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January-February 2009

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The Rain Machine

rain machineSaid Jeremy Jonathan Joseph Jones,
  “The weather is far too dry,
  So I reckon I’ll have to stir my bones
  And try the effect of concussive tones
  Upon the lazy sky.”
  - The Rhyme of the Rain Machine
  F. W. Clarke, 1891

Attempts to draw rain from the skies are nearly as old as civilization itself. There is no end to what has been tried. The Greeks used prayer along with the dipping of an oak bough into spring water. In other parts of the world, during severe droughts, holy images are drenched daily until rain comes. The magician of a tribe in Australia appealed for rain by putting water into his mouth and squirting it over himself and everything nearby. In some cases part of the rainmaking magic was using something black to stimulate the clouds (because clouds that produce rain are often somewhat darker than non-raining, fair-weather clouds.) In ancient India people would face a black horse to the west and rub him with a black cloth until he neighed. It was thought that the neighing imitated thunder.

Modern-day attempts at producing rain and snow through artificial means mainly revolve around the dubious science of cloud seeding, which remains exploratory even today. While working in Hawaii for the Woods Hole Oceanographic Institution, I was fortunate enough to be present at one of the earliest attempts at cloud seeding.
The basic science behind cloud seeding had its beginning in 1946 with Vincent Schaefer’s discovery that dropping dry ice in supercooled clouds produced ice crystals that grew rapidly into snowflakes. These would fall out of the cloud as snow or, in warmer air, melt into raindrops.

Schafer worked in the laboratory of the Nobel Laureate Irving Langmuir. Langmuir’s Nobel Prize was for his work in surface chemistry, but he was interested in many other areas of science. In the atmospheric sciences he was the first to derive the equations for the collection efficiency of cloud droplets by rain drops.

Langmuir was a brilliant and forceful speaker who had a gift for convincing skeptical audiences to see his point of view. One atmospheric scientist told me he once heard a lecture by Langmuir but did not believe Langmuir’s conclusions were correct. To prevent himself from falling under Langmuir’s spell and mesmerizing words, he had to keep repeating to himself, “It’s not true.”

Langmuir’s ability to convince skeptics when it came to scientific topics was brought to bear in one of the earliest experiments in cloud seeding, which took place on the Big Island of Hawaii in 1951-1952.

Rain on the Big Island, which is the southernmost of all the Hawaiian islands, falls from clouds carried by the northeast trade winds. On the windward side of the island, rainfall is plentiful, exceeding 200 inches per year and feeding rainforests on the slopes of the 14,000-foot volcanoes, Mauna Loa and Mauna Kea. On the lee side, rainfall can be as little as 10 inches a year and cactuses often dot
the landscape.

The lee side of the Big Island is home to several large cattle ranches, including the Parker Ranch, which, at about 150,000 acres, is one of the largest in the country. A smaller one, the Kahua Ranch, has about 8,500 acres. Although in many ways ideally located for the business of raising cattle, the Parker and Kahua ranches were constantly struggling with lack of rainfall.

In 1951 Langmuir said it might be possible to increase rainfall by seeding the clouds from below with an updraft carrying finely ground salt particles (sodium chloride). In the clouds, condensation of water vapor onto the hygroscopic particles would initiate the formation of raindrops. Langmuir had discussed salt seeding with his group, but to my knowledge neither he nor other scientists had carried out the experiment.
Langmuir convinced some of the cattle ranchers, specifically those working the Kahua Ranch, which was managed by Ronald Kamehameha von Holt, of the validity of salt seeding. Von Holt’s ancestry goes back to the most distinguished pioneer families in Hawaii. (His colorful middle name was that of the first ruler of all the Hawaiian Islands.)

It is unclear how much input Langmuir had in helping von Holt and his engineers build the “rain machine,” but by February 1952 it was ready for some preliminary tests.

The main body consisted of a horizontal metal cylinder about 4 feet in diameter and 8 to 12-feet long, and it was lined with firebrick. At one end a large blower attached to the cylinder pulled air heated by propane flames and forced it upward through a vertical, five-foot long pipe of about one foot in diameter. The salt particles were injected through a hopper into the hot air as it was blown rapidly upward through the pipe. One or two men stood on a platform near the hopper and poured the salt particles from 50- or 100-pound bags into the hot air. They believed that this hot, salt-laden air, being lighter and more buoyant than the surrounding air, would rise rapidly toward the clouds.

