earth science

Hail cannon

Hail cannon is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Hail cannon rather than just read about it. In short: A hail cannon is a shock wave generator claimed to disrupt the formation of hailstones in the atmosphere. These devices frequently engender conflict between farmers and neighbors when used, because they are loudly and repeatedly fired every 1 to 10 seconds while a storm is approaching and until it has passed through the area, yet there is no scientific evidence for their effectiveness.

Key takeaways

Hail cannon belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hail cannon to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hail cannon from memory before moving on to harder problems.

Reference excerpt

A hail cannon is a shock wave generator claimed to disrupt the formation of hailstones in the atmosphere. These devices frequently engender conflict between farmers and neighbors when used, because they are loudly and repeatedly fired every 1 to 10 seconds while a storm is approaching and until it has passed through the area, yet there is no scientific evidence for their effectiveness.

Historical use In the French wine-growing regions, church-bells were traditionally rung in the face of oncoming storms and later replaced by firing rockets or cannons.

Modern systems A mixture of acetylene and oxygen is ignited in the lower chamber of the machine. As the resulting blast passes through the neck and into the cone, it develops into a shock wave. This shock wave then travels through the cloud formations above, a disturbance which manufacturers claim disrupts the growth phase of hailstones. Manufacturers claim that what would otherwise have fallen as hailstones then falls as slush or rain. It is said to be critical that the machine is running during the approach of the storm in order to affect the developing hailstones. One manufacturer claims that the radius of the effective area of their device is around 500 m (1,600 ft).

Lack of scientific evidence There is no evidence in favor of the effectiveness of these devices. A 2006 review by Jon Wieringa and Iwan Holleman in the journal Meteorologische Zeitschrift summarized a variety of negative and inconclusive scientific measurements, concluding "the use of cannons or explosive rockets is a waste of money and effort". There is also reason to doubt the efficacy of hail cannons from a theoretical perspective. For example, thunder is a much more powerful sonic wave, and is usually found in the same storms that generate hail, yet it does not seem to disturb the growth of hailstones. Similarly, hail cannons are placed at ground level, while hail formation occurs at altitudes above 10,000 meters; a device with an effective range of 500 meters, above, would be unlikely to have an impact at an elevation 20 times higher. Charles Knight, a cloud physicist at the National Center for Atmospheric Research in Boulder, Colorado, said in a July 10, 2008, newspaper article that "I don't find anyone in the scientific community who would validate hail cannons, but there are believers in all sorts of things. It would be very hard to prove they don't work, weather being as unpredictable as it is."

See also Cloud seeding Cloudbuster Pseudoscience

References

External links

Hail Storms by NOAA on Google Maps Changnon, Stanley A. Jr; Ivens, J. Loreena (March 1981). "History Repeated: The Forgotten Hail Cannons of Europe". Bulletin of the American Meteorological Society. 62 (3). Champaign, Ill: Illinois State Water Survey: 368. Bibcode:1981BAMS...62..368C. doi:10.1175/1520-0477(1981)062<0368:HRTFHC>2.0.CO;2. eISSN 1520-0477.

Illustrations

Worked examples

Example 1 — a first encounter with Hail cannon

Start with the simplest possible case. Write down what Hail cannon claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hail cannon before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hail cannon ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hail cannon

In research: Hail cannon appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hail cannon in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hail cannon is common in secondary-school and first-year university syllabi. It links to neighbouring topics Hail, Pseudoscience, Shock waves, so understanding it makes those chapters shorter.
In everyday life: Look for Hail cannon outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Hail cannon in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hail cannon means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hail cannon out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hail cannon in simple terms?

Why does Hail cannon matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hail cannon?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hail cannon.