Seasonality and extent of extratropical TST derived from in-situ CO measurements during SPURT

P. Hoor (1, 2) , C. Gurk (2) , D. Brunner (1) , M. I. Hegglin (1) , H. Wernli (1, 3) , H. Fischer (2)

1 IAC - Institute for Atmospheric and Climate Science [Zürich]
2 MPIC - Max Planck Institute for Chemistry
3 IPA - Institute for Atmospheric Physics [Mainz]

We present airborne in-situ trace gas measurements which were performed on eight campaigns between November 2001 and July 2003 during the SPURT-project (SPURenstofftransport in der Tropopausenregion, trace gas transport in the tropopause region). The measurements on a quasi regular basis allowed an overview on the seasonal variations of the trace gas distribution in the tropopause region over Europe from 35°?75° N to investigate the influence of transport and mixing across the extratropical tropopause on the lowermost stratosphere.

From the correlation of CO and O₃ irreversible mixing of tropospheric air into the lowermost stratosphere is identified. The CO distribution indicates that transport and subsequent mixing of tropospheric air across the extratropical tropopause predominantely affects a layer, which closely follows the shape of the local tropopause. In addition the seasonal cycle of CO₂ illustrates the strong coupling of that layer to the extratropical troposphere. Both, horizontal gradients of CO on isentropes as well as the CO-O₃-distribution in the lowermost stratosphere reveal that the influence of quasi-horizontal transport and subsequent mixing weakens with distance from the local tropopause.

However, at large distances from the tropopause a significant influence of tropospheric air is still evident. The relation between N₂O and CO₂ indicates that a significant contribution of air originating from the tropical tropopause contributes to the background air in the extratropical lowermost stratosphere.

Domaines: Océan, Atmosphère

P. Hoor, C. Gurk, D. Brunner, M. I. Hegglin, H. Wernli, et al.. Seasonality and extent of extratropical TST derived from in-situ CO measurements during SPURT. Atmospheric Chemistry and Physics Discussions, 2004, 4 (2), pp.1691-1726. ⟨hal-00301166⟩