Meterology Flashcards
What is Absolute humidity?
- The amount of water vapour in a unit volume of air.
- Measaured in grams per cubic meter (g/m3).
What is relative humidity?
The ratio of absolute humidity to the maximum amount of water vapour that can be contained within the air at that temperature.
- Usually expressed as a percentage.
What is Dew point?
- The temperature at which a parcel of air is saturated and has a relative humidity of 100%.
- When the air parcel is cooled below the dew point the water vapour within the air mass will begin to condese out.
What are the cuases of saturation?
- Mixing.
- Evaporation.
What is ‘Mixing’ in relation to causes of saturation?
- When two high-humidity with a large temperature difference mix resulting in a saturated mixture of air.
- May occur at the boundary between a warm and cold air mass.
What is ‘Evapouration’ in relation to causes of saturation?
- When unsaturated air can become saturated if water evaporates into it from a body of water.
- As the water evaporates into the air, water vapour will increase and excess vapour will condense out.
What is the ‘Adiabatic’ process?
- Where a parcel of air changes temperature due to expansion or compression, without heat energy being added to, or removed from the parcel by external sources.
What will hapen if an unsatureated parcel of air is cooled beyond its dew point?
The air will become saturated and some of the water vapoiur will condense out, forming clouds.
What is the differnece between absolute and relative humidity?
Absolute Humidity:
- The amount of water vapour in a unit volume of air.
- Measaured in grams per cubic meter (g/m3).
Relative Humidity:
- The ratio of absolute humidity to the maximum amount of water vapour that can be contained within the air at that temperature.
- Usually expressed as a percentage.
What is the troposphere?
- The lowest layer of the atmosphere.
- The layer which contains almost all of the water and most of what we consider as ‘weather’.
What happens to air as it rises?
It cools due to expansion.
What is Dry Adiabatic LApse Rate (DALR)?
- The rate that an unsaturated parcel of air cools as the altitude increases.
(Unsaturated means that the parcel of air is at a temperature that is above its dew point).
What is Saturated Adaibatic Rate (SALR)?
- The rate that a saturated parcel of air cools as the altitude increases.
(Saturated means that the parcel of air is at a temperature that is below its dew point).
What is Enviromental Lapse Rate (ELR)
The rate that the air around the parcel cools as the latitiude increases. It varies due to height, season, location etc.
What is Lapse rate?
- The rate of temperature change with altitude.
- Measured in Degree C/Km.
At what rate does unsaturateed air cool with altiutude?
10 Dergee C/Km.
What type of atmospheric stability results in clear skies?
Absolute stability, where the parcel of air is always cooler than the surrounding air and there fore wants to sink back down to its original latitude.
What does SALR stand for?
Saturated Adaibatic Rate.
What height are low clouds found at?
Below 6,500 ft (approx 2,000m).
What height are medium clouds found at?
Between 6,500ft and 20,000ft (approx 2,000-6,000m).
What height are high clouds found at?
Above 20,000ft (approx 6,000m).
What are the characterisitcs of stratus/strato form clouds?
- Flat.
- layered.
- Smooth.
What are the characterisitcs of cumulus/cumulo form clouds?
- Heaped up.
- Fluffy.
What are the characterisitcs of cirrus/cirro form clouds?
- High.
- Wispy.
What are the characterisitcs of alto form clouds?
Medium level clouds.
What are the characterisitcs of nimbus/nimbo form clouds?
Rain-bearing.
What is Convection?
When the land is heated by infrared radiation from the sun, warming the air directly above it. This decreaes the air density above the land causing it to rise.
What is Convergence?
- When air coverages on one point it is forced to rise as it cannot go down and cannt accumulate in one location.
- Commonly found at the Inter-Trpocial Convergence Zone (ITCZ), at the end of a depression (located at or near to the equator).
What is it called when air is forced to rise due to land?
Orographic uplift.
What is a ‘fluffy cloud at a low altitude called?
Cirus form cloud.
What are the characteristics of a nimbostratus cloud?
- Flat.
- Layered.
- Brings rain.
How may clouds change as a depression is approaching?
As the depression approaches, high cloud will appear, then thickening and lowering as the depression gets closer.
What is a Squall?
- A sudden dramnatic increase in wind speed, lasting longer adn more significantly than a regular gust.
- Can also result in a shift in wind direction.
Where does the tropical Continental air mass come from?
North Africa/Sahara Desert.
Where does the Tropical Maritime air mass come from?
Southerly parts of the Atlantic.
Where does the Polar Continental air mass come from?
Russia/Central Europe.
Where does the Returning Polar Maritime air mass come from?
Greenland/Northern Canada, with a detour further south into the North Atlantic.
Where does the Polar Maritime air mass come from?
Greenland/Northern Canada, via the North Atlantic.
Where does the Arctic Maritime air mass come from?
Arctic Sea.
What are the characterisitcs of maritime air?
Maritime air Masses are more humid (contian more water) than continental air masses.
What are the expected conditions when the UK is under influence of a Tropical Maritime?
- Warm and moist.
- Low cloud.
- Drizzle.
- Potentially generating fog.
What is an onshore breeze?
A breeze that blows from the sea towards the land, caused by a low pressure forming over the warmer land.
What is an offshore breeze?
A breeze that blows from the land towards the sea, caused by a high pressure area forming over the cooler land.
What causes an offshore breeze?
The land cooling quicker than the sea at night creates a high pressure in contrast tothe lower pressure over the sea resulting in a pressure gradient causing the breeze.
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