Air masses
The five main air masses
An A large body of air with similar characteristics of temperature and humidity. is a large volume of air which travels from one area to another. The weather an air mass brings is determined by the region it has come from and the type of surface it has moved over.
There are five main air masses which affect the UK.
To describe and explain the weather that air masses bring consider the following:
- Where has the air mass come from - is it the north (cold air) or the south (warm air)?
- Has the air mass passed over sea or land?
These two pieces of information will help you name the air mass and describe its characteristics. The basic ideas are as follows:
| Source Area | Characteristics |
| Land | Dry |
| Oceans | Wet |
| Tropics | Warm |
| Arctic | Cold |
| Source Area | Land |
|---|---|
| Characteristics | Dry |
| Source Area | Oceans |
|---|---|
| Characteristics | Wet |
| Source Area | Tropics |
|---|---|
| Characteristics | Warm |
| Source Area | Arctic |
|---|---|
| Characteristics | Cold |
Weather characteristics
You should learn the information in the table below.
| Name | Source area | Weather characteristics |
| Tropical Maritime (mT) | Atlantic Ocean | Warm and wet |
| Tropical Continental (cT) | Southern Europe and North Africa | Warm and dry |
| Polar Maritime (mP) | North Atlantic | Cold and wet |
| Polar Continental (cP) | Northern Europe | Cold and dry |
| Arctic Maritime | Arctic Ocean | Very cold and wet |
| Name | Tropical Maritime (mT) |
|---|---|
| Source area | Atlantic Ocean |
| Weather characteristics | Warm and wet |
| Name | Tropical Continental (cT) |
|---|---|
| Source area | Southern Europe and North Africa |
| Weather characteristics | Warm and dry |
| Name | Polar Maritime (mP) |
|---|---|
| Source area | North Atlantic |
| Weather characteristics | Cold and wet |
| Name | Polar Continental (cP) |
|---|---|
| Source area | Northern Europe |
| Weather characteristics | Cold and dry |
| Name | Arctic Maritime |
|---|---|
| Source area | Arctic Ocean |
| Weather characteristics | Very cold and wet |
The temperature of an air mass is also determined by seasonal changes. Temperatures in the summer months are always higher than in winter months.
The air mass known as the A very cold and wet air mass. does not occur very often, but when it does it brings heavy snow.