METEOROLOGICAL REPORTS.

Otago Witness, Issue 3102, 27 August 1913, Page 14

METEOROLOGICAL REPORTS.

Farmers are generally very sceptical about any weather reports which are issued by the Rev. Mr Bates, largely because they do not understand the terms employed or follow the significance of the statements made. In England the Intelligence Department is so complete that meteorologists can indicate with remarkable precision what the prevailing weather is - to be in any defined locality. The reports are found to be of great assistance in practical work, and the farmers lean on them when planning out their work. They enable losses, for instance, in haymaking to be avoided which would have taken place without them. The subject is taught in a number of the secondary and public school's, and the interest of the pupils is stimulated by the practice of recording the data procurable from the thermometer rain-guage, sunshine-re-corder, etc. Very few have any conception of the rules upon which weather forecasts are based, or appreciate the fact that the variations of the weather are regulated by laws as constant almost as day and night, or that the forecasts are prepared upon a strictly scientific basis and only require interpreting with knowledge to be wonderfully accurate in a general way. Regular reports are sent in from many centres in the Dominion; but there are not half enough of them, and it is not possible to get f.s many reports as desirable from a wide expanse of sea. In Europe the advantage is secured of reports from a much vyider area of country. The readings of the barometer and thermometer, the state of the wind and weather are registered and marked on an outline plan or chart. Lines are drawn 'connecting all positions in which the barometer stands at the same level. Thus high and low regions of pressure are defined, and the observations show the prevailing weather in the neighbourhood of these high pressure and low pressure regions. With this data recorded daily, the forecaster has to form an opinion of what the weather ‘ will be 24 hours later; or, in other words, what changes are likely to occur in the given conditions of barometer, wind, and weather. He knows already what lias led up to these conditions. Bad weather is usually associated with cyclones or areas of low pressure, while fine weather is characterised by anti-cyclones or areas of persistent high barometric pressure. The conditions prevailing in one are continually battling with these in the other. As these terms are not so familiar as they might be, it might be explained that a cyclone is a movement in the air resembling a whirlwind, and usually owes its

'ri'in to some local excess of heat. It mnv derive its start from a heavy rainfall. It requires heat to turn water into vapour, and as evaporation always produces cold, so the change back again from vapour into water sets free some of this heat. raising the tcmnerature of the air, of the rain itself, and of the land. Hie ascent of warm air keeps up an area of low pressure which forms the centre of a cyclone. The inrush of cool air which follows begins a circular or whirling motion which may continue and extend, till the space covered has a diameter of 100 miles or •more. The moist air in front of tkc cyclone gives up its moisture with the resulting fall of temperature (from the inrush of cool air) causing the rains which are. invariably experienced in front of such a movement. Such space, relieved of its moisture, forms in turn a new centre which causes a forward movement in the cyclone, assisted thereto by the rotation of the earth. The opposing systems which determine the weather are usually in motion. In this way the forecaster finds upon his chart a cyclone of a particular size and violence approaching the country. His information enables him to define its limits. His business is to determine in what direction it will move, and whether its progress will he fast or slow, and how it will affect local conditions in the different centres. The accompanying weather is usually sufficiently constant to enable a successful forecast in a general way to be made. In his remarks on the practical utility of weather forecasts, Dr Shaw states that “the fact is that the effective use of telegraphic forecasts requires practice, and it also requires co ordination with the prognostics, general or local, with which the user is familiar.

A well-informed correspondent in possession of the general inferences could probably give a local forecast which would be better applicable to the particular district than the general official forecast.” And again ‘‘it would be a matter of great interest to know the actual yield of farm produce each year estimated as a percentage of the maximum possible under the most favourable conditions of weather, and by how much a promising result is spoiled by bad weather. The ■destruction of lambs by heavy snowstorms, or fruit and potatoes by late frosts, the shortage of hay or roots for want of water, and the loss of crops by inclement harvest weather all put together would total up to a large percentage and a vast sum of money.” But the farmer who is accustomed to a loss of 30 per cent, to 40 ner cent, takes a philosophical view of the situation, and hardly troubles about a margin of 1 per cent, 'or 2 per cent. But “the difference might easily reach a figure which would convert a loss on the year into a profit, and whatever is gained by improving our knowledge of the weather is so much to the good, even though it be not the whole. So that there is certainly a golden opportunity for successful forecasts of weather.”