Luca Famooss-Paolini (2023-05-26): Ocean–atmosphere interaction at the Gulf Stream sea surface temperature front: variability and impacts on midlatitude atmospheric circulation. PhD thesis, Ca’ Foscari University, Italy. http://hdl.handle.net/10579/25044 .
Summary: Recent studies show that the Gulf Stream Front (GSF) is an essential ingredient of the Northern Hemisphere climate. However, the nature of the air-ocean interaction associated with the GSF variability is not understood. This thesis first analyses the atmospheric response to the meridional slip of the GSF and its dependence on model resolution, using multi-model atmospheric simulations and the ERA5 reanalysis. Finally, the thesis analyses the spectral features of the NAO-GSF interaction and the mechanisms through which the NAO forces the GSF slip, using atmospheric and oceanic reanalyses. Regarding the first point, the results show that the GSF slip induces local diabatic heat anomalies that are mainly balanced by the vertical motion and meridional transport of transient eddy streams. On the large scale, the GSF slip is associated with the homo-directional slip of the eddy-driven jet and the storm-track. However, the atmospheric response is dependent on model resolution. Only those with a resolution higher than 50 km reproduce a response similar to the observed anomalies. Regarding the second point, the results show that the NAO and the meridional position of the GSF covary on the decadal scale, but only during 1972-2018. The non-stationarity of this decadal covariability is also shown by the time dependence of their lead-lag relationship. The lag between the NAO and the GSF response on the decadal scale can be interpreted as the effect of several mechanisms. However, not all of them are stationary. There is evidence of Rossby wave propagation only before 1990, which can explain the time dependence of the NAO-GSF lead-lag relationship..
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