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Volume 18, issue 3 | Copyright
Atmos. Chem. Phys., 18, 1457-1474, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Feb 2018

Research article | 02 Feb 2018

Assessing the ability to derive rates of polar middle-atmospheric descent using trace gas measurements from remote sensors

Niall J. Ryan1, Douglas E. Kinnison2, Rolando R. Garcia2, Christoph G. Hoffmann3, Mathias Palm1, Uwe Raffalski4, and Justus Notholt1 Niall J. Ryan et al.
  • 1Institute of Environmental Physics, University of Bremen, Bremen, 28359, Germany
  • 2Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA
  • 3Institute of Physics, University of Greifswald, Felix-Hausdorff-Str. 6, 17489, Greifswald, Germany
  • 4Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden

Abstract. We investigate the reliability of using trace gas measurements from remote sensing instruments to infer polar atmospheric descent rates during winter within 46–86km altitude. Using output from the Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM) between 2008 and 2014, tendencies of carbon monoxide (CO) volume mixing ratios (VMRs) are used to assess a common assumption of dominant vertical advection of tracers during polar winter. The results show that dynamical processes other than vertical advection are not negligible, meaning that the transport rates derived from trace gas measurements do not represent the mean descent of the atmosphere. The relative importance of vertical advection is lessened, and exceeded by other processes, during periods directly before and after a sudden stratospheric warming, mainly due to an increase in eddy transport. It was also found that CO chemistry cannot be ignored in the mesosphere due to the night-time layer of OH at approximately 80km altitude. CO VMR profiles from the Kiruna Microwave Radiometer and the Microwave Limb Sounder were compared to SD-WACCM output, and show good agreement on daily and seasonal timescales. SD-WACCM CO profiles are combined with the CO tendencies to estimate errors involved in calculating the mean descent of the atmosphere from remote sensing measurements. The results indicate errors on the same scale as the calculated descent rates, and that the method is prone to a misinterpretation of the direction of air motion. The true rate of atmospheric descent is seen to be masked by processes, other than vertical advection, that affect CO. We suggest an alternative definition of the rate calculated using remote sensing measurements: not as the mean descent of the atmosphere, but as an effective rate of vertical transport for the trace gas under observation.

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We used model output and instrument data to assess how well polar atmospheric descent rates can be derived using concentration measurements of long-lived gases in the atmosphere. The results indicate that the method incurs errors as large as the descent rates, and often leads to a misinterpretation of the direction of air motion. The rates derived using this method do not appear to represent the mean vertical wind in the middle atmosphere, and we suggest an alternate definition.
We used model output and instrument data to assess how well polar atmospheric descent rates can...