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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 15 Nov 2019

Submitted as: research article | 15 Nov 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Observational evidence of moistening the lowermost stratosphere via isentropic mixing across the subtropical jet

Jeffery Langille1, Adam Bourassa1, Laura Pan2, Daniel Letros1, Brian Solheim1, Doug Degenstein1, and Daniel Zawada1 Jeffery Langille et al.
  • 1Institute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, S7N 5E2, Canada
  • 2National Center for Atmospheric Research, Boulder Colorado, 3090 Center Green Drive, CO 80301, USA

Abstract. Isentropic mixing across and above the subtropical jet in the presence of a double tropopause may be a significant mechanism for moistening the lowermost stratosphere. We present an analysis of high spatial resolution two-dimensional measurements of the water vapour distribution that were obtained using the Spatial Heterodyne Observations of Water instrument during a demonstration flight from NASA’s high altitude ER-2 airplane. We focus on a set of measurements from 37° to 44° North, obtained on July 21, 2017 during a flight off the West coast of North America, where the instrument sampled the region above and poleward of the subtropical jet. Analysis of these measurements reveals poleward mixing of moist filaments in the region of a double tropopause. These moist filaments are examined in the context of the meteorological fields in the ECMWF (ERA-interim) model output. It is shown that the observed moist filaments are consistent with isentropic mixing across and above the sub-tropical jet. These new observations provide further evidence that the tropospheric intrusion associated with the double tropopause contributes to moistening of the lowermost stratosphere

Jeffery Langille et al.
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Jeffery Langille et al.
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Short summary
Water vapour (WV) is a highly variable and extremely important trace gas in Earth’s atmosphere. Due to its radiative and chemical properties, it is coupled to the climate in an extremely complex manner. This is especially true in the lowermost stratosphere (LMS). Despite its importance, the physical processes that control mixing and the distribution of WV in the LMS are poorly understood. This study provides observational evidence of moistening the LMS via mixing across the subtropical jet.
Water vapour (WV) is a highly variable and extremely important trace gas in Earth’s...