Frost in the South

We’ve looked at the world from the top; this is the view from beneath: Antarctica in the centre, South America at top, South Africa right, Australia and New Zealand bottom left. Streamlines show near-surface wind, colours indicate temperature, dots mark rain and snow. All data are from the Met Office global analysis.

One reason why weather forecasting and climate research are hard is that the atmosphere is complicated: There’s a lot going on – all sorts of different motions and changes occurring simultaneously all over the world. So while it’s often useful to use simplified views – perhaps to look only at mean-sea-level pressure, for example – it’s also good sometimes to embrace the complexity, and remind ourselves why we need a supercomputer to keep track of it all.

So this time I’ve put as much as possible in the video: sea-ice, wind speed and direction, temperature and even rainfall. It’s still only a tiny fraction of the full three dimensional atmospheric state that our forecast models have to simulate, but there’s plenty to look at: We can see not only the small-scale complexity of the winds, but also some larger-scale patterns: the strong clockwise circulation around Antarctica formed by the southern hemisphere westerlies, the cyclones forming in that strong flow, and atmospheric waves folding outwards.

This isn’t really old weather, it’s almost new – from only last month. But I used this example because it illustrates that the weather is not only complicated and interesting, it also matters. If you set the video to September 16th you’ll see a low pressure (clockwise circulation) off Marie Byrd land, linking with a high pressure (anti-clockwise circulation) in the south-east Pacific. These combined to channel cold Antarctic air up toward central Chile, which contributed to a late frost which cost their fruit industry an estimated $1 billion. Expect to pay extra for peaches, cherries, and even Cabernet Sauvignon, as a result.

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