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Fruit-Spray and Harvest-Weather Forecast Work of the Weather Bureau
in New York State
By E. B. Calvert

Scab, a fungus disease, is a serious menace to the apple growing industry in New York State. It remains dormant so long as the weather is dry. The spores come into activity when moistened, and, unless killed by spraying, a tree may become infected within less than 24 hours. The problem is to apply spray containing poison ingredients just before rain or a prolonged period of misty weather begins, because it is necessary that the poisons be present when the spores start to grow.

The fruit-spray forecast service was begun in 1919 and was brought about by the need for more definite and specialized information as to the coming of rains than was obtainable and interpretable from the regular daily forecasts issued by the Weather Bureau. This service extends from April to the latter part of June. The forecasts are issued at night from the Weather Bureau office at Ithaca, N. Y. They are telegraphed or telephoned to key men or field leaders in the principal apple growing counties. If they indicate rain, advices to spray are at once issued by the field men to all orchardists in their districts.

The harvest-weather forecast service was begun in 1921 and extends from the latter part of June through the month of August. As in the fruit-frost service, these forecasts are distributed through field agents, but the area covered is considerably larger, embracing most of the agricultural portions of the State. The forecasts are for the guidance of farmers in harvesting hay, oats, wheat, and other crops liable to damage if unfavorable weather occurs between the time of cutting and shocking. They are distributed both by telephone and by radio-in the first three years, from Syracuse, N. Y., but during the past year from Ithaca, N. Y. A feature of the forecasts which has made a special appeal is an expression indicating the degree of confidence of the forecaster, and the weight that should be given. For example, "strongly indicated" means 90 to 100 per cent probability; "indicated," 70 to 80 per cent; and "unsettled or probable," 50 to 60 per cent.

In both of these services a special message is sent to Ithaca containing the views of the Washington forecaster, the only difference being that the fruit-spray forecasts are based on the evening weather charts and the harvest-weather forecasts on the morning charts. Thus, the advices finally issued represent the combined judgment of the Washington and Ithaca forecasters.

At the end of the 1924 harvest season a questionnaire was circulated, requesting a statement as to the value of the special service.

With few exceptions, the replies indicated general satisfaction and a desire for its continuance.-W. R. G.

Discussion MR. L. M. TARR inquired if the use of fungicide spray or dust makes any difference, so far as the weather element is concerned. Dr. C. R. Crosby of the New York State College of Agriculture, Ithaca, N. Y., replied that there is no difference in the two, except as to the method of applying.

MR. E. S. CLOWES wished to emphasize the importance of having these forecasts expressed in popular language. He was stationed at the Syracuse office during the inauguration of the harvest-weather service and he recalled that it was not uncommon to hear people say that they "liked Mr. Sanford's (Weather Bureau forecaster at Syracuse) forecasts better than those in the newspapers" (also issued by the Weather Bureau!)

Other praiseworthy features, according to his view, are the promptness of distribution, the longer period covered and the statement as to probability of verification.

MR. J. S. HAZEN remarked that distribution of forecasts by radio is the only quick and efficient means in his section, northern New York, or for that matter in any sparsely settled region. He has been giving also once a week a little story of the weather and this service seems to have made a very large appeal.

PROF. W. I. MILHAM wondered why radio broadcasts at about noon are in some sections based on the weather maps of the preceding evening. Mr. Calvert replied that expense at present prohibits any other arrangement. All synopses of weather, except for special service, are broadcast from Arlington and then distributed through press associations. Efforts are being made, however, to arrange for broadcasts in all cases from the most recent weather maps.

