cogitator: "...it is also true that the stratospheric ice clouds that form in the Antarctic polar vortex are the catalytic surfaces that enable ozone destruction by CFCs."
To my knowledge, it has never been shown that CFC's themselves destroy ozone, rather it is the chlorine atoms, that allegedly originated from CFC's, that have been shown to be one mechanism of O3 breakdown. The problem with ascribing this breakdown to CFC's is that natural sources of chlorine outweigh those from CFC's by many orders of magnitude.
I knew and spoke often with the manager of the U-2 environmental recon program run by NASA out of Moffett NAS here in Silicon Valley. His squadron was the one that did the high altitude sampling out of Norway over the north pole. When he returned from that mission, I asked him if they sampled CFC's in the upper stratosphere. He said yes, they had. I asked him again, are you sure you mean CFC's or do you mean chlorine that you attributed to CFC's. He corrected himself and said that it was actually only the chlorine they were detecting, but that he was sure that it had to have come from CFC's!
cogitator: "However, it is hard to reconcile what Dobson wrote with the Halley Bay data that doesn't show seasonal ozone depletion over Antarctica prior to about 1965."
First, the Halley data doesn't extend back far enough in time to state that there was no ozone thinning prior to 1965. Second, one of the greatest mistakes of scientific experimentation, is to ignore data that doesn't fit with expected results. That Dobson's data is at variance with the Halley Bay data, merely underscores the depth of our own ignorance of the part ozone plays in atmospheric chemistry. To me, the difference in the data sets simply implies that a natural variation in polar ozone levels exists and requires further study to find out how much a variation, what is its period and what causes the periodicity.
The discovery of periodic ozone depletion is not unlike Galileo's discovery of sun spots. Prior to that discovery, the sun was believed to be perfect and unblemished product of God's handiwork. Can you imagine the panic when these blemishes were discovered. And even worse, the finding that year by year, the number, size and frequency of those sun spots continued to increase? OMG, the sun's going to be entirely covered with them if this keeps up!
That is precisely where we are today with the discovery and controversy surrounding the periodic changes in ozone levels. The problem though, has been compounded and the science essentially stopped in its tracks, by this nonsense that the thinning is caused by CFC's.
cogitator: "The graph posted shows an approximate decline in October ozone concentrations by a factor of 3 in the 'hole'." It boggles my mind that Dobson saw larger ozone variability than that."
The quote from your post #78 referred to "a dramatic loss of ozone" that occurred just during the 1970's and that decline was far less than the "factor of 3" you mention. Not only was the 1970's decline, that was described as being a "dramatic loss", only a 75 DU decline, but it was even less than the 0.1cm (100 DU) variability that Dobson observed in the 1920's. So by that standard, the variability observed by Dobson was not only "large", but indeed, it was "a dramatic loss" of ozone way back in 1929!
cogitator: "I wouldn't be surprised if such periodicity could be shown, but there isn't any data to indicate that it has happened."
The only way that you can assert that there isn't any data to support a natural variability, is to ignore Dobson's data from the 1920's. Absent any concrete evidence that his data was flawed, it is dangerous and highly speculative to ignore it simply because it doesn't support someone's expectations.
cogitator: "I find it doubtful that Dobson observed larger variability than exists in the ozone hole today."
Nor is it necessary to assert that it was larger then. It is sufficient for the moment to simply state that the scientific record (Dobson) contains reliable and unrefuted data that shows a large natural seasonal variation (0.1 cm or 100 DU) in atmospheric ozone does occur and that it was first detected prior to the introduction of CFC's.
As a parting note, have you noticed in the TOMS photos, that while there is a seasonal thinning over the South pole, there is a commensurate increase in ozone levels in areas immediately adjacent to the Antarctic? (examples here) In other words we may be witnessing an ozone transport event, rather than a genuine thinning.
Please forgive the length.
--Boot Hill
You are both correct and incorrect. Natural sources of chlorine are much larger, but those sources do not contribute Cl to the stratosphere. Because CFCs do not break down easily, they reach the stratosphere (and NASA instruments on the UARS satellite measure CFC concentrations directly -- I can provide a graphic image if you want one), where they are subject to energetic reactions due to high-energy solar radiation (the same thing that makes ozone, ironically). That breaks them down into various chlorine compounds (which were also measured by UARS instruments), which then participate in the ozone-destroying reaction pathway.
If you would read the Web site that I provided, you would learn all of this.
First, the Halley data doesn't extend back far enough in time to state that there was no ozone thinning prior to 1965. Second, one of the greatest mistakes of scientific experimentation, is to ignore data that doesn't fit with expected results. That Dobson's data is at variance with the Halley Bay data, merely underscores the depth of our own ignorance of the part ozone plays in atmospheric chemistry. To me, the difference in the data sets simply implies that a natural variation in polar ozone levels exists and requires further study to find out how much a variation, what is its period and what causes the periodicity.
The Halley Bay data goes back before 1965. Dobson's data definitely shows seasonal variability, and there are obvious reasons for that, but it doesn't show the level of ozone depletion that was observed in the Antarctic over Halley Bay. The decline began in the 1970s, and is now much larger than 100 DU (0.1 cm, according to you).
Nor is it necessary to assert that it was larger then. It is sufficient for the moment to simply state that the scientific record (Dobson) contains reliable and unrefuted data that shows a large natural seasonal variation (0.1 cm or 100 DU) in atmospheric ozone does occur and that it was first detected prior to the introduction of CFC's.
Nonsense! There is seasonal variability. It's called the Brewer-Dobson circulation pattern (and to your credit, I had to brush up on something that I learned ten years ago and forgot).
Here's what you need to do. Read the Web site provided below. Take your time. Take a week, or at least a weekend. Become acquainted with all that is now known about ozone in the atmosphere (you may be surprised). Then please reply to me and tell me if your knowledge has changed. If it hasn't, then there is nothing I can do in a piecemeal fashion that would be better than the comprehensive treatment below. (Note that the Web site includes the measurements of stratospheric CFC concentrations which I referred to earlier.)
Stratospheric Ozone: An Electronic Textbook
Finally, you wrote: As a parting note, have you noticed in the TOMS photos, that while there is a seasonal thinning over the South pole, there is a commensurate increase in ozone levels in areas immediately adjacent to the Antarctic?
It's a consequence of the air mass isolation in the polar vortex. Because ozone that is being produced in the lower latitudes cannot mix into the vortex area, it builds up (the atmospheric circulation pattern gets "dammed up" against the polar vortex wall. One of the reasons that the ozone hole disappears so rapidly when the vortex circulation breaks up is that this higher concentration of ozone mixes in quickly.