AU596224B2 - An improved method of seeding clouds - Google Patents

Description

"r PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE P/00/011 Form Short Title: Int. Cl: 596224 Application Number: Lodged: Cpnplete Specification-Lodged: o Accepted: L Lapsed: Published: SPriority: S w Related Art: t t Name of Applicant: Address of Applicant: TO BE COMPLETED BY APPLICANT VERNON ARTHUR LUCKMAN 22 BANNISTER GARDENS, GRIFFITH, A.C.T. 2603.

Actual Inventor: Address for Service: Care VERNON ARTHUR LUCKMAN of PAUL F. KILDEA, Patent and Trade Mark Attorney, 19 LOGAN STREET, NARRABUNDAH, A.C.T. 2604.

Complete Specification for the invention entitled: AN IMPROVED METHOD OF SEEDING CLOUDS The following statement is a full description of this invention, including the best method of performing it known to me:- CIUmrrl i 2 The invention relates to a method of producing rain by seeding atmospheric clouds. Clouds form when water vapour in the atmosphere condenses on small particles which are called condensation nuclei. A cloud so formed is composed of tiny droplets or spheres of water having a diameter of the order of 1 to 50 microns. The density of cloud droplets per cubic centimeter may range up to 1,000; an average value being of the order of 200/cc.

For seeding purposes an important characteristic is cloud temperature. When cloud temperature is above 0°C, the cloud is said to be warm. Clouds may develop ,t 9 'l" 1 at altitudes where temperatures are below 0°C, but the droplets do not freeze because of the purity of the c f .water. These clouds are said to be supercooled.

Supercooled clouds at temperatures down to abou- C t S may be experienced. The lower the temperature, the greater the likelihood that the droplets will intercept so-called ice nuclei, which cause them to freeze. At temperatures of about -40°C, virtually all clouds are composed of ice crystals.

Whether warm or supercooled, all-liquid clouds where the water droplets are small are usually stable. Such clouds may last for some time without precipitation.

It has been found that the addition of ice nuclei can o 9, 0*9* 0** 9 a, 9* *t *0 0 0. 20 0 3 upset the cloud stability by causing ice crystals to form, which may then grow and lead to precipitation.

Warm clouds have been seeded with such materials as sodium chloride or calcium chloride particles or by water spray. This is intended to cause large cloud droplets which will grow by coalescence and fall.

Aircraft have been used to disperse a water spray or salt particles. This procedure has several disadvantages and a limited value for increasing rainfall. In another procedure, solid sodium chloride particles in powdered form have been projected up from the ground.

Most cloud seeding that has been attempted is with supercooled clouds and has involved the introduction of ice nuclei. One substance found to be effective as a cloud seeding agent is dry ice. At a temperature of about -78°C, ice crystals are readily formed from atmospheric water vapour. The most common procedure for dry ice seeding is to fly over a cloud and disperse small crushed dry ice particles. The particles of dry ice mix with the cloud, extracting heat therefrom during evaporation. A typical seeding rate might be several pounds of dry ice per mile of flight.

Although dry ice is widely used as a seeding agent, it -4suffers from the disadvantage that the dry ice must be delivered to the supercooled parts of the cloud and that, once the particle of dry ice has evaporated, it can no longer affect the cloud.

There are some other substances which can be used for the seeding of supercooled clouds. For example, silver iodide or lead iodide may be burned to produce a smoke of tiny particles. These particles can produce ice crystals in supercooled clouds.

In one procedure, silver oidide seeding has been done by ground generators, air currents being used to transport the nuclei into supercooled parts of the cloud. In another procedure, aeroplanes have been used Sf, to disperse silver iodide particles. For example, silver iodide in acetone has been burnt in generators suspended from the wings of an aircraft. In some cases, silver iodide and a pyrotechnic mixture have been dropped from above into clouds.

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Although several materials have been tried, the success factor has been variable over a wide range.

Predictability has been largely non-existent and remains a serious problem. Even now, the effectiveness of cloud seeding by known methods is questioned. At most, it may be said that, under some meteorological conditions, some of the known methods of cloud seeding may produce some small increase in rainfall. On the other hand, those same methods in the same meteorological conditions may have no effect, or even a negative effect. Moreover, existing practices relate to the treatment of existing cloud systems. If there are no clouds present, there can be no cloud seeding.

