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MyMET > Thunderstorms > Flashcards

Thunderstorms Flashcards

1
Q

What cloud formation are thunderstorms associated with?

A

Cb

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2
Q

What is the definition of a thunderstorm?

A

One or more sudden electrical discharges in the form of a flash of light (lightning) and a rumbling sound (thunder)

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3
Q

3 requirements for a thunderstorm to form

A
  1. Deeply unstable air
  2. A lot of moisture
  3. A trigger to cause the air to rise
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4
Q

What is the key feature of the initial stage?

A

The cell only contains updraughts (30m/s/60kt

Lasts 15-20 minutes

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5
Q

What are the key features of the mature stage?

A

Updraughts (50m/s/10,000ft/min) and downdraughts (2,000ft/min or 6,000ft/min in a microburst) coexist
Rain begins to fall
Lasts between 15-30 minutes

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6
Q

What can a Cb do when the updraughts are strong enough?

A

Overshoot the anvil and punch through the tropopause

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7
Q

What happens in the dissipating stage?

A

The downdraught cuts off the updraught
The storm no longer has a supply of warm moist air
Light rain and weak outflow winds may remain for awhile, before leaving behind just a remnant anvil top
May last 1.5 to 2 hours

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8
Q

4 thunderstorm triggers

A
  1. Convection
  2. Frontal
  3. Orographic
  4. Low level convergence
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9
Q

4 thunderstorm types

A
  1. Single cell
  2. Thunderstorm cluster (multi cell)
  3. Squall line
  4. Supercell
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10
Q

Characteristics of a single cell

A

Form on warm and humid days

May be severe with hail and microburst winds

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11
Q

Multi cell thunderstorm characteristics

A

Multiple cells covering a large area

Individual cells can move in different directions to the cluster

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12
Q

Supercell characteristics

A

A single long-lived thunderstorm

Responsible for tornadoes and large hailstones

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13
Q

Squall line characteristics

A

A line of thunderstorms

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14
Q

What is a mesoscale convective system (MCS)?

A

Collection of thunderstorms that act as a system. Can spread across an entire state and last more than 12 hours. May appear on radar as a solid line, broken line or cluster

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15
Q

What is a mesoscale convective complex (MCC)?

A

Is a type of MCS. Large, circular, long lived cluster of showers and thunderstorms. Area of cloud top at least 100,000km^2 at a temperature of -32 degrees or a cloud top of 50,000km^2 at a temperature of -52 degrees

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16
Q

What is a gust front?

A

Downdraught air flows underneath the warm air inflow. Can spread up to 20-30km/15-20nm in front of the cell.

17
Q

What are roll and shelf clouds?

A

Roll shaped clouds associated with gust fronts

18
Q

What is a microburst?

A

Rapidly descending air that lasts up to 5 min with a diameter less than 4km, can occur multiple times in a single cell. Can be 50kt or 6,000ft/min

19
Q

What is a macroburst?

A

Descending air that lasts between 5-20 mins normally greater than 4km in diameter, can occur more than once in a single cell

20
Q

Biggest danger of downbursts

A

At low level during take-off and approach

21
Q

What are the dangers of Virga?

A

Can generate intense downdraughts that can be difficult to detect

22
Q

What is the danger of hail?

A

Can cause damage to the airframe, in particular the nose which is made from a weaker material in order to reduce radar interference

23
Q

Where’s the best place to fly if approaching a cell?

A

On the windward side

24
Q

Where’s the greatest risk of hail?

A

In the anvil and beneath the anvil, but danger anywhere near the system. Hail can be shot out of the top of the cell by intense updraughts

25
Q

Greatest risk of rain

A

High ingestion leading to engine flame out

26
Q

How do aircraft protect against lightning?

A

They have a faradays cage which allows the charge to flow though the aircraft to discharge points

27
Q

How can lightning effect crew?

A

May cause temporary blindness and deafness

28
Q

What are the 4 types of lightning?

A
  1. Cloud to air
  2. Cloud to ground
  3. Intra cloud
  4. Cloud to cloud
29
Q

What is St. Elmo’s fire?

A

Visible discharge of the surface of the aircraft, appears as a blue plasma

30
Q

Which airframes are at particular risk to lightning?

A

Ones made from composite materials that do not conduct charge as well

31
Q

Which pressure instruments can show errors in a thunderstorm?

A
  1. Altimeter
  2. VSI
  3. Airspeed indicator
32
Q

Which magnetic instruments can show errors in a thunderstorm?

A
  1. ADF (navigation)

2. Magnetic compass

33
Q

What causes a tornado?

A

Strong inward convergence and updraught intensify and narrow a column of air, this increases speed of rotation and makes the pressure fall sharply

34
Q

What are the characteristics of a tornado?

A

Diameter 100m-150m
Winds can exceed 200kt
Most common in spring and summer

35
Q

What is a water spout?

A

Tornado over water

36
Q

What is a dust devil (PO)?

A

A small tornado in hot, calm, dry conditions

Can be 10-100ft wide and can reach up to 650ft

37
Q

Avoidance criteria for thunderstorms

A

5000ft vertical separation

20nm lateral seperation (can be 10nm below 20,00ft if using weather radar)

38
Q

What is a stormscope display?

A

Simple lightning detector

Scans 120 degrees in front within a 200nm radius to show potential storm activity

39
Q

What are the actions if unable to avoid a thunderstorm?

A

Secure items, passengers and crew
Plan, set and maintain speed and attitude
Ensure all anti-icing equipment is on
Use weather radar to help navigate

MyMET (22 decks)

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