air mass weather lesson 33/34 what is an air mass? an air mass is a large volume of air covering...
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What is an Air Mass? An air mass is a large volume of air covering many thousands of square miles and having fairly uniform properties. The characteristic of the air mass depends upon: a) the source region b)the surface over which it is travellingTRANSCRIPT
Air Mass Weather
Lesson 33/34
What is an Air Mass?
• An air mass is a large volume of air covering many thousands of square miles and having fairly uniform properties.
• The characteristic of the air mass depends upon:a) the source regionb) the surface over which it is travelling
What is an Air Mass?
• The main source regions are the stable high pressure belts:– Sub-tropical– Polar
Air Mass Modification
• As air masses move away from their source region, they are affected by moisture and heat exchanges from the surface.– They may be heated from below,
• this causes instability.– They may be cooled from below,
• this increases the stability.– A sea track increases the moisture at low level,– A land track will not modify the moisture content to
any great degree.
Air Masses Affecting the UK
Source Regions of Air Masses
• Worlds stable high pressure regions.– Classified chiefly on the basis of two primary factors:
• Temperature» Polar» Arctic» Tropical
• Surface of origin:» Maritime» Continental
Cold Air-masses
• Polar Maritime– Between Greenland and N. Canada
• Arctic Maritime– From above the Arctic Circle
• Polar Continental– From the Siberian High over central Asia.
Warm Air-masses
• Tropical Maritime– From the Azores High in the mid Atlantic Ocean.
• Tropical Continental– from the North African sub-tropical high pressure
belt.
Summary of Air Masses
• Summer & Winter Air Masses:– Tropical Maritime – Polar Maritime– Returning Polar Maritime
Summary of Air Masses
• Winter Only– Polar Continental
• Short sea track.• Long sea track.
– Arctic Maritime• Summer Only
– Tropical Continental
Air Mass Properties
• Characteristic properties are:– Uniform mean temperature– Moisture content– ELR– Stability– Weather– Visibility
Air Mass Characteristics
• Tropical air cooled from below
• Polar air heated from below
Tropical Continental
L
H
Tc Air Mass PropertiesWinter Summer (only)
Temperature Very warm
Humidity Relatively dry.
Change of lapserate
Little change
Stability Generally stable
Weather Little cloud/Fair WxCu/ Poss CB if seatrack.
Visibility Mod to poor. Thickhaze.
Polar Continental (Short Sea
Track)
L
H
Pc (Short Sea Track) Air Mass PropertiesWinter(Only) Summer
Temperature Very cold
Humidity Vry dry
Change of lapserate
Little change
Stability Stable
Weather Clear with frost/fogor St
Visibility Poor
Very dry
Polar Continental (Long Sea
Track)
Pc(Long Sea Track)Air Mass Properties
Winter (only) Summer
Temperature Cold
Humidity Moist in lowerlayers
Change of lapserate
Heated from below
Stability Unstable
Weather Rain or SNSH, thickSC, embd Cu.
Visibility Good but poor inSNSH.
Tropical Maritime
Tm Air Mass PropertiesWinter Summer
Temperature Near seatemperature
Warm
Humidity Very moist Very moist
Change of lapserate
Cooled from below Cooled from below
Stability Stable Stable aloft
Weather Low St and DZpenetrates wellinland
Broken Sc/DZRA oncoasts
Visibility Mod topoor/Advectionfog/Cloud coveringhills
Mod to poor/seafog/cloud coveringhiils
Polar Maritime
Pm Air Mass PropertiesWinter Summer
Temperature Rather cold Cool
Humidity Moist Moist
Change of lapserate
Heated from below Heated from below
Stability Unstable Unstable
Weather Cu/CB, showersmainly on W coast
Cu/CB, showerspenetrating wellinland.
Visibility Good Good
Arctic Maritime
Am Air Mass Properties
Winter (only) Summer
Temperature Colder than Pm.
Humidity Fairly moist aftersea track.
Change of lapserate
Heated from below.
Stability Very unstable.
Weather Heavy snow SNSHfrom freq. CB.
Visibility Very good outsideshowers.
Returning Polar Maritime
rPm Air Mass PropertiesWinter Summer
Temperature Warmer than Pm. Cool
Humidity Moist Moist
Change of lapserate
Lowest layerscooled from below.
Cooled from below
Stability Stable in lowerlayers, unstablealoft.
Stable in lowerlayers, unstable aloft.
Weather St, Sc, Ac, possiblelight rain.
Turreted Ac, prob ofshowers and Ts overland.
Visibility Moderate Moderate