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In this paper we compare two methods for estimating the size of personal networks using a nationally representative sample of the United States. Both methods rely on the ability of respondents to estimate the number of people they know in specific subpopulations of the U.S. (e.g., diabetics, Native Americans) and people in particular relation categories (e.g., immediate family, coworkers). The results demonstrate a remarkable similarity between the average network size generated by both methods (approximately 291). Similar results were obtained with a separate national sample. An attempt to corroborate our estimates by replication among a population we suspect has large networks (clergy), yielded a larger average network size.Extensive investigation into the existence of response effects showed some preference for using certain numbers when making estimates, but nothing that would significantly affect the estimate of network size beyond about 6 percent. We conclude that both methods for estimating personal network size yield valid and reliable proxies for actual network size, but questions about accuracy remain.

The feasibility of using the network scale-up method to estimate heroin use is described. A random sample was asked 'How many people do you personally know' who use heroin, and how many in other subpopulations--robbery, assault, burglary, auto-theft victims, binge drinkers, and marijuana users--whose size is more accurately known. A model estimated the overall number of persons each respondent knew and the size of each subpopulation. Estimates of the subpopulation are compared with known subpopulation sizes to assess the plausibility of the model. Data came from the 1999 survey evaluating the 'Fighting Back' substance prevention program. Fourteen sites with clear political boundaries were used (n = 5892). Heroin use varied from city to city. Rates estimated for heroin use correlated .832 with the level of respondents' sense of 'crime in their neighborhood.' The average ratio between the known populations and the estimates is .943. Members of each subpopulation, especially drug users, tended to know more people within their own subpopulation.

A model is presented for a consistent equivalent-barotropic solution for Antarctic Circumpolar Current flow. Components discussed include self-similar velocity, horizontal velocity, closed-contour, vertical structure, topography, density and free surface height.

A new eddy parameterization that considers steadily changing linear baroclinic instability is tested. When compared with the predictions of multi-year averages, the descriptions are found to be as accurate as a tuned version of earlier schemes, including the framework proposed by McWilliams and Gent (1990). However, a tuned version of this new scheme is able to duplicate the long-term average of the eddy-resolving solution and the initial slumping of a narrow front. Lastly, both schemes are shown to effectively reproduce the bolus transport.

A possible eddy parameterization scheme was examined for mean flows which are compared with a deformation radius. The behavior of potential vorticity and thickness fluxes in linear instability is partly the basis of the scheme. It was found that the scheme leads to a diffusivity which varies strongly with depth and is smallest at surface and floor. Also, such parameterization schemes must satisfy a necessary consistency condition in the form of a vertical integral. Methods to compute approximate diffusivities efficiently and their results are discussed.

A study validates that transient, inertia-gravity oscillations have no impact on the slower, quasi-geographic, oscillations of nonlinear rotating fluid systems in terms of the leading order in Rossby number. This result is proved numerically with reduced-gravity two- and one-layer initial value problems with Laplacian or biharmonic frictions. Di Discrepancies in numerical and experimental data are possibly due to frictional components active in numerical figures which tend to damp the enstrophy cascade.

A general condition for the hydraulic control and maximal flow in rotating stratified hydraulics show that the maximal flow occurs only if the flow is controlled. Control involves two conditions, one condition concerns the flow itself and the second concerns the local geometry of the stratification.

A compelling problem in a population is to estimate the number of people the average person knows. A consequential related problem is to estimate the size of important subpopulations. A random sample of a population is asked whether they know anyone in a given subpopulation of size e, thus yielding an estimate of the probability that this occurs in the population. Using an equal likelihood probability model, this leads to a lower bound estimate for c, the average number of people a person in the population knows. When the number of people a person knows has a binomial distribution over the population this value is an estimate for c itself. Here we test this method on data from Mexico City, where a large random sample of people was asked whether they knew anyone in each of several different subpopulations in Mexico City of known and unknown sizes. We develop procedures for obtaining various bounds and estimates for c and determine some of the respondents' attributes on which variation in probability of knowing someone in a subpopulation and variation in personal network size seem to depend. We apply these to the estimation of e for rape victims in Mexico City and the estimation of c from data on AIDS victims in the United States. [C] 1991 Academic Press, Inc.

The two-dimensional geostrophic adjustment problem for a uniformly rotating, stratified and inviscid fluid is examined by determining the upper and lower bounds of the energy conversion ratio. Designated as gamma, the energy conversion ratio was shown to be bounded above by 1/2 and below by 0. Since the adjustment was 'two-dimensional,' the initial isopycnal displacement field becomes a function of the vertical coordinate and an individual horizontal coordinate. To derive the upper bound for gamma, a vertical normal mode expansion technique is utilized.

