In:
Ocean Science, Copernicus GmbH, Vol. 15, No. 6 ( 2019-12-09), p. 1627-1651
Abstract:
Abstract. Very-near-surface ocean currents are dominated by wind and wave
forcing and have large impacts on the transport of buoyant materials in the
ocean. Surface currents, however, are under-resolved in most operational
ocean models due to the difficultly of measuring ocean currents close to, or
directly at, the air–sea interface with many modern instrumentations. Here,
observations of ocean currents at two depths within the first meter of the
surface are made utilizing trajectory data from both drogued and undrogued
Consortium for Advanced Research on Transport of Hydrocarbon in the Environment
(CARTHE) drifters, which have draft depths of 60 and 5 cm, respectively.
Trajectory data of dense, colocated drogued and undrogued drifters were
collected during the Lagrangian Submesoscale Experiment (LASER) that took
place from January to March of 2016 in the northern Gulf of Mexico.
Examination of the drifter data reveals that the drifter velocities become
strongly wind- and wave-driven during periods of high wind, with the
pre-existing regional circulation having a smaller, but non-negligible,
influence on the total drifter velocities. During these high wind events, we
deconstruct the total drifter velocities of each drifter type into their
wind- and wave-driven components after subtracting an estimate for the
regional circulation, which pre-exists each wind event. In order to capture
the regional circulation in the absence of strong wind and wave forcing, a
Lagrangian variational method is used to create hourly velocity field
estimates for both drifter types separately, during the hours preceding each
high wind event. Synoptic wind and wave output data from the Unified Wave
INterface-Coupled Model (UWIN-CM), a fully coupled atmosphere, wave and
ocean circulation model, are used for analysis. The wind-driven component of
the drifter velocities exhibits a rotation to the right with depth between
the velocities measured by undrogued and drogued drifters. We find that the
average wind-driven velocity of undrogued drifters (drogued drifters) is
∼3.4 %–6.0 % (∼2.3 %–4.1 %) of the wind
speed and is deflected ∼5–55∘
(∼30–85∘) to the right of the wind, reaching higher
deflection angles at higher wind speeds. Results provide new insight on the
vertical shear present in wind-driven surface currents under high winds,
which have vital implications for any surface transport problem.
Type of Medium:
Online Resource
ISSN:
1812-0792
DOI:
10.5194/os-15-1627-2019
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2183769-7
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