Lecture - Air Masses

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    Anticyclone

    Name for a system of high pressure.

    Small pressure gradientlight winds

    Classed as COLDor WARM

    Can be Permanent or Semi-permanent.

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    Formation of Anticyclone

    Cold Anticyclone

    Air mass is cooled by

    the landthe cold air

    has a greater densitythan warm air

    = high pressure

    Warm anticyclone

    Larger than normal

    amounts of warm air

    over an area(subsidence in the

    horse latitudes)

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    Subsidence

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    Air Masses

    Air masses are large bodies of air which

    have the same characteristics throughout.

    The air must remain over an area for

    several days.

    The ideal conditions will be found where

    there is a permanent anticyclone.

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    Description of air masses

    Air masses are either warm or cold

    Source region

    Polaror tropical.

    Air masses either form at sea or land

    SeaMaritime

    Land - Continental

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    Qu. What is an air mass?

    An air mass is a large body of air with

    similar temperatureand/or humidity.

    Qu. Where do air masses form.

    They form in stable source regions such

    as the sub tropics or near the poles.

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    Source regions of Air Masses

    Permanent

    anticyclone

    Azores

    Sahara

    Greenland

    Siberia

    Arctic

    Air mass (name)

    Tropical Maritime

    Tropical Continental

    Polar Maritime

    Polar Continental

    Arctic

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    Air Mass Characteristics

    Cold & MoistArctic Maritime

    Cold & dryPolar Continental (Pc)

    Cool & moistPolar Maritime (Pm)

    Warm & dryTropical Continental

    (Tc)

    Mild & moistTropical Maritime (Tm)

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    Tropical maritime (Tm)

    Source region

    Azores (Caribbean)

    Cooled by the sea

    Stable Little or no moisture

    lost

    Coastssea fog Weathersouth west

    dull, warm ocast.

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    Tropical

    Continental

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    Tropical continental (Tc)

    Source region Sahara

    (North Africa)

    Cooled from below

    Stable (Un?) Dry air mass

    Heat wave in Summer

    Usually good vis(haze? Pollution)

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    Polar Maritime (Pm)

    Most common

    Source region

    Greenland

    Warmed by the seaunstable

    Showers on West

    coast

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    Polar

    Continental

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    Polar Continental (Pc)

    Source regionSiberia

    Reaches UK with NE or E

    winds.

    High pressure North ofUK

    Mainly wintertime

    May pick up moisture

    (track?) Perhaps clouds

    Vis varies

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    Arctic

    Maritime

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    Returning Polar Maritime

    Source region

    Greenland but travels

    south before turning

    North towards the UK

    Cold air mass which is

    warmed heading south

    and cooled heading north

    leads to a wide variety

    of weather Stratus cloudhill fog or

    Cb clouds and showers

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    Characteristics of air masses

    reaching the UK

    Air

    Mass

    Source Temp. RH Sky AirCondition

    Tm

    Tc

    Pm

    Pc

    A

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    Characteristics of air masses

    reaching the UK

    Air

    Mass

    Source Temp. RH Sky AirCondition

    Tm Azores

    Tc Sahara

    Pm Greenland

    Pc Siberia

    A Arctic

    Ocean

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    Characteristics of air masses

    reaching the UK

    Air

    Mass

    Source Temp. RH Sky AirCondition

    Tm Azores High

    Tc Sahara VeryHigh

    Pm Greenland Low /

    HighPc Siberia Very

    Low

    A Arctic

    Ocean

    Very

    Low

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    Characteristics of air masses

    reaching the UK

    Air

    Mass

    Source Temp. RH Sky AirCondition

    Tm Azores High High

    Tc Sahara VeryHigh

    Low

    Pm Greenland Low /

    High

    Medium

    Pc Siberia Very

    Low

    Low

    A Arctic

    Ocean

    Very

    Low

    Low

    Medium

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    Characteristics of air masses

    reaching the UK

    Air

    Mass

    Source Temp. RH Sky AirCondition

    Tm Azores High High Covered

    with StTc Sahara Very

    High

    Low Clear

    Pm Greenland Low /

    High

    Medium Cu

    Pc Siberia Very

    Low

    Low St?

    (turb)

    A Arctic

    Ocean

    Very

    Low

    Low

    Medium

    Cu

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    Characteristics of air masses

    reaching the UK

    Air

    Mass

    Source Temp. RH Sky AirCondition

    Tm Azores High High Covered

    with St

    Stable

    Tc Sahara VeryHigh

    Low Clear Stable

    Pm Greenland Low /

    High

    Medium Cu Unstable

    Pc Siberia Very

    Low

    Low St?

    (turb)

    Stable

    A Arctic

    O

    Very

    L

    Low

    M di

    Cu Unstable