Natural Modes and Time Scales in Atmospheric Chemistry

本项目研究大气化学中的自然模式，定义为大气化学物质浓度的模式。该模式可以包括偶联化学物质（例如甲烷、一氧化碳和羟基自由基）的共变，微量气体（例如氧化亚氮、臭氧）的垂直和/或纬度梯度，或者甚至微量气体在一个位置的季节循环。先前的研究表明，自然模态在数学上是严格的，是化学输运系统的基本性质，不依赖于强迫的方式；一种独特的混合模式被扰动激发到一个单一的物种；大气化学中的真实时间尺度通常不同于稳态寿命；从自然模态可以推导出稳态寿命和模式。因此，在当前的大气化学输运模式中识别自然模态不仅对诊断有用，而且对预测也有用。特别是，用于了解人为排放微量气体（如甲烷、甲基溴或氧化亚氮）对全球臭氧分布的影响的模式已经达到了相当复杂的程度。自然模态分析可以帮助分析模型结果，并解释在停止排放甲基溴等短寿命气体后臭氧消耗恢复延迟的影响。在这个项目的过程中，这种分析技术将进一步发展和扩展到更复杂的一维系统，以及二维和三维系统。＊＊＊

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. ***