摘要:

Western Pacific westerly wind bursts of 1‐ to 3‐week duration are potentially important in triggering and sustaining El Niño‐Southern Oscillation events. One such burst of 10‐day duration and maximum speeds of greater than 10 m s−1occurred in May 1986 west of the date line. The response to this westerly wind burst is documented from equatorial current meter moorings, thermistor chain moorings, and sea level and hydrographic data. At 0°, 165°E in the western Pacific the thermocline was depressed by 25 m, sea surface temperature dropped by 0.3°–0.4°C, and sea level rose by 10–15 cm a few days after the maximum in westerly wind speed. Likewise, the South Equatorial Current rapidly accelerated eastward and attained speeds in excess of 100 cm s−1. Vertical shear in an approximately 100 m deep surface layer reversed within a few days of the winds, consistent with a simple model of equatorial mixed layer dynamics in which vertical eddy viscosities are inferred to beO(100 cm2s−1). A sharp Kelvin wavelike pulse in sea level propagated out of the directly forced region into the central and eastern Pacific. The pulse took 45 days to travel from Tarawa (1°N, 173°E) to La Libertad (2°S, 81°W) on the South American coast, at an average phase speed of about 300 cm s−1. This is of the same order of magnitude as, but significantly higher than, the phase speed of a first baroclinic mode Kelvin wave and is probably the result of Doppler shifting by the Equatorial Undercurrent. A rise in sea surface temperature of about 1°C in 2 days occurred at 0°N, 110°W with the passage of the pulse. However, coincidental meridional advection of a sharp sea surface temperature front, rather than zonal advection of downwelling associated with the pulse, appears to be responsible for this warming. The relevance of this wind‐forced pulse to the subsequent evolution of the 1986–1987 El Niño‐Southern Oscillation event is discus

ISSN:0148-0227    

DOI:10.1029/JC093iC09p10589

年代:1988

数据来源: WILEY

摘要:

Currents and winds measured over the continental shelf and upper continental slope during the first half of 1984 are analyzed to determine the character of the flow off central California (Point Conception to San Francisco). The mean flow was poleward from Point Conception to Point Sur, in opposition to the equatorward wind stress. The mean flow was equatorward north of Point Sur. Fluctuations in alongshore currents over the shelf were highly correlated with local winds everywhere except off Point Conception, where currents were not only uncorrelated with wind but also poorly correlated with currents farther north. North of Point Buchon there is evidence for poleward propagation of shelf current variability at 175–200 cm/s. The correlation between currents and local wind forcing dropped considerably beyond the shelf break, only 10–15 km offshore from the shelf moorings. During extended periods of weak equatorward winds, the poleward shelf flow south of Point Sur spreads farther offshore over the continental slope. A three week period of calm winds in July 1984 resulted in a 100‐km‐wide tongue of poleward flow extending 300 km along the California coast. Similar, but somewhat weaker, poleward surface flow occurred during the same period in 1981; a 2‐ to 3‐week period of calm winds in late June and early July 1981 resulted in a 100‐km‐wide tongue of poleward flow extending at least 150 km along the California coast. In contrast to the poleward flow on the shelf, which appears to be normal during spring and summer, the poleward surface flow observed over the slope in July 1981 and 1984 is unusual, based on historical hydrographic surveys off the central California coast. Poleward surface flow over the continental slope occurs seasonally in the winter but is not generally observed

ISSN:0148-0227    

DOI:10.1029/JC093iC09p10604

年代:1988

数据来源: WILEY

摘要:

A new method (called constrained sinusoidal crossover adjustment) for removing the orbit error in satellite altimetry is tested (using crossovers accumulated in the first 91 days of the Geosat nonrepeat era in the tropical Pacific) and found to have many excellent qualities. Two features distinguish the new method from the conventional bias‐and‐tilt crossover adjustment. First, a sine wave (with wavelength equaling the circumference of the Earth) is used to represent the orbit error for each satellite revolution, instead of the bias‐and‐tilt (and curvature, if necessary) approach for each segment of the satellite ground track. Second, the indeterminacy of the adjustment process is removed by a simple constraint that minimizes the amplitudes of the sine waves rather than by fixing selected tracks. Overall, the new method is more accurate, more efficient, and much less cumbersome to implement than the old method. The idea of restricting the crossover adjustment to crossovers between tracks that are less than certain days apart in order to preserve the large‐scale long‐term oceanic variability is also tested with inconclusive results because the orbit error was unusually nonstationary in the initial 91 days of the Geo

