physics

Hail spike

Hail spike is a physics 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 spike rather than just read about it. In short: A hail spike or three body scatter spike (TBSS) is an artifact on a weather radar display indicative of large hail. They are identified by a spike of weak reflectivity echoes that extend out from a thunderstorm, and away from the radar site.

Key takeaways

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

Reference excerpt

A hail spike or three body scatter spike (TBSS) is an artifact on a weather radar display indicative of large hail. They are identified by a spike of weak reflectivity echoes that extend out from a thunderstorm, and away from the radar site.

Cause

Generally known as hail spikes, these are the result of energy from the radar hitting hail, very heavy rain, or in extreme cases, debris being lofted by a tornado, and being reflected to the ground, where they reflect back to the hail and then to the radar as in the image on the left. This results in the radar picking up the energy from the multiple path at a later time than the energy that came back directly from the hail to the radar. Both are however on the same radial angle from the radar as the antenna did not have the time to turn significantly. The multipath echoes are then analyzed on the radar display as echoes extending in a radial direction behind the actual location of the hail/heavy rain core. The loss of energy due to multiple reflections means weaker return echoes. The hail spike region has thus comparatively quite weaker echoes than the echoes directly from the hail or heavy rain core. Since hail cores are most intense at higher elevations, hail spikes usually appear at the levels aloft that accompany the most intense hail. Because of this, hail spikes are usually not seen at lower elevations. Another restriction to detection is that the signal of the radar beam has to do multiple reflections, each time weakening it, and are therefore usually noticeable only in extremely large hailstone cases.

Multiple TBSS Signatures

In rare cases more than one hail spike has been documented with a single storm in one volume scan. This indicates that more than one hail core exists in the same storm and far enough apart that each core can be sampled by the radar individually.

Use in forecasting

Because of their observed accuracy in indicating large hail aloft, TBSS's are used operationally by the National Weather Service to identify thunderstorms that could likely produce large, severe hail. This would warrant the issuance of a severe thunderstorm warning or mention of large hail in a tornado warning.

See also Convective storm detection Severe weather terminology (United States) Severe weather terminology (Canada) Tornado debris signature aka "debris spike"

References

External links Three-Body Scatter Spike course by the National Weather Service

Illustrations

Worked examples

Example 1 — a first encounter with Hail spike

Start with the simplest possible case. Write down what Hail spike claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 spike 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 spike 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 spike

In research: Hail spike appears in physics 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 spike 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 spike is common in secondary-school and first-year university syllabi. It links to neighbouring topics Hail, Radar meteorology, Radar theory, so understanding it makes those chapters shorter.
In everyday life: Look for Hail spike 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 spike in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hail spike 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 spike out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hail spike in simple terms?

Why does Hail spike matter?

Because it connects several physics 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 spike?

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 spike.