The size of the ozone hole fluctuates on a regular basis. From August to October, the ozone hole increases in size—reaching a maximum between mid-September and mid-October. When temperatures high up in the stratosphere start to rise in the southern hemisphere, the ozone depletion slows, the polar vortex weakens and finally breaks down, and by the end of December ozone levels return to normal.
DB2
Lead author Hannah Kessenich, PhD candidate in the Department of Physics, says they found there is much less ozone in the centre of the ozone hole compared to 19 years ago. “This means that the hole is not only larger in area, but also deeper throughout most of spring.”…
“More study is warranted to determine the precursors for the changes we identify…”
DB2
At least one cause is illegal CFC emissions from China.
In addition to not shrinking in area, the minimum concentration hasn’t been increasing. Here is a graph of the annual minimums:
DB2
I may be missing something, but I do not understand why they use the term “Minimum”. Is that shorthand for minimum average?
I reviewed the paper at the link, but it appears that the methodology for measurement was not included in the author’s summary or working practices.
IIRC, it is the lowest level each year of the ozone concentration in DU (Dobson Units) at the South Pole. The OP of this thread looked at the size of the depleted zone (which has not really been shrinking).
DB2
Another fall has cycled through and the ozone hole remains stubborn. Over the last 20 years the trend of maximum area is slightly down (-0.18 million sq km/year) but the trend is not statistically significant (p=0.23).
https://ozonewatch.gsfc.nasa.gov/meteorology/figures/ozone/to3area_0907-1013_toms+omi+omps.txt
DB2
Has it grown? Was it growing prior to some materials, like Freon, being banned? Is the first step, when you find yourself in a hole, to stop digging?
Steve
It is about the same, I believe. The reason is in the first post in this thread:
Greenhouse gases to have a cooling effect in the middle and upper stratosphere which leads to ozone depleting conditions in the polar regions.
