Field observations at an offshore observation tower during the typhoon seasons

Abstract

This paper shows some results of intensive field observations carried out in the summer seasons since 2009. The intensive field observations have been conducted at the observation tower of Shirahama Oceanographic Observatory (SOO), DPRI, Kyoto University. The observation tower of SOO is an offshore platform for the oceanographic and meteorological observation and it is located at the bay mouth of Tanabe bay, the southwestern part of Kii Penisula, Japan. One of the aims of the observations is field data measurements to comprehend the vertical mixing process due to wind and wind wave. During the observations, five typhoons (Melor in 2009, Ma-on, Talas and Roke in 2011 and Jelawat in2012) hit the Kii peninsula. Three of them (Melor, Roke and Jelawat) passed along the southern coast of Japan and they have similar tracks around the Kii peninsula. Only Talas in 2011 passed across the main island of Japan and reached the Sea of Japan. In the observations, the vertical profiles of currents and water temperature have been measured as well as wind and wave conditions. The main results are as follows: Wind and wave conditions have common characteristics like the temporal variation of wave period and the incidence of high wave peak even though these conditions are affected by the typhoon tracks. The temporal variations of water temperature have also similar trends when the typhoons come close to the observation site, however, the vertical profiles of water temperature before and after the typhoon coming have big difference. The observed results underline the needs for the continuous observation activities and multidimensional data analysis combined with numerical simulations in order to investigate the mixing process under stormy conditions.