ENSO-related quadriennial variations in European rainfall (original) (raw)
El Ni�o-southern oscillation events and associated European winter precipitation anomalies
International Journal of Climatology, 2005
The winter precipitation anomalies in the European area have been analysed over the period 1900-98 based on the El Niño-Southern oscillation (ENSO) state. A set of winter and autumn ENSO events is first selected using the Sea-Surface temperature (SST) data of the Niño 3 region, with the constraint that the ENSO event is well developed during the winter and autumn of study, and that it is an extreme event. Cold and warm ENSO events and periods that can be regarded as normal are selected. For the selected winter ENSO events and for the winter following the selected autumn ENSO events, composites of European winter precipitation anomalies have been obtained and compared with each other. A study of the consistency among events of the relationship between ENSO and precipitation anomalies was also carried out. The analysis of the winter precipitation anomalies based on the selected winter ENSO events shows the existence, for the European area and during La Niña events, of a statistically significant precipitation anomaly pattern with positive precipitation anomalies north of the British Isles and in the Scandinavian area and negative anomalies in southern Europe, resembling the precipitation pattern associated with the positive phase of the North Atlantic oscillation (NAO). Particularly, for the southwestern area of the Iberian Peninsula, the negative anomaly reaches 20% of the winter average precipitation. The consistency analysis shows that this precipitation pattern is not the result of a few major events, but rather that it is stable and qualitatively similar to that found during the positive phase of the NAO. A non-linear response to ENSO is found in the eastern Mediterranean area: negative precipitation anomalies are found, having similar amplitude anomalies, both during El Niño and La Niña events. The analysis of the precipitation anomalies for the winter following the selected autumn ENSO events shows very similar results to those found for the previous analysis, thus suggesting the existence of a potential source of seasonal forecasting of European precipitation. An analysis of the sensitivity of the precipitation anomalies to the strength of the ENSO events shows that, when the strength of the ENSO increases, the magnitude of the rainfall anomalies does not change, but the area influenced and the coherence between events do increase slightly.
Euro-Mediterranean rainfall and ENSO- A seasonally varying relationship
Geophysical Research Letters, 2002
1] 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.
International Journal of Climatology, 2003
The link between El Niño-southern oscillation (ENSO) variability in boreal winter (represented by the NIÑO3 index, i.e. East Pacific sea-surface temperature anomalies) and the large-scale circulation and weather conditions over Europe-northwest Africa in spring is explored, considering station reports of precipitation, sea-level pressure (SLP) anomalies and two North Atlantic oscillation (NAO) indices. It is found that these relations have undergone consistent and simultaneous changes in the 20th century. Three characteristic periods can be identified. During 1900-25 and 1962-87, positive NIÑO3 index values are associated with enhanced precipitation over central Europe and reduced rainfall in southern Europe and northern Africa. The ENSO influence on precipitation over Scotland and Norway is small. The rainfall anomalies can be explained from the advective and dynamical implications of a north-south dipole in SLP correlations (warm ENSO events followed by low pressure in northern Europe and high pressure over the Mediterranean Sea-North Africa). This dipole hardly projects on the commonly used NAO centres (Iceland and Azores/Gibraltar) and thus ENSO-NAO correlations are insignificant. During 1931-56 the NIÑO3 index reveals little influence on precipitation over the Iberian Peninsula and Morocco, but there are large negative correlations with precipitation over Scotland and Norway. This is related to an alteration of the NIÑO3-SLP correlation pattern, which implies high pressure over northern Europe and low pressure over central Europe after warm events, and thus a virtually inverted dipole with respect to the other two periods. The large westward extension of the dipole leads to a significant NAO-NIÑO3 correlation of r = −0.5. These alterations were accompanied by substantial large-scale circulation changes during the period 1931-56, as revealed by anomalously high pressure and dry conditions over central-western Europe, a change in precipitation-producing SLP patterns for Morocco and an anomalously low number of positive NAO and NIÑO3 index values. It is left for discussion as to whether the decadal variations described are due to a change in the physics of the teleconnection or to stochastic fluctuations.
Interannual oscillations in winter rainfall over Europe. Iberia study case
Finisterra, 2012
Low -frequency variability is a good starting point for modelling the climate system and understanding mechanisms that can give us some indication of future climate evolution. this work aims to better understand the degree of association between the atmospheric circulation and precipitation over europe and the iberian Peninsula. to achieve this goal, the standard precipitation anomalies in europe and the anomalies of sea level pressure (sLP) in the north atlantic region during the twentieth century were subjected to Multi -Channel singular spectrum analysis (Mssa). this procedure allows us to measure the degree of association between the sLP and precipitation fields. the identification of common oscillations between the two climatic fields led not only to the confirmation of the physical meaning of these oscillations, but also to the identification of the dynamical evolution of the ocean -atmosphere system in the north atlantic. two oscillations, statistically significant, common to...
Spatial-temporal structures of quasi-periodic oscillations in precipitation over Europe
International Journal of Climatology, 2000
Based on a 5°×5° gridded monthly precipitation data set from 1911 to 1990, quasi-periodic oscillations are identified by performing a multichannel singular spectrum analysis (MSSA) on the first ten principal components (PCs; explaining 53.1% of total variance) of normalized monthly precipitation fields over Europe. Two robust quasi-periodic oscillations are isolated with periods of 23.8 months (2.0 years) and 43.5 months (3.6 years), respectively. Applying a reconstruction technique and composite analysis, spatial structures and temporal propagation of the quasi-periodic oscillations are revealed. The two oscillations behave differently: the 43.5-month oscillation clearly propagates northward; however, the 23.8-month oscillation seems quasi-stationary, although it propagates slowly southward. This may imply that the causes of these two oscillations are different. Oscillatory behaviour in the time series of a North Atlantic Oscillation (NAO) index has also been analysed by performing singular spectrum analysis (SSA) for the same period used for the analysis of precipitation. However, in the time series of the NAO index, the dominant oscillation is a 27.7-month (2.3-year) period, with no robust oscillation with a period of 3.6 years being detected. Furthermore, the two oscillations cannot be identified by MSSA from the precipitation fields regressed upon the NAO index. Therefore, it appears that the two quasi-periodic oscillations are not well related to the NAO, which may not be the most important atmospheric pattern associated with non-seasonal precipitation variability over Europe.
