Low Frequency Surface Flow in Panay Strait

posted 28 Mar 2017, 01:56 by Abigail Melendres   [ updated 3 Apr 2017, 00:45 ]
Charina Lyn Amedo-Repollo, PhD
University of Hawai'iat Manoa

Physical Oceanography Laboratory, Marine Science Institute

University of the Philippines, Diliman, Quezon City




High Frequency Doppler Radar (HFDR), shallow pressure gauges (SPG) and Acoustic Doppler Current Profiler (ADCP) time-series observations during the Philippine Straits Dynamics Experiment (PhilEx) were analyzed to describe the tidal and mesoscale currents in Panay Strait, Philippines.


Low frequency surface currents inferred from three HFDR (July 2008 – July 2009), reveal a clear seasonal signal concurrent with the reversal of the Asian monsoon. A mesoscale cyclonic eddy west of Panay Island is generated during the winter Northeast (NE) monsoon. This causes changes in the strength, depth and width of the intraseasonal Panay coastal (PC) jet as its eastern limb. Winds from QuikSCAT and from a nearby air port indicate that these flow structures correlate with the strength and direction of the prevailing local wind.


An intensive survey in February 8-9, 2009 using 24-hour of successive cross-shore Conductivity - Temperature - Depth (CTD) sections, which in conjunction with shipboard ADCP measurement show a well-developed cyclonic eddy characterized by near-surface velocities of 50 cm/s. This eddy coincides with the intensification of the wind in between Mindoro and Panay Islands generating a positive wind stress curl in the lee of Panay, which in turn induces divergent surface currents. Water column response from the mean transects show a pronounced signal of upwelling, indicated by the doming of isotherms

and isopycnals. A pressure gradient then is set up, resulting in the spin-up of a cyclonic eddy in geostrophic balance. Evolution of the vorticity within the vortex core confirms wind stress curl as the dominant forcing.