Turbulence Read Free

sound, is the one with which most people are familiar.
    The Ryman number, by contrast, is a criterion by which the turbulence of weather systems and other flows can be measured. It is dimensionless, which means it can be applied anywhere as a co-ordinate of comparison across space and time. A low Ryman number (less than one) indicates significant turbulence; a higher score (above one) indicates a more typical, ‘stable’ state.
    These dimensionless numbers are all about information. They are used as a way of gauging information received. There has been an occasion in my life when (to cut a long and complicated story short) I think I may have had some significant historical influence in employing the Ryman number in this way. The context of this was the meteorological preparations for Operation Neptune in 1944, the first phase of Overlord – or, more popularly, D-Day.
    In winter that year I was sent on a special task by Sir Peter Vaward, director of the Meteorological Office. From its reluctant originator I was to discover how to apply a range of values of the Ryman number to a fifty-mile-long invasion site on thecoast of France or Belgium. The Ryman number has a direct effect on weather forecasts, because turbulence is associated with patterns of expectation and uncertainty.
    Ryman lived in Scotland. Sir Peter had organised a place for me on a meteorological reconnaissance plane on its way from London to Prestwick, which then served the city of Glasgow and the large volume of air traffic arriving from America. It was late January when I set off, and snow was blowing across the airfield as I made my way to the plane (a Halifax), whose propellors were already turning.
    In the absence of meteorological information in areas where the enemy operated, a large number of these reconnaissance flights flew daily on sorties all round the British Isles. The plane I was flying in was due to continue from Prestwick to Stornoway on the Isle of Lewis, from where it would fly on the BISMUTH sortie towards Iceland. The aircraft was part of Met 518 Squadron and carried their famous badge painted on its nose – a fist grasping a key with Thaan iuchair againn-ne written underneath, which is Gaelic for ‘We hold the key’.
    What did I think was going to happen, as I climbed up into the cabin with my suitcase? Did I have a sense of knowledge about to dawn? What did I feel ? It’s very hard to get back to all that. It doesn’t just come gushing out. I often didn’t know what I felt at the time; I often don’t know what I think now. So many of our deepest feelings, in any case, come to us as doubtful, tangled, compound experiences. Events themselves as they happen condition the way we see previous events, making us recalibrate the chain of causation even as we teeter along it, casting all the while a speculative eye at a web of possible futures … This is what living – conscious living – is.
    As we took off at around ten I could still taste the baked beans I’d had for breakfast. No doubt about that, even after so many years. I remember the old advertisements, too, with their‘Always ready to serve’ slogan (more patriotic in those troubled times than ‘57 varieties’, I suppose) and picture of a soldier eating. And then: Don’t think Heinz are making less. We are making more! Fighting men must be fed first; so civilian supplies are limited. But those with a quick eye for the famous name …
    Something like that.
    I sat up front. The cockpit was cold and draughty. Like the pilot, I had a throat mike and a flying helmet with earphones and goggles – through which, once we were underway, I watched the blizzard increase. The snow hit the glass in loosely defined units, then moved across it fast in a joining mass before being whipped off to the wingtips, where it whirled round like a thick vapour and was flung into our trail. It was in my nature to plot the journey of