Non-stationary NAO—Gulf Stream SST front interaction
- 1Department of Physics and Astronomy, University of Bologna, Bologna, Italy (luca.famoosspaolini@unibo.it)
- 2Department of Environmental Science, Informatics and Statistics, Ca’ Foscari University, Venice, Italy
- 3Fondazione Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC), Bologna, Italy
- 4Geophysical Institute, University of Bergen and Bjerkenes Centre for Climate Research, Bergen, Norway
- 5Consiglio Nazionale delle Ricerche, Istituto di Scienze dell’Atmosfera e del Clima (CNR-ISAC), Bologna, Italy
- 6Nansen Environmental and Remote Sensing Center, Bergen, Norway
The interaction between the North Atlantic Oscillation (NAO) and the latitudinal shifts of Gulf Stream sea surface temperature front (GSF) has been the subject of extensive investigations. There are indications of non-stationarity in this interaction, but differences in the methodologies used in previous studies make it difficult to draw consistent conclusions. Furthermore, there is a lack of consensus on the key mechanisms underlying the response of the GSF to the NAO forcing. This study assesses the possible non-stationarity in the NAO—GSF interaction and the mechanisms underlying this interaction over the last few decades, using reanalysis data.
Results show that the NAO and GSF indices covary on the decadal timescales but only during 1972—2018. A secondary peak in the NAO-GSF covariability emerges on multiannual timescales but only during 2005—2015. The non-stationarity in the decadal NAO-GSF covariability is also manifested through the dependency of their lead—lag relationship on the analyzed time period. Indeed, the NAO leads the GSF shifts by 3 years during 1972—1990 and by 2 years during 1990—2018.
The lag between GSF shifts and NAO can be interpreted as the joint effect of the fast response of wind-driven oceanic circulation, the lagged response of deep oceanic circulation, and the propagation of Rossby waves. However, there is evidence of Rossby wave propagation only before 1990. Here it is suggested that the non-stationarity of Rossby wave propagation causes the time lag between the NAO and the GSF latitudinal position on decadal timescales to differ before and after 1990.
Considering the impact that the GSF variability has on the North Atlantic variability, the non-stationarity in the NAO—GSF covariability has important implications for the predictability of the North Atlantic sector.
How to cite: Famooss Paolini, L., Omrani, N., Bellucci, A., Athanasiadis, P. J., Ruggieri, P., Patrizio, C. R., and Keenlyside, N.: Non-stationary NAO—Gulf Stream SST front interaction, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-11, https://doi.org/10.5194/ems2023-11, 2023.
