CLOUDS

Are a mass of tiny droplets or ice particles formed when water vapour condenses.

Three Cloud Forms

1. Cirroform

-Thin and wispy clouds composed of ice crystals.

2. stratiform

-Appear as greyish sheets covering most of the sky and are rarely broken into units.

3. Cumuliform

-Are massive rounded with a flat base and limited horizontal extent and billow upwards to great heights.

Basic Cloud Types

1. Stratus Clouds

-Are found in layers, are flat in shape and resemble fog.

2. Nimbus Clouds

-are dark at the base and sometimes white at the sides and cause rain and thunderstorms.

3. Cirro-cumulus

-Are white clouds consisting of white ice crystals.

4. Nimbostratus

-A rain cloud which is dark grey and spreads over the sky in low uniform layers.

5. Cumulus Clouds

-Clouds with a flat horizontal base, massive, rounded and less horizontal extent.

6. Alto cumulus

-High clouds composed of ice crystals which indicate fair weather.

World distribution of Pressure Zones and the Planetary wind System/World Prevailing Winds

The Equatorial Low pressure Zone (ITCZ-low)

1. Found between 23 ½ ◦N and 23 ◦N
2. Experiences high temperatures.
3. A zone of low pressure and doldrums (light and intermediate winds).
4. Zone where S.E and N.E Trade Winds converge.
5. Associated with convectional rain and thunderstorms.
6. Migrates to the N and with the apparent movement of the overhead sun.

The Sub-tropical High Pressure Zone

1. Found within 30◦N and 30◦S.
2. A zone of high pressure.
3. A region of calm descending air.
4. Source of Trade Winds and Westeries.
5. Zone of divergence of T. Winds and Westeries.

The Temperate Low Pressure Zone

1. Found within 60◦N and 60◦S.
2. A low pressure zone.
3. Zone of convergence of westeries and polar easteries.

The Polar High Pressure Zone

1. Found over the poles 90◦N and 90◦S.
2. A high pressure Zone.
3. Zone of descending calm air of low temperature.
4. Source of polar easteries.

The Worlds Prevailing Winds

These are the major winds blowing over the earth frequently and consistently and which influence the world weather.

1. Trade Winds

Blow from sub-tropical high pressure zone and blow to the equatorial low pressure belt.

2. Westeries

Originate from sub-tropical high pressure zone and blow to the temperate low pressure belt.

3. The Polar Easteries

Originate from polar high pressure zone and blow to temperate low pressure zone.

Monsoon Winds

1. Seasonal winds which reverse in the direction of flow.
2. They blow towards the land during summer (onshore) and from the land during winter (off shore).
3. Bring heavy rains when onshore which can cause severe flooding.
4. Well developed in the Indian Sun-continent, china, Japan and S.E Asia.