【作者】 丛培秀；

【导师】 管长龙； 郑桂珍；

【作者基本信息】 中国海洋大学 ， 物理海洋学， 2009， 博士

【摘要】 海浪是一种常见的海洋现象，通常指一种小尺度海洋表面重力波，包含风浪和涌浪。可将其看作一系列振幅和相位均不相同的随机简单波动的叠加。海浪在海洋遥感和小尺度海气相互作用中扮演重要角色。中小尺度的短波是海表粗糙度的主要成份。小尺度粗糙度可影响电磁波在海表面的散射。涌浪、内波以及锋面等造成的非均匀流场对于海面小尺度粗糙度有调制作用，这种调制作用也是这些海洋现象微波遥感的基础。通常，使用水动力调制传递函数描述涌浪对短波的影响。有关短波调制的研究对于海洋遥感和海气相互作用意义重大。尽管前人在理论和观测中都获得了不少成就，但是目前对于该调制机制和规律的认识还存在很多问题。为观察短波被长波的调制情况，在实验室产生混合浪并测量波面位移数据。使用本征模态分解法(IMD)方法分析混合浪波面位移数据。与经验模态分解(EMD)方法相比，IMD方法避免了模态混淆。将混合浪数据分解为若干本征模态函数。许多数据最高频本征模态频率范围非常接近，这反映了即使外界条件不同，仍然存在某一特定频率的波动。对比风浪中不同尺度的三个本征模态：风浪主要波、中等波与小尺度波，分析长波对它们的作用。将每个长波周期均分为8个小的位相区间，计算各本征模态在各小区间内的均方位移，以此代表某一模态的能量沿长波的分布。风浪主要波、小尺度波和介于二者之间的中等尺度波，其能量沿长波位相的分布具有不同特征。风浪主要波的能量随长波波陡增加而减少，其分布与长波同相且关于长波波谷对称。中等尺度波的能量则随长波波陡增加而增加，在长波波峰迎风面略微高于背风面。小尺度风浪的能量随着风速和长波波陡的增加而增加，随着风区长度的增加而减少，在长波波峰迎风面明显高于背风面。风浪能量分布在长波波峰迎风面高于背风面，具有不对称特征。这一特征主要由小尺度波的能量分布体现。考虑能使短波能量分布发生相移的各种影响因素，结合观测，可以认为长波遮拦效应是导致短波能量分布不对称的主要原因。长波的轨道流场导致了多普勒效应。对于给定波数，短波表观频率在长波一周期内经过加权平均的值相对于固有频率产生了净降低量。在长波不同位相，同样的表观频率对应的固有频率不同。分析短波谱的调制传递函数随波数的变化，结果显示，最高频模态内各种尺度的短波，其所受调制几乎不随波数变化。如此一来，最高频模态所受调制可代表其包含的各种尺度的小波所受的调制。对现有调制模式和相关理论综合分析的基础上，考虑了长波通过风应力对小波的影响，提出了一个新的理论调制模型。模型结果显示，对于传播方向与风向相同的波浪，短波能量的最大值位于长波波峰迎风面；对于高频小波，其调制随波数变化不大。更多还原

【Abstract】 The Study of Modulation of Short Waves by the Long WavesAbstractWave is a normal phenomenon on the ocean and it affects the living of humandirectly.Usually it is the name of surface gravity wave concluding swell and windwaves which are relatively short.And it could be seen as a sum of waves of differentphases and amplitudes.Waves play an important role in ocean remote sensing and air-sea interaction.Ocean surface roughness of ocean is contributed mostly by intermediate and smallscale surface waves.The non-uniform flows caused by some phenomenon such asswells and fronts could modulate small-scale roughness.And this modulation is alsothe foundation of the microwave remote sensing to these phenomenon.Hydrodynamicmodulation transfer function is used to describe the effect of long waves to the shortwaves.The research about wave modulation is very important.During severaldecades a lot of improvements have been made and a lot of important facts are found.However the mechanism of wave modulation is not well understood yet.Experiments were conducted in the laboratory to observe the modulation of shortwind waves by mechanically generated monochromatic long waves.The surfaceelevations as well as the surface gradients are measured.Some alterations are made tothe Empirical Mode Decomposition (EMD) approach to avoid the blending ofIntrinsic Mode Function (IMF).In the altered mode decomposition approach,the IMFdecomposition is done in frequency space instead of in time domain.With this method,every surface elevation record is decomposed into a few IMFs.The high frequencyIMFs of the same ordinal number extracted from different wave records have almostidentical frequency ranges,therefore represent the surface undulations of a particularfrequency scale under different wave conditions.The squared elevations of each high frequency IMF are phase averaged to find its variation along the long wave profile.Itis found that the energy of high frequency waves are asymmetry on the surface oflong wave,with its maximum occurs at the upwind quadrants of the long wave crests.In view of the different phase shifts induced by various modulation mechanisms,together with the above observations,we credit the asymmetric distribution ofsmall-scale wave energy on long wave profile mainly to the wind sheltering effect oflong waves.The orbital velocity provide a background current to the short waves.And theDoppler effects should be noticed when the wave number spectrum are transferred tothe frequency spectrum.The advection of the wave number component by the orbitalcurrent of background waves produces a net downshift in the encounter frequency.After some theoretical analysis of recent modulation model and mechanisms,anew modulation model is made.This model connects wind stress to the spectrum ofshort waves.And calculation results from this model show that when a train of longwave travels with the wind,the maximums of short wave spectrum occurs at theupwind quadrants of the crests of the long wave.And the modulation of the shortwave changes little with the wave numbers.更多还原