L. K. (Nick) Shay, J. Martinez-Pedraja and M. Archer

Department of Ocean Sciences, RSMAS

To improve our understanding of surface processes and their linkages to atmospheric and oceanic boundary layer processes in the coastal ocean.

http://isotherm.rsmas.miami.edu/~nick

Acknowledgments: M. Wang, K-W Gurgel, L. Wyatt, B. Haus, T. Cook, B. Parks

Coastal Ocean Current and Wave Response to Hurricane Jeanne Using High Frequency Radar: Implications for Surge Modeling

Hurricane Jeanne (2004)

Introduction:

During 2004/2005 hurricane seasons, several (intense) hurricane landfalls in Florida.

Most intense (cat 3 or above) hurricanes in the Atlantic Ocean basin occur in Gulf of Mexico and Southeastern US (i.e. GCOOS and SECOORA).

A fully integrated Ocean Observing System would provide valuable data in improving and evaluating predictive models for landfalling scenarios including storm surge.

HF radar network, supported through NOAA’s Integerated Ocean Observing System Program, is one such tool in accurately mapping currents, winds and waves in real-time.

WERA in phased array mode with cells of about 1 km over a range of ~80 to 90 km (Research Phase). Monitoring Phase provides hourly currents at 2 km intervals. Radar are (will be) deployed at Key Largo, Key Biscayne, (Ft. Lauderdale, Virgina Key).

Focus today on currents, waves and wind directions during Hurricane Jeanne (04).

[Source: http://oceancurrents.rsmas.miami.edu]

Venue: Florida Current

Drifter Trajectories between 1978 - 2003

Doppler Spectra : Bragg Backscatter

Frequency shift off the Bragg Frequency (~0.41 Hz:red line) is proportional to the radial current...Need at least two sites for a 2-D vector current.

Note 2nd order returns has information on surface waves!

Current Resolution (cm s-1)

Resolution of Current Velocity versus Averaging Time@ different centre frequencies

0

5

10

15

20

25

30

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

Time in Minutes

Res

olut

ion

in c

m/s

ec

fo = 5 MHz

10 MHz

15 MHz

20 MHz

30 MHz

WERA Range (km) 80-120 Resolution (km) 1.200 Depth of Measurement (m) 0.75 Type FMCW Accuracy Current Speed (cm s-1) 5 Vector Direction (o) 3 Operating Frequency (MHz) 16.4 Receive Antennae 16 Frequency Scanning (KHz) 250 Peak Power (W) 30 Average Power (W) 30 Baseline Distance (km) 55

Table 1: WERA Operating parameters in SE Florida.

WERA System / Crandon Park →

WERA Experimental Designs.

• WERA deployed 28 July-4 Oct 2003 in Venice Beach FL, and Bradenton Beach FL in support of SEA-COOS.

• Transmit frequency of 16.045 MHz, bandwidth of 200 KHz (~1 km resolution).

• Tested different sample intervals-since WERA is FMCW system (512, 1024, 2048…) represented 2.2, 4.4, 9 min... samples.

• Ranges approach 100 km about 50% of the time.• Real Time WERAs in KL, KB started in May 04-Several years of

continuous data (now in Dania Beach and Virginia Key. • Mini-Waves Experiment tested wave spectral algorithms.

Example of HF Radar Performance and Measurement Grid In 2005.

Operational Times For HF radar Domain and Distribution of Good Data in 05

Angles and GDOP (Chapman et al. 1998) and Accuracy Based on SNR (Gurgel, 2005)

Under Quiescent Conditions WERA (blue) and 14-m (black) ADCP Record From Dec 04 – Feb 05 (Parks

et al., JGR, 2009).

Surface Current Response to Hurricane Jeanne: (Movie)

Note the solid yellow vectors associated with the Florida Current/Gulf Stream.

Fowey Rocks CMAN Station provided surface winds adjusted to 10-m height.

Current (left) and Current Acceleration (right x 104 cm s-2) Relative to Fowey Rocks CMAN

Station (upper left)

Directional Wave Spectra During Jeanne (04)

Wind Directions and Speed Comparisons at Fowey Rocks During Jeanne:24-25 Sept 2004

Wind Speeds Wind Directions

Current and Surface Friction Velocity (left) Correlation and Phase Angles (o) of Wind Vector

Relative to Fowey Rocks (right).

Correlation Phase

Estimation of Cd at Fowey Rocks CMAN Station Following Jarosz et al. (Science, 2007)

)1(HrU

HfV

tU sx

)2(.

HrUfV

tU

WWHC

xairD

where ρ is a reference density (1025 kg m), f is the Coriolis

parameter, U and V are the depth-integrated along-shelf and

cross-shelf velocity components, H is the water depth, r is a

constant resistance coefficient at the sea floor, and τsx is the

cross-shelf wind stress.

Note the wind stress (τsx in (1)) is defined as :

xDairsx WWC

where Wx is the cross-shelf wind velocity component following

Jarosz et al. using the Ivan data.

Recent Cd Formulations (x 1000) ….Inferred Cd’s Consistent In 15-20 m/s In Left Front Quadrant!

Bell et al. JAS (2012)

Holthuijsen et al. JGR (2012)

Summary of Progress:

HF Radar sites must be hardened to withstand severe hurricane conditions (i.e. GCOOS and SECOORA) with its power (generators) and built-in redundancy.

Surface velocity response represents can be used to infer momentum flux from surface winds associated with TCs. Linkage to cd!

Velocity response can be used to assess the depth-integrated currents associated with the surge. Not done very often in testing storm surge models.

As part of the National Network of HF Radars and the NOAA IOOS program this is one of the priority items in improving surge prediction (Paduan et al. 2004). Important to the Gulf of Mexico and Southeastern US states.

Wind directions are proportional to the ratio of the Bragg peaks in the Doppler Spectrum.

2nd-order returns have wave information such as significant wave height and directional wave spectra.

How really good are the surge models? Water levels change in response wind-driven currents and waves.