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Basic Navigation
Lecture 6
ACP32 Vol2
Basic Navigation
By the end of this lecture you should
understand:
 Weather
 Fronts
 Cloud Types
Weather
Much of the weather in Britain is caused by massive
areas of air at differing pressures.
To visualise pressure
areas on a chart or map
meteorologists join
areas of the same
pressure together in
a line, an ISOBAR.
Weather
Think of Isobars as contour lines on a map.
Steep/concentrated Isobars indicate high winds.
Shallow, spaced out Isobars indicate slower moving
air.
Areas of LOW pressure, depressions, bring
unsettled weather.
Areas of HIGH pressure, anti-cyclones, bring calm
weather.
Fronts
 When masses of cold air and warm air meet a
FRONT occurs.
 The COLD air/front will bring poor weather.
 The WARM air/front will bring stable weather.
Fronts
COLD and WARM air meet and the warm rises.
Fronts
As the WARM air rises the cold rushes underneath and
begins a spin.
Fronts
WARM air is trapped above the cold, spinning stops and the
front dissipates. This is now known as an OCCLUDED Front
Fronts
 In an OCCLUDED Front both the WARM and
COLD air are present in the same space
Fronts
 Similar to a front is an Anticyclone
 This is a mass of high pressure air
creating light winds that spin clockwise (in
the northern hemisphere) around the
centre of high pressure.
 They are stable slow moving systems,
consisting of warm dry air, bringing long
periods of fine clear weather.
Cloud Types
 There are 3 main types of cloud:
 1 Cirrus high altitudes and composed of ice
crystals. The word cirrus means a thread or
hair.
 2 Cumulus a lumpy or fluffy cloud.
 3 Stratus a featureless layer of cloud.
Cloud Types
These three words can be used to describe
distinct types of clouds.
 The words cumulus and stratus on their
own identify clouds whose base is below
2000m.
 Cumulus may be combined with nimbus
(Latin for rain), to give cumulonimbus - a
heaped rain cloud.
 A layer of cloud from which rain is falling is
nimbostratus.
Cloud Types
Cloud Types