Roles of mean meridional circulation and eddy diffusion in the transport of trace substances in the lower stratosphere

Abstract

Recent estimates of mean meridional motions and eddy diffusion coefficients in the lower stratosphere and upper troposphere are used to study the roles of mean circulation and eddy mixing in determining the spread of tungsten 185 injected into the lower stratosphere in the Hardtack test series of 1958. The observed distribution of bungsten 185 is reproduced satisfactorily for a period of 18 months after the injection, provided that the diffusion coefficients estimated from heat flux data are reduced by a factor of about 8. The mean meridional circulation is found to play a minor role in the transport process, its chief contribution being to raise the center of maximum concentration by 2 to 3 km in the equatorial region, in agreement with the observations. The mean residence time for a tracer injected into the equatorial stratosphere between 18 anti 20 km is found to be about 10

On the long term variations of stratospheric aerosol content after the eruption of Fuego volcano observed by lidar.

“…In May 1976 the concentration was still higher than the pre-volcanic values. The gross features of the decline in the aerosol concentrations are compared with the calculated results based on the well known two dimensional atmospheric model presented by GUDIKSEN et al (1968). It is shown that the rate of decrease of the observed peak radar cross section is less than that obtained by using Gudiksen model and the gas to particle conversion process should be taken into account to account for the discrepancy.…”

“…The mean values of Kyy and Kzz in different seasons in the range of latitudes 10-30N at the heights 21 and 15 km are shown in Table 2, after some calculation using data of GUDIKSEN (1968). The present comparison between the theoretical and experimental results was carried out neglecting the time variations of the diffusion coefficients.…”

“…Thus the observed rate of decay is much slower than the calculated one. The discrepancy may be accounted for in several ways: the first contemplated is the gas to particle conversion process which increases the latter in contrast to the former without substantial change in the shape of the size GUDIKSEN et al (1968). Gudiksen et al (1968) distribution function; the second is the variation in the size distribution function which increases the number of particles in a subrange sensitive to the laser wavelength, and decreases the number of particles in the remaining subrange.…”

“…The discrepancy may be accounted for in several ways: the first contemplated is the gas to particle conversion process which increases the latter in contrast to the former without substantial change in the shape of the size GUDIKSEN et al (1968). Gudiksen et al (1968) distribution function; the second is the variation in the size distribution function which increases the number of particles in a subrange sensitive to the laser wavelength, and decreases the number of particles in the remaining subrange. According to HOFMANN and ROSEN (1977), the first material injected into the stratosphere after the Fuego eruption and detected by his counter seems to be the tephra particles.…”

“…Numerical calculations based on the models of meridional transport by eddy diffusion along inclined mixing surfaces have been presented by REED and GERMAN (1965), GUDIKSEN et al (1968), and further by LUTHER (1973 For the numerical calculation, the trace substance (tungsten 185) is assumed to have sources at 11N at the heights of 18 and 19.5 km on June 15 1958. The two dimensional distributions of the concentration were calculated by the model for a period of 18 months after the injection.…”