- The term Monsoon derives from the Arabic word ‘Mausin’, meaning ‘the season of the winds’
- Areas dominated by the north-east and south–east trade winds experience a distinctly wet rainy season and an exceptionally dry season. Regions within South Asia, the Gulf states of North America, the Pacific coast of central America, and Africa encounter monsoons. Asia has the most intense monsoon climate.
The South East Asian Monsoon
The monsoon displaces masses of energy to the north and south between 23 degrees latitude and 35 degrees latitude of the eqator, within the Tropics. The different heat capacity characteristics of continents and oceans determine the circulation pathways of the monsoon.
In summer, the winds usually flow from the sea to the land causing heavy rains inland. In winter, the winds reverse and flow from the continent to the sea culminating in dry conditions.
Follow this link below to activate the simulation model of migration of the monsoon season in Asia and Australia provided by the National Weather Service Climate Prediction Centre. It could be an effective, thought provoking lesson starter. The simulation could be left running to show the variations in precipitation, wind direction and wind speed throughout the summer and winter monsoon seasons. This will grab the students’ attention and they could guess the theme of the lesson.
Metlink provides resources for teaching weather and climate in schools which mirror the national curriculum requirements and has quick links to key specifications:
http://www.metlink.org/weather-climate-resources-teachers/key-stages-weather-climate/key-stage-4-weather/ks4-monsoons.html
Causes:
Pressure and wind – the land heats up and cools down disproportionately to the sea (oceans warm and cool more slowly than land), this inequality leads to the creation of pressure gradients and thus winds.
ITCZ (Intertropical Convergence Zone) – the seasonal migration of the ITCZ and it’s wind belts as it moves north and south. This movement is in response to seasonal differences in pressure gradient due to the changes in solar energy received throughout the year.
Mountain Chains – the presence of huge mountain chains such as the Himalayas results in orographic enhancement of rainfall because air masses are forced to rise and condense. They also can increase low-level convergence of air, creating zone of rising air when moisture laden clouds collide forcing water droplets to grow and fall. Therefore, mountain chains can induce exceptionally high rainfall in convergence zones, eg. Assam in northern India can receive greater than 10,000 mm of rain annually, 6 times that which falls on the coastal regions.
Jet Stream locality - During the winter, the winds flow north-easterly (the subtropical jet stream divides and follows two pathways, one stronger belt protrudes southwards and one weaker belt flows north of the Tibetan Plateau). High pressure systems develop, air descends beneath the jet and away from the continent seawards. Upper air flow reverses in the summer when the subtropical jet retreats north of the Tibetan Plateau and the Equatorial jet diverts north and flows over the Indian subcontinent in the opposite direction.
Concentrations of Carbon Dioxide - The concentration of carbon dioxide in the atmosphere over India due to the effect of uplift over the Himalayas means that less heat is absorbed and cooling takes place.
Facts and Figures:
Summer monsoon occurs from June to September
90% of western and central India’s total annual rainfall is received during the summer.
Average monthly rainfall totals 200 – 300mm
Winter monsoon occurs from October to May
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