Ch 6 Weather Flashcards
Unstable air
- cloud, rain, turbulence, visibility
more vertical development, moist and warm
- cumulus clouds
- shower rains
- rough turbulence
- good visibility
Wake Turbulence
1. when departing after lg aircraft landed
2. landing behind lg aircraft
3. taking off behind lg aircraft
4. lg aircraft just taken off & you approach to land
- lift off beyond their touchdown
- land beyond their touchdown
- lift off before the lg aircraft rotation pt.
- touchdown before the lg aircraft’s liftoff point.
- Rime ice
- Clear ice
- Mixed
- can be found in stratus clouds, instant icing, small drops -20C & -15C
- develops in an area of large supercooled water droplets, difficult to see, -10C & 0C
- occurs in temp. between -10C & -15C
Classification
Polar or tropical
- cool or warm
Continental or Maritime
- dry or moist
Clouds with vertical development
- cumulus= can indicate a shallow layer of instability, turbulence, little icing
- Towering Cumulus= indicate a fairly deep area of unstable air, moderate to heavy turbulence w/ icing. Often develop into thunderstorms
- Cumulonimbus (rainmaker)= large, vertically developed, in very unstable air. contain large amount of moisture
Temperature inversions
occur in stable air calm winds, near the sfc on cool, clear nights
sfc is cooler than the air above it and visibility is poor, restricted by fog / low clouds
- Gas to Liquid
- Liquid to Gas
- condensation
- evaporation
- air mass thunderstorm
- severe thunderstorm
- short-lived, no strong winds
- wind gusts +50 kt, tornadoes, hail
Mountain Breeze
night, downslope flow, 5 to 15 kt
Convective turbulence
aka ?
aka thermal turbulence
daytime over land in fair weather
rising heated air from the sfc
when air is moist, the currents may be marked by build-ups of cumulus clouds
Squall line
Mixture of storms in a continuous line
Land Breeze
night, from the cooler land to the warmer water
Alt: 1,000 to 2,000 AGL
extend between 5 and 100 NM inland
High Clouds
Alt: base above 20,000 agl
serius icing and turbulence
- cirrus= above 30,000, thin, patches or narrow bands. can warn approaching bad weather
- cirrostratus= thin, layer/ sheet, low moisture, no icing
- cirrocumulus= patchy, light turbulence
LLT (low-level turbulence)
4
- Below 15,000 MSL
- due to sfc heating or friction
1. mechanical
2. convective
3. wake turbulence
4. frontal turbulence
Cold front
1. fast moving
2. slow moving
- sfc friction slows the mvmt
leading edge bulge out & steepen front’s slope - leading edge shallower
- meets stable air = stratus form behind
- unstable air = lg # of vertical clouds form
The greatest instability occurs when
the air is both warm and moist
- Wind Shear
- Microburst
- drastic shift in wind speed and direction, wind shear turbulence is associated with all thunderstorms
- can last more than 15 min. and wind speed of 25 kt
Convection
cool air= heavier, denser > sinks
warm air= lighter, less dense > rises
movement of air up and down
Mountain Wave Turbulence
stable air moves across a ridge
wind is +40 kt
When you encounter turbulence when approach for landing
- fly a power-on approach at an airspeed slightly above the normal approach speed.
- fog
- ground fog
- radiation fog
- any low cloud within 50ft of ground
- less than 20ft deep
- flat sfc on clear, calm, humid nights. stable air associated w/ H pressure systm.
Atmospheric Pressure
The unequal heating of the sfc modifies air density, creates circulation patterns and causes changes in pressures
Atmospheric Composition
78% Nitrogen
21% Oxygen
1% other gases
A cubic foot of the atmosphere can contain from 0 to 4% of water vapor. Responsible for major changes in the weather.
What changes when crossing a front
temp.
pressure
wind
Source Region
Area where air mass gets the properties of temp. and moisture that determines its stability
Precipitation induced fog
Warm rain falling though cold air, evaporation occurs and saturates the air causing fog. Fog doesn’t clear until the rain moves away.
