Friday, 6 January 2012

Explosive Lows, Sting Jets, Blocking Events and Resilience


Two weeks ago today, on Scotland's extra New Year bank holiday, you might remember a nasty winter storm caused extensive damage to property and infrastructure all over the country. In other parts of the UK there were a couple of deaths caused in one instance by a falling tree and in the other by adverse conditions at sea. While these human tragedies happened in the southernmost part of Britain, the greatest rage of the storm was visited upon the central belt of Scotland, where, due to the extra New Year's bank holiday, most folk were enjoying a day off work at home and so thankfully there were few injuries and no fatalities. The central belt is the most populous part of Scotland; an area of relatively low-lying land situated between the Highland massif and the southern uplands, it comprises the valleys of the River Forth and River Clyde with Scotland's two major cities - Edinburgh and Glasgow - at either coast along with all the concomitant housing, transport facilities, businesses, infrastructure and population density associated with them. The central belt is the cinch for Scotland's waist, giving the physical geography of the country that distinctive and familiar hourglass figure.

When the storm came, its greatest intensity was funnelled by this topography into the central belt. This being the area of maximum human habitation and activity, the storm had greatest possible impact upon the human geography of Scotland. This is the second such notably intense storm to hit Scotland this season, the first being European Windstorm Friedhelm Hurricane Bawbag which famously caused a social-media sensation when unilaterally re-named by internet gobshites on Twitter.

Notwistanding the fact that it was more the location of maximum intensity rather than the intensity itself which was newsworthy (conditions like those two weeks ago - had they happened, say, in the Cairngorms or on Shetland would not have attracted much reportage) there were a couple of terms used by TV weatherfolk which drew the attention. Firstly, before the storm hit, forecasters scrambled suddenly to intensify their weather warnings, as the incoming low-pressure weather system became subject to a sudden deepening to become what they called an "explosive low". After the storm had passed, meteorologists noted that the storm had been characterised by a "sting jet", a phenomenon first identified after the Great Storm of 1987 which affected the south of England.


A sting jet is a meteorological phenomenon which is believed to be the cause of the most damaging winds in European windstorms.
Following reanalysis of the Great Storm of 1987, led by Professor Keith Browning at the University of Reading, researchers identified a mesoscale flow where the most damaging winds were shown to be emanating from the evaporating tip of the hooked cloud head on the southern flank of the cyclone. This cloud, hooked like a scorpion's tail, gives the wind region its name the "Sting Jet".
It is thought that a zone of strong winds, originating from within the mid-tropospheric cloud head of an explosively deepening depression, are enhanced further as the "jet" descends, drying out and evaporating a clear path through snow and ice particles. The evaporative cooling leading to the air within the jet becoming denser, leading to an acceleration of the downward flow towards the tip of the cloud head when it begins to hook around the cyclone centre. Windspeeds in excess of 80 kn (150 km/h) can be associated with the Sting jet.

The Sting Jet

The preceding three winters here have also been characterised by unusual conditions. In the winter of 2008/9 and then again but even moreso in 2009/10 a rare and persistent omega-shaped kink in the high-altitude jet stream (a high-speed river of air which girds the earth and flows west-to-east) caused high-pressure anti-cyclonic weather systems to become "stuck" over Britain - blocked from continuing their more usual west-to-east progress. The attendant clear skies associated with high-pressure weather systems allowed heat to escape directly into the stratosphere and so the country those winters was characterised by rime frost and morning fogs, starry nights and windless calm. For the sharp-eyed and patient, rare atmospheric phenomena like moonbows and sun dogs and parhelic arcs became commonplace daily sights. In 2010/11 a similar jet stream "blocking event" occurred, but that season's high pressure system got stuck over the central North Atlantic with the effect that weather systems marched in formation one after the other down from the high arctic, causing record snowfall and record low temperatures all over Britain. Nasty. These blocking events are becoming more common, and can be dangerous. Summer blocking events over Russia are responsible for thousands of heat-related deaths and the destruction of land, real estate and habitat by wildfire.

No blocking event over Britain this season (so far at least) and the winter, while rough and windy, has been unusually mild. So, selfishly, in Scotland we might feel thankful for the mild temperatures. But that gratitude comes with a sense of unease, for how many seasons in a row can we experience unusual weather and continue to label it "unusual"?

A BBC Scotland weather-news special - Storm-Force Scotland - was broadcast last weekend, and as I watched, I felt that there was a bit of a "Keep Calm and Carry On" air about it. Archive footage was shown to demonstrate that, yes, from time to time damaging winds can occur in Scotland and the participants appeared to be under special orders not to use the terms "Global Warming" or "Dangerous Climate Change".

But Alex Reid, the Scottish Government's special meteorological advisor let the mask slip…

We should not be surprised that these unusual weather patterns continue to surprise the authorities, for the disruption they bring takes a different form each time. And as this pattern-with-no-pattern continues we hear much from Government spokespeople talking of the need for "resilience". When, two years ago, freezing conditions and a shortage of grit/salt made Scottish roads unusable, a Transport Secretary lost his government position and steps were taken to ensure future superabundance of grit/salt. This year, those stockpiles lie unused. And then when floods swept low-lying areas of Moray and Perthshire tens of millions of pounds were spend on flood defence measures. Bunds and dykes and gates now lie unneeded, silent witnesses to wind-felled chimneystacks, and roads and railways closed by fallen trees. It seems that when the state and big business talk of "resilience" they mean "hardening" - a futile enterprise, for all human effort is ever dwarfed by the magisterial power of nature.

On the Isle of Bute, in that first week of 2012, the storm had cut the electricity supply from the mainland. The chainstores and supermarkets, reliant as they are on Kanban and PLU systems were unable to operate. They closed their doors to customers. Despite the fact that there might still have been stock on the shelves, the employees felt so disempowered by being un-powered that they could not take their customers ready-money - for the tills were not working. Without electricity, the threads of big-business commerce unravelled. But by contrast, the sole trader and small-scale local enterprises (which that island community remains blessed to retain) - the butcher and baker, ironmonger and inn - remained trading perfectly well. Marking their accounts by pencil in notebooks, locking cash taken in a strongbox in a cupboard. But what about people with no cash until the banks are back online? Well, they had no worries - the community-based enterprises were the local heroes who knew their customers by name. A little note; an IOU on a post-it pad written by candlelight - and trust - was their currency.

Resilience is not to be found, cannot be found, in engineering projects which jut their chin at nature, hoping to stand fast against the storm, or the cold, or the desertification, or the flood, or the heat, or the landslide, or the drought or the tide, or whatever combination surprises us next. Hubristically strengthening our civil-engineering defences merely increases the severity of the impact when those defences will be finally, inevitably breached. "Look upon my works ye mighty and despair". No - resilience is, rather, to be found in those activities - those systems - which fail-safe, which are unaffected by cascade failure, which are discreet nodes unconnected to artificial dependency networks. This true resilience stands founded in the strength of our communities and operates within the envelope described by the sustainability of our activities. We should take note of the sole traders of Bute and how they reacted during the time that the island was off the grid at the start of 2012. We should study carefully how they sustained their community for a whole week without electricity - without missing a beat, for there is a real lesson of true resilience for our future contained within their sustainable activities and self-reliant attitudes.

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