Atmosphere Theory Flashcards
What is humidity?
Compare humidity at a given temperature at 5,000 feet with that at sea level:
Measurement of water vapor in air relative to dewpoint.
For a constant temperature, but a difference in air pressure, the vapor pressure (absolute humidity) at 5,000 feet will be lower than at the surface, simply because the air pressure is lower (the partial pressure of all molecules would be less). However, the saturation vapor pressure (which is dependent solely on temperature) at 5,000 feet will be the same as at the surface, if the temperature at the surface and 5,000 feet is the same.
Relative humidity is the ratio of vapor pressure to saturation vapor pressure. The relative humidity would be less at 5,000 feet than at the surface, because the vapor pressure is less at 5,000 feet
What is the composition of the earth’s atmosphere?
78% Nitrogen
21% Oxygen
1% Other
Static Pressure results from:
The static pressure of the air at any altitude results from the mass of air supported above that level.
At 40,000 feet what is the percentage of:
1. Static Pressure
2. Density
Compared to standard sea level?
- 19% (20%) Static Pressure
- 25% Density
Of the sea level volume.
What is the standard sea level temperature, pressure and density?
15C
14.7psi / 29.92 in.Hg
1.225 kg/m3 or 0.002378 slugs per cubic foot
(A slug (sl) is an Imperial unit of mass that accelerates by one foot (per second) (per second) (1 ft/sec²) upon force of one pound-force (1 lbf))
What is the most important property when studying aerodynamics? (Static Pressure, Temperature, Density, Viscosity, etc.)
Density (density altitude and temperature)
Define the density of the air:
The mass of air per cubic foot and a direct measure of the quantity of matter in each cubic foot. Decreases with an increase in altitude.
How much does air weigh at a standard sea level condition?
0.0765 pounds per cubic foot (3/4 of 1/10 of a pound)
Define viscosity:
Viscosity is a measure of resistance to flow. (Thickness)
Why are the viscosity of gases unusual?
Because the viscosity is generally a function of temperature alone and an INCREASE in temperature increases the viscosity. (Low viscosity flows easily because its molecular makeup results in very little friction when it is in motion. Higher temperature increases the frequency of intermolecular collisions at higher temperatures.)
Define Pressure Altitude:
The altitude that the altimeter reads if the altimeter is set to the standard sea level pressure value of 29.92. It is not corrected for local pressure variations.
Define Density Altitude:
What will cause an increase in density altitude?
Density altitude is air density given as a height above mean sea level. The more appropriate term for correlating aerodynamic performance in the nonstandard atmosphere.
Both an increase in temperature, decrease in atmospheric pressure, and, to a much lesser degree, increase in humidity will cause an increase in density altitude.
In the lower regions of the atmosphere temperature decreases with altitude at a fairly uniform rate up until what altitude and why?
Approximately 39,000’ (36,089’ = Geopotential of the Tropopause). The atmosphere is warmed by convection from Earth’s surface, this lapse or reduction in temperature is normal with increasing distance from the conductive source. There is a temperature inversion in the Stratosphere due to the ozone layer which absorbs most of the sun’s UV radiation.
In Bernoulli’s tube what stays constant at all stations along the length and what changes?
Density of the flow remains constant.Static pressure and velocity are the variable quantities.
Define air mass:
A body of air with horizontally uniform temperature, humidity, and pressure.
Define air pressure:
The force exerted by the weight of tiny particles of air (air molecules). At sea level the air pressure is 14.7 psi.
Define anticyclone, also known as a high pressure system:
A weather system with high atmospheric pressure at its center, around which air slowly circulates in a clockwise (northern hemisphere) or counterclockwise (southern hemisphere) direction - associated with calm, fine weather.
Define argon gas:
An inert gaseous element of the noble gas group (The noble gases make a group of chemical elements with similar properties: under standard conditions, they are all odorless, colorless, monatomic gases with very low chemical reactivity). Argon is the most common noble gas, making up nearly one percent of the earth’s atmosphere. Used in welding.
Define an atmosphere:
The envelope of gases surrounding the earth or another planet.
What are auroras and where do they occur?
A beautiful display of light in the sky that come from interactions between particles from the sun’s atmosphere and gases in the ionosphere.
Carbon dioxide:
A colorless, odorless gas produced by burning carbon and organic compounds and by respiration. It is naturally present in air (about 0.03 percent) and is absorbed by plants in photosynthesis.
Define coalescence in regards to clouds:
The process by which cloud droplets collide and join together to form larger droplets.
Define a cold front:
A cold front is defined as the leading edge of a cooler mass of air, replacing (at ground level) a warmer mass of air, which lies within a fairly sharp surface trough of low pressure. Temperature changes across the boundary can exceed 30 °C (54 °F). When a cold front catches up with the preceding warm front, the portion of the boundary that does so is then known as an occluded front.
Define condensation:
The change in state from a gas to a liquid
What are condensation nuclei?
Small particles in the atmosphere around which cloud droplets can form.
Continental polar air mass:
Cold arctic air masses that originate from the snow covered regions of northern Canada etc. Because of the long winter nights and strong radiational cooling found in these regions, the overlying air becomes very cold and very stable.
Continental tropical air mass:
Type of tropical air produced over subtropical arid regions; it is hot and very dry. The air has low dewpoints and warm to hot afternoon temperatures but with mild night time temperature. Skies are generally clear. This allows daytime heating during the day and radiational cooling at night.
Convection:
The transfer of energy by which a substance, such as a gas or liquid, is heated and the warmer, less dense fluid rises, then cools and becomes more dense and thus sinks.
