WEATHER DATA

Greymouth Evening Star, 6 September 1934, Page 10

WEATHER DATA

THE NEW FORECASTING. . “The year has been remarkable for the number of times, the Tasman Sea has been successfully crossed by aeroplane. It seems certain that in quite a few years a regular transTasman service will .lie established. This will undoubtedly entail a ’m.'.tecrological service for aviation of .quite a different character from anything which can at present be provided,” remarks Dr. E. Kidson, Director of Meteorological. Services, in his report of the year’s working of the .Meteorological Office, which is ' incorporated in the annual report of the Department of Scientific and Industrial Research.

“On ying routes.” he goes on to say, “it is necessary to know the weather in far greater detail than is required for other purposes, and frequent rapid collection and dissemination ci information is an essential /feature. The number cf weather reports which can be got from the Tasman Sea, and their distribution, depends entirely on. the number and i location cf the ships crossing it. It [Can never be adequate, and' frequently lit is rcdit’ced' almost to zero. This is ione of tire itermanent drawbacks to weather toTecastiilg- in New Zealand. .Nevertheless, this, difficulty can be overcome to quite a large extent if sufficiently complete report's be available from Australia. For these to'he 'secured, the first essential is adequate facilities for communfcat’ion by wireless. The reports receiveci would be extremely vahrahle in connection' with the preparation of forecasts for genera! purposes as well as those for aviation. The need for increased wireless facilities has been referred to in previous reports. . Nearly all important meteorological’'. services now have stations'' of thear own, and it is difficult to see how ■ satisfactory . conditions can be. reached in New Zealand, except by. development on the same lines.’’

Discxxssiixg the new Norwegian methods of foiecasting. Dr. Kidson says that the essential idea in these is that the weathex* is due principally to the intel-action of “aix s '-masscs” of diffei'cnt characteristics, as regards temperature, humidity, and speed and direction of motion. Rainfall: is, for the most part, produced by the forcing of warm aix* to rise- in the atmosphere by ccldei* and, therefore, heaviex* air-masses. Warm aix* almost, invariably contains more watex* vapour than cold. The enforced rise in the atmosphere leads to the cooling of the warm air and to the condensation of some of its moisture in the form of rain. The forecastex* conse-q-uently tries to define the boundaries of tho different air-masses, to ascertain thcii’ characteristics, to estimate llicir future motion, the changes in tbeir properties will result irom this motion, and the fiction of one mass upon another. We have long known tlxat in the lo’w-pres.-'ure trough between two of the moving anticyclones which characterise the weathex* of this region, travelling with considerable regularity from west to oast, z theie is to the eastward of the lowest pressure a current of warm, moist air from tho north and to the

west cf it a cold current from a southerly direction. The line of .lowest pres'sure must generally, there-, I fore, separate two different air--1 musses. Such a line is called a

“front” and- since in this case the front is- moving, in the main, from west to east it must , characteristically be a. “cold front.” This would be in accordance with the sudden rise of pressure and fall 1 of. temperature, the squally change of wind direction from north-west to south-west, and the rain, which are the common features of tho. line of lowest pressure.

“A large proportion of our weather changes can be accounted for in this way, but clearly not all. A long front such as that mentioned has been shewn by the Norwegian school on both theoretical and observational ground’s to be unstable. Consequently,- instead of running in a straight cr gently and uniformly cujfved line, it tends to break into waves. Some of these waves become very strongly developed and form what have always teen recognised here as cyclones. But the difference between them and smaller waves, which were in many cases not recognised at all, is a matter of degree only. The smaller waves account for many of the irregularities' in wind, rain, etc., which occur in our normal westerly depression. The waves move rapidly along the main cold, front in a poleward direction. The cold air spreads out into the warm air on the northern side cf the wave, while in the middle,’ the. warm air forms a bay in the cold. On the southern side of this warm sector i's what is called the ‘warm front’ where the warm air is climbing up over the cold. Owing, however, to the almost constant eastward advance of. the low-pressure trough, carrying tho waves along with it, warm front phenomena are seldom easily recognisable in New Zealand. There is no doubt that the introduction of frontal methods will explain many phenomena in New Zealand weather which have hitherto been obscure.

NEW ZEALAND LN LUCK. “It is interesting to note that, the Norwegian methods were officially adopted for all work a yeax* ox* two ago in Great Britain and a recent Commission of inquiry in America recommended their gradual adoption by the United States Wcatlicr Bureau as officers were able to become expert, in frontal meteorology merely by reading published papers. In Norway tho method has been developed by a coterie of brilliant researchers and is continually being improved and expanded. In 1931, the writer was able to get a good preliminary appreciation of .the method in the course of a week’s visit to Bergen. Thereafter, gradual progress was being made in the application of the method to local conditions, which diffex* very considerably from those of Europe. Fortunately for t-his branch, however, an experienced Norwegian forecaster, in the person of Mi* Jorgen Ilolinboe, was attached to the Lincoln Ellsworth Antarctic Expedition. Mi* Holniboe lias spent a considerable time at the Meteorological Office, Wellington, partly before the departure of the expedition and partly since its return. While here, he lias, in such time as was available thrown himself enthusiastically into the study of local weather conditions, and, with the assistance of hie special knowledge, it has been possible to gain a much Clearer insight.into the methods used by his countrymen. Owing to New Zealand's isolation, this is not likely to lead to any revolutionary improvement in the weather forecast, but it Will add greatly to the interest and

understanding of weather processes. This is bound to produce a gradual increase of accuracy in forecasting, especially when it comes to the detailed work required for aviation purposes. For the method to be used successfully, however, we need, in addition to the Australian reports already mentioned, additional staff in cider that reports may be chartered as expeditiously as possible and the forecasting officer have time to consider the position fully and give proper attention to all of the various forecasts required. At present tho officer has to plot his reports hurriedly and without further consideration proceed immediately to the preparation of the various reports and forecasts. In no other service is the forecaster so pressed fox* time. In the greater majority of cases a forecast has to be issued without any information from west or New Zealand, which for our purpose, is the most important region.” The report adds that .the number of inquiries fox* climatological data, especially ixx connection with industrial concerns, continues to increase, as also does the amount of special forecasting for the farming community, aviators, trampers, and holidaymakers, carried out through the wireless broadcasting services. “To the voluntary co-operative observers who sacrifice their time on week-days, Sundays, and holidays throughout the year in order that a continuous record of our climate may be obtained, the country owes a. debt which it is somewhat slow to recognise,” concludes the report.