Elevation of the Sea Surface Caused by Typhoons

Abstract

In this paper, the author has determined empirically the height of the upheaval of the sea level caused by an approaching typhoon, only from the practical point of view. The result may be quite unsatisfactory giving only the lowest limit of the upheaval which may actually occur, because the upheaval due to the astronomical tide and the wind waves of very short period which may play an important role in the disaster over the coastal district has been neglected.
The principal results can be judged only by common sense, and summarized as follows:
(1) The time of maximum upheaval of the sea surface generally coincides with the time of the lowest barometric pressure at the station. In other words, owing to the general character of the typhoon that attacks Japan and moves northward along the Pacific coast, the highest water usually occurs when the center of the typhoon has reached the nearest distance from the station, as expected by the common sense. And at that time N-NE winds are generally the strongest. And when S-SW wind begins to blow, the sea level begins to lower very rapidly.
(2) Dividing the elevation into two parts, i. e., the elevation due to the suction of low pressure and the elevation due to the drift of the wind, it was found that the latter is almost negligible for the wind force less than Beaufort's scale 4, however long such weak wind may persist. But as soon as the wind force exceeds that speed, the sea surface begins to rise very rapidly.
(3) The total elevation is proportional to the difference between the normal barometric pressure at that place and the lowest pressure of the typhoon on its track, and is inversely proportional to the shortest distance from the center to that station, to which the typhoon approaches.