01 Feb 2022
01 Feb 2022
Status: this preprint is currently under review for the journal ACP.

Estimation of isentropic stirring and mixing and their diagnosis for the stratospheric polar vortex

Zhiting Wang1, Nils Hase2, Wenshou Tian1, and Mengchu Tao3 Zhiting Wang et al.
  • 1College of Atmospheric Science, Lanzhou University, 730000 Lanzhou, China
  • 2Institute of Environmental Physics, University of Bremen, Bremen, Germany
  • 3Carbon neutrality research center, Institute of Atmospheric Physics, Chinese Academy of Science, China

Abstract. Isentropic stirring and mixing are important processes that determine the distribution of long-lived trace gases in the stratosphere. Stirring stretches tracer contours into filaments and mixing dissipates tracer variance. The combined effects on tracer transport by stirring and mixing are quantified by the effective diffusivity in the modified Lagrangian-mean (MLM) theory that diagnoses tracer transport in an areal coordinate. Here a method is developed to diagnose transport processes based on tracer contours in geographic coordinates. Compared to the MLM theory this method has resolving ability along tracer contours and quantifies stirring and mixing separately. Also, the influence of diabatic motion on the diagnosed stirring is reduced, which is useful for stratospheric analysis where diabatic motion is uncertain. The developed method is validated in a methane simulation experiment. The diagnosed stirring effects are consistent with established knowledge about stratospheric dynamics. Finally, stirring and mixing effects on trace gases in the polar vortex are diagnosed during a northern polar vortex period. According to the diagnosis stirring and mixing always increase the methane concentration in the polar vortex. However, their effects are reversed by vortex movement and deformation in most cases. Only in a few cases, planetary waves can penetrate into the vortex and stirring increases the methane concentration in the vortex. The developed method is readily applicable to diagnose stratospheric transport processes from satellite observed trace gas distributions.

Zhiting Wang et al.

Status: open (extended)

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Zhiting Wang et al.

Zhiting Wang et al.


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Short summary
The distribution of trace gases in the stratosphere impacts the thermal and dynamical structures of the atmosphere. The spatial structure of the trace gases is determined by the residual circulation and stirring and mixing processes. Currently the stirring is purely constrained due to lack of observation. Here we develop a diagnosis for stirring mainly based on the trace gas contour. The method is applied for estimating stirring and mixing effects on methane concentration in a polar vortex.