Microlight » Meteorology » Water Vapour
- Water vapour is the gaseous form of water in the atmosphere.
- It is invisible until it condenses into cloud, rain or ice.
- Air in the lower regions of the atmosphere nearly always contains some water vapour, varying from almost zero to some 5% by volume.
How the temperature of air influences its capacity to hold water vapour.
- The warmer the parcel of air, the more vapour that parcel can hold.
Humidity refers to the amount of water held in a mass of air.
Relative humidity gives the ratio between;
- the weight of the actual amount of water held,
- to the maximum weight of water that could be held as a vapour,
- expressed as a percentage.
Therefore 90% RH means the air mass is holding 90% of the water vapour that it could hold.
100% RH would mean that the air mass could not hold anymore water vapour (Saturated) and if it did it would release it through condensation.
Dew point gives us a good idea of the amount of water vapour present in the air.
It is defined as “the temperature at which a parcel of air saturates under constant pressure”.
Further cooling beyond the dew point will result in condensation.