沙漠研究 24-1, 65-68 (2014)
Ἃ₍◊✲ 24-1, 65 - 68 (2014)
Journal of Arid Land Studies
Journal of Arid Land Studies－ DT11 Refereed Paper －㸫DT11 Refereed Paper㸫

Artificial Rainfall by the Seeding of Liquid Carbon Dioxide near Miyake andMikura Islands of Izu Islands in 2012 and 2013
Taichi MAKI*1), 3), Osamu MORITA2), Yoshinori SUZUKI3) and Kenji WAKIMIZU4)
Abstract: An artificial rainfall experiment was carried out by an aircraft seeding operation of liquid carbon dioxide (LCD) with theseeding rate of 5 g/s on February 27, 2012 and March 14, 2013 near Miyake and Mikura Islands of Izu Islands in Tokyo, Japan. Thedevelopment of convective cloud was significant 0.5 to 1 hour after the seeding near Miyake Island and reached to the heights of 4000
m on Feb. 27, 2012. Artificial cloud appeared and rain was recognized by eye around Mikura Island, and it was presumed that theamount of rain increased on the mountainous area. The artificial cloud echoes were successfully recognized about 1.5 hour later after
the seeding as a chain-type cloud echo at ENE of Mikura Island on radar echo. The echo height reached on 3000 m to 5000 m when
the artificial cloud moved to leeward side of Miyake Island. The development of cloud was after 0.5 hour of the seeding near Miyake
Island and reached to height of about 3000 m on Mar. 14, 2013. Rain clouds with the rain stream under the cloud, i.e., virga were
found at Mikura Island after 1 hour of the seeding. The trail and hole of disappeared cloud were found after about 1 hour and 2 hourlater, respectively. It was recognized that seeding rate of liquid carbon dioxide with about 5 g/s was suitable in a little insideconvective cloud with air temperature below -5°C.
Key Words: Aircraft seeding, Artificial rainfall, Convective cloud, Liquid carbon dioxide, Miyake and Mikura Islands

1. Introduction

2. Materials and Methods

A global water crisis is predicted in the 21st century. Thewater demand continues to increase as the population increases
and the demand may outpace the supply. Droughts and otherwater-related problems are increasing in frequency as aninstance of abnormal weather due to global warming. Water
deficits are already extant or expected to occur around theworld. New and effective techniques for producing artificial
rainfall are being sought to contribute the world’s water needs.
It is hoped that an effective technique will also protect against
desertification in green arid and desert areas.
There are several techniques for artificial rainfall such as
the seeding of dry ice, seeding of silver iodide, and thescattering of liquids such as water, salt water and so on.
However, these methods present a small amount of water. An
artificial rainfall technique of liquid carbon dioxide (LCD) wasinvented by Fukuta (1988), and was proven successful at
Fukuoka on Feb. 2, 1999 as the first effective rainfall
production. There are successful results on Feb. 2 and Oct.
27, 1999, Feb. 4 and Nov. 7, 2006, Jan. 8 and 17, 2007, Jan. 24,2009 (Maki et al., 2012) and other results included (Maki et al.,2013a, b). Main objectives of this paper are that direct andindirect effects by the seeding are made clear, particularly
topographical effect.

The LCD technique developed by Fukuta (1988) is asfollows. LCD seeding is done by aircraft in an air layer inwhich the temperature is below 0°C and a little inside a cloudat its bottom. The LCD at -90°C changes instantaneously toice crystals (1013 or ten trillion particles per 1 g CO2) (Fukuta,1988; Fukuta et al., 2000). These ice crystals connect withthe ambient air vapor and produce snow or rain.
The LCD technique was used in experiments operated
around Miyake Island (34°ௗ7’N, 139°ௗ31’E) and Mikura Island(33°ௗ53’ௗN, 139°ௗ36’ௗE) of the Izu Islands of Tokyo in Japan.
The aircraft used was a Beechcraft of Diamond Air Service.
We flew from Nagoya to Miyake Island and LCD wasseeded on about 5 km west side from Miyake shore on Feb. 27,
2012, and 10 km from Miyake and Mikura Islands on Mar. 14,
2013 and flew back to Nagoya.
The LCD was seeded from a nozzle on the bottom of theaircraft at the rate of 5-6 g/s. We flew around Miyake andMikura Islands for 1 h to evaluate the effects of the seeding,observed the rain and took photos.
The seeding rate was about 5 g/s and seeding times were 2
series with each 10 minute-operation. The total weight of
CO2 was 6.7 kg in about 20 min at 5 g/s of seeding rate. The
seeding areas were at about 10 km north from Miyake Island* Corresponding Author: maki@affrc.go.jp

