ISSN:0148-0227    

DOI:10.1029/JC083iC09p04499

年代:1978

数据来源: WILEY

摘要:

The recent improvement of infrared scanners on the polar and geostationary environmental satellites operated by the National Oceanic and Atmospheric Administration has enabled the detection of many sea surface temperature fronts associated with ocean currents and upwelling. The present capabilities and limitations of these satellites in ocean applications are summarized. Examples of infrared imagery are used to illustrate the horizontal temperature distribution at the ocean thermal fronts. It is postulated that future improvements in satellite systems will increase further our capability to detect ocean fronts.

ISSN:0148-0227    

DOI:10.1029/JC083iC09p04501

年代:1978

数据来源: WILEY

摘要:

During the winter of 1976–1977 a time series of NOAA satellite data was obtained which documented the seasonal cycle of sea surface temperatures. Data were obtained as both marine‐enhanced images and computer compatible tapes. Fall cooling initially affected only the lakes and estuaries. A band of cold inner shelf waters then formed along the coast. This expanded seaward to the shelf break as the winter season progressed. At the extreme of winter cooling, two major thermal fronts remained: one near the shelf edge, separating the shelf from deep gulf surface waters, and the other the cyclonic boundary of the Loop Current. The onset of spring warming was indicated by an increase in surface temperatures in the shallow inshore areas. The seasonal cycle was completed with the formation of nearly isothermal surface waters throughout the region, a condition characteristic of the summer sea

ISSN:0148-0227    

DOI:10.1029/JC083iC09p04523

年代:1978

数据来源: WILEY

摘要:

Examination of the Subtropical Front in the western North Pacific along 137°E, using routine hydrographic cruise data from 1967 to 1974, reveals it to be narrow, located between 17.5° and 25°N, and associated with a sharp northward rise of the upper portion of the main thermocline which detaches itself from the deeper main thermocline near 17.5°N. The climatological front depicted in various oceanographic atlases (e.g., USSR Navy Atlas, 1976) is thus revealed as a smoothed version of the more narrow synoptic frontal feature that moves latitudinally and varies in strength on both a seasonal and a secular basis. The narrow Subtropical Front is superimposed upon the weaker north/south gradient of thermocline temperature that exists between the North Equatorial Current and the Kuroshio Countercurrent. The present study extends our knowledge on the space/time variability of the Subtropical Front by analyzing all available mechanical bathythermograph, expendable bathythermograph, and hydrographic data taken in the western North Pacific from 1954 to 1974. These data are interpolated onto a regular space grid (2.5° latitude by 5° longitude) on both a monthly climatological basis and an individual yearly basis from 1954 to 1974. Because the data distribution lacked the data density required, the method of interpolating could not reproduce the narrow character of the Subtropical Front but rather smoothed it in space and over a year's time. However, a maximum in the meridional gradient in temperature over the upper 200 m consistently appeared each year from 1954 to 1974 in the approximate vicinity of the synoptic front, although it showed much less strength. Changes in both the latitude location and the strength of this smoothed version of the Subtropical Front show interesting behavior on both the seasonal and the secular time scale. On the seasonal scale (i.e., 3 months) the Subtropical Front is twice as strong in spring as it is in fall, with some tendency for it to be located farther north when it is stronger and farther south when it is weaker. This seasonal variability has a maximum north/south displacement of ±4° of latitude in the west at 135°E, decreasing to the east, associated with a maximum range in strength of ±35% about the annual mean. On the secular scale (i.e., 1–1.5 yr) the Subtropical Front from 1954 to 1974 had a maximum range in strength of ±15% about the annual mean, and it had some tendency to be more intense when it was displaced farther north, showing a maximum north/south displacement of ±2° latitude. From 1954 to 1974 the years 1957–1958, 1963–1965, and 1970–1971 find the Subtropical Front to have been stronger than normal, in phase with the secular variability of the two major current systems both north and south of it (i.e., the Kuroshio and the North Equatorial Current). These periods of years (i.e., 1957–1958, 1963–1965, and 1970–1971) are the same as those characterizing the El Niño phenomenon in the equatorial and tropical Pacific, an indication of the more broad‐scale natur

ISSN:0148-0227    

DOI:10.1029/JC083iC09p04531

年代:1978

数据来源: WILEY

摘要:

A simple prognostic model based on Ekman dynamics and available satellite sea surface temperature and wind data is used to estimate rates of frontogenesis and frontolysis in the central North Pacific in the winter of 1977. The computed patterns and rates are compared to those sensed by satellite, and reasonable agreement is found. In the subtropical region, frontogenetic and frontolytic bands tend to occur in pairs, an occurrence which is attributed to a wind stress maximum over the area. Typical observed frontogenetic rates are 0.5–1°C/100 km per week. The computed rates underestimate the observed on

