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Coastal circulation from ADCP

Par ecola — Dernière modification 09/10/2014 11:40

Near-coastal circulation in the Northern Humboldt Current System from shipboard ADCP data

A. Chaigneau, G. Eldin (LEGOS/IRD)

The near-coastal circulation of the Northern Humboldt Current System is described analyzing ~8700 velocity profiles acquired by a shipboard acoustic Doppler current profiler (SADCP) during 21 surveys realized between 2008 and 2012 along the Peruvian coast by the Peruvian R/V José Balandra Olaya. Processing of the data was made possible after training of one of us (ND) in 2012 through a specific IRD grant.
This data set permits observation of (i) part of the Peru Coastal Current and the Peru Oceanic Current that flow equatorward in near-surface layers close to the coast and farther than ~150 km from the coast, respectively; (ii) the Peru-Chile Undercurrent (PCUC) flowing poleward in subsurface layers along the outer continental shelf and inner slope; (iii) the near-surfacing Equatorial Undercurrent renamed as Ecuador-Peru Coastal Current that feeds the PCUC; and (iv) a deep equatorward current, referred to as the Chile-Peru Deep Coastal Current, flowing below the PCUC. A focus in the PCUC core layer shows that this current exhibits typical velocities of 5–10 cm s-1. The PCUC deepens with an increasing thickness poleward, consistent with the alongshore conservation of potential vorticity. The PCUC mass transport increases from ~1.8 Sv at 5°S to a maximum value of ~5.2 Sv at 15°S, partly explained by the Sverdrup balance.

Figure 1: Distribution of ADCP profiles along the Peruvian coast, 2008-2012

The PCUC experiences relatively weak seasonal variability and the confluence of eddy-like structures and coastal currents strongly complicates the circulation. The PCUC intensity is also affected by the southward propagation of coastally trapped waves, as revealed by a strong PCUC intensification in March 2010 coincident with the passage of a downwelling coastal wave associated with a weak El Niño event.


Figure 2: Mean cross-shore sections of alongshore velocity (in cm s-1) in different latitude bands.

 

Chaigneau, A., N. Dominguez, G. Eldin, L. Vasquez, R. Flores, C. Grados, and V. Echevin (2013), Near-coastal circulationin the Northern Humboldt Current System from shipboard ADCP data, J. Geophys. Res. Oceans, 118, doi:10.1002/jgrc.20328.


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