we find a consistent and statistically significant ENSO signal in late winter and spring. The responses to El Niño and La Niña are close to symmetric. In agreement with studies using twentieth-century data only, the ENSO signal in precipitation is different in fall than in late winter. Moving correlation analyses confirm a stationary relationship between ENSO and late winter climate in Europe during the past 300 years. However, the ENSO signal is modulated significantly by the North Pacific climate. A multi-field cluster analysis for strong ENSO events during the past 300 years yields a dominant pair of clusters that is symmetric and represents the ‘classical’ ENSO effects on Europe.” S. Brönnimann, E. Xoplaki, C. Casty, A. Pauling and J. Luterbacher, Climate Dynamics, Volume 28, Numbers 2-3, 181-197, DOI: 10.1007/s00382-006-0175-z. [Full text]

North Atlantic Winter SLP Anomalies Based on the Autumn ENSO State – Pozo-Vázquez et al. (2005) “The winter sea level pressure (SLP) anomalies in the Northern Hemisphere have been analyzed over the period 1873–2000 based on the ENSO state during the previous autumn. First, a set of extreme cold and warm ENSO events and periods that may be regarded as normal is selected using the SST data of the Niño-3 region. This selection is carried out for autumn and with the constraint that the ENSO event is well developed. For the winters following these selected autumn events, composites of Northern Hemisphere SLP anomalies have been obtained and compared to each other. A study of the consistency among events of the relationship between ENSO and SLP anomalies was also carried out. Results show the preference for a positive NAO-like SLP anomaly pattern in the North Atlantic region during the winters following autumns of strong cold ENSO events and, thus, suggest the existence of a potential source of predictability for the North Atlantic climate. An additional analysis of the winter North Atlantic Oscillation (NAO) index confirms this finding. The possible physical basis of this source of predictability for the North Atlantic climate is discussed.” Pozo-Vázquez, D., S. R. Gámiz-Fortis, J. Tovar-Pescador, M. J. Esteban-Parra, Y. Castro-DÍez, 2005, J. Climate, 18, 97–103, doi: 10.1175/JCLI-3210.1.

Extreme climate of the global troposphere and stratosphere in 1940–42 related to El Niño – Brönnimann et al. (2004) “Although the El Niño/Southern Oscillation phenomenon is the most prominent mode of climate variability1 and affects weather and climate in large parts of the world, its effects on Europe and the high-latitude stratosphere are controversial. Using historical observations and reconstruction techniques, we analyse the anomalous state of the troposphere and stratosphere in the Northern Hemisphere from 1940 to 1942 that occurred during a strong and long-lasting El Niño event. Exceptionally low surface temperatures in Europe and the north Pacific Ocean coincided with high temperatures in Alaska. In the lower stratosphere, our reconstructions show high temperatures over northern Eurasia and the north Pacific Ocean, and a weak polar vortex. In addition, there is observational evidence for frequent stratospheric warmings and high column ozone at Arctic and mid-latitude sites. We compare our historical data for the period 1940–42 with more recent data and a 650-year climate model simulation. We conclude that the observed anomalies constitute a recurring extreme state of the global troposphere–stratosphere system in northern winter that is related to strong El Niño events.” S. Brönnimann, J. Luterbacher, J. Staehelin, T. M. Svendby, G. Hansen & T. Svenøe, Nature 431, 971-974 (21 October 2004) | doi:10.1038/nature02982.

