WEATHER "'FRONTS"

Evening Post, Volume CXXIII, Issue 136, 10 June 1937, Page 11

WEATHER "'FRONTS"

WHAT THEY SIGNIFY

NORWEGIAN FORECASTING

In meteorological publications and talks the word "front" is now of common occurrence, and in a lecture to the Philosophical Society on meteorology and aviation recently, Dr. M. A. F. Barnett, explained the significance of this term.

At first sight, he said, one might expect that the atmosphere would be well mixed and that there would be little likelihood of relatively sharp discontinuities between adjacent masses of air. 'The contrary was, however, often the case, and the boundaries between the differing air masses were spoken of as fronts. Actually the principal changes in the weather were associated with the development and. movement of fronts. Gcnorally there was an .abrupt change in the direction and force of the wind on either side of a front so that there was a sliding motion between the two, air masses. This sometimes gave rise to a form of instability which caused large waves to form. Further, the boundary plane between a warm and, a .cold air mass was not vertical, but sloped upwards at a gentle angle in the 'direction which ! made the warm air overlie the cold, and it was the elevation of the warm air as it slid upwards over the cold that produced the rain associated with fronts. . A number of lantern slides illustrating the weather sequences > which led up to the. great storm of February 2 last year were shown on the screen and made the lecturer's descriptions very clear. The credit of having introduced and elaborated what is generally spoken of as "frontal methods" in meteorology lay with the Norwegians, arid was associated with such names as Bjerknes, father and son, Solberg, Be'rjeron, Petterssen, and others, said Dr. Barnett. The Norwegians were still preeminent in the field of. forecasting technique, and remained the leaders in the rapid developments which were being made in this field. "At Bergen, in Norway, it is now a matter of regular routine for one of the meteorologists, after the morning map has been plotted, to deduce by actual calculation what changes should take place and to draw a map showing the distribution of fronts and isobars for the following morning. During the few-weeks I had the privilege of being in Bergen the'correspondence between the prognosis' and the map which was subsequently drawn from next morning's observations was most striking." The Bergen office had for many years' published 'daily weather maps for the European area, and recently they had introduced" the practice of showing on these maps, by means of- arrows and symbols, the changes which calculation led them to expect would occur during the subsequent 24' hours. Copies of these maps were received in Wellington, and it was very "impressive to see how accurately the day to day' changes were fortcast. "The Norwegian methods are followed to the best of our ability in the New Zealand Meteorological Office, but our ' isolation naturally makes it difficult to "keep' fully abreast of the latest-advances which are continually being made. This is particularly so because the rapid expansion required as a result of aviation, has created a demand for trained • meteorologists which is far in excess of the supply, and as a consequence the proportion of experienced and trained men in the New Zealand service, as in others, has become correspondingly' smaller. The training of new staff is, in fact, one of the principal- problems -; placqd on meteorological services as a result of the rapidity with- which, aviation has increased."- :-.-•■• ■-•••■•