摘要:

We examine data from 23 surface drifters which were deployed between June 1983 and July 1984 at 4°W, 1.5°–4°S. The drifters were equipped with a window shade drogue centered at 15‐m depth and in most cases a 117‐m‐long thermistor chain. Drift data indicate a westward South Equatorial Current with typical speeds of about 20 cm s−1south of the equator. Maximum westward flow of 30–40 cm s−1occurred in June through September of 1983 and 1984, consistent with climatology. Near‐zero westward flow, which was significantly weaker than was expected from climatology (by about 20 cm s−1), occurred from February to April, 1984. This probably represents real interannual variability and may be related to the fact that the equatorial Atlantic was warmer than usual in the spring and summer of 1984. Energetic variations on time scales ofO(1 month) and less and space scales ofO(100 km) and less are ubiquitous in the drift and temperature data. Kinetic energy levels associated with these variations south of the equator are typically 100 cm2s−2, with slightly higher values in boreal summer. Energy levels north of the equator are about 500 cm2s−2on the basis of data available only during the boreal summer and fall. The sources of this energy include inertia‐gravity waves, instabilities of the general circulation, and other phenomena for which ther

ISSN:0148-0227    

DOI:10.1029/JC091iC05p06569

年代:1986

数据来源: WILEY

摘要:

A warm outbreak is a large body of Gulf Stream water with apparent anticyclonic circulation that detaches from the Gulf Stream and exists as a well‐defined entity in the Sargasso Sea. Because warm outbreaks are warmer at the surface than Sargasso Sea water, they are often clearly visible in satellite thermal infrared imagery. From a survey of over 750 satellite images covering the Sargasso Sea immediately to the south of the Gulf Stream between 64° and 74°W and spanning a 5‐year period, 18 possible outbreaks have been observed. All formed west of 65°W, with the majority forming between 67° and 72°W. Five of the 18 were observed to detach completely from the Gulf Stream and have the following properties in common: (1) they all formed in several days at or near the point of maximum cyclonic curvature of a large Gulf Stream meander, (2) the surface expression was relatively short‐lived, of the order of 10 to 20 days, and (3) their dimensions (and those of the other 13) were of the order of 100 by 200 km. Given the similarity between the characteristics of warm outbreaks and those of “opposite vortices” predicted by Ikeda and Apel (1981) from a two‐layer, quasi‐geostrophic model of an eastward flowing jet, it is suggested that the two phenomena are related. Further support of this hypothesis is the fact that the rate of formation of warm outbreaks, between two and six per year, is similar to that of anticyclonic eddies observed in expendable bathythermograph su

ISSN:0148-0227    

DOI:10.1029/JC091iC05p06583

年代:1986

数据来源: WILEY

摘要:

The major El Niño event of 1982–1983 affected the entire California Current system. The anomalous conditions along the west coast of North America were related to the equatorial anomalies and also to the anomalous atmospheric circulation in the northeast Pacific, where the Aleutian Low was east of its usual position and the associated 700‐mbar height reached its lowest value on record in February–March 1983. Positive temperature and negative salinity anomalies in the upper ocean, extending from the coast to at least 200 km offshore, were reported from San Diego to Vancouver Island. In data acquired in domains centered approximately 180 km off northern California by the Ocean Prediction Through Observation, Modeling and Analysis Program, anomalies in both temperature and salinity were most pronounced subsurface. Spatially and monthly averaged temperatures were about 3°C warmer than normal at 80 to 100 m in April and again in December 1983. At 100 to 120 m, salinity was about 0.4 parts per thousand lower than normal in July 1983 and July 1984, several months later than the temperature anomaly maxima. The temperature anomalies may be related to the poleward propagation of the equatorial El Niño perturbation by coastally trapped waves, with offshore propagation by planetary Rossby waves possibly playing some role in the relaxation of the perturbed eastern boundary current circulation. Anomalous onshore advection associated with the perturbed atmospheric circulation, deeper than normal mixed layers, or depression of the thermocline and halocline by the passage of Rossby waves could each account for coincident positive temperature and negative salinity a

ISSN:0148-0227    

DOI:10.1029/JC091iC05p06597

年代:1986

数据来源: WILEY

摘要:

In the radar altimeter measurement of the satellite height above the instantaneous sea surface, radial orbit errors are “mapped” on the earth with the spacecraft motion. In many geophysical and oceanographical applications of satellite altimetry, a precise knowledge of the mapped error features is necessary to estimate sea (or ice sheet) surface topographies and to assess their absolute accuracies. So we derive a general formulation to infer from any a priori time spectrum of orbit errors the characteristic wavelengths of the mapped error biasing the recovery of a sea surface topography. Because of commensurability between the satellite motion and earth rotation, radial orbit errors at the nodal or orbital periods and their harmonics are mapped into smooth long‐wavelength surfaces and fully aliased in the steady surface topography. As this phenomenon presents a close relationship with the resonance of the orbit perturbations, we suggest naming it the mapped orbit error resonance. Our formulation also provides an explicit account of both time and space sampling effects on the correlation of the mean sea surface, oceanic tides, and orbit errors. For instance, the typical wavelength of a resonant mapped error is scattered by the land gaps in all the near wavelengths of an oceanic surface. The derived mapping function also seems to indicate that the statistics of the crossover differences are unable to estimate the absolute precision of altimetric surfaces because a nonnegligible portion of radial orbit errors falls into the steady component of the sea su

ISSN:0148-0227    

DOI:10.1029/JC091iC05p06609

年代:1986

数据来源: WILEY

摘要:

Statistics of two dimensional wave groups, of steep wave events, and of a cascade pattern manifested in the surface geometry in a developed sea state are derived. However, mathematical theories used to parameterize these as well as many other features of random surfaces have very limited ranges of validity. For example, high‐order moments of wave spectra appearing in the calculations of wave slope statistics cannot be evaluated because of divergence of the corresponding integrals. In the present paper the restrictions are reviewed and the difficulties are shown to be due to a pseudo‐fractal geometry of the sea surface whose spectrum is known only within a limited range of frequency (characterized by either the resolution of a measuring technique or the constraints of a theoretical model). An approach is presented that solves the problem: treating the surface elevation field as specified on a spatial (temporal) running grid, an averaging procedure is developed employing the Taylor microscale as the mesh size. The technique is illustrated by first exposing errors in direct calculations of the effective surface impedance for a coherently reflectedLband radio wave. The errors arise from the use of wave spectra whose high‐frequency tail is identified with the Phillips saturation range. The technique is then employed in the study of wave groups and steep waves for a Gaussian, two‐dimensional, time‐varying surface. In particular, it is found that wave groups are not observable in a developed sea. Finally, the theory is applied to estimating breaking wave statistics. A comparison with field observations is

ISSN:0148-0227    

DOI:10.1029/JC091iC05p06629

年代:1986

数据来源: WILEY

摘要:

A 5° × 5° climatological field of the extinction coefficient of solar irradiance versus depth is obtained for the world ocean. A simple method of merging various data (prior to 1974) concerning the water transparency has been used. The final product is obtained through a careful subjective analysis. It should be useful for the purpose of climatological modeli

ISSN:0148-0227    

DOI:10.1029/JC091iC05p06642

年代:1986

数据来源: WILEY