(Source: DLR, KNMI, ACRI)
The ozone hole is not always present. It is formed in August when the light returns to the cold winter Pole and when the catalytic processes involving chlorine and bromine rapidly destroy the available ozone. The ozone hole disappears around November-December when the stratospheric vortex - which traps the ozone depleted air - is warming up and becomes unstable. Figure 1 (left) shows the thickness of the ozone layer in September over the Southern Hemisphere, with a large ozone hole which is characteristic for the period 1990-present, coinciding with the cold polar vortex.
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Figure 1. Left: Ozone hole on 26 September 2003, derived from SCIAMACHY ozone column observations. Right: Break-up of 2002 ozone hole in September 2002, as derived from GOME observations. Shown is the thickness of the ozone layer over the South Pole on 26 September. Scale in Dobson units (DU). |
In figure 2 the evolution of the ozone hole over the past ten years is shown. It demonstrates this characteristic development between August and December, with a maximum size around the first of October. The year 2002 is a clear exception. During this year the vortex broke up in September (see figure 1, right), an event which is referred to as a sudden stratospheric warming. Such warming events are well known from the northern hemisphere, where it occurs every few years. In the southern hemisphere, however, this event is completely unique and has not been observed before as far back as routine measurements over Antarctica are available, since the 1950s.
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Figure 2: Evolution of the surface area covered by the ozone hole, combining measurements from GOME and SCIAMACHY. The ozone hole is defined here as the area where the total column of ozone is less than 200 DU. |
More information about teh recent situation of the ozone hole can be found in our special ozone bulletin.. This bulletin also includes the UV radiation at the South pole and a historic archive of images.
These instruments sound the atmosphere at the Earth’s limb. While MIPAS measures emissions of molecules in the infrared, SCIAMACHY in limb mode is sensitive to backscattered solar radiation in the UV and visible part of the spectrum. The gathered spectra at different altitudes enable to retrieve a plenitude of chemical constituents of the atmosphere.
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Figure 3 shows the split of the Antarctic polar vortex on 26 September 2002 at 56 hPa as analysed by assimilating MIPAS ozone and ClONO2 observations. |
All MIPAS and SCIAMACHY limb observations are assimilated using the chemistry-transport model ROSE/DLR in order to derive consistent global chemical analysis of the stratosphere (Figure 3). The focus is on a multi-year ozone record. MIPAS observations of O3, H2O, HNO3, CH4, N2O and NO2 are considered as well as O3, NO2 and BrO of SCIAMACHY. Sequential assimilation is performed using an optimum interpolation scheme with error propagation and Chi² diagnostics. The assimilation system contributes significantly in fulfilling the general objective to better monitor and study the chemical composition of the middle atmosphere.
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Figure 4: The ozone hole variations in 2003 observed by GOMOS (aboard ENVISAT) and assimilated in a chemistry - transport model. The originality of the GOMOS instrument is that it sounds the atmosphere by measuring the light of a star filtered by the atmosphere while setting down at the horizon. GOMOS has a twin brother on board the Mars Express that performs the same job on Mars. |
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The movie shows the Antarctic total ozone distribution from July to December 2002 based on assimilated GOME observations. The variability of the total column in time and space governed by atmospheric dynamics is striking and peaks in the split up of the polar vortex on September 25. |
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Figure 5: ESAs Global Ozone Monitoring Instrument (GOME) has been successfully monitoring the Antarctic ozone hole since 1995. The image shows the total ozone monthly means for September from 1995 to 2004. This long-term monitoring reveales the ozone hole variations from year to year that result from coupled chemical-dynamical processes. From 2002 on GOME is supplemented by SCIAMACHY. |
Ronald van der A, Thilo Erbertseder, Henk Eskes. Last modified: June 2005