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Written by Dinda Amalia Ichsani – AIYA National’s Blog Editor
Edited by Meylisa Sahan – AIYA National’s Blog Editor
Translated by Lotte Troost – AIYA National’s Content Translator
When rain continuously hits Indonesia in January, Australia experiences summer. This phenomenon can be explored more deeply if we know what monsoons are. Monsoon winds blow through a regional scale in a continental coverage and occur due to a difference in air pressure between land and ocean. Based on the astronomical and geographical location of Indonesia and Australia, these winds blow periodically. Eventually, this system affects the weather in various parts of Australia and Indonesia. The term monsoon is also known as munsoon or moonsun, which derives from the Arabic word for ‘season’. The monsoon winds are divided into two types, namely the northeast monsoon and the southwest monsoon.
Illustration of monsoons movement. Source: Bobo grid
From October until April in Indonesia, the northeast monsoon blows from the Asian region and passes through the Indian Ocean towards the Australian continent. In this condition, the sun is positioned in the southern hemisphere and will cause high pressure in the Asian region, including Indonesia. However, the pressure will be lower in the Australian region. According to the Law of Buys Ballot, the wind blows from high pressure (cold) to low pressure (hot). When moving towards the equator, the Coriolis force will cause the wind to turn leftwards. The wind that passes this vast ocean contains a large amount of water vapour, which causes the rainy season in Indonesia from October till April. Especially the western regions experience high rainfall. Vice versa, summer hits Australia from December till February. Subsequently, these winds continue to move from the west towards Australia and bring water vapour that causes winter and rain in Australia in July and August.
The northeast monsoon (left) and the southwest monsoon (right). Source: Fish consult
Meanwhile, the southwest monsoon blows from the Australian region towards Asia from April till October. This wind blows when the sun is at the northern hemisphere and causes winter in the Australian region, with maximum air pressure. Contrastingly, the Asian continent will be warmer, with minimum air pressure. When moving towards the equator, the Coriolis force will cause the wind to turn rightwards. The monsoon wind blows from Australia causes the dry season in Indonesia, because this wind mainly derives from desert areas in northern Australia and also passes through the narrow sea. Therefore, the water vapour contained is not as much as brought by the northeast monsoon wind.
The rainy season and the dry season as caused by the movements of the wind have various positive and negative impacts on the lives of Australians and Indonesians.
The positive effects of this northeast monsoon for Indonesia include greener and more fertile plants, less air pollution, reduced risk of forest fires and artificial waters to irrigate rice fields become unnecessary. However, the negative effects include an increased occurrence of dengue fever, increased risk of floods and landslides and a disrupted sea voyage for fisherman. Meanwhile, the positive effects of the southwest monsoon cause fishermen to enter the sea calmly, that farmers can harvest calmly, and of course that clothes will dry quickly. On the other hand, this wind causes many crops to dry up and these eventually may die when water is lacking. It also increases the risk of bushfires and it makes it more difficult for people to get clean water.
Rain. Source: Sains kompas
Drought (ANTARA FOTO/Dedhez Anggara) CNN Indonesia
The impacts of the monsoons on Australia are not very different from what happens in Indonesia. However, the main difference lies in the timing of the movement of the western and eastern monsoon. Broadly speaking, the impact depends on the current season, namely in the summer or in the winter when it rains.
So we have learned that the rainy season and the dry season in Indonesia and Australia are caused by monsoon winds that blow periodically and regularly. At certain times, Indonesia experiences the rainy season and passes its water vapour to Australia, causing rain and winter. Likewise, winds originating from dry areas in Australia cause drought in Indonesia.