Are a mass of tiny droplets or ice particles formed when water vapour condenses.
Table of Contents
Three Cloud Forms
-Thin and wispy clouds composed of ice crystals.
-Appear as greyish sheets covering most of the sky and are rarely broken into units.
-Are massive rounded with a flat base and limited horizontal extent and billow upwards to great heights.
Basic Cloud Types
- Stratus Clouds
-Are found in layers, are flat in shape and resemble fog.
- Nimbus Clouds
-are dark at the base and sometimes white at the sides and cause rain and thunderstorms.
-Are white clouds consisting of white ice crystals.
-A rain cloud which is dark grey and spreads over the sky in low uniform layers.
- Cumulus Clouds
-Clouds with a flat horizontal base, massive, rounded and less horizontal extent.
- 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)
- Found between 23 ½ ◦N and 23 ◦N
- Experiences high temperatures.
- A zone of low pressure and doldrums (light and intermediate winds).
- Zone where S.E and N.E Trade Winds converge.
- Associated with convectional rain and thunderstorms.
- Migrates to the N and with the apparent movement of the overhead sun.
The Sub-tropical High Pressure Zone
- Found within 30◦N and 30◦S.
- A zone of high pressure.
- A region of calm descending air.
- Source of Trade Winds and Westeries.
- Zone of divergence of T. Winds and Westeries.
The Temperate Low Pressure Zone
- Found within 60◦N and 60◦S.
- A low pressure zone.
- Zone of convergence of westeries and polar easteries.
The Polar High Pressure Zone
- Found over the poles 90◦N and 90◦S.
- A high pressure Zone.
- Zone of descending calm air of low temperature.
- 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.
- Trade Winds
- Blow from sub-tropical high pressure zone and blow to the equatorial low pressure belt.
- Originate from sub-tropical high pressure zone and blow to the temperate low pressure belt.
- The Polar Easteries
- Originate from polar high pressure zone and blow to temperate low pressure zone.
- Seasonal winds which reverse in the direction of flow.
- They blow towards the land during summer (onshore) and from the land during winter (off shore).
- Bring heavy rains when onshore which can cause severe flooding.
- Well developed in the Indian Sun-continent, china, Japan and S.E Asia.