Local Vertical Mixing Research Articles

Thermohaline circulation in the deep South China Sea basin inferred from oxygen distributions

On the basis of the historical oxygen data available, distributions of dissolved oxygen were analyzed in detail to investigate the thermohaline circulation in the South China Sea (SCS). The analyses confirmed the existence of a layer of minimal oxygen content at intermediate depths of the basin, which shows a low‐oxygen (<1.6 mL L−1) core in the southern basin with water “ages” shorter than 100 years after entering the SCS and which appears isolated from its counterpart of the western Philippine Sea. North to the core along the northern slope, there is a band of oxygen‐rich water in both upper and intermediate layers. Above 700 m the band can be attributed to the intrusion of high‐oxygen water through the Luzon Strait, while vertical flux appears to be responsible between 700 and 1500 m. The oxygen distribution provides additional evidence for a sandwiched vertical structure in transports through the Luzon Strait, with outflows in the intermediate layer and inflows above and below. While the abyssal water of the SCS is being replenished by the deep inflows, an abrupt change of water properties was observed in both upper and intermediate layers across the Luzon Strait, suggesting possible domination of local vertical mixing over horizontal spreading of inflows in the northern SCS. A four‐cell conceptual model was proposed for the thermohaline circulation, which consists of a three‐layer, cross‐basin exchange cell in the Luzon Strait, an active ventilation cell in the upper and intermediate layers along the northern slope, an abyssal replenishment cell in the deep, and a cyclonic recirculation cell in the interior basin.

Evening Transition Observations in Phoenix, Arizona

AbstractPast research has suggested that the evening transition in complex topography typically has several main features, such as (a) continued weak upslope flows persisting 3–5 h after sunset (if the sidewalls of the valley prevent Coriolis-induced turning of winds), thus signifying delayed transition; (b) unsteady local stagnation and vertical mixing within tens of meters above the surface; and (c) transition of stagnation fronts to downslope/downvalley gravity currents during the evening hours, especially at higher-elevation (steeper) slopes, and their arrival at adjoining low-elevation gentle slopes as “slope breezes.” This transition process typically occurs in locales such as Phoenix, Arizona, which has expansive exposure to plains in one direction (to the west and south) and is adjacent to abrupt change in the terrain in other directions (primarily to the north and east). An analysis of wind records from several automated weather stations and a radar wind profiler for selected characteristic periods representing all four seasons and data from a previous major field campaign in the greater Phoenix valley illustrate (i) the shallow nature of transition flows that develop on a year-round basis during frequent clear, calm nights in the desert Southwest and their seasonal sensitivity; (ii) a spatial variation of transition times relative to the only first-order National Weather Service station in the region (Sky Harbor International Airport); (iii) the dependence of transition time (and hence the delay of transition) on the exposure, the elevation, and the magnitude of slope; and (iv) a possible heat-island influence. These observations are quantified using theoretical estimates, and the results are placed in the context of multiscale flows in urban basins.

Observations and modeling of seasonal variability in the Straits of Georgia and Juan de Fuca

The Strait of Georgia is a large semi-enclosed basin on the southern coast of British Columbia. Its main connection to the Pacific is to the south, through Juan de Fuca Strait. Abundant freshwater discharge, mainly from the Fraser River, forces an estuarine exchange with oceanic shelf water. The resulting circulation is modulated by tides and winds. Both the coastal wind stress and the flux of freshwater are subject to strong seasonal modulations, producing a marked seasonal cycle in the water properties and circulation of the region. The seasonal variability of the Strait of Georgia and Juan de Fuca Strait is described using data from a series of recent cruises conducted over a five-year period, in addition to longer term historical data sets. To complement the observations, the data are compared with numerical simulations based on the Princeton Ocean Model (POM). Forced with tides, freshwater discharge and seasonal wind stress, the model is integrated over a few years until the system approaches statistical equilibrium. Results show good agreement with observations from Juan de Fuca Strait, as well as over the upper part of the water column within the Strait of Georgia. However, simulation of the seasonal cycle of the deeper waters of the Strait of Georgia is more problematic. The deep water properties apparently are determined by a delicate balance between dense intrusions from the sill area and local vertical mixing.

