Marine Meteorology Applications
(Weather on a Global Scale)
Dr. Omar Badokhon
High And Low Pressure Systems and Fronts
the two basic causes of all weather conditions on the
earth’s surface are heat and moisture.
The Heat Machines in the Weather Factory
• The landmasses heat up and cool down very rapidly
and easily
• so large areas in the tropics will reach very high
temperatures during the daylight hours.
• Similarly, the Polar Regions will rapidly radiate what
little heat they obtain from the sun and become
extremely cold.
• Air flowing over such areas will be respectively
warmed or cooled.
The Heat Machines in the Weather Factory
The sea, on the other hand, absorb or release heat
slowly
so it must be accepted that, in the tropics, its average
sea temperature will be less than that of the land and
warmer than the land in polar regions.
Moisture (or The Lack of It)
• Air that is flowing over the sea is going to absorb
moisture by evaporation,
• while similar air, flowing over the dry land areas, can
be expected to remain dry.
Moisture (or The Lack of It)
So, dependent on their geographical positions, we can
classify the various air masses over the earth’s surface
as follows:
[1] Tropical: over the tropics (warm)
[2] Polar: over the poles (cold)
[3] Maritime: over the sea (moist)
[4] Continental: over the land (dry)
Moisture (or The Lack of It)
This leads to the further classifications:
[a] Tropical maritime: warm and moist (Tm)
[b] Tropical continental: warm and dry (Tc)
[c] Polar maritime: cold and moist (Pm)
[d] Polar continental: cold and dry (Pc)
This has now combined the moisture content with the
heat factor and the various combinations and
permutations of these classifications will decide the
weather in all parts of the globe.
Weather on a Global Scale
• The processes we’ve been
discussing lead to the
formation of two types of
weather systems.
• First, in the polar regions, the
cool, dense, relatively dry air
forms high pressure domes
called the polar highs.
• Then, in tropical areas we find
warm, light, moist air forming
low pressure areas.
Weather on a Global Scale
In between these two
regions, at around 30 degrees
latitude, there is another
area of subsiding air, only this
one is warmer and much
more moist than that which
falls over the poles. This is
called the subtropical high
pressure area.
Weather on a Global Scale
Between the polar high
and the subtropical high
are shear lines, usually
referred to as polar
fronts.
These typically are found
around 60 degrees
latitude.
Movement of Air Masses
the Southern Ocean westerlies, which have come south
from the Tropical Regions and have curved to the right
under the influence of the Earth’s rotation. These winds,
as might be expected, bring with them waves of warm,
moist air – (tropical maritime).
Movement of Air Masses
In the cold Polar Regions the airflow is from the south
to the north and, like everything else in the Southern
Hemisphere, curves to the left to become an easterly
wind. The air is polar maritime – cold and moist – and
somewhere along the way is going to collide with the
warm, moist air from the north.
Movement of Air Masses
This collision has immediate and far-reaching effects.
The warmer air will ride up over the cold air. Part of the
cold air will be warmed and start to rise and this
upward funnelling effect will create a lowered
barometric pressure.
Atmospheric Regions
Across the globe, there are several regions where the
air pressure is remarkably consistent. This can result in
extremely predictable weather patterns in regions like
the tropics or the poles.
Equatorial low-pressure trough
This area is in the Earth's equatorial
region (0 to 10 degrees north and
south) and is composed of warm,
light, ascending, and converging air.
Because the converging air is wet and
full of excess energy, it expands and
cools as it rises, creating the clouds
and heavy rainfall that are prominent
throughout the area. This low-
pressure zone trough also forms the
Inter-Tropical Convergence Zone (ITCZ)
and trade winds.
Subtropical high-pressure cells
Located at 30 degrees north/south,
this is a zone of hot, dry air that forms
as the warm air descending from the
tropics becomes hotter. Because hot
air can hold more water vapor, it is
relatively dry. The heavy rain along the
equator also removes most of the
excess moisture. The dominant winds
in the subtropical high are called
westerlies.
Subpolar low-pressure cells
This area is at 60 degrees north/south
latitude and features cool, wet weather.
The Subpolar low is caused by the
meeting of cold air masses from higher
latitudes and warmer air masses from
lower latitudes. In the northern
hemisphere, their meeting forms the
polar front, which produces the low-
pressure cyclonic storms responsible for
precipitation in the Pacific Northwest and
much of Europe. In the southern
hemisphere, severe storms develop along
these fronts and cause high winds and
snowfall in Antarctica.
Polar high-pressure cells
These are located at 90 degrees
north/south and are extremely cold and
dry. With these systems, winds move
away from the poles in an anticyclone,
which descends and diverges to form
the polar easterlies. They are weak,
however, because little energy is
available in the poles to make the
systems strong. The Antarctic high is
stronger, though, because it is able to
form over the cold landmass instead of
the warmer sea.
Atmospheric Regions
By studying these highs and lows, scientists are better
able to understand the Earth's circulation patterns and
predict the weather for use in daily life, navigation,
shipping, and other important activities, making air
pressure an important component to meteorology and
other atmospheric science.
