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J. Blaha and R. Reed

Abstract

Monthly sea-level elevations at Naze and Aburatsu, sites on either side of the Tokara Strait through which the Kuroshio flows, were analyzed for the period 1963–74. The sea-level elevations were adjusted to uniform atmospheric pressure using a barometric factor of 1 cm mb−1. The adjusted elevations are presented as 1) long-term mean seasonal values and 2) deviations from the long-term means. Differences in the elevations between the two sites were then used as indices of the transport of the Kuroshio.

The seasonal amplitude of the elevation differences across the Kuroshio, Naze minus Aburatsu, is ∼13% of the mean surface geopotential anomaly difference of 0.6 dyn m (0/1000 db). The phase of this difference signal indicates maximum northward flow in summer. Zonally integrated wind-stress curl at this latitude in the Pacific interior, however, is most anticyclonic during winter. Instead, the seasonal fluctuations of the Kuroshio are more nearly in phase with the fluctuations in the latitudinal gradients of Ekman pumping in the western North Pacific. The seasonal winds between 7 and 15°N drive a westward interior flow to the western boundary, and winds north of 15°N drive flow away from the western boundary. We speculate that this mechanism effects the seasonal fluctuations of the Kuroshio. The seasonal cycle of Ekman pumping, particularly between 11 and 19°N, is not constant across the Pacific, which helps to reconcile seasonal differences in the fluctuations of the Kuroshio and the North Equatorial Current.

Significant interannual variations are observed in the Kuroshio and at sea-level stations within the North Equatorial Current, e.g., at Guam and Legaspi (Philippines). However, there are fluctuations clearly associated with El Niño at Legaspi, Guam and San Diego which do not appear in the Kuroshio during the 12-year period we examined.

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R. Wexler, R. J. Reed, and J. Honig
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R. K. Reed and J. D. Schumacher

Abstract

Long-term records from four current meters in the Alaskan Stream off Kodiak Island are presented. The net flows decreases with depth and appeared to be in approximate geostrophic equilibrium. Large fluctuations were not common, and the flow was dominated by low-frequency energy. This behavior, which is also supported by temperature and salinity data, suggests a vertically coherent flow with occasional lateral meanders.

The eddy kinetic-energy levels in this region of the Alaskan Stream were quite low, especially in comparison with those in the Kuroshio and Gulf Stream. The flux of momentum across the inshore edge of the Stream appeared to be onshore and to represent a transfer of energy fron3 the mean flow to smaller scales; an eddy viscosity of not more than 106 cm2 s−1 was indicated. The impact on shelf waters of the small, onshore eddy heat flux is unclear.

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R. K. Reed and J. D. Schumacher

Abstract

Data from current moorings at four sites near the shelf break in the Gulf of Alaska are used to present information on the flow, to examine the effects of local winds, and especially to investigate momentum transfer between the offshore and inshore circulation. Net flow at the shelf break in the central and western appears to be similar through the year, but it intensifies appreciably in winter in the northeast Gulf. Only records in the northeast Gulf suggest significant effects on flow by local winds. The eddy fluxes of momentum at the shelf break were extremely small. Although the offshore Alaskan Stream was previously found to transfer momentum toward shore, this flux apparently does not reach the shelf break and influence shelf waters. It appears rather that the gradients of heat and salt observed near the shelf edge result from offshore effects of the coastal flow.

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P. J. Stabeno and R. K. Reed

Abstract

From 1986 through April 1993, 86 satellite-tracked buoys were deployed in the North Pacific and Bering Sea. Most of the buoys were drogued at 40 m. A composite current pattern is derived using these data. The two principal currents (the Alaskan Stream and Kamchatka Current) are clearly evident. Eddy kinetic-mean kinetic energy ratios are low in the stream and along the western Bering Sea basin. An eastward flowing current occurred along the north flank of the Aleutian Islands, this flow was modified by inflow at the passes. Westward flow occurred north of 56°N; its source was the Bering Slope Current. The Kamchatka Current originated near 175°E along the Russian coast. Numerous eddies and meanders were observed in the Kamchatka Current; eddies were also present on the eastern side of the basin.

