382
MACHTA
the mean residence time on the assumption that the loss is due to transfer into the troposphere. Finally, a less reliable technique, but one
which is independent of stratospheric inventories, compares the observed deposition during two successive years. The decrease in the
annual fallout amount suffices to fix both the mean residence time and
the stratospheric content with an assumption of an exact exponential
decrease in the stratospheric burden with time. This last procedure has
provided anomalous results in he period 1960 and 1961 (but before the
resumption of tests) when the annual fallout rate during the second year
was equal to or greater thanthefirstyear. As already noted, the amount
of ‘Rh increased between the first and second yearof fallout, giving
rise to a negative mean residence time.
Some of the deficiencies of the simple exponential model may be
corrected by several empirical procedures that can incorporate fallout
experience and some meteorological thinking. The first attempts to do
this were made by Machta,” as illustrated in Fig. 8 to 11. In Fig. 8 the
Stratosphere is subdivided into a series of boxes, each representing a
characteristic removal rate. It is argued that empirical knowledge can-
not justify further subdivision at this time. The time history of the
lower equatorial and the lower northern-hemisphere polar stratosphere
appear in Fig. 9. The vertical bars delineate the spring seasons during
which the maximum fallout rates are expected. It may be noted that a
much greater fraction exits from the stratosphere in the first year
200 rf
o
iL
u 120
o
“
|
|
3 80
x
LOWER
POLAR
oltt |
90PN 60°N
tf
|
UPPER EQUATORIAL
|
'
A
<
|
t
~—_—UPPER
POLAR
9
Z
|
A
|
|
30°N
{
l
UPPER
POLAR
|
B
|
t|
A
LOWER EQUATORIA
(eR
EQUATORIAL
|
B
|
iis A
MEAN TROPOPAUSE
|
of
of
o
LATITUDE
—
ft
LOWER
POLAR
ft ft
30°S
jt ft tt
60°S 90°S
Fig. 8—Schematic subdivision of stratosphere into regions having
characteristic removal rates.