Radon measurements in the lower tropical Stratosphere: Evidence for rapid vertical transport and dehydration of tropospheric air

The authors report on measurements of radon concentrations made by the ER-2 aircraft as part of the Stratosphere-Troposphere Exchange Project (STEP) Tropical mission. Radon has a half life of 3.8 days, and physical and chemical properties which do not favor its being scavenged from the atmosphere by any of the projected processes which might drive the drying cycle. Its major source is from the decay of 226Ra in the continental crust. Radon activities in the free troposphere are typically near 1pCi/scm (picocurie per standard cubic meter) near the tropopause. Observations are reported for three large tropical cyclones, and one large cumulonimbus cloud cluster. These measurements show elevated levels of radon in the stratosphere, in conjunction with low water vapor measurements, which provides strong evidence for rapid convective air mass movement. In addition, radon activities were found to be consistent with values necessary to account for elevated 210Pb densities observed in the stratosphere