Numerical models are used to test whether the sea surface height (SSH) can be used as an indicator for the variability of Atlantic meridional oceanic mass transports. The results suggest that if the transports over the western boundary current region and those in the eastern part of the basin are considered separately, significant correlations (0.3–0.9) are found between zonal SSH differences and the meridional transports in the top 1100 m. Much weaker correlations are found for the basinwide transport, which corresponds to the surface branch of the meridional overturning circulation (MOC). For the eastern and western branches of the meridional transport, combining the SSH signal with the baroclinic structure obtained from Rossby wave theory enables calculation of a quantitative estimate of the transport variability in the top 1100 m. The results of the method are less convincing for the variability of the MOC. The reason for this is that even small relative errors in the variability of the eastern and western branches can be large compared with the MOC variability. These errors project onto the sum of the eastern and western transports and therefore onto the surface branch of the MOC. Nevertheless, being able to infer transport anomalies from SSH signals in the eastern and western parts of the Atlantic might prove useful in interpreting MOC observations from the U.K. Natural Environment Research Council Rapid Climate Change (RAPID) mooring array at 26°N, which show a large subannual variability that is mainly due to changes at the western boundary. Transports inferred from the SSH could help to identify the origin of this variability and whether transport anomalies propagate into the western boundary region from the basin interior or from other latitudes. [ABSTRACT FROM AUTHOR]

This paper examines the representation of eddy fluxes by bolus velocities. In particular, it asks the following: 1) Can an arbitrary eddy flux divergence of density be represented accurately by a nondivergent bolus flux that satisfies the condition of no normal flow at boundaries? 2) If not, how close can such a representation come? 3) If such a representation can exist in some circumstances, what is the size of the smallest bolus velocity that fits the data? The author finds, in agreement with earlier authors, that the answer to the first question is no, although under certain conditions, which include a modification to the eddy flux divergence, a bolus representation becomes possible. One such condition is when the eddy flux divergence is required to balance the time-mean flux divergence. The smallest bolus flow is easily found by solving a thickness-weighted Poisson equation on each density level. This problem is solved for the North Pacific using time-mean data from an eddy-permitting model. The minimum bolus flow is found to be very small at depth but larger than is usually assumed near the surface. The magnitude of this minimum flow is of order one-tenth of the mean flow. Similar but larger results are found for a coarse-resolution model. [ABSTRACT FROM AUTHOR]

The part of the meridional overturning circulation driven by time-varying winds is usually assumed to be an Ekman flux within a mixed layer, and a depth- and laterally independent return flow beneath. For a simple linear frictional ocean model, the return flow is studied for a range of frequencies from several days to decades. It is shown that while the east–west integral of the return flow is usually, but not always, almost independent of depth, the spatial distribution of the return flow varies strongly with both horizontal and vertical position. This can have important consequences for calculations of the northward heat flux, which traditionally assumes a spatially uniform return flow. [ABSTRACT FROM AUTHOR]

An eddy-permitting numerical ocean model is used to investigate the variability of the meridional overturning circulation (MOC). Both wind stress and fluctuations of the seawater density contribute to MOC changes on subannual and seasonal time scales, whereas the interannual variability mainly reflects changes in the density field. Even on subannual and seasonal time scales, a significant fraction of the total MOC variability is due to changes of the density field in the upper 1000 m of the ocean. These changes reflect perturbations of the isopycnal structure that travel westward as Rossby waves. Because of a temporally changing phase difference between the eastern and western boundaries, the Rossby waves affect the MOC by modifying the basinwide east–west density gradient. Both the numerical model used in this study and calculations based on Rossby wave theory suggest that this effect can account for an MOC variability of several Sverdrups (Sv ≡ 106 m3 s-1). These results have implications for the interpretation of variability signals inferred from hydrographic sections and might contribute to the understanding of the results obtained from the Rapid Climate Change (RAPID) monitoring array deployed at 26°N in the North Atlantic Ocean. [ABSTRACT FROM AUTHOR]

