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Estimating the Rate of Change of Stratospheric Ozone using Deep Neural Networks
  • +3
  • Helge Mohn,
  • Daniel Kreyling,
  • Ingo Wolthmann,
  • Merlin Barschke,
  • Markus Rex,
  • Ingo Wohltmann
Helge Mohn
Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam

Corresponding Author:helge.mohn@awi.de

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Daniel Kreyling
Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam
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Ingo Wolthmann
Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam
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Merlin Barschke
Technische Universit├Ąt Berlin, Technische Universit├Ąt Berlin
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Markus Rex
Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam
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Ingo Wohltmann
Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam
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Abstract

We present a fast model for stratospheric ozone chemistry based on a neural network approach. The model is intended to replace the detailed chemistry schemes of chemistry and transport models (CTMs), general circulation models (GCMs) or Earth system models (ESMs), which are computationally very expensive. The neural network (NN) model estimates the rate of change of ozone in 24 hours at a grid point and is trained on data of the detailed full chemistry model of the ATLAS chemistry and transport model (CTM). The benefit of this surrogate models is a much lower computation time (minutes instead of days) while the same level of accuracy is achieved. This represents a necessary step from understanding the chemistry and building sophisticated CTMs towards the usage of this knowledge in climate models, which is only feasible if much lower computation times can be achieved. Modelling of the Earth system is a complex task and models usually contain a large number of sub-modules and parameterizations. This applies for example to the atmosphere, hydrosphere, solid earth and the ice sheets. Atmospheric chemistry is complex and usually involves dozens of species and hundreds of reactions with a wide range of concentrations and lifetimes. This project concentrates on the estimation of the rate of change of ozone in the extrapolar stratosphere. The dynamics from the polar regions and from other layers of the atmosphere regarding the ozone change are not treated within this work. The ATLAS model is a Lagrangian CTM for stratospheric chemistry. It solves a coupled differential equation system using a stiff solver and a variable time-step. The stratospheric chemistry scheme of ATLAS has 46 active species, 171 reactions and heterogeneous chemistry on polar stratospheric clouds. It is not using the concept of chemical families. The application of the ATLAS CTM has high requirements on computational power. This is the reason why the coupling of full chemical models to climate models is generally not feasible with respect to the computation time of a global climate model. However, the incorporation of detailed chemistry is often desirable, in order to account for various feed-backs between chemistry, atmosphere and ocean. These complex chemical models motivate the formulation of faster but still accurate surrogate models, that are tailored to the coupling into earth climate models. This project builds on the SWIFT project, which has a polar and an extrapolar surrogate model for the stratospheric ozone chemistry. We investigate an alternative approach to the polynomial approach used by extrapolar SWIFT by exploiting the improved approximation capability of NN with respect to nonlinear contexts.