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Robert J. List
and
Kosta Telegadas

Abstract

Since 1952 a number of radioactive substances suitable for use as atmospheric tracers have been injected into the stratosphere. Information on large-scale stratospheric processes derived from measurements of strontium-90, carbon-14, tungsten-185, rhodium-102, cadmium-109 and plutonium-238 is summarized. Although the tracer data are too sparse to define an unambiguous model of the large-scale circulation features of the stratosphere, they should not be ignored in the process of constructing models from other considerations.

The tracer data indicate a summer-to-winter hemisphere flow above about 37 km and a mean descending motion in the winter stratosphere between 25° and about 70°. Ascending motion occurs near the equatorial tropopause and in the lower winter stratosphere poleward of 70°. Virtually the entire summer stratosphere and the winter stratosphere equatorward of 25° between 18 and 25 km is dominated by mixing processes with no evidence of organized circulations in the meridional plane.

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Gene C. Stevens
,
Sigmund Fritz
, and
Robert J. List
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Greg M. McFarquhar
,
Roland List
,
David R. Hudak
,
Robert P. Nissen
,
J. S. Dobbie
,
N. P. Tung
, and
T. S. Kang

Abstract

During the Joint Tropical Rain Experiment of the Malaysian Meteorological Service and the University of Toronto, pulsating raindrop ensembles, hereafter pulses, were observed in and around Penang Island. Using a Doppler radar on 25 October 1990, a periodic variation of precipitation aloft 30 km from the radar site, with an approximate 8-min period, was established and seemed to be caused by the evolution and motion of horizontal inhomogeneities existing within the same cell. On 30 October 1990, using a new volume scanning strategy with a repetition cycle of 3.5 min, pulsations of the same frequency were observed up to 3 km above the radar and at the ground by a disdrometer. High concentrations of large drops were followed by high concentrations of successively smaller drops at the ground. This provides observational evidence to support the recent argument for using a time-varying release of precipitation-sized particles to model observed pulsating rainfall.

Many cases of nonsteady rain from convective clouds displayed repetition periods of between 8 and 25 min.

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