12 Dec 2022
12 Dec 2022
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Effects of denitrification on the distributions of trace gas abundances in the polar regions: a model-data comparison

Michael Weimer1, Douglas E. Kinnison2, Catherine Wilka3, and Susan Solomon1 Michael Weimer et al.
  • 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
  • 2Atmospheric Chemistry Observations & Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 3Department of Earth System Science, Stanford University, Stanford, CA, USA

Abstract. Polar stratospheric clouds (PSCs) play a key role in the polar chemistry of the stratosphere. Nitric acid trihydrate (NAT) particles have been shown to lead to denitrification of the lower stratosphere. While the existence of large NAT particles (NAT "rocks") has been verified by many measurements especially in the Northern Hemisphere (NH), most current chemistry-climate models use simplified parametrizations, often based on evaluations in the Southern Hemisphere where the polar vortex is stable enough that accounting for NAT rocks is not as important as in the NH. Here, we evaluate the probability density functions of various gaseous species in the polar vortex using one such model, the Whole Atmosphere Community Climate Model (WACCM), and compare these with measurements by the Michelson Interferometer for Passive Atmospheric Sounding onboard the Environmental Satellite (MIPAS/Envisat) and two ozonesonde stations for a range of years and in both hemispheres. Using the maximum difference between the distributions of MIPAS and WACCM as a measure of coherence, we find better agreement for HNO3 when reducing the NAT number density from the standard value of 10−2 used in this model to 5 × 10−4 cm−3 for almost all spring seasons during the MIPAS period in both hemispheres. The distributions of ClONO2 and O3 are not greatly affected by the NAT density. The average difference of WACCM to ozonesondes supports the need to reduce the NAT number density in the model. Therefore, this study suggests to use a NAT number density of 5 × 10−4 cm−3 for future simulations with WACCM.

Michael Weimer et al.

Status: open (until 08 Feb 2023)

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Michael Weimer et al.


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Short summary
We investigate the influence of the number density of nitric acid trihydrate particles on associated trace gases in the lower stratosphere using data from satellite, ozonesondes and simulations by a community chemistry climate model. By comparing probability density functions between observations and model, we find that the standard NAT number density should be reduced for future simulations with the model.