PO 403 - Meteorology (unit 3)

Layers of Atmosphere, bottom - up

1. Troposhpere

2. Stratosphere

3. Mesosphere

4. Thermosphere

5. Exosphere

Troposphere

Surface to 28,000 ft (poles), 54,000 ft (equator). Weather occurs here

Stratosphere

up to 50, 000 ft above troposphere, contains ozone layer

Mesosphere

Up to 275,000 ft.

Meteors burn here, temp drops to -100 degrees C

Thermosphere

up to 500 km, auroras and satelites

Exosphere

500 - 600 km in space; outermost layer

Gas composition

78% nitrogen

21% oxygen

less than 1% other gasses

Temp Scales + differences

0 degrees = freezing

100 degrees = boiling

Horizontal variations:

Diurnal: Day heats, night cools

Seasonal: caused by Earths axis tilt

Latitude: Equator receives stronger radiation than poles

Topography: Land heats/cools faster than water, snow reflects radiation, vegetation insulates

Clouds: Reflect solar radiation (day), trap terrestrial radiation (night)

Properties of Atmosphere

Properties:

mobility - air flows like water

Compression - air compressed at higher pressure - occupies less space

Expansion - rising air expands/cools - condensation - clouds/precipitation

ICAO standards (Intoernational Civil Aviation Organization)

determines sea level for NA

Pressure - 29.92 Hg (1013.25 hPa)

temp - 15 degrees celsius

air is perfectly dry gas

lapse rate: 1.98 degrees per 1000 ft.

Density + Temp (atmospheric pressure + measurement)

Cold air = dense, sinks, molecules close/packed

Warm air = less dense, rises, molecules fast/spread

Pressure Gradient

rate of change of pressure over given distance measured at right angle to isobers.

Close isobars

steep gradient - stronger windsW

Wide isobars

Shallow gradient - weak winds

Coroilis Force

Deflects air right in NH - winds parallel to isobars

Buys Ballots Law

Back to wind in NH - low pressure on left (opposite in SH)

low pressure - counterclockwise direction, high pressure - clockwise direction

Station Pressure

Pressure measured at location (decreases with altitude)

Rule of thumb:

10 ft = -0.01 in Hg

100 ft = -0.1 in Hg

1000 ft = -1.00 in Hg

Relative Humidity

Ratio of water vapor present vs. maximum possible at saturation

Dew point

Temp at which air becomes saturated

Latent Heat

Energy absorbed/released during phase changes (evaporation, condensation)

Drives cloud formation + storms

Heating

1. Radiation (solar)

2. Troposphere heating (terrestrial radiation + conduction - process=convection, turbulent mixing, latent hear release, etc

Cooling

1. Radiation Cooling (at night, affects lower - 4000 ft, stronger in arctic winter

2. Evaporation cooling (rain evaporates - absorbs heat, cools air)

3. Advection cooling (air moves over cooler surfaces - fog/stabillity

Lapse Rate

Rate at which air temp decreases with altitude

Steep lapse rate = unstable air

Shallow lapse rate = stable air

Inversion

Temp increases w/ height (opposite of normal lapse rate)

Isothermal Layer

Temp constant with height for some depth

Often marks an inversion

Below layer - unstable, above layer - stable

Associated with haze (poor visibility)

NOT GOOD - SOARING/LIFT CONDITIONS

Types of Turbulence

1. Convection (thermal turbulence) - hot sunny days, uneven heating, rising currents - turbulence

2. Mechanical turbulence (eddies) - friction with ground, terrain, manmade obstacles. Usually within lower few thousand feet AGL

3. Orographic Turbulence (montain wave/rotors) - Wind over mountains, turbulence on windward, crest, lee side - dangerous rotor clouds/downdrifts on lee side

4. Wind Sheer - sudden change in wind speed/direction with height. Causes severe turbulence esp near thunderstorms)

Classification of Clouds

High (16,500 - 45,000 ft)

Middle (6,500 - 23,000 ft)

Low (surface - 6,500 ft)

Vertical development (start at 1,500 ft, grow upward)

