Icelandic Low and Azores High Migrations Impact Florida Current Transport in Winter

Abstract

Previous work to find an association between variations of annually averaged Florida Current transport and the North Atlantic Oscillation (NAO) have yielded negative results (Meinen et al. 2010). Here we show that Florida current in winter is impacted by displacements in the positions of the Azores High and the Icelandic Low, the constituent pressure centers of the NAO. As a one-dimensional representation of North Atlantic atmospheric circulation, the NAO index does not distinguish displacements of the pressure centers from fluctuations in their intensity. Florida Current transport is significantly correlated with Icelandic Low longitude with a lag of less than one season. We carried out perturbation experiments in the ECCOv4 model to investigate these correlations. These experiments reveal that east-west shifts of the Icelandic Low perturb the wind stress in mid-latitudes adjacent to the American coast, driving downwelling (through longshore winds) and offshore sea level anomalies (through wind stress curl) which travel to the Florida Straits within the same season. Florida Current transport is also correlated with the latitude variations of both the Icelandic Low and the Azores High with a lag of four years. Regression analysis shows that latitude variations of the Icelandic Low and the Azores High are associated with positive wind stress curl anomalies over extended regions in the ocean east of Florida. Rossby wave propagation from this region to the Florida Straits has been suggested as a mechanism for perturbing FCT transport in several previous studies (DiNezio et al. 2009; Czeschel et al. 2012; Frajka-Williams et al. 2013; Domingues et al. 2016, 2019).

Interannual to decadal sea level variability in the subpolar North Atlantic: the role of propagating signals

“…We have shown that the observed propagation of the dynamic SSH anomalies in the SPNA is linked to the NAO-like atmospheric pressure and wind patterns that change their location and intensity. The importance of accounting for the position and intensity of an atmospheric center of action for determining causal relationships within the coupled oceanatmosphere system in the North Atlantic has been reported earlier (e.g., Hameed and Piontkovski, 2004;Hameed et al, 2021). Our results provide further evidence that the attribution of oceanic signals to the conventional NAO index, which generalizes and often oversimplifies the atmospheric variability, is not always appropriate.…”

Remote Impact of the Equatorial Pacific on Florida Current Transport

“…However, they found that wind stress curl changes over the ocean interior induced by the meridional migrations of the Azores High and the Icelandic Low pressure centers can result in FCT changes 4 years later through the Rossby wave propagation mechanism. The small difference in the time lag is probably because we used monthly instead of wintertime data as in Hameed et al (2021). When we use the wintertime (DJF) FCT and NAO during 1993-2020, the correlation between them becomes 0.27 at 4-year lag.…”

“…Hameed et al. (2021) examined the wintertime FCT and the NAO during 1983–2017 and found no significant correlation between the two. However, their analysis suggested that the zonal migrations of the Azores High are associated with alongshore wind stress changes close to the North America coast.…”

“…The majority of earlier studies on FCT has attributed its variability to wind forcing either remotely from upstream or downstream of the FS (Anderson & Corry, 1985a, 1985b; Czeschel et al., 2012) or from ocean interior (e.g., Di Nezio et al., 2009; Domingues et al., 2016), or locally from along‐stream winds (e.g., T. N. Lee and Williams, 1988; Schott et al., 1988; Beal et al., 2008). The North Atlantic Oscillation (NAO), eddy activity east of the Bahamas, and the excursions of the Loop Current have also been identified as drivers for the FCT variability (Baringer & Larsen, 2001; C. S. Meinen et al., 2010; Domingues et al., 2019; Frajka‐Williams et al., 2013; Hameed et al., 2021; Hirschi et al., 2019; Lin et al., 2009; Mildner et al., 2013).…”

“…This anti-correlation was linked to the propagation of the first mode baroclinic Rossby waves forced by NAO-induced wind stress curl changes in the ocean interior (Di Nezio et al, 2009). However, C. S. Meinen et al (2010) found that this mechanism only holds during the period 1984-1998. Hameed et al (2021 examined the wintertime FCT and the NAO during 1983-2017 and found no significant correlation between the two.…”