Accuracy of Florida Current Volume Transport Measurements at 27°N Using Multiple Observational Techniques

Abstract

For more than 30 years, the volume transport of the Florida Current at 278N has been regularly estimated both via voltage measurements on a submarine cable and using ship-based measurements of horizontal velocity at nine historical stations across the Florida Straits. A comparison of three different observational systems is presented, including a detailed evaluation of observational accuracy and precision. The three systems examined are dropsonde (free-falling float), lowered acoustic Doppler current profiler (LADCP), and submarine cable. The accuracy of the Florida Current transport calculation from dropsonde sections, which can be determined from first principles with existing data, is shown to be 0.8 Sv (1 Sv [ 10 6 m 3 s 21 ). Side-by-side comparisons between dropsonde and LADCP measurements are used to show that the LADCP-based transport estimates are accurate to within 1.3 Sv. Dropsonde data are often used to set the absolute mean cable transport estimate, so some care is required in establishing the absolute accuracy of the cable measurements. Used together, the dropsonde and LADCP sections can be used to evaluate the absolute accuracy and precision of the cable measurements. These comparisons suggest the daily cable observations are accurate to within 1.7 Sv, and analysis of the decorrelation time scales for the errors suggests that annual transport averages from the cable are accurate to within 0.3 Sv. The implications of these accuracy estimates for long-term observation of the Florida Current are discussed in the context of maintaining this key climate record.

Accelerated sea level rise and Florida Current transport

“…Specifically, two-thirds of the variance is at sub-annual timescales, less than 10 % annually, 13 % interannually (13-42 months), and less than 10 % at periods longer than 42 months. Meinen et al (2010) also found no evidence for a long-term linear trend in Florida Current transport based on data for 1982-2007, and variability on decadal timescales of roughly ±1 Sv during 1982. Garcia and Meinen (2014 recently assessed accuracy of the cable transport estimates, finding that annual transport averages are accurate to within 0.3 Sv and that the cable is capable of observing small but important climate-induced The reconstructed data are uniformly sampled from distributions constructed from all available data for a missing yearday.…”

“…Gulf Stream dynamics in the Middle Atlantic Bight of North America (between Cape Hatteras and Cape Cod) is known to express similar influences on MSL (Thompson et al, 2014;Goddard et al, 2015). For example, Woodworth et al (2014) related AMOC and wind stress to MSL finding that wind stress dominates at interannual and shorter timescales.…”

Measuring the Atlantic Meridional Overturning Circulation at 26°N

“…The Gulf Stream has a mean strength of 32 Sv, with a daily standard deviation of 792 about 3 Sv and a small seasonal cycle with a peak-to-peak amplitude less than 3 Sv. It is 793 estimated that the daily transport measurements are accurate to within 1.1 Sv and annual 794 averages are accurate to within 0.3 Sv over the time period of the RAPID measurements 795 (Meinen et al (2010), Garcia and Meinen (2014 )). The Gulf Stream in the Florida Straits 796 has had a remarkably constant strength with no statistically significant long term trends 797 discernable relative to the energetic shorter term variability.…”

Florida Current Salinity and Salinity Transport: Mean and Decadal Changes

“…Routine hydrography/velocity transects (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) were initiated in 2001 and have been sustained to the present by NOAA/Atlantic Oceanographic and Meteorological Laboratory (AOML) (Garcia & Meinen, 2014;Meinen & Luther, 2016;Szuts & Meinen, 2013), using a Seabird CTD and a Teledyne RDI LADCP (Lowered Acoustic Doppler Current Profiler) sampling system. Transects are collected 3-4 times per year, and each represents a single DOF as the sections are always more than 2Γ apart in time.…”