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David A. Brooks
and
Melbourne G. Briscoe

Abstract

Experiences with two prototype telemetry systems developed for potential use with moored or drifting ocean instruments are described. The systems transfer data and commands between remote and base stations using direct high-frequency (HF) ionospheric radio propagation (shortwave radio) without intervening relay stations or satellites. The strategy exploits recent developments in digital packet-switching technology, which is readily available and can be inexpensively applied to oceanic problems. The potential advantages of packet methods over satellite methods include low cost, autonomy, two-way exchanges with the remote stations, and typical data rates of 1–10 bit s−1 averaged over several days. Coverage is effectively global but intermittent. Disadvantages mostly result from the interference and skip zones that characterize HF propagation. The tests described here took place near the time of a sunspot minimum; the utility of HF packet telemetry will be greatly increased when the sunspot cycle is near its maximum.

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Angelika Lippert
and
Melbourne G. Briscoe

Abstract

This study of low-frequency oceanic variability is based on data collected during the Long Term Upper Ocean Study (LOTUS), which was a two year program of (mainly) moored meteorological and oceanographic measurements. The mooring arrays were centered at 34°N, 70°W over the Hatteras Abyssal Plain. With a distance of about 300 km to the mean Gulf Stream axis and the continental slope, LOTUS was the most northern and western long-term mooring site in the Gulf Stream recirculation region to date.

The observed low-frequency variability is dominated by zonally elongated motions of the secular time scale (periods <100 days) even great depths (4000 m). In contrast to observations in other parts of the recirculation region, the spectral shapes are strongly depth dependent.

The vertical structure of the variability was examined by EOF analysis. Different kinds of EOFs were tested; the best representation of the observed variability was obtained by an EOF representing a undirectional nonrotating (with depth) flow. The first and second EOF together explain 96% of the observed energy. The first EOF (66%) is almost barotropic with a slight increase at the surface and the bottom of the ocean; the second mode closely resembles the first baroclinic dynamical mode. The barotropicity decreases with increasing frequency. Motions with periods less than 30 days are almost surface trapped, and a strong bottom intensification additionally exists for periods between 10 and 30 days.

The low-frequency flow at LOTUS is consistent with a stochastic, quasi-geostrophic wave field that may be affected by mean current, but our observations are insufficient to test this hypothesis.

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M. Benno Blumenthal
and
Melbourne G. Briscoe

Abstract

This paper examines high-frequency (0.1-0.5 cph) internal waves, waves previously characterized by the Garrett and Munk spectral fits (GM72, GM75, GM79) as being vertically symmetric propagating waves (or equivalently “smeared” standing modes—GM72). Coherences at large vertical separations measured with deep sea moorings show significant differences from the GM79 predictions. The differences can be explained by modifying the purely propagating model to one that includes the spectral truncation and phase locking associated with a spectrum of standing modes. A model consisting of only standing modes, however, is also inadequate, whereas a more general spectral model, which effectively allows both propagating waves and standing modes, is not. These results show that much of the simplicity of the GM79 spectral fit can be attributed to lack of spectral resolution in the set of measurements to which the GM models were fit. The GM79 simplicity is not an intrinsic property of the internal wave field.

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Eli J. Katz
and
Melbourne G. Briscoe

Abstract

Constant depth and isopycnal‐following tows are used to estimate the, towed vertical coherence of the internal wave field, at vertical separations of 8.5, 18, 28 and 70 m. The depths of the tows are ∼750 m at the maximum of the buoyancy frequency in the main thermocline of the Sargasso Sea, and near 350 m in the buoyancy frequency minimum between the main and seasonal thermoclines.

The towed spectra and towed vertical coherence are compared with three model spectra (GM75, GM76 and IWEX): at 750 m the agreement between data and models is very good, with IWEX being slightly better. At 350 m several of the measured towed vertical coherence spectra are more complex than the spectra from the deeper tows, there are anomalously high coherences in a band from 0.7 to 2 cycles per kilometer that are not predictable by the models. We suggest this coherence bump may be evidence of Eckart resonance, i.e., modes tunneling between the two thermoclines into the region of low buoyancy frequency.

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Lothar Stramma
,
Peter Cornillon
,
Robert A. Weller
,
James F. Price
, and
Melbourne G. Briscoe

Abstract

Data from a surface mooring located in the Sargasso Sea at 34°N, 70°W between May 1982 and May 1984 were compared with satellite data to investigate large diurnal sea surface temperature changes. Mooring and satellite measurements are in excellent agreement for those days on which no clouds covered the site at the time of the satellite pass. During the summer half-year at this site, there is a 20% charm of diurnal warming of more than 0.5°C, with values of up to 3.5°C observed in the two-year period.

Diurnal warming observed at the mooring has been simulated well by a one-dimensional model driven by local beat and momentum fluxes. Under the conditions of very light wind and strong insolation that produce the Largest surface warming, the surface mixed-layer depth reduces to the convection depth, and wind-mixing becomes unimportant. The thermal response is then limited to depths between 1 and 2 m, making it likely that such events have been underreported in routine ship observations.

In all cases observed, the spatial extent of warming events as determined by satellite data are well correlated with the corresponding atmospheric pressure patterns. Conditions giving rise to the largest diurnal warming events are often associated with a westward-extending ridge of the Bermuda high. In the region studied, 57°–75°W and 29°–43°N, diurnal warming of more than 1°C was found on occasion to cover areas in excess of 300 000 km2, with warming of more than 2°C coveting areas in excess of 130 000 km2.

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Worth D. Nowlin Jr.
,
Melbourne Briscoe
,
Neville Smith
,
Michael J. McPhaden
,
Dean Roemmich
,
Piers Chapman
, and
J. Frederick Grassle

The Global Ocean Observing System (GOOS) was initiated in the early 1990s with sponsorship by the Intergovernmental Oceanographic Commission, the International Council for Science, the United Nations Environment Programme, and the World Meteorological Organization. Its objective is to design and assist with the implementation of a sustained, integrated, multidisciplinary ocean observing system focused on the production and delivery of data and products to a wide variety of users. The initial design for the GOOS is nearing completion, and implementation has begun.

The initial task in developing a sustained observing system is to identify the requirements of users for sustained data and products. Once such needs are known, the next task is to examine observing system elements that already exist; many necessary elements will be found to exist. The next tasks are to identify and integrate the useful elements into an efficient and effective system, while removing the unneeded elements, and to develop and implement effective data management activities. Moreover, the system must be augmented with new elements because some requirements cannot be met with existing elements and because of technological advances.

Our key objective is to discuss the mechanism whereby new candidate observing system elements are transformed from development status into elements of the sustained system. Candidate systems normally will pass through many different phases on the path from idea and concept to a mature, robust technique. These stages are discussed and examples are given:

  1. Development of an observational/analysis technique within the ocean community.

  2. Community acceptance of the methodology gained through experience within pilot projects to demonstrate the utility of the methods and data.

  3. Pre-operational use of the methods and data by researchers, application groups, and other end users, to ensure proper integration within the global system and to ensure that the intended augmentation (and perhaps phased withdrawal of an old technique) does not have any negative impact on the integrity of the GOOS data set and its dependent products.

  4. Incorporation of the methods and data into an operational framework with sustained support and sustained use to meet societal objectives.

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