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G. S. Kent and W. Keenliside

Abstract

The results of two years of laser radar observations, of the mesosphere and lower thermosphere over Kingston, Jamaica (18.0N, 76.8W), are described. These show the existence of a clear annual variation in atmospheric density with a maximum occurring between January and March and an amplitude of a few percent. Superimposed on this is a longer term trend producing a decrease in the mean density over the period of observation. A comparison is made with the U. S. Standard Atmosphere Supplements for 15N and with an existing model for atmospheric density variations based on other measurement techniques.

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G. S. Kent and W. Keenliside

Abstract

The laser radar system at Kingston, Jamaica (189N, 17°W) has been used to study periodic variations in atmospheric density at altitudes between 68 and 100 km. A major feature of these variations is an oscillation with a vertical wavelength of 12–14 km, descending phase, and a probable period of 24 h. This has been identified as the θ3 ω,1 atmospheric tidal oscillation and a comparison of its observed characteristics with theoretical predictions for this tidal mode shows good agreement.

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G. S. Kent and M. T. Philip

Abstract

Lidar observations of the stratosphere were made at Kingston, Jamaica (18.0°N, 76.8°W) following the eruptions of the Soufrière volcano of St. Vincent (13.2°N, 61.2°W) between 13 and 23 April 1979. Anomalous optical scattering was observed, at a height of ∼16 km, between 1 and 5 May 1979. This is discussed in relation to the relevant meteorological wind data and is interpreted as being due to volcanic dust which has been carried eastward once round the earth in the strong, upper tropospheric, zonal winds.

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G. S. Kent, F. Köpp, and Ch Werner

Abstract

Remote sensing of the lower atmosphere by lidar yields profiles of the backscattering cross section along the optical path. These may be simply converted to give a qualitative picture of the distribution of atmospheric aerosol, but quantitative values can only be obtained if further information is available on aerosol properties such as refractive index and size distribution. In the experiments described below, use was made of a solar radiometer to give information on the second of these. This is then used to calculate an improved value for the ratio of backscattering to aerosol mass (β/m) for the interpretation of the lidar data. Comparison is made of the results of radiometer measurements, taken at a rural area outside Munich, with airborne lidar measurements of the tropospheric aerosol made in the same locality. Aerosol density profiles obtained in another flight made near Augsburg on 22 July 1977 show the presence of a heavy aerosol concentration over the city and the effects of the north wind are clearly visible.

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G. S. Kent, L. R. Poole, and M. P. McCormick

Abstract

Airborne lidar measurements of backscattering at 0.6943 μm from polar stratospheric clouds, made in January 1984, are reported. The clouds, whose altitudes and geographical locations coincided with ambient atmospheric temperatures below about 193 K, were observed to cover a greater area of the polar cap than had previously been apparent from satellite measurements. They were seen on three separate flights north of Thule, Greenland (76.5°N, 68.7°W), on one occasion extending continuously from approximately 80°N to the North Pole. Pronounced layering of the clouds was observed and the maximum backscatter enhancement, relative to that from the background aerosol, was between 100 and 200. These values occurred at an altitude of about 20 km, close to the region of minimum stratospheric temperature. Depolarization of the order of 20–50% in the backscattered signal was measured, in support of the hypothesis that the aerosols forming the clouds are frozen. Comparison of the experimentally determined backscattering-temperature relationship with a theoretical model, based on a volcanic aerosol and using best available estimates for water vapor concentration, shows good agreement at the 100- and 70-mb pressure levels. A small systematic error at the 50- and 30-mb levels may be due to inaccurate characterization of the temperature field at these altitudes and locations.

