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Supplementary material to “The Florida Current: A Clean but Challenging Energy Resource”
25 January 2010
Howard P. Hanson, Southeast National Marine Renewable Energy Center, Florida Atlantic University, Boca Raton
Alexandra Bozek, Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee
Alana E. S. Duerr, Department of Ocean and Mechanical Engineering, Florida Atlantic University, Boca Raton
Citation:
Hanson, H. P., A. Bozek, and A. E. S. Duerr (2011),The Florida Current: A clean but challenging energy resource, Eos Trans. AGU, 92(4), 29–30, doi:10.1029/2011EO040001. [Full Article (pdf)]
The baroclinic flow field of the Florida Current has important implications for renewable energy development. Figure S1 shows the observations of Leaman et al. [1987], a 28-month average from repeated Pegasus float measurements across 27°N, and the December, 2008 average across 27°N from the HYCOM global assimilation run (HYCOM is the HYbrid Coordinate Ocean Model, e.g., Bleck [2002]; Chassignet et al. [2010]; see http:/www.hycom.org for details and discussion). Hanson et al. [2010] showed that the Pegasus data imply a strong relationship between the power of the flow and the cut-in speed of a generating system, that, in particular, systems with lower cut-in speeds have access to an increasingly large power resource
Fig. S1. Florida Current cross-section at 27°N from (left) Leaman et al. [1987] and (right) the HYCOM 1/12° assimilation run for December 2008, in which the southward flow on the east side is a transient feature.
This observational result is reflected in results from numerical simulation as well. The upper twelve panels in Figure S2 show how the HYCOM reproduces the cut-in speed dependence of available power in the Florida Current on a month-to-month basis. Because these results are taken from the model’s integrated in assimilation mode, they represent a composite of both observations and numerical model physics. HYCOM has a low bias in total power compared to observations, and the black model curves have been corrected for that here.
Fig. S2. Total available power (109 W) of the flow of the Florida Current at 27°N as a function of generating system cut-in speed (m s-1), for the months of 2008 from the HYCOM 1/12° assimilation run (see Chassignet et al.,[2007]; Rousset and Beal [2010]).. The lower panel shows how the total power can be fit to the total volume transport through the Florida Straits.
The multiple, overlying curves in the monthly panels of Figure S2 show the power of the Florida Current that is available above a given (x-axis) cut-in speed. Thus, the total power in the E-W section across the Florida Straits is the ordinate’s crossing point, and the curve crosses the abscissa at the maximum current speed that month. The self-similarity of the power/cut-in-speed relationship for the various months (black curves) is striking, to the point that the various months’ relationships can be described rather well by a single, second-order formula with one free parameter:
P = Po + 3.71·U – 7.50·U2 (to within ±~10%) (S1)
where P is the power (GW = 109W) above a particular cut-in speed U (m s-1), and Po is the total power, the free parameter. Note that Po is the power of the flow in the entire channel of the Florida Straits. The gray bands in the monthly panels of Figure S2 show the range of individual monthly regressions, and Equation S1 is plotted in the monthly panels of Figure S2 as the red curves using the value of Po for that month.
Of further interest is the result that Po can be related via linear regression to the Florida Current’s volume flux T, the familiar ~31 Sv (Sv = 106 m3 s-1) transport that is monitored, for example, by induction on trans-Straits communications cables [Meinen et al. 2010]:
Po = 1.72·T – 34.08 (to within ±~10%). (S2)
This regression is shown in the lower panel of Figure S2.
Equations S1 and S2 are used with the abscissa values of T in Figure S2, in Figure 2 of the main text.
Additional References
Bleck, R. (2002), An oceanic general circulation model framed in hybrid isopycnic-Cartesian coordinates, Ocean Modell, 37, 55-88.
Chassignet, E.P., H.E. Hurlburt, O.M. Smedstad, G.R. Halliwell, P.J. Hogan, A.J. Wallcraft, R. Baraille, and R. Bleck, (2007) The HYCOM (HYbrid Coordinate Ocean Model) data assimilative system, J. Mar. Sys., 65, 60-83, DOI: 10.1016/j.jmarsys.2005.09.016.
Chassignet, E.P., H.E. Hurlburt, E.J. Metzger, O.M Smedstad, J.A. Cummings, G.R. Haliwell, R. Bleck, R. Baraville, A.J. Wallcraft, C. Lozano, H.L. Tolman, A. Srinivasan, S. Hankin, P. Cornillon, R. Weisberg, A. Barth, R. He, F. Werner, and J. Wilkin (2009), US GODAE: Global ocean prediction with the HYbrid Coordinate Ocean Model (HYCOM). Oceanography, 22, 64-75.
Rousset, C., and L. Beal (2010) Observations of the Florida and Yucatan Currents from a Caribbean Cruise Ship, J. Phys. Oceanogr., 40, doi: 10.1175/2010JPO4447.1.