Meteorology Flashcards
Layers of the Atmosphere (T, T, S, S, M, M, T, T, E)
Troposphere Tropopause Stratosphere Stratopause Mesosphere Mesopause Thermosphere Thermopause Exosphere
Troposphere
Lowest layer
Contains most of the water vapour in the atmosphere
Temperature decreases as altitude increases
Majority of weather and clouds occur here
Tropopause
Upper boundary layer of the troposphere
The temperature has dropped to about -56C
Jet streams, CAT, thunderstorms
Stratosphere
Extends to 160,000’
Temperature increases as altitude increases
Initially, -56 C but gradually rises to 0 C
Strong vertical air motions
Some weather can extend into stratosphere
There is virtually no weather above the stratosphere.
The Standard Atmosphere
At sea level:
Air is a perfectly dry gas
Temp 15°C
Standard lapse rate Temp changes 1.98°C per 1000 ft
Pressure 29.92”hg or 1013.25mb at sea level
Pressure - the “Compressibility” of air.
Air is not empty space.
It has mass and weight just like any other solid, liquid, or gas.
Density = is mass per unit of volume.
affected by temperature.
Warm air molecules move around faster and take up more space.
(warm air is less dense).
The Barometer
The more force applied to the surface of the mercury in the bowl, the higher the mercury rises in the tube.
Units of Measurement
A pressure decrease or increase equals 1 inch of mercury per 1000’.
Ex:
01.00 = 1000’
29.92 Hg is standard pressure for sea level (ISA).
If the pressure were to rise or fall 1 “Hg, the result would be:
30.92 = -1000’
28.92 = +1000
Station Pressure
The actual weight of air (pressure), at the station.
Sea Level Pressure
The pressure calculated down to mean sea level pressure; or, the station pressure plus the weight of the air extending from the station to mean sea level
City A is at sea level with pressure of 29.92 Hg
–City B is at 5000’ MSL what is their Hg?
5,000 = 5.0 Therefore 29.92 -5.0 = 24.92.
Remember when higher in the air (+5,000ft) = less pressure = take away from the mercury reading.
Density Altitude
is pressure altitude corrected for temperature.
“Density altitude is the altitude the airplane feels it is at.”
–airplane will be most vulnerable to a high density altitude during takeoff.
Pressure Systems
govern the evolution of fronts and weather.
Low Pressure Systems
- -aka: depression or cyclone.
- -Winds converge at surface = upward motion
- -Winds flow counterclockwise and toward a low.
- -weather associated with a low is always bad however the temperature becomes more stable
- -may cover anything from a very small localized area to half a continent.
High Pressure Systems
aka: anti-cyclone.
- -Winds blow clockwise and away from a high
- -Winds converge at altitude = descend then diverge at the surface.
- -Weather is usually fair and clear.
Convergence and Divergence
–always flow away from highs and towards lows.
Isobars
These are lines of equal pressure depicted on a pressure map
- these lines circle areas of pressure and never cross
- separated by 4 millibars (another word for hpa) intervals
Ridge
A ridge is an elongated area of high pressure
–Fine to fair weather can be expected.
Trough
A trough is an elongated area of low pressure.
Poor frontal weather can be expected.
Col
A col is an area of neutral pressure.
Weather can be unpredictable.
Wind and Pressure Gradient
[pressure gradient = rate of change of pressure over a given distance]
- -Isobars spaced closely together indicate rapid change of pressure = Expect strong winds.
- -Isobars spaced further apart indicate slow change of pressure = Expect light winds
Coriolis Force
air is influenced by earth’s rotation.
doesn’t flow in straight lines
–high to a low. It is deflected to the right (north)
–deflected to the left in southern hemisphere
Deflection is more pronounced at the poles and zero at equator.
Buy-Ballot’s Law
northern hemisphere, winds blow
- -counterclockwise around low pressure (cyclone)
- -clockwise around a high (anticyclone).
stand with your back to the wind, the low pressure will always be on your left.
Surface Friction
The reduction of wind speed decreases the Coriolis effect, causing wind to flow outward from a high, and inward to a low.
Veer
A wind change in a clockwise direction
In a climb, wind usually veers and increases.
Back
A wind change in a counter-clockwise direction.
In a descent, wind usually backs and decreases.
Gusts
A rapid irregular fluctuation in the upward and downward movement of air currents.
Squalls
A sudden and sustained increase in the strength of wind lasting longer than a gust.
Land Breezes
winds blow from land –> sea
at night
when the land is cooler than the water.
Sea Breezes
winds blow from sea –> land
during the day
when the water is cooler.
Valley Breezes
These anabatic winds flows up the slope of a valley during the day, when the air on the sun-facing side becomes warmer and rises.
Mountain Breeze
These katabatic winds flow down the slope of a valley at night as the air is cooled and is pulled down the slope by gravity.
Mountain Wave
air flows over a ridgeline it also flows down the other side = oscillations or waves to occur.
- -can last for several hours
- -can reach up to 30 nm past the mountain range.
Mountain Wave Clouds (3 types)
1) Cap Cloud - Forms along top of ridge and the wind carries it downstream.
2) Lenticular - Lens shaped clouds that form along the crest of wave.
3) Rotor Clouds - Form in eddies downstream about ridge height.
Wind Shear
A distinct change in wind speed and/or direction.
Types of wind sheer (2)
1) Performance Increasing Shear
Increased head wind
Airspeed increased, aircraft comes in high, overshoots runway
2) Performance Decreasing Shear
Decreased head wind
Airspeed decreases, potential stall at low altitude, undershoots runway