Sub-seasonal to interannual variations of sea surface temperature, salinity, oxygen anomaly, and transmissivity in Santa Monica Bay, California from 1987 to 1997

While the basic hydrographic and circulation pattern of Santa Monica Bay (SMB) are relatively well known, the seasonal and interannual variations of these patterns are not well established nor are the mechanisms behind them well understood. We analyzed 10 years of hydrographic observations (1987–1997) in the surface layer of SMB off southern California to establish the mean seasonal cycle and to deduce patterns of sub-seasonal to interannual variability of sea surface temperature, salinity, oxygen anomaly (the difference between oxygen concentration and its solubility), and transmissivity using empirical orthogonal functions and time-lagged cross-correlation methods. All four variables exhibit distinct seasonal variations, whose spatial distributions are a consequence of the interaction of bottom topography, vertical mixing, horizontal advection, freshwater discharge, and biological processes. The seasonal anomalies of all four parameters were estimated by removing the mean seasonal cycle; they exhibit three basic patterns: (1) an inshore/offshore gradient; (2) a balance between horizontal advection of the California Current from the northwest and the Southern California Countercurrent from the south; and (3) freshwater discharge from Ballona Creek. Air/sea heat flux and vertical mixing are the main factors regulating the dynamics of sea surface temperature. Freshwater discharge centered at Ballona Creek is the principal factor creating the salinity pattern. The annual mean oxygen anomaly shows a substantial supersaturation across the entire SMB. The variations of oxygen anomalies are regulated by local biological productivity, vertical mixing, and horizontal transport. Vertical mixing influences water transparency by suspension of sediments and nutrient supply stimulating phytoplankton growth. A remarkably clear pattern of spatio-temporal variations of all parameters is observed in a relatively small basin; these variations are regulated by both local meteorological factors (air temperature, wind, atmospheric precipitation) and remote forcing, including the El Niño–Southern Oscillation cycle.

Sub-seasonal to interannual variations of sea surface temperature, salinity, oxygen anomaly, and transmissivity in Santa Monica Bay, California from 1987 to 1997

While the basic hydrographic and circulation pattern of Santa Monica Bay (SMB) are relatively well known, the seasonal and interannual variations of these patterns are not well established nor are the mechanisms behind them well understood. We analyzed 10 years of hydrographic observations (1987–1997) in the surface layer of SMB off southern California to establish the mean seasonal cycle and to deduce patterns of sub-seasonal to interannual variability of sea surface temperature, salinity, oxygen anomaly (the difference between oxygen concentration and its solubility), and transmissivity using empirical orthogonal functions and time-lagged cross-correlation methods. All four variables exhibit distinct seasonal variations, whose spatial distributions are a consequence of the interaction of bottom topography, vertical mixing, horizontal advection, freshwater discharge, and biological processes. The seasonal anomalies of all four parameters were estimated by removing the mean seasonal cycle; they exhibit three basic patterns: (1) an inshore/offshore gradient; (2) a balance between horizontal advection of the California Current from the northwest and the Southern California Countercurrent from the south; and (3) freshwater discharge from Ballona Creek. Air/sea heat flux and vertical mixing are the main factors regulating the dynamics of sea surface temperature. Freshwater discharge centered at Ballona Creek is the principal factor creating the salinity pattern. The annual mean oxygen anomaly shows a substantial supersaturation across the entire SMB. The variations of oxygen anomalies are regulated by local biological productivity, vertical mixing, and horizontal transport. Vertical mixing influences water transparency by suspension of sediments and nutrient supply stimulating phytoplankton growth. A remarkably clear pattern of spatio-temporal variations of all parameters is observed in a relatively small basin; these variations are regulated by both local meteorological factors (air temperature, wind, atmospheric precipitation) and remote forcing, including the El Niño–Southern Oscillation cycle.

Investigating the sources of synoptic variability in atmospheric CO2 measurements over the Northern Hemisphere continents: a regional model study

