中间层大气行星波局地激发机制研究

Planetary waves can exert great impacts on the structures and variations of the middle and upper atmosphere. Planetary waves observed in the middle and upper atmosphere could be generated in the troposphere, then propagate upward and reach the observation altitude, or be excited in situ by the instability of mesospheric gravity waves. Our understanding of the latter excitation mechanism need to be advanced. Based on the built three-dimensional/two-dimensional fully- nonlinear dynamical numerical model in spherical/local coordinates for the compressible atmosphere,and utilizing the combination of satellite (SABER, HRDI, and COSMIC) and radiosonde observational data, we would investigate the physical mechanism and detailed process of mesospheric planetary waves excited in situ by gravity wave instability, as well as the effects of this forcing process on the dynamic and thermodynamic structures of the middel and upper atmophere.We would quantitively study the associated parameter variations of the forced planetary waves, the breaking gravity waves, and the background field during this in situ forcing process, and explore their internal correlations. The seasonal varibility and spatial distribution of the in situ forcing process and its effects, especially the associated energy coupling between different atmospheric regions , and the associated longitudinal variations of the dynamic and thermodynamic structures of the middle and upper atmosphere, would be analyzed in detail. This project research would be helpful to clarify the basic physical mechnisms for the structures and variations of planetary waves in the middle and upper atmosphere, and to further advance our understanding of interaction processes among the planetary waves, gravity waves, and the background field and their effects in the middle and upper atmosphere.

行星波对中高层大气的结构和变化有重要影响。在中高层大气中观测到的行星波除了可能是在对流层激发而向上传播至观测高度外，还有可能是通过中间层重力波的不稳定而局地激发。人们对后一种激发机制的理解尚有待深入。本项目拟在我们已经建立的三维全球和二维局地可压大气的全非线性动力学数值模式的基础上，结合SABER、HRDI、COSMIC卫星观测和无线电探空资料，研究中间层重力波不稳定局地激发行星波的物理机制和细致过程，以及这种激发过程对中高层大气动力学和热力学结构的影响。定量研究激发过程中行星波、重力波和背景场的参数变化及其内在关联；细致分析该激发过程及其效应的季节变化和空间分布，特别是与该过程关联的大气不同层区的能量耦合、中高层大气动力学和热力学结构的经度变化等。该项目的研究有利于我们辨明中高层大气行星波结构和变化的基础物理机制，进一步理解中高层大气中行星波-重力波-背景之间的相互作用过程及其效应。

行星波作为一种全球尺度的大气波动，对低层和中高层大气的结构和变化都有着重要影响。行星波的强迫源主要位于低层大气，但在中高层大气中也存在局地激发源。低层大气中的强行星波会调制局地的重力波活动，这些被调制的重力波向上传播到中间层和低热层区域后将能量和动量释放，在局地激发产生行星波。我们利用地基MST雷达数据联合MERRA数据，给出了香河上空低层大气的主导行星波，即准16天和准10天行星波的基本特征：两者具有类似的季节和高度变化，表明它们具有类似的激发源和耗散过程；两者都在对流层急流高度附近呈现出准垂直驻波结构且向东的传播占优；两者都对对流层急流的形成和维持贡献巨大，并且能够强烈调制对流层急流的大小和所在高度。同时，我们还利用全球的无线电探空数据细致研究了低层大气重力波的空间（纬度和高度）分布和时间（逐月、季节和年际）变化。在观测研究的基础上，我们利用可压大气的全非线性动力学数值模式，模拟了重力波在低层大气中受行星波调制、向上传播到中高层、在中高层破碎激发行星波的完整过程，分析了该过程中波与流的变化、能量与动量的交换。此外，我们还利用地基和卫星观测数据，对准2天行星波的半球差异、短期变化，以及从低层大气向中高层大气的传播进行了研究。在项目执行过程中，我们将模式研究和观测研究紧密结合，并尝试用数值模拟结果和理论估算来解释观测现象，揭示观测现象背后的物理机制，增进了人们对行星波相关的一些大气动力学过程的认识。