LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class TYPES OF AUSTRALIAN WEATHER. By HENRY A. HUNT, Second Meteorological Assistant, Sydney Observatory. [With Forty Diagrams.] TYPES OF AUSTRALIAN WEATHER. By HENRY A. HUNT, Second Meteorological Assistant, Sydney Observatory. [With Forty Diagrams.] IN continuation of the valuable work on Australian Meteorology which the Hon. Ralph Abercrouiby initiated several years since, by offering a money prize for the best essay on Southerly Bursters ; he has recently selected the phases of Australian Weather which are treated in the following twenty studies of " Types of Austra- lian Weather." Many of these appear to be peculiar to Australia, and at the same time connected with Equatorial and other weather. That they throw much new light upon the source of the greater part of Australian rain, and show how these rain storms develop out of ordinary weather conditions is certain ; at the same time they form an important contribution to the study of weather in the Southern Hemisphere generally. The work has been done by Mr. H. A. Hunt, at Mr. Abercromby's expense, and Mr. H. C. Russell, has edited the work. GENERAL REMARKS. As a general rule, weather is set fine when anticyclones move rapidly, and in a straight line across Australia, i.e., at a rate exceeding five hundred miles per day. And weather is unsettled when they move slowly, and not in a straight line, i.e., in a zigzag line, especially if they show no appreciable forward motion for a day or two. When anticyclones move in low latitudes the con- ditions favour dry weather, in high latitudes, wet weather, especially if they rest for a time south of South Australia. All the examples of weather phases which follow have been selected from the Sydney Weather Charts, and illustrate each type. The originals were carefully traced, and then reduced from 22" x 17" to the size used in this essay by means of the camera. Go Dec. 4, 1895. 228374 " "" * ** ** * "** "tfENRY A. HUNT. Ordinary symbols have been used, except the circle half filled for thunderstorms, and the straight line shading ; parallel lines indicate the area of rainfall under one inch, crossed shading over one inch. TYPE I. MOVING ANTICYCLONES. One of the best marked features of Australian weather is the steady easterly progression of all the types, and the governing type, that in fact about which all the other types seem to congre- gate, is the anticyclone ; it has therefore been placed first in the series, with three charts to show the progress made by a quick moving one in forty-eight hours. The average daily progress of anticyclones is four hundred miles per day, but the speed at times rises to one thousand miles. 1 Investigation so far leaves no room to doubt that in these lati- tudes a series of anticyclones surround the globe ; the latitude pf the average one varies with the season, being farther south in summer than in winter. The normal circulation about an anti- cyclone brings southerly winds in front of them, and northerly winds in the rear, hence our cold and our hot winds. Chart No. 1 shows the position, on 15th August, 1893, of the eastern half of an incoming anticyclone; it rests over Western Australia, while the departing one is seen over the Tasman Sea; between these is seen the usual \ depression, which is of average intensity, and a dormant tropical low pressure to the north. In Chart No. 2 the anticyclone has moved nearly nine hundred miles in the twenty-four hours, the centre being located near Fowler's Bay, north of the Australian Bight ; the antarctic \ depression is well across the Tasman Sea, while the tropical or monsoonal isobar depicted in the previous chart has apparently merged into the high pressure system, a curious and not unusual kink being formed to the north-east of it, following the contour of the Gulf of Carpentaria. On Chart No. 3 the anticyclone is shown to have moved a further seven hundred and fifty miles, or a total of l Eussell Quarterly Journal E. M. S., Vol. xix., No. 85. TYPES OF AUSTRALIAN WEATHEK. TYPES AUSTRALIAN WEATHER Moving Anticyclones /to 3 *&>-** 7 LOW TYPES OF AUSTRALIAN WEATHER N2 one thousand six hundred and fifty miles in forty-eight hours; the monsoonal dip is still noticeable south of the Gulf, while the antarctic \ depression has its centre to the east of New Zealand. HENEY A. HUNT. TYPES or AUSTRALIAN WEATHER N3 The passage of this anticyclone was an unusually rapid one, and is presented as portraying with a minimum number of charts the easterly motion of anticyclones over Australia. TYPE II. MONSOONAL RAIN STORM. This type is undoubtedly the chief rain agent in the Australian Continent. Monsoonal depressions or tongues may occur at any time of the year, but particularly between the months of September and April, and most frequently during January, February and March. The readings of barometers in the depression seldom fall very low, the grade from the surrounding areas to the centre of the tongue ranging from one to three-tenths of an inch generally; the depression may intensify, that is the tongues between high pressures may protrude further south anywhere during their passage across Australia, but show a preference