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| Applying Statistical State Dynamics to Explain Spontaneous Shear/Buoyancy Layering in Stratified Turbulence | |
| 项目编号 | 1640989 |
| Brian Farrell | |
| 项目主持机构 | Harvard University |
| 开始日期 | 2017-05-15 |
| 结束日期 | 04/30/2022 |
| 英文摘要 | This research aims at advancing a new approach to explaining formation of small-scale horizontal structure in the shear and buoyancy fields of stratified turbulence in the atmosphere based on direct solution of the statistical state dynamics (SSD) equations. Direct solution of the SSD equations is a new approach to investigating the dynamics of turbulent flows that makes accessible to study mechanisms and phenomena in the dynamics that are inaccessible to analysis based on simulations of individual turbulent state realizations or on statistical mean quantities obtained by averaging ensembles of individual turbulent state realizations. Illustrative of such a mechanism is the cooperative instability of turbulence/mean-flow interaction that results in small scale shear and buoyancy layering in the stratified turbulence of both the atmosphere and ocean. This layering instability arises as an analytic bifurcation in the SSD of stratified turbulence while having no analytic counterpart in the dynamics of realizations, although the same layering phenomenon is seen in both SSD and realizations. In this research, SSD will be extended to obtain a theory for the spontaneous emergence of layering in the shear and buoyancy fields of stratified turbulence. The goal is to use SSD to understand the mechanism by which coherent layered structures are formed, maintained and equilibrated by interaction between the incoherent turbulence and the coherent layered structures. Intellectual Merit: The SSD method constitutes a conceptual as well as methodological advance in understanding turbulence in planetary atmospheres. By directly solving the statistical equations for the turbulent state dynamics the underlying coherent structures together with their associated incoherent eddy fields are obtained explicitly allowing e.g. analytic prediction of shear and buoyancy layer formation and of the sensitivity of the layer structure and its associated turbulent fluxes to changes in system parameters. Direct solution of the SSD equations reveals that shear/buoyancy layering and the associated turbulence is supported as a novel dynamical state in which coherent layered structures interact in a synergistic manner with small-scale turbulence to produce emergent layering instabilities leading to finite amplitude coherent equilibria in the shear/buoyancy/turbulence fields. The SSD approach allows exploration of these new cooperative dynamical regimes by providing analytic and numerical methods for obtaining turbulent statistical equilibria directly from the SSD of the turbulence. Broader Impacts: SSD allows analytical exploration of mechanisms by which coherent components of turbulence interact with incoherent components synergistically to produce emergent dynamical phenomena. The concepts and methods being developed are widely applicable to deepening understanding of turbulence in a wide variety of physical systems including mechanisms underlying formation and maintenance of coherent structures and regulation of turbulent transport in the atmosphere at all scales from the planetary to the boundary layer. SSD is broadly applicable to the study of a new class of emergent instabilities which are essentially related to mean flow/turbulence interaction but unrelated to laminar flow instability. Among other applications, this instability concept provides an explanation for the phenomenon of abrupt reorganization of atmospheric turbulence as a function of parameter change. Using SSD insight can be gained into the role of eddy fluxes in determining the climate response to boundary forcing (such as SST variation during ENSO events). This capability is important because the direct response to e.g. boundary condition changes can be small compared to the indirect effect brought about by subsequent changes induced in eddy statistics. SSD constitutes a general theory of turbulence in shear flow and among the broader impacts of this work are its application to turbulent phenomena in other physical contexts including plasma turbulence, the turbulence of wall-bounded shear flows and MHD turbulence. The broader impacts of this work also include support of a graduate student in atmospheric dynamics. |
| 资助机构 | US-NSF |
| 项目经费 | $506,652.00 |
| 项目类型 | Continuing Grant |
| 国家 | US |
| 语种 | 英语 |
| 文献类型 | 项目 |
| 条目标识符 | http://gcip.llas.ac.cn/handle/2XKMVOVA/213298 |
| 推荐引用方式 GB/T 7714 | Brian Farrell.Applying Statistical State Dynamics to Explain Spontaneous Shear/Buoyancy Layering in Stratified Turbulence.2017. |
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