This page describes some aspects of the effect of the the El Niño Southern Oscillation (ENSO) on Europe in winter, which manifest via atmospheric circulation teleconnections. The positive phase of the oscillation, El Niño events, usually lasts 9 to 12 months, reaching a peak intensity between November and January (although the events can sometimes last years). The negative phase of the oscillation, La Niña events, also typically peaks during the northern hemisphere winter. At the end of the page, some global effects are also quantified in charts available for all months.
Circulation teleconnections
ENSO events are characterised by large-scale anomalies in sea temperatures and atmospheric winds taking hold in the equatorial Pacific. These are associated with shifts in large-scale patterns of atmospheric circulation which result in effects a very long way from the centres of action (for example, changes to the Walker circulation 'propagate' the effects in a zonal direction, across the tropics). However, away from the tropics other factors, independent of ENSO or, more generally, of perturbations in the tropics, can affect the climate at certain times of year. They come into competition with the ENSO teleconnections, modulating the latter in a variety of ways. The 'average' behaviour - often determined by calculating statistics conditioned on a phase of the oscillation - is by no means a guarantee of outcomes in a single instance (year). This is particularly the case for the North Atlantic/European sector, where influences from polar regions, or the stratosphere, can play a significant role in winter, as well as in summer.
The following plots are ERA5 mean sea level pressure (MSLP) composites for the northern hemisphere, constructed from El Niño and La Niña events. They show the average circulation patterns which have occurred during these events during winter (Dec-Feb), separately for Nov-Dec and Jan-Feb. The European/North Atlantic region (70W-30E, 25N-80N) is highlighted on these maps in black.
In these charts composite MSLP anomalies in units of hPa are shown for El Niño (left) and La Niña (right), for Nov-Dec (ND, top) and Jan-Feb (JF, bottom).
Average effects
ENSO events tend to peak at the end of the calendar year; accordingly, impacts over Europe tend to be stronger in winter than at other times of year.
The composites above reveal differences in the response in North Atlantic-European (NAE) atmospheric circulation between early winter and late winter. For early winter (November-December), the response shows a strong 'symmetry' (high spatial correlation) between El Niño and La Niña composites but the amplitude is larger during the El Niño phase, when a strong negative anomaly is located over the North Atlantic and positive anomalies are found to the south and east. The late-winter (January-February) teleconnection is visibly different from the early-winter equivalent; the spatial correlation between El Niño and La Niña composites decreases.
These circulation anomalies would be associated with anomalies in temperature and precipitation patterns (not shown).
Diversity of outcomes
As mentioned above, the average behaviour shown in composites is not guaranteed to occur during each ENSO event.
This can be illustrated by looking at past European winters during ENSO events, specifically at MSLP, near-surface air temperature (t2m), precipitation and 10m windspeed. The 'postage stamp' charts below show early- and late-winter (November-December and January-February) anomalies for El Niño/La Niña years. Here, El Niño/La Niña years are selected based on the December-February (DJF) NINO3.4 SST anomalies, calculated using ERA5 data from 1970 to 2022, using the upper/lower quartiles as thresholds (so these are the same years which contributed to the composites above). The anomalies are calculated using the entire period as the reference.
These 'postage stamp' charts highlight that, despite the typical behaviour described above, there is a large diversity of outcomes associated with the effect of the oscillation in the North-Atlantic and Europe, in both atmospheric circulation and surface conditions. The plots are labelled by the year in which January falls (so 2019 is winter 2018/2019), and with the NINO3.4 index for the period used to make the selection, Dec-Feb. Each set of charts can be expanded by clicking the links below.
These MSLP anomalies are in units of hPa.
The NINO3.4 anomalies printed above each map are DJF means, which were used for the selection.
El Niño years, ND anomaly, MSLP  | La Niña years, ND anomaly, MSLP |
El Niño years, JF anomaly, MSLP  | La Niña years, JF anomaly, MSLP
|
These temperature anomalies, relative to the reference-period mean, are in degrees Celsius.
The NINO3.4 anomalies printed above each map are DJF means, which were used for the selection.
El Niño years, ND anomaly, t2m  | La Niña years, ND anomaly, t2m
|
El Niño years, JF anomaly, t2m
| La Niña years, JF anomaly, t2m  |
These precipitation anomalies are percentages of the reference-period mean.
The NINO3.4 anomalies printed above each map are DJF means, which were used for the selection.
El Niño years, ND anomaly, precip
| La Niña years, ND anomaly, precip  |
El Niño years, JF anomaly, precip
| La Niña years, JF anomaly, precip  |
These windspeed anomalies are percentages of the reference-period mean.
The NINO3.4 anomalies printed above each map are DJF means, which were used for the selection.
El Niño years, ND anomaly, windspeed  | La Niña years, ND anomaly, windspeed
|
El Niño years, JF anomaly, windspeed  | La Niña years, JF anomaly, windspeed
|
Global effects - temperature and precipitation
Using the ENSO years selection approach outlined above (here with a choice between the period 1940-2022 and 1970-2022), typical effects on temperature and precipitation are illustrated, by displaying the number of years falling into the upper or lower tercile category of the distribution of the respective variable. Colours are only shown when the number of years is statistically significant. This concept and methodology is similar to that used in Davey et al. 2014.
These charts can be used to identify regions where, according to this analysis method, there is a statistically significant ENSO teleconnection for temperature or precipitation for each calendar month. Due to the variability seen within the postage stamp charts shown above for Europe, there is not a strong signature in the composites below.
In the table below ENSO events are indicated by the shading of the cells corresponding to the three-month means centred on the time used as 'label' (the title of each column is the numerical value of the month at the centre of the three-month period - e.g, '2', denoting February, represents January-March averages): red indicates El Niño and blue La Niña.
Only the table for the 1970-2022 period is shown:
References
- Molteni, F., Brookshaw, A. Early- and late-winter ENSO teleconnections to the Euro-Atlantic region in state-of-the-art seasonal forecasting systems. Clim Dyn 61, 2673–2692 (2023). https://doi.org/10.1007/s00382-023-06698-7
- , , , et al. The ERA5 global reanalysis. Q J R Meteorol Soc. 2020; 146: 1999–2049. https://doi.org/10.1002/qj.3803
- Davey, M.K., Brookshaw, A. and Ineson, S., 2014. The probability of the impact of ENSO on precipitation and near-surface temperature. Climate Risk Management, 1, pp.5-24. https://doi.org/10.1016/j.crm.2013.12.002