A new tool for the study of the ozone hole dynamics over Antarctica C.A. Varotsos * , C. Tzanis Climate Research Group, Division of Environmental Physics and Meteorology, Faculty of Physics, University of Athens, University Campus Bldg. Phys. V, Athens 15784, Greece article info Article history: Received 14 February 2011 Received in revised form 12 October 2011 Accepted 17 October 2011 Keywords: Dynamics Ozone Entropy Natural time analysis abstract An analysis of the time series of the maximum daily ozone hole area over Antarctica for each year during the period 1979e2009 is presented, based on the entropy S defined in a new time domain termed natural time domain, that captures characteristics of the dynamics of the ozone hole complex system. The results obtained show that the entropy in natural time for scales 3e7 years and its value under time reversal for all scales (3e15 years) almost stabilizes during the last several years. On the other hand, characteristic features of this entropy are clearly found before the unprecedented event of the major, sudden strato- spheric warming and the subsequent break-up of the Antarctic ozone hole into two holes in September 2002. In particular, the following precursory changes have been identified: First, for scales larger than 8 years, the entropy in natural time exhibits a gradual increase after around 1999. Second, from 2000 to 2001, the entropy in natural time under time reversal shows an increase for all scales (3e15 years) except for the scale of 13 years. Third, the values of the entropy change in natural time almost coincide at 2000 for the short scales 3e7 years and then decrease. The analysis in the natural time domain is also applied on the eddy heat flux, which is proportional to the vertically propagating wave activity affecting the ozone hole over Antarctica. The results drawn confirm those deduced from the ozone hole area diagnostics. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Each year for the past few decades (after 1984) during the Southern Hemisphere spring, chemical reactions cause ozone in the southern polar region to be destroyed rapidly and severely forming a region known as the “ozone hole”. The depth and area of the Antarctic ozone hole are mainly governed by the amounts of chlorine and bromine in the stratosphere, the temperature of the stratosphere and the amount of sunlight reaching the south-polar region (Dameris, 2010). As polar winter arrives, a vortex of winds develops around the pole and isolates the air within it. Because it is completely dark, the temperatures inside the vortex drop enough (below 78  C), and form polar stratospheric clouds (PSCs) which are thin clouds of ice, nitric acid, and sulphuric acid mixtures. Then heterogeneous reactions take place and convert the inactive chlo- rine and bromine reservoirs to more active ones (especially Cl 2 ). Nowadays, special attention is given to the point defects in various categories of solid particles (Varotsos, 1976; Varotsos and Alexopoulos, 1984), which plays a substantial role in the ozone content depletion via the heterogeneous reactions mechanisms. Rapid ozone depletion takes place, when sunlight returns to the air inside the polar vortex (UV light rapidly breaks the bond of Cl 2 ) and the “ozone hole” appears. Hence, the ozone hole begins to grow as the sun is rising over Antarctica at the end of the winter and reaches its largest area in depth in the middle of September to early October period, covering often an area comparable to Antarctica or bigger. When the temperature warms and the polar vortex weakens the air from the lower latitudes enters the polar region, and the ozone- destroying chemicals disperse, allowing the stabilization of the polar ozone until the next spring. In addition, very large-scale weather systems or waves move or propagate upward into the stratosphere warming the polar region. This upward flow of wave energy is measured with the eddy heat flux, where the 45-day average of it is strongly anticorrelated with the stratospheric temperature lagged prior to it. A more negative value of eddy heat flux indicates that wave systems are moving into the stratosphere and are warming the polar region. Upward- propagating planetary waves forced from the troposphere trigger rapid zonal wind deceleration (disturbances of the polar vortex caused by planetary wave activity), polar temperature increase, and distortion and sometimes splitting of the winter vortex. Undoubtedly, marked progress has been achieved in studying atmospheric ozone depletion and its impacts, since the discovery of the Antarctic ozone hole (Cracknell and Varotsos, 1994, 1995; * Corresponding author. Tel.: þ30 210 7276838. E-mail address: covar@phys.uoa.gr (C.A. Varotsos). Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2011.10.038 Atmospheric Environment 47 (2012) 428e434