Increased UV radiation due to polar ozone chemical depletion and vortex occurrences at Southern Sub-polar Latitudes in the period [1997–2005]

[摘要] The variability of total ozone and UV radiation from Total Ozone MappingSpectrometer (TOMS) measurements is analyzed as a function of polar vortexoccurrences over the southern subpolar regions during the 1997–2005 period.The analysis of vortex occurrences showed high interannual variability in the40° S–60° S latitude band with a longitudinal asymmetryshowing the largest frequencies over the 90° W–90° E region.The impact of vortex occurrences on UV radiation and ozone in clear skyconditions was determined from the comparison between the measurements insidethe vortex and a climatology obtained from data outside the vortex over thestudied period. Clear sky conditions were determined from TOMS reflectivitydata. For measurements outside the vortex, clear sky conditions were selectedfor reflectivity values lower than 7.5%, while for measurements inside thevortex, a relaxed threshold was determined from statistically similar UVvalues as a function of reflectivity. UV changes and ozone differences fromthe climatology were analyzed in the 40° S–50° S and50° S–60° S latitude bands during the spring period(September to November). The largest UV increases and ozone decreases,reaching ~200% and ~65%, respectively, were found in the50° S–60° S latitude band in September and October. Theheterogeneous ozone loss during vortex occurrences was estimated using achemical transport model. The largest impact of vortex occurrences was foundin October with mean UV increase, total ozone decrease and accumulated ozoneloss in the 350–650 K range of, respectively, 47%, 30% and 57%. Theregion close to South America is the most affected by the Antarctic ozonedepletion due to the combined effect of large number of vortex occurrences,lower cloud cover and large ozone decrease. This region would be the mostvulnerable in case of cloud cover decrease, due to more frequent occurrenceof ozone poor air masses during austral spring.

[学科分类] 大气科学