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W. J. Emery

Abstract

All available historical expendable bathythermograph data are used to compute means and standard deviations in temperature for the upper 500 m in the North Atlantic and North Pacific. To take advantage of marked spatial differences in data coverage a variable grid scheme is employed. Both surface and subsurface annual mean temperature distributions agree well with published maps of these quantities. Climatological mean temperature-salinity and salinity-depth curves are used to infer salinities for the mean temperature profiles in order to compute 0/500 db inferred dynamic height and its standard deviation. These mean curves are also used to compute eddy potential energy at 300 m. The maps of mean annual inferred dynamic height agree well with traditional dynamic height maps and appear similar to the maps of mean temperature at 400 m. The North Atlantic eddy potential energy distribution is similar to an earlier calculation. Maps of the standard deviations in inferred dynamic height also represent the geographical variability in mesoscale activity and compare well with a recent global map of mesoscale variability based on satellite altimetry from SEASAT.

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M. Ikeda and W. J. Emery

Abstract

Infrared satellite images from the west coasts of Oregon and northern California are used to identify meander patterns in sea surface temperature which appear as large cold tongues extending offshore. Two relatively long series of images from 1982 and a few examples from 1980 and 1983 demonstrate the evolution of the cold tongues from an initial variety of scales (60–200 km), to the fastest growing waves (110–130 km) and then finally to tongues with longer wavelengths (400 km). This is observed to occur over periods of about three months in summer and fall when the coastal circulation is composed of a southward surface current over a northward undercurrent. The initial shorter scale features are believed to be excited by the interaction between the mean current and the coastal topography. Baroclinic instability associated with the vertical shear between the surface current and the undercurrent is found to be responsible for the growth of the features observed in the satellite imagery. A nonlinear numerical model is used to simulate the evolution of these features in summer/fall including the initial excitation, the growth of the dominant waves and the red cascade to longer wavelengths. In winter or spring when the current no longer reverses with depth but flows north or south respectively, the meanders have scales of about 100–120 km consistent with the horizontal scale of features in the bottom topography.

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G. Siedler, W. Zenk, and W. J. Emery

Abstract

Long-term temperature and current-meter records from moorings in the northern Canary Basin display strong current events with time scales between one and three months and large vertical scales of several thousand meters. The data are compared to hydrographic surveys in the area that show a meandering subtropical front. The strong current events are found to be related to the passage of the front through the mooring positions. An analysis of composite time series, for selected depths, indicates cases of westward and of eastward propagation of frontal meanders. The frontal pattern is also found in geopotential anomalies inferred from historical XBT data sets, suggesting that the front is a persistent feature of the density field. In two cases strong current events appear to be related to a Mediterranean Water lens.

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M. Miyake, W. J. Emery, and J. Lovett

Abstract

Venical profiles from expendable conductivity-temperature (XCTD) and sound velocity-temperature (XSVT) instruments are compared with simultaneous profiles sampled with Guildline CTD and Plessy CTD-SV systems. From these comparisons the estimated accuracies of these instruments are 0.08°C for the XCTD and 0.03°C for the XSVT in temperature, and 0.13% for the XCTD and 0.18% for the XSVT in salinity. These measurement errors are compared to the locally observed upper ocean variability.

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W. J. Emery, W. Lee, W. Zenk, and J. Meincke

Abstract

An XBT interface is described for use with Commodore and other 6502 based microprocessors. This interface takes the form of a single circuit board mounted inside the microcomputer and is completely software controlled. The application of this digital XBT system to the real-time computation of density and dynamic height, using historical or recent temperature-salinity relationships, is also described. Comparison between XBT and CTD measured temperatures from the Northeast Atlantic yield a mean temperature difference of −0.08°C and an rms temperature difference of 0.33°C for the upper 800 m. Examples of dynamic topography maps and a temperature section computed using this technique are also presented and comparison between objectively analyzed XBT and CTD dynamic topographies demonstrates the reliability of the method for mapping the baroclinic flow.

