Time lag between the tropopause height and 7Be activity concentrations on surface air.

ABSTRACT

A strong positive correlation between the seasonal changes of the tropopause height and the concentration of (7)Be in the surface air (R = 0.94, p < 0.0001) was observed at 40°N. Moreover, a strong positive correlation was revealed between the activity concentrations of (7)Be and the temperature T (°C) (R = 0.97, p < 0.001), confirming that the increased rate of vertical transport within the troposphere, especially during warmer months, has as a result the descent to the surface of air masses enriched in (7)Be. The results of the present work suggest that the temperature and the tropopause height are good indicators for transport time of air masses enriched in (7)Be to the surface. Higher values of temperature or tropopause height seem to result to shorter transport times. This is attributed to atmospheric convection which provides an effective mechanism for vertical transport of air masses. Increasing tropospheric temperature has generally as a result that convection penetrates more deeply which in turn leads to an increase in tropopause height. But, the atmospheric procedures do not occur immediately after the fluctuations of correlated factors. Thus, a time lag is expected between the tropopause height and (7)Be activity concentrations on surface air that might be from hours to days or weeks. The result suggests that (7)Be concentrations fully respond within three days after the changes in the tropopause height.