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Kenneth H. Brink, David W. Stuart, and John C. Van Leer

Abstract

Coordinated meteorological and oceanographic (CTD) measurements were made near Point Conception, California, during March–April 1981. The goal of the observations was to study coastal upwelling and the local characteristics of the assumed wind driving. Results showed substantial topographically-induced spatial structure in the near-surface winds, with weaker winds generally occurring within the Santa Barbara Channel. The 1981 “spring transition” event was monitored by mews of hydrographic and sea level measurements. The details of the event suggest that it was not entirely driven by lead wind stress. The mean sea surface temperature pattern suggests the existence of an upwelling center between Points Arguello and Conception. The individual sea surface temperature charts are all dominated by patchiness on a scale of 5–15 km. The nature of these structures is not well understood, but on the one occasion when a patch was isolated by a CTD survey, its structure penetrated to at 1east 50 db.

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Walter R. Johnson, John C. Van Leer, and Christopher N. K. Mooers

Abstract

In August 1973, 320 vertical profiles of temperature and horizontal velocity were recorded during a 64 h period by an array of three Cyclesondes in the coastal upwelling region off Oregon. The mean interior along-shore velocity was geostrophic and a linear function of density, with a near-surface, equatorward jet at mid-shelf, and a poleward undercurrent at the shelf break. The mean cross-shelf flow was relatively weak and substantially ageostrophic; it was suggestive of a two-cell (co-rotating) circulation within the mid-shelf frontal zone and a two-cell (counter-rotating) circulation near the shelf break. The direction of the mean, near-bottom, cross-shelf flow was consistent with a bottom Ekman layer driven by the mean near-bottom alongshore flow. At mid-shelf, near-inertial motions with a vertical wavelength of 50 m, upward phase velocity, and downward group velocity persisted throughout the record. The hourly vector shears indicated a layer of persistent shear instability at the base of the upwarped permanent pycnocline at mid-shelf. There the near-inertial shear was twice as great as the mean shear; therefore, it may have played a dominant role in mixing processes. Off Oregon, a vertical resolution of 5 m and a tri-hourly sampling rate, or greater, are required to significantly resolve the tidal, inertial and cross-isobath flows. In contrast, only two current meters per mooring, with supporting hydrography, are required to adequately resolve the mean (over two or more inertial periods) interior alongshore flow at any position. In coastal upwelling regions, a vertical resolution of 10–20% of the water depth and a temporal resolution of 10–20% of an inertial period are probably necessary and sufficient to produce coherent fields of the slowly-varying horizontal velocity.

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James F. Price, Christopher N. K. Mooers, and John C. Van Leer

Abstract

Two observed cases of mixed-layer (ML) deepening due to storms are analyzed and simulated. The primary goal is to learn whether the relevant scale velocity in the parameterization of wind-driven deepening is U *, the wind stress friction velocity, or δV, the magnitude of the horizontal mean velocity difference across the base of the ML. ML deepening is isolated from air–sea exchange and horizontal advection by diagnosing the entrainment tendency of ML temperature.

ML deepening is found to be highly intermittent on the storm time scale. Deepening in response to a wintertime atmospheric cold front occurred as δV was accelerated during the initial rise in wind stress. Deepening abruptly ceased as wind stress began to decelerate δV, though the stress magnitude continued to increase. A similar relationship between wind stress δV and ML deepening was also observed in a summertime case and is evidence that the relevant scale velocity is δV not U *.

In both cases the observed phase and extent of ML deepening are simulated realistically by the parameterization of Pollard et al. (1973) in which an overall Richardson number, Rv = ghV 2, where g′ and h are the ML buoyance and thickness, sets a lower bound on the ML thickness. The value of Rv is ≅0.65.

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Hans C. Graber, Eugene A. Terray, Mark A. Donelan, William M. Drennan, John C. Van Leer, and Donald B. Peters

Abstract

This paper describes a new, compact buoy, the Air–Sea Interaction Spar (ASIS), capable of reliably and accurately measuring directional wave spectra, atmospheric surface fluxes, and radiation in the the open ocean. The ASIS buoy is a stable platform and has low flow disturbance characteristics in both atmospheric and oceanic surface boundary layers. The buoy has been deployed for sea trials in the waters off Miami, Florida; in the northeastern region of the Gulf of Mexico; and in the northwestern Mediterranean. The acquired measurements of directional wave spectra, momentum and heat fluxes, and profile data—as well as general meteorological and oceanographic parameters—obtained from the buoy are well suited for enhancing research on air–water interfacial processes, wave dynamics, remote sensing, and gas transfer. In this paper the design is described and the performance of the buoy using field data is characterized.

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