meteorology - 5 cyclone air cadets · 2019. 10. 21. · cumulus, cumulonimbus, towering cumulus....
TRANSCRIPT
Meteorology
5.06 Turbulence, Visibility, and FrontsReferences:
Air Command Weather Manual Chapters 7, 8, 10 and 11
FTGU pages 133, 138, 140-145, 147, 155 and 156
Aviation Weather Student Guide
http://www.tpub.com/content/aviation2/P-303/index.htm
5.06 Turbulence, Visibility, and Fronts
• MTPs:
– Types of Turbulence
– Wind Shear
– Visibility Obstructions
– Definition of a Front
– Front Formation
– Warm Front
– Cold Front
– Fronts on Maps
• MTPs:
–Air Masses – Definition and Characteristics
–Formation
–Classifications
–Modification
–Geographic factors
–Seasonal Effects
5.06 Turbulence, Visibility, and Fronts
Types of Turbulence
1. Convection
Turbulence
Thermal Turbulence
• Hot sunny days - sun heats the
earth’s surface unevenly
Isolated convection
currents cause turbulence
Types of Turbulence
2. Mechanical
Turbulence
Also known as “eddies”
• Friction between air and ground
• Irregular terrain and man-made
obstacles cause severe eddies.
• http://www.youtube.com/watch?v=vQH
XIHpvcvU
Types of Turbulence
3. Orographic turbulence• Known as mountain wave
• Can be expected on the windward side and over the crests of mountains, along the downward slope
Avoid rotor cloud and strong downdraft on the leeward side of mountain
Wind Shear
4. Wind Shear
• Any marked change in wind speed and
direction with height that produces local areas
of turbulence
• When changes are large, quite
severe turbulence can be expected
• Low level wind shear occurs as a
result of gust fronts and downbursts
– Associated with thunderstorms
Wind Shear
Inversions• Overnight cooling creates temperature inversion a few hundred feet
above ground that can produce significant wind shear
• Can also form where cold air trapped in low lying areas (ex. valleys)
as cold air denser than warm air
– At night this air will “flow” into low lying areas
Confirmation
1. Wind shear is a sudden change in the
wind’s ____________ and/or
___________.
2. ________________ is the condition when
the temperature increases with altitude.
3. _____________ causes turbulence due to
uneven heating of the ground.
speed
direction
Inversion
Convection
Visibility Obstructions
• Haze – Very small water droplets, dust or salt particles
– Cannot be felt or individually seen with naked eye
– Uniform veil, restricts visibility
– Only a problem in stable air.
Visibility Obstructions
• Smoke– Created by industrial pollutants, vehicle exhaust in
urban/industrial areas – thick blanket of haze severely restricting visibility
– Worse when flying towards the sun
– Forest fires can also contribute in more rural areas.
Visibility Obstructions
• Smog– Combination of smoke and fog
– Has a yellow colour to it due the pollution mixed in with it
– Often occurs with an inversion– Type of air pollution derived from vehicular emission from internal
combustion engines and industrial fumes
– Fumes react in the atmosphere with sunlight to form secondary pollutants
Confirmation
• 1. What are some of the visibility obstructions a pilot can face?
• 2. How is thermal turbulence created?
• 3. How is an inversion formed?
• 4. Which part of a mountain would see the worst turbulence?
Haze, Smoke and Smog
Uneven heating of the ground – uneven radiation
Warm air flows over top of cold air in a valley
Windward side
• Definition:
– A large section of the troposphere with uniform properties of temperature and moisture
• May be several thousand miles across
Cold Air Masses Warm Air Mass
Instability Stability
Turbulence Smooth air
Good visibility Poor visibility
Cumuliform clouds Stratiform Clouds and Fog
Shower type precipitation Drizzle type Precipitation
Hail, Thunderstorms may occur
Air Masses
• Formation:
– Air masses develop uniform properties of temperature and
moisture
– Source Regions:
• Formed over the ice and snow surfaces of the Arctic would
be cold and dry
• Formed over the South Pacific would be warm and moist
Air mass formation
• Three main sources over North America
– Arctic (A)
• Cold
• Extends from the North Pole south to the permafrost line
– Polar (P)
• Cool
• Extends south from the permafrost line to where the
temperature is 10°C
– Tropical (T)
• Very warm
• Lies below Latitude 30°N.
Air mass formation
• Two Sub-Categories:
– Continental (c) - Dry
– Maritime (m) - Moist
Air mass formation
• Continental Arctic (cA):
– Forms over poles
(usually in winter)
– From polar regions
across prairies, into
east
– Low moisture, Very
cold, Very stable
– Very low
tropopause.
PacificOcean
AtlanticOcean
Gulf ofMexico
Air mass classifications
• Maritime Arctic (mA):
– Forms over Alaska or Siberia
– Spends short time over North Pacific Ocean
– Moist, Cold, Unstable in low levels
– Low tropopause.
PacificOcean Atlantic
Ocean
Gulf ofMexico
Air mass classifications
• Maritime Polar (mP):
– Forms over Arctic,
Alaska and Northern
Russia
– Spends longer time over
Pacific Ocean than mA
– Moist, Warmer than mA,
More stable than mA
– Medium height
tropopause.
PacificOcean
AtlanticOcean
Gulf ofMexico
Air mass classifications
• Maritime Tropical (mT):
– Forms over oceans and
bodies of water in the
Tropics
– Rarely appears north of
Great Lakes
– Causes fog that effects
Atlantic provinces
– Moist, Very warm,
Unstable
– High tropopause.
PacificOcean Atlantic
Ocean
Arctic
Air mass classifications
• As air masses move from their source
region, they become modified
• Degree of modification depends on three
factors:
1. Speed at which the air mass moves
2. Make up of the surface (i.e. land or
water)
3. Temperature difference between air
mass and new region’s surface
temperature.
