Thunderstorms

Question 1

Conditions required for development of thunderstorms

Answer 1

Cb cloud only
Conditional instability from surface to above freezing level
Sufficient water vapour to form/maintain cloud
Trigger action/lifting force to increase instability

Question 2

Describe characteristics and development of stationary thunderstorms (4)

Answer 2

Occur early - mid afternoon
Most likely over land in summer or autumn
No windshear a lot so no tilt to the cloud
Up and down draft mix which weaken storm

Question 3

Describe 3 stages of thunderstorm and how long they last for convectice localised (stationary)

Answer 3

Formative - 15-20 minutes
Mature - 15-20 minutes
Decaying 1-2 hours

Question 4

Describe characteristics and development of convective travelling thunderstorms (4)

Answer 4

• Wind shear with height causes thunderstorms to move and therefore tilts cloud which separates up/downdrafts

last longer than stationary as sucks up more moisture
- move in direction of 10,000ft (700hPa) wind

Question 5

Describe orographic thunderstorms characteristics and development

Answer 5

• Air forced up by mountains
• anytime of day but stronger early-mid afternoon
• can last for days with fresh supply of moisture from sea

Question 6

Describe characteristics of nocturnal tropical thunderstorms and its formation

Answer 6

• Occur 10º latitude either side of equator. Most active towards dawn and stop by mid morning

Cumulus cloud is formed during the day via convection and remains cumulus cos air is stable. At night the ocean stays warm and air cools creating instability, and now theres no incoming solar radiation at night to burn off cloud top by offsetting the loss of terrestrial radiation which therefore steepens lapse rate.

Consequently temperature at top of cumulus cools down steepening pressure lapse rate and instability

Question 7

Describe characteristics and development of frontal and convergence-type thunderstorms

Answer 7

Frontal - trigger is the lifting of warm, unstable air at the frontal surface. These tend to form in line grouped along the frontal surface, (squall line) in which they move with the front. They’re embedded in multi layered Ac, As, and Sc cloud.

Convergence - tend form in clusters. If formed on a trough they’re likely to be travelling and will be experience as an increase in heavy showers with Ts often precede and followed by lesser showers.

Question 8

Describe characteristics and development of surface trough and upper trough thunderstorms

Answer 8

• occur when cold upper air moves over low level warm air in the mid latitudes, large change in temperatures creates instability which usually develop isolated or cluster of storms

Question 9

Describe characteristics and development of warm front embedded thunderstorms

Answer 9

• Occur infrequently due to stability of warm fronts
• requires large amounts of latent heat released
• caused by cloud formation creating conditional instability

Question 10

Describe turbulence in thunderstorms

Answer 10

• Superimposed gusts in-between updrafts/down with worst between 12-20,000ft.
  updrafts in growing stage, up/downdrafts in mature stage and downdrafts in decaying stage

gust fronts in advance of storm in mature stage

Question 11

Describe icing in thunderstorms (3)

Answer 11

• severe icing from freezing level up to 10,000ft
• occur between 0-40ºC
• 0 to -12ºC worst icing

Question 12

What are microbursts in reference to thunderstorms

Answer 12

• Usually last 5 minutes and are 1-4km across
• Air descends at high speed and is colder than surrounding air
• occur during mature stage/onset of downdrafts
• can be dry or wet microbursts

Question 13

What are gustfronts/first gust

Answer 13

Strong downdraught containing cold dense air spread out horizontally at the base of the storm. Sudden wing change, and lowered temp have characteristics of cold front.

Occurs in mature stage on leading edge of storm and is felt 24-32km ahead and up to 6000ft in depth. warm air above travels into storm creating shear zone

Question 14

Describe electrical phenomena (5

Answer 14

• Occurs +/- 5000ft and +/- 10ºC of freezing level
• starts at onset of precipitation/mature
• hail stones gain negative charge when colliding with lighter precipitation
• lighter precipitation rises and hail sinks to bottom of cloud
• 20% strikes earth, 80% stays in cloud

Question 15

Describe tornadoes in thunderstorms

Answer 15

• Frequently in severe thunderstorm weather where they occur a lot in summer months usually in afternoon. starts horizontal by windshear causing rotation and then is lifted by updrafts rotating it to the vertical
• Maximum diameter of 100-150m

Question 16

Describe hail in thunderstorms

Answer 16

• Develops due to strong updrafts, SCWD freeze and grow on small hail or snow with large hail stones being encountered just above freezing level and when they get to big for updrafts they fall.
• occurs from surface to 45,000ft
• severe hail between 8 - 25,000ft