to do so after they have crossed central Australia, a fact which suggests that the heated interior has at least some influence in their development. When and wherever the tongue is well denned, rain certainly follows in its track, and thunderstorms as a wide spread and simultaneous feature are never experienced without it. TYPES OF AUSTRALIAN WEATHER. On April 18th and 19th, 1894 (Chart Nos. 4 and 5) occurred one of the finest monsoonal rain storms on record, the area affected being very extensive, embracing the whole of the eastern colonies, Tasmania, and the greater part of South Australia. Many inches up to five and six of rain were recorded on the north-east coast of Queensland, and over the eastern half of the rain area the country benefitted to the extent of over two inches generally before the storm was over. TYPES UU AUSTRALIAN WEATHER Monsoonal Rain On this Chart No. 4 the monsoonal isobars, after passing the most southern part of the tongue, are shown sweeping round a high pressure of considerable energy, situated over the Great Bight. Following these isobars to the eastward, we find them recurving over another high pressure of greater energy in the Tasman Sea. On Chart No. 5, both anticyclones will be noticed to have worked northward, and while so doing they have lost some- what in pressure, and the low pressure tongue has extended further south and broadened ; at the tip, two cyclonic rain centres will be observed to have formed. The chart antecedent to 18th April presented the general characteristics of Chart No. 1, except that the antarctic \ depress- 6 HENRY A. HUNT. ion was a considerably less active feature, but on the other hand the monsoonal dip was somewhat more pronounced, and possessed two instead of one isobar. Following the 19th, the chart of 20th revealed no sign of the monsoonal tongue, and the continent was covered with a high pressure of very slight energy. TYPES AUSTRALIAN WEATHER ire. .5 TYPE III. DEVELOPMENT OF A CYCLONIC STORM IN LOW LATITUDES FROM A MONSOONAL DEPRESSION. In Type No. 3 we have the development of a cyclonic storm out of a monsoonal depression. The seasonal peculiarity of this phase of the tropical low pressure is similar to that in Type No. 2. The cyclone seems to develop when the southern extension of the monsoon is out of proportion to its width, and it becomes so narrow at one part of it that the opposing winds which circulate round it interfere, set up the cyclonic circulation, and it then progresses eastward as a rain storm. (See Charts 6 and 7.) These storms frequently develop in South-east Queensland, and they are generally most severe there ; the quantity of rain which sometimes comes with them is very remarkable, as in the case of the phenomenal flood in Brisbane in 1893, which was the result of one of these storms. TYPES OF AUSTRALIAN WEATHER. 7 The example selected and shown in Charts 6 and 7 took place on September 28th and 29th, 1892; on the 28th (Chart 6), it appears that one of these storms had developed in the previous twenty-four hours, at the southern end of a narrow tropical or monsoonal tongue of low pressure. An anticyclone of good energy lies to the east of it, with its isobars extending well to the north and contracting the width of the tongue in the north ; another anticyclone lies to the west, and this also seems to be pressing on the narrow monsoonal tongue and helping to contract its diameter, at the same time the energy in both high pressures is adding force to the circulation of the wind, and so aiding in the development of the cyclonic circulation. A modified \ depression exists to the south-east of the Australian Bight, and there is another over New Zealand. TYPES AUSTRALIAN WEATHER N6 Cyclone from Monsoonal depression 6&7 ^ O On September 29th, (Chart 7), the small cyclone has extended its area and energy on its way to the coast, but its motion of rotation has been rapid, and this probably accounts in a measure for the comparatively small area over which rain has fallen, although, in this instance, over an inch of rain fell in the central 8 HENRY A. BUNT. and eastern parts of New South Wales. The winds circulating about the western isobars of this storm are rather stronger than usual in such cases. In the twenty-four hours both anticyclones have lost a considerable portion of their energy, while that of the depression in New Zealand is about the same as on the previous day. TYPE IV. DEVELOPMENT OF A CYCLONIC STORM IN HIGH LATITUDES FROM A MONSOONAL DEPRESSION. These are somewhat similar to Type 3, but. the rainfall is usually not so heavy, and the wind much more violent. Chart No. 8 shows the development of one of these cyclones on April 15th, 1889; in this case the monsoonal depression had extended across Australia into the Australian Bight. The development of one of these storms is heralded by the strong easterly gales on the south-east coast of South Australia and south coast of Victoria. The energy of wind circulation increases over South Australia, and as the whole system moves bodily east- ward from the Australian Bight to the mainland, the circulation is seen to be that of a fully developed cyclone of small area, with a TYPES OF AUSTRALIAN