Vertically integrated liquid

Key takeaways

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

Reference excerpt

Vertically integrated liquid (VIL) is an estimate of the total mass of precipitation in the clouds. The measurement is obtained by observing the reflectivity of the air which is obtained with weather radar.

Definition Reflectivity (Z) in dBZ represents the intensity of radar echoes returning from a clouds. According to the wavelengths used in weather radars, only precipitation can be noted (drizzle, rain, snow, hail), not the cloud droplets nor water vapor, so Z is proportional to the rain rate. Using the sum in the vertical of Z, one can find the total mass of water equivalent in and below the precipitating cloud and that is what is VIL. From the studies of Marshall and Palmer on the drop size distribution of rain drops, it is possible to find VIL:

V I L = ∑ i = 0 i = i m a x 3.44 ∗ 10 − 6 [ ( Z i + Z i + 1 ) / 2 ] 4 / 7 d h ( i n k g / m 2 ) {\displaystyle VIL=\sum _{i=0}^{i=i_{max}}3.44*10^{-6}\left[\left(Z_{i}+Z_{i+1}\right)/2\right]^{4/7}dh\qquad \left(in\ kg/m^{2}\right)}

Where :

Zi and Zi+1 are reflectivities of two scanning angles and (Zi + Zi+1)/2 is the mean value in the layer. dh is the thickness of the layer (in meters). To note, the unit kg/m2 multiplied by water density (1 kg/liter) gives the surface accumulation in millimeters of rain: 1 kg/m2 = 1 mm.

Usage The VIL measurement is usually used in determining the size of prospective hail, the potential amount of rain under a thunderstorm, and the potential downdraft strength when combined with the height of the echo tops. VIL can be used to triage storms based on their severe potential. It is sometimes still used to assess storms for their potential severity.

Multicells Multicells usually have alternating VIL values. Multicells can have high VIL values on one radar picture, yet much smaller values in the next radar picture.

Wet microbursts When VIL values quickly fall, it might mean that a downburst is imminent. This is the result of the updraft within the cell weakening, thereby losing its ability to hold the copious amounts of moisture (including hail) within the storm's structure. Downbursts of this type are referred to as 'wet microbursts' by the National Weather Service for two reasons: (1) they contain heavy rainfall and (usually) hail; (2) they have damaging winds of greater than 58 mph (50 kn; 93 km/h). Microbursts are classified as being 'a swath of damaging winds not exceeding 2.5 miles (4.0 km) in diameter'. Thus, wet microbursts have been sometimes mistaken for a tornado by the general public, as the damage can be quick, hard hitting, and as important or more than an EF-1 tornado. An algorithm has been developed by S. Stewart, a meteorologist for the US National Weather Service, to estimate the potential maximum gust with a descending downdraft using VIL and the Echotop on radar:

M a x i m u m G u s t = [ ( 20.628571 m s − 2 ) ∗ V I L − ( 3.125 ∗ 10 − 6 s − 2 ) ∗ E c h o t o p 2 ] 0 , 5 ( i n m / s ) {\displaystyle Maximum\ Gust=\left[\left(20.628571\ ms^{-2}\right)*VIL-\left(3.125*10^{-6}\ s^{-2}\right)*Echotop^{2}\right]^{0,5}\qquad \left(in\ m/s\right)}

Illustrations

Worked examples

Example 1 — a first encounter with Vertically integrated liquid

Start with the simplest possible case. Write down what Vertically integrated liquid 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 Vertically integrated liquid 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 Vertically integrated liquid 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 Vertically integrated liquid

In research: Vertically integrated liquid 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 Vertically integrated liquid 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: Vertically integrated liquid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cloud and fog physics, Radar meteorology, so understanding it makes those chapters shorter.
In everyday life: Look for Vertically integrated liquid 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.

How to study Vertically integrated liquid in 20 minutes

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

Frequently asked questions

What is Vertically integrated liquid in simple terms?

Vertically integrated liquid (VIL) is an estimate of the total mass of precipitation in the clouds. The measurement is obtained by observing the reflectivity of the air which is obtained with weather radar.

Why does Vertically integrated liquid 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 Vertically integrated liquid?

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 Vertically integrated liquid.