Atmospheric and oceanic turbulence

所请求的资金用于研究大气和海洋流体湍流，主要采用高分辨率数值模拟，但以微扰分析技术、统计闭合理论和量纲分析为指导。湍流显然是流体动力学中最复杂的突出问题，更好地理解它对于改进高分辨率环境和气候模型是绝对必要的。对大规模建模者来说，至关重要的是地球物理流动如何混合各种量，而这些量的分布是社会如此关注的。此外，许多研究领域，包括污染物扩散建模、城市气象和风能发电，都需要小时时间尺度和10到100公里长度尺度的统计预测技能，我和我的团队一直在探索更复杂的动态。本申请只涉及基础研究问题。申请人亦非常重视与数值天气预报界和香港一个新的城市气象小组的长期合作，以及他们的HQP和实物资助。******特别地，旋转和分层对经典湍流统计的影响将被检查。这门学科属于在某些极限下对波浪和漩涡的研究，经典理论表明，大尺度的温度、压力和风是平衡的，这样高频波的振幅就很低。近十年来，世界范围内的许多研究小组在比大气和海洋中的斜压涡旋更小的尺度上，对湍流的波浪/涡旋性质进行了表征，取得了快速进展。这是在实地观察、实验室实验、数值模拟和理论方面，这一领域目前的活力是由这样一个事实来解释的，即现实的模型现在已经达到了解决方案，而我们对动力学的缺乏了解不利于进展。*** ***我自己的小组已经发现，在旋转不那么重要的小规模体制中，平衡动力学是不可能存在的。在这里，存在一个单一的湍流时间尺度，波/涡分解被打破。在更大的尺度上，高阶平衡动力学引起-3能谱的陡波数，而平衡的破坏产生与观测一致的-5/3能谱。自发不平衡主要发生在应变大的区域。下一步是制定参数化方案，在正确的时间准确地在正确的地点消耗平衡的能量，而不是基于长期的全球平均值。第二个新奇之处是，我们现在包括了实际的垂直不均匀性，如地面、海洋表面、温跃层和对流层顶等，有人建议我们现在准备包括波在边界层湍流中的作用

The requested funds are for the study of atmospheric and oceanic fluid turbulence mainly employing high-resolution numerical simulations, but guided by perturbative analytical techniques, statistical closure theories and dimensional analysis. Turbulence is clearly the most complex outstanding problem in fluid dynamics and understanding it better is absolutely necessary to improve high-resolution environmental and climate models. Of crucial importance to large-scale modellers is how geophysical flows mix the various quantities whose distributions are of such great concern to society. In addition, many fields of study including pollutant dispersion modelling, urban meteorology and wind energy generation, require statistical forecast skill on time scales of hours and length scales of 10's to 100's of kilometers, where my group and I have been exploring the more complicated dynamics that prevail. This application concerns only the fundamental research issues. The applicant also values his longstanding collaborations with the numerical weather prediction community and a new urban meteorology group in Hong Kong, along with their HQP and in-kind funding.****** Specifically, the influence of rotation and stratification on classical turbulence statistics will be examined. The subject belongs to the family of studies of waves and vortices in some limits and classical theory suggests that large-scale temperature, pressure and wind are balanced in such a way that high-frequency waves have low amplitudes. The last 10 years have seen rapid progress by many groups worldwide in characterising the wave/vortex nature of turbulence at scales smaller than those of the baroclinic eddies in both atmosphere and ocean. This has been in field observations, lab experiments, numerical simulation and theory and the current vigour in the field is explained by the fact that realistic models have now reached resolutions where our lack of dynamical understanding is detrimental to progress. *** *** My own group has found that balance dynamics cannot exist in the small-scale regime where rotation is less important. Here, there exists a single turbulent time scale and wave/vortex decompositions break down. At larger scales higher-order balance dynamics give rise to steep wave number to the -3 energy spectra, whereas a breakdown of balance yields a -5/3 spectrum consistent with observations. Spontaneous imbalance occurs primarily in regions of large strain. The next step is to formulate parameterisation schemes that dissipate balanced energy in precisely the right locations at the right time, instead of being based on global averages over long periods. The second novelty is that we now include realistic vertical inhomogeneities, such as the ground, ocean surface, thermocline and tropopause, etc., where it is proposed that we are now ready to include the role of waves in boundary-layer turbulence.**