Hi, I’m Peter Clift, Professor of Geosciences at Louisiana State University. Much of my research
is concerned with young sedimentary rocks and sediments in and around Asia. When I say young,
I mean sediments that were deposited in Cenozoic time, which is the last 66 million years of Earth
history. In this video, I’d like to explain four basic concepts about the Asian Monsoon:
what is Monsoon, where is the Asian Monsoon, why is the Asian Monsoon
important, and what causes the Asian Monsoon. What is the Monsoon? The word monsoon comes from
the Arabic word “mausim”, meaning season or weather . Monsoon is a seasonal wind that is not
unique to Asia. For example, the southwestern USA experiences something like a monsoon,
as does Ethiopia. Asia just has the strongest, most important, and most famous monsoon.
Where is the Monsoon? Although the monsoon can occur anywhere between a large
continent next to a warm sea, for the remainder of this video, when I talk about the “Monsoon”,
I mean the “Asian Monsoon”. OK, what happens with monsoon winds in Asia? It’s simple: they blow out
of cold, dry Asia towards the Indian and Pacific Oceans in the winter and from the warm, wet
Indian and Pacific Oceans towards the continent in the summer. The summer winds bring rainfall
deep into the continental interior and not just along the coast as seen in non-monsoon areas.
Why is Monsoon important? The winter monsoon is not so important, but the summer monsoon
rains are the single most important feature controlling and allowing agriculture across the much of densely populated
regions of South, Southeast Asia, and East Asia. The summer monsoon also supplies
water to the great river systems that flow out of the Asian highlands, including the Indus,
Ganges, Brahmaputra, Mekong, Red, Yangtze, and Yellow rivers. Many early civilizations started in
these river valleys, such as the Harappan or Indus Valley Culture. The rainfall is also important in
sculpting the mountains of Asia especially the Himalaya and erosion provides detritus
that covers the floodplains and deltas of these rivers, detritus that quickly becomes fertile soil
for agriculture. The winds are also important in causing upwelling of nutrient-rich seawater
adjacent to coastal regions, allowing fish and other marine life to thrive.
What causes the Monsoon? The Monsoon is caused by the differential heating of the land and ocean during
the summer and winter seasons, coupled with the fact that warm air rises and cold air sinks.
In summer, the land is warmer and the air over it rises.
This effect is more powerful if the land is high like a mountain plateau.
Given that the Himalayas are the highest mountains in the world and Tibet is the highest plateau,
it is no surprise that the Monsoon is powerful in adjoining regions.
Moist ocean air flows onshore to replace the air that has risen,
bringing moisture with it, and this moisture turns to rain – torrential rain. In the winter,
the continental interiors are cold and the oceans are warm, so cold, dry air flows offshore.
That’s the Monsoon in a nutshell, although there are some complications. For example,
some researchers emphasize the warming of air across the Tibetan plateau, while others argue
that the air is mostly heated in northern India ponded there by the barrier of the Himalayas.
Regardless of the details, there is no question that the Monsoon
is one of the most important climate phenomena on Earth.
I hope you have enjoyed learning a bit about the Monsoon. If you want to learn more, you can look
at the two references cited at the end of this video. Also, please watch the next video, which
explains how the solid Earth and the Asian Monsoon evolved together over the last 50 million years.