Meteorology for Aviators

TEMPERATURE

The degree of heat a body contains, measured with a thermometer.

Degrees Celsius

Freezing point of water 0C

Boiling point of water 100C

Fahrenheit

Freezing point of water 32F

Boiling point of water 212F

Conversion - To change from Centigrade to Fahrenheit,

multiply the degrees Centigrade by 1.8, then add 32.

RADIATION

Radiation From the Sun

Is called insolation. Short wave radiation passes through the atmosphere and heats up the

earth's surface.

Re-radiation From Earth ( Terrestrial radiation )

Long wave radiation from the earth heats up the atmosphere. Because it does not pass out

of the atmosphere but is absorbed, the more impurities in the atmosphere, the more

longwave radiation will be absorbed, “trapping” in the heat. This serves to keep night time

temperatures higher than they would be without this phenomena.

NOTE: SOLAR RADIATION BY DAY ONLY

TERRESTRIAL RADIATION BY DAY AND NIGHT

METHODS OF HEAT TRANSFER

Conduction

Transfer of heat from one heated body to another in contact with it. Still air is a poor

conductor of heat.

Convection

Transfer of heat vertically. Hot surface heats up air in contact with it (CONDUCTION). Air

heats and expands - Becomes less dense - rises (CONVECTION).

Advection

Transfer of heat horizontally. After heated air has risen (CONVECTION), cooler dense air

moves in laterally to replace it (ADVECTION).

SURFACE EFFECTS

Land heats up and also cools down faster than water.

VERTICAL TEMPERATURE DISTRIBUTION

The earths surface is warmed by solar radiation, and the air in contact is warmed by conduction. Since air is a poor conductor the warmest layers are adjacent to the ground.

By looking at the diagram below you will notice that as you increase in altitude the temperature decreases, until the presence of Ozone in the upper layers of the atmosphere causes the air to heat up, this is due to the Ozone layer absorbing radiation.

As can be seen the atmosphere is divided into layers. The lower of the division is the Troposphere. It is within this part of the atmosphere that almost all the cloud and weather occurs.

The Tropopause divides the Stratosphere from the Troposphere. Its height fluctuates from approximately 16km over the equator to 8km over the poles.

It is normal for temperaure to decrease with height, this is called a POSITIVE LAPSE RATE. When temperature increases with height this is referred to as a NEGATIVE LAPSE RATE. If the temperature is found to be the same through a depth of the atmosphere its called ISOTHERMAL.

The International Standard Atmosphere

This is a theoretical atmosphere that has been set up by I.C.A.O. in order to determine engine and aircraft performance at different altitudes.

ISA assumes at Mean Sea Level:

q Temperature is +15C.

q Pressure is 1013,2 hPa (or 29.92" Hg. )

q Lapse rate is a decrease of 1.98C/1 000 feet until 36 090 feet.

q Then constant at - 56.5C up to 20 km.

q Pressure drops 1 hPa/30 feet ( or 1"Hg/1 000 feet ).