Download Air Masses

Air Masses
Science 10
Air Mass


A large mass of air that has nearly uniform
properties such as temperature, humidity
and pressure
There are five air masses of importance
that you should know.
Arctic Air Mass

Extremely cold temperatures and very
little moisture. Originating over the Arctic
ocean in winter, when high pressure
dominates and differs only slightly from
the continental polar (cP) air masses that
develop over Siberia and northern Canada.
Continental polar (cP)


Cold and dry, originating from high
latitudes, typically as air flowing out of the
polar highs.
This air mass often brings the rattling
cold, dry and clear weather on a perfect
winter day and also dry and warm
weather on a pleasant day in summer.
Maritime polar (mP):


Cool and moist, often originating as continental
polar air over the North American and Asian land
masses and is modified as it moves out over the
Atlantic and Pacific Oceans.
Heated by the relatively warm water bodies this
air mass becomes rather unstable resulting in
blustery showers over the sea and windward
coasts.
Continental tropical (cT):

Hot and very dry, orginating from the arid
and desert regions during summer. The
least common air mass to affect the British
weather. However, approaching from the
south and south-east in summer it can
bring record heat to southeast Britain,
particulary in late-summer.
Maritime tropical (mT)



Mild and damp in winter, very warm and muggy
during summer.
Originating from the Azores this air mass
approaches the British Isles from the west,
leading to overcast skies with prolonged rain for
the western half of the country and to many
clouds, sometimes broken with drizzle for the
eastern half.
In summer tropical maritime air often produces
warm weather with abundant sunshine in the
southeast.
High Pressure Systems



When an air mass cools over an ocean or
a cold region of land, a high pressure
system forms.
The cooling, descending air exerts more
pressure on the region below. This is why
it is called a high pressure system.
High pressure systems bring clear bright
skies.
Low Pressure Systems



Air masses traveling over warm land or
oceans may become low pressure
systems.
The warming air rises and leaves less
dense air below.
Water vapour in the air condenses as it
reaches the higher altitudes, producing
clouds and precipitation.
How wind forms:


Wind is caused by the movement of air
from an area of higher pressure to an area
of lower pressure.
The rotation of the earth cause wind to
move in a clockwise direction around the
high pressure centre.
The Coriolis Effect


The Coriolis effect is the change in the
direction of moving air, water or any
objects on the Earth’s surface due to the
rotation of the Earth.
It deflects winds to the right in the
Northern Hemisphere and to the left in the
Southern Hemisphere.
Polar Easterlies



also Polar Hadley cells
dry, cold prevailing winds that blow from
the high-pressure areas of the polar highs
at the north and south poles towards lowpressure areas within the Westerlies at
high latitudes
often weak and irregular
Prevailing Westerlies



prevailing winds in the middle latitudes between
30 and 60 degrees latitude, blowing from the
high pressure area in the horse latitudes
towards the poles.
blow from the west to the east, and steer
extratropical cyclones in this general manner
strongest in the winter hemisphere and times
when the pressure is lower over the poles
Trade Winds



the prevailing pattern of easterly surface winds
found in the tropics
The trade winds blow predominantly from the
northeast in the Northern Hemisphere and from
the southeast in the Southern Hemisphere
the trade winds have been used by captains of
sailing ships to cross the world's oceans for
centuries
Horse Latitudes



Horse Latitudes or Subtropical High are
subtropical latitudes between 30 and 35 degrees
both north and south
This region, under a ridge of high pressure
called the subtropical high, is an area which
receives little precipitation and has variable
winds mixed with calm.
The consistently warm, dry conditions of the
horse latitudes also contribute to the existence
of temperate deserts
Doldrums




a low-pressure area around the equator where
the prevailing winds are calm
The low pressure is caused by the heat at the
equator
the air rise and travel north and south high in
the atmosphere
The doldrums are also noted for calm periods
when the winds disappear altogether, trapping
sail-powered boats for periods of days or weeks