Describe the elements that influence the amount of incoming solar radiation.

Ozone is the gas in the atmosphere, that protects us and influences the amount of Ultraviolet and X ray solar radiation reaching the Earths surface. 

Clouds, dust and water vapour also help in influencing the amount of incoming solar radiation. 

Explain what is meant by solar radiation.

Solar radiation is the energy given off by the sun.
Solar radiation includes ultraviolet radiation, X Rays and visible light

Explain the importance of correct subscale setting.

If a depression is moving overhead, the altimeter needle will read at a higher altitude even though the aircraft has not moved and the subscale setting has not been altered

The reverse works just as well
ie – the subscale knob function is to allow the correct QNH to be set in the subscale window so the altimeter can read correctly with reference to sea level on any given day. 

 Explain why an altimeter requires a subscale adjustment.

Altimeters in aircraft contain one or more aneroid capsules which expand as pressure around the aircraft reduces and contracts as the pressure increases or decreases.

As the ambient pressure changes every day, there is a need to adjust the strength or setting of the leaf spring, so that when sea level pressure does changes the altimeter can be adjusted so it continues to read correctly.

Define:
a)  QNH; 
b)  QFE; 
c)  altitude; 
d)  height; 
e)  pressure altitude. 

QNH stands for the atmospheric Pressure at Mean Sea Level.

A common mnemonic for QNH is “Nautical Height” or “Nil Height”

Or QNH as “Query Newlyn Harbour”. Newlyn Harbour in Cornwall, UK is home to the National Tidal and Sea Level Facility which is a reference for mean sea level.

QFE stands for Atmospheric Pressure at Field Elevation “Query Field Elevation” or “Fixed Elevation”

Aviation altitude is measured using Mean Sea Level (MSL) which gives us a height above mean sea level, or altitude. 

Height is normally measured above the Ground. It is our altitude taken above a fixed datum (normally the elevation of the surrounding terrain) 

Pressure Altitude is the air pressure in terms of altitude in the International Standard Atmosphere
or elevation above a standard datum with the air-pressure of 1013 hPa; also called QNE

Explain how deviation from ISA values influences performance of aircraft and their engines.

When conditions do not meet ISA (which they rarely do) the aircraft will perform differently. 

For the ideal conditions for max performance of the aircraft and engines, we want a high pressure coupled with a low temperature. 

The lower the temperature and the higher the pressure, the better the performance. 

List the assumed conditions on which the International Standard Atmosphere (ISA) is based.

The International Standard Atmosphere (ISA) is a set of atmospheric conditions which are used as a ‘yard stick’ to calculate aircraft performance given these conditions. The conditions are rarely the same as ISA on any given day, but calculations can be made for changes.   

ISA consists of the following conditions: 

Sea level Pressure = 1013.2 hPa
Air Temperature = +15c at sea level
Temperature lapse rate = 1.98c/1,000ft
Temperature above 36,090 = Constant -56.5c
Pressure lapse rate = 1 hPa per 30 feet 

State the unit of pressure commonly used in meteorology.

The unit used in aviation used to measure pressure is the Pascal, commonly referred to as hectoPascal (hundreds of pascals). 

HectoPascals are written as hPa 

 State the average pressure lapse rate in the lower atmosphere.

The average Pressure Lapse Rate in the lower atmosphere is a;

Reduction of 1 hPa per 30 feet gained

Define Pressure Lapse Rate.

Pressure Lapse Rate is the reduction in ambient pressure with the increase in height. 

This is due to there being less weight of air above the measuring point; as elevation increases there is less overlying atmospheric mass, and so less ambient pressure. 

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