Weather Eye E-Book

Brendan McWilliams

• Herausgeber: The Lilliput Press
• Kategorie: Geisteswissenschaft
• Sprache: Englisch

Seitenzahl: 239

Veröffentlichungsjahr: 1993

Beschreibung

Weather Eye is a selection from the famous column in The Irish Times, which over the years has described and evoked all aspects of that most perennial of subjects for exchange and conversation – the lingua franca of country – and townspersons everywhere. Subjects encompassed include weather in history, weather in literature, weather in folklore, weather in mythology and weather in religion: auguries and forecasting; the science of meteorology; winds, rain, atmospheric pressure, cloud formations; macabre extremes; nomenclature; thoughts on snow, water, fog, dew, hail; thunder and lightning, rainbows and mirages; chroniclers and personalities (from Pepys to William Molyneux, Ben Franklin and Francis Beaufort, Mary Shelley and Percy French); lineaments of air and space; anomalies and optical phenomena; weathermen and weatherwomen. Weather Eye is a fascinating and authoritative compendium which will interest the serious student and delight the general reader curious about the workings of the world.

Leseprobe

WeatherEye

BRENDAN McWILLIAMS

THE LILLIPUT PRESS MCMXCIV

TO ANNE SINE QUA NON

Quelqu’un pourrait dire de moi que j’ai seulement fait ici un amas de fleurs étrangères, n’y ayant fourni du mien que le filet à les lier.

Montaigne, Essais, III, xii

ItcouldbesaidofmethatinthisbookIhavemerelymadeupabunchofotherpeople’sflowers,providingfrommyselfonlythestringthattiesthemalltogether.

Contents

Title Page

Dedication

Epigraph

ACKNOWLEDGMENTS

FOREWORD

I SearchingfortheSecrets

II TheElementsExplained

III ComingtoBlows

IV BlowingHotandCold

V TheVapours

VI AnOpticalAssortment

VII ForecastersandForecasting

INDEX

Copyright

Acknowledgments

I am grateful to successive Directors of the Meteorological Service for their support and encouragement over the years; to Lisa Sheilds, the Service’s Librarian, for her unstinting and never-failing efforts to provide precisely whatever reference might be needed; and to my colleagues in the Meteorological Service for their help in answering my silly questions, and their frequent tolerance at finding what appeared to be a casual conversation over coffee reproduced in TheIrishTimes a few days later.

The editorial team at TheIrishTimes deserve my thanks for their eternal vigilance in weeding out the worst excesses of the ever-present gremlins. I am also in debt to the hundreds of readers who have written to me over the years with comments, suggestions and details of their own experiences in the world of meteorology; I have replied to most of them – but alas not all, and I hope that those whose overtures have met with silence will rest assured that their information has been read, appreciated, and very often used. At the very least it is reassuring to learn that someone actually reads the words one writes.

Most important of all, I am grateful to my wife Anne for her advice, research, encouragement and solid practical help in producing the daily column down the years. She has cheerfully tolerated the solitude of my nightly sojourn to the keyboard in the interests of meteorology and art, and without her this book would not exist. And finally I thank Stephen and Laurie, whose irrelevant and irreverent advice and welcome interruptions have helped to make the journey tolerable.

Foreword

The very first ‘Weather Eye’ appeared in TheIrishTimes on 9 August 1988. A month or so previously I had submitted to that paper a series of four feature-length articles on meteorology; I assume the reaction of the readers must have been benign, because shortly afterwards I was asked if I would consider the tyranny of a daily column – and being younger and less wise than I am now, I readily agreed. Since then, nearly two thousand individual pieces have appeared, and although it is not always easy to maintain the pace, it is a discipline I have come to quite enjoy.

As regular readers of the column will be well aware, the subject matter of ‘Weather Eye’ strays frequently from the narrow path of meteorology regarded purely as a science. I have been conscious that if the reader, and indeed I myself, merely wanted to find out how the weather works, it is only necessary to consult a standard text-book on the subject. But behind the science lie the stories of the people who developed it, of the mistakes they made along the way, and of the plausible misapprehensions in which they found their inspiration. These, even more than the wonders of the atmosphere and the miracles achieved by modern technology, lend vitality and fascination to the subject.

