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ANTARCTIC OZONE

This page gives information about ozone at Halley, Rothera and Vernadsky/Faraday stations. It was either updated or new data was added on 2012 July 5.

Situation at 2012 May 3

The 2011 Antarctic ozone hole is over.  The  weak summer circulation is changing to the winter mode,  but ozone gradients remain generally small.   Minimum ozone values are currently around 250 DU and well above the ozone hole threshold.   Maximum values are near 330 DU, well down from peaks above 400 DU in early spring.   The lower stratospheric temperature is falling, and temperatures generally remain a little below the normal for this time of year.  It is too warm for stratospheric clouds to form.

The hole began to form in mid August, and by mid September had reached an area of around 25 million square kilometres, larger than the average for the last decade and remained near this size into early October.  It had shrunk to around 20 million square kilometres by mid October and remained a similar size till mid November, when its size dropped rapidly but remained at a few million square kilometres until mid December.  It  filled by the summer solstice.   Its size from October to mid November was near to or above the record area for the time of year.  The hole became more elliptical in mid October and the edge of the ozone hole passed over the tip of South America and the Falkland Islands, but then returned to a more circular form.  The edge of the ozone hole  passed over the tip of South America around September 26 to 28, October 9, 16 to 19.  The edge again passed over this area from November 7 to 8.  Significant differences between the various satellite analyses of ozone distribution remain.

Although the amount of ozone destroying substances in the atmosphere is going down, the inter-annual variation in the size and depth of the ozone hole is largely controlled by the meteorological conditions in the stratosphere.  This year the polar vortex was cold and stable, allowing substantial ozone depletion.  It is still too soon to say that we have had the worst ever ozone hole.

The northern circulation pattern is beginning to enter the summer mode, with peak ozone levels declining.  Minimum temperatures were close to the seasonal extreme in late 2011 and well below the PSC formation temperature, but a spring warming in mid January pushed them above the threshold.  Arctic ozone levels are within 30% of normal, with areas that are higher and lower than the mean.  There was substantial Arctic ozone depletion over the northern winter of 2010/11, particularly in March 2011.   

See the final situation report for last year for information on the 2010 - 2011 season.

Notes:  The Antarctic ozone hole is usually largest in early September and deepest in late September to early October.  September 16 is world ozone day, and in 2009 the final UN Member State to ratify the Montreal Protocol signed up.  2007 was the International Year of the Ozone Layer.  Prior to the formation of ozone holes, Antarctic ozone values were normally at their lowest in the autumn (ie March).  

Click on a thumbnail to get the latest graph or high resolution image, which is updated more frequently than the thumbnails.  

Halley - Total ozone:  The observing season at Halley began at the start of September with the station already experiencing ozone hole conditions, and mean values around 190 DU.   Relatively less depleted air was over the station in early September, but mean values began to drop significantly and had reached 125 DU (60% depletion) by the end of the month.  Mean values rose during October, though the seasonal daily minimum of 106 DU (65% depletion) was reached on October 4.  Ozone values reached the ozone hole threshold of 220 DU (40% depletion) by the end of November, and peaked at around 300 DU (12% depletion) around Christmas.  Values slowly fell to reach around 260 DU (15% depletion)  in mid April, which was the end of the observing season.  The maximum value reached since the equinox is 314 DU on December 19.  Note: the instrument constants for #73 were revised in 2012 February, and the above values have been updated to reflect the improved calibration.  Dobson 31 began observations on February 4 and became the operational instrument on February 14 when observations with Dobson 73 ceased.  The zenith calibration of #31 needs improvement, so the figures from mid February onwards will be revised when enough data has accumulated. 

Rothera - Total ozone:    Real-time graphs showing current ozone and NO2 levels.   Mean values slowly declined from around 300 DU at the beginning of 2011 to around 285 DU in mid June, though with an excursion to around 270 DU in the first half of March.  Values began to drop quickly in July and there were brief excursions to ozone hole levels on July 1 and at the end of the month.  Mean values had reached 160 DU by mid September, and then slowly declined to reach 140 DU by late October when a rise to 175 DU took place.  Values fell to around 160 DU in November and then slowly rose back to 175 DU before rising rapidly to 310 DU by the end of the month.  The rise continued more slowly and values peaked at around 345 DU in mid December.  Values fell to around 255 DU towards the end of the year as a remnant of low ozone passed over the station, before rising to 300 DU at year end.  They began 2012 at around 295 DU and had slowly declined to 270 DU by early May, with fluctuations on a timescale of around 20 days.  Since then values have risen to around 320 DU.  The lowest daily value recorded this season was 116 DU on September 28.  The highest daily value since the spring equinox is 354 DU on December 12.  Surprisingly, the low values that were seen in early August were not captured by most of the analyses, with only TOAST giving values close to the observed 178 DU. Superimposed on the general trends are fluctuations with periods of days to around a month and values can change by over 50% in a few days in the spring when the polar vortex rotates across the station.  Some data was lost following a station power down in mid June and the data between June 16 and 29 may have errors.