The first test was carried out not on the Big Island but on Oahu about 10 miles northwest of Honolulu. It was indeed a momentous occasion! In addition to the several people who had built the machine, there were a few meteorologists and a couple politicians who, if all worked as planned, probably looked forward to claiming the credit for bringing modern rainmaking to Hawaii. There were few clouds overhead that day, so the test was primarily to see if the machine could produce dense, whitish plumes of salt.

There were two other highly interested observers that day: Alfred Woodcock and myself. We both worked at the Woods Hole Oceanographic Institution and had arrived in Honolulu several months earlier to carry out experiments on whether the sea-salt particles being produced by whitecaps at sea were providing the nuclei for the formation of raindrops in the trade-wind clouds. This is nature’s way of doing salt seeding. While I was watching the long, whitish plumes of salt, which looked just like smoke rising from the machine, Woodcock exposed glass slides from a small airplane as the pilot flew at low altitude over the machine. These were the same slides Woodcock had been using for many years to obtain the sea-salt particle distribution in the marine atmosphere. From my view on the ground, it appeared that he had flown through the salt plume, but upon examining the slides under a microscope back at the lab, he did not find any salt particles. He told me he wasn’t even sure he could see the plume from the airplane. It was apparent that Woodcock’s plane had missed the salt plume.

About two months later, the machine was shipped to von Holt’s ranch on the Big Island and mounted on the flatbed of a large truck. It was ready to wring water from the clouds and milk them dry. Woodcock and I had been on the Big Island for about a month doing our own experiments, so when we heard about the upcoming experiments with the rain machine, we drove to the ranch to observe them. We arrived to see several men on the platform from which the salt was poured into the hopper, making adjustments to the machine. After a short delay and with the propane burners on to heat the air, they took off at a rapid pace to get beneath some clouds. Bouncing and bumping over the arid landscape, they stopped when they thought they were beneath a cloud 1,500-2,000 feet above them.

One of the ranch hands tore open a large bag of the powdered salt and fed it into the machine. A long plume of salt smoke made its way into the air. But by this time the cloud, sailing along at perhaps 15-20 mph, was far downwind and no longer above the salt machine. Even if the cloud had stood still, the salt smoke could never have reached it. Carried by the hot air, it rose rapidly to only about 50 feet, and then mixed with the surrounding air as it was carried horizontally over the ground. There was no way for the salty smoke to make its way into the base of the cloud.

There was another problem with the machine:  a lot of the salt fell to the ground not far downwind. Although the testers had tried to grind the salt into small enough particles that could be carried in the smoke, it appeared they had been unsuccessful. At one point I walked downwind about 100 yards and my glasses instantly became covered with many salt particles.

That day, the experiment seemed to have failed.

A week or two later Woodcock and I returned to von Holt’s ranch because we heard that there would be another attempt. We found the machine and some of the ranch hands on a small hill. Earlier that day there had been a very light rain that covered a wide area, but it had stopped before we got there.

“Look, we make rain,” said the ranch hand’s foreman as I approached. I smiled but didn’t have the heart to tell him his machine had nothing to do with it. The stratiform clouds had been producing rain many miles upwind and continued to rain as they moved in and past the machine.

We never saw the rain machine in action again, nor did we hear anything about it after our return to Woods Hole. But in 1967 we returned once again to the Big Island for some more experiments in cloud physics. One day I decided to drive over to von Holt’s ranch to see if I could find out what happened to the rain machine. But Von Holt had died in 1953. I found a memorial to him on a small building that had a magnificent view overlooking much of his ranch. There was a plaque on the wall with his name, and beneath it, inscribed in parentheses, were the words Keiki Hanau o ka Aina, which is Hawaiian for “Child born of the land.”

In the nearby barn I found an elderly ranch hand and asked him if he remembered the rain machine. He said he did, but added that most of it had been sold for scrap and only a piece or two remained. He took me into the barn, where, nearly hidden from sight, was a section of the hopper into which the salt had been poured.

“Is there any salt left?” I asked.

“No,” he replied. He said the boss had most of it dumped into the sea around 1952.

When I asked him if the rain machine had ever made rain fall from the clouds, he smiled and said “Sometimes.”                  

DUNCAN BLANCHARD  holds degrees in engineering, physics, and meteorology and has conducted research in the atmospheric sciences at General Electric, the Woods Hole Oceanographic Institution, and the Atmospheric Sciences Research Center, SUNY-Albany. He has published more than 150 articles and books. His book, From Raindrops to Volcanoes, written for a popular audience, has been printed in seven languages.

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