SESSION IIIB DISCUSSION
695
obtain approximate estimates of the transient-eddy momentum trans-
ports
over
North America to 60 km; with only two stations in the
southern hemisphere, we can make no comparison between hemispheres.
Ozone transports over North America to about 30 km are available
from Hering’s work. Since most of the seasonal ozone change occurs
in the height interval of 10 to 25 km, one does not need to know the
circulation changes above 25 km to account for the spring maximum
in ozone.
In the case of fallout, events are a little more complicated. We
argued at the conference here in 1961 that the spring maximum was
due to extra mixing in the lower stratosphere in late winter which
brought debris down to the region above the middle-latitude tropopause from where it could excape into the troposphere by the processes
discussed by Danielsen and Reiter. We felt that seasonal changes in
the lower stratosphere rather than seasonal changes in these processes accounted for the spring maximum.
An additional item that is involved when one considers the magni-
tude of the fallout maximum rather than ozone is the availability of
material at about 25 km to be mixed downwards. This availability
obviously depends on the testing pattern and on mixing above 25 km.
Thus eventually we would like to compare meteorological observations above 25 km in both hemispheres.
REITER: Dr. Newell mentioned the upper stratospheric circulation in winter, and this leads into another question I wanted to ask
Dr. Danielsen about the transport processes induced by the jet stream.
It is quite possible, in my opinion, that the polar night jet stream might
have a Similar dynamic effect on vertical debris transport in the
stratosphere as has the tropopause jet stream for transport processes
from stratosphere to troposphere. Unfortunately, at this time I don’t
think there is sufficient data on the polar night jet stream to allowa
sophisticated treatment of its dynamics. It should be very worthwhile,
however, to tackle this interesting problem.
DANIELSEN: I agree with Dr. Reiter on the need for studying the
polar jet. I cannot contribute anything on that subject, but I would like
to hazard an interpretation of the data Dr. Volchok presented today.
He showed that the values of surface-air radioactivity first exceeded
the normal during January and February at low-latitude stations
(10°N) in the northern hemisphere, i.e., midwinter in the northern
hemisphere. In contrast, the corresponding increase in the southern
hemisphere was in September and October, i.e., spring in the southern
hemisphere, The bimonthly profiles of excess concentrations of Sr
for the two hemispheres matched with an eight-month lag (northern
to southern) rather than with a six-monthlag.