Consideration of Lifetimes of Tracers for the Determination of Stratospheric Age Spectra and the Brewer Dobson Circulation (CoLiBri)

该项目的目标是探索在考虑示踪剂寿命的情况下，使用长寿命的痕量物质来限制平流层环流。通过迈克尔逊被动大气探测干涉仪（MIPAS）测量SF6、CFC-11、CFC-12、HCFC-22、CH4、N2O和H2O的全球分布。从SF6分布推断平流层空气的年龄是直接的，因为没有平流层汇，并且已经用于评估布鲁尔-多布森环流的强度。其他示踪剂用于此目的更具挑战性，因为必须考虑其特定的使用寿命。由于这些物种的分解取决于海拔和纬度，它们的有效寿命反过来取决于布鲁尔-多布森环流的速度。本项目应按下列步骤处理这一问题：(a)将开发一种与海拔和纬度有关的示踪剂寿命参数化方法，以便使这些气体可用作年龄示踪剂；(b)根据MIPAS SF6测量所得的与纬度和高度有关的空气分布年龄，将推断出环流和混合模式；(c)根据这些环流和混合模式以及当地寿命估计，将推断出示踪剂分布，并与MIPAS测量的示踪剂分布进行比较；(d)将分析计算和测量的示踪剂分布之间的差异，以确定对混合和输送过程的不适当假设。

The goal of this project is to explore the use of long-lived trace species to constrain stratospheric circulation under consideration of tracer lifetimes. From Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measurements global distributions of SF6, CFC-11, CFC-12, HCFC-22, CH4, N2O and H2O are available. The inference of age of stratospheric air from SF6 distributions is straight forward since there are no stratospheric sinks, and has already been performed to assess the intensity of the Brewer Dobson circulation. The use of the other tracers for this purpose is more challenging, since their specific lifetimes have to be considered. Since the decomposition of these species is altitude and latitude-dependent, their effective lifetimes depend in turn on the velocity of the Brewer Dobson circulation. This project shall tackle this problem in the following steps: (a) An altitude- and latitude-dependent parametrization of tracer lifetimes will be developed, in order to make these gases usable as age-tracers; (b) from latitude- and altitude dependent age of air distributions derived from MIPAS SF6 measurements, circulation and mixing patterns will be inferred; (c) on the basis of these circulation and mixing patterns and local lifetime estimates, tracer distributions will be deduced and compared to the tracer distributions measured by MIPAS; (d) discrepancies between calculated and measured tracer distributions will be analyzed to identify inappropriate assumptions on mixing and transport processes.