基于卫星数据改进计算白冠覆盖率的模型

本文基于白冠覆盖率的历史研究,总结了计算白冠覆盖率的参数化方案和海浪破碎统计模型,并分析比较其优缺点。通过结合基于卫星数据的参数化公式,利用最优拟合的方法,得到不同限制条件下模型中的系数C_en和n。通过分析考虑海浪破碎条件,确定了适用于一般海浪状况的系数值。通过比较白冠覆盖率的卫星数据和原始模型的模拟结果,可知改进后模型的结果更合理,同时与历史研究结论相符。文中还分析了从1998年到2008年十年平均的全球白冠覆盖率的季节性分布特征。在中高纬度海域,全年白冠覆盖率的值最大,而在低纬度和赤道海域,白冠覆盖率小于0.5%,全球白冠覆盖率的平均值大约为1% ~3%。北半球中高纬度海域的白冠覆盖率的季节性变化显著大于南半球。     

海洋环境因素对白冠覆盖率的影响及其数值估算

波浪破碎是一个强非线性过程,破碎时产生的大量气泡在海面上表现为白冠,白冠覆盖率是刻画波浪破碎一个重要参数。研究表明,白冠覆盖率与海上风速、海浪状态和大气稳定度等多种海洋环境因素有关。综合前人的观测数据,本文给出了更为可靠的依赖风速的白冠覆盖率公式,发现海水温度越高,白冠覆盖率越大。提出了以波浪破碎耗散函数为参数的白冠覆盖率公式,同时发现波龄小于某个临界值时,白冠覆盖率随波龄增大,波龄大于临界值时,白冠覆盖率保持不变,该临界值随风速增大而减小。     

白冠破碎空间分布模式的统计推断

白冠空间分布模式分析是海浪破碎统计研究的前提。本文提出利用空间点过程统计分析工具研究白冠空间分布模式,并结合实际白冠破碎观测录像资料,计算观测数据的L-函数和K-函数,与Markov chain Monte Carlo(MCMC)方法生成的模拟包迹进行比较,推断得出其白冠空间分布模式类型为空间齐次Poisson过程。研究表明空间点过程统计分析工具适用于白冠破碎研究。     

非线性海浪波面斜率的概率分布和白浪覆盖率的计算

依二维非线性海浪模型,在三阶近似下,利用特征函数展开技术和直接求矩的方法,导出了波面斜率的概率分布。据此分布,利用极限表面斜率判据,给出了白浪覆盖率的一个解析模式。该模式依赖于3个参量,这3个参量可由线性意义下的海浪波数谱及三类波-波相互作用所确定。     

海洋飞沫参数化方案在台风数值模拟中的应用

海洋飞沫作为海气相互作用的重要因子, 在台风的发生、发展过程中扮演着重要角色.将Fairall和Andreas海洋飞沫参数化方案加入到WRF模式中对两个台风--"珊珊"、"桑美"进行了模拟, 以研究不同海洋飞沫参数化在WRF模式中对台风模拟效果的影响.结果表明, 加入Fairall方案后潜热通量、感热通量得到很大程度的加强, 使得台风的热力结构得以改变, 暖心结构十分明显, 从而影响了动力场结构.相对涡差解释了台风移动路径变化的原因, 热成散度、涡度以及水汽通量的改变影响了台风的强度.Andreas方案由于界面通量算法在考虑海表面动量粗糙度、热力粗糙度及水汽粗糙度随风速、相对湿度变化的情况下, 得到的潜热通量、感热通量较Fairall方案为弱, 因而台风的强度不强.飞沫参数化方案对模拟台风路径的影响较小.     

