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R. G. De Pena
and
E. A. Caimi

Abstract

The aerosol produced by a commercial device used for cloud seeding experiments was studied by electron microscopy, electron diffraction, chemical analysis and a replica method to test the hygroscopicity of the particles. The electron micrographs obtained from the aerosol when applying the replica method showed the hygroscopic nature of the aerosol particles.

We deduced from chemical analysis that the aerosol is composed of silver and potassium iodides in the ratio of approximately 2:1.

From an electron diffraction pattern and other considerations, the formation of a double salt or a solid solution is indicated; its nature should be considered in further work.

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R. G. De Pena
,
J. V. Iribarne
, and
E. M. De Achával

Abstract

The freezing characteristics of supercooled droplets of electrolytic solutions were studied for a set of 22 electrolytes and for concentrations of 10−2, 10−2 and 10−1 N. Ethyl alcohol was also tested. The freezing curves were found to be similar to those of water. The mean freezing temperature was compared in each case with that of the water sample used as a solvent. The differences were interpreted for the more diluted solutions in terms of the theory of heterogeneous nucleation.

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J. A. Reagan
,
J. D. Spinhirne
,
D. M. Byrne
,
D. W. Thomson
,
R. G. De Pena
, and
Y. Mamane

Abstract

Particulate size and height distributions, complex refractive index and mass loading have been measured and inferred from direct aircraft and indirect lidar-solar radiometer observations made during a unique joint experiment conducted the week of 18 November 1974 in Tucson, Ariz. The aircraft and lidar-solar radiometer measurements were first analyzed independently and the results were then intercompared. Vertical profiles of particulate extinction obtained from the lidar (monostatic) and aircraft measurements were found to be in excellent agreement on both a relative and absolute basis. Lidar (bistatic and monostatic) inferences of particulate mass loading agreed favorably with the aircraft mass monitor measurements. The aircraft and lidar (bistatic) size distribution determinations were found to be similar in shape and agreed in absolute value within an order of magnitude. The mean particle refractive index inferred from the lidar (bistatic) measurements (n = 1.40 − i0.000) agreed with the index of a significant fraction of the particles identified by electron microscope analysis of impactor samples collected with the aircraft.

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J. C. Doran
,
S. Abbott
,
J. Archuleta
,
X. Bian
,
J. Chow
,
R. L. Coulter
,
S. F. J. de Wekker
,
S. Edgerton
,
S. Elliott
,
A. Fernandez
,
J. D. Fast
,
J. M. Hubbe
,
C. King
,
D. Langley
,
J. Leach
,
J. T. Lee
,
T. J. Martin
,
D. Martinez
,
J. L. Martinez
,
G. Mercado
,
V. Mora
,
M. Mulhearn
,
J. L. Pena
,
R. Petty
,
W. Porch
,
C. Russell
,
R. Salas
,
J. D. Shannon
,
W. J. Shaw
,
G. Sosa
,
L. Tellier
,
B. Templeman
,
J. G. Watson
,
R. White
,
C. D. Whiteman
, and
D. Wolfe

A boundary layer field experiment in the Mexico City basin during the period 24 February–22 March 1997 is described. A total of six sites were instrumented. At four of the sites, 915-MHz radar wind profilers were deployed and radiosondes were released five times per day. Two of these sites also had sodars collocated with the profilers. Radiosondes were released twice per day at a fifth site to the south of the basin, and rawinsondes were flown from another location to the northeast of the city three times per day. Mixed layers grew to depths of 2500–3500 m, with a rapid period of growth beginning shortly before noon and lasting for several hours. Significant differences between the mixed-layer temperatures in the basin and outside the basin were observed. Three thermally and topographically driven flow patterns were observed that are consistent with previously hypothesized topographical and thermal forcing mechanisms. Despite these features, the circulation patterns in the basin important for the transport and diffusion of air pollutants show less day-to-day regularity than had been anticipated on the basis of Mexico City's tropical location, high altitude and strong insolation, and topographical setting.

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