The Surface Velocity Structure of the Florida Current in a Jet Coordinate Frame

• Published in: Journal of geophysical research. Oceans 2017-11, Vol.122 (11), p.9189-9208
• Main Authors: Archer, Matthew R., Shay, Lynn K., Johns, William E.
• Format: Article
• Language: English
• Subjects: Annual variations; Climate change; Climate system; Coastal circulation; Coastal environments; Deceleration; Eddy kinetic energy; Florida Current; Geophysics; HF radar; high‐frequency (HF) radar; jet meandering; jet or stream coordinates; Kinetic energy; Local winds; Meandering; Meanders; Ocean current measurements; Ocean currents; Phase velocity; Radar; Sea level; Sea level changes; Sea level fluctuations; Sea level variability; Seasonal variations; Seasonality; Shear; Straits of Florida; Surface velocity; Transport; Two dimensional analysis; Two dimensional jets; Variability; Volume transport; Vortices; western boundary current; Width; Wind; Wind stress
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/2017JC013286

The structure and variability of the Florida Current between 25° and 26°N are investigated using HF radar ocean current measurements to provide the most detailed view of the surface jet to date. A 2‐D jet coordinate analysis is performed to define lateral displacements of the jet in time (meandering), and associated structural variations over a 2 year period (2005–2006). In the jet coordinate frame, core speed has a median value of ∼160 cm s−1 at the central latitude of the array (25.4°N), with a standard deviation (STD) of 35 cm s−1. The jet meanders at timescales of 3–30 days, with a STD of 8 km, and a downstream phase speed of ∼80 km d−1. Meandering accounts for ∼45% of eddy kinetic energy computed in a fixed (geographical) reference frame. Core speed, width, and shear undergo the same dominant 3–30 day variability, plus an annual cycle that matches seasonality of alongshore wind stress. Jet transport at 25.4°N exhibits a different seasonality to volume transport at 27°N, most likely driven by input from the Northwest Providence Channel. Core speed correlates inversely with Miami sea level fluctuations such that a 40 cm s−1 deceleration is associated with a ∼10 cm elevation in sea level, although there is no correlation of sea level to jet meandering or width. Such accurate quantification of the Florida Current's variability is critical to understand and forecast future changes in the climate system of the North Atlantic, as well as local impacts on coastal circulation and sea level variability along south Florida's coastline. Key Points The Florida Current surface jet exhibits dominant variability from 3 to 30 days in meandering, core speed, width, and shear The jet structure undergoes a robust annual cycle in core speed, width, and shear, corresponding to local wind stress The annual cycle of jet transport is very different between 25.5°N and 27°N, likely driven by input from the Northwest Providence Channel