7Be Measurements in Ground Level Air and the austausch within the Lower Part of the Troposphere

Abstract

THE concentrations of fission products and spallation products show a yearly variation with a maximum in early summer and a minimum in winter. This holds for concentration measurements in atmospheric precipitation and to a lesser extent for measurements in ground level air. Spallation products originate predominantly in the stratosphere which is also the main reservoir for fission products. The generally accepted explanation for the concentration maximum in precipitation is an increase in the strato-tropospheric austausch during the period of the maximum, but there is some disagreement over measurements in ground level air. There are several reasons; first, there are few long-term measurements in ground level air. Second, different authors recorded yearly variations of different magnitude. Third, they disagree over the causes of the variation. Apart from the assumption that, as in the case of precipitation, the yearly variation reflects an increased strato-tropo-spherical austausch, the view was taken that the yearly maximum results from increased inner-tropospheric turbulence1. To obtain information on the cause of the yearly variation, measurements on 7Be in ground level air (GLA) performed at two different locations at the same time will be discussed in the following.