Anticyclone

“ On the 24th the system covered the North Sea, England, and the north-western half of France. For a day or two more the anticyclone grew higher, temperature became very low over - 101 - the inland counties as the anticyclone increased, so that early on the 24th minima were recorded as low as 27°. The centre of the system now moved westward, and the temperature rose decidedly. On the 25th the anticyclone moved to the westward of Ireland, and had afterwards decreased in intensity. The winds during its prevalence were light to moderate at most of the coast stations, calm inland ”

“ In anticyclones a slow gyratory descending motion of the air is assumed. Ferrel considers the cyclone and anticyclone one system, and believes that air flowing into the cyclone from a "high" at the ground passes out into the higher atmospheric strata. ”

“ The tropical belt of high pressure persists all the year round, but the immense demand for air to supply the ascending currents over the heated land surfaces in summer causes the normal descending movement to be largely reinforced; hence the “North Atlantic anticyclone” is much larger, and its circulation more vigorous, in summer than in winter. Again, during the winter months pressure is relatively high over North America, Western Eurasia and the Arctic regions; hence vast quantities of air are brought down to the surface, and circulation must be kept up by ascending currents over the ocean. ”

“ On the map there will probably appear also an area of high pressure where the surface air flows leisurely outward and away from the place of highest pressure. Such an area is called an anticyclone, a word first used by Sir Francis Galton in 1863 to designate not only high pressure, but general flow of the air in a reversed or opposite direction to that of the low area or cyclone. ”

“ Anyone who is interested in the weather is always on the lookout for 'lows' and is very keen to know whether he is going to be on the south of the centre or the north of it. He is, of course, interested in the anticyclone too, because as long as an anticyclone is there, there cannot be a depression; but it is the depression which has the life and movement about it, giving it a claim to the attention of everybody who wants to know what the weather and its changes are going to be. ”

“ There is a distinct gyratory movement in large disks of air, clockwise, outward from the center, and to a slight extent descending, in the anticyclone, while it is counter-clockwise, inward toward the center, and to some degree ascending in the cyclone. The sharp fall in temperature forming the cold wave is caused primarily by the horizontal transportation of huge masses of cold air from the cold continental interior, and is heightened by the increased radiation from the ground through clear, dry air thus brought in. ”

“ A few of the storm hunters thought that some upper air movement—a “steering current”—controlled the hurricane’s path. The most obvious influence of this kind is the general air circulation over the Atlantic—the large anticyclone nearly always centered over the ocean near the Azores but often extending westward to Bermuda or even to the American mainland.
In the central regions of the Atlantic High, the modern sailor, unlike his predecessor in the sailing ship, is delighted by calms or gentle breezes and fair weather. ”

“ The circumstance that 'Föhn' winds blow from the west doubtless partly accounts for their relatively high temperature; but there are other reasons, notably the comparatively high barometric pressure experienced with south-west winds, which indicate a local anticyclone in winter such as would form over a land surface. ”

“ The south-east circulation about this anticyclone increases in force with the increasing barometric grade, and also by the wind circulation about the cyclone, and the effect of the two causes acting together is to produce a most serious gale. Rarely, these storms originate in a monsoonal depression somewhere over South Australia, which travelling eastward intensifies on the east coast. Heavy rain is a marked feature of these storms, but it is confined to the coast, and rarely if ever extends inland. ”

“ V-shaped Depression, in meteorology, a narrow area of low pressure usually occurring between two adjacent anticyclones, and taking the form of a V or tongue, as do the isobars representing it on a weather-chart. Such a depression may be regarded as a projection from a cyclonic system lying to one side of the two anticyclones. A similar depression, however, is frequently formed within a larger area of depression, i.e. an ordinary cyclone, and sometimes develops so far as to have a complete circulation of its own ”

“ A depression can make little headway if to the north or east the normal path is blocked by what is known as a stagnant "HIGH." So therefore, if the anticyclone is a slow mover, a Texas storm, which would normally pass not far from southern New England, may be deflected farther north than when the HIGH moved rapidly east. ”

“ Its cause is found in an extensive col, the rear of one anticyclone being at rest over this coast, while another lies over the Australian Bight. If the grade is rather steep and the system at rest for several days, then the north-east wind persists with force proportionated to the grade, until the whole system moves forward; the southerly winds in the front of the approaching high pressure then displace the north-easter and the storm is over. ”

“ While it is true that the air aloft is colder than that at the ground, and that up to a height of about six miles there is a more or less uniform decrease of temperature with increase of height, cold waves owe their origin to a number of factors. Nearly all cold waves of the United States occur in the area forming the rear of a passing cyclone and the front of an approaching anticyclone. During the winter half-year this region is characterized by relatively strong northerly or northwesterly winds, clearing skies, decreasing humidity, and the conspicuous fall in temperature. ”

“ When it is remembered that the winds circulate outward from the high pressure center of an anticyclone spirally, from left to right, clockwise, while the winds move into the low pressure of a cyclone spirally, from right to left, counter clockwise, some idea of the simplicity of weather causation is gained. ”

“ In winter they may bring to us the continental cold, and make our weather abnormally severe, though often bright and fine. On the other hand, in summer they bring to us continental warmth, so that “good” summers are those in which anticyclonic conditions are most frequent, while “severe” winters are due to the same cause. Anticyclones also sometimes induce a curious form of inversion, in that places to the north of a given spot may have temporarily a higher temperature than places to the south. ”