These stories are not difficult to find. Anyone assisted by the ‘six honest serving men’ described by Kipling is faced with a myriad of unanswered questions on any weather topic that might come to mind. The six, if you remember, were ‘What and Why and When, and How and Where and Who’: they, combined with a certain familiarity with the classics which perhaps betokens a youth that was not sufficiently misspent, have helped to make ‘Weather Eye’ whatever it may be to you.

Almost since the very first article appeared, there have been frequent requests that an anthology be published in more permanent form. I have been slow to rise to the occasion, and have found it difficult to choose a selection that might encapsulate the flavour of the daily column. But here they are at last – over a hundred ‘Weather Eyes’ that I hope may be enjoyed.

BRENDAN MCWILLIAMS

June1994

ISearching for the Secrets

ATalenttoPeruse

The forecasters of ancient Rome occupied a position of great power and influence. Unlike today’s practitioners, they were not obliged to confine themselves to predictions of the weather. The Roman augurs had a wide remit, and their pronouncements on the likely course of future events were awaited with eager anticipation at the start of any important enterprise.

It was the duty of the augurs to observe the signs – or auspices – which were sent by the gods to indicate their approval or otherwise of any proposed undertakings. The auspices took many forms. Signs from the birds – relating to their pattern and direction of flight, to the sounds they made, and to the ways in which they took their food – were of particular significance.

In general, signs from the right-hand side were considered to be good, while those which manifested themselves from the left were unlucky or sinister. Indeed they were literally so: sinister is the Latin word for ‘left’. But the most trusted sources of information for the augurs were the entrails of sacrificial animals. The liver was found to be particularly reliable in this regard, because of the subtle variations to be found in its size and shape, and in its colour and the pattern of its veins.

The operation was taken very seriously. Before taking the auspices the augur marked out the templum, or consecrated space, within which his observations were intended to be made. Anything outside the templum did not count; within its limits, the augur pitched his tent, asked the gods for signs, and waited for his answer.

Since magistrates were legally bound to take appropriate action on the advice of an augur, the office could be used by unscrupulous practitioners for personal political purposes. An unfavourable report could be used to obtain the postponement of unwanted meetings of the Senate, or to cancel the results of an election whose outcome might prove to be somewhat inconvenient. In 59 BC, for example, the augur Bibulus succeeded in holding up the entire legislative programme of Julius Caesar by merely, as he put it, ‘watching the heavens’.

For these sensitive reasons, the office of augur was bestowed only on persons of the most distinguished merit. This tradition of excellence has continued for those required to gaze into the future nowadays but the power, the influence, the flamboyant trappings of office, and indeed the talent for omniscience, have long since disappeared. Otempora,Omores!

AnEarlyEnthusiast

‘Those whom the gods love die young’ according to the Greek play-wright Menander. Perhaps that was the case with William Molyneux, who died on 11 October 1698, at the early age of forty-two. But despite his somewhat premature demise, William Molyneux has achieved a lasting place in climatological history, he is credited with being Ireland’s very first scientific weather observer.

Molyneux was educated at Trinity College, Dublin, and later studied law in London. His interests throughout his life were wide, and he was no stranger to political controversy. Indeed only a few months before he died, he wrote ‘The Case of Ireland’s being bound by Acts of Parliament in England Stated’, a tract which attracted sufficient attention for it to be condemned by the London parliament in June of that year for being ‘of dangerous tendency to the Crown and to the people of England.’

Molyneux lived in an era of rapid development in the field of scientific instrumentation, and he quickly realized the potential of these new instruments for gaining an insight into the behaviour of the atmosphere. He was discouraged, however, by his difficulty in acquiring them: ‘I am living in a kingdom barren of all things’, he lamented in 1681, ‘but especially of ingenious artificers; I am wholly destitute of instruments on which I can rely.’