ISSN:0148-0227    

DOI:10.1029/JC093iC09p10621

年代:1988

数据来源: WILEY

摘要:

Nonlinear unstable waves in the eastern ocean basin are analyzed using a three‐layer quasi‐geostrophic numerical model. The upper two layers are forced to maintain a mean circulation in the absence of mesoscale motion. The waves are produced by initial small perturbations added to the mean flow. Two experiments, focused on the eastern ocean basin and differing only by mean flow strength, are performed. A region of high eddy kinetic energy is formed in the southern region, but the eastern and northern regions are vacant of eddies because of the energy efflux by westward and southwestward propagating unstable waves. Regional energetics are calculated to highlight the differences between the eastern and southern regions. Two dominant waves are found in the southern region. Waves with a period of 120 days propagate to the west and form several wave trains parallel to the southern boundary. Longer‐period waves with a period of 200 days propagate to the southwest. Comparisons with observed eddies in the northeast Pacific are discussed. Besides baroclinic instability, it is found that the energy flux by propagating waves is very important in the finite amplitude stability of the eastern ocean general circul

ISSN:0148-0227    

DOI:10.1029/JC093iC09p10630

年代:1988

数据来源: WILEY

摘要:

Data collected in the eastern Gulf of Mexico during 1974, 1975, and 1976 show that the penetration of the Loop Current into the gulf is strongly correlated with the location of the Yucatan Current on the Campeche Bank. The Loop does not penetrate far into the gulf when the Yucatan Current separates from the bank in the vicinity of the Catoche Tongue (i.e., the eastern Campeche Bank). Deep Loop penetrations are correlated with separations farther west on the bank. The angle of the Yucatan Current at separation is also correlated with the location of separation (i.e., smaller angles relative to due east are correlated with separations from farther east on the bank). Thus small angles at separation are correlated with shallow intrusions of the Loop. Historical temperature data collected in the eastern gulf are reviewed and support these correlations. Simple conservation of potential vorticity considerations can explain the correlation between the angle at separation and the penetration of the Loop.

ISSN:0148-0227    

DOI:10.1029/JC093iC09p10645

年代:1988

数据来源: WILEY

摘要:

When observations are too sparse to determine the state of a dynamical model, it is necessary to make use of prior knowledge or prejudice. The approach discussed here is to require that the model state be the best smooth fit to the sparse data. The requirement of smoothness is enforced by introducing bogus data, which correspond to hypothetical observations that properties such as slope, curvature, or temporal tendency of model fields have zero values within some specified accuracy. The bogus data serve to increase the effective ratio of data to model degrees of freedom. The concept of bogus data allows a bias toward smoothness to be incorporated easily into the adjoint method for fitting time‐dependent models to asynoptic data. Computational examples using a simple three‐wave model show that reasonable fits can be obtained even when the number of real data is considerably less than the number of model degrees of free

ISSN:0148-0227    

DOI:10.1029/JC093iC09p10655

年代:1988

数据来源: WILEY

摘要:

The extent and area of sea ice and the amount of open water within the ice boundaries have been computed for the Arctic, Antarctic, and global ice covers every 2 days from November 1978 to August 1987 utilizing the Nimbus 7 scanning multichannel microwave radiometer (SMMR) observations. During this 9‐year period, no significant trends were found in the ice areas of the Arctic and Antarctic packs or in their sum, the global ice area. Also, no significant trends were found in the maxima and minima of the annual ice extents for either polar pack. However, during these 9 years, significant negative trends were found in the annual global ice extent maxima (5%) and in the annual maxima of the global open water area within the sea ice boundaries (7–14%). Significant negative trends were also found in the annual open water maxima in the Antarctic (5–10%) and the annual open water minima in the Arctic (13–23%). The open water within the ice boundaries averaged approximately 14% in the Arctic and 18% in the Antarctic, at the time of their maximum extents. This negative trend in the global ice extent maxima during 1978–1987 also occurred during 1973–1976, found by an analysis of the monochromatic microwave observations obtained by the Nimbus 5 satellite. The combined 15‐year negative trend is 6%. A significant change between the 1973–1976 and the 1978–1987 periods in the Antarctic ice pack is that the very large polynya that formed and persisted in the Weddell Sea during three out of four of the austral winters in the earlier period did not form in any of the 9 years of the latter period. This study, in conjunction with recent studies of global temperature change, lends support to the thesis that climatic changes in the global average temperature might be detectable by observing variations in glob