㸦Received, September 8th, 2013; Accepted, December 2nd, 2013㸧

1-1 Ohwashi, Tsukuba, Ibaraki, 305-8686, Japan
1) Japan International Research Center for Agricultural Sciences, Japan

3) Professor Emeritus, Kyushu University, Japan

2) Office for a Sustainable Future, Fukuoka University, Japan

4) Faculty of Agriculture, Kyushu University, Japan66

SWwindDirect
Cloud effectdevelopedSeedingat2100Ͳ2300m
813m

Indirect
effectMiyakeIsland(1)(2)

Fig. 1. Undeveloped cloud (1) and Developing cloud (2) by theseeding of liquid carbon dioxide on Feb. 27, 2012.

and at about 10 km north east from Mikura Island.

3. Results and Discussion
3.1. Experiment results on Feb. 27, 2012 and discussion
On Feb. 27, 2012, the seeding height near the bottom of amain cloud layer was 2130 m for the first seeding and 2290 m
for the next three seedings. The seeding times were about 9min. The cloud bottom was 1830 m and the cloud top was
2960 m making the cloud thickness 1130 m. There were twolayers of cloud. One was main cloud and the other was aseparate and sparse cloud under the main cloud at about 1000
m. The thickness of two layers included separated cloud wasabout 2000 m. The wind direction was SW and the windspeed was 8.2 m/s at 2100 m, and the air temperature was-4.0°C at 2130 m and -5.5°C at 2290 m. The wind direction
and speed were W and 8.7 m/s at 3050 m and WNW, 18.5 m/s
at 3660 m, respectively.
On Feb. 27, the seeded cloud moved in an ENE direction
after the seeding and the artificial cloud appeared. The photos
at about 1 h later shown in Figure 1(1) and (2) as an
undeveloped and developing cloud present natural cloud andartificial developed cloud with rain. A cloud developed
quickly, the development of convective cloud was significant
after 0.5 to 1 h of the seeding at the easterly leeward side of
Miyake Island and an artificial cloud reached to the heights of3500 m and 4000 m at 0.5 h and 1 h after the seeding,respectively.
The artificial cloud moved further, and it was raining under
the cloud recognized by eye. A virga, i.e., rain cloud as cloudwith rain, was also found at a lower layer under the seeded
cloud. The virga reached around Mikura at about 1 h after theseeding, moved by a NNE-NE wind around 1500 m high.
We could observe the cloud by eye, and the aircraft flew
through and over the cloud as shown in the photos (Fig. 1).
We detected the rain hitting on a front window. These
convective clouds recognized by eye during a flying wereevaluated by the wind direction and wind speed concerned tocloud heights and virga.

Distance:20km
After0.5䡚1 hMikura Island
Until2000m

Feb.27,2012

851m

Seeding:9:58Ͳ10:27(9min)

NEͲNNE
10 m/sFirst
directeffectDistance:100km

ExperimentofArtificial
Rainfall,
SeedingofLiquidCarbon
DioxideUpͲstreamDevelopingcloudUntil2000m
NEͲNNE
10m/sAfter3 hHachijo Island

854m

Virga orrainunder
cloud

Mikura Island

Secondary
indirect
effectFig. 2. Models of the wind direction and wind speed affected on
artificial rainfall of LCD seeding around Miyake Island andof the effect to Mikura and Hachijo Islands.

