"without gain or loss of heat". If air rises because it becomes warmer than its surroundings, it will lose heat by expansion as it ascends, and it will not entrain any air from its immediate surrounds
Define the term "dry adiabatic lapse rate". What is its numerical value?
A thermal which is not 100% saturated will cool adiabatically at a fixed rate. The rate is 3 degrees Celsius per 1,000 feet (BGK)
Why are temperatures taken at various heights (the "temp trace flight") at the start of a soaring day?
To establish the "Environmental Lapse Rate" (ELR) for the day (BGK)
Do thermals drift downwind at the same rate as the windspeed?
Probably not. Actual rate of drift is a function of the combination of climb rate and the windspeed. They do drift downwind, but at something less than the wind speed
What is the definition of saturated air?
Air which has become 100% saturated with moisture. Anything less than 100% saturation is regarded as dry air
What is the definition of "dew point"?
The temperature at which the air transforms its water vapour into visible water droplets (BGK)
What is a "Stueve Diagram"?
A graphical diagram used by meteorologists to plot various parameters in the atmosphere, such as temperature, humidity, etc
Define the terms "stability" and "instability" when applied to the atmosphere.
Stability is when a thermal cools below the temperature of the surrounding air and therefore stops ascending. Instability is when a thermal remains warmer than its surrounds as it ascends, thus tending to keep ascending (BGK)
What is a "depression"?
A depression is an area of low pressure. In an extreme form, a depression is a cyclone. A depression rotates clockwise in the Southern Hemisphere
What is an "anticyclone"?
An anti-cyclone is an area of high pressure, rotating anti-clockwise (BGK)
On a cross-country flight, if you are drifting to the left, will your altimeter over-read or under-read when you outland?
If you are drifting to the left, you must be going from high to low pressure. Therefore your altimeter will over-read when you land
What do the terms "backing" and "veering" of the wind mean?
"Backing" is an anti-clockwise shift in wind direction. "Veering" is a clockwise shift
What are the implications of high surface temperatures and an unstable atmosphere?
Strong convective activity, big thermals, probable cumulus cloud development and possible thunderstorms
In a damp airstream, what is the cloudbase likely to be on the lee side of a mountain range, compared with on the windward side?
What do the expressions "convergence" and "divergence" mean in meteorology?
"Convergence" is the tendency of air to flow in toward the centre of a depression. It implies instability and is favourable for soaring, provided storms do not develop. "Divergence" is the tendency of air to flow out away from the centre of an anticyclone, resulting in stability and conditions less favourable for soaring.
What are the main requirements for good thermal-soaring conditions?
An ELR equivalent to or better than the DALR (i.e. some degree of atmospheric instability), fairly high surface temperatures, low humidity to suppress over-development and inhibit the formations of storms. Light winds.
Assuming the terrain is suitable, what are the main requirements for wave-soaring to be possible?
A reasonably strong surface wind (15-20 knots), with the wind increasing in strength with height but remaining fairly constant in direction. Low-level instability capped by an inversion is also helpful
What is the so-called "coriolis" force and what is its effect in meteorology?
The effect of the earth's rotation on an air mass. It causes depressions and anticyclones to have a spiral motion (BGK)
How would you find the general direction of the centre of an anticyclone?
Stand with your back to the wind and the centre of the anticyclone is to your left (Buys Ballot's law)
What is the definition of a "cold front"?
Cold air overtaking warm air, undercutting it and forcing it to rise (BGK)
What is a "trough"? What conditions would you expect in a trough if the surface temperatures are high?
An elongated area of low pressure, often pre-frontal, which usually contains unstable conditions.
What is a "microburst" and where would you expect to find one?
A rapidly descending mass of cold air from the edge of a developed thunderstorm. It frequently reaches ground level and is characterised by extreme values of sink in the microburst itself and very high winds where it strikes the surface and bursts outwards (BGK)
If a large thunderstorm is visible and green streaks are hanging down underneath it, what does this mean?
Large hailstones, the green colour being clear ice refracting the light
What is "water vapour"?
Unseen moisture latent in the air
What is an inversion and what effect does it have on soaring conditions?
A layer of air in which the normal temperature reduction with height is reversed (temperature increases with height). Bad for soaring, because it stops thermals ascending. Inversions are common in anticyclonic conditions, when very high surface temperatures are required to break through them and enable soaring to take place to reasonable heights
What is "virgo" and what does it mean to a glider pilot?
"Virgo" is rain which does not reach the ground. It appears as grey-coloured sheets hanging down from under rain-bearing clouds. Glider pilots should avoid areas of virgo, firstly because of the possibility of getting the wings wet and losing performance, secondly because there will be areas of strong sink in and around the virgo itself.
What is "pileus" and what does it mean to a glider pilot?
"Pileus" is a small lenticular or eyebrow cloud seen at the top of a cumulus cloud on an unstable day. It indicates the presence of wave around the cumulus top, resulting from strong instability at lower levels and a wind which strengthens with height. When such conditions exist, it is possible to soar the thermal to cloudbase, then move upwind, clear of the cloud, and find good lift up the upwind side of the cloud