Air mass classifications
Air mass classifications
The temperature of the oceans is a major factor
– North Pacific Current supplies warm water along the
West Coast of Canada
– This warm water current maintains the Gulf of Alaska
ice free through the winter
Geographic factors
Mountains
• On land the Rocky Mountains and the Coastal Range
barrier extends unbroken from Alaska to Mexico with
peaks extending up to 10,000 - 15,000 feet
Geographic factors
Lakes
• Northern Canada is covered with lakes that are open
and provide moisture to the air in summer, but are frozen
in winter.
Geographic factors
Seasonal effects
• What are the characteristics of a Cold Air Mass?
– Instability, Turbulence, Good visibility, Cumuliform clouds
– Shower type precipitation (Hail and thunderstorms may occur)
• What are the three main source regions for North
America?
– Arctic (Cold), Polar (Cool), Tropical (Warm)
• What are the two air mass sub-categories?
– Maritime and continental
• Name some factors that affect air masses
– Geographic location
– How fast they move
Confirmation
What Season they form in
Latitude they form in
Definition of a Front
• Definition:– FTGU: Transition zone between two air masses– What’s happening at a front?
• Large change of temperature within a relatively short distance of 50-100 miles in the zone between air masses
– The interaction zone between the air masses is responsible for weather changes
Front
Front Formation
• Requirements:
– a cold air mass and a warm air mass lying adjacent
– mixing action
Warm Front
• A warm front is the retreating edge of a cold air mass
• Warm air advances and overruns retreating cold air
• Warm air rises since it is less dense than cold air
• Usually moves slower than a cold front
• Long gentle frontal slope.
Simulation
http://www.phschool.com/atschool/ph
sciexp/active_art/weather_fronts/
Warm Front
Warm front weather
• Warm air mass pushes moisture up the slope, causing cloud and precipitation
• Overrunning, moisture content and stability of warm air determines severity of weather
• If the warm air is unstable, thunderstorms may be embedded
1313
11
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IPIPRR ZRZR
CICICSCS
ASAS
NSNS
SS
MOIST/STABLE - WINTER 12
Warm Front
Ceiling Low ceiling can persist for long periods of time
Visibility Restricted
PrecipitationBegins in altostratus layer
Becomes heavier as front approachesVery heavy showers indicate potential thunderstorms
Turbulence Less severe than cold front (unless cumulonimbus clouds embedded)
CloudsCirrus, Cirrostratus, Altostratus, Nimbostratus, Stratus
Warm Front
• Indication of Approaching Warm Front:
– CCANS
• Cirrus
• Cirrostratus
• Altostratus
• Nimbostratus
• Stratus
Cold Front
• A cold front is the leading edge of an advancing cold air mass
• Cold air undercuts the warm air
• Rising warm air expands and cools
– Cumulus cloud
1 MILE
50 MILES
SLOPE OF A
COLD FRONT
5
Cold Front
– Slope can be very steep
– Weather severity determined by moisture
content and stability of the warm air mass
Simulation
http://www.phschool.com/
atschool/phsciexp/active_
art/weather_fronts/
Cold Front
CeilingLow, with clouds of vertical development, icing and
turbulence
Visibility Good, Usually improves after the passage of the front
Precipitation Usually a narrow band
Turbulence Flight through a cold front can be expected to be rough
CloudsCumulus, Cumulonimbus, Towering cumulus
Cold Front
• Temperature– May drop sharply after front passes
– Usually drops gradually as air behind is warmed by the ground
• Pressure– Decrease, followed by a marked rise after frontal
passage
Warm and Cold Front
Fronts on Maps
• Red = Warm
• Blue = Cold
• Sometimes an air mass is
neither advancing nor
retreating
• Results in Stationary
Front
• After a few days, the front
may dissipate or start
moving
Simulation
http://www.phschool.com/
atschool/phsciexp/active_
art/weather_fronts/
Stationary Front
Occluded front
• Cold air moves faster than
warm air therefore cold
front may catch up to warm
front
• Cold front undercuts and
lifts existing warm front
Simulation
http://www.phschool.com/atschool/ph
sciexp/active_art/weather_fronts/
Occluded Front
• Results is a trough of warm air aloft » TROWAL
• TROWAL weather varies
– Combination of cold and warm frontal conditions
Occluded Front
• Upper Cold Front: Cold
front crosses valley where
there is colder air that
cannot be undercut
– Front is lifted
• Upper Warm Front: Warm
front crosses cold air
trapped on the ground
– Very shallow frontal
edge, followed by a
sudden steepening of
the frontal slope
-25°C -25°C
-10°C-5°C
-5°C
-15°C
upper cold front
upper warm
front
23
Upper Front
Another type of Upper Warm Front:
Occurs on a hot day
Cold air is heated at the until it is no longer considered
cold
Results in Upper Warm front.
Upper Front
Confirmation
1. Label where the cold front and where the warm front is.
2. Label what clouds are associated with the fronts
3. Draw an arrow to show which direction the front is moving
Cold
FrontWarm
Front
Altostratus
Cirrus
Cumulonimbus
Confirmation
• What weather is associated with a cold front?Low Ceiling, with clouds of vertical development, icing and turbulence
Good Visibility, Usually improves after the passage of the front
Usually a narrow band of precipitation
Turbulence
Cumulus, Cumulonimbus, Towering cumulus
• What weather is associated with a warm front?Low ceiling can persist for long periods of time
Restricted Visibility
Begins in altostratus layer, becomes heavier as front approaches
Very heavy showers indicate potential thunderstorms
Less severe than cold front (unless cumulonimbus clouds embedded)
Cirrus, Cirrostratus, Altostratus, Nimbostratus, Stratus
Severe Frontal Weather