Loop Current Variability as Trigger of Coherent Gulf Stream Transport Anomalies

Abstract

Satellite observations and output from a high-resolution ocean model are used to investigate how the Loop Current in the Gulf of Mexico affects the Gulf Stream transport through the Florida Straits. We find that the expansion (contraction) of the Loop Current leads to lower (higher) transports through the Straits of Florida. The associated surface velocity anomalies are coherent from the southwestern tip of Florida to Cape Hatteras. A simple continuity-based argument can be used to explain the link between the Loop Current and the downstream Gulf Stream transport: as the Loop Current lengthens (shortens) its path in the Gulf of Mexico, the flow out of the Gulf decreases (increases). Anomalies in the surface velocity field are first seen to the southwest of Florida and within 4 weeks propagate through the Florida Straits up to Cape Hatteras and into the Gulf Stream Extension. In both the observations and the model this propagation can be seen as pulses in the surface velocities. We estimate that the Loop Current variability can be linked to a variability of several Sverdrups (1Sv = 106 m3 s−1) through the Florida Straits. The exact timing of the Loop Current variability is largely unpredictable beyond a few weeks and its variability is therefore likely a major contributor to the chaotic/intrinsic variability of the Gulf Stream. However, the time lag between the Loop Current and the flow downstream of the Gulf of Mexico means that if a lengthening/shortening of the Loop Current is observed this introduces some predictability in the downstream flow for a few weeks.

The Atlantic Meridional Overturning Circulation in High‐Resolution Models

“…Any snapshot (or averaging on timescales shorter than about monthly) of the AMOC reveals the much more intricate, complex nature of the ocean circulation. Currents implied to be coherent flows in AMOC schematics can be seen to consist of a succession of eddies and filaments (with some coherent jets in places such as the Gulf Stream between Florida and Cape Hatteras; e.g., Hirschi et al, ). For surface currents, this picture is confirmed in both satellite observations and in high‐resolution ocean models and for many features there is remarkable agreement between observations and model simulations (Figure ).…”

Synergy of In Situ and Satellite Ocean Observations in Determining Meridional Heat Transport in the Atlantic Ocean

“…This changing dominance can be explained by the reduced anomalies in the Q FC since 2004, dominated by the anomalous volume transport. Florida Current transport has been the subject of numerous studies (Hirschi et al, 2019 and references therein) and its variability has been attributed to changes in the surface wind stress curl and in the Loop Current. Our preliminary analysis also suggests a strong link between local meridional winds and the strength of the Florida Current transport.…”

Eddies Connect the Tropical Atlantic Ocean and the Gulf of Mexico

“…The past few decades have provided a large number of observational and numerical circulation modeling studies on the LC system (e.g., Candela et al., 2019; Chang & Oey, 2010, 2013; Hirschi et al., 2019; Liu et al., 2016; Oey et al., 2005; Sturges & Leben, 2000; Xu et al., 2013; Weisberg & Liu, 2017). Despite these and others, a fundamental question remains: What controls the trajectory of the LC?…”