topic 4.1.c formation of clouds / lapse rates Flashcards
when does cooling of water occur?
- Air warmed by contact with ground or see rises freely through the atmosphere → as it rises and pressures falls it cools by expansion ( this movement convection)
- Air mass moves horizontally across a cooler surface (advection)
- warm air mass mixes with a cooler one
What happens as air rises ?
1) Sun heats up the earth
2) The sun will also heat the air around the earth
3) As the warm air near the surface rises vertically upwards and expands = convection
4) As long as the air remains warmer than the surrounding air it will continue to rise
- In clouds Air continues to rise so as long as internal temp is greater than surrounding atmosphere
What is the process called when air cools as it rises?
Adiabatic expansion
What is adiabatic expansion?
- As when it is near the surface it is smaller → meaning the particles hit each other more frequently creating kinetic and heat energy
- As the air parcels rise and expands there is less frequent collisions, a low pressure so less energy and temp drops
What is humidity ?
The amount of water in the atmosphere
What is relative humidity?
how full of water vapour a parcel of air is → an air parcel will only become saturates and condense when it reaches 100% relative humidity
What is absolute humidity?
is the total amount of water vapour a parcel of air can hold → measured in cubic metres of air
What is the dew point?
the point at which the pocket of air is where it reaches 100% relative humidity → so will condense at this point
Does warmer air hold more water vapour than cooler air?
Warmer air = more water vapour held
Cooler air - less water vapour to become saturated
What is a lapse rate?
the vertical distribution of temperature in the lower atmosphere and the temp changes that occur within an air parcel as it rises.
What is environmental lapse rate?
- Vertical temperature profile of the lower atmosphere at any given time
Average temp falls 6.5 *c for every 1 km height gained
What is dry adiabatic lapse rate ?
- This is a change in temperature of a air below 100% RH
As it gets colder the RH will rise - this 9.8 * per 1000m
When the air parcel becomes colder than the air around it it will not rise any higher
What is saturated adiabatic lapse rate?
Change in temp of a air parcel at 100% RH so condensation occurs
Condensation gives out heat so air cools at 8*c per 1000m
If the air parcel remains warmer than the surrounding air it will continue to raise
Example of how a cloud forms through convection
- Ground heated up by sun warms air in contact with surface to 18*c
- Because this air is more warmer than its surroundings → it is less dense and therefore buoyant → ie atmospheric instability
- This results in a freely rising convection current -> when internal currents reach dew point (8*) condensation occurs clouds begin to form
- Air continues to rise so as long as internal temp is greater than surrounding atmosphere
- When it reaches an equilibrium air no longer rises because it is cooler and therefore heavier than its surroundings
When does air continue to rise?
In clouds Air continues to rise so as long as internal temp is greater than surrounding atmosphere
