February
1973
AS.
Nucleation
Ramachandra
Behaviour
in the
Murty
and
Bh.
of Iodide
Presence
V.
Ramana
and
of soluble
Murty
Iodate
61
Systems
salts
By A.S. Ramachandra Murty and Bh. V. Ramana Murty
Indian Instituteof TropicalMeteorology,Poona-5,India.
Abstract
Using a simple drop-freezingtechnique as in earlier studies, the ice nucleationactivitiesof
certain iodide and iodate systems,with and without solublesalts, have been investigated. It has
been found that, of the systemstested, the iodide systemscommonlyused in the conventional
cloud seeding,which are AgI.NaI and AgI.KI, are the least active. Also, the iodate system
used in the pyrotechnicseeding,which is AgIO3+KIO3,is not the most active. Betternucleating
systemshave beennamedfor possibleuse in both the types of seeding. The comparativeactivities
noticed of the systemstested have been explainedon certain qualitativeconsiderations.
1.
Introduction
Identification of particles which will nucleate
supercooled drops to ice crystals, at warm temperatures, is of primary importance in studies of
weather modification. Acetone solution of AgI
using NaI or KI or NH4I as solubilizer and
pyrotechnic mixture using AgI03 or AgI03 + KIO3
are the commonly reported silver iodide and
iodate systems respectively for production of such
particles.
From the experiments, using wind
tunnel and cloud chamber facility for measurement,
the silver iodide system using NH4I was found
to be more active for ice nucleation than the one
using NaI (St. Amand et al., 1971). The present
authors, using a different technique of measurement, which is drop-freezing, and unaware of the
results referred to above, reported on the nucleation
activities
of
silver
iodide
systems
(Ramachandra Murty and Ramana Murty, 1971)
which also pointed out that the one using NH4I
is most active followed by those using NaI and
KI. This feature is now confirmed. Using that
same technique, the authors, in an earlier study,
examined the nucleation activities of silver iodide
suspensions containing certain soluble salts; and
the study suggested that whereas the presence of
sulphates improves the nucleating activity of the
silver iodide suspension, that of the chlorides
decelerates it (Ramachandra Murty and Ramana
Murty, 1972a). This aspect is now thoroughly
examined. Also, the nucleation activity of iodate
systems has been studied.
These investigations
have enabled the sorting out, according to activity,
of the various iodide and iodate systems which
have been tested.
The results obtained are
presented below. While no explanation had been
offered while reporting the results referred to
earlier (Ramachandra Murty and Ramana Murty,
1971 and 1972 a), attempt has been made now to
explain qualitatively the results obtained so far.
2.
Measurements
The equipment and the technique of measurement are as described earlier (Ramachandra
Murty and Ramana Murty, 1971 and 1972b). The
salient features are as follows : Drops of diameter
2.2 mm from the systems (aqueous suspensions)
to be tested are placed in equal numbers of 30
each in two identical metal dishes. The dishes
are sealed with glass covers and then cooled by
transferring both of them simultaneously on to a
cold stage which has been kept cooled, initially,
to any of the pre-determined temperatures -3°C,
- 5°C and -10°C . The number of drops freezing at successive one-minute time intervals is
noted with naked eye until all the drops taken
in both the dishes have frozen. The fractions of
drops frozen at successive time intervals and the
total time taken for all the 30 drops to freeze,
for each of the systems tested, formed the basic
data for the study. For the initial temperatures
of the cold stage which are referred to above,
i.e. -3°C, -5°C and -10°C, the dishes attained,
62
Journal
of the Meteorological Society of Japan
Vol. 51, No. 1
in the quasi-equilibrium conditions, temperatures
which are respectively -2.7°C,
-4.7°C
and
-9 .8°C. The temperatures are measured by
thermocouples, using SWG-36 copper-constantan
wires, at successive one-minute time intervals.
cloud chamber (Mason and Van Den Heuvel,
1959). The results on AgI and PbI2 have been
obtained earlier and reported (Ramachandra Murty
and Ramana Murty, 1972b). These along with
the results now obtained on CuS are presented
in figure 1 and summarised in Table 1. These
3. Reliability of measurements
experiments have been conducted with the cold
The reliability of the present measurements for stage initially at -10°C.
