7. There is little variation in the frequency of different directions at the surface. Above it there is a pronounced swing to westerly directions, with the result that a west component is found 85 to 90 per cent of the time at 4 k., except in Florida and southern Texas where, in summer, an east component predominates. 8. Winds of 10 m.p.s. or more occur from 5 to 10 per cent of the time at the surface. At flying levels, 500 to 1000 m., their frequency increases to about 30 to 35 per cent, with a large seasonal and latitudinal range. Velocities of 20 m.p.s. or more occur at these levels less than 5 per cent of the time. At greater heights there is an increasing frequency of the higher velocities, those of 10 m.p.s. and over occurring more than 50 per cent of the time at 4 and 6 km. and those of 20 and over, about 15 per cent. The highest velocity recorded in this country is 83 m.p.s. (186 m.p.h.) at 7200 meters above Lansing, Mich. Discussion-Professor Marvin expressed his pleasure at the progress of the aerological work of the Weather Bureau, complimented Mr. Gregg en his paper, and pointed out that much of the work discussed in it would be of value in long-range forecasting. Mr. W. H. Alexander also emphasized the value of such a discussion.. The Wind Factor and the Air Mail Southward From Kansas City (Illustrated by lantern slides) By John A. RILEY The Air Mail between Kansas City and Dallas is part of one of the feeder lines of the transcontinental Air Mail. That part of the route from Wichita to Dallas is almost due north and south. Upper air records in Oklahoma indicate that at ordinary flying levels south winds predominate over north winds by seven miles per hour, so that northward flight will be made at a rate of about 14 miles per hour faster than southward flight. It is known that the wind reduces the average speed of aircraft traveling on a regular schedule, and that the stronger the prevailing winds the more will the speed of flight be reduced. Assuming an airplane to have a normal cruising speed of 100 miles per hour the winds of Oklahoma are sufficient to reduce the speed to 97 miles per hour when flying a north-south course. This plane will therefore travel northward across this region at 104 miles per hour, and southward at 90 miles per hour. Mail schedules call for a speed of about 90 miles per hour in each direction. Most of the winds of the southern Plains states from the surface to 1600 feet are north or south winds; very few come from east or west. Sixty per cent are southerly winds and 40 per cent northerly winds. The average speed of the wind for various directions increases nearly in proportion to the average frequency; that is the most frequent winds have the highest speeds. Strong winds are most frequent from the S.S.W. Two-thirds of all winds of 30 miles per hour or more are from directions between south. and southwest, and the ratio increases for winds of higher speeds; more than half of all 50- and 60-mile winds come from S.S.W. alone Thirty-mile winds occur about twice a week; 40-mile winds once a week; 50-mile winds once a month; and 60-mile winds about four times a year. As one round trip a day is to be made—northward in the morning, and southward in the afternoon over this portion of the route daily changes in wind speeds are found materially to affect schedules. At flying levels the daily changes are just the reverse of those at the surface, for while surface winds are strongest during the day, upper winds are strongest at night. The observation at 7 A. M. represents nocturnal conditions. The average difference in wind speed 1600 feet above the surface from 7 A. M. to 3 P. M. is 10 miles per hour and varies from 12 miles per hour in summer to 8 in winter. The greatest daily range in speed occurs with southwest winds. The reason for this is the difference in the vertical temperature distribution for winds of different directions, especially at night. In south winds the air several hundred feet up is likely to be warmer than that in contact with the ground. In this condition, the upper air being lighter than that beneath, different strata do not mix and the upper air flows along at a high speed. Conversely in north winds the upper air is colder and heavier than surface air. This causes turbulence and mixing and a more uniform speed at the surface and aloft. As a consequence strong winds are far more frequent from S.S.W. than from north or other directions. The schedule of the Air Mail, northward in the morning and southward in the afternoon, is therefore the best so far as winds are concerned. Flying speeds are thus appreciably increased in both directions, because of the average daily range in wind speeds. Also, as 78 per cent or more of all strong winds occur in the morning and most of them are southerly winds, the morning trip will often be greatly advanced. In the afternoon head winds will not retard the speed of southward flight nearly so much as if it were made in the morning. The greatest percentage of delays on account of wind may be expected when southward trips