Natural Modes and Time Scales in Atmospheric Chemistry

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9632633 Prather This project addresses natural modes in atmospheric chemistry, defined as patterns in the concentrations of atmospheric chemical species. The pattern can include co-variation of coupled chemicals (e.g., methane, carbon monoxide, and hydroxyl radical), the vertical and/or latitudinal gradients in trace gases (e.g., nitrous oxide, ozone), or even the seasonal cycle of a trace gas at a location. Prior work has show that natural modes are a mathematically rigorous, fundamental property of the chemical transport system and do not depend on the manner of forcing; a unique mixture of modes is excited by perturbations to a single species; true time scales in atmospheric chemistry are often different from the steady-state lifetimes; and the steady-state lifetime and pattern can be derived from the natural modes. Therefore, identification of the natural modes in current atmospheric chemical transport models is useful for diagnostics, but also for prediction. In particular, models used for understanding the impact of anthropogenic emissions of trace gases such as methane, methyl bromide, or nitrous oxide on global ozone distribution have reached a large degree of complexity. Natural mode analysis could help in analyzing model results and explain effects such delayed recovery of ozone depletion after stopping emissions of a short-lived gas like methyl bromide. In the course of this project, this analysis technique will be further developed and extended to more complex 1-dimensional, as well as 2- and 3-dimensional systems. ***