一种白浪覆盖率与风要素关系模式

采用Ｇｌａｚｍ ａｎ 提出的“微尺度平均”的方法,在合理选择平均尺度的基础上计算了ＪＯＮＳＷＡＰ谱的四阶矩,并将此结果与Ｓｎｙｄｅｒ提出的白浪覆盖率模式结合,从而建立起依赖于风速和风区两者的半经验、半理论的白浪覆盖率与风要素关系模式。此模式给出的结果与Ｍｏｎａｈａｎ 等汇集的海洋白浪覆盖率测量数据总体符合良好。     

台风"森拉克"的数值模拟研究:海洋飞沫的作用

台风作为一种在海洋上生成和演变的强烈天气现象，除了环境流场、自身结构以及地形等因子对它产生影响外，海气间的热量动量交换也是台风演变过程中不可或缺的因子。台风期间在海气界面生成大量海洋飞沫，这些飞沫在台风边界层的蒸发必然对海气之间的通量传输过程产生影响，进而影响到台风本身的演变。文章将海洋飞沫参数化引入大气中尺度模式中，对2002年16号台风“森拉克”的演变进行了数值模拟研究。结果表明，引入海洋飞沫参数化方案，可使台风期间海气界面的潜热通量增加50％，10m层风速最大值增加30％，从而使模拟台风的强度明显增加，使模拟结果更趋于合理。因此，在台风数值模拟和预报中考虑海洋飞沫的作用是十分必要的。     

台风期间海洋飞沫对海气湍通量的影响研究

本文以2006年9月日本以南海域的台风YAGI为例,应用黑潮延伸体附近的KEO浮标观测资料,并结合卫星遥感等融合资料,分析海洋飞沫在台风不同发展阶段对海气界面间热量通量和动量通量的影响。首先,定量地分析台风期间海洋飞沫对海气热通量的影响。结果表明,在台风YAGI过境期间,海洋飞沫能够显著地加剧海气界面间的热量交换,尤其是潜热交换。海洋飞沫增加的热通量随着风速的增强而增大,随着波龄的增大而减小。随后,通过动量分析表明,在台风YAGI过境期间,海洋飞沫显著地增强了由大气向海洋的动量转移。当风速达到台风量级后,考虑海洋飞沫所增加的动量通量与界面动量通量大小相当,同时,在此风速条件下,海洋飞沫在海气界面形成极限饱和悬浮层,抑制风到海表面的动量转移,导致海气界面间总的动量通量的增长率随之减小。     

海洋飞沫对热带气旋边界层结构的影响

将海洋飞沫参数化引入到一个高分辨率、非静力中尺度WRF模式中,对0908号热带气旋Morakot进行数值模拟,探讨了海洋飞沫对热带气旋Morakot边界层结构和强度的影响。模拟结果表明:采用新参数化后,对热带气旋Morakot的强度预报有改进,但对热带气旋移动路径改进不大;其次,通过对边界层过程的改进,使得眼墙区域的平均径向风速、切向风速、温度、相对湿度、垂直风速、热通量,降水等物理量均有增强,各物理量的贡献对热带气旋Morakot强度和结构变化的影响十分重要。     

基于拟层流风波生成机制的海浪谱模型

海浪谱的能量可以视为由具有不同相速度的谐波携带的能量所组成。基于对风波形成、发展过程的认识,认为各组成谐波的能量由谐波自平均风摄取而来,由此根据拟层流模型推导出谐波能量密度的计算公式,建立以等效风速和峰值频率等为基本参数的海浪谱模型——随机Fourier函数模型,并给出了确定谐波频率、波长、相速度、振幅以及等效风速等模型参数的原则和计算方法。在59个实测样本谱基础上,采用随机建模方法确定模型参数的取值及其概率分布。结果表明,海浪谱模型可以很好地预测谱能,所计算的物理谱与实测谱均值吻合良好。     

Probability distribution of surface slope for nonlinear random sea waves and calculation of whitecap coverage

Based on the nonlinear model of two-dimensional random sea waves, a statistical distribution of wave surface slope exact to the third order is derived by using the expansion of the characteristic function and direct calculations of each order moment. Based on the distribution of wave surface slope derived in this paper, a whitecap coverage is proposed by using the limit surface slope as a criterion of wave breaking. The whitecap coverage expressed by the model depends on three parameters which can be determined in principle by the linear wave spectrum and three kinds of wave-wave interaction.     

