Popular Science Monthly/Volume 18/January 1881/A Japanese Typhoon

From Wikisource
Jump to: navigation, search

By Professor T. C. MENDENHALL.

CONSIDERABLE information has been gathered, and much has already been published, concerning the damage inflicted upon this coast and in the vicinity by the typhoon which visited us during the night of October 3d and 4th.

The unpleasant frequency, in this part of the world, of storms of the same character, renders their careful investigation by competent meteorologists a matter of the utmost importance. What is chiefly demanded, therefore, is the collection of such meteorological records and observations as may, perhaps, render it possible to trace completely the rise, progress, and varying intensity of the storm. Of course, considerable time must elapse before such an investigation can be completed ; and, unfortunately, even at best the number of accessible and reliable series of observations will be greatly less than could be desired for the successful study of the phenomenon.

In the mean time we deem the matter of sufficient local interest to justify a brief presentation of the principal meteorological features of the storm, based upon observations and records made at the observatory of the University of Tokio.

Although it can hardly be said that this storm gave any marked indications of its immediate approach, yet it is important to observe that

Chart showing the Height of the Barometer from 8 a. m. on the 3d to 2 p. m. on the 4th of October, 1880.

PSM V18 D371 Barometric pressure chart of a typhoon.jpg

there was a steady fall in the barometer from the previous Thursday—September 30th—up to the time of maximum violence of the wind. The first of the accompanying charts exhibits the barometric curve during the most interesting period; i. e., from 8 a. m., on the 3d of October, to 2 p. m., of the 4th. Previous to one o'clock on the morning of the 4th but three observations are recorded: at 7 a. m., at 2 p. m., and at 10 p. m. These indicate a steady decline in the barometer, and it is not likely that any extraordinary fluctuations occurred during this time. After 1 a. m., the observations were made hourly, and during a considerable portion of the time they were half-hourly. It will be seen, however, that a very important portion of the curve, from 10 p. m. to 1 a. m., is doubtful, and it is not at all unlikely that, had intermediate observations been recorded, the fall of the barometer would have appeared much more sudden than it does. The minimum observed height was 28·735 inches at 2 a. m. At three o'clock the height was only a trifle greater than this, and, from the nature of the curve before and after the interval from two to three o'clock as well as from the velocity of the wind, it seems highly probable that between these hours a lower point than any observed was reached. The curve is constructed to show the actual vertical movement of the mercurial column. From the minimum it rose rapidly until 6 a. m., at which hour the height was 29·386 inches, and from that hour the rise continued with less rapidity but with great steadiness, until the night of the following Wednesday, when the reading was 30·378 inches. Thus the range of the barometer in three days was 1·643 inches. This is more than two tenths of an inch greater than the range for the whole of the last year. At no time during last year did the barometer reach so low a point as 29 inches, and the mean height for the year was 29·952 inches.

The second chart shows the velocity of the wind at different hours, extending over the same interval of time. These velocities are computed from a continuous record made by an anemograph consisting of a Robinson's anemometer with Beckley's registering apparatus attached. From this curve it will be seen that, so far as the wind is concerned, up to about 11 p. m., there were no indications of the coming storm. At that time a breeze sprang up, which continued at less than twenty miles per hour until about 1 a. m. when it suddenly increased in velocity, and at 2 a. m. the record shows a speed of sixty miles per hour. Unfortunately, shortly after two o'clock, the clock-work which keeps the registering portion of the apparatus in motion was stopped, the motion of the pendulum being undoubtedly arrested by a sudden blast of great violence. This stoppage was not discovered until 3 a. m., so that between these hours the record is lost. At three o'clock the instrument was put in motion again, and, for about fifteen or twenty minutes after that hour, the record shows the extraordinary velocity of ninety-five miles per hour. From this time the violence diminished rapidly, a velocity of fifty miles per hour being registered at 4 a. m., and at 5 a. m. it had fallen to less than twenty miles per hour. Twice afterward, as will be seen by the chart, the speed rose to about twenty-five miles per hour, after which it rapidly declined.

Owing to the interruption in the continuity of these records, it is impossible to affirm that the maximum velocity of the wind was recorded. In fact, there are reasons for believing that the storm reached its greatest violence somewhat before three o'clock.

It seems quite certain, then, that at times during the storm the velocity

Chart showing the Velocity of the Wind from 7 a. m. on the 3d to 2 p. m. on the 4th of October, 1880.

