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By the end of this lecture you should know:By the end of this lecture you should know: The 6 Major Air MassesThe 6 Major Air Masses

Major Air MassesMajor Air Masses

The Earth’s atmosphere is constantly The Earth’s atmosphere is constantly moving as warm air rises, cold air descends moving as warm air rises, cold air descends and the Earth spins.and the Earth spins.

There are 6 Major Air Masses that influence There are 6 Major Air Masses that influence British weather.British weather.

Major Air MassesMajor Air Masses

Major Air MassesMajor Air Masses

Arctic MaritimeArctic Maritime Originating in the very cold Arctic seas, picks up a Originating in the very cold Arctic seas, picks up a

little moisture as it travels south. Typical weather little moisture as it travels south. Typical weather conditions are:conditions are:

Summer - Very cold with frequent heavy showers.Summer - Very cold with frequent heavy showers.

Winter - Very cold strong north, north-easterly Winter - Very cold strong north, north-easterly winds. Heavy snow showers in north.winds. Heavy snow showers in north.

Major Air MassesMajor Air Masses

Polar ContinentalPolar Continental Originates in Siberia. In southern Britain the weather is dry Originates in Siberia. In southern Britain the weather is dry

as it has not crossed much water. In northern Britain the as it has not crossed much water. In northern Britain the air mass has travelled over the north sea, losing heat and air mass has travelled over the north sea, losing heat and picking up moisture.picking up moisture.

Summer - Warm and dry, cloud free. East coast tends to Summer - Warm and dry, cloud free. East coast tends to be cool and showery with coastal fog in the north.be cool and showery with coastal fog in the north.

Winter - Sleet and snow showers in the north. Cold strong Winter - Sleet and snow showers in the north. Cold strong east winds.east winds.

Major Air MassesMajor Air Masses

Tropical ContinentalTropical Continental Originates in North Africa, warm air moves north over Originates in North Africa, warm air moves north over

Europe and has little opportunity to pick up water vapour. Europe and has little opportunity to pick up water vapour. Typical weather conditions are:Typical weather conditions are:

Summer only - Very hot and dry, hazy with occasional Summer only - Very hot and dry, hazy with occasional thunder storms.thunder storms.

Major Air MassesMajor Air Masses

Tropical MaritimeTropical Maritime Originates in warm tropical oceans around the Originates in warm tropical oceans around the

equator. Brings warm and wet air. Typical equator. Brings warm and wet air. Typical weather conditions are:weather conditions are:

Summer - Warm south-west winds. Low stratus Summer - Warm south-west winds. Low stratus cloud over west coast.cloud over west coast.

Winter - Stratus cloud, hill fog and drizzle. Warm Winter - Stratus cloud, hill fog and drizzle. Warm with prolonged rainfall.with prolonged rainfall.

Major Air MassesMajor Air Masses

Returning Polar MaritimeReturning Polar Maritime Originates in Canada as very cold, dry air. Initially Originates in Canada as very cold, dry air. Initially

it moves south, gains warmth and moisture. By it moves south, gains warmth and moisture. By the time it reaches the Britain. Typical weather the time it reaches the Britain. Typical weather conditions are:conditions are:

Summer - Warm with squally showers and storms Summer - Warm with squally showers and storms inland.inland.

Winter - Stratus cloud. Showers in the western Winter - Stratus cloud. Showers in the western mountains.mountains.

Major Air MassesMajor Air Masses

Polar MaritimePolar Maritime Originates in north Canada and Greenland, crosses the Originates in north Canada and Greenland, crosses the

Atlantic Ocean picking up water vapour before reaching Atlantic Ocean picking up water vapour before reaching Britain. Typical weather conditions are:Britain. Typical weather conditions are:

Summer - Cool winds, heavy showers, thunder storms in Summer - Cool winds, heavy showers, thunder storms in mountainsmountains

Winter - Heavy showers in west with snow in mountains. Winter - Heavy showers in west with snow in mountains. Clear skies at night in the east giving frost.Clear skies at night in the east giving frost.

Major Air MassesMajor Air Masses1 Arctic 1 Arctic MaritimeMaritime

2 Tropical 2 Tropical ContinentalContinental

3 Returning 3 Returning Polar Polar MaritimeMaritime

4 Tropical 4 Tropical MaritimeMaritime

5 Polar 5 Polar MaritimeMaritime

6 Polar 6 Polar ContinentalContinental