Vernadsky - Total ozone:   Vernadsky station is run by the National Antarctic Scientific Centre of Ukraine.    The observing season at Vernadsky began in late July, when mean values were around 250 DU (20% depletion).  During August they remained around 240 DU but fell to ozone hole levels in early September and had reached around 180 DU by the middle of the month (45% depletion).  Values varied around this level until late October, before a rapid rise to 240 DU (35% depletion).  Values fell again in November to around 185 DU (50% depletion) in mid month, but then rose, reaching 305 DU (20% depletion) in early December.  A slower rise continued, and values peaked at around 330 DU (5% depletion) mid month.  Values irregularly fell, with occasional rises to near normal levels, to reach around 270 DU (15% depletion) by the end of April.  There were brief sharp rises during the spring period, with daily values reaching 309 DU on September 24, 335 DU on October 29 and a peak of 350 DU on December 13.  The lowest daily value recorded this season was 134 DU on September 28.  Superimposed on the general trends are fluctuations with periods of days to around a month and values can change by over 50% in a few days in the spring when the polar vortex rotates across the station.  

Temperature and PSCs:   The 100 hPa pressure level is near the base of the ozone layer, but is reached by most radiosonde flights.    The temperature at this height is sufficiently cold from July to October that polar stratospheric clouds (PSCs) can form.   Note: "the normal" is used to refer to the long term mean for the time of year.

Both Halley and Rothera have seen displays of nacreous clouds; they were seen from Rothera on 2011 June 26, July 5, 30, 31, September 22, October 28.  Those at Halley are of the form described during the IGY as "ultra-cirrus".  The 2012/13 season began early at Rothera, with sightings on May 30, 31, June 13, 26.

Halley - 100 hPa temperature:  The 100 hPa temperature was generally a little below the normal during the autumn and close to the normal during early winter.  Temperatures during August and September remained roughly around -82°C, and whilst close to the normal early in the period, were 3° below it by the end.  From mid September to early November the temperature rose rather slowly and was substantially below the normal.  There was a more rapid rise until the December solstice, when it reached -46°C, which is some 5° below the normal.  It then rose rather more slowly to reach -42°C in late January, which is near the normal for this time of year.  It is now falling and had reached -60°C by the end of April.  It remained significantly below, and occasionally close to, the normal from September to March.

 Peninsula - 100 hPa temperature:   The mean 100 hPa temperature in the Antarctic Peninsula  has mostly been below the normal since May.  The temperature is normally at its lowest at the end of August at around -76°C.   At -78°C it was significantly below the normal in the first half of August, but returned to near normal late in the month.  It then dropped back to around -79°C in September.  A slow and irregular warming began in October, becoming more rapid from mid November, with the mean temperature reaching near normal levels around -44°C in early December.  It fell, declining to around -49°C after the solstice, but then slowly rose reaching around  -44°C in early February, close to the normal.  The temperature is now falling and had reached -59°C by the end of April.  A short-lived spring warming occurred at the end of October.  The temperature was substantially below the normal during September, October and November.  There is often large day to day variation because the area is in the edge region of the circumpolar vortex.  

Satellite: Satellite imagery gives a global perspective on the ozone hole, though there are notable differences between the different satellites, demonstrating the need for verification by ground based stations.  Our 2011/2012 Antarctic ozone hole movie is produced from OMI images, which are generally well calibrated with respect to ground based measurements.   The NCEP and KNMI analyses are shown on the Canadian Met Service daily ozone maps pages.  The KNMI model is generally better at analysis and forecasting in the Antarctic.   In general the NCEP analysis in the Southern Hemisphere tends to over-emphasise ozone depletion and the forecast further increases the amount of depletion, but on occasion (for example in early August 2011)  also ignores real ozone depletion.  The SMOBA and TOAST analyses both use SBUV and TOVS data, but the TOAST algorithm may at times over-estimate ozone depletion.  US NWS CPC plots from NOAA show the current area of the ozone hole.  The Sciamachy uv index from the ESA  Tropospheric Emission Monitoring Internet Service shows the exposure risk at any location.