PSM V18 D373 Wind velocity chart of a typhoon.jpg
Note.—The break between 2 a. m. and 3 a. m. In the curve representing the velocity of the wind is due to the tact that, between those hours, the registering apparatus connected with the anemograph was not in motion.

of the wind exceeded one hundred miles per hour; and especially must this have been the case during some of the most violent blasts, which where generally of too short duration to show with their full effect upon the register made. The fact that the pendulum of the anemograph was stopped between two and three o'clock by one of these blasts, and that after three o'clock its motion was not interfered with, would indicate that more violent disturbances took place before than after that hour. A smaller anemometer of Robinson's model was torn from its fastenings between two and three o'clock, and so completely demolished that no record even of the work which it had already done could be obtained. This is much to be regretted, as otherwise a means of verifying the extraordinary velocity registered by the anemograph would have existed. Concerning the latter it should be said that, regarding the smaller anemometer as a standard, it has been found upon examination to somewhat over-estimate the velocity of very high winds, and to under-estimate those of low speed. At the same time it can not be positively stated which of the two instruments was in error.

A continuous record of the direction of the wind is kept. Upon examining this it is found that, during the whole of the period considered, the direction varied between north and west. Up to 1 a. m., of the 4th, the wind was steadily from the north-northwest. From that hour until 5 a. m., its fluctuations were confined between northwest and west. A decided change in direction seems to have taken place between the hours of two and three o'clock.

The early part of the storm was accompanied by an unusually heavy fall of rain. The violence of the wind prevented the reading of the rain-gauges during the night, but when emptied at 7 a. m. they showed a total of 4·66 inches, nearly all of which must have fallen during—at most—two or three hours.

It may be interesting to make some comparisons between the violence of this storm and that which was undoubtedly the immediate cause of the destruction of the Tay Bridge, on the evening of December 28, 1879. Unfortunately, it does not appear that any very exact or reliable observations of the velocity of the wind on that occasion were made; but an approximate measure of it may be obtained from the testimony of several of the witnesses, who were men of considerable experience in the observation and estimation of high winds. The following selections from the "Times" report of the Board of Trade inquiry are of interest in this connection. Captain Scott, R. N., who was superintendent of a training-ship stationed in the Tay, testifies that his barometer fell from 29·60 inches at noon to 29 inches at seven o'clock—that being the lowest point reached. Also, that, in the navy, storms were described by numbers from 1 to 12, 12 being the maximum. Upon that scale he would describe this storm in the Tay as from 10 to 11. He had on rare occasions in China and the West Indies rated storms as high as 12.

Admiral William Heriot Maitland Dougal, who had resided at the mouth of the Tay continuously for twenty-nine years, stated that his barometer fell from 29·40 inches to 28·80 inches. The difference between these and the previous barometric heights is easily explained by the fact that his house was at an altitude of two hundred feet above the level of the sea. He declared that the gale was like a typhoon in violence, and that in all the time during which he had lived on the Tay he had never experienced a gale of equal severity. In his opinion the velocity of the wind was from seventy-five to seventy-eight miles per hour, and that during the lulls it would fall to something like thirty.

Charles Clark, who was an amateur observer, gave evidence that 29·00 inches was the minimum point reached; that he had marked the storm 4 on a scale of 6; and that he had never yet recorded 5 or 6.

Other witnesses testified in about the same way, all agreeing reasonably well as to barometric depression and probable velocity.

On comparing these statements with those already made concerning the recent typhoon here in Japan, it will be seen that both in barometric range and in wind-velocity the recent storm considerably exceeded that which was the occasion of the Tay Bridge disaster. The barometric change was not greater, but more sudden in the former than in the latter. Concerning the direct measurement of the pressure of the wind in pounds per square foot, it must be said that the instruments for doing this are, at present, to a great extent crude and unreliable. It is generally assumed that the pressure is proportional to the square of the velocity. Upon a scale adopted by the Smithsonian Institution and by the United States Signal Service, the velocity of twenty-five miles per hour corresponds to a pressure of three pounds per square foot. Assuming the correctness of this, and also of the law given above, the pressure per square foot in the Tay storm must have been nearly thirty pounds, and in the recent typhoon here it must have been nearly fifty pounds. It was shown, in the tests made upon the material of the Tay Bridge, that it might have been expected to give way under a wind-pressure considerably less than forty pounds. The French and many English engineers have adopted fifty-five pounds per square foot as a standard, and about the same number is used in America, but it seems doubtful if even that furnishes a sufficient "factor of safety."

In conclusion, the affirmation may be made, supported as it is by the constantly accumulating evidence of the damage done to buildings, shipping, etc., that this was one of the most violent storms experienced here for many years. From facts already known concerning other points along the coast of Japan, it would seem that, had an efficient system of observations, telegrams, and signals existed, timely warning might have been given of its approach, and possibly much property and many lives saved. In view of this fact it appears hardly necessary to repeat the suggestion, the importance of which has been frequently urged in these columns, that the Government should, at the earliest practicable moment, inaugurate an efficient and complete signal service for the benefit of the whole country.—Japan Weekly Mail.