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Shawn W. Miller and William J. Emery

Abstract

An automated neural network cloud classifier that functions over both land and ocean backgrounds is presented. Motivated by the development of a combined visible, infrared, and microwave rain-rate retrieval algorithm for use with data from the 1997 Tropical Rainfall Measuring Mission (TRMM), an automated cloud classification technique is sought to discern different types of clouds and, hence, different types of precipitating systems from Advanced Very High Resolution Radiometer (AVHRR) type imagery. When this technique is applied to TRMM visible–infrared imagery, it will allow the choice of a passive microwave rain-rate algorithm, which performs well for the observed precipitation type, theoretically increasing accuracy at the instantaneous level when compared with the use of any single microwave algorithm. A neural network classifier, selected because of the strengths of neural networks with respect to within-class variability and nonnormal cluster distributions, is developed, trained, and tested on AVHRR data received from three different polar-orbiting satellites and spanning the continental United States and adjacent waters, as well as portions of the Tropics from the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The results are analyzed and suggestions are made for future work on this technique. The network selected the correct class for 96% of the training samples and 82% of the test samples, indicating that this type of approach to automated cloud classification holds considerable promise and is worthy of additional research and refinement.

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W. J. Emery, W. G. Lee, and L. Magaard

Abstract

Long-term mean temperature and salinity profiles, computed from an edited set of historical hydrographic data, have been used to calculate mean profiles of density and Brunt–Väisäl&auml frequency by 5° squares for the North Atlantic and the North Pacific. With these stratification profiles the internal Rossby deformation radii are computed and displayed in map form alone, with the external Rossby radii. Seasonal variations are examined in a limited number of 5° squares selected to have an equal number of hydrographic observations for each of the four seasons. In most Brunt–Väisäl&auml frequency profiles significant seasonal variations are limited to the upper 250 m; seasonal variations in internal Rossby radii are everywhere surprisingly small.

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W. J. Emery, K. Cherkauer, B. Shannon, and R. W. Reynolds

Abstract

The design and deployment of an inexpensive hull temperature sensor and data logger system was undertaken for the purpose of improving the measurement of sea surface temperature (SST) by ship-of-opportunity merchant vessels. The resulting hull sensors and data logger systems were installed on four merchant vessels and one research vessel. A variety of installations tested the effects of placement and insulation on the temperature sensors themselves. The resulting hull SST data were compared with monthly SST analyses using optimal interpolation (OI) as well as with data from the thermosalinograph (TSG) on board the research vessel. The data collected from the hull sensor systems, while being slightly offset from the TSG data (likely due to a TSG calibration problem), were found to be in excellent agreement with the monthly OI data.

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M. J. Suarez, W. J. Emery, and G. A. Wick

Abstract

A new multichannel infrared sea truth radiometer has been designed and built to improve validation of satellite-determined sea surface temperature. Horizontal grid polarized filters installed on the shortwave channels are very effective in reducing reflected solar radiation and in improving the noise characteristics. The system uses a continuous (every other cycle) seawater calibration technique. An analysis of the data from its first deployment is presented and recommendations are made for further improving the experimental method.

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W. J. Emery, C. C. Ebbesmeyer, and J. P. Dugan

Abstract

Six multiship XBT surveys in the area between 29 and 42°N in the North Pacific and North Atlantic Oceans were examined with respect to the following questions: What fraction of significant vertical isotherm deflections may be associated with horizontally closed eddies, and which of these eddies have identifiable thermal expressions at the sea surface? From all six surveys 45 significant deflection features, with amplitudes exceeding one standard deviation, were selected from isotherm deflections in the central vertical temperature sections. Approximately half of these deflections could be identified as parts of horizontally closed eddies (mean diameters ∼ 150 km). In turn, approximately one-third of the eddies were associated with a significant anomaly (⩾0.5°C) of sea surface temperature. Examples of both isolated and close-packed eddies wore observed. Most of the eddies identified in the western North Atlantic were in the region of increased eddy kinetic and potential energies associated with the Gulf Stream. In this area the number of eddies per unit area equaled approximately 0.14 eddies per 104 km2 (∼1 square degree).

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