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Richard J. Reed and Kenneth R. Hardy

Abstract

Widespread and persistent clear air turbulence (CAT) occurred over the Eastern Seaboard of the United States between New York and South Carolina on 18 March 1969. The major synoptic features and a qualitative discussion of the factors contributing to the development of the large vertical wind shears associated with the turbulence are presented. The turbulent region in the vicinity of Wallops Island, Va., was probed with a NASA T-33 research aircraft and with sensitive radars. The clear air radar echoes and the most intense turbulence occurred principally within an upper level frontal zone of about 2 km depth which was produced by the confluence of two currents of widely different origin. The smoothed Richardson number was less than 1.0 throughout the zone and reached its lowest value of ∼0.25 in the region of strongest turbulence. Three distinct types of wave structures were evident in the clear air radar echoes. These were: 1) long sinusoidal arches moving at approximately the wind speed which were oriented in the direction of the wind and wind shear and which had wavelengths of 15–30 km and crest-to-trough amplitudes of nearly 2 km; 2) unstable waves or billows of about 1.6 km wavelength which were superposed on a portion of the long arches and were also oriented in the shear direction; and 3) braided wave-like patterns having a wave-length of ∼5 km and a crest-to-trough amplitude of more than 1 km which were oriented in the cross-wind (and cross-shear) direction.

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N. J. Beyers, B. T. Miers, and R. J. Reed

Abstract

Wind and temperature soundings from a series of 16 meteorological rocket firings over a period of 51 hours between 30 June and 2 July 1965 are presented. Harmonic analysis revealed large diurnal oscillations in the zonal and meridional winds. Both components displayed amplitudes of about 12 m sec−1 near the stratopause (52–56 km) with the phase of the meridional (v) component leading the zonal (u) component by about 5–7 hours at that level. The v component was generally more uniform in both phase and amplitude over the two-day period. Harmonic analysis of the temperatures also revealed a diurnal oscillation with an amplitude of 8.2C at 52 km with the maximum occurring near 1330 hours local time. An attempt to arrive at an independent estimate of the temperature cycle, based essentially on a generalized thermal wind equation, yielded inconclusive results. When this series was combined with previous data, it was concluded that an unmistakable, dominant, diurnal tidal oscillation exists in the stratopause region over White Sands Missile Range (32N) during most or all seasons, particularly in the meridional component.

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R. K. Reed, J. D. Schumacher, and J. P. Blaha

Abstract

A current record during February -August 1980 over the continental slope off Kodiak Island provided the first Eulerian measurements in the high-speed region of the Alaskan Stream. The net flow at 980 m during the 6-month period was 6 cm s−1 at 235°, but there were major low-frequency variations in the current. These appeared to result from the occasional advection of meanders past the mooring, however, rather than from features such as planetary waves. The ratio of fluctuating to mean kinetic energy was much lower than reported values in the Kuroshio and Gulf Stream, probably as a result of important kinematic differences in these flows.

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R. K. Reed, J. D. Schumacher, and L. S. Incze

Abstract

Extensive hydrographic surveys were conducted in Shelikof Strait in March and October 1985. The data are used to describe circulation and property distributions and the changes that occurred. The upper layer flows to the southwest throughout the year, but greatest speeds occur in the fall when surface waters are least saline because of a maximum in freshwater discharge. The deep water has its source to the south, and the properties seem to result from vertical mixing of this southern water. Thus Shelikof Strait has an estuarine-like circulation with a northward, deep inflow.

Property distribution showed that isolines were usually deepest on the right side of the channel looking to the southwest; greatest baroclinic speeds were often there also. Differential Ekman pumping may contribute to the development of this structure and its changes. Volume transport estimates varied considerably. In October the southwest flow bifurcated, with part continuing along the Alaska Peninsula and the rest exiting the main channel to the south; in March all upper-layer flow followed the main channel. Shelikof Strait appears to be a system influenced by both density-driven and wind-driven effects.

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R. J. Reed, A. Hollingsworth, W. A. Heckley, and F. Delsol

Abstract

Substantial changes were made to the ECMWF model in May 1985. The extensive revisions to the physical parameterizations were designed to improve the treatment of the large-scale flow in the tropics. In addition, the resolution was increased substantially to a triangular truncation at T106. The purpose of this paper is to evaluate the performance of the new forecasting system on the analysis and forecasting of easterly waves and their associated tropical storms over Africa and the tropical Atlantic.

A wave history generated for the months of August and September 1985 with use of operational analyses and METEOSAT imagery provides the framework for evaluating the performance of the analysis system. The difficulties caused by lack of data are discussed. Shortcomings of the analysis system are illustrated using an example of a short-scale disturbance with a marked convergence line. On the other hand, examples are also presented demonstrating the ability of the analysis system to make sense of widely scattered observations.

The maxima in the vorticity field provide a set of useful markers to track the easterly waves, both in the analyses and in the forecasts. The 48-h forecasts of the positions and intensities of the vorticity maxima are verified those cases for which there is sufficient observational data to have confidence in the low-level wind analysis. The verification results are quite encouraging.

A particular feature of the paper is the series of synoptic studies of the four waves which gave rise to named storms (Danny, Elena, and Gloria) during the period.

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