Predictability of Winter Climate over the North Atlantic European Region during ENSO Events – Mathieu et al. (2004) “The predictability of winter climate over the North Atlantic–European (NAE) region during ENSO events is investigated. Rather than employing traditional composite analyses, the authors focus on the impacts of six individual events: three El Niño events and three La Niña events. The investigation is based on the analysis of ensemble simulations with an atmospheric GCM forced with prescribed sea surface temperatures (SST) for the period December 1985–May 2001, and on observations. Model experiments are used to separate the respective roles of SST anomalies in the Indo-Pacific basin and in the Atlantic basin. A significant (potentially predictable) climate signal is found in the NAE region for all six ENSO events. However, there are notable differences in the impacts of individual El Niño and La Niña events. These differences arise not simply from atmospheric internal variability but also because the atmosphere is sensitive to specific features of the SST anomaly fields that characterize the individual events. The different impacts arise partly from differences in Indo-Pacific SST and partly from differences in Atlantic SST. SST anomalies in both ocean basins can influence tropical convection and excite a Rossby wave response over the North Atlantic. The evidence presented here for the importance of Atlantic Ocean conditions argues that, in the development of systems for seasonal forecasting, attention should not be focused too narrowly on the tropical Pacific Ocean.” Mathieu, P-P., R. T. Sutton, B. Dong, M. Collins, 2004, J. Climate, 17, 1953–1974. [Full text]

A high resolution AGCM study of the El Niño impact on the North Atlantic/European sector – Merkel & Latif (2002) “An atmospheric general circulation model (AGCM) sensitivity study has been performed with the ECHAM4 model forced by anomalous sea surface temperatures to investigate the role of the horizontal resolution (T42 versus T106) in determining the El Niño/Southern Oscillation (ENSO) response in the North Atlantic/European region. The higher resolution has been chosen in order to represent more realistically the transient eddy activity that is supposed to play a crucial role in the signal communication to regions remote from the tropical Pacific. In contrast to the T42 experiments, the T106 experiments reveal significant changes both in the mean of selected atmospheric variables (sea level pressure, temperature, precipitation) over Europe and in the transient and stationary wave activity. A cyclone tracking analysis reveals a southward shift of the North Atlantic low pressure systems in the winter season during El Niño events.” Merkel, U., and M. Latif (2002), Geophys. Res. Lett., 29(9), 1291, doi:10.1029/2001GL013726. [Full text]

Euro-Mediterranean rainfall and ENSO—a seasonally varying relationship – Mariotti et al. (2002) “Using observational datasets and atmospheric reanalyses, we show that interannual variability of rainfall in the Euro-Mediterranean sector is significantly influenced by ENSO in a way that is seasonally varying. Spatially coherent correlation patterns are found in central and eastern Europe during winter and spring, and in western Europe and the Mediterranean region during autumn and spring. A composite analysis of ENSO events indicates that during an El Nino western Mediterranean rainfall has a 10% increase (decrease) in the autumn preceeding (spring after) the mature phase of an event, corresponding to a rainy season arriving (retreating) earlier compared to the climatology. The atmospheric reanalyses show that an anomalous atmospheric circulation and moisture transport extending from the Atlantic Ocean into the Euro-Mediterranean region accompanies the observed rainfall anomalies. Multidecadal variations characterize the ENSO Euro-Mediterranean relationship during the 20th century.” Mariotti, A., N. Zeng, and K.-M. Lau (2002), Geophys. Res. Lett., 29(12), 1621, doi:10.1029/2001GL014248. [Full text]

The Association between ENSO and Winter Atmospheric Circulation and Temperature in the North Atlantic Region – Pozo-Vázquez et al. (2001) “The association among ENSO, the Northern Hemisphere sea level pressure (SLP), and temperatures in Europe has been analyzed during the period 1873–1995. In the first part, the SST of the Niño-3 region has been used to select extreme cold and warm ENSO events and periods that can be regarded as normal. The study was carried out for winter with the constraints that the ENSO events were well developed during the winter of study, and that they are extreme events. Composites of winter SLP and temperatures have been made for the selected cold and warm events as well as for normal cases and compared with each other. In the North Atlantic area, no statistically significant SLP anomaly patterns were found associated with warm events, while during cold events a statistically significant anomaly pattern resembling the positive phase of the North Atlantic oscillation (NAO) was found. The temperature analysis shows statistically significant negative anomalies during cold events over the Iberian Peninsula and positive anomalies over the British Isles and southern Scandinavia, consistent with the SLP anomalies. The SLP and temperatures have also been analyzed for spring. The patterns resemble those found for winter but the anomalies have lower amplitudes. For the completion of the composite analysis, the consistency among events of the relationship between ENSO and SLP as well as between ENSO and temperatures was examined. The results show that the significant patterns found in the composite analysis in the North Atlantic area are not the result of a few major events, but rather because both the SLP and temperature anomalies in this area during cold ENSO events are stable and qualitatively similar to those found during the positive phase of the NAO. The possible physical basis for this association between NAO and ENSO is discussed.” Pozo-Vázquez, D., M. J. Esteban-Parra, F. S. Rodrigo, Y. Castro-Díez, 2001, J. Climate, 14, 3408–3420. [Full text]