The local response of an ocean with slowly varying mean flow, stratification, and topography to two sources of disturbance is examined, concentrating on whether the resulting surface elevations are observable. The first is the ocean response to surface forcing (Ekman pumping or buoyancy forcing). For typical amplitudes of random forcing, while much of the ocean response is small (surface elevations less than 1 mm), there are sufficient near resonances (or pseudoresonances involving a critical layer) to produce elevations of 1 cm or more in much of the ocean. The second source is baroclinic instability. The fastest linear growth rate, as well as those for specific wavelengths, is computed globally. Almost all of the ocean is baroclinically unstable, and the most unstable waves are found to possess a small wavelength (often less than 10 km) with a disturbance concentrated near the surface: e-folding times O(20 days) are frequently found. However, the phase speed for the disturbances is almost everywhere slower westward than free planetary waves with mean flow and topography. Since the free waves propagate at speeds similar to observations, instability may be a good source of variability but is probably not responsible directly for observed wave propagation. [ABSTRACT FROM AUTHOR]

This article estimates the variation in personal network size, using respondent data containing two systematic sources of error. The data are the proportion of respondents who, on average, claim to know zero, one, and two people in various subpopulations, such as "people who are widows under the age of 65" or "people who are diabetics." The two kinds of error—transmission error (respondents are unaware that someone in their network is in a subpopulation) and barrier error (something causes a respondent to know more or less than would be expected, in a subpopulation)—are hard to quantify. The authors show how to estimate the shape of the probability density function (pdf) of the number of people known to a random individual by assuming that respondents give what they assume to be accurate responses based on incorrect knowledge. It is then possible to estimate the relative effective sizes of subpopulations and produce an internally consistent theory. These effective sizes permit an evaluation of the shape of the pdf, which, remarkably, agrees with earlier estimates. [ABSTRACT FROM AUTHOR]

The one-dimensional examples of the dispersion relation for planetary waves under the Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) assumption given in Part I are extended to two dimensions and analyzed globally. The dispersion relations are complicated, and there is a nontrivial lower bound to the frequency given by the column maximum of what would be the local Doppler shift to the frequency. This generates short waves of a much higher frequency than would be expected from traditional theory; these waves can have larger phase velocities than long waves but do not appear to have faster group velocities. The longer waves possess phase speeds in excellent agreement with recent remotely sensed data. Waves cannot propagate efficiently across ocean basins, suggesting that mechanisms other than eastern boundary generation may be playing a role in the ubiquitous nature of planetary waves. [ABSTRACT FROM AUTHOR]

This paper shows the existence of a growing planetary-wave-like ocean mode, with a decadal period and growth rate, which appears when a stratified, diffusive ocean is coupled to a simple atmosphere via an energy balance model (EBM). Such modes are not found when simpler surface ocean conditions are applied. The mode is low order in the vertical and, because of its slow growth, is likely to be observed in Earth System Models using an EBM in place of a fuller set of atmospheric dynamics. There is no apparent physical energy source for such a mode, and therefore it should not be expected to arise in such a model. The mode is analysed through a hierarchy of simple models, which differ only through their surface boundary condition. [ABSTRACT FROM AUTHOR]

Two aspects of the effects of eddies on ocean circulation have proven difficult to parameterize: eddy effects in regions of neutrally stable (or convecting) fluid and the mixing of passive tracers. The effects of linearized eddies, although a restrictive parameter regime, can be straightforwardly computed in these cases. The eddy effects in areas of neutral stability—for example, mixed layers—blend naturally into those in the stably stratified water below, although losing the concept of bolus velocity. Instead, the mixed layer density is advected by an extra overturning velocity and is diffused laterally by a diffusion that is the same as the eddy diffusion at the top of the stably stratified fluid. Passive tracers are advected by the bolus velocity and mixed by the same diffusivity as is used to compute the bolus velocity at that location, so that two different diffusivities are not needed. [ABSTRACT FROM AUTHOR]

A preoperational scheme has been implemented to calculate sea surface height fields at 7-day intervals over the North Atlantic. Input data from Argo floats is downloaded and processed in near–real time. The solution method is by Bernoulli inverse. Early results are encouraging. Features of the results are compared with both model and satellite data and show good agreement. [ABSTRACT FROM AUTHOR]

Eddy-resolving quasigeostrophic simulations of wind-driven circulation in a large ocean basin are presented. The results show that strong modes of low-frequency variability arise in many parameter regimes and that the strength of these modes depends upon the presence of inertial recirculations in the flow field. The inertial recirculations arise through advection of anomalous potential vorticity by the western boundary current and are barotropized by the effect of baroclinic eddies in the flow. The mechanism of low-frequency oscillations is explored with reference to previous studies, and it is found that the observed mode can be linked to the gyre mode but is strongly modified by the effect of eddies. [ABSTRACT FROM AUTHOR]