the purpose of comparing the ice nucleation
The temperatures found of the first freezing
activities of substances has been ensured. This is event for the suspension drops containing AgI,
done by testing on substances about the threshold PbI2 and CuS are -4.2°C, -6.5°C and -6.8°C
nucleation temperatures of which there is general respectively, and these values agree closely with
agreement. The substances considered are AgI, the accepted threshold temperatures referred to
PbI2 and CuS for which the threshold temperatures
above for these substances. Also, the total time
quoted are -4°C, -6°C and -6°C (vide Mason, taken for all the drops to freeze was found to
1971). These substances have been tested using be minimum in the case of AgI and maximum
aqueous suspensions of 1 % concentration, for the in the case of CuS. The findings confirm that
threshold nucleation temperatures found at 1
the temperature of the first freezing event as well
concentration for different substances in bulk as the total time taken for all the drops to freeze,
water (millimeter drops) agreed closely with those as from the present study, serve as indicators
found for the respective substances in conventional of the comparative nucleation activities of given
substances.
4.
Fig.
1.
Fraction
of drops frozen with the
cold
stage
initially
at
-10°C.
Temperatures
intervals.
Table
1.
Freezing
characteristics
of suspension
drops
of various
composition
when
the
* Generally
are given at 5 minute
cold stage initially
accepted
threshold
was at -10°C.
temperature.
Nucleation activities of AgI in the presence of
sulphate and chloride
The effects of sulphates and chlorides on the
nucleation activity of the aqueous suspension
of AgI have been examined. The sulphates tested
are of ammonium, lithium, sodium, potassium,
caesium and magnesium and the chlorides tested
are of sodium, potassium and magnesium. The
results are presented in figure 2 and summarized
in table 2 and these refer to the cold stage temperature initially at -5°C.
It is seen that, whereas the sulphates improve
the nucleation activity of AgI, chlorides do the
opposite. (NH4)2SO4 has been found to improve
the activity of AgI most, followed by Cs2SO4.
Li2SO4 has improved its activity least.
S. Nucleation activity of AgI in the presence of
other iodides (solubilizers)
The effects of various other iodides on the
nucleation activity of the aqueous suspension of
AgI have been examined. The iodides considered
are NH4I, LiI, NaI, KI and CsI. The results are
presented in table 3, and these refer to the cold
stage temperature initially at -10°C.
Except for ammonium iodide, the other iodides
decelerated the nucleation activity of AgI. Lithium
iodide decelerated it least and caesium iodide
most.
February
1973
A.S.
Fig. 2.
Table
2.
Freezing
drops
Ramachandra
Fraction
characteristics
of
various
of drops
Murty
and
Bh.
frozen
with
cold stage
of suspension
composition
V.
Table
Ramana
initially
3.
is 10 gm per litre
salt 0.1 M.
have
now
experiments
stage
* Plus symbol '+'
alone
iodates
at
-5°C.
The
figures
AgI03
than
containing
have
not
are
found
+KI03.
and
results
3b
the
AgI.
with
either
shown
These
the
cold
obtained
and
to
be better
to be
The
combinations
+ KI03
are found
The
are
summarised
triple
alone
All
ice
Also,
ice
to
be better
AgI03
than
the
KI
three
nucleants
than
NaTO3
and
nucleants
than
+NaIO3
and
ice nucleants
AgI03
+ NaI03
combination
combination
or
the
both
better
combination
ice nucleant
The
NaI
freezing.
iodides.
found
AgI03.
a better
3a
with
in
4.
are
AgI.
along
conducted
corresponding
KI03
tested
been
in
Systems
the
been
have
initially
presented
in table
It has been pointed out that the smoke obtained
by burning the mixture AgI03 +KI03 is efficient
for ice-formation, being better than the smoke
obtained by burning AgI03 alone (Odencrantz,
1969). In this operation, the contribution due
to KIO3 separately is, however, not known. The
substances AgIO3, KI03 and NaIO3 and combinations thereof, as well as the substances NaI and
of suspension
The
concentration
of AgI
suspension
is 2 gm per litre.
and of
Iodates versus Iodides
characteristics
drops of various
composition
when
the cold stage initially was at -10°C.
KI,
6.
63
at -5°C.
Freezing
when
the cold stage initially was at -5°C.
The concentration
of AgI
in the
suspension
the soluble
Murty
AgI03
AgIO3
+ NaIO3
indicates that , in the given system, compounds are present, by weight, only in the
stated ratio. For instance, in the system AgI+(NH4)2SO4, the compounds AgI and (NH4)2SO4 are
present in the ratio 1 : 1.