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B. R. Clemesha, G. S. Kent, and R. W. H. Wright

Abstract

This paper describes equipment designed to observe variations in atmospheric density at heights up to 65 km by measuring the intensity of light back-scattered from a laser beam. The basic theory of the technique is briefly described, and an expression is derived for the sensitivity of the laser radar. The design of the equipment is then discussed from the point of view of optimization of the equipmental parameters for maximum sensitivity, with a view to obtaining measurements at the greatest possible height. The paper continues with a description of the actual equipment, a discussion of problems encountered in its application, and the methods used to overcome these problems. Finally, a very brief description is given of the results obtained with the laser radar.

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G. S. Kent, P. Sandland, and R. W. H. Wright

Abstract

A brief discussion of the laser-radar method for investigating atmospheric properties above the troposphere is given. A detailed description is then presented of a large new system which has been constructed in Jamaica. The system is designed to have a telescope receiver whose collecting area is 16 m2, made up of a mosaic of spherical mirrors each of 30 inch diameter with an 80-ft focal length. The photomultiplier systems in use are designed to achieve a quantum efficiency of about 15% with the 0.6943-μm ruby laser light.

The equipment is about three orders of magnitude more sensitive than the usual laser-radar system. The problems which were met in the design and construction of such an equipment and the ways in which they were overcome are discussed.

The results of a typical operation sequence are given. These show that the equipment can, in the absence of aerosols, make measurements of atmospheric density up to about 100 km with a relative accuracy of ∼10%.

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M. T. Philip, G. S. Kent, and M. T. Ottway

Abstract

Results are presented from an intensive study of the stratospheric aerosol layer over Kingston, Jamaica, made in 1978–79, using a ruby lidar system. The aerosol layer is found to extend up to an altitude of about 35 km, with the layer maximum varying between 20 and 26 km. Comparison has been made of the principal layer characteristics with those obtained from other lidar and from direct measurements. Short-term fluctuations in the layer, occurring over a few hours or days, have been studied and are believed to be caused by the movement of irregularities in aerosol concentration. The long-term lidar record from 1965–79 is presented, showing the fluctuating volcanic influence during this period.

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G. S. Kent, C. R. Trepte, U. O. Farrukh, and M. P. McCormick

Abstract

Aerosol extinction data obtained by the Stratospheric Aerosol Measurement II (SAM II) satellite instrument during the 1979/80 Northern Hemisphere winter season have been analyzed in relation to the cyclonic polar vortex. A synoptic approach has been employed to study the behavior of aerosol extinction ratio and optical depth between altitudes of 8 and 30 km as a tracer of mean atmospheric motions in and near the polar vortex. As the polar vortex intensifies, a gradient of extinction ratio is established across the polar-night jet stream, which is associated with subsidence within the vortex. Maximum subsidence occurs at the center of the vortex. Calculated descent rates relative to isentropic surfaces are of the order of 8 × 10−4 m s−1 near 20 km, at the center of the vortex between September and December. Below an altitude of 14 km, taken as the base of the vortex, and outside the vortex, horizontal movements occur freely, masking any systematic vertical motions. Extinction enhancements by polar stratospheric clouds and changes produced by sudden warmings in the second half of winter have prevented a similar study for this period. An estimate of the aerosol mass transferred downward through the base of the vortex for the entire season is 7000 tonnes. Comparison of the inferred stratospheric motions with earlier studies using radioactive tracers shows good agreement.

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G. S. Kent, U. O. Farrukh, P. H. Wang, and A. Deepak

Abstract

The SAGE-I and SAM-II satellite sensors were designed to measure, with global coverage, the 1 μm extinction produced by the stratospheric aerosol. In the absence of high altitude clouds, similar measurements may be made for the free tropospheric aerosol. Median extinction values at middle and high latitudes in the Northern Hemisphere, for altitudes between 5 and 10 km, are found to be one-half to one order of magnitude greater than values at corresponding latitudes in the Southern Hemisphere. In addition, a seasonal increase by a factor of 1.5–2 was observed in both hemispheres, in 1979–80, in local spring and summer. Following major volcanic eruptions, a long-lived enhancement of the aerosol extinction is observed for altitudes above 5 km.

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