Description: Impact of Lagrangian transport on lower-stratospheric transport timescales in a climate model

This title appears in the Scientific Report : 2020

Impact of Lagrangian transport on lower-stratospheric transport timescales in a climate model

We investigate the impact of model trace gas transport schemes on the representation of transport processes in the upper troposphere and lower stratosphere. Towards this end, the Chemical Lagrangian Model of the Stratosphere (CLaMS) was coupled to the ECHAM/MESSy Atmospheric Chemistry (EMAC) model a...

Personal Name(s):	Charlesworth, Edward J. (Corresponding author)
	Dugstad, Ann-Kristin / Fritsch, Frauke / Jöckel, Patrick / Plöger, Felix
Contributing Institute:	John von Neumann - Institut für Computing; NIC JARA - HPC; JARA-HPC Stratosphäre; IEK-7
Published in:	Atmospheric chemistry and physics, 20 (2020) 23, S. 15227 - 15245
Imprint:	Katlenburg-Lindau EGU 2020
DOI:	10.5194/acp-20-15227-2020
Document Type:	Journal Article
Research Program:	Chemical Lagrangian Model of the Stratopshere (CLaMS) Chemisches Lagrangesches Modell der Stratosphäre (CLaMS) Composition and dynamics of the upper troposphere and middle atmosphere
Link:	Get full text OpenAccess
	Publikationsportal JuSER

Please use the identifier: http://hdl.handle.net/2128/26643 in citations.
Please use the identifier: http://dx.doi.org/10.5194/acp-20-15227-2020 in citations.

We investigate the impact of model trace gas transport schemes on the representation of transport processes in the upper troposphere and lower stratosphere. Towards this end, the Chemical Lagrangian Model of the Stratosphere (CLaMS) was coupled to the ECHAM/MESSy Atmospheric Chemistry (EMAC) model and results from the two transport schemes (Lagrangian critical Lyapunov scheme and flux-form semi-Lagrangian, respectively) were compared. Advection in CLaMS was driven by the EMAC simulation winds, and thereby the only differences in transport between the two sets of results were caused by differences in the transport schemes. To analyze the timescales of large-scale transport, multiple tropical-surface-emitted tracer pulses were performed to calculate age of air spectra, while smaller-scale transport was analyzed via idealized, radioactively decaying tracers emitted in smaller regions (nine grid cells) within the stratosphere. The results show that stratospheric transport barriers are significantly stronger for Lagrangian EMAC-CLaMS transport due to reduced numerical diffusion. In particular, stronger tracer gradients emerge around the polar vortex, at the subtropical jets, and at the edge of the tropical pipe. Inside the polar vortex, the more diffusive EMAC flux-form semi-Lagrangian transport scheme results in a substantially higher amount of air with ages from 0 to 2 years (up to a factor of 5 higher). In the lowermost stratosphere, mean age of air is much smaller in EMAC, owing to stronger diffusive cross-tropopause transport. Conversely, EMAC-CLaMS shows a summertime lowermost stratosphere age inversion – a layer of older air residing below younger air (an “eave”). This pattern is caused by strong poleward transport above the subtropical jet and is entirely blurred by diffusive cross-tropopause transport in EMAC. Potential consequences from the choice of the transport scheme on chemistry–climate and geoengineering simulations are discussed.