BLUE SKIES AROUND THE CORNER BY c. A. WOOD

‘ Blue skies, smiling at me : Nothing but blue skies DO I see.’-Populur song

“ Blue are her eyes as summer skies,’’ said Joe. He frowned, and licked

I paused in the act of inserting a nasty little secondary depression on the

“ I n the words of the prophet‘corny,”’ I remarked. Joe was

“ What’s wrong with it ? ’) “ What’s right with it 1 How many blue summer skies have you seen-

in this country, I mean ? ) )

‘‘ Lots,” said Joe. “ Lots last year, anyway.” He rubbed his nose vigorously. ‘‘ Maybe I’ll make it rhyme with ‘ paradise ’ instead.”

“ Or polar-air skies. Now thpre’s a true simile for you : blue are her eyes as polar-air skies. . . ”

Joe wasn’t impressed. “ I don’t t hiiik she’d appreciate having her eyes likened to polar-air skies,’’ he said.

Elizabeth’s only reply was to hammer the keys of her typewr&er even more rapidly than before. ‘‘ Statistics are a curse,” she murmured, apropos of nothing. Joe sighed. ‘‘ I think you’re jealous,” he declared. “ Ever since you started turning out those blank verse monstrosities for the Christmaa numbers of Weather- ”

“I’ve paid for it-a thousand times. If you only knew what the readers said in their letters to the editor- ”

the pencil he had borrowed from my desk. “ Not bad for a start, eh ? ”

south side of the Icelandic Low.

indignant,

“ What do you think, Liz ? ”

“Don’t ! ’) I said, shuddering.

“ He does know,” said Elizabeth. I ‘ Traitor.” ‘‘ Let’s not argue,” said Joe.

“ I told him.”

‘‘ What about a rhyme for ‘ eyes ’ ? ’) Why not ‘ anticyclonic skies ’ ? ” I suggested. “ It depends, of course,

on the exact shade of the young lady’s optics, but if they’re of a pale, cobalt shade, then ‘ anticyclonic skies ’ would just fit the bill.” I took the Meteoro- logical Glossary from the bookshelf. “ The shades of blue in the sky have been classified by a chap called Linke, of the Meteorologische-Geophysikalische Inatitut, Frankfurt. He devised a scale that ranges from zero, which is white, to fourteen, which is the ultramarine blue of a polar air-mass sky. Now, if you got hold of a copy of Linke’s scale, you could match the exact shade : something, like ‘( Her eyes are heaven, Linke’s ‘ number seven ), for instance.”

“ What was the point of drawing up such a ucale ? ’) asked Joe.

As a matter of fact the colour of the sky is a measure of the amount of atmospherio pollution present. A lot of dust in the atmosphere gives you a hazy, pale blue. You get a lot of dust and smoke in the atmosphere with an anticyclme.”

Why 3 ”

The idea was received coldly. “ Linke wasn’t a poet, too, was he 1 ’)

“ Not to my knowledge.

“ Because of the inversion.” “ What’s an inversion ? ” I looked hard a t him. “ You wouldn’t be an Earnest Seeker After Know-

“Most decidedly not, old man,” ledge’, by any chance ? ” Joe shook his head.

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he said. “ My job’s accountancy, not metmrology, though-can’t expect me to krww what these lechnical terms of yours mean. As an honoured jest in this office, I think you ought to enlighten me : I’d like to hear tt bit more about anticyclones, if they bring blue skies and sunshine. So many of you meteoro- weather men take a fiendish delight in forecasting rain and gales ; now, if you could explain how to forecast j n e weather-well, it would be a pleasant change. ’ ’

“ Still,” I added, “ you’ve got something there. They show the succession of large ailticyclones which gave us our glorious weather in 1949.”

“ I’m afraid they don’t register,” he confessed. ‘I All these charts are pretty much the same to me.”

“ Maybe we’d better approach i t from another angle,” I said. “ Do you remember that article of mine in Weather some time ago, explaining how to plot ant1 draw up n synoptic weather chart ? ”

“ The G‘luss is Low Z “ You plot the QFF figures, which are the Mean Sea IAcvel pressures, on thc appropriate stations-”

“ On an ontliiie map of Britain, which you can obtain from H.M. Stationery Office, Imirlon, for a penny. Right ! Go on.”