It was rain in the mountain area of Mikura Island but there
was no rain in surrounding lowland area. This must be due tothe differences of mountain shape, elevation and cloud forest.
The virga was moved ENE by SW-SSW winds for 0.5 h,and the high humidity air mass rose up and was developed intoa higher cloud by the upwind based on the topography of
Mikura (Fig. 2). Artificial cloud developed by seeding of
LCD and developed more by the topographic effect of Mikura.
The topography is important for the formation of cloud by
upwind along the mountain slope.
The shape of Mikura Island is a sharp trapezoid, the area
over 500 m is relatively large and the island's total area is 20.55
km2. The highest point is Miyama Mountain at 851 m high.
The bottom of the artificial cloud and virga that moved toMikura was almost the same height as the peak of Mikura, andit could easily cover the island. Thus, the mountainous areaof Mikura could be covered by rain. These phenomena areagreed with the appearance of topographic cloud and rain (Setoet al., 2011).
The radar image is shown in Figure 3 and there is noimage at 10:00 (Fig. 3) to 11:00. The cloud developed as anENE line- or chain-type typically after 11:10 and became highand thick by 11:30 (Fig. 3) to 12:10. The cloud could be seen
by radar clearly, and the radar echoes reached 3000-5000 m.
And the artificial cloud disappeared until 14:00 after 3 h.
The possibility of artificial rainfall by LCD was very highand remarkable. The artificial cloud development isimportant, that is the cloud with the virga rose up along theslope of the island, and the cloud developed further. Thecloud was transported by a SW wind around 2200 m andmoved in an ENE direction. It eventually rose and appearedon the radar image as a chain-type cloud (Fig. 3). Such aphenomenon of the clouds appeared in about 1 h and67

10:00

Feb.27,
2012

Miyake Island
Mikura Island

Verticalprofileofairtemperature
500013:00 Mar.14,2013

4500
4000
H 3500ei 3000
g2500
ht 2000咁m
1500
咂

MiyakeCloudtopSeedingheight:1070m

1000
500

11:30

Feb.27,
2012

Cloudlayer
Cloudbottom0
Ͳ15

Ͳ10

Ͳ50
Airtemperature䠄Υ䠅

5Fig. 4. Vertical profile of air temperature with inversion layer on
Mar. 14, 2012.

ChainͲtype
artificial
cloud

Fig. 3. Radar cloud echoes at 10:00 and 11:30 Feb. 27, 2012 around
Miyake, Mikura and Hachijo Islands (JMA).

disappeared in about 3 h is an expected result as an artificial
effect. If the seeding was not done artificially, these clouds
were not found at all we presumed and concluded. We
concluded that the cloud was successfully developed by theseeding of LCD.
The amount of rain or water was estimated as 1 million ton
by the direct effect of LCD seeding around the main area of 10
km width and 100 km length with precipitation intensity about
2 mm/h. The efficiency of LCD for rain was predicted 3
million ton per 1 kg LCD. So, it was presumed roughly 100times of rain comparing with old three methods of dry ice, AgIand salt-water seeding.
3.2. Experiment results on Mar. 14, 2013 and discussion
Phase 1: The seeding area was about 10 km north of
Miyake Island and the direction of WSW to ENE at 2 times of
3 and 3 min and the direction of S to N at 1 time of 4 min
which seeding path was like a sign of inequality (). The
seeding time was at 13:29 to 13:46. The height of the seeding
cloud was 1070 m, air temperature was -2 to -1°C, winddirection was NE and wind speed was 15.4 m/s. The heightof top cloud was 1940 m, where air temperature, winddirection and wind speed +2.0°C, WSW and 9.1 m/s,respectively. The height of bottom of the cloud was 580 m,+ 2.3°C, E and 17.0 m/s. The thickness of cloud was rather(1)(2)

Fig. 5. Convective cloud and virga (1) and disapperared cloud by theseeding (2) near Mikura Island on Mar. 14, 2013.

