NO2 and Lightning Observations During GOES-R Validation Flights: A Demonstration of Future TEMPO and GLM Synergy

Deep convective clouds affect atmospheric chemistry in a variety of ways. Lightning produces nitric oxide (NO), which quickly comes into equilibrium with NO₂ in the atmosphere. However, global production of NO_x (NO + NO₂) from lightning is uncertain by a factor of four. Geostationary Lightning Mapper (GLM) instruments have been launched on the GOES-16 and GOES-17 satellites. These instruments will continuously record lightning flashes at 10 km spatial resolution over the Americas and surrounding oceans with high detection efficiency. Geostationary measurements of NO₂ are expected to be available over the Americas beginning with the launch of the TEMPO UV/Vis spectrometer on a communications satellite, which will likely occur by 2021. Use of NO₂ data from TEMPO along with flash data from GLM will allow more robust estimates of NO production per flash and reduce uncertainty. The GOES-R Validation Campaign provided an opportunity to demonstrate the synergy of the future TEMPO observations with the GLM data. The NASA ER-2 aircraft overflew thunderstorms in several regions of the US during the March - May 2017 period. The GEO-CAPE Airborne Simulator (GCAS) provided spectra in the UV/Vis range from which NO2 columns were retrieved, and the Fly's Eye GLM Simulator (FEGS) provided measurements through the cloud top of optical emissions from lightning providing a comparison with GLM observations. Spectral fitting of the GCAS data was performed in the range of 425-460 nm, yielding differential NO₂ slant column densities with respect to a reference location. Air mass factors (AMFs) necessary to convert slant columns to vertical columns are computed using the VLIDORT code, using the Lambertian surface assumption, cloud top height from the Cloud Physics Lidar onboard the ER-2, and NO₂ and NO_x vertical profiles attributed to lightning taken from NASA GMI-Replay model simulations performed with and without lightning NO_x emissions. Correlations are performed between the GCAS NO₂ vertical columns and the FEGS flashes. Mean NO_x column amounts derived from GCAS and accumulated GLM flashes are used to estimate mean NO_x production per flash in the observed storms.