Glider-based Observations of the Kuroshio and Philippine Archipelago

Glider-based Observations of the Kuroshio andPhilippine Archipelago: Operational Lessonsand Early ResultsKuroshio: Craig Lee (APL-UW) and Dan Rudnick(SIO-UCSD)Philippines: Craig Lee, Joseph Martin (APL-UW)and Mary Jane Perry (U. Maine)With thanks to David Tang, Ya-Ting Chang (NTU), Ruey Wei(NSYSU), Jason Gobat, Geoff Shilling, Neil Bogue, Joe Martin, Kai-Chieh Yang, Adam Huxtable (APL), Russ Davis, Shaun Johnston,Jeff Sherman, David Black, Kyle Grindley (SIO) and the Captainsand crews of R/V Melville and OR2.

Objectives• Technical– Demonstrate utility of gliders for sampling strongboundary currents and complex archipelagoenvironments.• Scientific– Characterize the annual cycle of the Kuroshio andassociated mesoscale field.– Quantify spatial structure, temporal evolution.– Understand the means and direction by whichsignals propagate through a complex archipelago(e.g. multiply connected straits or interconnectedbasins).

Spray and Seaglider• ~50 kg•~2 m length• Deploy/recover onsmall boats →research vessels

Glider operations • Cycle 0-1000 m, ~6 km, ~6 hours• Horizontal velocity ~0.25 m/s (20km/day)• Vertical velocity ~0.1 m/s• Typical deployment 3-5 months,longest to-date 7 months.• Endurance depends on ambientstratification, dive depth anddesired speed.Extended endurance…- Remote deployment (swim in)- Persistent presence (patrol).Slow speeds limit synopticity,rapid response.Can compensate by using moregliders.• 2-way Iridium comms, slowremote control• Temperature, salinity, pressure,current, optics, dissolved oxygen,depth-average velocity (inferred).• New developments: One-yearendurance, under-ice (acousticnav), hardening, new CPU.http://iop.apl.washington.edu

ProgressKuroshio• Two gliders deployed (1 APL, 1 SIO,) April,recovered July 2007.‣ 400 dives up to 1000 dbar‣ 2000 km distance‣ 100 days• Four gliders deployed (2 APL, 2 SIO) July, replacewith four fresh gliders in October 2007.Philippines• Pilot deployments- 2 APL seagliders (southernMindoro Strait and Mindinao Sea).‣ Little historical data- exploratory measurementsand operational evaluation.‣ Assess potential risks due strong currents,complex geometry and heavy fishing.

Model Currents•Usefulplanning andpiloting tool• Modeledfeatures oftenqualitativelysimilar to thoseobserved bygliders

Glider tracks

• Controlled navigation where currents weaker thanglider speed.• Must work with current when flow is strong.• At extremes glider behaves like a float.• Mesoscale variability dominates flow field.• Kuroshio present, but often obscured by mesocale.• Strong currents extend to coast.• Kuroshio weak off Luzon, strengthens northward?

Optimum Glider PathsNorthward current,exponential profileNormalized by glider speedMin distance, time pathsInitial position (1.5,0)Waypoint (0,0)Glider heading, degrees trueGlider speed over ground,normalized by speedthrough water

Multiple Occupations of a SectionSPSGSGSGSPSP

Philippines: Exploratory MissionsMindinao Sea• Strong currents,internal tide ateastern end.• Weak flow atwestern boundary.• Self-inflicted errorpinned glider onsurface, fishing boat‘recovery’ < 48 h.Southern Mindoro Strait• Compass failure (bogus strongcurrents, poor navigation) endedmission prematurely.• Hint of anticyclonic circulation.

0.25 kg/m 3 contoursSprayDeployment1Section 3

SeagliderDeployment1Section 4PotentialTemperature,Salinity, andPotential Density

Velocity Autocovariance

Observed Currents during SW and NE Monsoons30 m shipboard ADCP(Liang et al. 2003)