Continuous measurements of atmospheric CO2 over the continents are potentially powerful tools for understanding regional carbon budgets, but our limited understanding of the processes driving the high-frequency variability in these measurements makes interpretation difficult. In this paper we examine the synoptic variability (∼days) of surface CO2 concentrations in four continental records from Europe and North America. Three source functions corresponding to the ocean, land biosphere and anthropogenic sources and sinks for CO2 have been implemented in a regional atmospheric transport model. In previous carbon studies, monthly biospheric fluxes have typically been used, but here high spatiotemporal (daily, 1 ◦ × 1 ◦ ) resolution biospheric fluxes are obtained from the NCAR Land Surface Model (LSM). A high-pass filter is used to remove atmospheric variability on time scales longer than 2 months, and the resulting simulated concentration fields replicates reasonably well the magnitude and seasonality of the synoptic variability across the four observation sites. The phasing of many of the individual events are also captured, indicating that the physical and biogeochemical dynamics driving the model variability likely resemble those in nature. The observations and model results show pronounced summer maxima in the synoptic CO2 concentration variability at the two stations located in North America, while a slightly different seasonality with high variability throughout fall and winter is observed at the European sites. The mechanisms driving these patterns are studied and discussed based on correlations between the concentration anomalies and the driving atmospheric physical variables and surfaces fluxes in the simulations. During the summer, the synoptic variability over the continents has a significant contribution from variations in regional net primary production, which in turn is modulated by regional, synoptic temperature variability. In winter the synoptic variability is partitioned about equally between biospheric and anthropogenic CO2 and is mainly driven by local vertical mixing and synoptic variations in atmospheric circulation working on the large-scale atmospheric gradient. This study highlights the importance for future modeling work of improved high temporal resolution (at least daily) surface biosphere, oceanic and anthropogenic flux estimates as well as high vertical and horizontal spatiotemporal resolution of the driving meteorology.

Investigating the sources of synoptic variability in atmospheric CO2 measurements over the Northern Hemisphere continents: a regional model study

Continuous measurements of atmospheric CO2 over the continents are potentially powerful tools for understanding regional carbon budgets, but our limited understanding of the processes driving the high-frequency variability in these measurements makes interpretation difficult. In this paper we examine the synoptic variability (⊼days) of surface CO2 concentrations in four continental records from Europe and North America. Three source functions corresponding to the ocean, land biosphere and anthropogenic sources and sinks for CO2 have been implemented in a regional atmospheric transport model. In previous carbon studies, monthly biospheric fluxes have typically been used, but here high spatiotemporal (daily, 1¼×1¼) resolution biospheric fluxes are obtained from the NCAR Land Surface Model (lsm). A high-pass filter is used to remove atmospheric variability on time scales longer than 2 months, and the resulting simulated concentration fields replicates reasonably well the magnitude and seasonality of the synoptic variability across the four observation sites. The phasing of many of the individual events are also captured, indicating that the physical and biogeochemical dynamics driving the model variability likely resemble those in nature.The observations and model results show pronounced summer maxima in the synoptic CO2 concentration variability at the two stations located in North America, while a slightly different seasonality with high variability throughout fall and winter is observed at the European sites. The mechanisms driving these patterns are studied and discussed based on correlations between the concentration anomalies and the driving atmospheric physical variables and surfaces fluxes in the simulations. During the summer, the synoptic variability over the continents has a significant contribution from variations in regional net primary production, which in turn is modulated by regional, synoptic temperature variability. In winter the synoptic variability is partitioned about equally between biospheric and anthropogenic CO2 and is mainly driven by local vertical mixing and synoptic variations in atmospheric circulation working on the large-scale atmospheric gradient. This study highlights the importance for future modeling work of improved high temporal resolution (at least daily) surface biosphere, oceanic and anthropogenic flux estimates as well as high vertical and horizontal spatiotemporal resolution of the driving meteorology.

Oxygen minimum zone and internal waves as potential controls on location and growth of Waulsortian mounds (Mississippian, Sacramento Mountains, New Mexico)

Lower Mississippian Waulsortian mounds in the Sacramento Mountains grew on a south-dipping homoclinal ramp at depths ranging from approximately 110 to 250 m, a setting in which nutrient sources and pathways are poorly understood in ancient carbonate depositional systems. Lithologic, biotic, and chemical data suggest that the mounds grew in an area on the ramp within a dysoxic oxygen minimum zone (OMZ) resulting from the concentration of organic matter below a thermocline. The abundance of organic matter there, perhaps a consequence of upwelling, enhanced the productivity of the major sediment contributors to the mounds—sponges, pelmatozoans, bryozoans, and heterotrophic carbonate-producing microbes. The siting and growth of individual mounds within the OMZ is best explained by two factors. One is the positive low-relief intra-ramp topography on and around which the mounds grew. The other is that nutrient supply for carbonate producing microbes was concentrated at the sites of mounds growth by internal waves on the pycnocline coincident with the thermocline. The internal waves mixed the nutrient-rich water of the OMZ with the better-oxygenated adjacent water mass, stirred the substrate and resuspended organic matter so that it was more available for the primarily suspension-feeding macrofauna both above and below the pycnocline, and generated local vertical mixing. Because of initial intra-ramp topography and subsequently increased relief as the mounds grew, internal waves focused and localized these processes, thus enhancing carbonate production at individual mound sites in a positive feed-back loop.

