Numerical Simulations of Gravity Wave Instabilities, Wave-Wave and Wave Mean Flow Interactions, Momentum Transport, and Spectral Evolution in the Mesosphere and Lower Thermosphere

该项目将进行全面的建模研究，旨在量化重力波（GW）不稳定性动力学和非线性波-波和波-平均流相互作用，这些相互作用驱动能量和动量沉积以及在中间层和低层热层（MLT）的GW频谱内的能量转移。GW动量输运是中高纬地区大尺度环流和热结构的主要驱动因素，在赤道纬度地区也起着重要作用。观测和模拟还表明，GW动量通量受到潮汐和行星波（PWs）的强烈调制，而变化的GW动量通量可以反过来调制这些更大尺度的运动，并将其GW过滤的影响映射到更高的高度。尽管这些过程至关重要，但迄今为止，控制这些大规模响应的GW不稳定性和相互作用动力学仅在非常理想的环境中被量化。在各种大尺度大气环流模式、气候和数值天气预报模式中，通过GW参数化对这些动力学的描述被广泛认为是在许多应用中对这些动力学的较差近似，尽管它们对整个大气的大尺度动力学有重要影响。该项目的目标是充分定义大域和广泛GW光谱的各种不稳定动力学，以提供对最重要组成部分的批判性理解，并在这些GW影响的参数化设计中提供有价值的指导，这将大大提高依赖于它们的各种天气和气候模型的性能。为了尽可能全面地量化最重要的GW不稳定性和相互作用动力学及其平均和可变响应，将进行非常高分辨率的直接数值模拟（DNS）和大涡模拟（LES），以评估不同不稳定性类别（包括波-波相互作用）之间的竞争，以及在各种环境中，其中一个或另一个在各种GW尺度、频率和振幅中明显占主导地位的情况；局域化GW失稳事件在GW耗散、振幅（和动量通量）约束和光谱演化中的重要性；GW（和平均剪切）叠加对不稳定发生和类型以及湍流混合和输运的影响。该项目旨在对GW动量沉积、光谱演化以及MLT的平均和大尺度强迫提供更定量的动力学表征。

This project will perform comprehensive modeling studies intended to quantify gravity wave (GW) instability dynamics and nonlinear wave-wave and wave-mean flow interactions that drive energy and momentum deposition and energy transfers within the GW spectrum in the mesosphere and lower thermosphere (MLT). GW momentum transport is the major driver of the large-scale circulation and thermal structure of the MLT at middle and high latitudes and appears to play an important role at equatorial latitudes. Observations and modeling also suggest that GW momentum fluxes are strongly modulated by tides and planetary waves (PWs) and that variable GW momentum fluxes can in turn modulate these larger-scale motions and map the effects of their GW filtering to much higher altitudes. Despite the critical importance of these processes, the GW instability and interaction dynamics controlling these large-scale responses have been quantified only in very idealized environments to date. The descriptions of these dynamics via GW parameterizations in various large-scale general circulation model, climate, and numerical weather prediction models are widely recognized to be poor approximations of these dynamics in many applications, despite their important influences on larger-scale dynamics throughout the atmosphere. The goal of the project is to define the various instability dynamics for large domains and broad GW spectra sufficiently well to provide a critical understanding of the most important components and guidance that is of value in the design of parameterizations of these GW influences that would substantially improve the performance of the various weather and climate models that depend on them. To quantify the most important GW instability and interaction dynamics and their mean and variable responses as fully as possible, very high resolution direct numerical simulations (DNS) and large-eddy simulations (LES) will be done in order to assess the competition between different instability classes (including wave-wave interactions) and the circumstances where one or the other is clearly dominant for various GWs scales, frequencies, and amplitudes in various environments; the importance of localization of GW instability events in GW dissipation, amplitude (and momentum flux) constraints, and spectral evolution; the consequences of GW (and mean shear) superposition for instability occurrence and type and turbulent mixing and transport. The project aims to provide a more quantitative characterization of these dynamics on GW momentum deposition, spectral evolution, and mean and large-scale forcing of the MLT.