But the situation did improve. In March of 1684 Molyneux was able to begin a ‘Weather Register’, which for the first time in Ireland included readings of barometric pressure. By June 2nd of that year he had compiled enough material to present a paper to the Dublin Society on ‘The Observations of the Weather for the Month of May, with the Winds and the Heights of the Mercury in the Baroscope.’ He sent a copy of his May Register to Oxford University where it remains to this day, preserved in the Bodleian Library.

In May of the following year, Molyneux handed over the exacting task of keeping weather records for Dublin to St George Ashe, later to become Provost of Trinity College, and Ashe maintained the continuity for another year or so. This series of observations, although it only lasted for the two-year period 1684–6 and only a small fragment of it still survives, is regarded as one of the most important milestones in the history of Irish meteorology.

FromMen-o’-WartoBitsofPaper

Long before the invention of instruments that could measure the speed of the wind accurately, people used to guess at it – and then describe it. But for hundreds of years such descriptions were purely subjective. Who would have thought, for example, that the pirate William Dampier, writing in 1697 and describing the wind as merely ‘blowing exceeding hard’, was in the middle of a full typhoon? At other times, however, gross exaggeration was the order of the day. Admiral Sir Francis Beaufort was the first to standardize the measurement of wind, and the scale which bears his name has survived since the beginning of the last century with changes of a mere cosmetic nature.

Beaufort was born in 1774 into a family of French Huguenot origin in Co. Louth, where his father, Dr Daniel Augustus Beaufort, was rector of the local church. At the tender age of fourteen, young Francis embarked on a naval career, his family having paid the not inconsiderable sum of 100 guineas for the privilege; he was taken aboard the good ship Vansittart at Gravesend on 20 March 1789, and in due course crowned a distinguished career by becoming Hydrographer to the Royal Navy and being made a knight.

It was in 1805 that Beaufort’s scale of wind force was officially adopted. For the lower range of his thirteen-point scale, he took his cue from the descriptive terms traditionally used by sailors. Force 0 was a ‘calm’, Force 1 a ‘light air’, and Force 2 a ‘slight breeze’. For the stronger winds, he realized that he had to define his scale in terms of some well-known yardstick, just as a standard measure might be used to determine the length or weight of another object. The criterion he chose was the full-rigged battleship or ‘man-o’-war’ of his day. He described the winds by the effect they might have on such a vessel – and in particular the amount of sail it could carry in high winds without getting into trouble.

A century later, in the early 1900s, there were no longer any men-o’-war by which to learn the wind speeds, and so the descriptions had to be revised. For maritime purposes, the winds were now defined in terms of their effect on the surface of the open sea. Force 8 or Gale Force, for example, represents winds averaging slightly over 40 miles per hour, and was described by Beaufort as a wind in which ‘a well-conditioned man-o’-war might carry triple reef and courses’; the new Gale Force 8 resulted in ‘moderately high waves, where … the foam is blown in well marked streaks along the direction of the wind.’

A further change to the Beaufort Scale was necessary to cater for the vast majority of the population who, like W.S. Gilbert’s Admiral, ‘stick close to their desks and never go to sea’. They were accommodated by Sir George Simpson, who in 1906 related the Beaufort numbers to familiar homely things like loose bits of paper, umbrellas, trees and chimney pots. And this, in essence, is the Beaufort Scale of Wind Force that is still in use today.

Rear-Admiral Sir Francis Beaufort (1774–1857). (Painting by S. Pearce, 1851, National Maritime Museum, Greenwich)

Drains,DykesandWeather-Maps

The inspection of drains appears to nurture creativity. Percy French, for example, before achieving more lasting fame as the composer of many of our best-loved Irish airs, began his career as the official inspector of drains for Co. Cavan. But far away, and a longer time ago, another member of the hydrological inspectorate carved out his own particular niche in history.

