Lesson 15 Meteorology
Atmospheric Composition
78 % Nitrogen
21% Oxygen
1% Inert gases (carbon dioxide, Neon, Helium etc.)
0 to 5% Particulate (water vapor, smoke, dust, sand, volcanic ash etc.)
Vertical Structure by Temp.
TROPOSHERE
Starts at the surface and goes up to an average of 7 miles high
20,000 ft at the poles to 65,000 at the equator
Lapse rate is 2 C/1000 or 3.5 F/1000
TROPOPAUSE
Signaled by an abrupt change in the temp lapse rate
Boundary layer between troposphere and stratosphere
STRATOSPHERE
Temp doesn’t change much
66,000 feet to about 31 miles
MESOSPHERE
This one gets colder the further out
31 to 53 miles high
THERMOSPHERE
This one gets warmer with an increase in altitude.
53 to 310 miles
EXOSPHERE
310 miles and further
Consists of atoms and molecules in loose orbit sometimes shooting off into space.
Temperature
Temperature is the degree of hotness or coldness of a body or environment.
Measurement of the energy of the molecules (movement)
Primary Cause of all Wx
Unequal heating of the earth causes the weather
Insolation is when the suns rays warm the earth
different surfaces radiate and receive at different rates
Terrestrial radiation is when the earth radiates the energy back into the atmosphere
Diurnal Variation is difference between day and night (coldest temp just after sunrise)
Primary Cause of all Wx
Seasonal variation – summer to winter
length of days and nights
Latitude variation – angle which the suns rays strike the earth
Topography variation – arid land Vs vegetation (wet / dry)
CONVECTION
Warm air rises
Cold air sinks
With convection, warm air rises cools then sinks
The wind sets up an advection process whereby the cool air is blown along the ground until it is warmed then it rises again and repeats the process.
Land and Sea Breezes
Day time- warm land, cool ocean
Night time- cool land, warm ocean
RECIPE FOR A THUNDERSTORM
1. Water Vapor
2. Unstable Lapse Rate
3. An initial upward boost or lifting action
LIFE CYCLE
1. Cumulus
2. Mature
3. Dissipating
Thunderstorms
Lightning
Squall Lines
Embedded Thunderstorms
Hail
High winds
Tornadoes
Wind Shear/Microburst
Fronts and Airmasses
Air Mass – Body of air that has fairly uniform temperature and moisture
Source Region – The region which an air mass acquires its particular properties of temp and moisture
mP mT cT cP
Fronts and Airmasses
Front – Zone between 2 different air masses
Temperature may or may not change when crossing a front
There is always a wind change when crossing a front
LOW PRESSURE
Cyclonic
Rotates counterclockwise
Area of rising air
Usually clouds present
Bad weather
HIGH PRESSURE
Anticyclonic
Rotates clockwise
Area of descending air
Usually no clouds
Good weather
PRESSURE GRADIENT
Pressure gradient = difference in pressure / distance
Sets up a flow from high to low
The closer the isobars, the stronger the pressure gradient force and the stronger the wind
CORIOLIS FORCE
This force describes the apparent force due to the rotation of the earth
All free moving objects such as ocean currents, artillery projectiles, air molecules and aircraft seem to deflect from a straight line path because the earth rotates under them.
Deflects wind parallel to the isobars
Deflection is less at the surface due to slower wind speed at the surface.
WIND SHEAR
Happens
Any altitude
Any direction
Any gradient
Low level temp inversions, frontal zones, clear air turbulence
WIND SHEAR
Mountain Wave 40kts or more
Lenticular Clouds 50kts or more
Expect wind shear in a temp inversion when wind speed is greater than 25 kts.
Cloud Formations
For the air to become saturated:
1. Cool the Temp
2. Raise the Humidity
Temp Dew Point spread is 3º or less usually fog will form
Cloud Formations
Evaporation
Condensation
Sublimation
CLOUD FAMILIES
High clouds 16,500 – 45,000
Middle clouds 6,500 – 23,000
Low clouds surface – 6,500
Extensive vertical development
DETERMINING BASES
Temp and dew point converge at a rate of about 4.4º F or 2.2º C
Temp = 59
Dew Pt = 50
9 / 4.4 = 2.045×1000 = 2045′
STABLE AIR
Stratiform clouds
Smooth air
Poor vis
Continous Precip
UNSTABLE AIR
Cumuliform clouds
Turbulence
Good vis
Showery precip
Fog
Radiation Fog- clear cool calm night no wind
Advection Fog- moist air over a cooler surface
Upslope Fog- warm moist air forced upslope
Precipitation Fog- warm rain falling through colder air (frontal fog)
Steam Fog- cold air moves over warmer water
Icing
1. Increases weight
2. Reduces lift – changes the shape of the airfoil
3. Decreases thrust – effects prop
4. Increases drag – sticks up into the wind
TO GET ICING
1. Must have visible water
2. Aircraft must be below freezing
THREE TYPES OF ICING
1. Clear – cumuliform clouds
2. Rime – stratiform
3. Mixed – cumuliform or stratiform
ICING
Freezing Rain
Ice Pellets