摘要:

Measurements made from R/P Flip using rapid profiling conductivity, temperature, and depth probes and vector‐measuring current meters provide a new and detailed look at the diurnal cycle of the upper ocean. A diurnal cycle occurs when solar heating warms and stabilizes the upper ocean. This limits the downward penetration of turbulent wind mixing so that air‐sea fluxes of heat and momentum are surface trapped during midday. The central problem is to learn how the trapping depthDT(mean depth value of the diurnal temperature and velocity response) is set by the competing effects of wind mixing and surface heating. In this data set the diurnal range of surface temperatureT˜swas observed to vary from0.05

ISSN:0148-0227    

DOI:10.1029/JC091iC07p08411

年代:1986

数据来源: WILEY

摘要:

Over a 1‐month period (October 5 to November 6, 1982) during the initial stages of the 1982–1983 El Niño, hydrographic and velocity profiling measurements were made in the eastern equatorial Pacific by two research vessels. Track lines approximated a square, centered near the Galápagos Islands with approximately meridional sections at 95°W and 85°W and nearly zonal sections at about 5°N and 5°S. Water mass characteristics and estimated currents of these sections are discussed. Sea surface temperature nearly everywhere was warmer than 25°C (an anomaly of 2°C–3°C). The equatorial thermocline, represented by the 20°C isotherm, was depressed by nearly 50 m at 85°W and more than 100 m at 95°W relative to a historical mean profile. Across 95°W, estimated geostrophic (relative to 500 dbar) and directly measured near‐equatorial velocity profiles indicated significant eastward surface flow. The South Equatorial Current south of the equator had disappeared. Estimated warm water transport (σt<24.5 kg m−3) indicated an influx into the region which was approximately that required to balance the observed low‐frequency sea level change at the Galápagos Islands. Temperature and salinity properties as well as the transport estimates indicated that this warm water came p

ISSN:0148-0227    

DOI:10.1029/JC091iC07p08428

年代:1986

数据来源: WILEY

摘要:

Anomalous sea level, anomalous observed dynamic height (0/400 dbar) and anomalous model dynamic height are compared at the locations of 13 island sea level stations in the tropical Pacific for each 2‐month interval of the 4‐year period 1979 to 1982. Sea level compares well with both observed dynamic height (0/400 dbar) based on temperature/depth observations made by volunteer observing ships, and model dynamic height derived from a linear two‐layer wind‐driven model. The cross correlation between sea level and either of the dynamic heights is generally greater than 0.75. The ratio of root‐mean‐square (Rms) differences about the mean annual cycle of the sea level to Rms differences of either of the dynamic heights is approximately unity. Starting in 1981, off‐equatorial Rossby wave activity propagated toward the western boundary of the Pacific basin; this also occurred in model dynamic height both north and south of the equator. Yet neither sea level observations nor observed dynamic height has the spatial and temporal resolution to establish a connection between the off‐equatorial Rossby wave activity and the equatorial Kelvin wave activity in the western boundary region. On the other hand, the model dynamic height does have this capability. Therefore at the western boundary, the model Rossby wave activity is found to have excited coastally trapped Kelvin‐Munk wave activity, which transmitted the anomalous sea level equatorward. At the equator this model coastally trapped wave activity excited eastward propagating equatorial Kelvin waves, yielding a pair of anomalous peaks in dynamic height variability in the eastern equatorial Pacific associated with the 1982–1983 El Niño/Southern Oscillation (ENSO) event. The evolution of these two peaks in anomalous dynamic height associated with the 1982–1983 ENSO event is examined at eight locations in the tropical and equatorial Pacific, The major peak originated in the off‐equatorial South Pacific and coincided with the wintertime 1982–1983 El Niño event in the eastern equatorial Pacific. The secondary peak originated in the off‐equatorial North Pacific and coincided with the anomalous peak which occurred in the eastern equatorial Pacific the summer be

ISSN:0148-0227    

DOI:10.1029/JC091iC07p08437

年代:1986

数据来源: WILEY

摘要:

An evaluation of surface currents measured by HF radar during November 29, 1983, to January 31, 1984, with radar sites at Jupiter and Stuart on the Florida east coast is carried out in comparison with currents and transports measured by moorings and submarine cable. While an earlier analysis of currents measured in summer 1983 with radars located at Palm Beach and Jupiter (Schott et al., 1985) found significant northward shear in the northward radar currents about 20 km offshore leading to concerns about a possible bias in the radar currents, this effect was not observed in the second application farther north. It is possible that the shear in the summer 1983 field might have been real and related to the topography in the southern part of the 1983 radar field where no intercomparison current data had been available. Concerning the usefulness of radar currents as Florida Current transport indicators, which was the prime intention of their application in the context of the Subtropical Atlantic Climate Studies, this second study finds much more encouraging results than the one based on the observations of summer 1983. While the first study was inconclusive because only small transport fluctuations occurred during the summer 1983 observation period, this second study finds significant correlation. Florida Current transport fluctuations had a total range of 15 × 106m3/s during the second observation period, and correlation with downstream radar currents, averaged zonally across the center of the radar field, was 0.85. Coherence was significant for periods longer than 5 days. Highest correlation with transport was found for radar currents farthest out, to the right of the axis of the stream

ISSN:0148-0227    

DOI:10.1029/JC091iC07p08451

年代:1986

数据来源: WILEY

摘要:

Long‐term measurements of Reynolds stress and kinetic energy are necessary to characterize the bottom boundary layer during storms which transport sediment in the High Energy Benthic Boundary Layer Experiment area on the Nova Scotia Rise. The benthic acoustic stress sensor current meter system employed an on‐board microcomputer to process 2‐Hz velocity vector data into 20‐min averages of velocity vectors and the turbulent Reynolds stress tensor. The data indicate a bottom boundary layer, which is usually transitional, with bottom roughness scaling between viscous (z0=v/9u*) and rough (z0=ks/30). During the periods of transitional flow the logarithmic layer was not a useful indicator of boundary stress. Direct stress and energy measurements showed that the stress was much less than that indicated by the slope of the transitional mean logarithmic velocity profile. Several westward high‐velocity events, which were modulated by a significant tidal component, were recorded. It appears from this data set that the mean westward flow must be accompanied by a train of internal tidal waves to achieve the velocities necessary to be the sediment transport events identified as “bent

ISSN:0148-0227    

DOI:10.1029/JC091iC07p08461

年代:1986

数据来源: WILEY

摘要:

Observations and numerical simulations of upwelling along the Galician coast of Spain during April 1982 are presented. In situ measurements include shipboard determinations of hydrographic and biological parameters from a grid of stations covering the continental shelf from Cape Finisterre to Ria de Vigo, sea level data from Vigo and La Coruña, and wind stress estimates derived from the ship winds and from surface pressure charts. Sea surface temperature information and pigment concentration information have been obtained from a sequence of satellite images from the NOAA 7 advanced very high resolution radiometer and the Nimbus 7 coastal zone color scanner, respectively. Since the Cape Finisterre sector of the Iberian peninsula is characterized by an abrupt change in coastline orientation, wind‐driven upwelling can occur in that region over a 270° range of wind direction. These data document the evolution of upwelling and the resultant coastal circulation in response to two wind events that occurred over a 10‐day period. Salient features of the circulation include a southward coastal jet and a northward flow further offshore along the western coast. Numerical simulations of the coastal currents, the vertical excursion of a density interface from a static equilibrium position, and coastal sea level are conducted using a wind patch characterized by constant direction and negative curl. The simulations show that during these wind events, the greatest upwelling will occur either at Cape Finisterre or along the northern coast as was observed in this case and as has been reported by others. It is suggested on the basis of the analysis of the sea level records and on the numerical simulations that wave disturbances propagate northward along the coast at a speed of 120–160 km/day. Finally, it is speculated that much of the organic material formed during upwelling events north of the Cape Finisterre is advected out to sea northwest of t

ISSN:0148-0227    

DOI:10.1029/JC091iC07p08470

年代:1986

数据来源: WILEY

摘要:

