Unit 3.b.i. - Air Masses and Associated Weather You need to know: What is an air mass? What air masses affect Britain? What weather is associated with each air mass?

An air mass is an homogeneous area of air which has similar properties of temperature and moisture Air masses form when air remains stationary in an area for several days. It tends to assume the temperature and humidity of that source region. Such stationary air can be found in high pressure belts of the sub tropics (Azores & Sahara) and in high latitudes (Siberia & N. Canada).

Source Regions High pressure belt in high latitudes (source region) Mid latitude area affected by air masses (e.g. UK) High pressure area in sub tropics (source region)

You need to learn these off by heart!

Air mass classification Based on 2 things: 1. Latitude of origin (determines temperature) Arctic (A), Polar (P), Tropical (T) 2.Surface over which they develop (affects moisture) Maritime (m) or continental (c) As air masses move they are modified by the surface over which they pass - affects humidity, temperature & stability In the British Isles air masses constantly interchange so lots of seasonal and diurnal variation in weather

Temperature Patterns in the UK Describe the general pattern of temperature from W to E? Where is more likely to be affected by a maritime air mass? Why? What evidence is there of the influence of a continental air mass?

Temperature patterns July Link the temperature patterns to air masses likely to be affecting the UK. What other factors may help you to explain these temperature variations?