Chp. 12 Weather Theory

Air is made up of

• 78% nitrogen 

• 21% oxygen 

• 1% other gasses

what is the first layer and how high up is it?

Troposphere, up to 20,000ft

The stratosphere is how high?

160,000ft (50km)

Cariolis force/effect

caused by the rotation of the earth

What rate does temperature decrease?

rate of 2c every 1,000 ft gained in altitude

What rate does pressure decrease?

Pressure decreases 1hg every 1000 attitude gained

What’s anticyclonic circulation?

 High to low pressure creates clockwise winds

clockwise aka anticyclonic circulation indicates

dry, stable, descending air movement

Cyclonic circulation

low to high pressure creates counterclockwise winds

cyclonic circulation aka counterclockwise indicates:

moist, unstable ascending air, poor conditions (clouds and precipitation)

Onshore winds are known as

sea breeze

offshore winds are known as:

Land breeze

sea breeze occurs when:

the land is hot, air rises towards the sea and cold air from the sea pushed onto the land

land breeze occurs when:

at night when the land is cooler, cooler dense air pushes into the sea

microburst is a type of

wind shearing

what is wind shearing?

Wind changes direction or speed suddenly over a short distance

How long does a microburst last?

5-15mins

why are microburst the most dangerous wind shearing?

can cause a faulty take off, first you’re climbing rapidly than a downward push and lastly an increase in tailwind

convection currents are:

pockets of high and low air

Why are convection currents more transparent over ______?

water because water has a different temperature

Stable atmosphere makes:

is dry air that makes vertical movement difficult

Unstable atmosphere

is moist warm rising air whose small vertical movements are large and can create turbulence with good surface visibility

convective turbulence mountains

aircraft is carried smoothly up the windward side of the mountain, but dangerous turbulence awaits the other side, tends to push aircraft into the side of the mountain

what to do during maneuvering speed (Va)(Velocity always) during turbulence:

don’t try to correct turbulence try and keep neutral

Isobar

lines drawn to depict wind behavior a few thousand feet up

What do closer and isobars mean?

steep pressure and strong winds moving faster

Inversion is

temperature rising with altitude

Inversion acts as:

smooth and shallow layer close to the ground acting as a lid for temperature

When does surface based temperature inversion occur?

in clear cool nights, because the night cools the ground

what is frontal inversion?

when warm air spreads over cool air or cool air forced under warm air

Dew point

is the temperature in which the air can no longer hold any more moisture

Broken clouds are:

⅝-⅞ clouds cover the sky

Overcast is:

entire sky is covered in clouds

air masses are:

regions or areas where the air remains stagnant for a period of days

Virga

when rain falls through the atmosphere but evaporates prior to striking the ground

Front

boundary layer of two types of air mass

Warm front

hot mass of air replaces a cold body of air pushing the cold body out of the area. The warm air often contains high humidity and as it lifts temperature drops and condensation forms

Signs of warm fronts:

cirriform/stratiform clouds, along with fog, light to moderate forms of precipitation, in summer months cumulonimbus clouds likely to form

During warm front:

stratiform clouds, little drizzle,

After warm front:

stratocumulus clouds exist and sometimes hazy conditions

Cold front

Cold, dense, stable air replaces a body of warm air

the cold air pushes the warm air up creating clouds

Are cold or warm fronts faster and why:

Cold fronts because they stay low to the ground and act like a plow

Indicators of cold fronts:

high dew point, falling barometric pressure, depending on the intensity heavy rain, thunder, lightning, hail, or tornado forms

During cold front:

lack of visibility with winds, gusty temperature and dewpoint drop

After cold front passage

cumulus clouds, decrease in precipitation, temp remains cool

Tailwind

moving with air creating higher speed

headwind

moving against the air lower speed

convective currents

uneven heating of the air above objects on the ground like rocks and hills can be the cause of turbulence

Stable atmosphere indicators:

stratiform clouds, smooth air, poor visibility

what is actual lapse rate used for?

to measure stability of the atmosphere

Sublimation

solid water (ice) to water vapor, bypassing liquid stage

Dew point

temperature which the air must be cooled to be saturated

Frost

Temperature of the Collecting Surface is at or below the Dew-point,

and the Dew-point is BELOW freezing.

Visibility is reported in

Statute Miles (SM)

Stratus

Uniform grayish clouds covering the entire sky, often associated with Drizzle or

Mist. NOTE: Moist stable air flowing up slope will form Stratus type clouds.

Cumulonimbus

Tallest of all clouds and can span all cloud layers. They may have large anvil-shaped tops and can produce lightning, heavy rain, hail, strong winds, severe or greater turbulence and tornadoes.

Towering Cumulus

Indicates Convective Turbulence = BAD FOR YOU!

Nimbus means

rain

Lenticular (Lens Shaped) clouds

appear stationary but can have high winds

Virgas dangerous because:

cold air causes quick sinking or downwardness

Radiation fog

Radiation fog forms in moist air over low, flat areas on clear, calm nights. Is known as ground fog if less than 20ft thick.

Advection fog

requires wind for formation.

Upslope fog

Moist, stable air force up Mountain Slopes

stream fog

Cold, dry air passes, over warm water. Low-Level turbulence, and icing are associated with steam fog.

frontal passage is

change in temp, wind direction, and pressure

where do squall lines develope?

in front of a fast-moving cold front, usually clear rapidly but leave behind turbulence and cold temperatures

Stages of thunderstorm

cumulus stage the continues upward action, rain, and dissipation

Thunderstorms occur by

water vapor, unstable lapse rate, and lifting action

Lightning

always associated with thunderstorms

Clouds that form low to the ground, 65,000ft agl below

stratus, stratocumulus, nimbostratus, fog

they can change fast

What are the middle clouds you will find 65,000ft to 20,000ft agl?

altostratus, altocumulus

are composed of ice crystals and super cooled water droplets

What clouds will you find high above 20,000ft AGL?

cirrus, cirrostratus, cirrocumulus

are made of ice crystals and pose no real threat usually only form in stable air

What is the layer of the atmosphere that is between troposphere and stratosphere?

tropopause which changes based on the latitude and season of the year. It traps moisture associated weather of the troposphere and is often associated with the location of the jet stream which is possible clear air turbulence.

Where and how do cumulus clouds form?

They form low and vertically move up. They indicate that the air around and inside them is unstable and turbulent. They will later form into cumulonimbus clouds or thunderstorms. Cumulonimbus clouds contain a lot of unstable air and moisture and therefore can create lightening, wind gusts, wind shears, and hail.

Nimbus clouds mean

rain bearing clouds

Fracto clouds

clouds that are scattered

source region

an area where weather has been stagnant for a few days

Cold air passing over warm air creates

poor visibility but not convective currents

Cirrus clouds

ringlets, fibrous high around 20,000 agl

what are squall lines?

lines of thunderstorms that usually occur in front of a cold front but can be found behind any front

Cold fronts vs warm fronts when they approach

cold fronts can approach in a few hours whereas warm fronts can be better predicted and can last for a few days

Wind shifts

low-pressure winds rotate counterclockwise, high-pressure winds rotate clockwise

occluded fronts

fast moving cold front catches up to a slow-moving warm front

cold front occlusion

cold air is stronger than the warm air Infront of it forcing the warm air up

warm front occlusion

warm air is stronger than the cold air behind it so the cold air is forced over it. This creates more severe weather

Tornadoes

can form outside a squall line and is caused by the winds creating vortexes

Supercold water

water touching aircraft and immediately turning into ice

rotor clouds

clouds rolling over mountains

stationary front

warm and cold air stagnant