** Dot symbol ' . ' indicates that, in the given system, compounds are present, by weight, in the stated
molar ratio, For instance, in the system 2AgI.NH4I, the compounds AgI and NH4I are pre present in
the ratio of 2 moles of AgI to one mole of NH4I.
is
64
Journal
of the Meteorological Society of Japan
Table
4.
Freezing
Vol. 51, No. 1
characteristics
drops of
the cold
of suspension
various
composition
when
stage
temperature
initially
was at -5°C.
Fig. 3(a).
Fraction of drops frozen with cold
stage initially at -5°C.
No freezing event was observed in the case
of drops containing NaI and KI.
+ KI03 is found
double combination
7.
to be even better
AgI03 + NaIO3.
Nucleation
activity
different sulphates
of
iodide
than
systems
the
with
In an attempt to know the extent to which the
nucleation activity of a given iodide system could
be improved by the addition of a sulphate to it,
measurements
have been made
with various
combinations
thereof.
The sulphates
and the
iodide systems considered
are Na2SO4, K2S04,
Fig. 3(b).
Fraction of drops frozen with cold
stage initially at -5°C.
Fig. 4(a).
(NH4)2SO4
and
AgI.NaI,
AgI.KI,
AgI.NH4I
respectively. The experiments have been conducted
with the cold stage initially at - 3°C on systems
containing
NH4I (these systems show freezing
even at about -1°C),
and at -10°C
on systems
containing
NaI
and KI
(these systems
show
Fraction of drops frozen with cold stage initially at
- 3°C . No freezing event was observed in the case of
drops containing AgI alone.
February
1973
A.S. Ramachandra
Murty
and Bh.
V. Ramana
Murty
65
freezing only below -5°C).
The results obtained
are presented in figures 4a to 4c and summarized
in table 5.
The nucleation activity of the three silver
iodide systems (NH4I.AgI, NaI.AgI and KI.AgI)
improved with the addition of a sulphate to them.
Of the three sulphates considered, that of ammonium rendered the iodide systems most efficient.
The most efficient triple combination is the one
which contained AgI, NH4I and (NH4)2SO4.
Fig. 4(b).
Fig. 4(c).
Table 5.
Fraction of drops frozen with the
cold stage initially at -10°C.
Fraction of drops frozen with the
cold stage initially at -10°C.
Freezing characteristics of suspension
drops of various composition.
The
concentration of AgI in the suspension
is 0.5 gm per litre.
8.
Discussion
8. 1. Materials for producing efficient ice nuclei
Among the substances tested in the present
study, the following is the choice for producing
efficient ice nuclei. If a single substance alone
is to be preferred, it is AgIO3. If it is a combination of two, its ice nucleation activity can be
more than that of the single substance chosen;
and that combination is AgIO3 + NaIO3. If it is
a combination of three, its ice nucleating activity
can be more than that of even the double combination chosen; and that combination is AgIO3
+ NaIO3 +KIO3.
The iodates are used in cloud seeding by pyrotechnic methods. The combination of the iodates
which is reportedly used by such methods is the
double combination AgIO3 + KIO3 (vide Simpson
et al., 1970) and this is now seen to be inferior
to the double combination AgIO3 +NaIO3 which
is itself inferior to the triple combination AgIO3
+ NaIO3 + KIO3. The latter two combinations
could, therefore,
advantageously
replace the
former in pyrotechnic methods. But, there is one
general drawback in the use of iodates.
Iodates
may be reduced to iodides at temperatures at
which pyrotechnic smokes are produced (Simpson
et al., 1970). There is no guarantee, therefore,
that the pyrotechnic smokes of the iodates
produced in the free air would behave as actively
as the aqueous suspensions of the corresponding
iodates. The alternatives which are suggested by
the present authors, therefore, are AgI + NH4I
for the double combination and AgI + NH4I +
(NH4)2SO4 for the triple combination; and these
will be free from such drawback.