Turbulence and stratification on the Tropical Ocean‐Global Atmosphere‐Coupled Ocean‐Atmosphere Response Experiment microstructure pilot cruise

On the Tropical Ocean‐Global Atmosphere‐Coupled Ocean‐Atmosphere Response Experiment pilot cruise, at 147°E, in the western Pacific Warm Pool, we profiled for 17 days at 0°N and for 5 days at 2°N. Winds were generally light and variable in direction, but rainfall was often quite intense. Contrary to what is seen in the central equatorial Pacific, we did not observe a deep diurnal cycle in dissipation extending below the mixed layer. Strong daytime restratification often prevented nightly convective deepening down to the seasonal thermocline, resulting in surface forcing remaining trapped in a shallow layer. The relaxation of horizontal density gradients into vertical appears to be an important process driving restratification. Turbulent fluxes in the bottom of the mixed layer were generally small. Following rainfall, we observed pools of fresh water that typically disappeared within a few hours, leaving the mixed layer nearly homogeneous in salinity; thus we did not observe a permanent barrier layer. Modeling such events using the Price‐Weller‐Pinkel model suggests a fresh pool will be mixed away on timescales of a few days, primarily by nighttime convection. The observed vertical structure can be accounted for by local vertical mixing processes.

Fluorescence structure in the region of the tidal mixing front on the southern flank of Georges Bank

Transects of fluorescence measurements were made across the region of the tidal-mixing front on the southern flank of Georges Bank in 1992, 1993 and 1994. The fluorescence distribution exhibited three characteristic patterns: (i) a subsurface maximum associated with the pycnocline in stratified water columns; (ii) a spatially incoherent variability with a characteristic spectral slope, believed to be related to the local vertical mixing processes; and (iii) a higher level of fluorescence within the front on some transects. This latter pattern was observed when the tidal current amplitude had recently increased with the local fortnightly/monthly variability.

Vertical mixing and coral death in the Red Sea following the eruption of Mount Pinatubo

THE eruption of Mount Pinatubo in the Philippines led to a cold air-temperature anomaly throughout the Middle East during the winter of 19921. Here we report that the vertical mixing in the Gulf of Eilat (Aqaba) that winter was unusually deep―extending to >850 m―resulting in increased supply of nutrients to surface waters, which fuelled extraordinarily large algal and phytoplank-ton blooms. By spring, a thick mat of filamentous algae covered broad sections of the underlying reef causing extensive coral death. Branching colonies and solitary mushroom corals were most severely affected. This sequence of events, in which a short-term atmospheric cooling leads to a remarkable ecological response, is made possible by the unusually weak water-column stratification of the Gulf of Eilat. The depth of local vertical mixing during winter is determined by the net heat loss across the seaa¤-air interface, so that anomalously cold winters drive the deeper mixing that can lead to increased phytoplankton blooms. Records of such events in fossil reefs may provide useful indicators of past variations in regional air temperatures.

Modelling ocean temperatures and mixed‐layer depths in the Tasman sea off the South Island, New Zealand

Abstract A vertical mixing model was applied to a location off the west coast of the South Island, New Zealand, with the aim of simulating the seasonal cycle of temperature and mixed layer depth in the region. Observed weather data for 1973–89 were used to drive the model. Model results for sea temperature and mixed layer depth were compared to measurements from ships, moored temperature sensors, and satellites. The main features of the variations in temperature and mixed layer depth can be explained by the local meteorological forcing and vertical mixing, together with a general southward flow in the study area. Superimposed are short‐term variations which are obviously related to variable currents and the associated horizontal heat transport.

Two- and three-dimensional numerical modeling of dispersion and mixing in shallow (tidal) waters