Question 17

Describe visibility in thunderstorms

Answer 17

• Below Cb in downdrafts with heavy showers
• in front of Cb with gust front
• visibility to 1000m or less, in tropics between 100-300m

Question 18

Describe characteristics of multi-cell thunderstorms

Answer 18

• Caused by gust front
• Creates multiple Cb storms overlapping each other
• Each one will be at a different stage in development
• lasts longer than normal thunderstorm as it regenerates

Question 19

Describe use of radar to identify thunderstorms (5)

Answer 19

•Strong updrafts cause turbulence/mixing
•Creates large water droplets or hail
•Shows strong return on radar
•Uses Doppler radar
•Can detect motion and intensity

Question 20

Precautions to be taken by pilots to avoid or minimise effects of flying in vicinity of thunderstorms (8)

Answer 20

• Switch on all de-icing equipment
  •Reduce airspeed to avoid structural damage
  •All freight/passengers securely strapped in
  •Avoid flying underneath

Disengage autopilot
•Avoid abrupt control inputs
•Turn lights to bright
•Find shortest track through storm

Question 21

Explain the importance of latent heat in development of thunderstorms (ATPL)

Answer 21

• Gives storm more energy
• vapour condensing releases latent heat, increases instability

Question 22

Describe the effect of entrainment of drier air aloft on the development of thunderstorms (ATPL)

Answer 22

• High speed dry air is injected into the clouds
  •Evaporates water droplets absorbing latent heat
  •Makes air more dense and sink
  •Increases downdraft speeds

Question 23

Describe process involved in development of lightning (3, ATPL)

Answer 23

• Rising and falling water droplets/hail produce build-up of static electricity
  •Positive at top of cloud, negative at mid-level near freezing level
  •Builds up then discharges as lightning and thunder

Question 24

Describe hazards associated with flight in and around thunderstorms (ATPL 5) turbulence

Answer 24

• Below the cloud, dangerous during take-off and landing
  •Loose articles being thrown around inside cabin
  •Pressure instrument error due to lag
  •Severe turbulence can destroy aircraft
  •Difficult to maintain altitude

Question 25

Describe hazards associated with flight in and around thunderstorms (ATPL 4) gusts and squalls

Answer 25

- Severe load factors imposed on airframe - causes large fluctuations in GS and Airspeed - structural damage due to abrupt changes in altitude - disorientation

Question 26

Describe hazards associated with flight in and around thunderstorms (ATPL 5) icing

Answer 26

- Build up of ice on airframe, engine intakes and pitot/static •Also on the aerials, control surfaces, propeller blades •Disfigures aerodynamic shape, increasing drag and weight •Restricts air intake and pressure instrument failure •Ice shedding can cause damage

Question 27

Describe hazards associated with hail (ATPL)

Answer 27

- Severe skin damage to airframe if hail is large - noise of hail stones hitting aircraft can be frightening - damage to instrument sensors and windscreen

Question 28

Describe poor visibility (ATPL) thunderstorms

Answer 28

- Beneath Cb reduced to 800-1000m - Within Cb - down to 10m - Worst in heavy showers or low level clouds in mountains - reduces situational awareness

Question 29

Describe tornadoes hazards (ATPL)

Answer 29

•Can destroy aircraft with strong winds and low pressures •Loss of visibility •Large amounts of noise •Biggest hazard is at low altitudes near the ground

Question 30

Describes hazards for microbursts

Answer 30

Forces aircraft into the ground. Winds intensify for about 5 minutes and dissipate within about 10-20 minutes. Horizontal extent of 4km and vertical speeds exceeding 100kts

Question 31

Describe hazards around gust fronts (ATPL)

Answer 31

Reduced visibility Large changes in wind direction

Question 32

Describe following hazards of noise (ATPL)

Answer 32

Distracting to pilots and causes fatigue Associated with lightning, hail, heavy rain, turbulence

Question 33

Describe hazards with loss of instruments and impairment of accuracy

Answer 33

- Loss of current position •Can fly into worst part of storm and cause engine flame out •Loss of altitude •Pilots become overloaded and disorientated

Question 34

Describe characteristics of super-cell thunderstorms (ATPL)

Answer 34

•Vortex of air also called a mesocyclone •Only thunderstorm to create tornadoes •Mature stage may last several hours •More common over land/continental than ocean/maritime