CPL met revision Flashcards
Solar radiation - absorption
Most of the sun’s UV rays are absorbed by ozone in the stratosphere, water vapour absorbs visible radiation as well as cloud and dust
Conduction
Transfers heat via direct molecular contact. Air is a poor conductor of heat so conduction normally occurs within a shallow layer of about 10cm above the earth’s surface
Convection
Heat transfer by vertical movement of mass (liquids and gases). It’s responsible for the distribution of heat from the equator to the poles and for transporting most of the heat away from the earth’s surface. Convection currents transfer water vapour up which releases latent heat into the atmosphere when condensation occurs
Heating at the earth’s surface - specific heat
When solar energy enters the waters of the oceans, oceans act as huge heat reservoirs (as vast amounts of energy are required to raise the temp of the ocean by a few degrees)
Heating at the earth’s surface - albedo
surfaces with a low albedo such as sand absorb most of the solar energy warming the earth’s surface whereas surfaces with a high albedo such as snow reflect most of the solar radiation cooling the earth’s surface
Heating at the earth’s surface - insolation
It is the solar radiation that is received at the earth’s surface or in the earth’s atmosphere
Barometric tendency
The difference between the atmospheric pressure at the time of observation and 3 hours earlier. The characteristics of the tendency observed may be described as rising, falling and steady
Flight levels
Altitude referenced from 1013hPa
Pressure altitude
Atmospheric pressure is expressed in the terms of the altitude which corresponds to that ISA pressure
Pressure gradient
The change in atmospheric pressure per horizontal distance
Rainfall development
When rising air is lifted above the condensation level and there is a presence of condensation nuclei, water vapour turns into cloud droplets, these droplets must grow either through the Bergeron process or through coalescence
Bergeron process
Involves the presence of ice crystals to which the water vapour deposits as water condenses more easily over ice. Ice crystals form as snowflakes and once they reach a large enough size through deposition and collision their weight exceeds their buoyancy and they fall, if surface temps are above 0 degrees ice crystals melt becoming precipitation
Coalescence
Is the fusion/coalescence of a drop when a large drop has formed and commenced descent. For a large drop to be formed it requires large condensation nuclei. Larger drops have a greater terminal velocity so they overtake smaller drops and the sweeping action in the wake of the falling drop sucks in drops close to the wake hence fusion/coalescence occurs
Freezing rain
Can occur in front of a warm front (rain doesn’t need to be supercooled) drops landing on the cold surface of the a/c will freeze on impact
Light icing
Minor coverage of a/c parts either rime or clear ice. a/s loss is very small/nil, no change of alt/track is needed
Clear/glaze ice
- A transparent sheet of ice that retains a/c shape
- Results from the slow freezing of large supercooled water droplets at temps of 0°C to -15°C,
- As the droplets begin to freeze latent heat is released slowing the rate of freezing and allowing droplets to flow back over the airframe.
- It will tend to form in CB/CU cloud where mixing will cause concentrations of large drops.
- The most severe level within this cloud is from FZL to 7000ft above FZL
Supercooled water droplets
The liquid state of the water droplets will continue provided no disturbance is applied. If a disturbance is applied the droplet will turn to ice at a given rate and having reached that condition it is said to be in a stable solid-state, this theory applies to water droplets at temps warmer than -40 degrees
Elevation
Height of a specified datum above MSL
QNE
ISA elevation used for flight levels (1013hPa set on subscale)
QFE
Field elevation (elevation of land set on subscale to a given height above aerodrome)
Pressure lapse rate
The rate at which pressure decreases as altitude increases (at sea level this is 1hPa/30ft), if 2 columns of air have the same sea level pressure but are at different temps, the warmer column will have a smaller pressure lapse rate
QNH
Height above sea level (sea level pressure is set on subscale)
Vapour pressure
The portion of atmospheric pressure that is exerted by moisture in the air, as evaporation occurs water vapour adds to the partial vapour pressure of air and when the water vapour pressure cant increase further the saturation vapour pressure has been reached
Condensation process
Vapour to liquid, commonly occurs through air cooling, it requires condensation nuclei for water vapour to cling to. An overabundance of condensation nuclei can act as an accelerant to condensation and a lack of condensation nuclei may prevent condensation from occurring at a temp where it usually occurs at (supersaturation)
Hoar frost
Forms when an a/c has been flying at an altitude then descends into a warm moist layer, the water vapour in contact with the cold a/c adheres instantly. It can also occur on a winters morning (both examples of deposition)
Radiation fog
At night the earth’s surface cools down due to the loss of terrestrial radiation. If the right conditions exist the air is cooled to dew point and fog will form
Radiation fog formation requirements
It needs a high RH, light wind (2-8kts) and a cooling surface (found during an anticyclone because it gives a long clear night)
Where does radiation fog occur
hollows, valleys and over land areas
Rime/Opaque ice
- White, opaque, brittle, rough form of ice which does not conform to a/c shape
- Caused by the fast freezing of small drops in situ
- Forms at -10°C to -20°C
- Because of the small droplet size it loses heat rapidly, trapping air between individual particles
- More common in stratiform cloud and is more likely to be found above a layer of clear ice
Moderate Icing
Substantial build-up of clear or rime ice on wings and other major a/c parts. a/s loss may become sufficient to cause concern. The safety of the a/c may be jeopardized if the rate of accretion increases or if anti-icing equipment is not coping adequately. it may be desirable to change alt/heading
