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Volume 16, issue 13
Atmos. Chem. Phys., 16, 8667–8693, 2016
https://doi.org/10.5194/acp-16-8667-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 8667–8693, 2016
https://doi.org/10.5194/acp-16-8667-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 15 Jul 2016

Research article | 15 Jul 2016

A semi-empirical model for mesospheric and stratospheric NOy produced by energetic particle precipitation

Bernd Funke1, Manuel López-Puertas1, Gabriele P. Stiller2, Stefan Versick2,3, and Thomas von Clarmann2 Bernd Funke et al.
  • 1Instituto de Astrofísica de Andalucía, CSIC, Apdo. 3004, 18008 Granada, Spain
  • 2Karlsruhe Institute of Technology (KIT), Institute for Meteorology and Climate Research (IMK-ASF), P.O. Box 3640, 76021 Karlsruhe, Germany
  • 3Karlsruhe Institute of Technology (KIT), Steinbuch Centre for Computing (SCC), P.O. Box 3640, 76021 Karlsruhe, Germany

Abstract. The MIPAS Fourier transform spectrometer on board Envisat has measured global distributions of the six principal reactive nitrogen (NOy) compounds (HNO3, NO2, NO, N2O5, ClONO2, and HNO4) during 2002–2012. These observations were used previously to detect regular polar winter descent of reactive nitrogen produced by energetic particle precipitation (EPP) down to the lower stratosphere, often called the EPP indirect effect. It has further been shown that the observed fraction of NOy produced by EPP (EPP-NOy) has a nearly linear relationship with the geomagnetic Ap index when taking into account the time lag introduced by transport. Here we exploit these results in a semi-empirical model for computation of EPP-modulated NOy densities and wintertime downward fluxes through stratospheric and mesospheric pressure levels. Since the Ap dependence of EPP-NOy is distorted during episodes of strong descent in Arctic winters associated with elevated stratopause events, a specific parameterization has been developed for these episodes. This model accurately reproduces the observations from MIPAS and is also consistent with estimates from other satellite instruments. Since stratospheric EPP-NOy depositions lead to changes in stratospheric ozone with possible implications for climate, the model presented here can be utilized in climate simulations without the need to incorporate many thermospheric and upper mesospheric processes. By employing historical geomagnetic indices, the model also allows for reconstruction of the EPP indirect effect since 1850. We found secular variations of solar cycle-averaged stratospheric EPP-NOy depositions on the order of 1 GM. In particular, we model a reduction of the EPP-NOy deposition rate during the last 3 decades, related to the coincident decline of geomagnetic activity that corresponds to 1.8 % of the NOy production rate by N2O oxidation. As the decline of the geomagnetic activity level is expected to continue in the coming decades, this is likely to affect the long-term NOy trend by counteracting the expected increase caused by growing N2O emissions.

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We present a semi-empirical model for the reconstruction of polar winter descent of reactive nitrogen (NOy) produced by energetic particle precipitation (EPP) into the stratosphere. It can be used to prescribe NOy in chemistry climate models with an upper lid below the EPP source region. We also found a significant reduction of the EPP-generated NOy during the last 30 years, likely affecting the long-term NOy trend by counteracting the expected increase caused by growing N2O emission.
We present a semi-empirical model for the reconstruction of polar winter descent of reactive...
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