Structure of the Atmosphere Flashcards
(27 cards)
Name the 5 layers of the atmosphere from top to bottom.
Exosphere
Thermosphere
Mesosphere
Stratosphere
Troposphere
Which layer do most civil flights and weather phenomena take place?
Troposphere
What are the main characteristics of the Troposphere?
A marked fall in density, pressure and temperature with height.
The presence of virtually all the atmospheric water vapour from which clouds and most atmospheric weather phenomena are derived.
What happens to temperature between the troposphere and stratosphere?
A temperature inversion takes place between the troposphere and stratosphere.
Which layer contains the biggest concentration of ozone?
Stratosphere
Is air exchanged between the troposhere and stratosphere?
No. The temperature inversion makes it virtually impossible for air to mix between the troposphere and stratosphere.
Is air dry or moist in the stratosphere?
Air is extremely dry in the stratosphere. This means basically no form of precipitation comes from the stratosphere.
What is the height of the troposphere?
The troposphere starts at ground level and reaches heights of 4-12 miles above the surface of the earth. 4 at the poles and 12 at the equator.
What is the composition of the atmosphere?
78% nitrogen
21% Oxygen
1% Other (Argon, hydrogen, helium etc)
What are some constituents present in the atmosphere?
Water Vapour, 1-4%
Cabron dioxide 0.03%
What is the temperature variation with altitude?
The temperature decreases with height and the rate of decrease is known as the lapse rate.
The average lapse rate is 1.98°/1000ft
What is the temperature lapse rate?
It is the rate at which temperature decreases with height.
At any time or place the lapse rate can take almost any value. The average value is 1.98°/1000ft
Does pressure decrease with height?
Yes
What is pressure and how does it change?
Pressure = Density x Depth
Pressure changes with height at a rate of 1hPa/30ft.
Pressure will also change depending on the temperature (density) and water content of the air (density).
What is the average pressure at mean sea level?
1013h.25Pa
What is density?
Density is defined as the mass in a unit volume.
A specific volume of air with a high density has a greater mass than the same volume of air with a low density.
Density of the air depends on pressure, therefore density also decreases with height.
Does density decrease with height?
Yes
What does density affect in aviation?
Density affects;
Take-off performance with required runway length
Aircraft lift, rate of climb and ceiling
Aircraft maneuverability due to the aerodynamic forces
Drag acting on aircraft
Power delivered by a jet engine, due to the oxygen intake
Propeller thrust due to the aerodynamic forces created by the blades
Oxygen content and as such a humans ability to survive without appropriate cabin pressurisation
What are some tools used for the collection of meteorological data?
Thermometer
Radar systems
Barometers
Rain Gauges
Wind Vane/Anemometer
Transmissometers
Hygrometers
Satellites
What is atmospheric pressure measured in?
Inches of Mercury (ins Hg)
Milibars (mb)
Hectopascals (hPa)
Are milibars and hectopascal different?
No, milibars and hectopascals have identical value.
What errors in a mercury barometer must be corrected for?
Index Error
Temperature Error
Gravity Error
What is replacing the mercury barometer?
Whilst mercury barometers are very accurate, they are large and cumbersome. It is gradually being replaced by the aneroid barometer.
Aneroid means “without liquid” and it utilises a partially evacuated metal capsule that reacts to changes in air pressure by either expanding or contracting.
What error does an aneroid barometer also suffer from?
Index Error
