The impact of different atmospheric phenomena to cosmogenic ²² Na/⁷Be ratio

• Main Authors: Leppänen, A.-P. (Ari-Pekka), Poluianov, S. (Stepan)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2022
• Subjects: Cosmogenic isotope production; Radiotracers; SSW; Teleconnections; Transport time; ²²Na/⁷Be; Arctic; Rovaniemi; North Atlantic; North Atlantic oscillation
• Online Access: http://urn.fi/urn:nbn:fi-fe2022070150819

Abstract The isotopic ratio of two cosmogenic isotopes, ²²Na and ⁷Be, has been recognized as a possible tracer for atmospheric dynamics. We studied how different atmospheric phenomena affect the ²²Na/⁷Be ratio that are known to affect the ground level ⁷Be concentrations. The ²²Na/7Be ratio was studied in the following context: estimation of aerosol residence time, in the intrusions of stratospheric air after Sudden Stratospheric Warming (SSW) events, seasonal variations due to different atmospheric mixing conditions and finally the interannual variations caused by the large-scale atmospheric circulation such as North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Scandinavian Pattern (SCAND) and Quasi-Biennial Oscillation (QBO). This study utilized airborne radioactivity monitoring data from three Finnish stations located in Rovaniemi (66.51 °N, 25.73 °E), Kajaani (64.08 °N, 27.71 °E) and Kotka (60.48 °N, 26.92 °E). The theoretical calculations were performed to see how the ²²Na/⁷Be ratio changes as a function of altitude during when produced by the galactic cosmic rays. The calculations showed that the ²²Na/⁷Be ratio is higher in the stratosphere and lower in the troposphere. At mid-stratosphere level the ratio was 0.001, at tropopause level approximately 0.0007 and at ground level approximately 0.00045. Due to the different half-lives of 22Na and ⁷Be the mean atmospheric residence time can be estimefrom the radioactive decay law by assuming an initial activity concentration ratio of 0.0007 and using the measured ground level ²²Na/⁷Be ratios. This resulted in the median atmospheric residence time as 91–95 days. The atmospheric impact on ²²Na/⁷Be ratio was studied at different time scales starting from short-term impact from SSW, the known seasonal cycle and variations at interannual timescale. SSW events caused rapid increases in the ground level ⁷Be and ²²Na concentrations while the impact on ²²Na/⁷Be ratio was relatively small. A clear seasonal cycle in the ²²Na/⁷Be ratio was observed where the ²²Na/⁷Be ...