-10 -
Since the vertical diffusion is very slow in the stratosphere
and the north-south mixing possibly slow¢ér-than—the—troposphere,
the meridionsl circulations may become important instruments for
the transfer of the debris. In the next figure, sre four published
models of meridional circulations in the lower stra tosphere,
The
models of Wulf, Goldie and the lower part of Palmsr display 8 cell
which calls for sinking motion in the equatorial area, rising
motion over the poles and appropriate north-south motions to
complete the cells,
The Palmar model suggests that above 89,600
fect in the tropics, there is a reversal to rising motion,
Kellogg and Schilling indicate that the main north-south drift
will be from the sumar toward the winter hemisphere. It should
be remembared that the magnitude of the air motions associated with
arrows on this figure are exceedingly small compared to the weste
east air motions; centimeters per second or less compared to
msters or tens of meters per second.
There is nothing unique about the problem of mixing across
the tropopause.
It is probable that the tropopause is the
separation between fast and slow vertical mixing, but in itself
represents no unusual barrier.
In addition to gir exchange through
eCsa.pe trom The Sptpheve
the tropopauss, there are other possibilities,
As was evident from
many of the figures, the tropopause 4s believed to have a break
in the temporate latitudes and the air exchange may occur here
without any crossing of a tropopause.
Secondly, in the courses of
everycay weather the tropopause disappears and reforms at different
altitudes so that exchange of tropospheric and stratospheric can
take place again without crossing the tropopause.
Finally, in the
polar areas the tropopause is often very indistinct and this
.with the expected sinking rotion over cold sources suggests
combined
thet=anZeh possibility that the polar areas may be a rezion of
transport from stratosphere to troposphere.