by Jean Osanz, Richmond River Independent
A month ago, the BoM declared a La Nina event, which means wetter than average conditions expected in the next few months
How does that work?
It all depends on the Walker circulation.
Gilbert Walker was a Cambridge University mathematician who became director general of observatories in India in 1904.
He studied the Indian Ocean monsoon and found the temperature difference between land and sea powered the monsoon.
You may know the afternoon sea breeze. The air over land heats and rises and the air above the sea comes in and replaces it. At high altitude, the air moves from land to sea. This forms a loop which is a mini Walker circulation.
Extend the idea to the Pacific’s tropical zone. The ocean surface is warm somewhere north of New Guinea and cold in the east near America. So trade winds blow from east to west at low altitude and the other way around further up in a Walker circulation.
Over PNG and northern Australia we have a lot of evaporation forming some big cumulonimbus and ”¦ rain!
In the neutral situation we get a just a nice amount of rain.
But in the La Nina situation, the Walker loop goes a bit crazy and everything gets amplified. So we get a lot of rain.
Apparently, we should get some of this in the next few months, but not as bad as in 2010–2011. Fingers crossed.
This article appeared in the Richmond River Independent, 28 October 2020.
