10 But I heard that Dobson saw an ozone hole in 1956-58...
Description
This article is from the Ozone Depletion: The Antarctic Ozone Hole FAQ, by Robert Parson rparson@spot.colorado.edu with numerous contributions by others.
10 But I heard that Dobson saw an ozone hole in 1956-58...
This is a myth, arising from a misinterpretation of an out-of-
context quotation from a review article by Dobson.
In his historical account [Dobson 1968b], Dobson mentioned that
when springtime ozone levels over Halley Bay were first measured,
he was surprised to find that they were about 150 DU below
corresponding levels (displaced by six months) in the Arctic.
Springtime arctic ozone levels are very high, ~450 DU; in the
Antarctic spring, however, Dobson's coworkers found ~320 DU, close
to winter levels. This was the first observation of the _normal_,
pre-1980 behavior of the Antarctic ozone layer: because of the
tight polar vortex (see below) ozone levels remain low until late
spring. In the Antarctic ozone hole, on the other hand, ozone
levels _decrease_ from these already low values. What Dobson
describes is essentially the _baseline_ from which the ozone hole
is measured. [Dobson 1968b] [WMO 1989]
For those interested, here is how springtime antarctic
ozone has developed from 1956 to 1995:
..............................................................
Halley Bay Antarctic Ozone Data
Mean October ozone column thickness, Dobson Units,
as measured at the British Antarctic Survey station
at Halley Bay (Latitude 76 south, Longitude 26 west)
1956 321 1971 299 1986 248
1957 330 1972 304 1987 163
1958 314 1973 289 1988 232
1959 311 1974 274 1989 164
1960 301 1975 308 1990 179
1961 317 1976 283 1991 155
1962 332 1977 251 1992 142
1963 309 1978 284 1993 111
1964 318 1979 261 1994 124
1965 281 1980 227 1995 129
1966 316 1981 237 1996 139
1967 323 1982 234 1997 139
1968 301 1983 210
1969 282 1984 201
1970 282 1985 196
Data from J. D. Shanklin, British Antarctic Survey, personal
communications, 1993-95. For published graphs, see
[Jones and Shanklin], [Hamill and Toon], [Solomon], or
[WMO 1991], p. 4.6. The original Farman et al. figure, which
includes the years 1957-84, is available on the web at
http://www.atm.ch.cam.ac.uk/images/easoe/total_ozone.gif
An updated version can be found on the British Antarctic Survey
web site: http://www.nbs.ac.uk/public/icd/jds/ozone/
Bulletins showing daily ozone measurements at Halley Bay and
at Faraday Station can also be obtained through this web site.
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