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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 ' 0.51ms21), high-precision autopilot (2-3 m), and flying altitude of ;500m 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 ;500m 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 opensource 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A three-dimensional numerical model was adapted to study the circulation, stratification and mixing patterns inside the port of El Sauzal. Salinity, temperature and density field data were measured, showing that density variations were mainly due to the temperature field with a very small contribution from salinity. The model simulated surface currents and the temperature field. The simulation was compared against field data showing that the model reproduces satisfactorily the circulation, stratification and mixing patterns. Surface circulation and vertical mixing were mainly forced by the tide, although winds greater than 6 m s-1 became the main forcing of vertical mixing and surface circulation. The surface currents traveled outside the port during ebb tide and vice versa during flood tide; however, with winds greater than 6 m s-1the surface velocity followed the wind direction. When a discharge of 0.2 m³ s-1 was introduced into the system, the simulation showed an increase of 0.5 cm s-1 in the surface current velocity, during ebb tide. The vertical temperature structure increased as much as the discharge temperature (17.2°C). This result verifies that a controlled discharge could improve circulation and mixing, reducing the residence time and improving the levels of oxygen in the water. [ABSTRACT FROM AUTHOR]

Fetch-limited wave growth was analyzed using high spatial and temporal resolution measurements obtained with high-frequency (HF) radars. To calculate the wave spectrum, the second-order echo (S2N) was extracted from the Doppler spectrum and mapped to the wave frequency domain. The conversion of S2N to the wave frequency spectrum was carried out using a linear parametric model dependent on wind speed. Wave growth, represented by the dimensionless energy and peak frequency as a function of dimensionless fetch, was determined from the spectra calculated for 25 cells (~400 km²) in the vicinity of a moored Air-Sea Interaction Spar buoy. The buoy data were used as reference and to provide the wind information required for the wave growth analysis. The simultaneous data from the buoy and HF radars showed a suitable agreement with the wave growth curves. The analysis of the 25 cells showed an adequate agreement and certain dispersion around the growth curves. Possible causes of this dispersion are related to errors in the estimation of the frequency spectrum and fetch, and the assumption of homogeneous wind conditions. From the limited data set used, it was not possible to prove any impact of swell on wave growth; however, it is possible that analysis over a wider range of swell heights may provide this evidence. Nevertheless, the results suggest that the linear parametric model is able to reproduce fetch-limited wave growth. This work represents the first effort focused on fetch-limited wave growth using HF radars. [ABSTRACT FROM AUTHOR]