CEDAR Postdoc: Analysis and Modeling of Breaking Short Period Gravity Waves and Their Effects on the Dynamic Mesosphere and Lower Thermosphere

该项目将进行模拟和观测研究，以调查在中层和低热层区域实际风和热力条件下短周期重力波的破裂以及由此产生的能量和动量沉积。短周期(5-30分钟)、小尺度(10-100公里)的重力波在整个中高层大气中提供了相当大的一部分波能量。这些波包括水平和垂直传播的波，在较短的周期内，那些被大尺度热结构或风结构引导而水平传播的波。这种波是由一系列过程产生的，包括通常与对流天气系统和雷暴有关的对流层强迫，以及主要由于局部化对流和切变不稳定或非线性共振相互作用造成的原地强迫。通过对重力波对中层顶气辉调制的大量地面观测，结合数值和理论模拟研究，近几十年来对小尺度重力波的产生、传播和方向性/季节性的理解有了显著提高。然而，目前对短周期重力波包的破裂，特别是那些受背景大气结构强烈控制的重力波包的最终能量和动量的沉积，我们知之甚少。该项目将侧重于两个特别的问题，以解决这一认识上的差距：(1)中纬度中间层/低热层的大尺度动态结构如何决定短周期重力波的稳定和破裂？(2)短周期重力波的破裂或消散如何通过动量和能量沉积改变当地的中间层/低热层结构？为了回答这些问题，将进行数值和观测相结合的研究。利用最近建立的重力波传播和气辉调制的二维完全非线性模型，将探讨大气不稳定和波浪破碎在准现实条件下对短周期重力波的作用和影响。这将由气辉图像数据集以及现有的雷达和激光雷达风场数据来补充，以确定背景动力学在短周期波浪破裂和整体大气动态稳定中的作用。该项目的更广泛影响是，它支持了一位新的博士获得者的努力，他开发了一个可供使用的模型。该项目所产生的短周期重力波对能量和动量沉积的量化将有利于中间层/低热层科学。

This project will conduct a modeling and observational study to investigate the breaking of short-period gravity waves and the resulting energy and momentum deposition under realistic wind and thermal conditions in the mesosphere and lower thermosphere region. Short-period ( 5-30 min), small-scale ( 10-100 km) gravity waves provide a significant fraction of wave energy throughout the middle and upper atmosphere. These include waves which propagate horizontally and vertically and, at shorter periods, those which are ducted by large-scale thermal or wind structure to propagate horizontally. Such waves are generated by a broad range of processes, including tropospheric forcing often associated with convective weather systems and thunderstorms, and in situ forcing due primarily to localize convective and shear instabilities, or to nonlinear resonant interactions. Through extensive ground-based observations of mesopause airglow modulation by gravity waves, in conjunction with numerical and theoretical modeling studies, understanding of small-scale gravity wave generation, propagation, and directionality/seasonality has improved significantly over recent decades. However, very little is currently known about the final deposition of energy and momentum via breaking of short-period gravity wave packets, particularly those which are strongly controlled by background atmospheric structure. The project will focus on two particular questions to address this gap in understanding: (1) How does the large-scale dynamic structure of the mid-latitude mesosphere/lower thermosphere dictate the stability and breaking of short-period gravity waves? (2) How does breaking or dissipating short-period gravity waves modify the local mesosphere/lower thermosphere structure through momentum and energy deposition? To answer these questions, a combined numerical and observational study will be carried out. Utilizing recent, two-dimensional, fully-nonlinear models of gravity wave propagation and airglow modulation, the role and effects of atmospheric instability and wave breaking will be explored for short-period gravity waves under quasi-realistic conditions. This will be complemented by airglow image data-sets together with available radar and lidar wind data to determine the role of background dynamics on short-period wave breaking, and overall atmospheric dynamic stability.The broader impact of the project is that it supports the efforts of a new Ph.D. recipient who has developed one of the models to be used. The quantification of energy and momentum deposition by short period gravity waves resulting from this project will benefit mesosphere/lower thermosphere science.