thin of 1360 m.
Phase 2: The seeding area was about 10 km north of
Mikura Island. The seeding of LCD was done as thedirection from NW to SE at 2 times of 3 and 3 min and thedirection of S to N as 1 time of 4 min which seeding path waslike a sign of inequality (). The seeding time was at
14:03-14:22. The seeding height was 1070 m and -2 to -1°C,
NE, 15.4 m/s. The height of the top cloud was 2060 m,-1.0°C, WSW, 7.7 m/s. The height of the bottom cloud was
670 m, +5.0°C, ENE and 20.6 m/s. The thickness of thecloud was 1390 m. The thickness of cloud was thin of about
1400 m.
The inversion layer was recognized at 1200 to 2200 m,significantly at the level of 2000 to 2200 m that was shown in
Figure 4. The air mass with rain under the cloud, i.e., virga
was found at the west side of Mikura Island shown as in thephoto of Figure 5(1).
It was probably rain under the cloud layer from 2000 to600 m. The cloud was destroyed as an artificial rain, and thewidth was about 2 km as a flight length of 50 km in a trace
during about 20 min. The cloud disappeared like a trench
shown as in the photo of Figure 5(2). It was interesting resultthat was found at 2 halls of disappeared cloud at about 1 hlatter of seeding, and that the diameter of 1 hall combined from

68

DisappearedcloudMiyakeIslandMikuraIslandDisappeared
cloud

16:00

16:30

physics estimation is 2.7 million ton. Then, the average isabout 1.8 million ton.
The experiment condition was not so perfect, but theartificial rain presumed to be successful and the changing
efficiency of rain was high. Table 1 shows the experimental
conditions and main results.

4. Conclusion
Disappeared
cloud

17:00

18:00

Fig. 6. Satellite cloud images of disappeared clouds at 16:00, 16:30
and 17:00 and of recovered cloud at 18:00 near Miyake andMikura Islands.
Table 1. Comparison of experiments on February 27 and March 14,2013.
DateExperimental conditions
Seeding height 2200 m

Feb. 27, Cloud thickness 2000 m
2012
Seeding air temperature -5 Υ℃Experimental results
Cloud with rain, i.e., virga found
Cloud developed at 3000-5000 m high
Chain type cloud as secondary effectCumulus and no inversion

Estimated rain amount 1.0 million ton

Seeding height 1100 m

Cloud with rain, i.e., virga foundMar. 14, Cloud thickness 1400 m
2013
Seeding air temperature -2 Υ℃Stratocumulus and inversion(1) The development of artificial convective cloud wassignificant after 0.5 to 1 hour of the seeding at the easterly
leeward side of Miyake Island and reached to the height of4000 m on Feb. 27, 2012. It was concluded that the cloud
was successfully developed by the artificial seeding of LCD.
(2) The artificial clouds appeared 0.5 to 1 h after theseeding at Mikura Island. The amount of rain increased on
the mountain area. The artificial cloud echoes wererecognized on the radar echo on Feb. 27. It was observed thatthe height of chain-type cloud echo reached on 3000 m to 5000
m, when the artificial cloud moved to the ENE leeward side of
Mikura Island.
(3) The experiment on March 14, 2013 was successfully
shown in as a photo and a satellite image of disappeared cloudby the seeding of LCD and inversion layer.

References

Cloud developed at 2000 m high
Cloud disappeared as a trail and hole
Estimated rain amount 1.8 million ton

2 halls of disappeared cloud area was about 50 km after about
2 h latter shown in Figure 6.
The wind direction near the bottom cloud was easterly wind
and the wind speed was strong at 17.0 to 21.0 m/s. The shearof wind direction and wind speed was large at the higher andlower levels.
The wind direction at the higher level was westerly wind.
The wind direction was NE and wind speed was 15.0 m/s atthe seeding height of 1070 m.
The amount of precipitation was presumed about 0.1 million
ton with the precipitation intensity of 1 mm/h as a disappearedarea of 2 km width and 50 km length of by after about 1 h as afirst affection.
The total amount of precipitation ofdisappeared cloud was presumed 2.0 million ton with theprecipitation intensity of 1 mm/h as a disappeared area of 50
km diameter by after about 2 h as a second affection.
Another estimation is 0.15-1.5 (mean 0.8) million ton as thewater content of Stratus cloud is 0.05-0.5 g/m3. The cloud

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