Tomokazu Murakami

A new typhoon bogussing scheme to obtain the possible maximum typhoon and its application for assessment of impacts of the possible maximum storm surges in Ise and Tokyo Bays in Japan

We developed the new typhoon bogussing scheme to obtain the possible maximum typhoon approaching any region under any climatic conditions by using a potential vorticity inversion method. Numerical simulations with the new typhoon bogussing scheme are conducted for assessment of storm surges by possible maximum typhoons under the present-day and global warming climatic conditions in Ise and Tokyo Bays in Japan. The results suggest that the storm tide higher than the maximum storm tide in recorded history can occur in Ise and Tokyo Bays even for the present-day climate and the storm tide higher than the design sea level can cause severe damage to Nagoya and Tokyo megacities, in particular, airport facilities in Ise Bay for the global warming climate. These results suggest that the new typhoon bogussing scheme we developed is useful for assessment of impacts of storm surge by the possible maximum typhoons.

A new index for evaluation of risk of complex disaster due to typhoons

This study examines a new index to evaluate complex disaster risk in coastal zones involving typhoons. Typhoons generate not only strong winds but also storm surges and high waves. Therefore, complex disasters attributable to typhoon forces can be expected to occur in coastal zones. The durations for which the wind speed, storm tide, and wave height simultaneously exceed their respective design values were calculated as simultaneous excess duration (SED) to evaluate the risk of a complex disaster. To verify the utility of SED, numerical simulations were conducted for intensified typhoons under both present-day and global warming climates in Ise Bay, Japan, using an atmosphere–ocean–wave coupled model with a typhoon bogussing scheme. Results showed that the middle part of Ise Bay is more dangerous from the standpoint of SED than the inner part of Ise Bay, which has been regarded as the most dangerous area from the standpoint of extreme values of storm tide. These results suggest that SED is important as an index of risk of complex disaster, and the risk of typhoon disaster should be evaluated not only from extreme values of storm tide but also from SED.

Bursting-Layer Modeling Based on the Assumption of the Averaged Sea Surface for Strong Wind-Driven Currents

Abstract In the sea, which is affected by strong winds that cover the water surface with wind-wave breakers, the sea surface layer, called the bursting layer by authors, is generated immediately below the mean water level. For treatment of strong wind-driven currents, it is necessary to model the bursting layer correctly based on observed data. However, an essential difficulty occurs in that, because of large water surface displacement caused by developed wind waves, water particle velocities above the wave trough level cannot be measured continuously in the Eulerian coordinates when measuring the velocity of strong wind-driven currents. Consequently, it is impossible to apply the Reynolds average rule to the velocity field above the wave trough level. In this study, an experiment that uses a wind-wave tank with a double bottom is performed to measure the horizontal velocity of currents driven only by the wind stress. The vertical distribution up to the mean water level is determined to make its verticall...

STORM SURGE INUNDATION PREDICTION DUE TO HUGE TYPHOON AT HEAD OF ISE BAY

伊勢湾沿岸域は世界有数の工業集積地帯であり,スー パー中枢港湾の名古屋港,四日市港を有し,我が国の経 済における重要度は極めて高い.一方,同沿岸域は, 1959年の伊勢湾台風などで甚大な高潮・高波被害を被っ てきたため,伊勢湾台風級の台風による高潮・高波に耐 えられる堤防・防波堤等が整備されてきた.しかし,昨 今,地球温暖化による台風の強大化が懸念されており, 将来的に伊勢湾台風を超える巨大台風の襲来について考 慮しておく必要がある.その場合,襲来する可能性があ る台風の規模,および台風襲来によって起こりうる高潮 災害の規模を予測することが必須となる. 村上ら1)は,現在気候の下で大気・海洋力学的に最大 級となる50通りの台風を取り上げ,大気-海洋-波浪結 合モデルを用いて伊勢湾の高潮計算を行った.その結果, 伊勢湾台風時における名古屋港での潮位偏差 3.5 mを超 える5.5 mの高潮が現在気候において発生する可能性を 示した.また,村上ら2)は,地球温暖化がIPCCのA1Bシ ナリオどおりに今世紀末まで進んだ場合の伊勢湾全域で 予想される可能最大級の高潮・高波について,大気・海 洋力学的に基づき,数値解析を実施した.そして,既往 の伊勢湾台風による高潮・高波の実測値との比較検討を 行い,温暖化時における可能最大級高潮・高波の実態と その危険度について示した.このように,過去最大級の 伊勢湾台風を超える巨大台風によって発生する高潮・高 波の特性を把握することは,沿岸防災の観点から非常に 重要である.しかしながら,村上ら1), 2)の研究では,現 在/将来気候下での高潮による浸水計算を実施していな いため,伊勢湾の沿岸陸域に及ぼす浸水影響について議 論することができない. そこで,本研究では,室戸台風級の超巨大台風時,お よび村上ら1), 2)が検討した現在/将来気候から予想され る最大高潮条件を対象に伊勢湾湾奥部の高潮浸水計算を 行い,超巨大台風による浸水特性について検討すること を主たる目的とする.

Influence of Wave and Sediment Transport on Coral Distribution in Amitori Bay, Iriomote Isrand

気象および河川の状況を実測し,これをもとに懸濁物の 挙動を再現した結果も,サンゴの分布やサイズ組成と比 較した.これらの結果より,従来から言われているよう に高波浪かつ懸濁物が少ない場所は様々なサイズのサン ゴが高被度で分布していることを確認した. 本研究はこれらの研究に引き続き図-1に示す沖縄県西 表島網取湾においてサンゴ分布の調査および各種物理条 件の調査並びに再現計算を行った.特に土粒子の河川から の湾内への流入パターンを数値計算により再現し,波高 分布とあわせて,サンゴ群集の分布を比較検討した. なお,網取湾には東海大学沖縄地域研究センター網取 施設があり,風向・風速や水温の観測が行われている。 サンゴは同じような形態を持っていても種によって環 境に対する耐性が異なると考えられる.さらに同じように 見える群集形態でも異なるいくつかの種が混在している 場合がある.そこで本研究では,形態による類型のみな らず,種同定が可能であった卓状サンゴ群集については, 種を識別して,種別の分布条件を評価した. 西表島網取湾のサンゴ種別分布に及ぼす波浪および土砂輸送の影響 Influence of Wave and Sediment Transport on Coral Distribution in Amitori Bay , Iriomote Isrand

Damage Simulation System for Coupled Hazards Caused by Maximum Possible Typhoons in Coastal Zones under a Future Climate

A numerical simulation system incorporating an atmosphere–ocean–wave coupled model and a typhoon potential vorticity bogussing scheme was developed to calculate strong winds, heavy rainfall, storm surges and high waves caused by maximum potential typhoons in a future climate. The risks of coupled hazards in Ise Bay, Japan, under a future climate were evaluated using this simulation system. Results demonstrate the possible occurrence of a 6.9-m storm tide at Nagoya Port, which remarkably exceeds the largest storm tide ever recorded in Japan, which is 3.5 m. Moreover, times exceeding design values for the storm tide, significant wave height, and wind speed were shown simultaneously to evaluate the risk of coupled hazards. Results show that Tsu Port is an extremely dangerous area for coupled hazards and that the time exceeding design values was 74 min.