An analytically derived whitecap coverage model

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Parameterization of Wave Breaking Probability and Whitecap Coverage

1 .Introduction Wave breaking and associated whitecapping have long beeninteresting due totheir close relationto many fields of ocean study,including air-sea interaction,remote sensing,ocean engineering,aswell as wave dynamics .The breaking probabilityBan…     

Effects of wave age and air stability on whitecap coverage

The paper considers the effects of wave age and air stability on the whitecap coverage at sea. This is made by using the logarithmic mean wind velocity profile including a stability function as well as adopting a recent wave age dependent sea surface roughness formula. The results are valid for wind waves in local equilibrium with the steady wind. Examples of results demonstrate clear effects of wave age and air stability on the whitecap coverage. Comparisons are also made with field measurements by Sugihara et al. [Sugihara, Y., et al., 2007. Variation of whitecap coverage with wave-field conditions. J. Mar. Syst. 66, 47–60], representing unstable air stability conditions. Although the data basis is limited, the wave age independent Charnock sea roughness based predictions capture the main features of the observed whitecap coverage, suggesting a stronger dependence on air stability than on wave age in the data.     

Impacts of sea spray on the boundary layer structure of Typhoon Imbudo

High winds in a typhoon over the ocean can produce substantial amounts of spray in the lower part of the atmospheric boundary layer, which can modify the transfer of momentum, heat, and moisture across the air-sea interface. However, the consequent effects on the boundary layer structure and the evolution of the typhoon are largely unknown. The focus of this paper is on the role of sea spray on the storm intensity and the structure of the atmospheric boundary layer. The case study is Typhoon Imbudo in July 2003. The results show that sea spray tends to intensify storms by increasing the sea surface heat fluxes. Moreover, the effects of sea spray are mainly felt in boundary layer. Spray evaporation causes the atmospheric boundary layer to experience cooling and moistening. Sea spray can cause significant effects on the structure of boundary layer. The boundary-layer height over the eyewall area east to the center of Typhoon Imbudo was increased with a maximum up to about 550 m due to sea spray, which is closely related with the enhancements of the heat fluxes, upward motions, and horizontal winds in this region due to sea spray.     

Effects of surface waves and sea spray on air–sea fluxes during the passage of Typhoon Hagupit

Air–sea exchange plays a vital role in the development and maintenance of tropical cyclones(TCs). Although studies have suggested the dependence of air–sea fluxes on surface waves and sea spray, how these processes modify those fluxes under TC conditions have not been sufficiently investigated based on in-situ observations.Using continuous meteorological and surface wave data from a moored buoy in the northern South China Sea,this study examines the effects of surface waves and sea spray on air–sea fluxes during the passage of Typhoon Hagupit. The mooring was within about 40 km of the center of Hagupit. Surface waves could increase momentum flux to the ocean by about 15%, and sea spray enhanced both sensible and latent heat fluxes to the atmosphere,causing Hagupit to absorb 500 W/m~2 more heat flux from the ocean. These results have powerful implications for understanding TC–ocean interaction and improving TC intensity forecasting.     

A Whitecap Coverage Model Based on the Surface Slope For Criterion of Wave Breaking

Using the limit surface slope as a criterion of wave breaking,a simple model for estimatingthe spatial fraction of breaking surface of sea at an instant,which is regarded as the whitecap coverge inthis paper,is analytically derived from the probability density of surface slope based on Gaussianstatistics.The resulting fraction is found depending on the fourth moment of wave spectum,m_4,as well asthe critical threshold of surface slope.By expressing the fourth moment in terms of the Neumannspectrum,a formula linking the fraction and wind speed for fully developed sea states is obtianed.Anotherformula relating the fraction to both wind speed and fetch(or duration)is achieved by expressing m_4 interms of the Krylov spectrum and applying the empirical relationships used in the SMB ocean wave pre-dicting technique.A comparison between these results and the field data of whitecap coverage collected byMonahan and O＇Muircheartuigh shows an encouraging agreement.