Moisture And Precipitation

Question 1

Saturated Vapour pressure and saturated mixing ratio

Answer 1

• unless the air is saturated, the vapour pressure and mixing ratio will always be less than the saturated vapour pressure and the saturated mixing ration
• as the temp decreases you will have a higher saturation pressure because a cool air parcel reaches saturation faster.

Question 2

Marine vs continental CCN

Answer 2

• division between marine and continental conditions depends primarily on the origin of the air and the particles it contains
• marine clouds tend to have smaller number of particles but a larger range of droplet sizes than continental clouds.

Question 3

Cloud condensation nuclei (CCN) common types

Answer 3

• dust
• clay
• organic particles from land surfaces
• salt crystals from the spray
• gas to particle conversation particles SO2
• dust coated with sulphates

Question 4

Condensation takes place when?

Answer 4

• temp of air reduced to dew point but volume remains constant
• adiabatic expansion causes cooling
• saturated Vapour pressure is reduced through change of temp and volume.
• evaporation or advection adds moisture to volume
• these processes cause different types of clouds

Question 5

Precipitable water vapour (PWV)

Answer 5

• the amount of water vapour present in a column above the surface of the earth
• measured in mm
• represents the maximum amount of water vapour that could fall to the surface as precipitation if all the water vapour converted into a liquid or a solid.
• can be measured directly by satellites and derived from weather balloon surroundings (radiosonde)

Question 6

Dew point (td)

Answer 6

• the temp at which the air will become saturated if the pressure and water content remain the same.
• the higher the dew point the more water vapour that is present in the atmosphere
• the temp is always greater than the dew point unless the air is saturated (when the temp and dew point are equal)
• very important when looking at storms and cloud formation

Question 7

How to calculate Relative humidity (RH)

Answer 7

• calculated using the actual water vapour content (mixing ratio) and the amount of water that could be present in the air if it were saturated (saturation mixing ratio)

Question 8

Mixing ratio

Answer 8

• the mass of water vapour present in the atmosphere compared to the mass of dry air in a given volume of air

Question 9

Vapour pressure

Answer 9

• amount if pressure exerted only by the water vapour in the air
• the pressure exerted by all the other gases are not considered
• units in hPa

Question 10

Type of surface

Answer 10

• the equilibrium vapour pressure in the atmosphere depends on whether there is a plane or water or a plane of ice
• the equilibrium vapour pressure in less than a water surface which means that ice at equilibrium at RH is less than 100%

Question 11

Saturation of the air

Answer 11

• refers to the equilibrium condition where the rate of the evaporation into the air equals the rate of condensation out of the air
• when the air is saturated, evaporation can still take place as long as the condensation of the same amount takes place
• the amount of water vapour present in the atmos at saturation depends on temp, ice vs water surface that molecules enter or leave

Question 12

Formation of cloud processes

Answer 12

• when the air reaches saturation the condensation of water vapour will turn into tiny cloud droplets.
• if any of these elements are missing you will not have condensation you may have high humidity but not necessarily cloud formation
• in order for water vapour to condense particles in the atmos called CCN are required
• without CNN a relative humidity of several 100% s would be needed to start the formation of tiny cloud droplets and to keep it from evaporating