Towards a scale-consistent lightning NOx source parameterisation in the MECO(n) model system

Abstract

Lightning flashes represent an important source of nitrous oxide (NOx) in the troposphere and therefore influence directly the tropospheric ozone chemistry. The occurrence of ligthning is closely related to strong convective events. In global and limited area models which do not resolve clouds and convection, the phenomenon therefore represents a sub-grid-scale process and needs to be parameterised accordingly. Several lightning NOx parameterisations exist based on different convective parameters such as updraft mass flux, convective cloud top height or convective precipitation. The MECO(n) (MESSy-fied ECHAM and COSMO models nested n-times) model system aims at the consistent description of atmospheric chemistry related processes on the global (ECHAM) and the regional (COSMO) scales by on-line nesting of one or more instances of the limited area COSMO model into the global ECHAM model for dynamical and chemical down-scaling. Thus, a scale-consistent representation of the lightning NOx source is required. We adapt the MESSy submodel LNOx which includes currently 4 different ligthning NOx source parameterisations to work consistently in both, the global and the regional models and compare the simulated flash frequencies with observations.