Assess the Relative Roles of Sub-Tropical Anticyclones and the Itcz in Creating the Characteristics of one Tropical Reigon

One tropical climate that is affected by the sub tropical anticyclones and the inter- tropical convergence zone is the monsoon climate of India. Anticyclones can be defined as weather systems that are characterised by areas of high pressure, low winds and relatively high temperatures. Subtropical refers to the regions of the Earth bordering on the tropics, just north of the Tropic of Cancer or just south of the Tropic of Capricorn; and the ITCZ can be defined as a belt of low pressure, which circles the Earth near the equator, where the trade winds of the Northern and Southern Hemispheres come together. The ITCZ’s position, shown below, varies seasonally and while it remains near the equator, it ventures farther north or south over land than oceans due to the variation in land temperatures. The location of the ITCZ can vary as much as 40° to 45° of latitude north or south of the equator based on the pattern of land and ocean.

India experiences two types of monsoons; the summer monsoon and the winter monsoon. The summer monsoon lasts from June until September where as the winter monsoon occurs from October until April. The summer monsoon is characterised by extremely heavy rainfall and the winter monsoons are largely dry.

The inter-tropical convergence zone is very important in the formation of the Indian monsoon. In June (summer monsoon) the ITCZ moves pole wards towards the Tropic of Cancer. This is due to the intense heating of the landmass that takes place over India. This intense heating and the movement of the ITCZ creates an area of low pressure over Northern India. Meanwhile, the sea surrounding India heats up slower than the landmass creating an area of high pressure- known as an anticyclone. The area of low pressure usually brings fine dry weather, with clear skys. The pressure gradient creates a cell of moving air; and because air moves from an area of high pressure to an area of low pressure, it moves in a southwesterly direction from the sea over to India in the north and northeast. The air is deflected right (northern hemisphere) due to the Coriolis force as the earth spins. As well as being deflected right, the air follows the natural configuration of the country. Due to the tropical maritime air moving over an area of sea, the air is full of moisture. The low pressure draws in the warm, unstable air from the Indian Ocean, which is laden with water vapour, bringing heavy rain to India.

Once the moisture-laden air reaches India, it is forced up and over the Western Ghats

on the western coast of India. This is illustrated in the diagram below. As the air attempts to move over the mountains it becomes cooler, due to the wet adiabatic lapse rate (0.5 degrees per 100m) and consequently reduces its ability to retain moisture, thus condenses and produces orographic rainfall in cumulonimbus clouds. As a result, there is a rain shadow effect on