NSFGEO-NERC: Wave-Induced Transport of Chemically Active Species in the Mesosphere and Lower Thermosphere (WAVECHASM)

潮汐、行星波和重力波在确定大气层中层/低热层区域（70 - 120公里）的热结构和大气环流方面起着重要作用。例如，由于重力波耗散引起的纬向环流，夏季中层顶区是大气中最冷的地方。不太为人所知和了解的是，波在垂直成分输运中发挥着同样重要的作用，这是一个基本的大气过程，对105公里左右的湍流层顶以下大气的化学和成分有着深远的影响。当波向上传播时，由于空气压力呈指数下降，它们的振幅增加，导致一部分波变得超绝热和“破裂”。波浪破碎是MLT中湍流的主要来源。波浪及其产生的湍流通过诱导大尺度平流、湍流混合引起的涡流输送、与消散有关的动力输送、非破碎波和与扰动化学有关的化学输送，对垂直成分输送作出贡献。最近出现的令人信服的证据表明，全球化学-气候模式中的动力和化学迁移被大大低估。最近用地面激光雷达技术测量了烧蚀流星产生的Na和Fe原子的垂直通量，其数值比最先进的气候模型大5至10倍。更高的通量得到了太阳系尘埃演化天文模型的支持。也有一个显着的赤字中的模拟浓度的O原子和O3在MLT。这些明显的模型缺陷的最可能的原因是，一小部分重力波谱没有明确地捕获在模型中，因为波长小于模型的水平网格尺度（通常> 100公里），这些小波对垂直传输做出了重大贡献。增加水平分辨率，包括小尺度波传输的影响，直接在全球模式的计算成本-特别是结合化学-目前是prohibiting.The WAVECHASM项目的目的是产生一个参数化，可用于计算垂直传输的所有组件在全球模式。该项目将分四个阶段进行。首先，我们将运行一个全球模型，将区域水平分辨率提高到~ 14 km，以证明短波的重要性。在第二步中，我们将参数化最近的数学处理的动力学和化学输运，这表明，这些输运项可以计算在一个相对简单的方式从每个模型网格框中的波谱。对于第三阶段，我们将组装一个数据库的测量垂直通量的钠，铁（在某些情况下）和热量在6个激光雷达站，钠密度在16个站，和卫星测量钠和其他MLT成分（如O，O3，NOx，CO2）。在最后阶段，新的全球波浪输送模式将运行20年（涵盖这些观测期间），以研究波浪输送对重要的化学活性物种的全球分布和季节变化的影响。一旦Na原子的垂直通量能够与90公里左右的层中Na的丰度相协调，我们将获得对进入大气层的行星际尘埃数量的准确估计，从而限制太阳系尘埃演化的天文模型，并提高我们对这种尘埃在整个大气层中的影响的理解。

Tides, planetary waves and gravity waves play major roles in establishing the thermal structure and general circulation of the mesosphere/lower thermosphere (MLT) region of the atmosphere (70 - 120 km). For example, the summer mesopause region is the coldest place in the atmosphere due to the meridional circulation induced by gravity wave dissipation. Less well known and understood are the equally important roles that waves play in vertical constituent transport, which is a fundamental atmospheric process that has profound effects on the chemistry and composition of the atmosphere below the turbopause at around 105 km.Atmospheric gravity waves are generated by a variety of mechanisms (e.g. orographic forcing, convection, wind shears) in the troposphere and stratosphere. As the waves propagate upwards their amplitudes grow because of the exponentially falling air pressure, causing a fraction of the waves to become superadiabatic and "break". Wave-breaking is the main source of turbulence in the MLT. A final fraction of the wave spectrum can survive and penetrate into the thermosphere.Waves, and the turbulence they generate, contribute to vertical constituent transport by inducing large-scale advection, eddy transport through turbulent mixing, dynamical transport associated with dissipating, non-breaking waves and chemical transport associated with perturbed chemistry. Recently, compelling evidence has emerged that dynamical and chemical transport is significantly underestimated in global chemistry-climate models. The vertical fluxes of Na and Fe atoms, produced from ablating meteors, have recently been measured by the ground-based lidar technique and are 5 to 10 times larger than in a state-of-the-art climate model. The higher fluxes are supported by astronomical models of dust evolution in the solar system. There is also a significant deficit in the modelled concentrations of O atoms and O3 in the MLT. The most likely reason for these apparent model deficiencies is that a fraction of the gravity wave spectrum is not explicitly captured in models because the wavelengths are smaller than the model horizontal grid-scale (typically > 100 km), and these small waves make a major contribution to vertical transport. The computational cost of increasing the horizontal resolution to include small-scale wave transport effects directly in global models - especially incorporating chemistry - is currently prohibitive.The aim of the WAVECHASM project is to produce a parameterization which can be used to calculate all components of vertical transport in a global model. The project will proceed in four stages. First, we will run a global model with the facility to increase the horizontal resolution regionally down to ~ 14 km, in order to demonstrate the importance of short wavelength waves. In the second step we will parameterise a recent mathematical treatment of dynamical and chemical transport, which shows that these transport terms can be computed in a relatively straightforward way from the wave spectrum in each model grid box. For the third stage we will assemble a data-base of measurements of the vertical fluxes of Na, Fe (in some cases) and heat at 6 lidar stations, the Na density at 16 stations, and satellite measurements of Na and other MLT constituents (e.g. O, O3, NOx, CO2). In the final stage, the new global model with wave transport will be run for 20 years (covering the period of these observations), to study the impact of wave transport on the global distribution and seasonal variations of the important, chemically active species. Once the vertical flux of Na atoms can be reconciled with the abundance of Na in the layer around 90 km, we will obtain an accurate estimate of the amount of interplanetary dust entering the atmosphere, and thus constrain astronomical models of dust evolution in the solar system and improve our understanding the impacts of this dust throughout the atmosphere.