Heinrich Wilhelm Brandes was born on 30 July 1777, in the little German town of Ritzebuttel. Brandes spent the first ten years of his adult life as an Inspector of Dykes on the River Weser, and might, had his talents led in that direction, have progressed to write Teutonic gems like ‘How are things in Ritzebuttel?’ Instead, however, he became a meteorologist, and he is credited with drawing the very first weather-map.

With a growing reputation as a mathematician, Brandes was appointed Professor of Mathematics at the University of Breslau in 1811, and it was there that he developed his interest in meteorology. The science was still in its infancy. From 1600 onwards, the invention of many of the now familiar meteorological instruments made scientific weather observations possible for the first time. It was nearly 200 years later, however, before any serious attempt was made to obtain simultaneous readings from a large number of places. And even then, nothing very much was done with them – until Brandes came along.

The most successful observing network of the era was one of thirty-seven stations throughout Europe, organized during the 1780s by what was called the Meteorological Society of Mannheim. Although the project was in operation for only twelve years, it was a very valuable step forward; for the first time observations were carried out with standardized methods and with carefully calibrated instruments.

More than thirty years later, during the period from 1816 to 1821, Brandes decided that there was a great deal to be learned from this valuable series of data. He entered the observations for each day of the year 1783 on 365 individual maps, and then drew lines to indicate deviations of the atmospheric pressure from its normal value. From these charts he hoped it would be possible to determine ‘the limit of the large rain cloud which lies over Germany and France in July…’ His charts identified for the first time the depressions and anticyclones which are so familiar to us today, and thus laid the foundations of modern meteorology.

AStormofConsequence

Shipwrecks are still a fact of life. The sea remains the scavenger it always was, a fickle opportunist, waiting with Pavlovian anticipation to subsume the unwary mariner into the oblivion of its murky depths. ‘The sea’, as Joseph Conrad said, ‘has no generosity.’

Wrecks, however, are not as common as they used to be. Stronger and more sturdy ships, better communications between ship and shore, modern navigational aids, and above all, accurate and timely weather forecasts, have all deprived the sea of countless victims. But in the middle of the last century it had its share; for example over 200 vessels, large and small, were wrecked in the waters around these islands between 21 October and 2 November 1859. The best remembered is the RoyalCharter.

On 25 October 1859 the steamship RoyalCharter called at Cobh (then Queenstown) in Co. Cork. It had left Melbourne, Australia, just two months previously and was on its way to Liverpool with 430 passengers and crew, and a cargo of £500,000 in gold bullion. The stay in Cork was brief, and the vessel left Queenstown later that day on the final leg of its long voyage. At 3 a.m. on the twenty-sixth, a vicious storm drove the ship ashore near Moelfe on the north-east coast of the isle of Anglesea. Within five hours it had been dashed to pieces; a few of those on board were saved, but over 400 persons perished in the wreck.

Although in those days organized meteorology was in its infancy, it had reached a stage where regular weather observations were carried out at a few places, and these records have made it possible to reconstruct the progress of the Royal Charter storm. It seems to have developed west of the Azores, and by 9 a.m. on 25 October a depression of 965 millibars, or hectopascals as they are now called, had reached Brest in northern France. From there it moved towards Plymouth, passing over the Eddys-tone lighthouse, and headed northwards over Wales. At 6 a.m. on the twenty-sixth, it was seventy or eighty miles to the east of Anglesea – and the RoyalCharter.

The tragedy is well remembered by meteorologists. It was as a result of the publicity given to this storm and the subsequent enquiry that the head of the ‘Meteorological Department’ of the British Navy, Vice-Admiral Robert FitzRoy, was charged with organizing a system of ‘storm warnings’ which were to be sent to threatened coastal areas.

FitzRoy organized a network of forty weather stations around the Irish and British coastlines, which provided him with daily weather reports by electric telegraph. His forecasting methods were primitive by today’s standards, although he was not one to oversimplify them for the benefit of the man in the street: ‘The weather of our country’, he told anyone who was interested, ‘usually depends completely on the collision, combination, alternating predominance, or successive exchanges of parts of competing polar and equatorial countercurrents.’ George Bernard Shaw – whose theory, if you remember, was that all professions are conspiracies against the laity – could reasonably claim a QED!