No doubt, it has been presumed that in pyrotechnic seeding it is the pure silver iodide smoke
produced which activates ice-formation at as
warm a temperature as -2°C to - 3°C (Elliott
et al., 1971). But, it has been shown that the
66
Journal of the Meteorological Society of Japan
Vol. 51, No. 1
nucleating activity of silver iodide particles made below to the available values of the ionic
decreases with increase of sample purity (Corrin refractions (cc per gram ion) and the molar
et al., 1967). In view of the fact that the iodate refractions (cc per gram mole) as the case may be.
suspensions have now been found to be better
8. 3. Effects of adding sulphate and chloride to
ice nucleants than the corresponding
iodide
drops o f AgI suspension
suspensions, it is considered that the iodates can
be used definitely beneficially in the place of
Water molecule is polar with a formal positive
iodides, only in 'Spray-Seeding'.
charge (0.33e) on hydrogen and negative charge
(0.66e) on oxygen. AgI is a covalent solid and,
8. 2. Ionic polarizability and ice nucleation
therefore, when AgI particle alone is present in
Effects noticed of sulphates, chlorides and other the water drop, water molecules can aggregate
iodides (solubilizers) on the nucleation activity of on the particle both from their O- and H+ ends.
silver iodide and the order in which the iodide Consider the situation when the particle is present
systems, with and without sulphate, and the iodate in the drop along with NaCl in one case and
systems exhibited nucleation activity, require to be along with Na2SO4 in another case. The ions
explained. While it is difficult to visualise a in the ionic pairs formed in the case of NaCI,
rigorous explanation for the features noticed, the Na+(H2O) Cl-, will be closer to each other than
authors have the following qualitative remarks to those formed in the case of Na2SO4, 2 Na+ (10
H2O) SO42-. In the case of Na2SO4, they will
offer.
Ice-formation, on the nucleating substrate, may be far separated
by the large number of
be facilitated by the possible aggregation of water intervening water molecules as against by one
molecules around the adsorbed solute ions present suchh molecule in the case of NaCl. Because of
on the substrate. The extent to which aggregation the closeness of the ions in the ionic pairs in the
of water molecules takes place around the adsorbed case of NaCl, the pairs exert nearly equal and
ion may depend, among other factors, upon the opposite forces on the water molecules, making
polarizability of that ion, its electronic configura- less possible for them to aggregate on the AgI
tion and the polarizing power of the oppositely particle either from their O- end or H end.
charged ion in the pair. It may be noted that, These features would cause the nucleation activity
according to Weyl (1951), a liquid surface consists of AgI + NaCl to be less than that of either AgI
of the most polarizable ions because polarizability
+Na2SO4 or AgI alone.
The SO42- has two negatively charged oxygen
permits an adjustment of the force-fields of the
surface ions and, as a result, a lowering of the atoms and two S = O groups with lone pair of
surface free energy. The implication of this pos- electrons. Water molecule has a lone pair of
tulate, as also discussedby Hosler (1951), is that a electrons on its oxygen atom.
Consequently,
small supercooled drop can be made to crystallize water molecules will be bound strongly to SO42by the addition of foreign molecules or ions that group. The addition of a sulphate to AgI in
reduce the surface free energy of the drop. Since suspension could, therefore, improve the nucleathe amount of surface free energy is a function tion activity of AgI in accordance with observaof the polarizability of the ions, the presence of tion.
more polarizable ions or molecules on the substrate
8. 4. Comparative effects of different sulphates
will reduce the amount of supercooling necessary
to form ice crystals. Based on these consideraOf the sulphates studied, (NH4)2 SO4 Improved
tions it is found possible to account for the the activity of AgI most. The reason for the
observed features in the present study.
observed feature is considered as follows. All
For a series of ions carrying the same charge the cations have structure breaking effect except
it is known that, in general, the polarizability NH4+ which has it the least because of its
increases and the polarizing power decreases with charge being directed tetrahedrally along the N-H
the size of the ion. The value of molar refraction bonds.
of a given substance gives its polarizability.
As
The remaining sulphates tested improved the
the values of neither the ionic radii nor molar nucleation activity of AgI in the following order :
This is
polarizabilities for all the substances tested are Cs2SO4 > K2SO4 > Na2SO4 > Li2SO4.
readily available to the authors, references are also the order in which the values of molar
February
1973
A.S.
Ramachandra
Murty
and
Bh. V. Ramana
Murty
67
polarizabilitythis is the factor which is con- refraction for the iodate and iodide ions reported
sidered responsible for the improvement of the respectively are 17.86 and 17.53 (Heydweiller,
nucleation activity -of
these sulphates lie. The 1925). The iodates should, therefore, lead to
values of the molar refraction, as calculated from more nucleation than the corresponding iodides.
the data of the physical constants, are 27.7, 19.1, Though the difference between reported values of
14.8 and 13.7 respectively for these sulphates. refraction of the iodate and iodide ions is small,
The values of molar refraction which were it may be noted that it is in the right direction
reported for Na2SO4 and Li2SO4 are respectively being consistent with what is anticipated on the
14.7 and 13.8 (vide Heydweiller, 1925).
basis of the present findings.