“ Of these local observations, the pressure readings are by far the most important. A falling barometer usually means the approach of a cyclone, with wind, or storm, or both. A rising111 barometer, on the other hand, is usually an indication of the fine weather associated with an anticyclone. The unsymmetrical distribution of weather, characteristic of our cyclones in the United States, and also of most cyclones in the Temperate Zone, is associated with their unsymmetrical form, and the unsymmetrical distribution of their temperature already studied. ”

“ The lows are called cyclones, because of the inward direction of their winds; and the highs are known as anticyclones, because the winds resulting from them flow outward.
The highs are caused by descending currents from the upper air due to increased density which results from cooling by radiation of heat from the upper air. The lows are caused by the air absorbing heat from large areas of the earth's surface where the sun has acted strongly. The heated air ascends and flows outward at the upper levels, reducing the barometric pressure. If the air is moist. ”

“ In Russia the name buran or purga is given to the cold wave when it blows along76 with it the fine dry snow from the surface of the ground. This buran is apt to cause the loss of many lives, both of men and cattle. In the Argentine Republic the coolest wind is from the southwest. It is known as a pampero, from the Spanish pampa, a plain.
Cyclones and Anticyclones.—A system of winds blowing towards a common center (such as is well shown over the Gulf States on the weather map for the second day, and over the middle Atlantic coast on the third day) is called by meteorologists a cyclone. ”

“ The continuous procession of cyclones and anticyclones across the United States involves continuous shifts of wind. Over much of the earth’s surface, however, the regularity and constancy of the winds are the distinguishing feature of the climate. Over a considerable part of the belts blown over by the northeast and southeast trades, roughly between latitude 30° N. and S. and the equator, the winds keep very nearly the same direction and the same velocity day after day and month after month. Thus the trades are of great benefit to commerce. ”

“ The fact that our northeast storms come from the southwest, which was first noticed by Benjamin Franklin some years before he put the suggestion just quoted in writing, was one of the great contributions to meteorology made by Americans. Modern weather forecasting essentially depends upon the general eastward movement of cyclones and anticyclones, with their accompanying weather conditions.
The daily weather map shows us the actual condition of the weather all over the United States at 8 A.M., “Eastern Standard Time.” The positions of cyclones and of anticyclones ”

“ In studying the dissemination of germs of the disease by winds, it is well not to confine attention to surface winds. It ia now found that atmospheric circulation takes place largely through cyclones and anticyclones, by means of which the levels of the currents are changed. ”

“ Cyclones and anticyclones are found to have considerable influence on one another, retarding or accelerating one another’s advance, or changing one another’s normal path of progression. While this mutual interaction is clearly seen, and may be successfully predicted in many cases, many other cases arise in which, under apparently similar conditions, the result is very different from the anticipation. Such are some of the difficulties with which weather forecasters have to contend, and which prevent the attainment of greater accuracy in weather prediction. ”

“ As the weather changes, the affected patients increase with a rush.
He is of opinion that the supposed rapid spread of influenza on the establishment of anti-cyclonic conditions may be explained in this way. The air in the cyclonic vortex, drawn chiefly from the atmosphere over the ocean, is moist, and contains none of [Pg 110] the contagion; the air of the anti-cyclone, derived from the higher strata, and thus from distant cyclones, descending, blows gently over the land to the nearest cyclone, and, being drier, is more able to carry suspended particles with it. ”

“ For this reason, if after a period of rainy weather we have an anti-cyclone in the winter without severe frost, and an absence of bright sunny days, we can usually depend on a scent. Instead of the air rising, there is during an anti-cyclone, as we all know, a tendency towards a gentle down-flow of air or at all events a steady pressure, and this causes smoke, whether from a railway engine or a tobacco pipe, to hang in the air and scent to lie breast high. ”

“ If it moves along a line south of any given place, the locality is affected by its easterly and northeasterly to northerly and northwesterly winds, which make up the coldest and stormiest side of the cyclone. As the barometer at its center is always low, the cyclone is called a 'low area,' or 'low,' for short, and as such appears in Weather Bureau reports. Storm intensity in a cyclone is in due relation to the minima of its own barometric pressures and to the maxima of the anti-cyclone nearest it. ”

“ The ascension of air with a higher sensible temperature would not alone suffice to supply the tremendous power of the cyclone. The difference of temperature, even in extreme eases between lower and higher strata, is wholly insufficient to account for the enormous energy developed by our cyclones of hundreds of miles in diameter. We therefore require another source of power. Nor have we far to seek it. The sun's rays falling upon dry earth heat it, and thus raise the temperature of the air in contact with it. ”

“ Not only may a cyclonic storm swerve from its predicted track; it also may fail to produce the rain or the snow which, according to popular tradition, constitutes the storm. As a matter of fact, the rain and the snow are merely an incident in a cyclonic movement. The essential feature of cyclone mechanics is the updraught. Now, in its progress if the cyclone invades an area of very dry air, the updraught may not be cooled to the temperature of condensation; in such a case there will be no precipitation. All lows are not rain storms or snow storms in the ordinary meaning ”

“ The effect of each.—Hence it appears that in a storm the wind may shift from any one of three causes, and we are not entitled to call it a cyclone unless the wind shift more than 180°. If the change of direction be less than 90°, the shifting may be due to diurnal rotation alone; if it be less than 180°, the shifting may be, and is probably, due to (1) and (2) . The sailor has therefore no proof to show that he has been in a cyclone unless the wind during the storm changed its directions more than 180°. Cyclones, there is reason to believe, are often whirlwinds in a storm. ”