Front Formation And Thunderstorms

Question 1

Polar front theory 5stages

Answer 1

1. Stationary stage
   Cold and warm flow in opposite directions where they meet
2. Wave stage
   Indentation occurs fronts advance on opposite sides
   Coreolis force diverts fronts
   Indentation creates low pressure
3. Open stage
   Old front chases warm front around squeezing warm sector up into atmosphere
4. Occluded stage
   Cold front starts to catch up
   Occlusion occurs
5. Dissipation stage
   Both fronts begin to dissipate
   (Low pressure reduces)
   Depression moves independently

Question 2

Air mass classification

Answer 2

A
Arctic

P
Polar

T
Tropical

C
Continental

M
Maritime

E
Equatorial

Question 3

Cold advection

Answer 3

K
Cold air moving to warm regions
Ex pm moving north towards nz and aus
Temp increases
Moisture increases over ocean
ELR increases (unstable)
Cu or Cb clouds
Cold moist southerlies
General southwesterlies
Western coast effected eastern sheltered

Question 4

Warm advection

Answer 4

W
Warm air to cold regions
Ex. Tm or e moving south to nz
Cools and adds moisture from ocean
ELR decreases (stable)
Cools to saturation (fog mist cloud)
Cloud more extensive if Orographic lifting occurs
Northern regions effected

Question 5

Polar depression

Answer 5

Comma shaped
Usually cb
Very intense
Often marked as cold front but temp contrast is minimal

Question 6

Warm sector (mid latitude) depression

Answer 6

Reasonably common
Subtropical air moving south rotational velocity increases
Convergence occurs
Extensive deep depression formed
Reasonable temperature contrast behind first cloud sheet

Question 7

Orographic depression

Answer 7

Wind flowing over and lower front lagging creates low pressure in lee of mountain
Associated weather similar to Fohn wind (gusty warm turbulent)

Question 8

Thermal depression

Answer 8

Extreme surface heating
Low pressure surface convergence and rising air
Occurs in Canterbury plains (resulting cyclonic flow pushes sea breeze northerly)

Question 9

Thunderstorm

Answer 9

Rain bearing cloud that produces lightning

Question 10

Thunderstorm requirements

Answer 10

Unstable atmosphere through a deep layer (very high ELR)
Adequate supply of moisture at low levels (determines height of cloud base)
(Release of latent heat as cloud forms destabilises environment and increases updrafts)
Some type of lifting mechanism
Mechanism to provide electrical discharge

Question 11

Thunder vs lightning

Answer 11

Thunder
Explosive expansion of air when lightning travels through it

Lightning
Electrical charge rendering the air white hot

Question 12

Hail

Answer 12

Rain drop lifted above fzl then tumbled around causing accretion
Eventually falling in cold down draft

Question 13

Cumulus/developing stage

Answer 13

Cb growing
Up draughts due to release of latent heat from cloud formation
Bulging freezing level
Up to 30000 ft

Question 14

Mature stage

Answer 14

Up draughts can no longer hold water
Severe turbulence with up and down draughts in close proximity and precipitation
Anvil starts to form
Produces gust front at front side of cloud
Low pressure with updrafting air pulls in cold air
Irregular freezing level
5-10 mile height

Question 15

Anvil/dissipating stage

Answer 15

Up draughts cease and bottom of cell will evaporate leaving ci anvil behind
Freezing level bulges down
Rain
Constant down draughts

Question 16

Ts hazards

Answer 16

Severe turbulence
Hail
Icing
Lightning
Noise
Microburst
Wind shear
Visibility

Question 17

Microburst wind sequence

Answer 17

Severe headwind
Severe downdraught exceeding climb performance
Tailwinds up to 50kts

Question 18

First gust gust front

Answer 18

Cold front at the leading edge of cb

Question 19

Tornadoes

Answer 19

Low level wind shear causes rotation
Severe updraughts pull rotating column vertical
High velocity reduces pressure causes air to condense
Severe winds (300+ km/h)