physics

Overshooting top

Overshooting top 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 Overshooting top rather than just read about it. In short: An overshooting top (or penetrating top) is a dome-like protrusion shooting out of the top of the anvil of a thunderstorm and into the lower stratosphere. When an overshooting top is present for 10 minutes or longer, it is a strong indication that the storm is severe.

Key takeaways

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

Reference excerpt

An overshooting top (or penetrating top) is a dome-like protrusion shooting out of the top of the anvil of a thunderstorm and into the lower stratosphere. When an overshooting top is present for 10 minutes or longer, it is a strong indication that the storm is severe.

Formation

When a thunderstorm forms, clouds build vertically into the atmosphere until the storm's updraft (warm rising air) has reached the equilibrium level (EL); the point where the surrounding air is about the same temperature or even warmer. This point of equilibrium is often marked by the tropopause. Rather than continuing to rise into the stratosphere, the vertical cloud growth abruptly stops, and instead clouds spread horizontally, forming an "anvil" shape on top of the thunderstorm. An overshooting top forms when a thunderstorm's updraft, due to momentum from rapid ascent and strength of lifting through the free convective layer (FCL), protrudes its equilibrium level, forming a dome-like structure above the anvil. This can occur with any cumulonimbus cloud when instability is high. Whereas anvils form at the equilibrium level, overshooting tops continue to the maximum parcel level (MPL).

Above-anvil cirrus plume

The strong updrafts delineated by overshooting tops can act as a barrier against the surrounding flow of air. Fast stratospheric winds may rise slightly upon encountering overshooting tops, cooling and producing a turbulent wake of cooler temperatures downstream of the updraft. This interaction also sheds ice and water vapor from the anvil cloud, forming a plume of cirrus emanating from the updraft region, though this is most evident in mid-latitude environments where the tropopause is typically lower and the associated inversion wider. These cirrus plumes may be warmer than the underlying anvil cloud due to the mixing of air from the warmer stratosphere. Termed above-anvil cirrus plumes (AACP), the emergence of such features on satellite imagery have been associated with severe weather events. A 2018 study published in Weather and Forecasting found that 73 percent of significant severe weather reports in the United States were associated with storms producing AACPs and that AACPs emerged an average of 31 minutes before the issuance of severe weather warnings. Simulations suggest that overshooting tops behave like hydraulic jumps in the presence of strong winds aloft, allowing the transport of over 7 t (7.7 tons) of water vapor into the lower stratosphere per second.

Severe weather

Many thunderstorms exhibit an overshooting top at some point in their life cycle. In weaker thunderstorms, the overshooting top is short-lived, and often takes on a wispy appearance. If the overshooting top is rising and falling in a cyclical fashion with each protrusion persisting only a few minutes, then it could indicate the storm is pulsing and not as strong as a storm with a continuous overshooting top. An overshooting top lasting for more than 10 minutes is a sign of a strong updraft in a thunderstorm, indicating a strong likelihood the storm is producing severe weather. If the overshooting top is continuous, it's an indication of enhanced probability that the storm is a supercell, i.e. a rotating storm. During a strong tornado, the overshooting top may roll or fold over as new activity climbs up the back while the front of the overshooting top collapses into the storm. During a long-track tornado, the entire top of the storm, including the overshooting top, may drop by thousands of feet.

Storm features A storm powerful enough to produce a lasting overshooting top typically produces the following:

Heavy rain; a deluge of rain could fall from this storm in a short amount of time. Strong straight-line wind from downbursts; the storm clouds have powerful winds churning inside them. These winds are likely to be felt at the surface and also a threat to aviation aloft. Sometimes a tornado may form; most strong tornadoes are associated with mesocyclones located near the interchange of the rotating updraft and the rear flank downdraft (RFD). Hail; if the updraft is strong enough to produce an overshooting top it can also carry large hail. A storm that features an overshooting top is a thunderstorm, and is thus likely to produce lightning.

Illustrations

Worked examples

Example 1 — a first encounter with Overshooting top

Start with the simplest possible case. Write down what Overshooting top 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 Overshooting top 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 Overshooting top 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 Overshooting top

In research: Overshooting top 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 Overshooting top 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: Overshooting top is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cloud and fog physics, Cumulus, Severe weather and convection, so understanding it makes those chapters shorter.
In everyday life: Look for Overshooting top 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Overshooting top in 20 minutes

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

Frequently asked questions

What is Overshooting top in simple terms?

Why does Overshooting top 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 Overshooting top?

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 Overshooting top.