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ENSO and NAO influence on climate variability in Europe

El Niño Southern Oscillation is one of the strongest sources of global climate variability. Although it has been examined extensively and its impact on climate variability of certain regions is clear and well explained, there are still a lot of questions regarding its effect on European and Mediterranean region. The ENSO related signal that is detected in this region is generally weak and shows spatial and seasonal dependence. On the other hand, Europe is under the dominant influence of the North Atlantic Oscillation (NAO), a mode of internal variability with a well established impact. Since both phenomena may exert a certain influence on European climate at the same time, it is not simple to distinguish these two effects. Thus, the ENSO impact, which is relatively weak, can be masked by the stronger impact of NAO. There is also a possibility that the NAO signal is modulated by ENSO, particularly during strong ENSO events. Therefore, we may pose a question whether it is possible to separate ENSO and NAO signals. Here we examine the relative ENSO and NAO impact on the European climate using a large ensemble of long numerical simulations. We analyze a 35- member ensemble of numerical simulations for 1855-2010 period performed with ICTP AGCM, an atmospheric general circulation model (AGCM) of intermediate complexity developed at International Centre for Theoretical Physics (ICTP). Positive, negative and neutral ENSO years are determined according to the strength of the wintertime (JFM) Nino3.4 index, while PC-based NAO index is used for classification of NAO years. Composite analysis is applied to the anomalies of different meteorological parameters (geopotential height, temperature etc.) with the aim to analyze the atmospheric patterns associated with specific ENSO-NAO combinations. Additionally, signal-to-noise analysis is also performed.

ENSO, NAO, signal, Europe

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