July 1964 E. K. Bigs 355
Correspondence
GEOGRAPHICAL DIFFERENCES IN CONCENTRATIONS OF ICE NUCLEI
E. K. BlGG
Radiophysics Laboratory, CSIRO, Sydney, Australia
ABSTRACT
On the basis of mising chambcr ni~asureni~nts of the conccntrations of ice nuclci a t Mauna Lao it is suggcstcd
that Kline's conclusion that the counts mcrc conspicuously lower than elsewherc, may h a w bccn instrumental in
origin.
Kline [I] discussed the results of a program of measure-
mcnt of ice nucleus conccntrntions a t 15 observational sites
in tlic United States using expansion counters and con-
cluded that they showed a dominant contribution by
terrestrial aerosols to the ice nucleus budget of the l o ~e r
atmosphere. This conclusion hinged on very extensive
nieawrements a t the high altitude obscrvntory (11,150 ft.)
on Rlauna Loa, Hawaii, which for a lnrge part of most
10
10
7
J
UI
0
UI
x L 0
(Y U
d
Y
-
10'
10-
x 4
I I
-14 -16 -18 -20 -22 -24 -26
Temperature , O C
(a )
0
07 0 4
0
0 4
X7
do x6 d
0 5
0 4
I 09 I I I I I I -14 -16 -18 -20 -22 -24 -26
Temperature, O C
( b )
FIGURE l.-(a) Mean of all ice crystal measurcnicnts by 1' C. intervals, a t Mauna Loa (x) Hilo (0 ) and for comparison, Sydney (solid line)
(b) Measurements of ice crystal conccn- 1956-57.
trations a t Mauna Loa in up-slope (0 ) and down-slope n-ind conditions (x).
The nuinbers are the number of nicasurements corresponding to each point.
356 MONTHLY WEATHER REVIEW Vol. 92, No. 7
days is well above tlie trade wind inversion. The fact
that counts were a fnctor of 10 lower thnn those madc a t
Hilo (near sea level on the same island) and a t all mainland
sites appears strong evidence in favor of this conclusion.
In order to operatc the counter successfully i t is neccs-
sary that the humidity within it should esceed water
saturation during the expansion and that the cloud which
forms should be stable for a t least a minute. Otherwise
ice crystals will fail to grow large enough to reach the de-
tecting solution a t the bottom of the chamber in the avail-
able time and an undcrcount will result.
Although pure glycerine is used on the walls to prevent
frost, the ambient clew point is usually sufficiently high for
its surface layer to become diluted during the period when
the air in the chamber is changed, and i t does not thercfore
depress the humidity unduly. When the dew point of
the outside air is less than the wall temperature of about
-10’ C. this does not happen and there is a risk of mi
undercount. Since the dew point on Mauna Loa, alone
of all the stations, is commonly less than this escept in the
afternoon, i t is essential to test mhcther a technique in
which moisture is addcd to the cold chamber for ench
experiment yields the same answer.
With the kind cooperation of MI.. Jack C. Pales (then
Physicist in Charge a t MtLuna Loa) and Mr. Kline, such
t~ check was made in August 1963.
T n the short time available the most important esperi-
nients were (a) to take measurements a t hlIauna Loa Ob-
servatory and a t Hilo with as little time separation as
possible; (b) to compare iiieasurements made a t the Observ-
atory in descending air (night and early morning) with
those made in rising air during the dternoon. The cs-
pansion instrument mas simply used as a mixing chamber,
by varying the \vall temperature in small steps, moisture
being added after each change of air.
Measurements were made from 1700 LST on August 16
to 0800 LST on August 19, with the exception of about
eight hours ewh night, and from 1100 to 1600 LST August
19 a t Hilo. The results are shown in figure 1 (a) and (b).
C1e:trly there is no appreciable difference among the
v:Lrious sets arid they are also remarkably similar to
mean values found a t sea level in AustraliiL, curves of which
have been publislied by Bigg and Hopwood [2].
This does not menn that Kline’s conclusions are wrong,
for there is always the chance in reltitively short sequences
of observations that tlie period wtis not a typical one.
It does suggest, however, that his conclusions cannot
be regarded as proven until a careful assessment is made
of why different techniques yield such different answers.
REFERENCES
1. D. B. Kline, “Evidence of Geographical Differences in Ice
Nuclei Concentrations,” Monthly ll’eather Reuiew, rol. 91,
2. E. IC. Eigg and S. C. Hopwood, “ICC Nuclei in the Antarctic,”
Journal o j the Atmospheric Sciences, vol. 20, No. 3, May 1963,
NOS. 10-12, Oct.-Dcc. 1963, pp. 681-686.
pp. 185-1ss.
[Received April 1, is641