It is important to note that the substances
8. 5. Effects of other iodides on AgI systems
NaIO3 and KIO3, which are highly soluble, are
When any of the iodides LiI, NaI, KI or CsI found to be better ice nucleants than even AgI.
is added to the AgI system, the resulting complex If it is considered that the observed ice nucleaion formed by adsorption (I-Ag-I)-1 could take tion activity of AgI is due to the combined effect
water molecules from only the H+ end. But, in of its polarizability and its crystal structure, the
the system containing AgI alone, which is neutral, above finding suggests that the iodate ion, on
it has been pointed out that AgI takes water account of its larger polarizability itself, has been
molecules from both the H+ end and the 0- end. surpassing AgI inspite of the combined effect of
The nucleation activity of the AgI system should, the polarizability and crystal structure of AgI.
therefore, be less with any one of the above The role of AgI in ice nucleation due to its
iodides than without it. However, the nucleation
polarizability was pointed out long ago (Weyl,
activity (of the AgI system) will be affected dif- 1951).
ferently by the different iodides depending upon
8. 7. Effects of other iodates on AgIO3 systems
the polarizing power of the corresponding cation.
For the same charge, the smaller size cation will
When KIO3 or NaIO3 is present in the system
have larger polarizing power (because of the containing AgIO3, the polarizability of the comlarger charge density), and so reduces the plex compound formed, by adsorption, will be
polarizability of the complex anion, (I-Ag-I)-1, by more than that of the system containing AgIO3
a lesser extent. As the polarizing powers of the alone because polarizability
is an additive
cations Li+, Na+, K+ and Cs+ decrease in sequence property.
However, between the combinations
the values of the polarizing power respectively
with NaIO3 and with KIO3 there is a difference,
are 1.6, 1.0, 0.57 and 0.37 (vide Ladd and Lee, which is similar to what has been pointed out,
1969) - the net polarizability of the complex as in the case of AgI combinations with NaI
anion (I-Ag-I)-1 formed in these cases also and with KI. Both Na+ and K+ reduce the
decreases in the same sequence. The observed polarizability of the corresponding anion IO3- in
sequence of the nucleation activities of the AgI the corresponding complex compounds formed,
systems, which progressively decreased from Li+ Na+ reducing it less than K+ on account of the
to Cs, supports this conjecture.
former's larger polarizing power. Also, the net
However, when NH4I is added to the AgI polarizability of the system containing the triple
system, the AgI forms a coordination complex combination, AgIO3 + NaIO3 + KI3, will be more
(NH3-Ag-I)0 which can take water molecules from than that of the system containing the double
both the H+ end and the O- end. Also, this combination, AgIO3 + NaIO3.
These consideracoordination complex, on account of its larger tions lend support to the comparative nucleation
size than AgI, will have larger polarizability than activities as observed in the case of the iodate
AgI. These features could lead to more nuclea- systems.
tion activity in the case of AgI +NH4I than in
the case of AgI alone, in agreement with observa- 9. Conclusion
tions.
8. 6. Iodates versus Iodides
The polarizability of the iodate ion is more
than that of the iodide ion. The values of ionic
The study pointed out that iodates are better
ice-forming nucleants than the corresponding
iodides. They improve in their ice nucleating
activity by the addition of certain soluble compounds to them in suspension. Ten of the systems
68
Journal
of the Meteorological Society of Japan
selected from the many tested in the present
study, when arranged in the order of their nucleation activity, can be listed as follows :
1. (a) Ag103 + NaI03 + KI03
(b) AgI +NH4I + (NH4)2SO4
2. (a) AgIO3 + NaIO3
(b) AgI + (NH4)2SO4
3. AgIO3 + KIO3
4. AgI + NH4I
5. AgIO3
6. NaIO3
7. KIO3
8. AgI
9. AgI +NaI
10. AgI + KI
It is seen from the above that the systems
most commonly used for conventional cloud
seeding, which are AgI + NaI and AgI + KI, occupy
only the bottom most levels in the list. The use
of AgI + NH4I, which is now gaining ground in
the conventional cloud seeding, should now be
adhered to in the place of AgI + NaI and AgI
+ KI. The use of the triple iodate combination
AgIO3 + NaIO3 + KIO3 should be considered for
the pyrotechnic seeding instead of the double
iodate combination AgIO3 + KIO3. Further, the
testing of the triple combination NH4I + AgI +
(NH4)2SO4, for use in the conventional and
pyrotechnic seedings, should receive consideration.
