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.
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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
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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.
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They are stable slow moving systems, consisting of warm dry air, bringing long periods of fine clear weather.

Cloud Types
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There are 3 main types of cloud:
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1 Cirrus high altitudes and composed of ice crystals. The word cirrus means a thread or hair.
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2 Cumulus a lumpy or fluffy cloud.
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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