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  • Author or Editor: Henry Perkins x
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Henry Perkins
and
John Van Leer

Abstract

Serial current and temperature measurements were made during the Global Atmospheric Research Program Atlantic Tropical Experiment (GATE) with unattended autonomous profilers (Cyclesondes) in the North Equatorial Counter Current between 0 and 200 m depth near 9°N, 23°W during September 1974. The data show a rich vertical structure in which internal semidiurnal tides are prominent and inertial waves are seen propagating downward. Patches of isothermal water in the extremely sharp thermocline are advected past the mooring site, suggesting intense vertical mixing in this area.

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Henry Perkins
,
Thomas Kinder
, and
Paul La Violette

Abstract

An extensive dataset collected in the Alboran Sea during the 1982 Donde Va? experiment is used to characterize the kinematics and dynamics of the inflow of Atlantic water into the Mediterranean Sea. The veering of the inflow toward the ENE after leaving the Strait of Gibraltar and the existence of an anticyclonic gyre that fills much of the western Alboran Sea in the upper 200 m are confirmed in the mean. Inflow variability with periods of 2 to 10 days is described. Particularly striking is one interval of about 9 days during which the gyre was not present and the inflow adopted a southerly course after leaving the strait. The observations are interpreted in terms of vorticity conservation and in the light of earlier theoretical and numerical results.

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E. A. D'Asaro
and
Henry Perkins

Abstract

Independent estimates of the frequency–wavenumber spectrum of near-inertial waves for the Sargasso Sea in late summer were made using 8 time series of horizontal velocity from a single moored vertical array and 58 vertical profiles of horizontal velocity from a horizontal array of expendable velocity profilers. The profiler data were analyzed to produce an internal wave frequency-wavenumber spectrum with sufficient resolution to resolve the details of the inertial peak and compute the vertical energy flux. Comparison with the lower resolution spectrum from the moored array shows qualitative agreement; the differences are most likely due to biases in both techniques and to intermittency of the internal wave field.

These data reveal a marked asymmetry of the near-inertial internal wave field, with a net downward enemy flux of 0.12±0.12 ergs cm−2 s−1. The downward propagating waves have more energy, a larger horizontal scale and a lower frequency than the upward propagating waves. The magnitude of the downward energy flux is comparable to the net input of energy into surface inertial currants, confirming the likely importance of the wind as an energy source for near-inertial internal waves.

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Henry Perkins
,
Toby J. Sherwin
, and
T. S. Hopkins

Abstract

During several days in July 1990, there was an abrupt increase in semidiurnal tidal current in the upper part of the water column seaward of the steep continental rise southeast of Iceland. This tidal burst was coincident with an alongslope current pulse formed by water from the Nordic seas, which had overflowed the Iceland-Faeroe Ridge. The tidal increase is shown to be caused by enhanced generation of internal tide when the alongshore current elevated otherwise deep isopycnals to higher levels, thereby increasing conversion from barotropic to baroclinic tides. A two-dimensional model, used to illustrate the mechanism, underpredicts the increased tidal amplitude and suggests that three-dimensional effects play a role in the present case.

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