Preprints
https://doi.org/10.5194/acp-2021-905
https://doi.org/10.5194/acp-2021-905

  03 Nov 2021

03 Nov 2021

Review status: this preprint is currently under review for the journal ACP.

Characterization of transport from the Asian summer monsoon anticyclone into the UTLS via shedding of low-potential vorticity cutoffs

Jan Clemens1,4, Felix Ploeger1,2, Paul Konopka1, Raphael Portmann3, Michael Sprenger3, and Heini Wernli3 Jan Clemens et al.
  • 1Institute for Energy and Climate Research: Stratosphere (IEK–7), Forschungszentrum Jülich, Jülich, Germany
  • 2Institute for Atmospheric and Environmental Research, University of Wuppertal, Wuppertal, Germany
  • 3Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland
  • 4Jülich Supercomputing Centre, Forschungszentrum Jülich, Jülich, Germany

Abstract. Air mass transport within the summertime Asian monsoon circulation provides a major source of anthropogenic pollution for the upper troposphere and lower stratosphere (UTLS). Here, we investigate the quasi-horizontal transport of air masses from the Asian summer monsoon anticyclone (ASMA) into the extratropical lower stratosphere and their chemical evolution. For that reason, we developed a method to identify and track the air masses exported from the monsoon. This method is based on the anomalously low potential vorticity (PV) of these air masses (tropospheric low–PV cutoffs) compared to the lower-stratosphere, and uses trajectory calculations and chemical fields from the Chemical Lagrangian Model of the Stratosphere (CLaMS). The results show evidence for frequent summertime transport from the monsoon anticyclone to mid-latitudes over the North Pacific, even reaching high latitude regions of Siberia and Alaska. Most of the low–PV cutoffs related to air masses exported from the ASMA have lifetimes shorter than one week (about 90 %) and sizes smaller than 1 percent of the northern hemisphere (NH) area. The chemical composition of these air masses is characterised by carbon monoxide, ozone and water vapour mixing ratios at an intermediate range between values typical for the monsoon anticyclone and the lower-stratosphere. The chemical evolution during transport within these low–PV cutoffs shows a gradual change from characteristics of the monsoon anticyclone to characteristics of the lower stratospheric background during about one week, indicating continuous mixing with the background atmosphere.

Jan Clemens et al.

Status: open (until 15 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Jan Clemens et al.

Jan Clemens et al.

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Short summary
Highly polluted air flows from the surface to higher levels of the atmosphere during the Asian summer monsoon. At high levels the air is trapped within an eddy. Here, we study how air masses can leave the eddy within eddy cutoffs, how they distribute and how their chemical composition changes. We found evidence for transport from the eddy to higher latitudes over the North Pacific and even Alaska. During transport trace gas concentrations within cutoffs changed gradually, showing steady mixing.
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