Two main mechanisms can be distinguished in the process of dispersion and mixing of dissolved or suspended matter in shallow waters: (1) vertical current shear and the accompanying vertical mixing and (2) spreading caused by the inhomogeneity and time dependence of the field of horizontal velocities. Both mechanisms have long been recognized and have been investigated by many researchers. The various studies usually concern only one of the two phenomena at a time. This is not necessarily a drawback from a theoretical viewpoint if care is taken that the values of parameters typical for one phenomenon, as derived from field data, are not significantly contaminated by effects caused by the other. In practice this type of error has been rather common. In several cases the existence of the other mechanism than the one described was entirely overlooked or at least neglected. There is an extensive range of time and length scales in which none of the two mechanisms has negligible influence. Most of the field data and many topics of interest are also in the range of simultaneous occurrence. In order to determine the relative importance of the two mechanisms one needs a mathematical model in which the two phenomena are explicitly modeled in such a way that the entire range of several orders of magnitude is covered with good accuracy. This was established by a three-dimensional numerical model in which the dispersing matter was represented by discrete particles. In this way, no bound is set to spatial resolution; the scale range that can be covered is unbounded at either end. Extension at small scales only requires a consequent decrease of time step length. The second mechanism (horizontal inhomogeneity) can be simulated in two ways, by scaled random walk and by synthetic velocity fields. The first technique is the most economical. The second has the advantage that it is directly related to energy and velocity spectra; it has become more feasible by applying a shifting spectral window. The final results of the two techniques, measured as variances of particle clouds as functions of time, were virtually identical. It was found that only for very short and relatively long times (after instantaneous point release), the mechanism of the horizontal velocity structure prevails. In the middle of the intermediate range, the vertical shear of the current is entirely dominant. In a basin like the North Sea this dominance occurs at horizontal length scales of a few kilometers and a time scale of a few hours to about one day, depending on the local vertical mixing rate and tidal energy. By adjusting the spectrum of the horizontal velocity structure to the rather extensive set of field data, a theoretical envelope was obtained from the model, enclosing the set of measured curves quite accurately. The resulting energy spectrum agrees well with estimates in the literature.

Multiport Diffusers for Heat Disposal: A Summary

This paper reviews the fluid mechanical characteristics - as derived from theoretical and experimental studies during the past dozen years - of submerged multiport diffusers used for heat disposal from thermal power plants into the water environment. Foremost among these characteristics is the near field instability produced by such thermal diffusers in typical receiving water conditions. Rather than forming a distinct buoyant plume as is the case for the traditional sewage diffuser, the high discharge momentum of thermal diffusers leads to a flow breakdown with local recirculation zones and full vertical mixing. Stability diagrams for both stagnant and flowing ambient conditions are presented. The flow and temperature fields at larger distances, in the intermediate field, are, in turn, critically dependent upon how the discharge momentum is introduced into the ambient fluid layer. Out of a spectrum of possible diffuser designs three major types have evolved. The unidirectional and staged diffusers are designs which result in concentrated vertically mixed plume motions. The alternating diffuser with appropriate nozzle control generates a stratified flow field outside the unstable near field. Predictive techniques for these basic types are summarized. A typical case comparison illustrates their differences in engineering design and environmental impact.

Lunar Regolith: Petrology of the <10 μm fraction

It has been known for some time that the part of the lunar regolith smaller than 10 micrometers (<10 μm) is chemically distinct from the bulk soil. Specifically, it is enriched in Al, Ca, Na, K, light rare earth elements, and Th, and depleted in Mg, Fe, Mn, and Sc. Three models have been proposed to explain those systematics. The Exotic Component model holds that a fine‐grained, KREEPy exotic component was distributed on a global scale, perhaps by the Imbrian impact. In the Simple Comminution model, the <10 μm chemical systematics are due to differential comminution processes with fine‐grained melt‐rock mesostasis and feldspar concentrating in this fraction. The Soil Mixing model states that the chemical systematics are due to mixing of compositionally distinct soils that have different grain‐size distributions. To determine which model is correct, modal petrographic data were obtained by scanning transmission electron microscopy with energy dispersive X ray analysis for the <10 μm fractions of four Apollo soils: 10084, 14163, 15271, and 64501. Modal results are consistent with chemical data regarding feldspathic and KREEP enrichments in the finest fraction. Soil glass contents, crystalline silica, and plagioclase/mafic mineral ratios are greater in the <10 μm fraction than in the coarser fractions for all soils. Grain‐size distributions are inconsistent with a fine‐grained exotic component derived from distant sources. Comminution of local lithologies, vertical mixing, and local lateral transport control the <10 μm soil composition.

