Open AccessFallout of chlorine 36 to the Earth's surface in the southern hemisphere
Author(s) -
Keywood M. D.,
Fifield L. K.,
Chivas A. R.,
Cresswell R. G.
Publication year - 1998
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/97jd03125
Subject(s) - stratosphere , southern hemisphere , northern hemisphere , equator , atmospheric sciences , atmosphere (unit) , latitude , climatology , geology , precipitation , troposphere , environmental science , longitude , geography , meteorology , geodesy
Chlorine 36 is a radioactive isotope produced in the atmosphere by the cosmic‐ray spallation of 40 Ar. It has many applications as an environmental tracer which require an understanding of 36 Cl in modern deposition. Data are currently available only for high latitudes in the northern hemisphere and for Antarctica. In the present work, the first data for 36 Cl in modern deposition for the southern hemisphere are presented. Excluding the tropical data, the latitude dependence of this fallout is found to follow the form predicted by Lal and Peters, and its magnitude is within 40% of their predictions. In tropical Australia, however, a substantial excess of 36 Cl is observed in rainfall from sites that derived most of their precipitation from the summer monsoon. If the high‐latitude northern hemisphere data are representative of the entire hemisphere, then the southern hemisphere fallout appears to be 2–3 times less than in the northern hemisphere. It is suggested that this may be due to enhanced stratosphere‐troposphere exchange north of the equator promoted by the greater area of landmass, while the symmetric thermal structure of the southern atmosphere dampens this exchange.