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S. Twomey
and
K. A. Davidson

Abstract

No abstract available.

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S. Twomey
and
G. T. Severynse

Abstract

This paper presents the results of measurements of size distributions of particulate matter in the atmosphere. The general shape of the distributions is discussed, particularly the appearance of maxima corresponding to particles with radii about 6×10−6 cm and the sizeable fraction of the total particle population in the region r≤10−6 cm. Size distributions obtained from the same air mass before and after fog formation show apparent removal of smaller particles (r≤10−6 cm) which is consistent with Smoluchowski's coagulation law. Several representations of size distributions are presented in order to compare the results obtained with those of other researchers.

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S. Twomey
and
G. T. Severynse

Abstract

An apparatus for the determination of the size distribution of an heterogeneous aerosol is described. The apparatus employs two diffusion batteries (series of narrow rectangular channels) through which an aerosol sample is passed to obtain attrition of its particle population by diffusion to the walls of the channels. Observations of particle concentrations after successive stages of “decay” produce a decay curve which represents an integral transform of the distribution function with respect to diffusion coefficient. After mathematical manipulation the size distribution of the aerosol is obtained.

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S. Twomey
and
K. A. Davidson

Abstract

No abstract available.

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S. Twomey
and
K. A. Davidson

Abstract

Automated equipment has been used to obtain hourly counts of cloud nuclei at Robertson, N.S.W., Australia (34°36′S, 50°36′E). The experiment is described and some results from the first year of continuous observations are given.

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S. Twomey
,
B. Herman
, and
R. Rabinoff

Abstract

An extension of the Chahine relaxation method for inverting the radiative transfer equation is presented. This method is superior to the original method in that it takes into account in a realistic manner the shape of the kernel function, and its extension to nonlinear systems is much more straightforward.

A comparison of the new method with a matrix method due to Twomey (1965), in a problem involving inference of vertical distribution of ozone from spectroscopic measurements in the near ultraviolet, indicates that in this situation this method is stable with errors in the input data up to 4%, whereas the matrix method breaks down at these levels. The problem of non-uniqueness of the solution, which is a property of the system of equations rather than of any particular algorithm for solving them, remains, although it takes on slightly different forms for the two algorithms.

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S. Twomey
,
H. Jacobowitz
, and
H. B. Howell

Abstract

If the radiation field is approximated by a discrete distribution at points or latitude circles on the unit sphere, matrix relationships can be written between incident and reflected or transmitted radiation fields. The reflection and transmission matrices thus defined are shown to satisfy algebraic equations which can be used to compute the properties of thick layers by building up the thick layers from thinner sublayers, the starting point being a layer so thin that it is effectively a single scattering layer only.

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S. Twomey
,
H. Jacobowitz
, and
H. B. Howell

Abstract

Results of calculations of diffuse reflection and transmission of cloud-model layers are presented. These calculations which are based on matrix methods developed by the authors and discussed in a previous paper include the effects of cloud thickness, absorption, drop-size distribution, liquid water content, and directions of the incident and emergent radiation.

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S. Twomey
,
H. B. Howell
, and
T. A. Wojciechowski

Abstract

No abstract available.

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S. Twomey
,
K. A. Davidson
, and
K. J. Seton

Abstract

Cloud nucleus concentration measurements made at hourly intervals between 1968 and 1973 at Robertson, N. S. W., show a very clear diurnal pattern with a maximum at approximately 1800 local time and a minimum at 0600 local time. It is suggested that photochemical reactions play a major role in the generation of cloud nuclei.

A close examination of the data suggests that the long-term trend, while indicating a general increase in pollution levels, could as readily be interpreted as fluctuations with changes in local or global meteorological factors. A much greater period of observation would be required to decide the question.

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