“ Yoii then join np, with continuous lines, all stations that have the same pressure. They form more or less conceihic circles round the region of lowest pressure- ) )

What if you get a chart like this- ”,

I opened a drawer, pulled out a copy of M.O. Form 2216, antl scribbled quickly : with pressures so-let’s call it Fig. 1 , as they do in all good demonstrations.

Now whcre’s the centre of low pressure ? ” “ Ask him anothcr,’’ said Elizabeth, sotto voce. Joe said, “ Silence,

slave ! ” antl concentrated hard. After a couple of minutes, he began to join up the pressure figures I hat1 written on the chart. “There aren’t many isobars,” he said.

“ Fig. 2-Excellent ! Now, that’s a typical anticyclone you’ve drawn. Instead of the isobars encircling a centre of low pressure, as thcy (lo with a depression, we have them encircling a centre of high prcssure, which is an anticyclone. As you observed, the isobars are very wide apart : that’s typical of an anticyclonc. Meteorologists call it a slack pressure gradient, or a flat pressure field. You often find, when an anticyclone is centred over the British Isles in summer, it’s only possible to get two or three isobars on the small synoptic charts.”

I told him it was easier said than done. Draw up a chair and take a look at these charts.

Joe looked at them.

I pondered.

M’yes,” said Joe.

These lines are isobclrs, and they never cross.

‘( Ah, that’s where we pick up !

“

“ I suppose it’s all right ? ” I took the chart from him.

“ Meaning precisely what ‘1 ” said Joe. “ Meaning that there’s very little difference in pressure between, say,

north-west Scotland and south-east England. Since the pressure field is more or less uniform, the winds are light and variable, because they’ve no incentive to hLlrry .from high pressure to low. Light variable winds are a feature of the central region of a high-pressure system.”

“ The win& do go round an anticyclone in a definite direction, though, don’t they 1 ”

“ They do. They have a clockwise circulation about the centre : just the opposite of the winds in a depression, which, you may reca11, have an snti- clockwise circulation.”

(‘I see,” said Joe. “ I suppose anticyclones are lazy things, seeing they’re large chunks of high pressure with only light winds in them ? ”

5

Fig. 3. What an anticyclone might look like if i t I~eeame visible. Tho rtir sinks from high levels (subsidences) and spirals (lownwarrls mid outwar(ls, wtlrrning by corn- pression--adictbat,ic heating--nu i t does so. Note clockwise c,irc*ulution *:

D A Y N I G H T

Fig. 4. Two aspects of a winter anticyclone : the days are cold and mrlrky, and tho sky is overcast with grey stratocumulus cloud. The nights are foggy or frosty. [~e rh~]~ ; . i both, but the sky is nsually clear above the fog blanket

6

“ Generally very lazy. Sometimes, they’re almost stationary for a ~\ecB or more ; at other timcs, they drift slowly and sluggishly €ram west to east-”

“ Maybe they drift down over Britain from the Greenland ice-cap, or from Russia, or-well, they can drift almost any way. Still, quite a number of migratory anticyclones do move from west to east. If you take the P a i l y Weather Report, you can follow such ‘ Highs ’ across the Atlantic, and at times forecast a fine week-end-if you’re lucky ! They travel quite slowly: much more sedate than depressions, which nip across from all angles a t anything up to six hundred miles it day.”

Joe was looking a t another chart I had passed over. “They arc big, lumbering things. See how they bulge out in the most unexpected places-”

Elizabeth stopped typing. “ Really ! ” she began. “ Anticyclones,” said Joe, sweetly. “ Not nearly so streamlined as

depressions.” “ And these high-pressure systems give us our blue skies ? ’’

“ Some of them. In summer, they usually give us our heat-waves, and droughts : I’ve already mentioned 1949 as an example. Just as water flows round the outskirts of a hill, so rain-belts flow round the outskirts of an anticyclone. It’s only very occa- sionally that a venturous rain-belt manages to invade an anticyclone, and even when it does, it becomes relatively feeble and slow-moving, with the rain tending to die out.”

“ Only from west to east 1 ” “ No ! ” I said, promptly.

He turned to me again.

“ Some of them,” I said, carefully.