Journal of Geophysical Research, 2007
1] In this paper, the temporal dynamics of precipitation in northwestern France in relation to the dominant climatic pattern in Europe were investigated. The general trends and the nonstationary behavior of the North Atlantic Oscillation (NAO) were described using fractal analysis and Fourier spectral and continuous wavelet analysis of a NAO index time series over the 1865-2004 period. The 44-year and 8-year multidecadal components showed a clear increasing power during the second half of the last century. The possible link between rainfall variability and the NAO was then investigated. The links between the NAO and rainfall were not as obvious, as NAO-like components were not easily retrieved in the precipitation records: Relationships between the NAO and rainfall were very likely at certain timescales but were not systematically very obvious. For instance, the characteristic quasi-biennal oscillation (QBO) of the NAO was barely detected in precipitation, but a %6-year fluctuation beginning in the 90s was found to be statistically significant at a 95% confidence limit After investigating a possible link with the Southern Oscillation Index, the occurrence of this fluctuation in the beginning of the 90s could be related to the observed shift of the QBO toward slightly higher frequencies in the NAO time series. On the other hand, a modulation of the QBO by a %6-year interannual fluctuation would suggest the existence of a %6-year climate pattern that could affect precipitation and, to a lesser extent, the NAO. Cross-wavelet analysis between the NAO and precipitation revealed a loss in correlation across the 1970-2005 period, which seemed to be the fact of a QBO-like fluctuation. This loss of correlation was related to the above-mentioned shift of the QBO and 6-year rainfall interannual band since the 90s. Citation: Massei, N., A. Durand, J. Deloffre, J. P. Dupont, D. Valdes, and B. Laignel (2007), Investigating possible links between the North Atlantic Oscillation and rainfall variability in northwestern France over the past 35 years,
Atmospheric Research, 2009
An analysis of winter intensity and frequency of precipitation is presented, based on 102 daily precipitation stations over Spain and the Balearic Islands for the 1997-2006 decade. Precipitation stations have been merged in the eight different regions which compose the analyzed area by the use of an EOF analysis. NAO influence on the intensity and frequency of precipitation of each region is described in terms of mean precipitation, mean rain frequency, the number of extreme events, changes in the precipitation distribution and the prevalent synoptic configuration. Results indicate a non-stationary response; NAO signal being more evident in mid-late winter. Strong regional differences in the response to NAO are also found, which vary according to the specific character of the precipitation under analysis. Thus, NAO exerts a clear effect on the intensity of total and extreme precipitation rates in northern and westernmost Spanish regions, whereas the frequency of precipitation is clearly affected by NAO in central and southwestern areas. While the correlation between NAO and precipitation is negative for most of the analyzed area, two regions reveal positive responses to NAO in total precipitation occurrence and intensity for specific months. Further analyses reveal asymmetric responses to opposite phases of NAO in the precipitation distributions of some regions. The complex regional relationship between NAO and precipitation is also revealed through the modulation of the former in the preferred Circulation Weather Types associated to precipitation in each region. This spatially non-homogeneous NAO signal stresses the need of caution when employing Iberian precipitation as a proxy for NAO.
Evolution of tropical and extratropical precipitation anomalies during the 1997-1999 ENSO cycle
International Journal of Climatology, 2001
The 1997-1999 ENSO period was very powerful, but also well observed. Multiple satellite rainfall estimates combined with gauge observations allow for a quantitative analysis of precipitation anomalies in the tropics and elsewhere accompanying the 1997-99 ENSO cycle. An examination of the evolution of the El Nifio and accompanying precipitation anomalies revealed that a dry Maritime Continent preceded the formation of positive SST anomalies in the eastern Pacific Ocean. 30-60 day oscillations in the winter of 1996/97 may have contributed to this lag relationship. Research Letters.
2004
December–February (DJF) extreme rainfall was analysed at 347 European stations for the period 1958–2000. Two indices of extreme rainfall were examined: the maximum number of consecutive dry days (CDD); and the number of days above the 1961–90 90th percentile of wet-day amounts (R90N). A principal component analysis of CDD found six components that accounted for 52.4 % of the total variance. Six components of DJF R90N were also retained that accounted for 39.1 % of the total variance. The second component of R90N has a very significant trend and the factor loadings closely resemble the observed linear trend in this index, suggesting that the analysis has isolated the mode of variability causing the trend as a separate component. The principal components of the indices were correlated with surface and upper-air observations over the North Atlantic. The best correlations were generally found to be with sea-level pressure (SLP) observations. A separate canonical correlation analysis of ...
On the El-Nino Teleconnection to Spring Precipitation in Europe
Eprint Arxiv Physics 9812040, 1998
In a statistical analysis of more than a century of data we find a strong connection between strong warm El Nino 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), and much stronger than the winter season teleconnection that has been the subject of other studies. Linear correlation coefficients between DJF NINO3 indices and 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 50N from 5W to 35E. The lagged correlation suggests that south-east Asian surface temperature anomalies may act as intermediate variables.