The term “monsoon” has traditionally been used to refer to the climate that has apparent seasonal reversing winds between summer and winter accompanied by corresponding changes in precipitation, notably in the tropics. However, the definition of the term has since been expanded to include seasonal changes in atmospheric circulation and precipitation resulting from asymmetric heating of sea and land. Monsoon regions are distributed globally over all the tropical regions such as continents and oceans. Monsoons are not the same in the tropics because the regional patterns of rain and wind are influenced by the location of oceans and continents. However, it is the dominant variation in the climate of the tropic.
Overview of the Global Monsoon
Almost half of the world’s population, mostly in developing countries, live under the influence of the monsoon-dominated climate. Their culture and economic activities, especially agriculture, have evolved around the cyclic nature of the monsoon. The world’s monsoon system consists of the Asia-Australian and West Africa monsoons. Strong monsoons are found where the Pacific Ocean and the Indian Ocean meet. This region comprises of South Asia and Australia. South Asia monsoon is especially strong because of the effects of the Himalayas which blocks the dry air coming from the north from entering the humid monsoon region. The monsoon also takes place in North and South America but tends to be very weak compared to other regions. Here are the types of monsoons and the countries they affect.
The African Monsoons comprises of West African Monsoon and the Southeast African monsoon.
The West Africa monsoon is experienced mainly by the West African countries such as Benin, Nigeria, Burkina Faso, Cameroon, Ghana, Gambia, Mali, Senegal, Niger, Sierra Leon, Liberia, Togo, Guinea, Guinea-Bissau, and Mauritania. Areas outside of this region also experience the monsoon but the influence decreases with distance. In these regions, the monsoon is as a result of the seasonal shift of the Intertropical Convergence Zone (ITCZ) and the seasonal humidity and temperature differences between the equatorial Atlantic Ocean and the Sahara Desert. The monsoon reaches West Africa on or around June 22 and withdraws towards the south by October. The West Africa monsoon is the alternation of the harmattan and southwesterly wind at the surface. The dry northeasterly wind and the harmattan are interrupted by the shift of the ITCZ to the north and the resulting southerly wind in the summer.
The East African monsoon is experienced in East African countries such as Kenya, Uganda, Tanzania, Rwanda, Somali, Zimbabwe, Zambia, Mozambique, and Malawi. This monsoon system is experienced when the ITCZ moves to the south of the equator. The monsoon arrives in the region in January and withdraws in March. The long rains are experienced during spring while the short rains are experienced in autumn.
The Asian Monsoon can be classified into several subsystems such as the South Asian monsoon, Southwest monsoon, Northwest monsoon, and East Asian monsoon.
The South Asian monsoon affects the Indian Subcontinent and is experienced in several countries such as Nepal, Sri Lanka, Pakistan, India, Bhutan, and Bangladesh. The monsoon is one of the most anticipated weather phenomenon in the Indian Subcontinent, experienced around June through to September. It significantly influences the overall lifestyle of the residents and has been nicknamed “the real finance minister of India.”
The Southwest monsoon occurs from July to September and is experienced mainly in the coastal Indian states of Kerala and West Bengal. It accounts for approximately 80% of the rainfall received in India, with agriculture heavily dependent on the rains. During the summer, the Thar Desert and the surrounding areas heat considerably causing a low-pressure area over the central and northern Indian subcontinent. The moisture-laden wind originating from the Indian Ocean will rush to the subcontinent to fill the void. The Himalayas will block these winds from reaching Central Asia, leading to a drop in temperature and precipitation fall.
The Northeastern monsoon is experienced in Sri Lanka and parts of India (Tamil Nadu). The dry cold wind traveling towards the Indian Ocean picks up moisture from the Bay of Bengal and deposits it in parts of India and Sri Lanka. This monsoon occurs from October to December in Southern Asia. The Northeastern monsoon is responsible for about 60% of rain in Tamil Nadu.
The East Asian monsoon is experienced in India, China, Taiwan, Japan, North Korea, South Korea, and the Philippines. This monsoon carries moist air from the Pacific Ocean and the Indian Ocean to East Asia and affects the climate of the region. The East Asian monsoon is accelerated by the difference in temperature between the Pacific Ocean and East Asia. The monsoon is divided into cold and dry winter monsoon and warm and wet summer monsoon.
The Indo-Australian monsoon is experienced from September through to February. It begins from the Maritime Continent and follows the heating maxima down the Malay Peninsula to the Indonesian islands of Borneo, Sumatra, Java, and Sulawesi, as well as the Philippines and northern Australia. This monsoon is responsible for about 75% of the annual rainfall in northern Australia.
North American Monsoon
The North American monsoon is experienced in Mexico and the southwest United States and occurs from late June through to September. In the US, it affects states such as Nevada, Arizona, Utah, New Mexico, California, Texas, and Colorado while in Mexico it is felt along the Sierra Madre Occidental.
The European monsoon, also called the “return of the westerlies,” is caused by the resurgence of the westerly wind from the Atlantic where they are loaded with rain and wind. The westerly winds commonly occur during the European winters and generally ease as spring sets in from late March through to May. The rains arrive at the beginning of June and also around mid or late-June. The European monsoon affects the North Atlantic coastline, especially in the United Kingdom, Ireland, Belgium, Netherlands, Luxembourg, northern France, and western Germany. However, the return to the westerly is considered as more of a conveyor belt delivering low-pressure centers to Western Europe rather than a monsoon.