- Liquid to solid
- Solid to Liquid
- freezing
- melting
Frictional force
Air moves from high pressure (clockwise) to low pressure (counterclockwise)
Within about 2,000ft AGL, Pressure gradient force if greater
At high altitudes, Coriolis Force is greater
Dewpoint
temp. at which air reaches a state where it can’t hold more water
anticipate fog when dewpt./ temp. is 4F (2C) or less and decreasing
dewpt. is the temp. to which air must be cooled to become saturated
Temperature inversions
occur in stable air calm winds, near the sfc on cool, clear nights
sfc is cooler than the air above it and visibility is poor, restricted by fog / low clouds
Atmospheric Circulation
movement of air relative to the earth’s sfc
pressure gradient:
1. trough - - -
2. col
3. ridge /\/\/\
- elongated area of low pressure
- neutral area between 2 highs or lows, or intersection of a ridge and a trough
- elongated area of high pressure
Capping Stable layer
top of convective layer, where smooth air begins
3 Cell Circulation Pattern
Polar Cell > 60 lat. to N
Ferrel Cell > 30 to 60 lat.
Hadley Cell > 0 to 30 lat.
CAT
Clear air turbulence
above 15,000 or any altitude with no visual warning
Stratosphere height
up to aprox. 160,000 ft
Atmosphere exists within:
30 km (100,000 ft)
Temperature inversions
occur in stable air calm winds, near the sfc on cool, clear nights
sfc is cooler than the air above it and visibility is poor, restricted by fog / low clouds
Airmass
large body of air w/ fairly uniform temp. and moisture
Sea Breeze
day, cool, dense air (H) moving inland from water
Alt:1,500 and 3,000 AGL
Speed: can reach 10 to 20 kt
- solid to gas
- gas to solid
- sublimation
- deposition
Relative humidity
actual amount of moisture in the air compared to the total amount that could be present at that temp.
Troposphere alt
sfc to about 36,000
Advection
lateral movement of temp./air
Atmospheric stability
atmospheric resistance to vertical motion
- LLWAS
- TDWR
- in-flight visual indicators
- low-level wind shear alert system
- terminal doppler weather radar
- ring of dust, virga, trees moving diff. directions
Low clouds
Alt: sfc to 6,500 agl
can create icing hazard to aircraft
- status = flat, cover a wide area
- stratocumulus= layer of white puffy clouds
- nimbostratus= dark clouds, rain or snow
Valley Breeze
day, upslope flow of air, 5 to 20 kt
Life Cycle
1. Cumulus stage
2. Mature stage
3. Dissipating stage
- start of vertical mvmt., updraft
- rain (downdraft) fall.
- 15-30 min after mature stage, mostly downdraft
- approaching a front toward the cool air
- approaching toward warm air
- pressure drops slowly until you cross, then rises quickly
- pressure drop abruptly, then rises slowly
stable air
- clouds, rain, turbulence, visibility
resists convection, cool and dry
- stratus clouds
- steady/ cont. rain
- little to none turbulence
- poor visibility
Virga
streaks of rain that evaporate before reaching the ground
Frontal turbulence
Friction between the two opposing air masses
- advection fog
- upslope fog
- steam fog
- hot, moist air moves over to cooler sfc. Common under cloudy skies coastlines. 15kt intensify fog. above 15 kt, turbulence and stratus clouds.
- moist, stable air moves up a mountain.
- cold, dry air moves over warm water. Can produce icing hazard and low-level turbulence bc it forms in unstable air
Layer of the atmosphere
- troposphere
- tropopause
- stratosphere
- mesosphere
- thermosphere
Middle Clouds
Alt: 6,500 to 20,000 agl
moderate turbulence and potentially severe icing
- altostratus = flat & dense, cover wide area
- altocumulus= patchy, uniform clouds. when altostratus break up
Mechanical Turbulence
when wind blows around hangars, trees, or perpendicular to steep hills or mountain ridges
Conditions for thunderstorms to develop
- lifting force
- unstable air
- high moisture
What to do when you encounter turbulence
- slow the plane to maneuvering speed or less
- maintain a level flight altitude
- accept variations in airspeed and altitude
Coriolis Force
- Affects all objects moving freely across the face of the earth.
- Airplane flight paths end up tracing a curved path due to the earth’s rotation.
- The greater the speed of the object, the greater the deviation.
Restrictions to visibility
-haze
-smoke
-smog
-volcanic ash
-dust
- Coriolis Force Northern hemisphere
- Coriolis Force Southern hemisphere
- deviation to the right
- deviation to the left
Tropopause
a level not a layer, acts as a lid to confine water vapor & weather
pressure gradient:
1. closely spaced isobars
2. spread apart isobars
- strong winds and large pressure changes
- low winds and weak pressure gradient
