Transcript Basic Nav Pt 5

Basic Navigation
Leading Cadet Training
Weather
Lecture
5
Air Masses
When air moves over the earth it acquires
the temperature of the land (or sea) below it.
Air Masses are large bodies of air
of the same temperature and humidity.
In the UK there are
Six Air Masses.
Arrow size
indicates
frequency
of occurrence.
Air Masses
The Blue arrows bring cold air into the UK.
Maritime air brings wet weather into the UK.
The Red arrows bring warm air into the UK.
Continental air brings dry weather into the UK.
Polar Maritime
is the most common
air mass in the UK.
These Air Masses
are called . . .
Polar
Polar
Maritime
Returning Polar
Maritime
Tropical
Maritime
Arctic
Maritime
Polar
Continental
Tropical
Continental
Air Masses
Arctic & Polar Maritime brings cold wet weather.
Returning Polar Maritime brings warm wet weather.
Tropical Maritime also brings warm wet weather.
Tropical Continental brings warm dry weather.
Polar Continental
brings warm & dry
in summer,
but cold & wet
in winter.
Polar
Maritime
Returning Polar
Maritime
Tropical
Maritime
Arctic
Maritime
Polar
Continental
Tropical
Continental
Pressure
Meteorologists draw lines through all points on a map
that have the same air pressure - Isobars.
Just as contour lines
on a map help you
picture the shape of
a particular feature,
Isobars help you to
visualise areas of
high or low pressure.
Isobars
Isobars
Isobars
Pressure
High pressure is formed when
cool air sinks to the
Earth’s surface, causing:
Calm dry weather, Clear skies,
Sunshine and high day temp,
but low night temp.
Low pressure forms when
warm air rises from
the Earth’s surface, causing:
Wet, windy, changeable weather,
Cloudy skies with mild temps.
Wind and Weather
Areas of high pressures are called anticyclones.
In the northern hemisphere, anticyclones move
in a Clockwise direction.
So with your back
to the wind,
the best of the weather
will be to the right.
High Pressure
High
Anticyclone
Wind and Weather
Areas of low pressure are called depressions,
In the northern hemisphere, depressions move
in an Anticlockwise direction.
So with your back to the
wind, the worst of the
weather will be to the left.
But it’s the upper wind
that is responsible for
the movement of
Depressions.
Low Pressure
Low
Depression
Wind and Weather
If you are at position A with your back to the low wind,
and the upper wind is moving from left to right –
the depression has not yet reached you.
If you are at position B
with your back to the wind,
it has passed you by.
If at position C or D
with your back to the wind,
then there is likely to be
little immediate change
in the weather.
Low Pressure
Depression
C
B
Low
D
A
Fronts and Depressions
As on a map, there are also Ridges, Troughs and Cols.
(elongated areas of high and low pressure)
Along with these features there are fronts,
where cold air meets warm air.
Where these fronts meet
is known as an
Occluded Front.
When two air masses meet,
instead of mixing together,
the warm air tends to
rise over the cold air
causing a drop in pressure.
Occluded
Front
Col
Cold
Front
Warm
Front
Check of Understanding
Which air mass is called Tropical Maritime?
W
X
Y
Z
Check of Understanding
Which of these types of air mass
brings cold dry weather with little or no cloud
to the British Isles in winter?
Returning Polar Maritime
Polar Continental
via the long sea-track
Polar Maritime
Polar Continental
via the short sea-track
Check of Understanding
Which air mass starts off very cold with dry air
but arrives in the UK warm and wet?
Polar Maritime
Arctic Maritime
Returning Polar Maritime
Tropical Continental
Check of Understanding
Which air mass is called Polar Maritime?
W
X
Y
Z
Check of Understanding
Which air mass originates around the equator
and brings warm, cloudy weather
to the UK in both summer and winter?
Tropical Continental
Arctic Maritime
Tropical Maritime
Polar Continental
Check of Understanding
What is an area of low pressure also known as?
An anticyclone
A warm front
A depression
An occluded front
Check of Understanding
Upper winds are generally responsible for?
Poor weather
Movement of a depression
Fine weather
The strength of the surface
wind
Check of Understanding
If you stand at ‘Y’ with your back to the lower wind,
what can you expect the weather to do next?
Likely to improve
Likely to remain as it is
Likely to deteriorate
Blow a warm breeze
onto your face
Check of Understanding
Lines on a weather chart joining points of equal
pressure are called:
Occluded fronts
Isobars
Warm fronts
Depressions
Check of Understanding
This diagram shows:
A cold front
An occluded front
A warm front
An anticyclone
Check of Understanding
Fronts occur where . . .
Two warm air masses meet
The atmospheric pressure
is very high
A cold air mass
meets a warm air mass
Two cold air masses meet
Basic Navigation
Leading Cadet Training
End of Presentation