On the Secondary Undulations of Tides caused by Cyclonic Storms (I)

[摘要] On the occasion of the cyclonic storm which swept along our Pacific coast from 1st to 5:h of April, 1936, conspicuous secondary undulations appeared on the mareograms of tidal stations in various parts of this country. In the present paper, is reported the result of investigation of periods, amplitudes as well as the time of occurrence of these conspicuous undulations, and some discussions are made on their relations with meteorological conditions. The results obtained are summarized in the following.(1) For stations situated along the Pacific coast of Honsyu, Sikoku and Kyusyu, conspicuous undulations of longer periods (proper oscillations of bays) began 6-12 hours before the time of nearest approach of the cyclonic centre to respective stations, and conspicuous undulations of shorter periods (swells or waves of 1-3 minutes periods) generally began somewhat later.(2) The conspicuous undulations of longer periods peculiar to the stations began about the time of arrival of 755mm isobar to respective station.(3) The conspicuous secondary undulations under question seem to have no close relation with the velocity of wind, gradient as well as the rate of variation of atmospheric pressure in the vicinity of the tidal station.(4) It seems that the present conspicuous undulations were not produced by the passage of lines of discontinuity and cold fronts as well as local showe_??_s. Besides, it seéms difficult to consider that the microbarographic oscillations in the vicinity of the tidal stations became the prime cause of the undulations.(5) The secondary undulations in question seen to have some apparent relation with the time variation of the atmospheric pressure gradient-the amplitude of the undulations is large when the rate of change of the pressure gradient is large.(6) It seems likely that the present conspicuous undulations were not produced directly by the meteorological changes in the immediate vicinity of the tidal stations, but chiefly by the waves which were produced once in some region near the centre of the cyclone, perhaps by some microbarographic change, and propagated toward the tidal stations.(7) As is naturally expected, the amplitude of the present secondary undulations has a close relation with the distance of the cyclonic centre from the tidal station. This relation is c_??_oser in the case of the undulations of shorter periods than those of longer periods.(8) There is a tendency such that the secondary undulation is large when the depression of the cyclonic centre is low.

[学科分类] 大气科学