Water in the atmosphere Flashcards
What happens when water changes state?
Latent heat takes heat (energy) from, or gives heat back to the atmosphere.
What happens to heat as water evaporates and condenses?
When water evaporates, it takes up energy from its surroundings and cools the environment. When it condenses, it releases energy and warms the environment.
What three states does water exist in?
Solid
Liquid
Vapour
What is condensation?
If saturated air is cooled, the water vapour content will become too great, and visible droplets will appear.
During condensation, latent heat is released, causing atmospheric warming.
What is sublimation?
Sublimation is the process where ice and snow (solid) changes into water vapour (gas) without moving through the liquid stage.
What limits the amount of water vapour present in the air?
Temperature
Can more water vapour be held at lower or higher temperatures?
The higher the temperature, the greater the quantity of water vapour that the air can hold in suspension and the density decreases.
What is the dew point?
A temperature to which air would have to be cooled for it to become Saturated, ie holding its maximum quantity of water vapour. Constant pressure and water vapour are assumed.
The name comes from the fact that at this temperature, dew starts to form.
What is Saturated air?
Air that is cooled until it is holding its maximum quantity of water vapour.
What ways may the temperature of air be cooled below its dew point?
Conduction - Through contact with the surface. (Ie condensation on a cold cup)
Evaporation - Energy taken from air turning liquid to vapour
Adiabatic Cooling - Air rises, expands and cools
Mixing - Different temperature air mixing during natural convection
Does temperature change during changes of state?
No, although heat energy is added while ice turns into water and water into steam, the temperature does not change. During the process all the heat energy is absorbed to produce the change of state.
Name the heat required to cause a change in state?
Latent heat
What is Relative Humidity?
This is the measurement of the amount of water vapour present in the air, relative to how much would be required to cause saturation at that temperature.
It is expressed as a percentage. If the air contained half as much water as required to saturate the air, the relative humidity would be 50%.
How does relative humidity vary throughout the day?
Relative humidity decreases during the day when air temperatures are higher and increases at night as the temperature drops.
What instrument is used to measure humidity?
Hygrometer
