Meteorology 3

1
Meteorology 3
2
FRONTS
Pg 6-7
3
Warm
Colder
Cold
Warm
Colder
Cold
Warm
Cold
Colder
4
Precipitation

• Precipitation occurs when water droplets grow
  sufficiently in size and weight and then fall due
  to gravity.
• Showery precipitation Cumulus
• Steady precipitation Stratus
• Condensation Nuclei
• Smoke, sea salt, etc.

5
MOISTURE CONTENT

_at_40OC one cubic metre of air can hold 50 grams of
water vapour. One M3 of air weighs about 1.35
kg. This represents about 3.5 by weight.
Pg 1-3
6

• CLOUDS
• PRECIPITATION
• THUNDERSTORMS
• FOG
• ICING
• VFR MVFR IFR WEATHER
• UPPER WINDS

7
CLOUDS

• CLOUDS ARE FORMED IN TWO WAYS
• air is cooled to its saturation point and
  condensation occurs OR
• Air absorbs additional water vapour until
  saturation is reached.
• LIFTING AGENTS
• Convection
• Orographic lift
• Frontal Lift
• Convergence
• Mechanical turbulence

8
UNSTABLE vs. STABLE
9
UNSTABLE
Steep lapse rate Cumulus type cloud Precipitation
in showers Thunderstorms Good visibility Bumpy
conditions
Shallow lapse rate Stratus type
cloud Precipitation is steady and
lighter Fog Poor visibility Smooth conditions
STABLE
10
Precipitation
.
Pg 8-17

• Any precipitation, in order to form, requires
  condensation nuclei. - Temperature to dew point
  spread must be small

11
Precipitation
Pg 9-2
12
THUNDERSTORMS

• Requirements
• Unstable air to high levels
• High relative humidity
• Lifting agent
• The three stages
• Cumulus
• Mature
• Dissipation

13
THUNDERSTORMS
Pg 15-2
14

• Cumulus Stage
• Cloud driven upward by the latent heat as water
  vapour condenses
• Temperatures in cell are higher than outside
  temperature at the same level.
• No precipitation as water and ice are suspended.
• Strong updrafts prevail throughout.
• Mature Stage
• Heights may reach 60,000 feet
• Updrafts up to 6,000 ft/min or over 100 km/hr.
• As the water droplets grow large enough to fall,
  they drag air down with them.
• Downdraft starts in the middle region of the
  cloud.
• Lightning, microburst, hail, wind shear.
• Arrival of precipitation on the ground in mature
  stage.
• Dissipation stage
• Downdraft spreads throughout the cell (except
  top)
• Gradual cessation of rainfall and the passing
  rain may cool the lower regions
• Anvil shape
• Total cycle
• Can form in 15-20 minutes although whole process
  usually 1 to 3 hours

15
Thunderstorm Types

• Air Mass
• Form singly or in clusters on hot days.
• Usually VFR weather around them
• Convection and/or orographic lifting
• Frontal
• Usually advancing cold front
• Squall line very turbulent and slows front
• NOTE
• Either type can penetrate the tropopause which
  can be based from 28,000 feet at poles to 54,000
  feet at equator

16
Convective Thunderstorms
Pg 15-11
17
Orographic Lift
Pg 8-15
18
Pgs 15-9,10,11
19
Thunderstorm Weather

• Turbulence has potential to overstress a/c max
  turb. near mid-levels 12,000 to 20,000 feet
• Lightning may blow out electrical fuses
  blindness structural damage ignite fuel cells
  greatest potential between -5/5
• Hail encountered between 10,000 and 30,000 ft
  may be encountered in clear air downwind of
  storm airframe damage
• Icing heaviest icing occurs just above
  freezing level where droplets are super cooled.
  Severe in the mature stage near cloud top.
• Pressure rapid barometric changes, altimeter
  may be unreliable.
• Rain reduced visibility, refraction on
  windscreen, hydroplane

20
Dos and Donts of Thunderstorms
Pg 15-18
21
Gust Front Hazards
Pg 15-18
22
Anvil, Multi-Cell Lightning
Positive build up in top and negative build up in
cloud base is usual
Pgs 15-3,5,7
23
FOG
24
FOG

• Fog is a cloud (usually stratus) that is in
  contact with the ground.
• forms in relatively stable air where the
  temperature
• to dew point spread is small, wind may be
  present
• requires condensation nuclei
• Usually needs a cooling process
• Types of Fog
• Radiation Advection
• Upslope Steam
• Frontal Ice

25
Radiation Fog clear night, light wind, high
humidity, often a high pressure area.
Pg 10-7
26
Radiation Fog at CYKZ
27
Advection Fog warm moist air moving over colder
land, horizontal movement, warm fronts/oceans,
sometimes strong winds (25kts)
Pg 10-8
28
Upslope Fog
Pg 10-9
29
Ice Fog Byproduct of engine is wateradded to
cold crisp air. (sublimation vapour to ice)
Pg 10-10
30
WATER VAPOUR WATER - ICE
Pg 1-2
31
Frontal Fog vapour addition raises the dew point
under a warm front
Pg 10-10
32
Steam fog cold air moving over a warm surface
Pg 10-9
33
Steam Fog at Collingwood
34
ICEpart 9

• Clear Ice skin warms to 0 while droplets freeze
  
• large super cooled water droplets
• bottom layers of cold clouds or tops of unstable
  clouds
• freeze just below 0 to -15
• tend to hit wing
• high collection efficiency
• large spreading droplets
• Rime Ice skin temperature lt 0
• small super cooled droplets can exist down to
  -40
• stable clouds, usually rime only -25 to -40
• tend to flow around wing
• low collection efficiency
• leading edge only (no spread)

35
Heaviest Icing Rate of Catch

• Skin temperature at or below freezing
• High water content held up in updrafts
• Large droplets
• Collection efficiency is inversely proportional
  to the surface geometry - thick vs. thin wings

Pg 9-10
36
Ice Formation - Stability
Pg 9-4
37
ICING

• Cumulus
• icing distributed vertically
• top of mature stage
• In 5000 ft above 0 level
• large droplets to -25

• Stratus
• icing distributed horizontally
• if turbulent, top of cloud will have the
  heaviest.
• snow means less icing

Warm clouds have more droplets with
altitude. Colder clouds have fewer droplets
with altitude.
Pg 9-5
38
WEATHER TERMINOLOGY

• SKY CONDITION
• Clear 0/8
• Few 1/8 to 2/8
• Scattered 3/8 to 4/8
• Broken 5/8 to 7/8
• Overcast 8/8
• IFR less than 1000 ft 3 miles
• MVFR 1000-3000 ft 3-5 miles
• VFR greater than 3000 ft better than 5

39
Clear 0/8
40
Few 1/8 to 2/8
41
Scattered 3/8 to 4/8
42
Broken 5/8 to 7/8
43
Overcast 8/8
44
UPPER AIR CHARTS standard pressure levels

• 850 mb 5000 feet asl
• 700 10000
• 500 18000
• 400 24000
• 300 30000
• 250 34000
• 200 40000
• 150 45000
• 100 53000

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STEEP PRESSURE GRADIENT GIVES HIGHER WIND SPEEDS
46
JET STREAM
Pg 12-11
Pg 12-13
47
Low Level Nocturnal Jet
Pg 11-13
40 KNOTS