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Describe the troposphere.
- Height: 28,000-55,000 in height
- Large amounts of moisture and condensation
- Nearlly all weather occurs here
- Temperature normally decreases with altitude
Describe the tropopause.
- Transition between troposphere and stratosphere
- Height over US 36,000ft
- Strongest winds occur just below the tropopause
- Temperature is constant with altitude
- Normally the coldest area in lower atmosphere
- Haze layer with definite top
- Contrails form here
Describe the stratosphere.
- Height up to 66,000 ft
- Increasing temperature as altitude increases
- Smooth with excellent visibility
Temperature lapse rate
The decrease in temperature with increasing altitude
Standard lapse rate:
2° per 1000'
Isothermal lapse rate:
Indicates the temperature is constant with increasing altitude
Inverted laps rate:
- Temperature inversion
- occurs in stratosphere when temperature increases with increasing altitude
What is the average weight of air on a square inch of the earths surface at sea level?
T or F: Does pressure always decrease with altitude?
- Pressure decreases more rapidly in the lower levels of atmosphere, than at higher altitudes, because density decreases with altitude
What is a standard day?
- 29.92 inHg; 1013.2mb
- 15°C or 59°F
- Lapse rate 1 inHg per 1000'
- Temperature lapse rate 2°C (3.5°F) per 1000'
What is station pressure?
Atmospheric pressure measured directly at an airfield or other weather station
What is a surface analysis chart?
- depict high and low pressure systems as they move across the country bringing differing weather patterns
- Lines of equal pressure are called isobars
What is a barometric altimeter?
Aneroid barometer calibrated to display altitude in feet
What the altimeter setting doing?
Its the value to which the scale of the pressure altimeter is set to so the altimeter indicates true altitude at field elevation
For every 11°C the temperature varies from the standard, there will be ___ altimeter error.
If the air is colder than standard atmosphere, the aircraft will be ____ than the altimeter indicates.
How do winds generally move?
In the same direction in the areas between pressure systems and parallel to the isobars
Define pressure gradient.
The rate of change in a direction perpendicular to the isobars
What is pressure gradient force (PGF)?
- isobar spacing
- The initiating force for all winds
- Tighter spacing of isobars shows a steep pressure gradient - strong winds
High pressure characteristics:
Low pressure characteristics:
- Ascending air
How does the Coriolis force and pressure gradient force affect winds?
- Gradient winds which flow perpendicular to the pressure gradient force
- Parallel to isobars
- Generally above 2000' AGL
What happens to winds below 2000' AGL?
- Friction reduces the speed of the wind which causes a reduction in Coriolis force
- Air blows at angles (45°) across the isobars
What is the jet stream?
- Maximum in the tropopause
- Narrow band of strong winds, +50 knots
- Average height 30,000 MSL
- 100-150+ knots
- 1000-3000 miles long
- 100-400 miles wide
- 3000-7000' deep
What are local winds?
Winds created by mountains, valleys, and bodies of water, and are superimposed on general wind systems possibly causing significant changes in the weather
What causes a sea breeze?
- During the day, lower pressure over the land and that over water is higher, causing the cool air to move to lower pressure over the land
How is an offshore breeze produced?
- Cold land, high pressure; warm water, low pressure. Air flows from high to low
What is a valley wind?
- Warm air near the ground being pushed up the mountain
- Air is flowing out of the valley
What is a mountain wind?
Dense air flows downhill into the valley
The higher the temperature, the ___ water vapor the air can hold.
Saturation occurs when?
Air contains the maximum amount of water vapor for a given temperature
What is dew point temperature?
- The temperature at which saturation occurs and is a direct indication of the amount of moisture in the air
- Higher the dew point, greater chance for clouds, fog or precipitation
What is relative humidity?
percent of saturation of the air or, percentage of water vapor in the air compared to the maximum amount the air could hold at that temperature
Three characteristics of precipitation are:
- Showers: starts, stops, changes intensity or sky conditions, cumuliform clouds
- Continuous: steady and changes intensity gradually, stratiform clouds
- Intermittent: Stops and starts at least once during the hour, cumuliform or stratiform clouds
Precipitation can take what forms?
- Bases: 6500 AGL
- Turbulence: none - moderate
- Precipitation: light rain - drizzle
- Can produce icing
- Bases: 6500 - 20,000'
- Prefix: alto
- Composed of ice crystals, water droplets
- Visibility: 1/2 mile to few feet
- Bases: +20,000 AGL
- Prefix: cirro or contain the word cirrus
- Composed of ice crystals
- Moderate turbulence
- No icing
- Towering cumulus and cumulonimbus
- Nearing thunderstorm stage and produce heavy rain and moderate turbulence
- Icing common above freezing level
- Bases: 1000' AGL
- Continuous rain snow, or ice pellets
- Poor visibility and low ceilings
- Thunderstorm clouds
- Extremely hazardous
Lifted air that is colder than the surrounding air indicates _____.
- Stable condition
- When the lifting action is removed, the lifted air settles because it is denser
Lifted air is warmer than the surrounding air, indicates a _______.
- Unstable condition
- When lifting is removed it continues to rise because it is less dense
Lifted air that has the same temperature as the surrounding air, indicates _________.
- Neutrally stable condition
- Lifted air will remain at the point where lifting was removed
Lifting by convergence:
- when two air masses or parts of a single air mass converge and force air upward because it has nowhere else to go
- Cold fronts moving through an area and lifting the air ahead of them
The force of wind against a mountainside pushes air upward
- Convective lifting:
- Cool air is over a warm surface and is heightened by intense solar heating
Stable atmosphere characteristics:
- Clouds: Stratus
- Turbulence: Smooth
- Visibility: Poor
- Winds: Steady
- Precip: Steady
- Icing: Rime
- Temperature inversions, low clouds or fog, rising temperatures while climbing
Unstable atmosphere characteristics:
- Clouds: Cumulus
- Turbulence: Rough
- Visibility: Good
- Winds: Gusty
- Precip: Showery
- Icing: Clear
- Thunderstorms, towering cumulous clouds, heavy showers, dust devils, decreasing temperature while climbing
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