Changes in the Potential Gradient During Thunderstorms
By J. C. Jensen

Out of a total of 316 observations in eight thunderstorms during the summer of 1924, 256 showed a reduction in the negative potential gradient below a cloud whose lower pole was negatively charged, while 60 showed a change of the opposite sign. When a thunderstorm is directly overhead, the nearby discharges are practically all such as to indicate a negative charge on the lower side of the cloud, while approaching or receding storms cause instrument deflections in either direction according to whether the discharge is from the upper pole to the ionized layer above or to an adjoining cloud, or from the lower pole to earth. These results are in general agreement with those of previous observers, but add to our knowledge of conditions directly below cumulo-nimbus clouds while rain is falling.—(Author's Abstract).

Discussion-J. S. MAUCHLY warmly commended the speaker on his work and hoped it would be continued. He commented on the interesting and puzzling fact that the earth continues to be negatively charged' although it is constantly receiving a large amount of positive electricity. He thought that perhaps a large number of observations would show much negative electricity coming down during thunderstorms.

PROF. W. I. MILHAM pointed out that negative electrons are always coming in from the penetrating radiation.

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Meteorology of Eclipses

By H. H. Clayton

(To be published in the Monthly Weather Review).

On the Mechanism of Fluid Rotation in the Atmosphere

By Lloyd D. Vaughan

The path of motion described by a system of particles of a fluid in changing from one configuration to another is always of such nature that all stresses or other restraining actions within the fluid which tend to act as a resistance to its motion are relieved or minimized wherever possible by a change in the direction of motion of the particles.

When two portions of a fluid, such as two currents of air, are in dynamical opposition to each other, the resulting type of flow is of such character that the internal stresses are equally distributed throughout the fluid surrounding the point or surface at which the opposing forces originate, and when these stresses exceed a certain value where the restraining action causes work to be done at the expense of the potential and kinetic energies of the system, then there is a change in the type or direction of motion of the fluid so that the stresses are everywhere less than the critical value required to produce a change in the total energy of the system.

Surfaces of discontinuity between fluid layers cause a very rapid dissipation of energy and are therefore unstable on account of the total differences of velocity and the resulting stresses being confined entirely to the surface forming the boundary of separation between any two oppositely directed fluid motions. For this reason such surfaces of discontinuity in actual fluids tend to roll themselves up and to form vortices or eddies between the two currents so that the stresses and shears which take place are symmetrically distributed through a much larger portion of the fluid, and so that any two or more volume elements in contact have but a very minute difference in velocity.

Rotary motion is therefore a necessary condition required for the conservation of energy as the fluid changes from one configuration to another, rather than a means for the most rapid dissipation of energy inside the fluid mass.

The supply of energy to vortices or eddy motion in the fluid is derived from the total energy of the two opposing currents and it is increased by the work done by the internal stresses upon the corresponding rates of mean strain.

Where two or more vortices with the same sense of rotation are formed between two oppositely moving layers of fluid, the increase in velocity and the consequent decrease in pressure between them will bring their centers nearer together so that part of the circulation in one will be drawn into that of the other, and since it requires only about .707 as much energy to maintain a vortex having twice the area in cross section of two smaller ones, they will (if their kinetic energy is increasing) ultimately unite into a single center.

However, in order for any vortex to become a stabilized system of circulation it must either have its axis of rotation, or filament, closed upon itself in the form of a ring, or else it must reach a boundary surface of the fluid.

Horizontal vortices in the atmosphere may sometimes be formed in a manner analogous to winding up a spring to a certain tension and then unwinding again without the filament ever reaching the earth as the boundary surface, or they may under exceptional conditions, depending on their height and the supply of energy involved, reach the earth's surface and assist in forming a whirling storm such as a tornado, or perhaps even a tropical cyclone.

The intensity of eddies or vortices in the atmosphere, their structure, velocity and path of movement are determined in each case by the energy of the two opposing masses of fluid and the variations of this energy with time or place, (the topography of the earth's surface, or other obstacles to atmospheric motion are here considered the same as an oppositely directed mass of fluid), and the variation in the supply of energy depends on the temperature and pressure gradients and the total quantity of air involved in the motion Simple observations and experiments show that eddy or vortical motion is produced by a very slight difference in velocity between two currents of air, or two fluid layers having a different rate of movement, especially if there is a certain difference in their temperature, humidity, etc. And also that there is a much more rapid inertial decay of atmospheric eddies after their supply of energy is suddenly cut off, than what is generally supposed.