FitzRoy was a practical man at heart. He produced the required forecasts, and instituted the storm warnings which began in February of 1861. When gales were expected, warnings were telegraphed to forty ports and harbours around the country; within thirty minutes appropriate signals were prominently displayed on shore to relay the word to passing ships. The signals were of a semaphore type: a cone pointing upwards meant a northerly gale; a drum or cylinder warned of successive gales from many directions; and other patterns had meanings which quickly became standard and widely understood.

FitzRoy’s storm warnings were noted with some scepticism by the general public, but were staunchly defended, and widely used and appreciated, by the shipping fraternity of the day. Although far from infallible, he was right often enough to be useful. Indeed four years later, on hearing of FitzRoy’s death, the wife of an Aberdeen fisherman was heard to exclaim: ‘Who will look after our men now?’

Robert FitzRoy (1805–65) as a young man.

TheFirstofMany

At eight o’clock in the morning on 8 October 1860 the very first Irish ‘real time’ weather observation was transmitted from Valentia Island in Co. Kerry. Weather reports have been coming in a continuous stream from that part of the country ever since, albeit not from precisely the same spot.

The historic message was sent on the electric telegraph to FitzRoy in London for use in his newly organized system of storm warnings. The observation was performed by Mr R.J. Lecky, who at the time was manager of the telegraphic station on Valentia Island. Lecky continued with this valuable service on a daily basis for many years; he was made redundant only by the establishment of an official Observatory on the island on 15 June 1868.

The new Observatory was at first a very modest undertaking. It occupied a rented house on the narrow strait which separates Valentia Island from the rest of Kerry, and from there the routine flow of observations continued until March of 1892. It was in that year that Valentia Observatory moved across the sound to its present site on the mainland near the town of Cahirciveen, retaining for auldlangsyne its traditional name – the name by which, somewhat confusingly, it is still known.

Its new home was Westwood House, theretofore the residence of one Captain Needham, the local agent of Trinity College which was at that time a very prominent landowner in the locality. Westwood was purchased for the not inconsiderable sum of £1400, and in the succeeding years was decked out with the impressive array of scientific instruments which was in due course to make Valentia Observatory one of the most important meteorological and geophysical observatories in all of Western Europe.

Valentia Observatory is today one of the Irish weather-observing stations whose hourly reports of current weather conditions are circulated around the globe; it performs upper-air measurements, using a radiosonde attached to a hydrogen-filled balloon to obtain values of pressure, temperature and humidity many miles above the earth; it monitors variations in the earth’s magnetic field, and carries out precise measurements of radiation coming from the sun; the Observatory also operates a seismograph, which detects and records tiny vibrations which may have their origins thousands of miles away in earthquakes half-way around the world.

TheWindsatWar

Modern meteorology has as its metaphor the stalemate that arose in Western Europe after the Battle of the River Marne in 1914. For the next four years two huge armies, roughly balanced in size, found themselves arranged against each other in a zigzag line of trenches which stretched for 300 miles from the North Sea to Switzerland. During that time, despite minor incursions costing hundreds of thousands of lives apiece, the battle line swayed no more than ten miles to and fro along the entire length of the Western Front.

Meteorologists at the time were just developing the ‘air mass’ theory. They saw an analogy between the current military impasse and the sharp transition zone in mid-latitudes which separates the cold polar easterlies from the temperate westerlies further south. They called this meteorological boundary the polarfront; it is the transitory movements of this front which bring to us the familiar sequences of our changeable Irish weather.

A weather front, by definition, is simply a boundary between two masses of air of contrasting temperature and humidity. As one would expect, bearing in mind the global temperature distribution, the ‘normal’ orientation of a front is roughly east-west, separating cold northern air from warmer air to the south. Consistent with this ideal, the polar front in this part of the world generally stretches from south-west to north-east across the Atlantic. Its average position varies somewhat with the seasons. In winter it normally runs from the West Indies to Portugal, while in summer it is much farther north, stretching from the Great Lakes towards the north of Scotland.

