The monsoon climate of India is effected by sub-tropical anticyclones and the inter-tropical convergence zone. In the ITCZ, trade winds meet and create a low pressure zone of rising air that cools and condenses forming frequent heavy rainstorms. The monsoon climate is split into wet and dry monsoons. The wet monsoon lasts 4 months from around June until September and the dry monsoon lasts for the rest of the year from October to May. The wet monsoon has extremely heavy rainfall and warm temperatures for very long periods of time and the dry monsoon is the opposite for the rest of the year and the land cools down. In summer in the wet season there can be up to 600mm of rain in a month whereas in the dry season in winter there is very little rain. On average there is around 3000mm a year, most of this rain falls in the wet season. This climate is due to many effects, most of them caused by subtropical and anticyclone and the movement of the ITCZ. Anticyclones are weather systems have high pressure, falling air, clear skys and warm temperatures. The air falls from the upper atmosphere and warms on the way down. This causes humidity to decrease as air masses hold more moisture as they get warmer. This also means that clouds don’t develop and conditions are very dry because air began over a land mass and has relatively low humidity and so not much moisture condenses.

The inter-tropical convergence zone is the area of the atmosphere that lies over the equator. It receives high daytime temperatures around 26-32⁰C, high rainfall of up to 3600mm a year and warm trade winds that vary in strength throughout the year. It also has low pressure and often high levels of cloud. The inter-tropical convergence zone moves throughout the year with the tilt of the Earth. There’s often high levels of cloud due to low pressure caused by rising air, this air is moist and so adiabatic cooling causes condensation as the air rises. In summer, the ITCZ moves pole wards towards the tropic of Cancer. The inter tropical convergence zone has extended 30°N, just to the North of India. This is due to the intense heating of the land mass that takes place over India. The intense heating and the movement of the ITCZ create low pressure over the North of India. The sea surrounding India heats up slowly, creating a zone of high pressure (subtropical anticyclone) off the Southern coast of India. Because winds blow from high to low pressure, air moves south westerly from the sea to the north of India. This wind is deflected by the Coriolis effect as the earth spins. The low pressure draws in warm air from the Indian Ocean bringing heavy rain to India. As the moisture reaches India it is forced up over the Western Ghats, a mountain range on the south west coast. The air cools adiabatically and so moisture condenses. The rapid rise in air creates tall cumulonimbus clouds and extremely heavy rain. This also happens over the Himalayas and is called orographic rain fall.

In winter, the ITCZ and the subtropical jet stream move southwards over the Equator and towards the Tropic of Capricorn. At the same time, the continental landmass at the centre of Asia around Mongolia and the Himalaya experiences intense cooling as the Northern hemisphere points away from the sun. The intense cooling creates an area of high pressure in Northern India and the low pressure of the ITCZ is found to the south of India. The winds blow from the North-East, away from the high pressure cell over northern India and into the Indian Ocean and this brings dry conditions to most of the Indian subcontinent as the winds travel over land it also warms as it travels toward the equator this also means no moisture would condense. A winter anticyclone forms in central Asia due to the ITCZ moving south creating the high pressure in Asia. In winter this creates conditions that are cold but clear causing the land to cool and the anticyclone worsens the effects of the dry winter monsoon as it means the air is colder and dryer which leads to little condensation over India. In conclusion, the movement of the inter-tropical convergence zone during the course of the year has a great effect on this climate. As the ITCZ moves North and South so do the areas of high and low pressure. The anticyclones in sub-tropical regions are developed by the movement of the inter tropical convergence zone and so the effect of the ITCZ is much greater than the anticyclones. I feel that the movement of the trade winds is mainly caused by the movement of the ITCZ and the movement of prevailing wind plays one of the largest parts in the creation of this climate’s characteristics along with the position of India relative to the warm Indian Ocean.