Atmosphere Flashcards
What is the “Karman line”?
The Karman line is defined as the “boundary” between the Earth’s atmosphere and outer space, sitting at 100 km altitude. It is not a real physical boundary.
Name the different sectors of the atmosphere starting from ground level
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
What aspects influences the choice of operational altitude and speed?
- Usual wind velocities
- Drag that depends non the air density (lower at higher altitudes)
- Increasing thermal efficiency of combustion engines due to lower air temperature
- Decreasing propulsion thrust due to lower air density
- Decreasing speed of sound with altitude
What is “geometric altitude”?
The geometric altitude is measured from sea level
What is “absolute altitude”?
Measured from earth’s centre
What is geopotential altitude?
Measured by earth gravitational field
What is “standard atmosphere”?
Mention one valid assumption for the standard atmosphere.
Standard atmosphere is constructed by variation of density, temperature and altitude.
Valid assumption: the composition of gases remain the same throughout all of the altitude.
What causes weather phenomena?
Temperature gradient dynamics, which in turn is caused by solar radiation, heat radiation cooling effects and humidity.
What is “lapse rate”?
Lapse rate is a measurement of the rate at which the earth’s atmospheric temperature decreases with increase altitdue, or increases with decreasing altitude.
Dry adiabatic air lapse rate is high.
Moist adiabatic air lapse rate is low.
For standard atmosphere, the air lapse rate is assumed to be the mean value for dry and moist adiabatic air.
Describe global wind systems
Global wind systems distributes thermal energy and causes water currents
Describe the different global wind systems that exists, in order from pole down to equator
- Polar cell: closest to the poles. Moves at sea level toward equator, then up and back toward pole. The winds within this cell are called polar westerlies.
- Polar front
- Ferrel cell: Moves at sea level toward poles, then up and back toward equator. The winds within this cell are called westerlies.
- Horse latitudes
- Hadley cell: Moves at sea level toward equator, then up and back toward poles. Within this cell, the winds are called trade winds.
- Intertropical convergence zone
Describe local wind systems
Diurnal wind change in costal areas
- By day: sea absorbs more heat, land absorbs less heat
- By night: sea releases more heat, land releases less heat
What are jet streams? Why do they exist? How can they be used?
Jet streams exist because of the global wind systems.
The jet streams are located close to the tropopause (border between troposphere and stratosphere).
There are polar jets and subtropical jets.
When planning and preparing flight routes they are used to make it possible to save energy and increase ground velocity.
They can generate clear air turbulences, but must not be confused with turbulence itself.
What is the Coriolis’ Force and what effect does it have?
It is a phenomenon that affects differently pressured areas.
NORTHERN HEMISPHERE: low-pressure areas turn against the clock, high-pressure areas turn clockwise
SOUTHERN HEMISPHERE: low-pressure areas turn clockwise, high-pressure areas turn anti-clockwise
How does the atmosphere influence the performance of aerial vehicles?
The atmosphere enables the creation of aerodynamic forces like lift and drag.
It supports oxidizers for combustion engines and enables component cooling.
It enables corrosion/surface oxidation which is mostly unwished for but sometimes desirable.
It supports a healthy environment for lift on earth.
