Unit 2 (3) - RH, Cloud, Precipitation Flashcards
(10 cards)
What is humidity?
The amount of water vapour in the air/atmosphere.
What is relative humidity?
The amount of water vapour actually in the air,
expressed as a percentage of the maximum amount of water vapour the air can hold at the same temperature.
To find it,
take the actual amount of water vapour in the air,
divide it by the maximum amount of water that the air can hold at a given temperature,
and multiply that by 100.
How is relative humidity affected by temperature?
A rise in the temperature makes the air warmed up, so the molecules expand and move further apart, thus allowing air to hold more water vapour. This decreases RH.
What is saturation?
When the amount of water vapour in the air is the same as the amount that the air can hold, the air is said to be saturated.
At saturation point, the air holds the maximum amount of water vapour it can hold.
When saturation occurs, the RH is 100%.
What is dew point temperature?
The temperature at which saturation occurs is known as dew point temperature.
At dew point temperature, condensation begins and water vapour changes to liquid form.
Full explanation on how the increase in temp affects RH.
The increase in temperature has resulted in the decrease in the relative humidity.
Warm air can hold more water vapour than cool air. When temperature increases, the
amount of water vapour stays the same, but the rise in temperature makes air more able to hold water vapour.
When the air holds the maximum amount of water vapour it can hold, it is said to be at dew point temperature. Saturation occurs when relative humidity is at 100 per cent (%). The temperature at which saturation occurs is known as dew point temperature. The process in which water vapour changes to a liquid form by cooling known as condensation, first starts to occur at dew point temperature.
How are clouds formed? (not full exp.)
When the earth’s surface is heated up, water evaporates to become water vapour.
As water vapour rises, it starts to cool.
When water vapour cools to dew point temperature, condensation takes place if there are condensation nuclei.
Condensation nuclei - These are minute particles found in the air such as dust, smoke
particles or tiny specks of wind-blown soil which allows condensation to take place at dew point temperature.
How are clouds formaed? FULL EXP.
With the presence of clouds, during the day, clouds reflect a large portion of the sun’s
energy back to space. This keeps the earth’s surface cool. At the same time, clouds also absorb heat radiated from the earth’s surface.
During the night, clouds absorb more of the heat that is radiated from the earth’s
surface and prevent it from escaping back to space. The air near the earth’s surface
is thus kept warm at night.
In the absence of clouds, during the day, large amounts of the sun’s energy reach the earth’s surface. The earth’s surface heats up quickly, so the air near the earth’s surface is warmer.
At night, the clear skies allow more of the heat radiated from the earth’s surface to escape into space. The air near the earth’s surface is thus cooler at night.
Hence, more cloud cover results in smaller difference between day and night temperatures, so the diurnal (daily) temperature range is smaller.
How is rain formed?
The sun’s energy heats up the ground surface. The air in contact with the warm ground is heated by conduction.
The heated air expands and becomes lighter than the air around it.
This unstable heated air which holds a lot of moisture rises.
As the warm air rises, it cools until dew point temperature is reached, when
water vapour condenses to form clouds.
In the updraft of rising air, water vapour continues to condense into water
droplets around the cool surfaces of suspended ice crystals, dust particles
and other impurities, to form towering cumulonimbus clouds.
Tiny water droplets in the clouds coalesce to form bigger water droplets.
When the water droplets become too heavy to be suspended, convectional
rain falls, usually accompanied by lightning and thunder.