WEATHER. diameter three to five hundred miles, formed out of the southern part of the extensive monsoonal depression. In Chart 8 a high pressure is shown over the south-western part of Australia, and evidently encroaching on the moonsoonal about central Australia. TYPES AUSTRALIAN WEATHER N8 HIGH Cyclone in high laiititdes from 4 * 5 Monsoonal depression 8loIO TYPES AUSTRALIAN WEATHER ue APRJJ- 18. tea. 10 HENRY A. HUNT. In Chart 9, the western anticyclone has extended northwards and has seriously contracted the diameter of the monsoonal low pressure, thereby facilitating or helping to cut off and start the cyclonic storm in the south ; which has now developed a much steeper barometric grade and an energetic wind circulation, and is moving eastward without extending the rain area. Chart No. 10 shows comparatively little motion in the cyclone, but it is considerably distorted, especially to the west, where the anticyclone is compressing the isobars by its easterly progress and in its endeavours to maintain its rate has overridden the cyclone in the north. As will be seen by a glance at these three charts, the rain resulting from this storm was most extensive and bene- ficial, and the winds under its influences were strong. TYPES or AUSTRALIAN WEATHER NIO 17... ia TYPE V. CONDITIONS FAVORABLE FOR THUNDERSTORMS. Upon comparison of charts setting forth this type with those of cyclonic thunderstorms, they will be found very similar ; the main difference being the absence in this set of the cyclonic area at the end of the monsoonal tongue. The chief feature indicating TYPES OF AUSTRALIAN WEATHER. 11 thunderstorms is the narrowness of the col 1 and somewhat con- gested state of isobars in the high pressures west and east of it, resulting in opposing winds. Those of the tropical tongues are hot and charged with moisture, while those of the \ depressions are strong and dry. This type is met with during the monsoonal season. The rains resulting from this feature are not generally heavy, and though thunderstorms may be experienced over exten- sive areas of Queensland, New South Wales, and Northern Territory, a number of them may occur without any rain falling. Chart No. 11, January 17th, 1893, shows an extended and narrow tongue lying between two relatively high pressures, a \ depression similarly situated also exists in the south, this col or area of low pressure separating these two depressions is very small, and opposing currents of wind are noted there as blowing within close limits. Thunderstorms were occurring or had occurred in Northern Territory generally, over a great part of Queensland and in central parts of New South Wales, the rains upon this occasion, as is often the case, were not heavy, though they fell over an extensive and generally unfavoured area. TYPES AUSTRALIAN WEATHER N H & 5 Conditions for thunderstorms //& 12 1 For explanation of this term see p. 18. 12 HENEY A. HUNT. On Chart No. 12, the following day, though a few storms were recorded, shows a great diminution in number. The col has widened and the monsoonal tongue has lost to some extent its thundery characteristics, having widened at the end. The accompanying barometric systems show no motion since the previous day, but the high pressures have intensified. TYPES AUSTRALIAN V7EATHEB NI2 TYPE VI. CYCLONIC THUNDERSTORMS. This also, like the preceding one, is allied to the tropical low pressures, but in this case a denned cyclonic circulation develops in the lower extension of the tongue without the usual intensifi- cation of grades. From this source the thunderstorms radiate in easterly and southerly directions, and at times, as in the instance presented, a vast area is affected. Chart No. 13, December 12th, 1893. As on the previous set the monsoonal tongue lies over much the same country, though with its axis more east and west; the high pressure to the west is very small, and the systems are somewhat fragmentary. TYPES OF AUSTRALIAN WEATHER. 13 TYPES AUSTRALIAN WEATHER N 13 DECEMBER l&ian LOW Cyclonic thunderstorms I3&.I4 TYPES OF AUSTRALIAN WEATHER On the following day, Chart No. 14, a cyclonic circulation has formed in the end of the tongue, while the \ depression over Sydney on the 12th has moved eastward and nearly filled up, and the high pressures have followed and intensified. The thunder- 14 HENRY A. HUNT. storms and rains were not so general as on the thunderstorm type, but curiously, were recorded in an almost parallel area of country, nearly three hundred miles wide by twelve hundred long. Though great barometric changes have taken place, the pressures remain about the same as on Chart No. 13. TYPE VII. A RAIN STOEM WITH VERTICAL AND NEARLY STRAIGHT ISOBARS. This type is one of the best denned and reliable of the series for forecasting purposes, because with them, good general rains almost invariably come. They are the rear isobars of a departing anticyclone, and the wind circulation from north and north-east brings into the interior winds laden with tropical moisture to meet in the west southerly winds laden with antarctic cold, and therefore precipitating power. The sequence of rain is rendered even more certain if rain be recorded in the north-east