Variability of Antarctic ozone loss in the last decade (2004–2013): high resolution simulations compared to Aura MLS observations

Abstract

Abstract. A detailed analysis of the polar ozone loss processes during ten recent Antarctic winters is presented with high resolution Mimosa-Chim model simulations and high frequency polar vortex observations from the Aura Microwave Limb Sounder (MLS) instrument. Our model results for the Antarctic winters 2004–2013 show that chemical ozone loss starts in the edge region of the vortex at equivalent latitudes (EqLs) of 65–69° S in mid-June/July. The loss progresses with time at higher EqLs and intensifies during August–September over the range 400–600 K. The loss peaks in late September/early October, where all EqLs (65–83°) show similar loss and the maximum loss (>2 ppmv [parts per million by volume]) is found over a broad vertical range of 475–550 K. In the lower stratosphere, most winters show similar ozone loss and production rates. In general, at 500 K, the loss rates are about 2–3 ppbv sh−1 (parts per billion by volume/sunlit hour) in July and 4–5 ppbv sh−1 in August/mid-September, while they drop rapidly to zero by late September. In the middle stratosphere, the loss rates are about 3–5 ppbv sh−1 in July–August and October at 675 K. It is found that the Antarctic ozone hole (June–September) is controlled by the halogen cycles at about 90–95% (ClO–ClO, BrO–ClO, and ClO–O) and the loss above 700 K is dominated by the NOx cycle at about 70–75%. On average, the Mimosa-Chim simulations show that the very cold winters of 2005 and 2006 exhibit a maximum loss of ~3.5 ppmv around 550 K or about 149–173 DU over 350–850 K and the warmer winters of 2004, 2010, and 2012 show a loss of ~2.6 ppmv around 475–500 K or 131–154 DU over 350–850 K. The winters of 2007, 2008, and 2011 were moderately cold and thus both ozone loss and peak loss altitudes are between these two ranges (3 ppmv around 500 K or 150 ± 10 DU). The modeled ozone loss values are in reasonably good agreement with those estimated from Aura MLS measurements, but the model underestimates the observed ClO, largely due to the slower vertical descent in the model during spring.

A quantitative analysis of the reactions involved in stratospheric ozone depletion in the polar vortex core

“…6 and extensive additional comparisons of the model to measurements in the Supplement). There was, however, a significant overestimation of HCl compared to measurements in our original model runs, which has also been observed in other models like SD-WACCM (Brakebusch et al, 2013;Wegner, 2013;Solomon et al, 2015) or MIMOSA-CHIM (Kuttippurath et al, 2015). Interestingly, the SLIMCAT CTM shows a discrepancy of the same order of magnitude, but with the opposite sign, in a recent publication (Santee et al, 2008).…”

“…It is obvious that the runs without a change to the HCl solubility significantly overestimate HCl, a behavior also observed in other models like SD-WACCM (Brakebusch et al, 2013;Wegner, 2013;Solomon et al, 2015) or MIMOSA- CHIM (Kuttippurath et al, 2015). Interestingly, the SLIM-CAT CTM shows a discrepancy of the same order of magnitude, but with the opposite sign in a recent publication (Santee et al, 2008), while in an older version, species mixing ratios depend on the model resolution (Chipperfield et al, 1997).…”

“…There was a significant discrepancy between the modeled and measured HCl mixing ratios in our original model runs, which has also been observed in other state-of-the-art models like SD-WACCM (Brakebusch et al, 2013;Wegner, 2013;Solomon et al, 2015), MIMOSA-CHIM (Kuttippurath et al, 2015) or SLIMCAT (Santee et al, 2008). The cause of these discrepancies in the different models is currently unknown.…”

Sulfur-isotope anomalies recorded in Antarctic ice cores as a potential proxy for tracing past ozone layer depletion events

“…This is because more significant ozone losses (with even lower mixing ratios) occur in the short-term on an annual basis over present-day Antarctica. Nevertheless, no evidence of S-MIF in tropospheric sulfate has been found ( 52 , 56 , 57 ). Moreover, with most of the ozone layer intact in the lower stratosphere during the Laschamp GE event, increasing tropospheric ozone is likely to impede further S-MIF-generating UV-induced photochemical processes.…”

The signs of Antarctic ozone hole recovery

“…Evident shifts in dynamical processes in the spring impeded clear attribution of chemical effects in a study of detailed, height-resolved ozonesonde measurements at South Pole and Neumayer stations 16 . Recent satellite measurements also show changes in ozone loss rates that are difficult to distinguish from an observed springtime dynamical shift in Antarctica in the past decade 17 , 18 . The reported springtime dynamical changes involve shifts in the location of the vortex and longitude of planetary wave structure 15 , as well as in the character of spring stratospheric minor warmings 16 .…”