The Horizontal Distribution of Air Pressure in January:

A study of the weather map of January reveals the following facts of the horizontal distribution of air pressure of this month:

1. The equatorial low pressure belt is situated south of the equator due to the southward apparent movement of the sun. Hence, the main low pressure cells are situated in Australia, South America and Africa.

2. The subtropical highs are located in the ocean in the southern hemisphere because the water is colder than the land in this month. It is summer there.

3. In the northern hemisphere, high pressure cells are not properly developed in semitropical areas but appear as a long high pressure ridge.

4. There are two low pressure cells in the subtropical areas of the northern hemisphere which are located over the Northern Atlantic and Northern Pacific Oceans. They are known as Icelandic.

5. In eastern Central Asia, there is a fully developed and broad based high Alentian low pressure cell which has all the characteristics favourable for intense heating. No such cell with such a high pressure is found in North America.

The Horizontal Distribution of Air Pressure in July: A study of the weather map of July reveals the following facts of horizontal distribution of air pressure:

1. The equatorial low pressure belt has shifted towards north of the equator due to the northward movement of the sun.

2. The whole pressure system has shifted to the north following the corresponding shift to the sun.

3. The subtropical high pressure belt of the southern hemisphere extends continuously more in July than in January.

4. The subtropical high pressure belt of the northern hemisphere exists over the North Atlantic and North Pacific Oceans.

5. The subpolar low is deep and continuous in the southern hemisphere but it is only a faint oceanic low in the northern hemisphere.