ISSN:0148-0227    

DOI:10.1029/JC093iC09p10666

年代:1988

数据来源: WILEY

摘要:

A 1‐year time sequence (November 1978 through October 1979) of surface pigment images from the South Atlantic Bight (SAB) was derived from the Nimbus 7 coastal zone color scanner. This data set is augmented with in situ observations of hydrographic parameters, freshwater discharge, sea level, coastal winds, and currents for the purpose of examining the coupling between physical processes and the spatial and temporal variability of the surface pigment fields. The SAB is divided into three regions: the east Florida shelf, the Georgia‐South Carolina shelf and the Carolina Capes. Six‐month “seasonal” mean pigment fields and time series of mean values within subregions were generated. While the seasonal mean isopleths were closely oriented along isobaths, significant differences between seasons in each region were found to exist. These differences are explained by correlating the pigment time series with physical parameters and processes known to be important in the SAB. Specifically, summertime concentrations between Cape Romain and Cape Canaveral were greater than those in winter, but the opposite was true north of Cape Romain. It is suggested that during the abnormally high freshwater discharge in the winter‐spring of 1979, Cape Romain and Cape Fear were the major sites of cross‐shelf transport, while the cross‐shelf exchange during the fall of 1979 occurred just north of Cape Canaveral. Finally, the alongshore band of high pigment concentrations increased in width throughout the year in the vicinity of Charleston, but near Jacksonville it exhibited a minimum width in the summer and a maximum width in t

ISSN:0148-0227    

DOI:10.1029/JC093iC09p10675

年代:1988

数据来源: WILEY

摘要:

A model of the nutrient and carbon cycles in the North Atlantic is formulated, and water flow rates, eddy mixing coefficients, particle fluxes and CO2gas exchange rates are calculated. The model incorporates geostrophy, wind‐driven Ekman fluxes and budget equations for a suite of seven tracers. Geostrophic transports are based on Levitus' (1982) climatological data, and nutrient distributions are obtained from historical station data. The model is solved by linear programming. Budgets of mass, heat, salt, oxygen, phosphate, nitrate, silicate, CO2, and alkalinity can be satisfied simultaneously in the North Atlantic. Water transports in the model depend largely on the geostrophic flows derived from the climatological data and agree quantitatively with independent transport calculations in the northern North Atlantic but seem to underestimate the shallow circulation and the upwelling in the tropical Atlantic. Meridional heat fluxes are northward in the whole model domain, and the pattern of air‐sea heat fluxes agrees with bulk formula estimates. Nutrient budgets in the tropical and subtropical Atlantic place strong constraints on shallow diapycnal mixing coefficients where the values are small and well determined (between 0 and 0.2 cm2/s). They are poorly determined in the deep wa

ISSN:0148-0227    

DOI:10.1029/JC093iC09p10699

年代:1988

数据来源: WILEY

摘要:

Solutions are presented for the shelf response of barotropic and stratified oceans to an oscillatory coastal flux through a strait. The flux is modeled as the return interior flow due to an Ekman transport that arises from a fictitious square‐wave longshore wind stress. The width 2d, of the square‐wave stress is taken to be that of the strait and the response due to the coastal flux determined from longwave wind forced solutions that exist in the literature. The net longshore energy flux for thenth strait forced shelf wave mode, wave numberkn, is shown to be proportional toU2(ω)¯[bnsin(knd)(knd)]2, whereU2(ω)¯is the coastal flux spectrum andbnthe modal “wind” coupling coefficients. Results compare favorably with existing barotropic theories and estimates of net longshore energy flux obtained for the Australian Coastal Experiment region are shown to be in reasonable agreement with observations at periods of 9 days, when forcing by Bass Strait is assum

ISSN:0148-0227    

DOI:10.1029/JC093iC09p10724

年代:1988

数据来源: WILEY