Towards a super-simplified OH chemistry for ICON-ART

Monitoring greenhouse gas (GHG) emissions is essential to face global warming and climate change. The ITMS project (“Integriertes Treibhausgas Monitoringsystem”, in English “integrated GHG monitoring system”)[1], is designed to establish at the German Meteorological Service (DWD) an operational GHG data assimilation service based on the model system ICON-ART[2] to enable Germany to operationally monitor the sources and sinks of three important GHGs: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). In the first phase of the ITMS project DWD together with the Karlsruhe Institute of Technology (KIT) and other partners are focusing on the emission, distribution and depletion of methane. In the troposphere, methane is mainly depleted by the chemical reaction with the OH-radical. Tropospheric OH is created mostly by the photolytic destruction of ozone (O3) and thus its abundance depends on the available solar radiation and the ozone concentration (i.a.). The calculation of this chemical system is computationally expensive. Therefore a simplified calculation of the OH chemistry has to be included in the ICON-ART forward model. Here, we present the current state of a super-simplified OH-chemistry for ICON-ART, a data-driven approach based on Minschwaner et al., 2011[3]. The OH concentration is hereby estimated based on the solar zenith angle (SZA) at the respective grid cell, as well as two parameters which are trained priorly on existing OH and SZA data. [1] www.itms-germany.de [2] Schröter, J., Rieger, D., Stassen, C., Vogel, H., Weimer, M., Werchner, S., Förstner, J., Prill, F., Reinert, D., Zängl, G., Giorgetta, M., Ruhnke, R., Vogel, B., and Braesicke, P.: ICON-ART 2.1: a flexible tracer framework and its application for composition studies in numerical weather forecasting and climate simulations, Geosci. Model Dev., 11, 4043–4068, https://doi.org/10.5194/gmd-11-4043-2018, 2018. [3] Minschwaner, K., Manney, G. L., Wang, S. H., and Harwood, R. S.: Hydroxyl in the stratosphere and mesosphere – Part 1: Diurnal variability, Atmos. Chem. Phys., 11, 955–962, https://doi.org/10.5194/acp-11-955-2011, 2011.