engleski

Delayed European precipitation response to wintertime ENSO: the role of the stratosphere and North Atlantic SSTs

Delayed impact of El Niño-Southern Oscillation (ENSO) on European late spring climate is examined using an intermediate complexity model. The focus of the analysis is response of the upper troposphere/stratosphere, downward propagation of the signal and its interaction with the North Atlantic. The stratosphere responds to El Niño (La Niña) events with substantial warming (cooling) occurring in the polar area accompanied by a corresponding modification of upper-level geopotential heights and zonal winds resembling the pattern of Northern Annular Mode. The atmospheric response propagates from the upper troposphere downward to the surface, interacts with North Atlantic where the wintertime ENSO signal is memorized and persists until the following spring when through the interaction with the overlaying atmosphere it is transmitted again into the atmosphere. Furthermore, it is demonstrated here that the late springtime ENSO signal over Europe may be considered as a result of two contributing processes: one is a direct (spring-to-spring) ENSO influence and the other is a delayed (winter-to-spring) ENSO influence. The delayed ENSO impact results partially from the persistence of the wintertime ENSO signal in the stratosphere, but it is also maintained by atmosphere-ocean interaction in the North Atlantic. The presented results also emphasize the role of the extratropical Atlantic as a contributing factor for climate variability linking wintertime atmospheric circulation and European climate during the following spring.

ENSO impact ; Europe ; stratosphere ; North Atlantic

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