INTERNATIONAL SYMPOSIUM ON TRACE GASES AND RADIOACTIVITY 3805 40 ~~—~—--— SSN — a —~ NNN 35/-| ee 27/28. 8.56 | 22-3h Experimental (WEXLER et al., 1955): o—— 25.10. Pet Ohio w——* 26.10. 1950 Calculated 2 JWN 20.5.56 NS 22-0h 12 7 56 0-4h 40 SSN, NNN, WNN Relative Rn- concentration (cpm/g) K-profile 50 ~~ 40 ~~ 50 WNW 7 r ground level under inve rsion 2 { 4 1 6 ! 8 i 10 12km Altitude ERNELAE:«te, the NNW case (normal tur buupper troposphere. The mean flights agrees rather well with orofile NNN for which the Rn™ t an altitude of 2 km is about ncentration near ground level, onsistent with observati ons of tk [1928] and Wilkening [1953]. on indicates that it is poss ible ertical profile of the tur bulent *nt from measurements of the an™ distribution. The avai lable thin the troposphere giv e some the K profile NNN, giv en in represents average turbul ence 0 0 Fig. 4. Comparison of observed and calculated relative Rn profiles in the troposphere. conditions in the troposphere. If we assume normal conditions of turbulence in the tropo- sphere, i., the profile NNN in Figure 1, a rather rapid decrease of the Rn™ concentration should be expected in the tropopause. In this case the part of the total activity in a vertical column of air which reaches the layer above 12 to 13 km (mean altitude of the tropopause in the temperate zone) is only about 1 to 2 per cent. If we assume the K profile SSN (strong tropospheric turbulence), however, this part in- creases to about 10 to 15 per cent. This suggests that considerable amounts of Rn™ can penetrate through the tropopause into the lower stratosphere only during periods of strong vertical turbulent mixing or convection, e.g. in case of cumulonimbus formation. Machta and Lucas [1962] recently reported the first results of Rn™ measurements in the tropopause and lower stratosphere which indicate new aspects of the exchange process through the tropopause (Figure 5). The air