Met Flashcards
The atmosphere makeup
78% Nitrogen
21% Oxygen
Small amounts of inert gases
What is pressure measured in?
1hPa = 100 Pascals = 1mb
What are isobars?
Lines of constant pressure
ICAO standard atmosphere?
MSL of 1013mb, MSL temp of 15deg decreasing 1.98deg per 1000’ to 56.5deg at 36,000’, above which stays constant to 80,000’.
- QFE?
- .QFF?
- QNH?
- QNE?
- Alt setting for highest part of the airfield/runway.(height)
- MSL pressure used on weather charts
- MSL pressure for altimeter(altitude)
- Height indicated on landing when 1013.25 is set.
Density characteristics
At constant temp - density decreases as pressure decreases.
At constant pressure - density decreases as temperature increases.
Density altitude calculation?
DA = Pressure altitude + (120 x (T - 15))
Name the 2 types of temperature radiation.
Short wave and long wave.
Temperature profile in the atmosphere is divided into two parts. Name them.
Troposphere - lowest region, temp generally decreases with height and most weather exists.
Stratosphere - The region above where temperature remains constant with height.
Tropopause - The boundary layer between the two.
Steep Lapse rate?
Temperature decreases quickly with height, occurs in cold unstable airflow.
Shallow Lapse rate?
slow decrease in temperature in height, occurs in warm stable airflow.
Isothermal?
a layer where the temp remains constant with height.
Inversion?
a layer where the temperature increases with height.
Environmental Lapse rate?
The actual temp structure of the atmosphere at a specific time and place; it varies considerably
What are 4 types of heat transfer?
- Convection
- Conduction
- Turbulence
4 Advection
What is convection?
occurs when warmer, less dense air moves upwards through cooler air. The cooler air sinks to replace this warmer air thus starting vertical circulation.
What is conduction?
occurs when air is warmed by contact with a warmer surface or it is cooled by contact with a cold surface.
What is Turbulence?
mixing of warming and cold air by the winds through adjacent layers.
Whats is advection?
occurs when warm or cold air is blown horizontally across the earths surface, heat transfer between the surface and air then takes place by conduction, convection or turbulent mixing, creating types of airmass that effect the UK.
What is adiabatic temperature change?
occur when a sample of air is warmed by compression or cooled by expansion with no heat added or taken away from the sample.
Dry adiabatic lapse rate?
Dry air displaced vertically in the atmosphere cools, or warms at about 3deg per 1000’
Saturated adiabatic lapse rate?
The release of latent heat reduces the rate of cooling to 1.5deg per 1000’
Unstable air?
When a parcel of air is warmer and less dense than its surroundings causing it to rise.
Stable air?
When a parcel of air is cooler than air above it. Air displace vertically tends to return to its original level.
How are clouds formed?
Lifting of moist air until saturation occurs resulting in the formation of cloud. The type of cloud is controlled by the stability of the environment.
What is water vapour?
Odourless , transparent, gas mixes invisibly with dry air.
What is water liquid?
exists in form of very small water droplets in cloud and fog, small drops in drizzle and larger drops in rain.
What is water solid?
ice particles occurs as crystals in high cloud, amalgamation of crystals in snow, solid lumps in hail, and coating s on objects as frost, rime or clear ice.
What is condensation?
When vapour turns to liquid, latent heat is released.Eg cold air in contact with the window of a warm room cools the window and condensation occurs.
What is evaporation?
When liquid water turns to vapour, latent heat is used up.
What is deposition?
When vapour turns directly to solid(ice) , latent heat is released.
What is sublimation?
Solid turns directly to vapour. Requires latent heat
What is relative humidity?
The amount of water vapour contained in a mass of air expressed as a percentage compared with that which would be contained by the same mass of air if it were saturated.
What is due point?
The temp to which air must be cooled to become saturated.
What is saturation?
Air is saturated when it holds the maximum possible amount of water vapour at any particular temp and pressure.
Define night.
It is between the end of evening twilight and the start of morning twilight.
Sources of light at night?
Moonlight, Solar Light, Background illumination and Artificial light.
What is a veering wind?
a change in a clockwise direction, ie W to NW.
What is a backing wind?
A change in a anticlockwise direction, IE S to SE
What is BUYS BALLOTS LAW?
With your back to the wind, low pressure will be on your left in a northern hemisphere.