8.1 - Physics of the Atmosphere Flashcards
State the different regions of the atmosphere and how temperature
changes within each region as a function of altitude
Troposphere - 2^C decrease per 1000 ft
Tropopause - constant -55 to -60 ^C
Stratosphere - Gradual rise in temperature
Ionosphere - Mesosphere and Thermosphere
Why is there no weather in the Stratosphere?
The water vapour content in the stratosphere is zero
What is the adiabatic lapse rate?
Adiabatic lapse rate is the 2^C decrease in temperature per 1000 ft of altitude
Calculate the outside air temperature at 25,000ft assuming the
temperature at sea level is 10°C
-40 ^C
( 25,000 / 1000 = 25)
(25 * 2^C = 50 ^c
10 - 50 => -40^C
What is the percentage of oxygen at 5,000ft?
21% Oxygen
What layer of the atmosphere is used to bounce radio waves across
the surface of the earth?
Ionosphere
Mesosphere and Thermosphere
At sea level on a standard day what is the pressure in Mb, HPa,
Lbs. per sq. in., Hg and mm of Hg?
Mb = Millibars = 1013.2 Mb
HPa = Hecto Pascals = 1013.2 Hp
psi = pounds per sq inch = 14.7 psi
Hg = inches of mercury = 29.92 Hg
mm Hg = mm of mercury = 760 mm Hg
What is the name of the layer of atmosphere dividing the
troposphere from the stratosphere?
Tropopause
What instruments are used to measure atmospheric pressure?
Aneroid altimeter measures Pressure altitude /atmospheric pressure
Barometer
What will happen to density when pressure increases?
Air density varies in direct proportion with the pressure
(density increases as pressure increases)
Density varies inversely with temperature. What does this mean?
Air Density varies inversely with temperature
(Density decreases as temperature increases)
What is the air temperature at sea level on a standard day?
Give in °C, °F and °K
15 ^C
59^F
288K
What is humidity?
Humidity is a condition of moisture or dampness
The higher amount of water vapour that the air can hold depends entirely on the temperature; the higher the temperature of the air, the more water vapour it can absorb.
- If the temperature and pressure remain the same, the density of the
air varies with the humidity. What does this statement mean?
By itself, water vapour weighs approximately five-eights as much as an equal volume of perfectly dry air. (Hydrogen is extremely light, H20)
On damp days the density is less than it is on dry days
What instrument is used to measure humidity?
Hygrometer is used to measure the aount of water vapour in air.
Why is the air lighter when there is moisture in it?
By itself, water vapour weighs approximately five-eights as much as an equal volume of perfectly dry air.
Therefore, when air contains 5 parts of water vapour and 95 parts of perfectly still dry air, it is not as heavy as air containing no moisture. This is because water is composed of hydrogen ( an extremely light gas) and oxygen. Air is composed principally of nitrogen, which is almost as heavy as oxygen.
How is relative humidity expressed?
As a percentage
This measurement is the ratio of the amount of water air will hold at this particular temperature.
Explain how density is affected by temperature, and pressure, versus altitude?
As altitude increases, both temperature and pressure decrease, the former tending to increase air density and the latter to decrease it. One effect does not exactly compensate for the other because the pressure drop affects density more than the temperature effect.
The net result is a gradual decrease in air density with increasing altitude
What is density measured in?
Kg / m3 (metric)
Ib / ft3 (imperial)
What effect will a drop in density have on the operation of an
aircraft?
If air density drops there will be a reduction in: -
- The lift produced by wings
- The thrust produced by propellers / Jet Engines
- The power or torque produced by piston engines.
(The last two of these is significant when checking engine operation on the ground)
What is pressure altitude?
Pressure altitude is the altitude in the standard atmosphere corresponding to a particular value of air pressure.
(With the altimeter of an aircraft set at 29.92 in Hg, the dial will indicate the number of feet above or below a level where 29.92 in Hg exist, not necessarily above or below sea level, unless standard day conditions exist.
What is density altitude?
Density altitude is pressure altitude (Standard day) corrected for differences in temperature.
The density altitude will differ from the pressure altitude when the temperature is not standard.
In the troposphere, there is a decrease of temperature with an increase of altitude approximately ___^C per ____ ft (Lapse rate)
2^C
1000ft
The temperature in the Tropopause remains reasonably constant at -__^C to -__^C
-55^C to -60^C
