Micrometeorology: theory and measurements of ground-air exchange

我的研究主要集中在大气层的最低（大约）100米处，这一层被称为大气表面层（ASL），它对我们生活和活动的许多方面（例如农药喷雾的顺风传播）发挥着至关重要的控制作用。我的计划的最重要的影响是发明，测试和应用一个简单的，非干预方法（“bLS”），用于估计地面空气气体排放量，可以应用在“整个农场”的水平（例如，从牛饲养场的氨排放量）。确定这种通量的能力是重要的，因为在某些管辖区的排放限制是有效的，或悬而未决的，我们的新技术已经在许多国家流行。在班夫举行的温室气体和畜牧业会议上（10月，2010年），我应邀参加了一个关于bLS的研讨会，以估计甲烷排放量，来自38个国家的400多名代表参加了研讨会，其中160人注册了bLS研讨会。 * 我提出了以下（连接）的研究路线，与地面空气交换有关：*a）我的小组已经发展出一种灵敏的新方法，用于确定地面空气通量，通过顺序地引导光束沿着向上和向下倾斜的路径越过源。我将支持研究生测量甲烷，氨和一氧化二氮通量与牛的管理和遗传变异。这将培养学生在这两个技术的工具和理论元素。* B）“拉格朗日随机”（LS）湍流混合模型是“bLS”通量测量技术的核心，因为它用于计算从检测器到源的气体向后（在时间和空间上）的运动。虽然LS模型是环境混合的最新理论，但它并不是一个完成的工作。我和学生们一起为LS模型的理论做出了许多贡献，并建议继续这样做。我们将建立是否最近的建议，延长著名的“朗之万模型”（最初用于解释布朗运动）适用于风运输的湍流ASL。*c）风速和风向随高度变化，我们的bLS方法采用理想化的剖面（由于Monin和Obukhov）。然而，场地缺陷（例如不平坦的地形）会影响这一假设。学生将确定由于风偏离MO剖面，bLS推断的通量在多大程度上变得不准确。* d）通量仪器对逆风表面附近区域进行采样，称为“通量足迹”，能够计算通量足迹至关重要。现有的公式采用了数学技巧，使用“幂律”来表示风速和（其他变量）的高度（z）剖面，而不是正确的（莫宁和奥布霍夫）定律。这使得现有的公式含糊不清。我们将通过扩展Wilson（1982年，边界层气象学）的方法，在风速和涡流扩散率的正确剖面的基础上，开发一种替代的“足迹模型”。23，85-103）。

My research is focused on the lowest (roughly) 100 m of the atmosphere, a layer known as the atmospheric surface layer ("ASL"), and which exerts a crucial control over many facets of our lives and activities (e.g. downwind spread of pesticide sprays). The most consequential impact of my program has been the invention, testing and application of a simple, non-intervening method ("bLS") for the estimation of ground-air gas emissions that can be applied at the "whole farm" level (e.g. ammonia emissions from a cattle feedlot). The capability to determine such fluxes is important because  in some jurisdictions emissions limits are in force, or pending; our new technique is already popular in many countries. At the Greenhouse Gases and Animal Agriculture conference in Banff (Oct., 2010) I gave an invited workshop on bLS for estimating methane emissions, and of the more than 400 delegates from some 38 countries attending, 160 registered for the bLS workshop. ***I propose the following (connected) lines of research, in relation to ground-air exchange:***a) My group has evolved a sensitive new method for determining the ground-air flux by sequentially directing a light beam along upward- and downward-slanting paths over the source. I shall support graduate students to measure methane, ammonia and nitrous oxide fluxes in relation to cattle management and genetic variability. This will train students in both the instrumental and theoretical elements of the technique.***b) A "Lagrangian stochastic" (LS) turbulent mixing model is central to the "bLS" flux measurement technique, for it is used to compute the movement of gas backwards (in time and space) from detector to source. Though the LS model is the state-of-the-art theory for environmental mixing, it is not a finished work. With students I have made numerous contributions to theory of the LS model, and propose to continue doing so. We will establish whether a recent proposal extending the famous "Langevin model" (originally used to explain Brownian motion) usefully applies to wind transport in the turbulent ASL. ***c) Wind speed and direction vary with height, and our bLS method adopts idealized profiles (due to Monin & Obukhov). However site imperfections (e.g. uneven terrain) compromise this assumption. The student will determine to what extent fluxes inferred by bLS become inaccurate, due to winds deviating from the MO profiles.***d) Flux instruments sample a nearby region of upwind surface, known as the "flux footprint," which it is vital to be able to compute. Existing formulae employ a mathematical trick, using "power laws" to represent the height (z) profiles of wind speed and (other variables) instead of the correct (Monin & Obukhov) laws. This makes existing formulae ambiguous. We will develop an alternative "footprint model" based on correct profiles of wind speed and eddy diffusivity, by extending a method of Wilson (1982, Boundary-Layer Meteorol. 23, 85-103).**