Stratospheric circulation studies based on natural and artificial radioactive tracer elements

Abstract

The nature of large scale stratospheric circulation is studied using the cosmic ray produced isotopes Par, Be", Sa6 and Nas2 as tracers. Supplementary information obtained from observations of the distribution of the bomb-produced Na** and radongenic Pbp10 is taken into account. The activities of these tracer elements have been measured in the stratospheric air, up to altitudes of 20 km, during 1960-64. Data are fairly extensive for studying the characteristics of the mean circulation in the stratosphere as well as seasonal changes in patterns of mixing/transport of air in certain regions of the stratosphere.The interpretation of the data on cosmic ray tracers is based on a comparison of their observed activities with the expected production rates due to cosmic rays. For this purpose, the work of La1 & Peters is extended to evaluate the variations in the relative production rates of the isotopes Par, Be', S" and Nag* in the atmosphere. These have to be taken into account when isotope data are compared for different altitudes and latitudes in the stratosphere where relative isotope production rates are different because of the markedly different prevailing energy spectrum of nucleons.The analysis allows us to distinguish three zones in the lower stratosphere (below 20 km), well separated from the tropopause, having distinct circulation patterns. These regions are separately well mixed either vertically or horizontally; the mean time of residence of aerosols in these regions differs appreciably too. The most stable region in the Stratosphere is found to be 18-20 km region at 0-30" latitude, where apparent residence times are of the order of twenty months. Polar regions are observed to exhibit an enhanced vertical mixing during November-February. Combining these results with the observations of dispersion of bomb-produced Naxz, which appeared in significant amounts from early 1962 onwards all over the stratosphere, we deduce that in the polar regions, vertical mixing occurs rapidly during November-February so that any activity injected in this region a t 20 km or so mixes downwards a t the rate of about 1.6 km month-'. It is concluded that the observed spring peaks in the troposphere are merely the consequence of this phenomena which is triggered in upper levels (above 20 km) of the stratosphere during October-November.The observations of concentrations of PbP1O in the stratosphere are discussed. The analysis reveals that an appreciable gravitational settling of Pb'l0 seems to have occurred, a t least during the period over which data were collected, from the stratospheric air between 56'-75' latitude. These observations imply that the residence time of air in this region of the atmosphere is appreciably higher than that deduced from tracers which attach themselves to aerosols. Lastly, the Pbglo data indicate that appreciable amounts of tropospheric radon presumably enter the equatorial stratosphere; this conclusion rests on the Observation that Pbz10 concentrations are higher in this region compared to that in the ...

Modelling the stratospheric budget of beryllium isotopes

“…However, few studies have reported beryllium measurements higher up in the stratosphere. Our simulated values of Be-7 concentration match quite well the range of measurements done at 20 km over the Â2 yr period August 1963ÁApril 1965 with low solar activity (F Â400 to 600 MV; Usoskin et al, 2011), compiled by Bhandari et al (1966). The simulated values are rather in the upper part of the range, except in sub-tropical latitudes (25Á358N) where they are lower by Â15%.…”

“…As a result, beryllium concentrations in the troposphere are one to two orders of magnitude lower than in the stratosphere (e.g. Bhandari et al, 1966;McHargue and Damon, 1991). This makes beryllium concentrations a potential tracer of stratospheric air inputs into the troposphere.…”

“…Some measurements, including high up in the stratosphere, were already compiled by Bhandari et al (1966) and Bhandari (1970), and the largest data set so far has been produced by Jordan et al (2003), but restricted to the lowest stratosphere. Between 308N and 708N and up to 2 km above the tropopause, measurements of stratospheric Be-7 concentrations range from roughly 50 to 250)10 Concentrations higher in the stratosphere should be less biased in the model because the gradients are certainly much smoother than in the tropopause region.…”

“…Bhandari et al, 1966). A special concern at that time was about fallouts of radioactive debris from nuclear bomb tests.…”

A history of solar activity over millennia

“…The first consistent model was developed by D. Lal et al (Bhandari et al 1966;Lal and Peters 1967;Lal and Suess 1968), using an empirical approach based on fitting simplified model calculations to measurements of the isotope concentrations and "star" (inelastic nuclear collisions) formations in the atmosphere. Next was an analytical model by O'Brien (1979), who solved the problem of the GCR-induced cascade in the atmosphere using an analytical stationary approximation in the form of the Boltzmann equation.…”