Hirokazu Nonaka

Estimating Wave Height Distributions in the Seto Inland Sea, Ise Bay and Tokyo Bay of Japan Generated by 3 Giant Typhoons in the Showa Era

Shallow water wave hindcastings are conducted in the Seto Inland Sea, Ise Bay and Tokyo Bay for each of the so-called 3 giant typhoons in the Showa Era (Muroto Typhoon in 1934, Makurazaki Typhoon in 1945 and Isewan Typhoon in 1959). The computations follow the spatial distribution of time-dependent wave height and maximum value. The sea wind distributions given as the driving forces are estimated using a method which transforms the land-based measurement wind data into the wind data at sea or coastal stations and applies a spatial interpolation technique to the data. The main conclusion is that any of the typhoons may have generated the largest wave height over the past 90 years in the sea area of the typhoon path.

Trend and Jump Analyses of Winds Speeds and Wave Heights Based on Their Long-Term Hindcasts in the Inner Sea Areas of Japan Using Measurement Data of Sea Level Pressure

Hourly wind distributions on 3 regional sea areas which include the Kanto Sea Area, Ise Bay and the Seto Inland Sea are estimated using the measurement data of sea level pressure around the areas over a 45-year period form 1961 to 2005, after which a 45-year wave hindcasting is conducted station by station. For monthly- and yearly-highest 1/3-averaged wind speeds and wave heights, hindcasts are in reasonable agreement with measurements. Trend and jump analyses for yearly-highest 1/3-averaged atmospheric pressures, wind speeds and wave heights yield the following results : 1) Pressure does not exhibit any trend or jump. 2) Both wind speed and wave height show a statistically significant increasing trend and positive jump putting a pivotal year at around 1986, and their intensities become weaker toward the western area.

A Long-Term Wave Hindcast System in Quasi-Closed Sea Areas

This paper presents a wave hindcast system for estimating climatic characteristics of waves over 23 years at an arbitrary point in a quasi-closed basin that is partly connected to an open ocean such as the Seto Inland Sea. A data set of hourly over-sea wind distribution is made using measured wind data acquired at many coastal and sea stations. A wave computation at each of the wave measurement stations is conducted using a backward ray tracing wave model on a grid with high spatial resolution. Comparison between calculated and measured wave data shows that the system yields a reasonable estimate of long-term wave characteristics and that the present system has a higher ability in a long-term wave estimation than previous systems.

INTERCOMPARISON OF EXTREME VALUE ANALYSES FOR CENSORED ANNUAL MAXIMUM SAMPLE

Accuracy of parameter estimation methods to be used in extreme value analyses for censored annual maximum samples is investigated using a Monte-Carlo simulation technique. The methods are maximum likelihood method (MLM), least square method (LSM) and partial probability weighted moment (PPWM) method, and probability distributions are Gumbel, shape parameter-fixed GEV and Weibull distributions. MLM yields more efficient estimates of quantiles than PPWM method and LSM even for censored samples. MLM-, LSM- and PPWM-based models are applied to extreme value analyses to several types of censored in-situ annual maximum samples. One finding is that inclusion of historical information in MLM- and PPWM-based models produces more efficient estimates of quantiles.