Strontium-90 in Surface Air and the Stratosphere: Some Interpretations of the 1963–75 Data

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  • 1 Department of Atmospheric Sciences, The University of Arizona, Tucson 85721
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Abstract

Stratospheric inventories of Sr-90 over the period 1963–75 yield T½* = 6–7 months for the inventory difference between Northern and Southern Hemispheres, T½N = 9–10 months for the decay of the Northern Hemispheric inventory by transfer to the troposphere and Southern Hemisphere, T½T=10–11 months for the decay of the total stratospheric inventory, and T½E=1.5–3.5 years for the decay of the Northern Hemispheric inventory by transfer to the Southern Hemisphere alone.

Mean monthly concentrations of Sr-90 in surface air along the 80th meridian are computed for the years 1963–75 and presented in time-latitude cross sections. The spring maximum in the Northern Hemisphere appears first at the lowest latitude (Miraflores-Balboa, 9°N) for which data are available. The reason for this appears to be seasonal precipitation scavenging associated with seasonal migrations of the equatorial trough (ITCZ). In the tropics and subtropics, where precipitation rate shows large seasonal variations, the Sr-90 concentration in surface air is related to precipitation rate in a manner qualitatively similar to that predicted by a simple theory based on precipitation scavenging and a constant source.

The standard error of the data is small in both hemispheres and similar to the pattern of SF-90 concentration. The standard error is inversely related to the precipitation rate. However, longitudinal comparisons are inadequate in the Southern Hemisphere to confirm that the Sr-90 concentrations of the 80th meridian network are representative.

Abstract

Stratospheric inventories of Sr-90 over the period 1963–75 yield T½* = 6–7 months for the inventory difference between Northern and Southern Hemispheres, T½N = 9–10 months for the decay of the Northern Hemispheric inventory by transfer to the troposphere and Southern Hemisphere, T½T=10–11 months for the decay of the total stratospheric inventory, and T½E=1.5–3.5 years for the decay of the Northern Hemispheric inventory by transfer to the Southern Hemisphere alone.

Mean monthly concentrations of Sr-90 in surface air along the 80th meridian are computed for the years 1963–75 and presented in time-latitude cross sections. The spring maximum in the Northern Hemisphere appears first at the lowest latitude (Miraflores-Balboa, 9°N) for which data are available. The reason for this appears to be seasonal precipitation scavenging associated with seasonal migrations of the equatorial trough (ITCZ). In the tropics and subtropics, where precipitation rate shows large seasonal variations, the Sr-90 concentration in surface air is related to precipitation rate in a manner qualitatively similar to that predicted by a simple theory based on precipitation scavenging and a constant source.

The standard error of the data is small in both hemispheres and similar to the pattern of SF-90 concentration. The standard error is inversely related to the precipitation rate. However, longitudinal comparisons are inadequate in the Southern Hemisphere to confirm that the Sr-90 concentrations of the 80th meridian network are representative.

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