【作者】 张婕；

【导师】 管长龙；

【作者基本信息】 中国海洋大学 ， 物理海洋学， 2010， 硕士

【摘要】 气候变化问题历来是各个国家最为关注的科学问题,而作为与之密切相关的海洋环境变化问题,尤其是海面风场、波浪场的发展变化也随着技术条件的发展,逐步引起重视并在上个世纪七十年代得到迅速发展。本文总结了波候研究的相关进展,阐述了波候研究意义,并指出波候的发展变化与大尺度大气环流的变异可能存在某种联系,同时针对1977/1978年出现的全球气候跃变讨论了波候特征相应的变化情况。本文利用了欧洲中尺度气象中心(ECMWF)提供的最新的近45年(1957-2002)全球数据资料同化集(ERA-40),该资料集提供每天4次的风场及波浪场的相关数据。本研究从其中提取了海面上10米的风速、有效波高、平均周期、平均波向等数据进行研究。论文首先研究了风速标量和有效波高的全球平均分布,发现风速和有效波高有较好的对应关系,并且高纬度地区比中低纬度强,南半球比北半球强,风速、波高极值出现于南大洋,同时风速和波高均有很强的季节变化特征。通过1977/1978年前后的比较,发现大洋中部高纬度地区的波高值有增加的趋势,而靠近大陆边缘的波高值似乎在减弱,风速的变化不明显。对于风速和有效波高重现期的研究,本文采用了三个常用极值分布函数曲线(皮尔逊Ⅲ型曲线、耿贝尔曲线和威布尔曲线),讨论了样本数据分别为年极值和月极值时对重现期估计结果的影响,并选取了皮尔逊Ⅲ型曲线估计了全球5年、10年、20年、50年和100年的重现期极值,发现风速和有效波高重现期极大值均出现于北大西洋,最小值在赤道区域。同样对其做77/78年前后的变化研究,发现风速重现期在西北太平洋上有增强的迹象,特别是50年一遇的极值,而百年一遇的极值没有发现变化,有效波高的变化比较复杂,全球分别有增强区和减弱区。由于大尺度大气环流的变异预示着大洋中的涌浪存在变异,因此本文首先提出了三个指标(风-浪相关系数、波龄和涌浪指标)来描述全球风浪-涌浪的分布情况,通过三个指标的纬向分布和季节分布分析,本文得出了大洋中的涌浪确实存在长期东向强化的趋势(即存在“涌浪池”),并有强烈的季节变化特征,这与前人的研究结果一致。同时通过对平均波向的季节变化分析,发现大洋中的涌浪来源于南北半球高纬度地区。而77/78年前后的变化也比较显著,太平洋的涌浪池在78年后加强了,并有向外扩张的趋势,而大西洋的涌浪池却明显缩小了,太平洋洋西岸的风浪主宰区在78年后有所减弱,此与东亚季风在78年之后减弱的趋势是一致的。为使本文研究结果具有实用意义,本文选取了三条从我国上海市到加拿大温哥华市的航线,分别对航线上大于5年一遇有效波高和风速极值的频率进行了统计,并分季节表示。结果显示,航线Ⅰ适合冬季航行,而航线Ⅱ适合春秋航行,夏季有效波高和风速都比较弱,三条航线统计结果相当。由于波候的变异对于气候变化有着重要的影响,因此,对其做进一步细致的研究有着重要的意义,特别对于重点变异区域,需要更多的高分辨率数据的支持,对其做更深刻的研究。更多还原

【Abstract】 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-Ⅲ, 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-Ⅲcurve 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, lineⅡto 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.更多还原