Wintertime ENSO influence on late spring European climate: the stratospheric response and the role of North Atlantic SST

The impact of the wintertime El Niño-Southern Oscillation (ENSO) on European late spring climate is examined using an atmospheric general circulation model of intermediate complexity. The analysis is focused on the response of the lower stratosphere/upper troposphere, downward propagation of the ENSO signal detected in temperature, zonal wind and geopotential height and contribution of the North Atlantic to the persistence of the associated surface anomalies. It is found that 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 the Northern Annular Mode. The atmospheric response is detected in the upper troposphere as well as at the surface where it interacts with the North Atlantic. In this way, the footprint of atmospheric wintertime ENSO signal is preserved in the ocean persisting until the following spring when it is transmitted back into the atmosphere through the sea–air interaction. Furthermore, it is showed 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. Two processes enable the delayed ENSO impact: the persistence of the wintertime ENSO signal in the stratosphere and the atmosphere–ocean interaction in the North Atlantic. Numerical simulations indicate that the memory of the ocean mixed layer is stronger than that of the stratosphere. In this manner, the presented results emphasize the extratropical Atlantic as a contributing factor for climate variability linking wintertime atmospheric circulation associated with ENSO forcing and European climate during the following spring.