The North Atlantic Oscillation and the latitude of the Gulf Stream

Abstract

The physical processes determining the path of the Gulf Stream as it leaves the continental shelf of the USA are complex and involved. Understanding these processes is important to global climate studies because the Gulf Stream plays a major rôle in the distribution of heat in the northern hemisphere. Here we show that during the last 3 decades, the latitude of the Gulf Stream has been clearly correlated with the North Atlantic Oscillation (NAO); high values of the NAO index, which correspond to stronger westerly and trade winds, favouring more northerly paths of the Stream about 2 years later. The time‐delay may be associated with the adjustment time of this part of the ocean circulation. If allowance is made for persistence of the Gulf Stream position from one year to the next, more than half the interannual variation in the position can be predicted.

North Atlantic climate variability: phenomena, impacts and mechanisms

“…Halliwell (1998). Observations of the relation between the latitude of Gulf Stream separation and the NAO are more equivocal: Taylor and Stephens (1998) and Frankignoul et al (in press) find that observed shifts do indeed lag the NAO but only by 2 years.…”

Can ozone depletion and global warming interact to produce rapid climate change?

“…Whether such a shift will, in time, serve to change the intensity or basic character of the thermohaline circulation has yet to be determined. There are indications that the latitude of the north wall of the Gulf Stream has shifted northward slightly in recent decades in response to the trend in the NAM (92). A continued northward shift would favor additional warming over Eurasia and the Arctic, above and beyond that associated with the trend in the NAM itself.…”

The role of Atlantic Ocean-atmosphere coupling in affecting North Atlantic oscillation variability

“…Indeed, the subtropical-subpolar gyres of the North Atlantic and the Gulf Stream-recirculation system strongly respond to NAO variability [Taylor and Stephens, 1998;Joyce et al, 2000;Curry and McCartney, 2001;Frankignoul et al, 2001b;Visbeck et al, this volume], but also show significant intrinsic variability of their own on interannual and longer timescales [e.g., Jiang et al, 1995;Meacham, 2000;Cessi and Primeau, 2001;Cessi and Paparella, 2001;Dewar, 2001]. Both intrinsic and forced dynamics lead to changes in heat transport across the mean path of the separated Gulf Stream through expansion -contraction of the gyres, or equivalently, through large-scale anomalous currents acting on mean temperature gradients.…”

“…As reviewed in Visbeck et al [this volume], the dynamical ocean response can occur on a broad range of timescales with distinct spatial patterns. Various observational studies have shown a fast response of the Gulf Stream/recirculation system to NAO variability (about a 1-year lag), leading to localized SST anomalies north of the Gulf Stream extension [e.g., Taylor and Stephens, 1998;Frankignoul et al, 2001b]. On longer (decadal and interdecadal) timescales, the ocean response involves basin-scale currents and SST anomalies, as hinted at in various numerical studies [e.g., Visbeck et al, 1998;Krahman et al, 2001;Eden and Jung, 2001;Eden and Willebrandt, 2001].…”