Typhoon Attack Research Articles

POM and Two-Way Nesting POM Study of Kuroshio Damping Phenomenon Caused by a Strong Wind

A Kuroshio damping phenomenon of a few days scale caused by a strong wind was studied using the Princeton Ocean Model (POM) and a two-way nesting model for the POM. We simulated an idealized eastward Kuroshio in a zonal channel in terms of the inflow/outflow condition at the western/eastern boundaries and examined responses of the idealized Kuroshio to a strong easterly wind. This study was motivated by observations of JMA research vessel Shumpu Maru which reported deformation of isopycnals and damping of the Kuroshio before and after the attack of Typhoon 6804. Deformation of isopycnals and damping of the Kuroshio are found to depend on magnitude of wind stress, intensity of stratification, distance of the Kuroshio from coast, and grid resolution. The deformation of isopycnals is related to the vertical circulation pattern caused by the divergence/convergence of the onshore Ekman transport. A simple stratification model composed of Niiler (1969)'s modification of the Ekman transport and the coastal boundary is proposed to explain the damping phenomenon. An idealized cape was added in other experiments in order to study whether the Kuroshio damping mechanism discussed here works in three dimensions. The newly developed two-way nesting model for the POM was applied for this experiment and made it possible to clarify more detailed features of response in the nested area than did the coarse grid model.

Multiquadric Solution for Shallow Water Equations

A computational algorithm based on the multiquadric, which is a continuously differentiable radial basis function, is devised to solve the shallow water equations. The numerical solutions are evaluated at scattered collocation points and the spatial partial derivatives are formed directly from partial derivatives of the radial basis function, not by any difference scheme. The method does not require the generation of a grid as in the finite-element method and allows easy editing and refinement of the numerical model. To increase confidence in the multiquadric solution, a sensitivity and convergence analysis is performed using numerical models of a rectangular channel. Applications of the algorithm are made to compute the sea surface elevations and currents in Tolo Harbour, Hong Kong, during a typhoon attack. The numerical solution is shown to be robust and stable. The computed results are compared with measured data and good agreement is indicated.

Patterns of pair formation in protandrous anemonefishes,Amphiprion clarkii, A. frenatus andA. perideraion, on coral reefs of Okinawa, Japan

At Sesoko Island, stocks of anemonefishes were observed for 2 years in a 350 m × 150 m area where host sea anemones were sparse. About 40% of the pairs separated, mostly due to typhoon attacks or displacement. Widowed mates remained and acquired new mates on the same sea anemone, except for one case. New mates were immigrant adults inAmphiprion clarkii and A.frenatus, but resident juveniles inA. perideraion. A. clarkii andA. frenatus moved between sea anemones and sometimes displaced smaller consexuals, butA. perideraion rarely moved. The difference in mobility among the 3 species was related to the mean difference in standard length between the largest juveniles in breeding groups and the minimum size of breeding males in each species, and that between breeding males and the minimum size of breeding females. InA. perideraion both of these differences were small, so pairs could be formed quickly by residents after mate loss. On the contrary, inA. clarkii andA. frenatus, either or both differences were large and it would take a longer time to form a pair after mate loss. Differences in mobility affected the patterns of pair formation, and then the size composition of members in breeding groups.

Detection of Accumulation-erosional Terrace Association formed in the Last 20, 000 Years

A radiocarbon dating analysis clarified that the latest accumulation terraces, which were found at eight river-basins in the Ou and the Dewa mountains (fault and fold mountains in the northern Japan), were simultaneously completed around 20, 000yr B. P. At the age of the terrace completion, the polar frontal zone began to recede to the present position, and subsequently caused a substantial increase in heavy-rainfall frequency due to a typhoon attack even in the northern Japan.Detailed field survey and tephrochronological analysis for the Kariya river-basin in the upwarped Kitakami mountains, located in almost the same latitude as the Ou and the Dewa mountains, revealed that the latest accumulation terrace was also completed around 20, 000yr B. P. Simultaneity of the terrace formation regardless of their great geomorphological difference among those mountains described above, proved that a great increase in the heavy-rainfall frequency was primarily responsible for the initiater of the accumulation terrace formation. Accordingly, it was safely concluded that the formation of the latest accumulation terraces occurred around 20, 000yr B. P. by the climatic change, not crustal movements in the northern Japan.A sizable volume of previous papers concerning the accumulation and the erosional terraces formed in the last 20, 000 years throughout Japan, was intensively reviewed, and the terrace distribution was mapped out. Consequently, it was confirmed that the formation of the accumulation terraces surely extended to the northern to central Japan, and that it commonly accompanied the erosional terrace formed at latest by 10, 000yr B. P. This accumulation-erosional terrace association characterized the river-landform development during the last 20, 000 years.In the southern Japan, only the erosional terrace without the accumulation terrace was identified at the Miya, the Ishite and the Mimi river-basins. Since fossil periglacial landforms in the last Glacial time, widely distributed in Japan, are known to be closely associated with the accumulation terrace, the accumulation-erosional terrace association was plausible to be formed in the southern Japan, and the erosional terrace, therefore, was considered to be the counterpart of the terrace association.In addition to the terrace association in the last 20, 000 years, if a similar key landform is detected in the landforms before 20, 000yr B. P., there is a great possibility to develop a new topographical analysis method.

Occurence of withered and completely sterile ears in rice plants by attack of typhoon, with special reference to varietal resistance. (1)

Occurence of withered and completely sterile ears in rice plants by attack of typhoon, with special reference to varietal resistance. (1)