The Origin of the Pacific Equatorial 13°C Water

Examination of the vertical distributions of temperature, salinity, oxygen, and nutrient salts in the thermostad of the Equatorial 13°C Water in the eastern Pacific Ocean indicates that local vertical mixing is unimportant in creating the thermostad and the characteristics of the 13°C Water. Maps are presented that show the oceanwide distributions of depth, geostrophic flow, salinity, oxygen, phosphate, silica and nitrate on the 160 cL t−1 isanosteric surface, which nearly coincides with the core of the 13°C Water. The maps suggest that the original characteristics of the 13°C Water are acquired in the surface and thermocline layers to the northeast of New Zealand and in the Tasman Sea by winter convection and vertical mixing. The acquired characteristics are advected to the thermostad in the eastern Pacific via a long route. Starting from the source region, the flow is first eastward in high latitudes and then returns westward in low latitudes around the anticyclonic subtropical gyre of the South Pacific; near the coast of Australia, the flow turns northward to reach the equator through the Coral and Solomon seas; eastward from here, the principal dew takes two separate paths along the Equatorial Undercurrent and the subsurface South Equatorial Countercurrent. Vertical sections of thermosteric anomaly, temperature, salinity, oxygen and phosphate also are prepared to examine the downstream changes in the characteristics in relation to the overlying and underlying waters. Lateral mixing, consumption of oxygen and regeneration of nutrients account for the observed gradual changes in the characteristics along these paths leading to the ultimate form of the Equatorial 13°C Water.

On the 14C to Tritium Relationship in the North Atlantic Ocean

Nuclear-weapon produced 14C (or bomb 14C) in the ocean can be traced by simultaneous tritium observations. Data are presented on the general relationship of bomb 14C and tritium in the North Atlantic. For the period 1965 to 1973, the excess 14C to tritium ratios in the surface water vary, systematically, over a factor of 10: the ratios monotonically increase with time, and decrease with latitude, particularly so for the later observations. The sub-surface water ratios show that the mid- and low-latitude water below about the 15° C isothermal horizon (~500m depth) originates from higher northern latitudes, rather than being renewed by local vertical mixing. It is further shown that in the North Atlantic, bomb 14C did not penetrate beyond the horizon where the presently observed 14C concentration is Δ14C = —75‰. Observed concentrations up to about —40‰ can be corrected for a bomb contribution if the tritium concentration is known because the bomb 14C to tritium concentration ratio is rather uniform in this range. A surface water 14C concentration versus time curve is presented for the period since 1957. This curve is based on a North Atlantic mixing model and is fitted to the 14C observations. Making use of a previously published tritium versus time curve obtained by the same model, a time curve for the average excess 14C to tritium ratio in North Atlantic surface water is given. This curve reproduces the observations well. The presented data and theoretical curves show the usefulness of simultaneous 14C and tritium observations for mixing studies and to provide corrections for bomb 14C in sub-surface 14C data in the North Atlantic.

Determination of water mass properties of water pumped down from the Ekman layer to the geostrophic flow below

In a subtropical gyre, the convergent Ekman layer forces water downward into the geostrophic flow below. The properties and depth of the mixed layer vary considerably during the course of the year, but this variability does not penetrate into the geostrophic region. Evidently there is some process at work that selects only late winter water for actual net downward pumping. It is a process much like that performed by Maxwell's Demon. Arguing from a particular example in a North Atlantic region where Sverdrup dynamics is presumed to prevail, an elementary description is given as to how the Demon works and a sample set of profiles by season is computed. Present day mixed layer models involve a local vertical mixing process. Thermocline theories involve adiabatic flow from high latitudes. There is an intermediate depth range at which the two processes operate alternatively, according to season.

On vertical mixing and the energy transfer from the wind to the water

Observations of the vertical mixing in the surface layer of the sea, on small time and space scales, in conditions of fairly strong winds and stably stratified waters, are used, together with relevant oceanographic measurements, to investigate the relation between the wind-generated vertical mixing and the energy transfer from the wind to the water. Only the energy transfer due to the work of the tangential stress is considered, i.e. the wave energy is not included in the considerations. It is found that only a very small part of the energy is consumed by the local vertical mixing. Furthermore, the observations are found to be consistent with expressing the energy transfer as the product of the surface wind stress and the wind-generated surface current. A relation between the vertical momentum transfer and the wind velocity is suggested on the basis of this result. DOI: 10.1111/j.2153-3490.1976.tb00663.x

Evaporation During Upwelling in Ghanaian Coastal Waters

Abstract To account for the salinity and temperature profiles measured during upwelling in Ghanaian coastal waters, it was proposed by Pople and Mensah that the upwelling is the result of local vertical mixing driven by evaporation. The results of heat budget calculations and direct evaporation measurements reported here do not support this novel hypothesis.