BERYLLIUM-10 BERYLLIUM-7 AS A TRACER OF STRATOSPHERIC TRANSPORT

We use the ratio between cosmogenic radionuclides beryllium 10 (t(1/2) 1.5 x 10(6) years) and beryllium 7 (t(1/2)=53 days) to study stratosp heric transport, particularly the exchange between the tropics and the high latitudes and as an indicator of stratosphere-troposphere exchan ge. Both tracers are generated steadily, with maximum production occur ring at midlatitudes of the stratosphere. During transport away from t heir source the ratio Be-10/Be-7 increases and thus acts as a clock fo r air mass age. According to model (GISS GCM) calculations, the tropic s is a reservoir of high-ratio air With the high magnitude of Be-10/Be -7 partly a. consequence of air mixed in from higher latitudes. The ob servations of Dibb et al. [1994] show a vertical maximum in Be-10/Be-7 in the lower arctic stratosphere during the spring of 1989; model res ults qualitatively reproduce this maximum and suggest that it may resu lt from transport of tropical air to high latitudes during winter. The model ratio values are not so large as in these observations, possibl y due to either excessive leakage into the troposphere near the pole o r to insufficient transport from the tropical stratosphere to the pole . Beryllium 10 and Be-7 observations, combined with model analysis, ca n be a useful indicator of transport processes in the troposphere/stra tosphere system.