That the presence of some soluble salts raises
the freezing point of water drops is well known
(Mason, 1954; Hosler and Hosler, 1955; Pruppacher,
1963; DePena et al., 1962; Sano and Uzu, 1965),
though there has been no satisfactory explanation
propounded about it. What is more important
in the context of weather modification is to exploit
this effect of the soluble salts for developing
suitable mixes which can be used for producing
efficient ice-forming nuclei. This aspect should
now receive attention.
Vol. 51. No. 1
DePena, R. G., J. V. Ireborne, and E. M. DeAchavel,
1962: The freezing of supercooled droplets of
electrolytic solutions. J. Atmos. Sci., 19, 302-308.
Elliot, R. D., P. St. Amand, and J. R. Thomson,
1971: Santa Barbara pyrotechnic cloud seeding
test results 1967-70. J. Appl. Meteor., 10, 785795.
Heydweiller, V. A. 1925: Optische Untersuchungen an
wasserigen Elektrolytlosungen.
Physikalische Zeitschrift, 26, 526--556.
Hosler, C. L., 1951: On the crystallization of supercooled clouds. J. Meteor., 8, 326-331.
and C. B. Hosler, 1955: An investigation of freezing of water in capillaries. Trans. Amer.
Geophy. Union, 36, 126-132.
Ladd, M. F. C. and W. H. Lee, 1969: Modern Physical Chemistry : an Introduction. Penguin Books
Ltd. England, p. 113.
Mason, B. J., 1954: Progress in cloud physics research.
A progress report on recent investigations
at
Imperial College, London. Archiv fur Meteorologie,
Geophysik and Bioklimatologie, Series A, Band 6,
1-52.
-,1971: The Physics of Clouds, Second
Edition. Clarendon Press, Oxford, p. 216.
and A. P. Van Den Heuvel, 1959
-,
The
properties and behaviour of some artificial ice
nuclei. Proc. Phys. Soc., 74, 744-755.
Odencrantz, F. K., 1969: Freezing of water droplets:
Nucleation efficiency at temperatures above - 5°C.
J. Appl. Meteor., 8, 322-325.
Pruppacher, H. R., 1963: Some relations between the
supercooling and the structure of aqueous solutions. J. Chem. Phy., 39, 1589-1594.
Ramachandra Murty, A. S., and Bh. V. Ramana Murty,
1971: Ice nucleation at warmer temperatures by
silver iodide and silver iodide systems. Submitted
to Journal de Researches Atmospheriques.
1972a: Freezing characteristics of rain water drops
with different solutes and their implication on
anomalous ice crystal concentrations in clouds.
Tellus, 24, 150-160.
1972b: Ice nucleation
by ordinary Portland
cement. Tellus, 24, 581-585.
Sano, I. and Y. Uzu, 1965: An experimental investigaAcknowledgements
tion on the freezing of droplets of water and
The authors express their deep sense of grataqueous solutions, with particular reference to the
itude to Professor S.K.K. Jatkar, formerly of the
influence of the solute. Proceedings of the InterPoona University, for the valuable suggestions
national Conference on Cloud Physics, May 24received from him in course of the work.
June 1, 1965, Tokyo and Sapporo, 181-184.
Simpson, J., W. L. Woodley, H. A. Friedman, T. W.
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and
manifestations.
6, 389-405.
可 溶 性 塩 を 加 え た 場 合 の 沃 素 化 合 物 系 及 び 沃 素 酸 化 合 物 系 の氷 晶 化 能 力
A.S.ラ
マ チ ャ ソ ドラ ムル テ ィ ・Bh. V. R.ラ
マナ ムルテ ィ
イ ソ ド熱帯気象研究所,プ ーナ
す でに示 した簡 易水滴 凍結法 に より,沃 素化合物系 と沃 素酸化 合物系 の氷晶化能力を調べた.実 験 は,可 溶性塩 を
加えた場合 と加えない場合について行な った.調 べた系の中で,雲 への種 まきに よ く用い られ るAgI・NaI系 とAgI・
KI系 の氷晶化能力が最 も悪 く,ま たAgIO3+KIO3系
のそれ も最 も良 くはなか った.本 論文 では,実 際の種 まきに
使えそ うな氷晶核物質の系を示 した他,調 べ た系 の氷晶化能力の相対的差異について定性的考察 を試 みた.