1. L. K. Shay, J. Martinez-Pedraja , A. B. Parks
Application of High Frequency Radar & Okubo-Weiss Parameter to Analyze Variability in the Florida Current
Ocean Sciences 2012
Matthew Archer
L. K. Shay, J. Martinez-Pedraja , A. B. Parks

2. [Source: http://oceancurrents.rsmas.miami.edu]
Florida Current
[Source:
Gulf Stream
IMPORTANCE – MOC/heat transport + wind driven gyre circulation. Previous research focused mainly on explaining this larger scale variability.
Loop
Current
Drifter Trajectories between

3. Florida Current Meanders Cyclonic eddies; Florida Atlantic Ocean
⌐ Bahamas¬
Cuba
Florida Keys
Cal Say Bank
Santaren Channel
 Gulf of Mexico
NW Providence Channel
South
Bight
Meanders
Cyclonic eddies;
Tortugas eddies (TE)
Frontal eddies (FE)
Submesoscale motions…
IMPORTANCE – MOC/heat transport + wind driven gyre circulation. Previous research focused mainly on explaining this larger scale variability.

4. Vortices in the Florida Current
Shay et al., 1998; Shay et al., 2000 ; Parks et al., 2009
Shay et al. [1998] ; Shay et al. [2000] ; Parks et al. [2009]
Forcing
Abrupt wind change
Length Scale
2-30 km (cross-shelf)
4-40 km (along-shelf)
Translational Velocity
km/day
Rotation
-Cyclonic
-Dipole excited by near-inertial wave propagation
Vortices research

5. Objectives
Using high frequency (HF) radar as tool to monitor the evolution of the Florida Current, for:
Oil spill mitigation procedures in the surface layer
Search and Rescue (Cuban Rafters)
Larvae transport
Optimizing commercial shipping interests (i.e. going with the flow)
FOCUS
To understand the surface current signals associated with energetic vortices to improve real time monitoring across the FC in addressing the above issues.

6. ADCP mooring (80-m depth)
Radar domain
Radar Site
ADCP mooring (80-m depth)
CMAN Buoy

7. WEllen RAdar (WERA) Specifications
Frequency Modulated Continuous Wave (FMCW) System:
Chirp Interval: 0.26 sec
Operating frequency: MHz
Range: 80 km
Horizontal resolution: 1.2 km
Sampling interval: 10 min
Flexible: can be altered to sample a few minutes to several hours (e.g. 128, 256, 512……samples in the averaging)

8. In Florida Current velocities often exceed 200 cm s-1
Accuracy
Total radial accuracy
~ 3-5 cms-1
In Florida Current velocities often exceed 200 cm s-1
ADCP Comparison:
[14-m bin depth Vs. radar cell]
Complex correlation ~ 0.8
ADCP Mooring
Adapted from Parks et al. [2009]

9. Case Study: Submesoscale Vortex
January 2005

11. Spatial Dimensions ~30-km Along-Shelf ≈ 17-km Cross-Shelf ≈ 24-km
Peters et al., 2002:
Radius of Deformation in the Florida Straits shelf break:
~30-km

12. = 46 km/day u-component velocity Slope ̴ 66 km/34 hrs Wind Shift
Cold Front
Wind Shift
Adapted from Parks et al., JGR [2009]
Wind Stress calculation following Fairall et al., JGR [1996]

13. Okubo-Weiss (OW) Criterion
Based on the eigenvalues of the velocity gradient tensor. Physically it describes the balance between vorticity and deformation:
OW = Sn Ss ω2
Normal Strain
Shear Strain
Vorticity
Refer to: McWilliams [1984]; Isern-Fontanet et al. [2003; 2004; 2006] ; Chelton et al. [2007]; Chaigneau et al. [2008]

14. Application of OW

15. Application of OW

16. Application of OW

17. Summary: Work In progress
WERA resolves submesoscale features.
Marked bin to bin coherence in the surface signals.
Several years of data sensing the FC
Regarding implementation of Okubo-Weiss …
Jury is still out on using OW given importance of shear and strain along the western flank of the Florida Current and its impact on submesoscale structures.
Need to change this – put future work at the very end (or very start) not just in the middle!
Frequency analysis to determine forcing mechanisms?

18. Future Work
Subsurface structure from ADCP suggests barotropic nature over the shelf break – relationship to the topography and bottom boundary layer?
Relationship to the wind stress field
Frequency decomposition
Parks et al., JGR [2009]