| Climate change has always been one of the most concerned scientific issues, and with the development of technical requirements, the ocean climate has been gradually taken into concern and got rapid development in the seventies of last century, especially the change of surface wind field and wave field.In the present dissertation, the phenomenon of wave climate is described, the art-of-state of wave climate is reviewed, and the correlation between wave climate and large-scale atmosphere circulation is discussed. Meanwhile, related to the global climate change in the 1977/1978, the relevant changes of wave climate are pointed out as well.Present study uses the 40-year reanalysis products (1957-2002) of European Centre for Medium-Range Weather Forecasts (ECMWF), which produces wind field and wave field datasets 4 times per day. Sea surface wind speed at 10-meter-height, significant wave heights, mean wave periods and mean wave directions have been derived for this study.At first, the global distribution of wind and waves are examined. It is found that there is a good relationship between wind and waves. The value of correlation coefficient is larger at high latitude than low latitude and at south hemisphere than north hemisphere and the extreme value appears at north Atlantic of both wave and wind. The phenomenon of seasonal variation is also notable. Compared the variations before and after 1977/1978, it is found that the significant wave height displays an increasing trend at high latitude while it become weaken near the edge of continent. The wind shows no significant change.Three extreme value distribution models (P-â…¢, Gumbel, Weibull) are used to fit the extreme value of wind and waves. It is discussed the different effect between the year-extreme-value and the month-extreme-value computed the return period. The P-â…¢curve is chosen to estimate the global return period of 5-yr,10-yr,20-yr,50-yr,100-yr. The biggest value is found in the north Atlantic and the smallest in the equator. Compared with the change as before, especially the 50-yr return period shows an increasing trend in the northwest Pacific of the wind return period, while the 100-yr return period has no change. The variation of significant wave height is rather complicated.Based on the theory that large-scale atmosphere circulation can be indicated by the variation of swells in the ocean, three indexes (wind-wave correlation coefficient, wave age and swell index) are proposed to describe the distribution of global wind waves and swells. Indicated by the zonal and seasonal distribution of the three indexes, it is seen that swells is strengthen at the east boundary of ocean (the'swell pool'exists), and seasonal variability is significant, similar to the previous result of studies. The study of the seasonal variability of the wave direction shows that the swells come from high latitude both in north and south hemisphere. There exists an apparent change before and after 1977/1978. The swell pool become stronger and outward expansive after 1978 in the Pacific, but contracted in the Atlantic. The areas dominated by the wind-wave become smaller after 1978 at the western Pacific, coinciding with the trend that the East Asian monsoon weakens after 1978.For practical significance, the wave conditions of three shipping lines from Shanghai to Vancouver are examined. Counting the frequency of the value bigger than the 5-yr return period of wind and waves for seasons, the result shows that line I is adapt to December, lineâ…¡to autumn and spring. Summer has the lowest wind speed and wave height, and three lines are all fitted.As the change of wave climate plays a significant effect on climate, it is of great significance to do some further detailed study. For some key variational regions, more high-resolution data are needed to support the study.
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