“ Why should it die out ‘2 ” I began to draw again. ‘‘ Well, here’s a sketch of what an anticyclone

might look like if you could see it. Notice the clockwise circulation, and the outflow of air a t the edges of the anticyclone. This outflow would, in time. drain the anticyclone of its air, and cause i t to collapse. Agreed ? ”

“ I suppose so,” said Joe. “ Because the anticyclone is kept up to its old strength by the slow

descent of air from the upper atmosphere. Don’t ask me where this air comes from : meteorologists all over the world would like to know. The fact remains that it does. Now, as this gradual sinking of air takes place, there’s a certain amount of compression. Compression of air makes it warmer, by a process called adiabatic heating-you can test this for yourself with a bicycle pump. The anticyclone, then, tends to warm up.’’

“ And so to dry up,” said Elizabeth, meaningly, busy rubbing a t a mistake on four carbon copies.

“ And so to dry out. This leads to a dispersal of cloud, since clouds depend on water-vapour for their formation. Comparative cloudlessness is yet another characteristic of many anticyclones. Such a situation, in summer, means a long spell of dry, fine weather, with blue skies.”

“ What about winter anticyclones T ”

You see, the warming of the air in an anticyclone by this compression business results in what is known as a temperature inversion.”

“ So you said before. You were going to explain what an inversion is.” ‘‘ And I will. Normally, you expect it to get colder as you ascend from

“ Why doesn’t it ? ”

“ You keep emphasizing the summer part of it,” said Joe.

“ I was afraid you’d ask that.

the surface of the earth, don’t you ? ”

8

JANUARY 1951 I To face p . 8 WEATHER

Photogrupfi by] [ A . Jarvis-Hickson.

Tho offect of glazed frost. A smzll troe borne clown t o the

photograph by]

PLATE 1

groulld by ice accretion

[ M . Hubbard

WILAT'H Ii.: R JANUARY 1961 To face p . 9 IZUK;8TTrICII BAT, TORKSHIRE

a. In fine weather

b. Summer anticyclone : Sea-fog drifting over the N.E. coast of Britain

Tho same view taken during the summer heat-wave of 1949, when holidaymakers on the beach shivei-ed in their thin clothing as the sea-fog rolled inland and blotted

out the sun Photographs by ]

PLATE 2

c. A. IFood

“ It does,” asserted Joe. ‘‘ I can remember wrapping myself in a blanket a t 12,000 f t over Bombay, with the temperature a t the ground simply sweltering.”

“ Horrible line,” said Elizabeth. “All right,” I interposed, hastily. “ That’s the normal state of affairs. In

a winter anticyclone, however, the temperature increases as you go up from the ground : the normal state of affairs is inverted.”

Joe looked incredulous. ‘‘ It’s true,” I declared. “ For the first couple of thousand feet or so,

a t any rate. After that, i t really does start to get colder as i t ought to-or, as meteorologists would put it, the normal lapse-rate sets in.”

“ Seems odd,” said ,Joe, “ but I’ll accept your word for it. What’s i t imply ? ) )

I reached for my pipe, and scraped the ashes out into the wastepaper- basket.

“ It implies lack of convection. You know that if the sun heats a mass of air near the ground, that air will start to rise. As it rises, it’ll cool off and the moisture in it will condense into a cumulus cloud.’)

“ I did convection at school,” said Joe. “ Everybody knows that hot air rises. What I don’t see is how i t can continue to rise, if it’s cooling off all the time, and the anticyclonic air all round it is made much warmer by com- pression--er-due to +is sinking from high levels.”

“ That’s the whole point : the rising air mass, with its cumulus cloud, soon finds itself running into a layer of air that is much warmer than itself. What happens ‘I This layer of warm air acts as a lid, and no further rising can take place. The cumulus cloud flattens out beneath the warm layer at about 2,OOOft, and with other similar clouds turns into a more or less con- tinuous sheet of grey stratocumulus cloud, which covers the sky in long parallel rolls. Under the cloud sheet, also trapped by the ‘ lid ’ of warm air, much smoke and dust, which would in normal times have been carried away by convection into the upper air, starts to collect. Thus you get the grimy, gloomy atmosphere of a winter anticyclone-it is particularly pronounced in industrial areas, where artiiicial lighting may be necessary even a t noon ; it’s often called ‘ high fog ’. Sometimes the sun peers through a chink in the stratocumulus cloud, and we get long ‘ ladders ’ of sunlight, or ‘ crepuscular rays ’, streaming down over the hazy landscape [Plate 11.” I rummaged in the desk.