Types of clouds

Stratus - layered

Cumulus - puffy

High Clouds

Cirrus (Ci) - thin, wispy, little flying significance)

Cirrocumulus (Cc) - cotton like, no weather indication

Cirrostratus (Cs) - thin sheet, signals approaching warm front)

Middle Clouds

Altocumulus (Ac) - rounded masses, little weather value

Altocumus Castellanus (Acc) - turreted edges, unstable, turbulence, showers, may grow into cumulonimbus

Altostratus (As) - grey viel covering sky, warm front indicator, light rain/snow, icing possible

Low Clouds

Stratus (St) - Uniform, fog like but off ground

Stratocumulus (Sc) - rounded rolls/layers

Nimbostratus (Ns) - thick dark layer, steady rain/snow, poor VFR

Vertical Development Clouds

Cumulus (Cu) - cotton balls, daytime growth, light turbulence, unstable

Towering Cumulus (TCu) - larger cumulus, heavy turbulence/icing, showers, unstable

Cumulonimbus (Cb) - Anvil top thunder/lightning, hail, severe turbulence

Obsturctions to visibility

Haze

Tiny water droplets/dust/sand, invisible individually

Creates uniform viel, bluish tint (dark background), yellow/orange (bright background)

forms in stable air - poor soaring

Smoke

From industry, vehicles, smog, forest fires

Severly reduces visibility, worse facing sun

Forest Fire smoke dangerous, CAR 601.15 prohibits flying less than 3000 ft AGL within 5 NM of fire

Pressure Gradient

Rate of change of pressure over a given distance, measured at right angles to isobers

Isobers

lines joining areas of equal pressure

Close Isobers, Wide Isobers in regards to pressure gradient

Close - steep gradient - strong winds

Wide - shallow gradient - weak winds

Coriolis Force

Earths rotation deflects wind to the right in NH - winds parallel to isobers

Veering

Wind shifts clockwise (to the right) happens:

• during day (speed increases, direction veers)

• with altitude increase

Banking

Wind shifts counterclockwise (to the left) Happens:

• at night (speed decreases, direction backs)

  • with descent (altitude decrease)

Surface Friction

slows wind, reduces Coriolis affect - wind crosses isobers

Local Variation

hills, mountains, water bodies can alter expected wind direction/speed

Gusts

Rapid irregular fluctuations in wind speed/direction

caused by mechanical turbulence or uneven heating

Squalls

Sudden increase in wind strength, longer duration than gusts

often linked to fast moving cold fronts or thunderstorms

Daily variation

Day - stronger, gustier winds, veering

Night - weaker winds, backing

Land breeze (night)

Land cools faster - high pressure over land, low over water, wind blows land - water

Sea breeze (day)

Land heats faster - low pressure over land, high over water, wind blows sea - land

Katabotic (mountain breeze) winds

night - slopes cool, air becomes dense, flows downhill

“kats come out at night”

Anabotic (valley breeze)

Day - sloped warm, air rises up slope

“Anna goes up the hill”

Cold air mass

Instabillity, turbulence, good visibility, showers, cumuliform clouds

Warm air mass

Stabillity, Smooth air, poor visibility, stratiform clouds, drizzle

Source Regions

Large regions where air sits long enough to take on surface properties.

Warm Front

Retreating edge of cold air mass, warm air ascends gently over cold air

Cold fronts

Leading edge of advancing cold air mass, replaces warmer air mass

Stationary Fronts

Air mass neither advancing nor retreating

Outcome: may dissipate or evolve into cold/warm front.

Occluded Fronts

Cold front overtakes warm front

Result: warm air lifted - trowal (trough of warm air aloft)

Weather: mix of cold + warm frontal conditions

Types of Icing

Frozen Dew - crystalline frost

Hoar Frost - feathery crystalline, clear nights

Rine Ice - Opaque, milky, instant freeaing of droplets

Clear ice - glass like, heavy coating, 0-10 degrees celsius, slow freezing.

Squall Line

Long line of thunderstorms, 50-300 NM ahead of cold front