1940: Meteorology

The year 1940 witnessed continued rapid advances in the field of meteorology, stimulated as in other recent years by the progress of aviation, particularly commercial, and by the general urge for improved long range weather forecasts. While no radical departures have been recorded, refinements of theories and of instruments for observations have been made.

For the first time since the adoption of the millibar as a unit of measurement of air pressure, this unit made its appearance upon daily weather maps other than the series issued from the Washington office. Isobars are labeled in both millibars and inches, the latter eventually to be entirely discarded. The millibar is a very small unit but much more accurate than the inch and is defined as a pressure of 1,000 dynes per square centimeter. (A dyne is approximately equivalent to the weight of one milligram.) In fact, whereas the inch is an index of length, the millibar is a unit of pressure which is actually what is measured. A comparative scale on the weather map enables persons unacquainted with the millibar to interpret it in terms of the inch. Thus the former standard air pressure of 30 inches, long adopted as the dividing line between high and low pressures, is equivalent to 1,016 millibars. Isobars are drawn at intervals of 3 millibars.

Five-Day Forecasts.

With the cooperation of the Massachusetts Institute of Technology, the United States Weather Bureau began the issuance of five-day forecasts in place of its former weekly predictions. The forecast is still somewhat experimental but sufficiently dependable to warrant publication for use. It is based upon recent accumulated knowledge with respect to air flow and particularly upon the relationship between upper air behavior and that at surface levels.

This forecast differs from the seven-day predictions in that departures from the normal are emphasized rather than absolute conditions. Thus instead of stating what the specific temperature or amount of precipitation will be, the probable deviation from the normal for the region is described. For example, temperatures will be 'normal,' 'above normal,' or 'below normal'; rainfall will be 'light,' none at all, 'heavy,' or 'moderate.' Trends and other general characteristics of the weather to be expected are included, all based upon averages over a period of years, combined with current data and present knowledge of atmospherics. Studies of averages of both surface and upper air data are especially important as bases for these forecasts.

At present, the forecasts are released to the District Forecasters of the Weather Bureau, who in turn have the privilege of making them more specific for their respective districts and localities. They may even deviate from them if their knowledge of the local region warrants so doing. The men issuing the five-day forecast recognize their own limitations, with respect to predictions for certain types of regions such as the western mountain areas, and therefore are willing to allow some discretion to the District Forecaster. Likewise since no attempt is made to predict for minor daily variations, nor are refinements introduced for small areas, the District Forecaster is permitted to introduce modifications based upon his own experience in the region.

As a further aid to forecasting, not only for land areas but for the sea as well, the United States Coast Guard, in cooperation with the Weather Bureau, stationed two ships one-third and two-thirds of the distance between the Bermuda Islands and the Azores. These ships transmit regularly 6-hourly surface observations, two daily pilot balloon observations and one radiosonde report daily. Special observations are made at other times upon call from other ships or from aircraft. The surface report includes: wind direction and velocity, state of the weather, barometric pressure, visibility, temperature, clouds and height of ceiling. The pilot balloon reports consist of data on wind direction and velocity at different levels, while the radiosonde report involves pressures, temperatures and humidity of the upper air. While the stationing of these ships is due immediately to the reduction in number of ships at sea owing to the war, this service might be profitably continued after the war has terminated.

Automatic Weather Stations.

Additional observations over the earth's surface made at isolated points have long been a need, but to station observers in such centers has never been practicable. Upon the request of the Navy the U. S. Bureau of Standards has succeeded in designing an 'Automatic Weather Station' to be placed at these isolated spots, particularly islands, where they will need servicing not oftener than once in two or three months. (Such stations can, of course, be set up in other remote localities such as on mountain heights.) Using the radiosonde principle, the instrument will send out at six-hour intervals, observations on the force and direction of the wind, air temperature, atmospheric pressure, relative humidity and amount of rainfall. The signals sent out by this instrument can be received with reliability at distances upwards of 200 miles. Power is supplied by special storage batteries, in some cases charged by wind-driven generators.

The Mechanical Voice.

The year 1940 seems to have been especially marked by improvements in facilities for making observations and disseminating data and forecasts. So it is worthwhile to note the experience derived from the 'mechanical voice' first tried out in 1939. This voice answers telephone requests for the immediate weather forecast. The inquirer telephones a given number, and when connected, at once hears the forecast from a special type of recording. The forecast is issued regularly four times daily and occasionally a special forecast is introduced if a critical change seems imminent.

In the first experimental trials in New York City, over 4,000 inquiries were made in a single hour. Upwards of 80,000 calls have been recorded in a single day. These numbers stand out in contrast with slightly more than 500 calls in a day as the maximum which could be handled direct by the local Weather Bureau office. As this new service, now also available in Chicago, and Newark, New Jersey, is extended to other cities and many more thousands of persons are accommodated, the public no doubt will become increasingly willing to support appropriations for further meteorological research.

Research.

Still another contribution to the advancement of meteorology was marked by increased opportunities for research in two outstanding universities. One announced a new department and the other a new Institute of Meteorology. Both have sufficient finances to enable them to provide adequate equipment for advanced studies. Without doubt the United States now stands first among the nations in the number of institutions of various types which have both men and materials of the highest order available to assure progress in the field of meteorology. Inclusive of stations associated with these institutions, there are now some 34 regular aerological stations in this country — a world record. Note should also be made of the continued revolution in Weather Bureau practice. The shift is from the earlier more or less empirical and somewhat 'instinctive' bases for forecasting to a practice based upon the most advanced scientific procedures.

In a war-torn world one might assume that the warring nations would have little time to press the academic aspects of atmospherics. A particularly noteworthy exception is the U.S.S.R. Observations along its Arctic coast have been continued in the vigorous pursuit to establish safe sea routes. These observations include undersea, surface, and upper air data. Owing to the high latitudinal location of the observing posts, these data should lead in an important way to the uncovering of further information relative to the general circulation of the atmosphere and perhaps to more dependable weather forecasts.