On the El Niño teleconnection to spring precipitation in Europe – Van Oldenborgh et al. (2000) “In a statistical analysis of more than a century of data, a strong connection was found between strong warm El Niño winter events and high spring precipitation in a band from southern England eastwards into Asia. This relationship is an extension of the connection mentioned by Kiladis and Diaz (1989. ‘Global climatic anomalies associated with extremes in the Southern Oscillation’, J. Climate, 2, 1069–1090), and is much stronger than the winter season teleconnection that has been the subject of other studies. Correlation coefficients between December–January (DJF) NIÑO3 indices and March–May (MAM) precipitation are higher than r=0.3 for individual stations, and as high as r=0.49 for an index of precipitation anomalies around 50°N from 5°W to 35°E. The lagged correlation suggests that southeast Asian surface temperature anomalies may act as intermediate variables.” Geert Jan Van Oldenborgh, Gerrit Burgers, Albert Klein Tank, International Journal of Climatology, Volume 20, Issue 5, pages 565–574, April 2000, DOI: 10.1002/(SICI)1097-0088(200004)20:53.0.CO;2-5.

Predictable winter climate in the North Atlantic sector during the 1997–1999 ENSO cycle – Dong et al. (2000) “The winters of 1997/98 and 1998/99 were marked by strikingly different weather conditions over the North Atlantic ocean and adjacent continents. We use a state‐of‐the‐art atmospheric general circulation model forced with observed sea surface temperatures (SSTs) to investigate the hypothesis that the anomalous conditions in the North Atlantic sector during the winters of 97/98 and 98/99 were related to the ENSO cycle and were therefore potentially predictable. We demonstrate that the major circulation anomalies observed in the North Atlantic sector are reproducible in both winters. We show further that these circulation anomalies were forced primarily by ENSO‐related SST anomalies in the Pacific Ocean, but that SST anomalies in the Atlantic Ocean also had an influence. Our results are encouraging for the prospects of useful seasonal predictions for wintertime in the North Atlantic sector.” Dong, B. ‐W., R. T. Sutton, S. P. Jewson, A. O’Neill, and J. M. Slingo (2000), Geophys. Res. Lett., 27(7), 985–988, doi:10.1029/1999GL010994.

The relationship between the North Atlantic Oscillation and El Niño‐Southern Oscillation – Huang et al. (1998) “We have applied a multiresolution cross‐spectral analysis technique to resolve the temporal relationship between the NAO and ENSO. The study shows significant coherence between NAO and Niño3 SST in about 70% of the warm ENSO events from 1900 to 1995, of which 33% and 37% are associated with a 5‐ to 6‐year period (E1) and a 2‐ to 4‐year period (E2) oscillation terms in the spectral decomposition, respectively. The dominant teleconnection pattern associated with changes in the mean atmospheric circulation during the initial winter of a typical E1 and E2 events is the positive phase of the Pacific/North American (PNA) pattern. Non‐coherence between the NAO and ENSO occurs during relatively weak Niño3 SST anomaly, with a teleconnection pattern which shows a strong negative phase of the NAO and a pattern which resembles a weak eastward shifted negative phase of the PNA pattern.” Huang, J., K. Higuchi, and A. Shabbar (1998), Geophys. Res. Lett., 25(14), 2707–2710, doi:10.1029/98GL01936. [Full text]

