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Charina Lyn Amedo-Repollo, Xavier Flores-Vidal, Cedric Chavanne, Cesar L. Villanoy, and Pierre Flament

Abstract

High-frequency Doppler radar (HFDR) and acoustic Doppler current profiler (ADCP) time-series observations during the Philippine Straits Dynamics Experiment (PhilEx) were analyzed to describe the 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 airport indicate that these flow structures correlate with the strength and direction of the prevailing local wind. An intensive survey in 8–9 February 2009 using 24 h of successive cross-shore conductivity–temperature–depth (CTD) sections, which in conjunction with shipboard ADCP measurements, show a well-developed cyclonic eddy characterized by near-surface velocities of 50 cm s−1. 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.

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Antonio Gómez Roa, Xavier Flores-Vidal, Orlando Avendaño Gastelum, Rogelio Núñez, Andrés Sandoval Rangel, Cesar A. Liera Grijalva, and Juan Ivan Nieto Hipólito

Abstract

In this work we present an unmanned aircraft vehicle (UAV) designed from off-the-shelf components to release ocean minidrifters. Its endurance (~1 h), payload (~5 kg), offshore range (~30 km), capability of operating into wind conditions of ~10 kt (1 kt ≈ 0.51 m s−1), high-precision autopilot (2–3 m), and flying altitude of ~500 m above sea level, along with its relatively low cost [<$5,000 (U.S. dollars)] enables quick and relatively easy oceanographic applications beyond 10 km offshore. We report here the very first successful ocean drifter releases, performed along the Baja California coast, between Tijuana and Rosarito, Mexico, and the technical details of the UAV. About 50 experiments (flights) allowed us to improve the takeoff and landing, the release tunnel for minidrifters, the cruise speed and altitude to release drifters safely, and to implement a parachute that controls the speed of the freefalling minidrifters. Quick release of up to six drifters (armed with real-time data transfer and web display) between 2 and 12 km offshore were performed at ~500 m above sea level, during a single flight in under 15 min, as opposed to classic techniques using boats or ships that, although can transport much more weight, can take several hours, use more human resources, and increase cost. Here we propose a novel open-source technique that can be used as a simplified method for scientific ocean measurements, as a quick-response emergency tool to map spills or for search and rescue.

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