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

潮汐、行星波和重力波在大气中层/低层热层（MLT）区域（70 ~ 120 km）热结构和环流的建立中起主要作用。例如，夏季中层顶区是大气中最冷的地方，这是由于重力波耗散引起的经向环流。不太为人所知和了解的是，波浪在垂直成分输送中发挥着同样重要的作用，垂直成分输送是一个基本的大气过程，对105公里左右的湍流顶以下大气的化学和成分有深远的影响。大气重力波是由对流层和平流层的各种机制（例如地形强迫、对流、风切变）产生的。当波向上传播时，由于空气压力呈指数级下降，它们的振幅增大，导致一小部分波变得超绝热并“破裂”。破波是MLT湍流的主要来源。波谱的最后一部分可以幸存下来并穿透到热层中。波及其产生的湍流通过诱导大尺度平流来促进垂直成分输送，通过湍流混合进行涡流输送，与耗散、非破碎波相关的动力输送，以及与扰动化学相关的化学输送。最近，令人信服的证据表明，动力和化学输运在全球化学-气候模式中被严重低估。由烧蚀流星产生的Na和Fe原子的垂直通量，最近被地面激光雷达技术测量到，比最先进的气候模型大5到10倍。较高的通量得到了太阳系尘埃演化的天文模型的支持。MLT中O原子和O3的模拟浓度也存在显著缺陷。这些明显的模式缺陷最可能的原因是，由于波长小于模式水平网格尺度（通常为100公里），模式中没有明确捕获重力波谱的一部分，而这些小波对垂直传输有主要贡献。提高水平分辨率以直接在全球模型中包括小尺度波输运效应的计算成本——特别是结合化学——目前是令人望而却步的。WAVECHASM项目的目的是产生一个参数化，可用于计算全球模式中垂直输送的所有组成部分。该项目将分四个阶段进行。首先，我们将使用该设施运行一个全球模型，以将区域水平分辨率提高到~ 14 km，以证明短波长的重要性。在第二步中，我们将参数化动力和化学输运的最新数学处理，这表明这些输运项可以以相对直接的方式从每个模型网格框中的波谱中计算出来。在第三阶段，我们将建立一个数据库，其中包括6个激光雷达站的Na、Fe（在某些情况下）和热量的垂直通量测量数据，16个雷达站的Na密度测量数据，以及Na和其他MLT成分（例如O、O3、NOx、CO2）的卫星测量数据。在最后阶段，新的全球模式将运行20年（涵盖这些观测期间），以研究波输运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 km左右的Na丰度相协调，我们将获得进入大气层的行星际尘埃数量的准确估计，从而约束太阳系尘埃演化的天文模型，并提高我们对整个大气中这些尘埃影响的理解。

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.