Variations in seasonal rainfall in Southern Europe during the present century: relationships with the North Atlantic Oscillation and the El Niño-Southern Oscillation – Rodó et al. (1997) “Analysis of data from seventeen rainfall stations in the Iberian Peninsula, Balearic Islands and Northern Africa has revealed significant El Niño-Southern Oscillation (ENSO) signals in Europe. Both North Atlantic Oscillation (NAO) and Southern Oscillation (SO) exert an influence on Iberian climate, but at different temporal and spatial scales. Though most of the peninsula is under NAO influence in winter, some stations in the eastern region show no connection with this phenomenon. The same is found for ENSO, with a positively correlated region appearing in the eastern part of Spain, while the rest of the peninsula remains insensitive. The correlation between ENSO and Iberian rainfall has increased towards the end of the present century, with strong positive signals spanning over half of the area studied. The percentage of springtime variability due to ENSO has similarly increased, reaching up to 50% in certain areas.
We also show how there are outstanding climatic sensors of these phenomena such as Lake Gallocanta, which manifests a positive response to ENSO while appears insensitive to NAO. Common long-term patterns are observed between SOI and an inferred lake level series, suggesting a constant influence of the low-frequency component of ENSO throughout the period considered. Lake drying phases every 14 years reflect the impact of this signal, approximately every four ENSO events.” X. Rodó, E. Baert and F. A. Comín, Climate Dynamics, Volume 13, Number 4, 275-284, DOI: 10.1007/s003820050165.

An ENSO impact on Europe? – Fraedrich (1994) A review article. “The possible influence of the El Niño/Southern Oscillation (ENSO) warm and cold extremes on mid-latitude circulation regimes in the North Atlantic/European sector is described in terms of a phenomenological, statistical and physical analysis of observational data. (1) The European circulation patterns (after Hess-Brezowsky, 1977) are combined to a binary set of cyclonic and anticyclonic (low and high pressure) centres of action. They reveal a regional ENSO response with predominantly cyclonic (anticyclonic) Grosswetter for warm (cold) ENSO events in winters at the peak of the episode. (2) Standard climate statistics of the same winter seasons (surface pressure, temperature and precipitation anomalies) supplement the Grosswetter phenomenology. They suggest a shift of the tail end of the cross Atlantic storm track and its rainbearing frontal systems from a more northern route (during warm events) to a more zonal orientation (in cold events). (3) Finally, the transient and stationary eddy–mean flow interaction is diagnosed from daily hemispheric 500 mb geopotential height fields. They are composited about most extreme anomalies in Europe (independent of ENSO) defined by the amplitude of the first simultaneous EOF of normalized monthly mean pressure, temperature and precipitation at 40 stations. Thus (upstream location and intensity of) dynamic sources of wave activity flux in the western North-Atlantic cyclogenesis area can be identified. They are associated with European climate anomalies and may represent the connection linking ENSO and Europe under favourable conditions.” Klaus Fraedrich, Tellus A, Volume 46, Issue 4, pages 541–552, August 1994. [Full text]

Climate anomalies in Europe associated with ENSO extremes – Fraedrich & Müller (1992) “Surface pressure, temperature and precipitation anomalies in Europe are composed for the El Niño-Southern Oscillation (ENSO) warm and cold extremes. During warm event winters, negative pressure departures at western and central European stations are associated with positive temperature and precipitation anomalies; the reverse signals are observed in northern Europe. During cold episodes the field of negative pressure deviations is shifted northward with positive temperature and precipitation anomalies, whereas higher pressure is observed over central Europe. This shift of the anomalies corresponds to a shift in the dominating cyclone track (deduced from weather maps), which may be interpreted as the response of the (sensitive tail end of the) cross-Atlantic storm track on the high-pressure anomalies occurring at times in the northern or central part of the North Atlantic/European sector during warm or cold ENSO winters, respectively.” Klaus Fraedrich, Klaus Müller, International Journal of Climatology, Volume 12, Issue 1, pages 25–31, January/February 1992. [Full text]