An eigenvalue problem for the dispersion relation for planetary waves in the presence of mean flow and bottom topographic gradients is derived, under the Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) assumption, for frequencies that are low when compared with the inertial frequency. Examples are given for the World Ocean that show a rich variety of behavior, including no frequency (or latitudinal) cutoff, solutions trapped at certain depths, coalescence of waves, and a lack of dispersion for most short waves. [ABSTRACT FROM AUTHOR]

Space sampling is a useful substitute for classical random sampling if the sampling universe is unknown. It is a family of sampling methods that uses geographical features such as patches on maps or geographical points. So far, the methods have been applied to problems in which the spatial dimensions of the sampling units are irrelevant (i.e., where the probability of sampling any unit is independent of its size, for example, persons surveyed with the street intercept method). If, however, space sampling is applied to problems in which the spatial dimensions of the sampling units matter, the existing evaluation procedures fail. This article describes evaluation procedures that work in such cases. [ABSTRACT FROM AUTHOR]

The design and implementation of a midlatitude basin-scale coupled climate model are described. The development of the model is motivated by the clear indications of important low-frequency midlatitude ocean variability in ocean-only models and the lack of the same in coupled climate models. Currently, the best comprehensive coupled climate models run at resolutions far coarser than those needed to model intrinsic ocean variability. The model presented here is an attempt to explicitly include ocean eddies within the framework of an idealized climate setting. It is proposed that the model will help resolve how intrinsic ocean variability is altered by coupling and the extent to which such variability may force the climate. The objective of this paper is to describe the theory behind the model formulation and its implementation. The basic model consists of a quasigeostrophic channel atmosphere coupled to a simple, rectangular quasigeostrophic ocean. Heat and momentum exchanges between the ocean and the atmosphere are mediated via mixed-layer models, and the system is driven by steady, latitudinally dependent incident solar radiation. Model spinup is described, some basic descriptors of the solution are discussed, and it is argued that the model exhibits skill in capturing essential features of the midlatitude climate system. [ABSTRACT FROM AUTHOR]

Tailleux makes a suggestion, basically that there is another relevant vertical mode (termed here pseudobarotropic) present in linear, long planetary wave motion in the presence of bottom topography, which was mentioned but little discussed by Killworth and Blundell. Tailleux raises several points. He argues that i) the neglected mode is faster than the first baroclinic mode studied by KB99 and could perhaps account for the discrepancy between observed and theoretical planetary wave speeds, ii) our continuous theory is at odds with results from two-layer models (and therefore the continuous theory must be wrong), iii) ray theory and local calculations are methodologically not equivalent, and iv) our statement that local topographic effects cancel when averaged over the basin scale is ambiguous.

One of the most successful theories to date to explain why observed planetary waves propagate westward faster than linear flat-bottom theory predicts has been to include the effect of background baroclinic mean flow, which modifies the potential vorticity waveguide in which the waves propagate. (Barotropic flows are almost everywhere too small to explain the observed differences.) That theory accounted for most, but not all, of the observed wave speeds. A later attempt to examine the effect of the sloping bottom on these waves (without the mean flow effect) did not find any overall speedup. This paper combines these two effects, assuming long (geostrophic) waves and slowly varying mean flow and topography, and computes group velocities at each point in the global ocean. These velocities turn out to be largely independent of the orientation of the wave vector. A second speedup of the waves is found (over that for mean flow only). Almost no eastward-oriented group velocities are found, and so features that appear to propagate in the same sense as a subtropical gyre would have to be coupled with the atmosphere or be density compensated in some manner. [ABSTRACT FROM AUTHOR]

Ray theory is used to predict phase and group velocities for long planetary waves under realistic, albeit slowly varying, oceanic conditions. The results are compared with local theory using fields smoothed to the same amount (9° latitude/longitude) as well as those with much less smoothing (1°). The agreement is excellent, showing that local theory forms a good proxy for ray theory results. The predicted speeds agree well with observations of planetary waves deduced from sea surface height data. The theory uses purely baroclinic mean flow; the inclusion of barotropic flow has little effect except at high latitudes. [ABSTRACT FROM AUTHOR]

Attempts to produce a simple descriptor of the propagation of internal, baroclinic, large-scale disturbances against a background ocean in steady motion. Details on the normal mode decomposition; Computation of the pseudovelocities; Effects of flow orientation on shear modal structure.