are made in the early morning. Discussion-Mr. Gregg stated that the possibilities of commercial aviation were certain to have a decided effect on air mail and that it was necessary to have important data available before routes were estab lished. Schedules of flight would have to be based on investigation of wind speeds at different hours of the day, time of the year, and elevation. Dr. Milham asked about co-operation between the Army, Navy, and Weather Bureau in aerological work. Mr. Gregg stated the meteorological services of the Army and Navy made observations for the current use of fliers that were telegraphed to the Weather Bureau offices at Washington, D. C., and San Francisco, Calif., and later detailed summaries were furnished the Weather Bureau. The Army and Navy do not discuss summaries, their object being to ascertain current conditions. This co-operation has been very gratifying to the Weather Bureau as its funds do not permit of the establishment of sufficient aerological stations for its purposes. = Tornadoes of the Middle West Of the three large cities of the Middle West, Omaha, St. Louis, and Kansas City, Omaha and St. Louis have already been struck by tornadoes that took heavy toll of human life and property. Many other destructive tornadoes have occurred within a radius of 200 miles of Kansas City in comparatively recent years and Kansas City itself has a record of a violent tornado in 1886. Few, if any, parts of the United States between the Alleghenies and the Rockies may be considered immune from tornadoes, and, by the law of probability, damage from these storms is likely to show a progressive increase as the country becomes more thickly settled, unless important buildings as well as residences are constructed so as to render them tornado proof or at least more resistant to violent winds. Insurance is the most general protection against tornado damage at present, but there is reason to believe the modern steel reinforced building, with extra bracing that will add but a small per cent to its total cost, will withstand the force of tornadic winds if not the full force of the vortex. A new type of residence, showing certain changes that will render it more resistant to winds, might also be developed for communities in what is also called the tornado belt. Discussion-Prof. Marvin stated it was important that construction of buildings in cities be of a type that would resist tornadoes as well as earthquakes and it was possible to construct concrete and steel buildings that would be safe. He also asked if Mr. Flora had verified that part of his report stating that poultry had been stripped of its feathers in a tornado without being killed. Mr. Flora replied that this had been taken from a newspaper account and there was no particular reason to doubt it. He had himself seen fowls stripped of feathers by a tornado, but these had been killed. Mr. W. E. Barron remarked that fright might be the cause of poultry losing their feathers in a tornado. [Maybe the quills explode in the low pressure.-C. F. B.] Mr. Barron thought that the apparent increase in tornado damage might be due to a more extensive system of reporting them. He also stated that in his examination of the Murphysboro, Ill., tornado there was evidence of the stability of better built buildings in the storm. Mr. Alexander doubted the ability of modern office buildings to withstand the full force of a torando, though he had not visited Lorain, Ohio, after the tornado there and witnessed the example mentioned by Mr. Flora in his paper. Mr. G. K. Greening raised the question of whether it would be feasible to issue warnings of the approach of a tornado after one was known to have formed. Dr. Milham doubted that it could be done. Mr. Barron stated the people in Mt. Vernon, Ind., knew of the destruction of Murphysboro before the tornado reached Mt. Vernon. Mr. Slaughter expressed his doubt of the advisability of issuing a warning after a tornado had formed, owing to the uncertainty of its path. Prof. Marvin stated that it was against the general policy of the Bureau to issue warnings of tornadoes, as such were liable to do more damage than good. As Dr. Humphreys was not present and Mr. Root had not yet arrived. owing to a railway wreck having delayed his train, papers to be read by them were passed over at this point. Weather and Potatoes in Wyoming By GEO. W. PITMAN The potato plant was first observed in Peru at an altitude of 10,500 feet. The ideal climate for the plant is one in which there is about 14 inches of rainfall and an average temperature of 64° for a period of 128 days, which includes dates of two weeks before planting until two weeks previous to digging. Artificial conditions of irrigated districts must approach the natural closely, to produce the best results. The potato districts of Wyoming average 61.6° with an average rainfall of 9.62 inches for a period of 138 days, but irrigation is practised in several localities. When rainfall is light, it is probable that not so much heat is required to change plant food into