Dynamic lightning NOx production rates obtained with space-based low-Earth orbiting and geostationary lightning imagers

Lightning is a crucial driver of nitrogen oxides (NO_x) in the free troposphere where tropospheric ozone formation is limited by the availability of NO_x. NO_x production per lightning flash in models is typically represented with a single temporally and spatially static value, likely affecting the accuracy in simulating past, present, and future lightning NO_x and consequent changes in tropospheric ozone (O₃) and other oxidants. We determine spatially (0.5° × 0.625°) varying hourly NO_x production rates (mol N fl⁻¹) using literature reported relationships between NO_x yields and lightning flash radiant energies from Lightning Imaging Sensors (LIS) aboard the Tropical Rainfall Measuring Mission (TRMM) and the International Space Station (ISS). The diurnal and spatial variability of the radiant energies from the LIS instruments are assessed to be overall consistent with optical energies from the Geostationary Lightning Mapper (GLM) instrument, which monitors the Americas every 5 minutes. The diurnal variability between the two datasets differs by < 15%. Our lighting NO_x production rates are added to GEOS-Chem, yielding global emissions of 6.5 Tg N yr^-1 for 2015-2019, closely aligning with 5.8 Tg N yr^-1 in the original parameterised representation, but with large differences in the spatial distribution of lightning NO_x. Our updated parameterisation causes increases of > 50 pptv in NO₂ across the troposphere, particularly in the tropics coincident with deep convection. The resultant changes in tropospheric composition improve agreement with satellite-derived vertical profiles of NO₂ obtained via cloud-slicing TROPOMI by decreasing the model underestimate in free tropospheric NO₂. Assessment against cloud-sliced O₃ is underway.