For very complex reasons, areas of low pressure called ‘depressions’ form on the polar front. As depressions develop, they cause a wedge of warm air to project into the colder air to the north – the familiar ‘warm sector’ of the weather-map, and analogous in the military context to a transitory incursion into enemy territory by one of the two opposing armies.

On our daily weather-map a series of depressions can often be seen strung out at regular intervals along the continuous, undulating length of the polar front. The weather sequence seems like an endless succession of individual rain-belts, but it is in fact usually the same front which returns time after time to bestow upon us its unwelcome attention, each episode being a battle won or lost in the perennial war of the elements.

IITheElementsExplained

TheDividingLines

As a front moves along the landscape, it brings an area which has been under the influence of one kind of air into a new regime with quite different characteristics. In general, the air on one side of a front is warm and humid, and that on the other side cooler and relatively dry. The boundary between the two is surprisingly well-defined, and as the two air masses sweep along the sudden change in temperature and humidity is very obvious from instrumental records as the front passes a particular spot. If the passage of a front results in the existing air mass being replaced by a warmer one, the front in question is a warm front; if the temperature afterwards is lower than before, then a cold front has passed.

The barbs drawn on a front indicate what kind of front it is. A warm front is identified by semicircular barbs; a cold front by triangular ones, and the barbs point in the direction towards which the front is expected to move. If the weather-map is in colour, each front can be even more clearly distinguished, since warm fronts are red, and cold fronts blue.

If you look closely at a weather-chart, you may notice that what is designated a warm front for part of its length, is a cold front for the remainder. This is not an attempt by the weatherperson to confuse you; it means that the wind pattern is such that the front moves in one direction on one part of the chart, and in the opposite direction elsewhere. And almost by definition, that which is a warm front moving east, will be a cold front if it moves west.

A typical North Atlantic weather-chart, showing a depression to the west, an occluded front over the north of Ireland, and a warm sector over France. (Weather, 42, 1987)

OddNumbers

Every hour, precisely on the hour, weather observers at many hundreds of meteorological stations around the world takes careful note of the prevailing weather conditions. They use instruments to measure some of the more important weather elements, and then compile all the available information into a special coded message. The completed report is fed into a dedicated world-wide telecommunications network to form the raw material for tomorrow’s forecast. It might look something like this:

Now, looking at this jumble of numbers, one might be reminded of the young Pip in Dickens’s GreatExpectations, who nightly ‘fell among those artful thieves, the nine figures, who seemed every evening to do something new to disguise themselves and baffle recognition’. But these numbers allow forecasters a great distance away to build up a precise picture of the weather they describe.

The first six-figure group is the time and date – in this case 1200 on the twenty-second. In the second set of numbers, ‘03’ tells us that the weather station is in Ireland, and ‘953’ is the identifying number assigned to Valentia Observatory in Co. Kerry. All the other figures give precise information about different aspects of the weather – the visibility, the type and amount of cloud and the height of the various layers above the ground, the temperature and humidity, the speed and direction of the wind – and so on. If you know the code, and it is not difficult to learn, all this information is at your fingertips.

Why do meteorologists choose this apparently complex way of doing things? Why not write the message in plain English, and circulate it in a much more readable form?

The use of a numerical code has a number of advantages. The first is that it is international: a meteorologist anywhere in the world can read the report and know immediately where it came from and what it means, even if he or she has not a word of English. The code is also very concise: the message in figures is much shorter than its verbal equivalent, and can be handled more easily and more economically by computer than if it was written in words. And finally it is precise: each of the code-figures is defined exactly, avoiding the ambiguity which might arise from using common words with differing shades of meaning.

TheWorldinaCircle

William Blake’s ambition to ‘see a world in a grain of sand’ requires the kind of apocalyptic imagination which is possessed by very few. But any forecaster can deduce the weather over the whole of Europe from a jumble of figures and dots. This feat implies no transcendental vision on his or her part; it is a happy consequence of the concise and orderly presentation of information.