The energy and action flow through the small‐scale part of the oceanic internal wave field is modeled by use of the eikonal technique, which is not subject to a weak interaction assumption. Both Monte Carlo calculations and a simplified model are presented and found to agree. It is found that the action flows toward slightly higher frequency (and thus the waves gain energy), in striking contrast to weak interaction predictions of a strong frequency decrease. The energy dissipation scales with depth asN2cosh−1(N/f), in agreement with measurements. The overall level is, however, a factor of 4 smaller than measurements. Possible sources of this discrepancy are discussed. A comparison is made with previous theoretical approaches for the depth dependence of dissipat

ISSN:0148-0227    

DOI:10.1029/JC091iC07p08487

年代:1986

数据来源: WILEY

摘要:

A numerical model has been used to investigate the wind‐driven circulation in a stratified basin of moderate size, Lake Tahoe, California‐Nevada. Two types of circulation are identified: “direct” circulations, in which the current directions remain relatively constant and the mean circulation formed over several days resembles the instantaneous circulation, and “residual” circulations, in which the currents fluctuate continuously and the mean circulation is characterized by small net displacements of parcels after large oscillations. Previous studies of stratified closed basins have emphasized residual circulations caused by cyclonically propagating internal basin modes, resulting in a single cyclonic mean gyre during light to moderate winds. Observations at Lake Tahoe have shown currents which are more constant in direction, with a double gyre pattern of surface circulation, dominated by an anticyclonic northern gyre. Model experiments of Lake Tahoe demonstrate that the curl of the wind stress must be included to obtain a direct, double gyre circulation similar to the observations. Horizontally uniform winds cause a residual circulation, similar to that reported at other lakes. Use of the model to calculate the vorticity budget clarifies the role of the wind stress curl in creating the direct

ISSN:0148-0227    

DOI:10.1029/JC091iC07p08497

年代:1986

数据来源: WILEY

摘要:

A line‐by‐line radiation transfer model is used to simulate the brightness temperatures measured in the atmospheric “window” between 10 and 13 μm by the advanced very high resolution radiometer (AVHRR/2) on the NOAA 7 satellite. The atmospheric properties are described by a large set of marine radiosonde profiles over the NE Atlantic Ocean and characterize the month of July. The effects of anomalous atmospheric conditions on the brightness temperatures are simulated by independently adjusting the humidity and temperature profiles, and it is found that the consequences of humidity anomalies are greater if they occur at height (pressure of<850 mbar), whereas temperature anomalies have greater effect if they are in the lower troposphere. Sea surface temperature (SST) retrieval coefficients, optimized for these July conditions, are derived and tested against simulated brightness temperatures derived using a “withheld” set of profiles and found to be accurate. Mean errors of several tenths of a kelvin were found when other, nonoptimized coefficients, taken from the literature, were applied to the original July conditions. The mean errors in SST derived using the optimized coefficients can also be a few tenths of a kelvin in extremely anomalous atmospheric conditions. These errors are large enough to be of concern to climate researchers but probably too small to permit direct verification by comparison with currently available conventional SST

ISSN:0148-0227    

DOI:10.1029/JC091iC07p08509

年代:1986

数据来源: WILEY

摘要:

EOF analysis of the data on grain‐size distributions of sediments in the Ø‐size class from the beach foreshore, backshore, dune, and nearshore environments of Colva and Calangute revealed that the first three Ø‐dependent eigenfunctions c1(Ø), c2(Ø), and c3(Ø) account for more than 97% to 99% of variation in the data set, the largest variation being represented by the first Ø‐dependent function c1(Ø) alone. This function showed significant differences in the concentration of grain‐size particles across the shore covering various physiographic units of Colva, i.e., dominance of very fine sands in the dunes and backshore, fine sands in the foreshore, and silt and clays in the offshore areas beyond 5‐m water depths, reflecting the impact of the changing character of the transportational and depositional processes affecting the sediments, thus implying different energy environments. This analysis also showed marked alongshore variations in the sediment distribution pattern in different sectors of the subaerial beach of Colva and suggests transportation of sediments from either ends to the central region. The three energetic eigenfunctions used to obtain the predictable or information rich part of the original signal are comparable with normalized input data and indicate the effic

ISSN:0148-0227    

DOI:10.1029/JC091iC07p08523

年代:1986

数据来源: WILEY