A sea breeze the size of a continent
What Is a Monsoon?
A whole continent heats up in summer and drags an ocean's worth of wet air inland.
-
Step 1 of 5
It is the beach breeze, scaled up.
Land heats faster than sea. Do that to an entire continent through a whole summer, and the flow of air becomes a season instead of an afternoon.
-
Step 2 of 5
The incoming air is soaked.
It has spent weeks crossing warm ocean, evaporating water the whole way. By the time it reaches the coast it is carrying enormous amounts of vapour.
-
Step 3 of 5
Hills and heat wring it out.
Forced upward by mountains and by rising hot air, the vapour cools and condenses. The result is rain measured in metres, not millimetres.
-
Step 4 of 5
In winter the whole thing reverses.
The land cools below the sea's temperature, air sinks over it and flows outward. The wind swaps direction and the dry season begins.
-
Step 5 of 5
Billions of people plan around it.
Crops are sown for its arrival. A monsoon two weeks late is a drought; one two weeks early is a flood. Predicting it is a national-scale problem.
Cherrapunji in India has recorded over 26 metres of monsoon rain in a single year.
The short version
A monsoon is a seasonal wind reversal: summer heat over a continent pulls in wet ocean air, and winter cold pushes it back out.
Try it yourself
Find the monsoon dates for a city in India and compare its June rainfall with its January rainfall. The gap is enormous.
Topics