before the isobars straighten, or in the \ depression to the south. The actual height of the barometers is not material, but the greater the number of isobars in a given area, the more extensive will be the rainfall ; the rain usually lasts three days. The rain begins to fall north-west of New South Wales, spreads southwards, then eastward, and finally northwards, crossing the mountains near the Queensland boundary. A fine example of this type occurred on 15th, 16th, and 17th October, 1894. (Charts 16, 17.) On the 15th, Chart 16, a departing anticyclone rests over Tasman Sea, and its rear isobars are shown running north and south over central Australia ; another anticyclone is shown over Western Australia and a \ depression east of the Australian Bight ; a trough of low pressure rests over Central Australia from north to south. On this day the only indications of the pending rain were found in the cloudy skies generally over South Australia, western parts of New South Wales and Queensland, and a small area of rain in South Australia. In Chart 16, the straight isobars of Chart 15 have entirely disappeared, but the rain has come over Central and South TYPES OF AUSTBALIAN WEATHER . 15 TYPES or AUSTRALIAN WEATHER Ni5 OCTOBER 13. * Australia. Excepting the Gulf country and its central area, all Queensland, all New South Wales, Victoria and Tasmania had rain. (See shading on Chart 16). For other instances of straight isobars see Charts 5, 27, and 28. TYPES AUSTRALIAN WEATHER Ni6 IS, e* * S rf 90 HIGH ;' 16 HENEY A. HUNT. TYPE VIII. CYCLONES FROM NORTH-WEST. Prom time to time fully developed cyclonic storms appear on the north-west and west coasts of Australia, and in the Australian Bight, but the absence of observing stations in the unoccupied country which lies between the overland telegraph line and the west coast of Australia, makes it impossible to trace them over that part of the continent, but cyclones are well known on the northern coast of Western Australia, and their formation in the tropics equally well known. There can therefore be no doubt that when we find a cyclone on the western coast of Australia or in the Australian Bight, that it is one which has come from the north-west, and is in fact recurving to the east and south-east as they do on the east coast. The one selected for Type 8 was picked up on the west coast of Australia in Latitude 28 on July 4th, 1892, (See Chart No. 17). The winds were light, but the rain heavy along the coast; an inert anticyclone rested over South Australia, Victoria, and New South Wales, where it was moving to the east and making room for the approaching storm. Cyclones from North West J7fot9 TYPES OP AUSTRALIAN WEATHER NI7 f . ...... ieoa TYPES OP AUSTRALIAN WEATHER. 17 Chart 18, July 5th, shows that the whole system has moved rapidly, that the cyclone now with an elongated centre lying north-west to south-east now rests over South Australia, strong winds are rapidly developing, and the barometric grade about the TYPES AUSTRALIAN WEATHER I8 HH Dec. 4,, 1895. 18 HENRY A. HUNT. centre is much steeper, and rain has fallen over the south coast generally and extended northwards almost to Central Australia. On July 6th at 9 a.m. the weather chart presented the features shown in Chart 19. The cyclone has intensified all round, and has moved rapidly to the east, its centre is just entering Bass' Straits ; very heavy gales from south-west are blowing in the rear of the centre ; heavy rain is falling over Victoria and extends over the greater part of New South Wales. All the winds controlled by this storm were very heavy, and during the 6th July, as the storm passed through Bass' Straits, extremely heavy weather was experienced there. On July 7th it had filled up. TYPE IX. TORNADOES. These occur during the summer months, and are most frequent in the western plains ; they are developed in hot weather and in the low pressure known as a " Col " between two high pressures, when there is not enough grade to control the winds and the heat- ing power of the sun is great ; if to these there is added the pre- sence of moisture from recent showers, we have all the conditions for the formation of a tornado. The force of wind is often suf- ficient to break off growing trees, two and even three feet in diameter, and the reason there is so little damage to life and property is not the want of power, but the sparse population and the very small number of towns. Chart 20, March 20th, 1894. An extensive anticyclone lies south of Australia, giving way in its central parts to an extensive monsoonal dip. The isobars are generally uniform and of even gradients, though a suspicious interval exists to the west of New South Wales between the 30-0 and 29-9 curves. This is un- doubtedly the area in which the secondary developed. Light rains were recorded in New South Wales and Victoria, but in Central Australia temperatures were high. Chart 21, March 21st. A marvellous change has taken place. The area of high pressure on the previous day over the Tasman Sea has lost two-tenths in pressure. The monsoonal dip so pro- TYPES OF AUSTRALIAN WEATHER. 19 TYPES OF AUSTRALIAN WEATHER N20 .. MARGJt SSSt*+ Tornado ~ '/ 20 & 21 '' < .(BRA!