Variation in C14 concentration in the atmosphere during the last several years

Variation in C¹⁴ concentration with time at various northern latitudes from 9°N to 78°N has been studied in the troposphere mainly since 1963 (Nydal, 1963, Nydal & Lövseth, 1965). Sampling has later been extended to 21°S. During 1965 sampling was also performed at 63°N at an altitude of 13 km.

Our tropospheric data has been compared with the HASL measurements (Hagemann et al., 1965) at an altitude of 20 km. It appears that the stratosphere at this height mixes very rapidly in the latitudinal direction at latitudes above 30°N. The diffusion coefficient for turbulent mixing in this region may be of the same order as that of the troposphere (10¹⁰−10¹¹ cm²/sec., Münnich, 1963).

In 1963 there seems to be a decrease in exchange rate below about 30°N, both within the stratosphere (20 km altitude) and within the troposphere. In summer 1964, however, this “barriere” in the troposphere is less convincing because all the C¹⁴ peaks occur nearly simultaneously from 9°N to 78°N. The peak at Dakar (15°N) is even higher than several peaks farther north.

The author's impression is that the simultaneous occurring C¹⁴ peaks in the troposphere in summer at various northern latitudes are partly due to a simultaneous removal of C¹⁴ from the stratosphere to the troposphere at the respective latitudes. It turns out that C¹⁴ from polar explosions in 1962 is transferred to the lower and southern latitudes both through the troposphere and through the stratosphere. C¹⁴ transfer through the last one seems to be important.