Chapter 14 - Thunderstorms

Question 1

Threats

Answer 1

Structural damage
Disorientation
Temporary loss of vision or hearing
Engine flame out
Severe icing hail + turbulence
Instrument error

Question 2

Thunderstorms develop in which cloud

Answer 2

Cumulonimbus

Question 3

3 main requirements

Answer 3

Lifting force - trigger action to initiate lifting of air (eg convection)
Unstable air mass (air rises) - layer depth of at least 1000ft
High relative humidity (lots of moisture) - so saturation and condensation can be achieved early as air rises

Question 4

Trigger actions

Answer 4

Convection
Orographic

Question 5

Thermal thunderstorm - ‘air ass thunderstorm’

Answer 5

Occur late afternoon
ELR increases rapidly with daytime surface heating

ELR becomes unstable through deep leather of 10000ft that’s above freezing level

Collisions/friction between hail particles

Question 6

Air mass thunderstorms due to advection

Answer 6

Cold air moves in over warm landmass - causes instability eg. Big ELR value compared to DALR value

Question 7

Frontal thunderstorms s

Answer 7

Cold air forces warmer air to rise rapidly

Cold nose develops due to friction

Warm air lying beneath cold air causes instability eg

Question 8

Squall line thunderstorms

Question 9

Orographic thunderstorms

Answer 9

Due to Orographic deflection - air forced to rise orographically

Occur at any time of day or night

Mountain is the lifting trigger

Question 10

Thunderstorms develop when

Answer 10

Intense surface heating leads to steep ELR
When cold air is adverted over warm surface

Question 11

Thunderstorm lifecycle - building (or cumulus or initial) stage

Answer 11

Air movement exclusively upwards (updrafts)

Last around 20 mins

Question 12

Thunderstorm lifecycle - mature stage

Answer 12

Small anvil may be present

Bigger droplets which have reached critical mass - indicates offsets of precipitation

Precipitation drags cold air down and out of cloud and dumped on earth surface - forms region of cold air called gust front

Also lasts around 20 mins

Question 13

Thunderstorm lifecycle - dissipating stage

Answer 13

Anvil is visible

Downdraughts only decreasing in strength

Rainfall continues but is reducing

Cloud base lifts due to evaporation

Last 1.5 - 2 hours

Question 14

Supercell thunderstorms

Answer 14

Conditions needed
- greater depth of instability but a very stable layer at low level which initially suppressses convection until critical surface temp is reached

-strong increase in wind speed with altitude —> causes storm vertical axis to be tilted

• downdraughts and up draughts currents are displaced - so during heavy precipitation the downdraghts don’t dominate = greater power
• strong vertical wind sheer causes airflow to become rotational