Tide and Storm Surge Simulation for Ryo-mong Invasion to Hakata Bay

Abstract

The second battle of Hakata Bay, known as the battle of Koan, was the second attempt by Koryo (Korea) and Mongol to invade Japan in the summer of 1281. In August 1281, Ryo-Mong invasion attempt failed due to the typhoon which sunk a sizable portion of the Mongolian fleets. The Japanese called this typhoon as divine wind (Kamikaze in Japanese). In this study an integrally coupled wave-tide-surge model was used to the simulation of wave and storm surge due to the typhoon in August 1281. The track and strength of this typhoonare reported to be similar to those of typhoon Songda recently experienced in 2004 (typhoon 200418) (Imamura, 2005). Because of the lack of observations and historical records for 1281, the meteorological data in August 1281 were estimated using the Dynamic Holland model and information of typhoon Songda. The tide and storm surge simulation for typhoon Songda using the same method to acquire meteorological data as that of the typhoon in August 1281 (the battle of Koan) was performed for the model validation.The model based on this method reproduced reasonably the water levels in Kyushu and the Seto Inland Sea, Japan. This study estimated the wind field, wave properties and tide and storm surge for August 1281. It is supposed that the maximum wave height was almost two times higher than the significant wave height computed by the model, i.e., the maximum wave height was approximately 4-6 m, which was sufficiently large damaging river-run flat-bottomed fleet, and the high surge storm surgedid not arise due to the counter-clockwise wind of the typhoon in 1281.