European grosswetter during the warm and cold extremes of the El Niñco/Southern Oscillation – Fraedrich (1990) “El Niňo/Southern Oscillation (ENSO) warm and cold events affect the synoptic climatology of the north-eastern Atlantic-European sector. The classification of cyclonic and anticyclonic European Grosswetter (1881–1987) is analysed for its response on 26 warm and 21 cold ENSO episodes. Bi-monthly ranked composites computed over idealized 2–year ENSO warm (cold) episodes show more days of cyclonic (anticyclonic) steering over Europe. This signal is largest in the winter months of January and February following the year of a warm or cold event. The distributions of the occurrence of cyclonic and anticyclonic Grosswetter days are significantly different for warm and cold event winters: (i) there is more variability between individual warm event winter months, whereas the response to cold episodes is relatively uniform; (ii) on average, cyclonic Grosswetter days are experienced on 60 per cent (46 per cent) of the 58 warm (cold) event winter. days-about 70 per cent (90 per cent) of the warm (cold) event winters realize more than 30 (< 36) days of cyclonic steering. Qualitatively corresponding results are obtained at a representative central European location for sunshine duration and the sum of daily negative temperatures, which characterize the winter strength." Klaus Fraedrich, International Journal of Climatology, Volume 10, Issue 1, pages 21–31, January/February 1990. [Full text]

The Association between the North Atlantic Oscillation and the Southern Oscillation in the Northern Hemisphere – Rogers (1984) “The North Atlantic Oscillation (NAO) and Southern Oscillation (SO) are compared from the standpoint of their association with Northern Hemisphere winter mean distributions of sea-level pressure (SLP) and 500 mb height. The NAO and SO are associated with significant SLP differences over much of the hemisphere except for Siberia and western North America. Significant SLP and 500 mb height differences occur in the NAO over the Atlantic Ocean and near Baja California, while in the SO they occur over the Pacific Ocean, India and the western Atlantic. Only over the latter region do large pressure and height variations consistently occur in the extremes of both oscillations; these are also associated with winter temperature variability over the southeastern United States. For example, during winter 1982–83, when the two oscillations simultaneously reached extremes, the NAO was associated with record December warmth east of the Mississippi River, but during January and February the SO dominated the height and air temperature distributions over the United States. The cospectrum of the NAO index and Darwin (Australia) pressure is largest at intermediate frequencies with periods of about 6 years, although the NAO itself has peak energy at 7.3 years. The NAO is characterized by a large trend toward lower index in the twentieth century through the 1960s; this is not associated with variations in the SO. In the 80 winters of data, simultaneous occurrences of particular modes of one oscillation with those of the other seem to occur by chance.” Rogers, Jeffery C., 1984, Mon. Wea. Rev., 112, 1999–2015. [Full text]

The Southern Oscillation. Part I: Global Associations with Pressure and Temperature in Northern Winter – van Loon & Madden (1981) The abstract doesn’t mention it, but the Europe situation is discussed in the paper, so see the full text. “We describe the global correlations between a measure of the Southern Oscillation and sea level pressure and surface air temperature in the northern winter. The stability of these correlations were tested on the Northern Hemisphere for an 80-year period, and it turned out that most stable correlation coefficients were found over India, the North Pacific Ocean, the Rocky Mountains, and the central and western North Atlantic Ocean. On the Southern Hemisphere most records are too short for a similar test, but the following may tentatively be said about the Southern Oscillation in middle and high southern latitudes: when pressure is low in lower latitudes over the South Pacific Ocean it tends to be high at higher latitudes of that ocean, high over East Antarctica and low in the belt of westerlies in the Indian and South Atlantic oceans. In the zonal average on both hemispheres the pressure gradients in this extreme of the oscillation tend to be steeper at lower latitudes and flatter at higher latitudes than in the other extreme. The apparent large-scale sympathetic variations between the SO and temperature are shown to occur over the relatively wide range of periods dust have been attributed to the SO itself.” van Loon, Harry, Roland A. Madden, 1981, Mon. Wea. Rev., 109, 1150–1162. [Full text]

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