ISSN:0148-0227    

DOI:10.1029/JC083iC09p04545

年代:1978

数据来源: WILEY

摘要:

We use hydrographic data to delineate a diffuse, large (nearly 1000 km long), and persistent (years) haline front which overlies the continental slope in the eastern Bering Sea. The front marks a transition between the waters above the deep basin, where the horizontal salinity gradient is almost zero and the flow is geostrophic, and the waters above the broad shelf, where salinity gradients are large and the flow is tidally dominated. We suggest that the change in mixing from the oceanic regime above the deep basin to the tidal regime over the shelf is responsible for the front. Because our arguments do not depend upon features unique to the Bering Sea slope, similar fronts should be found where freshwater runoff can dominate the density gradient and where strong boundary currents are absent.

ISSN:0148-0227    

DOI:10.1029/JC083iC09p04551

年代:1978

数据来源: WILEY

摘要:

The monthly horizontal thermal advection in the upper 250 m of the water column at ocean weather station (OWS) November was calculated by means of a divergent heat budget equation. This station is located on the southern boundary of the transition zone separating the subarctic and subtropic water masses. Bathythermograph data from 1962 to 1970 indicate that thermal advection occurs as surges of cold water across this front at intervals of 7–8 months with a duration of 3–4.5 months. Salinity data from 1968 to 1970 show a significant decrease (approximately 0.12‰ at 200 m) and a subsequent increase concurrent with each cooling and heating trend, respectively. Evidently, cool, low‐salinity subarctic water replaces the normally warm, salty subtropic water of OWS November in periodic but nonseasonal

ISSN:0148-0227    

DOI:10.1029/JC083iC09p04561

年代:1978

数据来源: WILEY

摘要:

A mesoscale investigation of the temperature structure of the Oceanic Polar Front in the Barents Sea established that the position of the front as indicated by strong horizontal temperature gradients was well correlated with the bathymetric features.

ISSN:0148-0227    

DOI:10.1029/JC083iC09p04567

年代:1978

数据来源: WILEY

摘要:

The thermal structures for the upper 500 m presented in four long meridional sections across the subantarctic and antarctic regimes of the Southern Ocean display a number of similar features as well as some differences. The similarities are associated with the latitudinal variation of depth and temperature of the temperature minimum (Tmin) layer and the common occurrence of much vertical relief of isotherms north of the polar front, which is believed to reflect the presence of transient features, sucfy as meanders and eddies. The differences seem to be related to the details of the thermal structure of the polar front, the continuity of theTmin layer at its northern extent, and the presence of strong thermal fronts north of the polar front. Neither local sea‐air flux of heat nor the wind‐induced Ekman drift is consistent with the presence of the polar front. Hence the front is not locally generated. The sea‐air heat flux in the vicinity of the front reverses the large‐scale trend of increased heat loss of the ocean as latitude increases: the heat flux is from ocean to atmosphere to the immediate north of the polar front and from atmosphere to ocean to the immediate south. Northward Ekman drift of surface waters is near the circumpolar maximum at the polar front, which means that the front divides the convergence region to the north from the divergence region to the south. The Antarctic Polar Front is quite similar to the Subantarctic Front of the North Pacific in nearly all r

ISSN:0148-0227    

DOI:10.1029/JC083iC09p04572

年代:1978

数据来源: WILEY

摘要:

Temperature and salinity data from a repeated salinity‐temperature‐depth station and temperature profiles from three expendable bathythermograph experiments are used to investigate both the spatial and the temporal characteristics of fine structure observed in the Antarctic Polar Front Zone. The fine structure was found to evolve considerably on time scales of 1 hour and less. From an experiment designed to elucidate the spatial scales of the fine structure, a marked anisotropy was revealed, suggesting that the temperature structures were elongated filaments aligned with the front. The data were also used to investigate the possibility that internal waves generate the observed fine structure. On the basis of the temperature‐salinity correlation of the fine structure and the extremely large required vertical displacements the vertical motions of internal waves can be ruled out as the primary cause of the fine structure. Because the Antarctic Polar Front Zone is a region of high horizontal temperature and salinity gradients and because there is an observed increase at one‐half inertial period in drop‐lagged coherences, it is hypothesized that the low‐frequency nearly horizontal internal wave motions are generating the observed fine structure. However, in the particular case where direct observations of the vertical motions of internal waves are available, assuming that the relationship between vertical and horizontal displacements prescribed by the Garrett and Munk (1975) model holds, horizontal displacements are also ruled out as the sole source of the observed fine structure, yielding neither enough total variance nor the expected spectral shape; thus much of the observed variability may be attributed to temperature fine structure of noninternal

ISSN:0148-0227    

DOI:10.1029/JC083iC09p04579

年代:1978

数据来源: WILEY