Weather Processes And Phenomena Flashcards
What is humidity?
Humidity refers to the amount of water vapour in the air.
How does temperature affect the capacity of air to hold water vapour?
Warmer air can typically hold more water vapour than cooler air. For every 1°C increase in temperature, air can hold 7% more water vapour.
What are the two sources of water vapour in the atmosphere?
Evaporation and evapotranspiration.
What is absolute humidity?
The amount of moisture in the air, measured in grams per cubic meter.
What is relative humidity?
The amount of water vapour in the air expressed as a percentage of the potential saturated volume.
What is saturated air?
Air with a relative humidity of 100%.
What is the dew point?
The temperature at which condensation occurs, allowing the formation of dew, mist, or fog.
What happens when the air temperature cools to the dew point?
Dew, fog, or clouds begin to form.
What is evaporation?
Water changes from a liquid to a gas, absorbing latent heat.
How much heat is required to convert 1 gram of water to vapour?
It takes 590 calories of heat.
What factors affect evaporation?
Initial humidity of the air, supply of heat, and wind strength.
What causes air to cool and condensation to occur?
Movement of air upwards, warm wind blowing over cold ground, warm air meeting cold air, movement of air poleward, and radiation from the ground overnight.
What is the environmental lapse rate (ELR)?
The actual temperature decline with height, on average 6.5°C per 1000m.
What happens to unstable air?
It rises, cools, and causes rainfall.
What is precipitation?
Water droplets condense or ice freezes out of air saturated with water vapour and falls towards the ground under gravity.
How does ground heat flux contribute to precipitation?
It heats the ground and the air near it, causing warm air to rise and cool adiabatically.
What are cumulus clouds?
Clouds formed by convection at altitudes of 2km or lower.
What are cumulonimbus clouds?
Very unstable storm clouds that can reach up to 15km in height and produce intense rainfall.
What is orographic rainfall?
Rainfall caused by air being forced to rise due to mountains or hills.
What is frontal rainfall?
Rainfall that occurs when warm air rises over cold air at a weather front.
What is an anticyclone?
A high-pressure system characterized by stable conditions and descending air.
What is advection fog?
Fog that forms when warm air passes over a cold surface.
What are the different types of clouds based on altitude?
‘Cirro’ clouds are high altitude, ‘Alto’ clouds are mid altitude, and ‘Strato’ clouds are low altitude.
What is required for rain to form?
Hygroscopic nuclei for cloud droplets to condense onto.
What is coalescence theory?
The idea that cloud droplets collide and merge to form larger droplets.
What is the Bergeron theory?
In a cloud, liquid water particles evaporate while ice particles grow, leading to snow or hail.
How is snow formed?
When water vapour deposits at temperatures below freezing, forming ice crystals.
What are the required conditions for hail formation?
Turbulence in the atmosphere, supercooled droplets, and updrafts.
What is dew?
Water droplets that form on surfaces due to cooling by the ground.
What conditions are required for fog to form?
Calm conditions, humid air, cooling at ground level, and condensation nuclei.
What is the difference between fog and mist?
The defining difference is visibility; fog is less than 1,000 meters, mist is greater.
