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R. R. Brook

Abstract

The heat stored in the ground and the transport of this heat to and from the atmosphere can be important considerations in numerical models of the atmosphere. This note considers the preformance of the conventional approach to the numerical modeling of ground flux using a number of levels in the ground. In particular, a simple efficient analogue is suggested which can be used to realistically derive the ground flux. Only the mathematical implications are considered; it is left up to the individual modeler to grapple with the problems of variable conductivity, homogeneity, etc.

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R. R. Brook

Abstract

It has been hypothesized by Dutton et al. (1969) that intermittent turbulence should show a frequency-phase organization. Because of inherent difficulties in measuring phase, confirmation of this effect has been difficult to obtain with real data. An analysis is presented here which, through the examination of the sample distribution of spectral ordinate estimates, permits the detection of such a phenomenon. Wind data from a 118 m tower in an urban environment are used to test the analysis, and the results seem to confirm the Dutton et al. hypothesis.

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R. R. Brook

Abstract

The self-similarity concept has proved useful in describing turbulence for aircraft design purposes. There is an increasing awareness of the interaction of the turbulent planetary boundary layer and buildings and structures. The aeronautical engineering approach could be extended to civil engineering design problems. Wind data from a 118 m tower at an urban site in Melbourne are used to test the appropriateness of the “self-similar” approach. A reasonable model for the site was devised, and it is conjectured that this may form the basis for a “discrete gust” scheme to allow for aerodynamic interactions in the planetary boundary layer.

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R. R. Brook

Abstract

The increasing requirement for data about turbulence in a city environment, particularly in relation to building design and the imminent operation of aircraft from this environment, has prompted the measurement of the structure of wind at a site in Melbourne, Australia. Fast response propellor-type anemometers located at three heights on an 18.5 m tower were used. Data on the frequency distribution of gusts, the intensity of turbulence, the surface drag coefficient, and the spectra of turbulence are presented. It is concluded that the turbulence is predominantly of mechanical origin, and thus dependent on terrain roughness. The spectra are found to be best described in wavenumber space and scaled by variance.

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THOMAS R. BROOKS

Abstract

No Abstract Available.

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R. R. Brook and K. T. Spillane

Abstract

The effects of time-averaging and length of record on the variance of horizontal wind speed are considered through power spectral techniques. These effects are applied to a height profile of intensity of turbulence (ratio of the standard deviation of horizontal wind speed to mean wind speed) derived from data published by Deacon. For stationary strong-wind regimes dominated by “mechanical turbulence,” maximum gusts are determined as a function of height and averaging time.

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R. R. Brook and K. T. Spillane

Abstract

Using an assumed spectral density function, the ratio of the maximum gust of t seconds averaging time, drawn from a sample duration of T seconds, to the maximum S-second gust from a Θ-second sample is derived using the theory of the effects of averaging times and finite sample lengths on estimates of population parameters. The spectral density function is defined so that only one parameter a has any effect on the ratio. This parameter may take varying values to allow for changes in stability and terrain. Suggested practical uses of the ratio include aviation landing advices for newer type aircraft particularly sensitive to gusts.

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David R. Brooks and Patrick Minnis

Abstract

Computer simulations of satellite-derived Earth radiation parameters are examined to determine the source and size of errors arising from averaging parameters over 1 month on a 2.5°×2.5° longitude-latitude grid. November 1978 data from the Geostationary Operational Environmental Satellite (GOES) have been used as a source of radiation parameter fields within each region. The regions are sampled according to various combinations of satellite orbits which have been chosen on the basis of their applicability to the Earth Radiation Budget Experiment. A mathematical model is given for the data-processing algorithms that are used to produce daily, monthly and monthly hourly estimates of shortwave, longwave and net radiant exitance. Because satellite sampling of each region is sparse during any day, and because the meteorological behavior between measurements is unknown, the retrieved diurnal cycle in shortwave radiant exitance is especially sensitive to the temporal distribution of measurements. The resulting retrieval errors are seen to be due to insufficient knowledge of the temporal distribution of both cloud fraction and albedo. These errors, in combination with similar sampling errors resulting from diurnal variations in longwave radiant exitance (especially over land), produce biases in monthly net radiant exitance which are complex, regionally-dependent functions of the local time of the measurements. The regions studied have shown standard errors of estimate for monthly net radiant exitance ranging from about 20 W m−2 for the worst single-satellite sample to ∼2 W m−2 for the three-satellite sampling assumed to be available.

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David R. Brooks and Patrick Minnis

Abstract

Simulations of the Earth Radiation Budget Experiment with several satellite sampling schemes have been used to compare three different approaches to modeling longwave diurnal behavior observed over certain kinds of land regions. November 1978 data from the GOES satellite have been used to produce a reference set of radiation parameters over the regions of interest. The monthly average longwave radiant exitance has been estimated first with linear interpolation between satellite measurements, then with a method that replaces linear interpolations across day-night boundaries with piecewise constant extrapolations to the boundaries, and finally with a trigonometric model which replaces some of the linear interpolations that go through daytime measurements over land. This third model consists of constant extrapolation of nighttime measurements to sunrise or sunset, with a half-sine curve fitted through existing daytime measurements and constrained at sunrise and sunset to an average of the surrounding nighttime measurements. It applies only when the daytime and surrounding nighttime measurements meet certain restrictive criteria, including tests that tend to limit the trigonometric model to cloud-free regions. For all satellite sampling strategies considered, the trigonometric model gave the best overall monthly estimate of longwave radiant exitance. For non-land regions, the linear interpolation model generally gave better results than the piecewise constant model.

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John R. Goss and F. A. Brooks

Abstract

Magnitudes of the constants in Brunt's empirical expression for nocturnal radiation were determined from continuous automatic recordings of atmospheric radiation in California under cloudless skies and interpreted for the humidity at 1400 hours on the previous day. With these constants, useful estimates of the average nighttime atmospheric radiation rate can be computed from the local 1400-hours vapor pressure and average nocturnal air temperature as reported by all first-order U. S. Weather Bureau stations. With careful interpretation of weather records, the probable error will be about 3 per cent. Comparisons are made with Loennquist's formula and with calculations by atmospheric radiation charts from known soundings for extreme conditions leading to radiation frosts in southern California. Limited observations of daytime atmospheric radiation indicate that there is little difference in the average value of the radiation ratio between night and day when the character of the overhead air mass is not changing.

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