Temperature fluctuations in the solar photosphere

The general problem of interpreting granulation data, in particular Edmonds' r.m.s. intensity fluctuation distribution against heliocentric angle , is discussed.A method is developed for investigating a variety of models of inhomogeneous departures from radiative equilibrium using two dimensional solutions of the equation of radiative transfer, and theoretical r.m.s. intensity fluctuation distributions are computed. It is found that only a very narrow range of models yields distributions which exhibit the essential features of Edmonds' distribution (a center-of-disk value of 14 % and a maximum value of 20.5 % at a heliocentric angle of 53°). The feature of these models is a maximum in the temperature fluctuations of about 660 K r.m.s., which represents a temperature difference between hot and cold regions of 2000 K, at a depth of about 250 km below ₅₀₀₀= 0.03. Below this the temperature fluctuations decrease rapidly in the next 70 km.These results are interpreted in terms of convective and radiative transport of energy. Velocities of the order of 8 km/sec are deduced in the essentially convective regime near 320 km, decreasing through 4 km/sec near the temperature fluctuation maximum to negligible values in the radiative region above 200 km.These features are shown to be consistent with modern theoretical and laboratory studies of convection in incompressible fluids. Further, these studies indicate that a second temperature fluctuation should occur at the bottom of a convective layer. For this reason, further photospheric models are studied in which, below the region of small temperature fluctuations near 320 km, the fluctuations increase sharply. For one of these models a theoretical intensity r.m.s. distribution is obtained which closely fits not only the maximum at = 53° in Edmonds' observed distribution but also the initial decrease and smaller minimum near 24°.Of the National Bureau of Standards and the University of Colorado.     

The Interference of Higher-Order Statistics of the Concentration Field Produced by Two Point Sources According to a Generalized Fluctuating Plume Model

The higher-order correlation functions for the concentrationfluctuations arising from a two-point-source configuration have beencalculated analytically within the context of the phenomenology of afluctuating plume model (viz., a meandering plume model that explicitlyincorporates internal fluctuations). Explicit expressions for thesecond-, third-, and fourth-order correlationfunctions between the concentrationfluctuations produced by two point sources are given in terms of the sourceseparation d and the five physically based parameters that define thegeneralized fluctuating plume model: namely, the absolute plume dispersion,_a, which determines the outer plume length scale; the relative plume dispersion, _r, which determines the inner plume length scale; the fluctuation intensity, i_r, in relative coordinates, which determines the internal concentration fluctuation level; the correlation coefficient, r,between the positions of the centroids of the two interfering plumes; and,the correlation coefficient, r^*, between the concentration fluctuationsof the two plumes in relative coordinates, which determines the degree ofinternal mixing of the two scalars. Furthermore, the form of the totalconcentration probability density function arising from the interferenceproduced by two point sources is presented. Predictions for the second-ordercorrelation function, , and for the total concentration probabilitydensity function have been compared with some new experimental data fora two-point-source configuration in grid turbulence generated in awater-channel simulation. These results are in good agreement with the dataand suggest that the analytical model for the second-order correlationfunction and the total concentration probability density function canreproduce many qualitative trends in the interaction of plumes from twosources.     

Higher Order Nuptial Fertility in New South Wales, 1996: Context,process, implications

In the face of below replacement and still declining national fertility rates in most Western societies, the proportion of reproductively aged women having a third or higher order birth has particular demographic significance. This paper seeks to complement previous survey-based studies of the socio-economic, behavioural and motivational characteristics of individuals progressing or intending to progress from a second to a third or higher order birth by examining the spatial patterning and ecological context of such births in NSW during 1996 and, in particular, the extent to which such births are especially characteristic of socially disadvantaged regions and localities in the state. The results suggest that while there is a clear, though not overwhelming, tendency towards such a concentration there is an equally clear tendency for older women living in some of the most socially advantaged areas of the metropolitan zone to engage in higher order childbearing, thereby suggesting the operation of multiple causal pathways. In the more disadvantaged areas of the metropolitan zone religious and/or ethnically based pro-natalist value sets also appear to play a significant role. In better-off localities, however, higher order reproduction would seem to reflect the greater choices - and resources - available to women, whether in or out of the labour force. Because ecological analysis cannot provide precise answers to behavioural questions and because only higher order births to women in current relationships have been taken into account in this study, further research, employing a variety of methodologies, operating at a variety of scales and drawing on alternative data sets would seem desirable if such questions are to be more fully elucidated and their policy implications better understood.     

Discrete polar motion equations for high frequencies

We examine several digital filter methods designed to accurately estimate excitation axis variations from observed polar motion at frequencies exceeding 1 cycle per day. These methods are developed from a discrete time series filter equation originally presented in 1940 by Harold Jeffreys, and subsequently revised over the past two decades. The filters derived here provide improved amplitude accuracy at the highest frequencies now observable in space geodetic polar motion data.     

The Spatial Variability of Energy and Carbon Dioxide Fluxes at the Floor of a Deciduous Forest

Fluxes of carbon dioxide, water and sensible heat were measured using three different eddy covariance systems above the forest floor of a closed deciduous forest (leaf area index approx 6). The primary objective was to examine the representativeness of a single eddy covariance system in estimating soil respiration for time scales ranging from one-half hour to more than one week. Experiments were conducted in which the eddy covariance sensors were in one of three configurations: i) collocated, ii) separated horizontally or iii) separated vertically. A measure of the variation between the three systems (CV',related to the coefficient of variation) for half-hour carbon dioxide fluxes was 0.14 (collocated systems), 0.34 (vertically separated systems at 1, 2 and 4 m above the surface), and 0.57 (systems horizontally separated by 30 m). A similar variation was found for other scalar fluxes (sensible and latent heat). Variability between systems decreased as the number of half-hour sampling periods used to obtain mean fluxes was increased. After forty-eight hours (means from ninety-six half-hour samples), CV' values for carbon dioxide fluxes were 0.07, 0.09 and 0.16 in the collocated, vertically separated and horizontally separated experiments, respectively. The time dependence of variability has implications on the appropriateness of using short-term measurements in modelling validation studies. There are also implications concerning the appropriate number of half-hour samples necessary to obtain reliable causal relationships between flux data and environmental parameters. Based on the longer-term measurements, we also discuss the representativeness of a single eddy covariance system in long-term monitoring of soil respiration and evaporation beneath forest canopies using the eddy covariance method.     

Econometric and learning curve estimation of U.S. potential oil supply

This study employs (1) a simple econometric model to generate a time series of drilling footage to the year 2040 and (2) learning models to estimate the oil reserve additions from that drilling, given scenarios of oil price and projected U.S. population. Reserve additions are estimated separately for the lower 48 states and Alaska regions by estimating separate drilling footage and learning models for each region. Generally, the estimates of potential supply from undiscovered oil fields and from extensions of known fields are more optimistic than recent estimates by others. For a $1989 price of about $20/barrel (bbl), which is similar to recent prices, the potential supply of oil is estimated to be approximately 60.7 billion bbl, with 95-percent confidence bounds of 54.3 and 67.1 billion bbl. For a price of $25.50/bbl, potential supply is estimated to be approximately 82 billion bbl, with 95-percent confidence bounds of 74.5 and 89.5 billion bbl. Although estimates of potential oil supply for the entire United States are more optimistic than other recent estimates, the part of that supply estimated to be forthcoming from Alaska is smaller than other recent estimates: 2.3 and 3.3 billion bbl for prices of about $20 and $25.50 per barrel, respectively. Thus, reserve additions from the lower 48 states through development drilling and through improved recovery and production technologies will become increasingly important to future U.S. oil supply.