Air masses

Air masses bring a variety of weathers. The UK has 6 air masses making it difficult to accurately predict weather unlike in other countries. Fronts form the boundaries of air masses which have differing properties and the most severe weather occurs when dry and cold polar continental fronts collide with warm humid maritime tropical air.

Different air masses can bring weather ranging from warm tropical days to cold and harsh arctic conditions.

The term ‘air mass’ was introduced by meteorologists from Bergen, Norway over 70 years ago. Air mass is a large body of air whose properties- temperature, humidity and lapse rate- are largely homogeneous over an area several hundred kilometres across.

3 factors determine the nature of air masses; source region, age, and modifications as they move away from their source region across the earth’s surface.

Primary classification- (A) Arctic, (P) Polar, or (T) Tropical, and the nature of the source region- (c) continental, (m) maritime.

A large variety of secondary air masses are also described. (E) Equatorial air for example. If a small (k) or (w) is attached to the air mass then this implies that the mass is either warmer or cooler than the surface. If warmer, the air mass is more stable.

Air Masses Prevalent for the British Isles are:

Arctic Air (A)

Continental arctic (cA): Extremely cold, very little moisture. Origin- Arctic Ocean in winter.

Maritime arctic (mA): Same source region but less dry and cold.

Polar Air (P)

Continental Polar (cP): Cold and dry, originating from high latitudes, typically as air flowing out of the polar highs. Brings rattling cold, dry and clear weather in weather and warm pleasant weather in summer.

Maritime Polar (mP): Cool and Moist. Often originating as cP over North America and Asia land mass. It modifies as it heads over Atlantic and Pacific oceans. Heated by relatively warm water masses. This makes the air mass relatively unstable and can result in blustery showers.

Tropical Air (T)

Continental Tropical (cT): Hot and very dry. Origin- arid desert reasons during summer. Least common air mass to affect Britain but can affect record temperatures in the south-east.

Maritime Tropical (mT): Mild and damp in winter, warm and muggy in summer. Origin- the Azores and approaches from the west. Results in overcast skies and prolonged rain.

Lesson starter:

I would ask students to label their maps of the UK with the correct air masses in the right places.
I would give Key Stage 3 students a paragraph and a list of words that they would have to fill the gaps. However, for Key Stage 4 students I would see if they could fill the paragraph in with no words given to them.
http://www.youtube.com/watch?v=hNz6eqzPZFc


Links

http://www.geographylwc.org.uk/A/A2/A2climchange/airmasses.html

http://www.weatheronline.co.uk/reports/wxfacts/Air-masses-and-their-sources.htm