Joe scrutinized the photograph, and nodded. “ They’re generally a fair-weather sign,” he said.

“ We’ll go on a little further. This continuous cloud-sheet keeps the feeble winter sunlight from the earth during the day, and at night, when the sun has gone down, the stratocumulus frequently disperses, leaving the earth exposed to a clear night sky. With light winds and a clear sky, the earth promptly starts to radiate out into spaco what bit of heat it has left, and the result is LL keen or hard night frost. This may go on for days and nights a t a stretch- and here’s another disagreeable feature of winter anticyclones : the smoke particles in the air form nuclei around which water-vapour condenses to give mist or fog. Frost fogs are common, especially in low-lying industrial arew where there’s plenty of smoke--in such areas the fogs are yellowish and very persistent. The fogs of the countryside are much whiter in appearance, and disperse more rapidly with SunriEe.”

“ Here’s a photograph to show you what I mean.”

“ Now I know why.”

“ Fvhat about spring and autumn anticyclones ? ’) asked Joe.

0

“ Similar to the winter ones: night frosts and fogs.

Elizabeth put the cover on her machine.

The fruit farmers

“ Don’t get him on that subject,” “ I once had a long lecture on frost-prevention machines

hate the spring ones, for the frosts endanger the blossoms.”

she advised Joe. simply because I made an incautious remark about Rickmansworth.”

I produced another photograph and passed it over to Joe. “ Everything depends on the position of the centre of the anticyclone.”

I said. “ For instance, if an anticyclone is centred to the north east of Scotland, the clockwise circulation will bring north-easterly winds down from Scandi- navia; if it’s centred over the North Sea, we shall get easterlies from the Continent or Russia, which are bitterly cold and dry in winter but warm or even hot in summer, since a t the latter season they are passing over a large

.hot land-mass. The photograph [Plate 2b] I’ve just handed to you shows what happens with an anticyclone centred to the south west of Britain : the winds come in from the tropical Atlantic, and are quite damp and mild : they give a lot of sea fog on coasts exposed to the wind. I can’t stress too much the importance of the position of the centre-it’s the great thing to look for when you see an anticyclone dominating the weather-chart.’’ I blew an accidental smoke ring, and watched it quivering on the still air. “ So maybe ‘anticyclonic skies’ wouldn’t be a good rhyme after all. Anyway, who is this person you’re writing verse about ‘1 ”

Joe got up quickly and made for the door. “ Oh, nobody in particu1a.r.

home ; perhaps that’ll tell me what I want to know.” she was putting on her hat.

deep in thought. “ Blue are her eyes,” I muttered. (‘ Now who- 1 ”

breathlessly. and her eyes were like Windermere under a sunny April sky. Jean will be here in a few minutes. You don’t mind, do you ? ”

Icelandic Low, and chuckled a most unmeteorological chuckle. have had a boring half hour, listening to my drivel about anticyclones.

Er-I think I have a rhyming dictionary at, g e glanced at Elizabeth ;

“ Can I give you a lift back to your digs, Liz ? ” The door closed behind them, and I was left

“ I forgot my gloves,” said Elizabeth Her face was flushed,

“ Oh-thanks !

I finished drawing the nasty little secondary on the south side of the Joe must

The Daily Weather Report of the Meteorological Office, London. Single copy 2d., or post free 3d. One calendar mcnth 7/-. One quarter IS/-. One year 70/-. Reaches sub- scribers outside the London area approximately 24 hours after the time of the latest chart reproduced. Obtainable from The Director, Air Ministry Meteorological Office, Kingsway, London, W.C.2. Author’s Note : The foregoing references to chart-plotting by amateur meteorologists were written before the much-lamented disappearance of Airmet. It is to be hoped that the near future will see a resumption of this excellent service.

“ Please,” said Elizabeth.

The door snapped open again. “ It’s a freezer outsidefoggy, too.”

Recommended :

Contains four weather charts and two pages of observations.

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