It is an object of the invention to provide a more effective and more predictable method of cloud seeding than have been used heretofore.

S Sr E According to my invention, a method of inducing rain by seeding atmospheric clouds is characterised in that a ,low freezing point alcohol is used as the seeding agent and is applied at a temperature close to its freezing point to the atmospheric clouds. Preferably, the low C temperature alcohol is in liquid form and is sprayed C C over and/or into the cloud mass. The clouds are preferably supercooled and further cooling is caused by vaporisation of the alcohol. The alcohol mixes with the cloud droplets which coalesce to increase size and weight and causing fallout.

One example is ethanol which has a freezing point of about -114 0 C. When ethanol in liquid form at a temperature close to its freezing point is sprayed over r- 6 -6the upper surface of or into a supercooled cloud mass, the ethanol will vaporise producing a cooling effect as it does so. This induces the condensation of ice nuclei. Even at 0°C, one volume of ethanol will freeze approximately 2.2 volumes of water. At loWer temperatures, ethanol is very effective in reducirg the temperature of supercooled clouds.

Ethanol may be dispersed in the clouds from any aircraft, preferably a propellor driven aircraft, and preferably one capable of night flying, The aircraft should be equipped with a belly tank or other type of 9 C storage container which may be carried outside the plane. The floats of flying boats or amphibious aircraft may be modified for storage purposes. By using a storage container outside the plane, ambient temperatures would be effective to extract the heat S from the ethanol. After reaching an altitude of 30 to thousand feet, the plane could be brought down to cloud level and the ethanol sprayed onto and into the clouds. The ethanol would mix and coalesce with water droplets increasing their volume and weight. Ethanol may be dispersed from the storage container by gravity feed, thus avoiding the use of mechanical devices such as pumps which would introduce heat. The storage container or belly tank would have a series of outlets 7 across the width of the plane. Alternatively, a pressurised gas which is inert to the alcohol may be used for dispersal purposes.

In one form, the aircraft may carry a refrigation device which could be used to deliver low temperature liquids or gases outside the aircraft and in heat exchange relationship with the ethanol in the storage containers and thereby keep the temperature of the ethanol as low as possible.

10 Instead of an airplane, an airship or other dirigible O tt craft may be used. It would be possible to use the helium gas used for suspension of the airship in i: suitable refrigera'ed apparatus.

Other low freezing point alcohols may be used such as methanol (-97 0 1-propanol (-126 0 2-propanol t (-88 0 1-butanol (-89 0 isobutyl alcohol (-108°C), 2-ethyl-l-hexanol and other alcohols with comparable freezing points.

Although some embodiments of my invention have been referred to, it is stressed that the broad concept of 4, my invention is set forth in the appended Claims and involves the use of a low freezing point alcohol. That broad concept may be embodied in different ways as would be clear to persons skilled in the art.

Claims (9)

1. A method of inducing rain by seeding atmospheric clouds, characterised in that a low freezing point alcohol is used as the seeding agent and is applied at a temperature close to its freezing point to the atmospheric clouds.

2. A method according to Claim 1, wherein the alcohol is in a liquid form.

3. A method according to Claim 2, wherein the alcohol is sprayed over the upper surface of or into the cloud ao mass. I

4. A method as claimed in any one of the preceding S* Claims wherein the atmospheric clouds are supercooled.

A method according to any preceding Cl2aim, wherein 4A the alcohol is ethanol.

6. A method according to any preceding Claim, wherein *the alcohol is transported in a storage container or i tcontainers carried outside an aircraft.

7 A method according to Claim 6, including the step of extracting heat from the alcohol in the storage container or containers. __1 t 9

8. A method according to Claim 6 or 7, wherein dispersal of the alcohol is assisted by the use of a pressurised gas inert to the alcohol.

9 A method of inducing rain by seeding atmospheric clouds substantially as herein described. DATED this 7th. day of October 1987. VERNON ARTHUR LUCKMAN By his Patent Attorney, PAUL F. KILDEA.