Friday, 15 March 2013

Strange Attractor

Migration Forecast #3  
(Updated Fri 15.3.13)
 “The results are correct – just don't ask how it can be like that. No-one understands how it can be like that.” 
Richard P. Feynman: Quantum Electrodynamics 1990

Edward Lorenz thought he was going nuts.

For days, he had been running a program on his LQP-300 computer. The machine was large, noisy, inconvenient and (by today's standards) desperately slow – but in June 1962, it was the best that his department at the Massachusetts Institute of Technology could afford. Because of the speed problem, he would start the program, let it run overnight, and study the results next morning. And he was getting nowhere. Slowly.

Lorenz was investigating the behaviour of something called “hydrostatic convection flows in a non-Hamiltonian system” and, as a starting point, had written down some simple equations for this.

The difficulty was: every time this program ran, it produced a different result!

As a good scientist, Lorenz decided that – assuming he was not really going mad – there must be something peculiar about the way the numbers themselves worked out. And this was important, because Edward Lorenz wasn't actually studying mathematical oddities at all – he was trying to find out why the simulation models used in long-range weather forecasting kept being wrong. In time, his work (and that of others) led to a completely new discipline of science: Deterministic Non-linear Dynamics, more popularly referred to as “Chaos Theory”...

You've heard of this before. It includes features such as the “butterfly effect” - the proposition that an immeasurably small difference in the initial conditions of a system, can result in very large-scale changes in how that system behaves over time. Almost all climate and weather mechanisms are non-linear systems but – like the animals in Orwell's 1984 - some are more non-linear than others. The north Atlantic jetstream is one such and, around this time of year, it starts bustin' some seriously sharp dance moves:-
Click for larger image

All these loops and whorls in the jetstream are the signatures of chaotic behaviour. Most stable oscillating systems have a topological pattern to which they keep returning: an “attractor.” But the jetstream is NOT inherently stable. It marks the places where two different masses of moving air interact with other and the degree of turbulent interaction changes at every different position, repeatedly switching from one state to another. When scientists first identified this phenomenon, they had to invent a new term to describe this class of weird behaviour in Nature: “Strange Attractors.”

As of this week, we've seen unseasonably cold weather over much of western Europe: carnage on the roads in France, and hundreds of flights cancelled at German airports. And twelve kilometres above our heads, unseen, the jetstream writhes and dances, until suddenly...

Click for larger image

This is the chart of 850Mb isobars and wind direction forecast for next Thursday 21/3. The blocking anticyclone south of Iceland has vanished and winds will shift into the south-west, bringing much milder conditions over the British Isles. Will the strange attractor bring a tide of migrants home for the new nesting season? It should be so. 

Interesting stuff is about to happen... 

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