vegetable matter. The average crop for 25 years in the state is 130 bushels an acre. Temperature conditions for July and May appear to affect yields most. If July was warm the crop was good about 22 per cent of the time, but if cool and wet the crop was normal or greater about 89 per cent of the time; if cool and dry the probability was on a 50-50 basis; only two Julys of the 25-year period were both warm and wet, and the crops were less than normal in both seasons. Temperatures for May appear to have an indirect influ. ence through advancing or retarding the season, which in turn either places the focal date of the hot spells of summer, July 16, within the period of blooming of "new potatoes," or else delays this period of development until after the focal date, when it is generally cooler and more favorable; an advanced season is accompanied by good crops only 14 per cent of the time, while crops are normal or better 90 per cent of the time when the season is delayed. Therefore, the average date of planting, May 10, should be postponed until the closing days of May. A Droughty Year (1925) With Bumper Crops (in Ohio) The droughty conditions referred to in the Monthly Weather Review for September, 1925, applied to Ohio to a very marked degree, the records showing a persistent, and at times very pronounced, deficiency during the first six months of the year, the accumulated deficiency at the end of June being 5.75 inches, or about 30 per cent of the normal. Or, if the review is extended backward to include the last six months of 1924, it will be found that of the 12 months thus covered only two, September and December, showed an excess and one of these, December, was slightly deficient over the southern portions of the state. The accumulated deficiency for these 12 months averaged for the state 9.17 inches, or about 24 per cent of the normal. Ordinarily such a shortage would be fatal to one or more of the major crops in Ohio. But what do we find? ! First, that Ohio produced in 1925 the largest corn crop in the history of the state, both as to the average yield per acre and the total number of bushels; second, the largest, save four, average yield per acre of oats in the history of the state; third, the largest, save four, average yield per acre of barley in the history of the state; fourth, the largest, save three, average yield per acre of potatoes in the history of the state, while nearly all the minor crops, including fruits and vegetables, were average or better. The only crop failure of consequence was the hay crop and even this in places was good. It is true the wheat crop was far below the average as to yield in bushels, but was excellent as to quality; this shortage was due not to the lack of moisture, but to severe winter con ditions. コ a How is the agricultural meteorologist going to account for the rather surprising results mentioned in the second paragraph in view of the conditions stated in the first paragraph? Is the explanation to be found in a happy chronological distribution of the precipitation through the crop growing season, especially at the critical periods of the major crops? Do the facts set forth confirm or contradict the conclusions of Prof. J. Warren Smith1 to the effect that "the 10-day period from August 1 to 10 has the greatest influence upon the yield of corn in central Ohio" and that "the rainfall for the 10 days following the date of blossoming has an almost dominating effect upon the yield of corn, the larger the rainfall, the larger yield"? If we accept the 10-day period, August 1 to 10, as the critical period in the corn crop of 1925, we are face to face with the fact that the rainfall during the critical period was far below even the normal amount; in fact, the entire month of August was markedly deficient. If the blossoming period is set forward to July, which seems more probable, we have difficulty in finding a 10-day period during which the rainfall was sufficiently excessive to account for the large yield in accordance with the conclusion that "the larger the rainfall, the larger the yield." The fact is the July rainfall was only slightly above the normal over the northern and middle sections, but was appreciably above over the southern. It appears, therefore, that a complete explanation is not to be found in the rainfall alone, for as is generally known plant development is the direct result of the action and inter-action of most of, if not all, the climatic elements, not only on the plant itself, but also on the soil a truly complex phenomenon. It is believed the facts justify the statement that although the amount of precipitation up to a certain minimum is absolutely essential, above that minimum the distribution in time is equally as important as the amount. As we look back over the daily record we find a rather interesting distribution of the rainfall as between day and night; for example, in March 69 per cent of the rain fell at night; in April, 56 per cent; in May, 63 per cent; in June and July only 23 per cent at night; 1 M. W. R. Feb., 1914, pp. 78-93. |