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

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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