Stratosphere key for wintertime atmospheric response to warm Atlantic decadal conditions.

Omrani, Nour-Eddine , Keenlyside, Noel S., Bader, Jürgen and Manzini, Elisa (2014) Stratosphere key for wintertime atmospheric response to warm Atlantic decadal conditions. Climate Dynamics, 42 (3/4). pp. 649-663. DOI 10.1007/s00382-013-1860-3.

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There is evidence that the observed changes in winter North Atlantic Oscillation (NAO) drive a significant portion of Atlantic Multi Decadal Variability (AMV). However, whether the observed decadal NAO changes can be forced by the ocean is controversial. There is also evidence that artificially imposed multi-decadal stratospheric changes can impact the troposphere in winter. But the origins of such stratospheric changes are still unclear, especially in early to mid winter, where the radiative ozone-impact is negligible. Here we show, through observational analysis and atmospheric model experiments, that large-scale Atlantic warming associated with AMV drives high-latitude precursory stratospheric warming in early to mid winter that propagates downward resulting in a negative tropospheric NAO in late winter. The mechanism involves stratosphere/troposphere dynamical coupling, and can be simulated to a large extent, but only with a stratosphere resolving model (i.e., high-top). Further analysis shows that this precursory stratospheric response can be explained by the shift of the daily extremes toward more major stratospheric warming events. This shift cannot be simulated with the atmospheric (low-top) model configuration that poorly resolves the stratosphere and implements a sponge layer in upper model levels. While the potential role of the stratosphere in multi-decadal NAO and Atlantic meridional overturning circulation changes has been recognised, our results show that the stratosphere is an essential element of extra-tropical atmospheric response to ocean variability. Our findings suggest that the use of stratosphere resolving models should improve the simulation, prediction, and projection of extra-tropical climate, and lead to a better understanding of natural and anthropogenic climate change.

Document Type: Article
Keywords: Meteorology; Atlantic decadal variability; North Atlantic Oscillation (NAO) and Northern Annular Mode (NAM); Atlantic Multidecadal Oscillation (AMO) and Variability (AMV); Major Stratospheric Warming (MSW) and stratosphere–troposphere coupling; Ocean–Atmosphere interaction; Tropical–Extratropical teleconnections; Multidecadal NAO and NAM trends and variability
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-ME Maritime Meteorology
Refereed: Yes
Open Access Journal?: No
Publisher: Springer
Projects: SUMO, STEPS, MiKlip
Date Deposited: 04 Jan 2012 12:46
Last Modified: 13 Sep 2016 12:16

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