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Meteorologists are unsung heroes – La Niña shows her teeth

Global weather | Meteorologists are unsung heroes – la Niña shows her teeth Anthony Harrington

Those engaged with the “soft” or agriculture related commodities markets watch the big, global weather patterns more closely than most of us. We’re all, of course, aware of global warming issues and the need for business to green up, but the more immediate weather cycles only impinge on the rest of us when a spate of disasters, such as the January floods in Australia, Brazil and Sri Lanka, hit the headlines.

Yet for meteorologists, and, indeed, for anyone who bothers to look at the major weather cycles and patterns, while this or that storm or shower might be surprising, taken in the round, things move in rather stable, predictable ways. The Arctic Oscillation is a case in point. The term refers to opposed pressure patterns in northern, middle and high latitudes. The National Snow and Ice Data Centre explains it thus:

"The oscillation exhibits a "negative phase" with relatively high pressure over the polar region and low pressure at midlatitudes (about 45 degrees North), and a "positive phase" in which the pattern is reversed. In the positive phase, higher pressure at midlatitudes drives ocean storms farther north, and changes in the circulation pattern bring wetter weather to Alaska, Scotland and Scandinavia, as well as drier conditions to the western United States and the Mediterranean. In the positive phase, frigid winter air does not extend as far into the middle of North America as it would during the negative phase of the oscillation. This keeps much of the United States east of the Rocky Mountains warmer than normal, but leaves Greenland and Newfoundland colder than usual. Weather patterns in the negative phase are in general "opposite" to those of the positive phase…"

In short, the Arctic Oscillation is formed by the ring of winds that blow round the North Pole, with the ring widening or shrinking, strengthening or weakening, depending on whether high or low pressure dominates. So if you bother to check the pressure over the Arctic, you have a pretty fair idea of whether the Arctic Oscillation is in a positive or a negative phase, and you have a reasonable idea, in broad terms, of the weather consequences that are likely to flow from this. But of course, there are complicating factors, overlapping patterns and events, that make weather prediction and explication a much deeper art that this suggests.

Which is where the meteorologist as hero comes in. One woman who has garnered a global reputation, following in her father’s footsteps, he was also a renown meteorologist, is Evelyn Browning Garriss, who produces a subscription only newsletter, the Browning Newsletter. A free, “lite” version of some of this appears in her regular column for the Old Farmer’s Almanac.

In her latest newsletter, Browning Garriss sketches out the main causes of a weather pattern that has cost hundreds of lives and many billions of dollars across multiple countries, from Australia, to the US, to Sri Lanka. The winds that form the Arctic Oscillation, she points out, were weakened in December 2010, when some obscure volcanoes on Russia’s Kamchatka Peninsula in the Arctic Circle began erupting, throwing climate changing debris into the stratosphere. Volcanic ash clouds cut down on the sun’s warming rays, cooling the air beneath, lowering air pressure and changing wind patterns. Dust in the air also collects moisture, creating rain-bearing clouds. As Browning Garriss puts it, “Obscure polar volcanoes can have very expensive consequences.”

But the Russian volcanoes didn’t do the whole job on their own. They coincided with an especially strong La Niña. Again, here is Browning Garriss doing her usual job of teaching the punters how the weather is formed:

“La Niñas occur when unusually strong tropical trade winds blow the sun-warmed surface waters of the Pacific towards the west. As a result the western Pacific is warmer than average, and the central and eastern regions are cooler. When the central and eastern waters are more than 0.5 degrees Centigrade cooler than normal, the phenomenon is officially declared a La Niña.”

On top of this there is the long lasting Pacific Decadal Oscillation (I said it was complicated!) which has the effect of exaggerating the cooling of the Eastern Pacific and the warming in the West. As might be expected, air pressure falls over cold waters and rises over warm waters, which impacts the winds. In an ordinary winter, cooler temperatures off the west coast of North America mean less moisture in the winds (cold winds hold less moisture than warm winds) and drier conditions.

Not this year. Putting it all together, we have the Russian volcanoes causing a deep kink in the Arctic Oscillation, enabling cold Polar winds to reach much further south, which is why Scotland had its heaviest snows for 30 years and the coldest December since records began and why some towns in England were hit with -21 degrees Centigrade. In the Pacific, the cold Polar air stream pushed the typical La Niña weather patters further south again. Where La Niñas would normally cause heavy rains in the Pacific north west, the Russian volcanoes ensured that the precipitation moved further south, hitting Los Angeles and San Francisco, generating massive rainstorms and sending chill Arctic winds across Florida and deep into Mexico.

On the other coast, the waters of the Atlantic are relatively warm and when the warm, moisture laden winds off the Atlantic hit the polar chilled continental land mass of America all that moisture fell as snow – lots and lots of snow.

Browning’s detailed analysis in her newsletter pays careful study. What it should bring home to corporates in every sector, as well as to investors, pension fund managers and commodities traders, is that the weather matters – big time. There is no point getting a deep understanding of current economic trends only to find that your carefully organized plans are upended by some obscure Russian volcanoes and a kink in the Arctic winds…

Further reading on climate and climate change:

Tags: Australia , climate change , Global trade , la nina , Russia , sri lanka
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