Micrometeorology: theory and measurements of ground-air exchange

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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).**