1. Surface Current Observations with Drifting Buoys in the Philippines Archipelago Carter Ohlmann University of California, Santa Barbara DRI Objective: Provide an observational understanding of the regional, sub- meso, and fine scale surface circulation that occurs in straits.

2. Research Summary: surface current observations with high-resolution drifting buoys  among the first regional observations of time-space flow evolution  data provide information on flows ubiquitous to straits - tidal circulation over many days - flow around small islands - sidewall eddy scales - fine scale (10’s of meters and minutes) structures  data help with interpretation of HF radar and model surface currents  observations for (Lagrangian) dynamical systems research Some DRI Goals: “spatial variability on short time scales”; “new in situ instrumentation”; “structure and evolution of flow”

3. Outline: instrumentation (2 types of drifters used)  descriptive summary of all data collected (~130 tracks; and counting)  focus on fine-scale flow in San Bernardino strait  validation of HF radar derived surface currents  mixing parameters

4. Instrumentation (Drifters): efficient method of observing flow patterns over a range of scales SVP Drifters: holey sock drogue centered at 15 m depth position recorded hourly w/ GPS data transmission through Argos 1 cm/s slip in 10 m/s wind 1 year life expectancy expendable pictures courtesy of Lumpkin and Pazos, AOML

5. Instrumentation (Drifters): efficient method of observing flow patterns over a range of scales Microstar Drifters: tri-star drogue centered at 1 m depth 10 minute position sampling w/ GPS data transmission through Iridium 1 cm/s slip in 10 m/s wind 7 day life expectancy real time data recoverable

6. Historical Drifter Data in Philippines Region Few Drifter Observations before Philex

7. drifters sample a wide range of scales Drifter Data Collected during Philex R/V Melville Filippino banca SVP drifters # tracks: 8 length: 7 – 94 days Microstar Drifters # tracks: 130+ length: hours - 10 days

8. IOP ’09; San Bernardino Strait Observational Goals flow around headlands island wakes fine scale structure sidewall eddy scales nearshore transport ~20 km + ending position

9. Sidewall Flow Structure in San Bernardino Strait starting position ending position Near shore velocity shear location: < ~1km from shore drifters move: ~1.0 - 10 km advection time: ~2 hrs velocity: ~0.14 to 1.4 m/s relative vorticity ~ 100f Quantify transport where towed vehicle can’t survey Novel observations of fine scale boundary layer flows + ~13 km

10. Sidewall Flow Structure in San Bernardino strait 500 m ~4 km

11. Sidewall Flow Structure in San Bernardino Strait ~13 km boundary layer < ~500 m from shoredrifters further offshore during weaker flow appear outside boundary layer

12. IOP ’09; San Bernardino Strait Observational Goals flow around headlands island wakes fine scale structure sidewall eddy scales nearshore transport ~20 km + ending position

13. Fine Scale Flow Structure in San Bernardino Strait convergence zones ( many others observed ) ~13 km velocity shears (( 0.1 - 0.75 m/s) / 1 km) temporal fluctuations ( dot spacing)

14. Interpretation of HF Radar Currents comparison of radial velocities from HF radar sites with the radial component of velocities from co-located drifter observations

16. Summary: instrumentation (2 types of drifters used)  descriptive summary of all data collected (~130 tracks; and counting)  focus on fine-scale flow in San Bernardino strait  validation of HF radar derived surface currents  mixing parameters

17. SVP drifters # tracks: 8 length: 7 – 94 days Microstar Drifters # tracks: 42 lengths: < 7 days Goals deploy/recover logistics overcome fishermen flow descriptions flow around small island Exploratory Cruise; June 2007 R/V Melville

18. February 2008 Microstar Drifters # tracks: 43 lengths: mostly hours Goals deploy/recover logistics flow descriptions Pandan Bay circulation Filippino banca

19. IOP ‘09; February 2009 R/V Melville Microstar Drifters # tracks: 45 lengths: < 11 days Goals HF radar validation relative dispersion values “sub-grid” motions/energy Surface “flow through straits”?

20. Sidewall flow structure in San Bernardino strait drifters located > ~1 km offshore no flow separation around headland starting position ending position ~6.5 km ~3 hrs ~0.6 m/s +