The foregoing principles, in combination with others, are extended and applied to a theory of the structure and movement of cyclones and other rotary wind systems in central United States and compared with other theories in the light of observational data for this locality.

Cyclonic circulation is considered as a necessary dynamical condition required for the interchange of energy between equatorial and polar air, caused by the difference in temperature between these two geographical positions. (Author's Abstract.)

Discussion-MR. E. W. WOOLARD complimented the speaker upon his interesting and suggestive paper. He pointed to the inadequacy of classical hydrodynamics as applied to atmospheric problems, and to the apparent suitability of Mr. Vaughan's work to these problems. He regarded it as an extension of the work done by G. I. Taylor and L. F. Richardson, and hoped that Mr. Vaughan would be able to develop it still further.

Weather Forecasting for Long Airplane Flights

By Capt. A. H. Thiessen, U. S. A.

Weather forecasting for long airplane flights differs somewhat from that for short airplane flights, and takes into consideration that in long flights the aviator will necessarily experience weather conditions differing greatly in character, and that during the time of the flight weather conditions may change very materially, The forecast for the short


flight may not refer to the conditions while en route, but in the forecast for the long flight which may occupy from five to seven hours, or even 16 hours, from sunrise to sunset, the forecaster and airplane pilots should be in intimate contact, so that the forecaster and the pilots may consult with each other, as to the best time to take off; and then the forecaster may formulate a forecast covering the weather generally over the entire route, which must further be amplified to indicate the weather which will be experienced by the aviator as he arrives at the various points along his route. The weather elements most affecting the flight of the airplane are wind direction, wind velocity at various altitudes, precipitation, temperature, conditions at the landing fields and visibility. -(Author's Abstract).

Discussion-MR. H. H. CLAYTON had always supposed that a roundthe-world flight, when undertaken, would be so planned as to take advantage of the prevailing winds, yet this one followed a course from east to west, against the prevailing winds. He also remarked that the dependence of aviation upon weather is decreasing as aircraft speed in


MR. E. B. CALVERT, referring to the forecasts furnished Capt. Thiessen by the Weather Bureau forecasters at Washington for the flight from Greenland to Labrador and thence to the United States, inquired as to the accuracy of those forecasts.

CAPT. THIESSEN, in reply, stated that the forecasts were generally satisfactory and of the utmost value. Some slight amplification was necessary at times, as the result of information gained locally from the natives as to the relation between wind direction and the occurrence of fogs on the coast of Labrador.

Some Meteorological Encounters of the Shenandoah

By Lieut. J. B. Anderson, U. S. N.

The rigid airship Shenandoah, built at the Naval Aircraft Factory, Philadelphia, was commissioned as a United States Naval vessel in October, 1923. During the fifteen months of her operation up to the present time, she has demonstrated an airworthiness highly gratifying to her designers and surprising to the millions of people who have followed her air voyages with keenest interest. She has outridden gale and storm with as much ease and greater comfort to passengers than the largest ocean vessel.

The first encounter of the Shenandoah with heavy weather was on January 16th, 1924. The ship was taken to its mooring mast for tests on Saturday, the 12th. On Monday the weather forecast indicated the probable formation of a depression which would bring gale winds to Lakehurst on the 16th or 17th. Inasmuch as winds of about sixty miles per hour were desired for the mooring test, it was decided to leave the ship at the mast. On Tuesday local winds of 55 mph., or more were forecast for Wednesday. About 6.45 P. M., a gust of 78 mph., wrenched the ship from her mooring mast and damaged her nose. In this crippled condition she outrode winds which at flying altitudes must have

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