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Lightning NOx Production in the Tropics as Determined Using OMI NO2 Retrieval...

Allen, D., K. Pickering, E. J. Bucsela, N. Krotkov, and R. Holzworth (2019), Lightning NOx Production in the Tropics as Determined Using OMI NO2 Retrieval and WWLLN Stroke Data, J. Geophys. Res., 124, 13,498-13,518, doi:10.1029/2018JD029824.

Nitrogen oxide (NOx) production by lightning in the tropics is estimated using tropospheric NOx amounts (LNOx*) over deep convective grid boxes derived from Ozone Monitoring Instrument (OMI) nitrogen dioxide (NO2) slant columns and detection‐efficiency–adjusted World Wide Lightning Location Network (WWLLN) flashes. The lightning NOx production efficiency (LNOx PE) in the tropics is determined for the austral and boreal summers of 2007 to 2011 by regressing regional mean daily values of LNOx* for individual seasons against daily flash totals during flash windows prior to the OMI overpass. LNOx PE is determined to be approximately two times larger over marine locations than over continental locations possibly because marine flashes are more energetic. Overall, the mean LNOx PE for the tropics is calculated to be 170 ± 100 mol per flash with values over the tropical Pacific (low flash rate region) being largest. The main contributors to uncertainties in PE are uncertainties in WWLLN flash detection efficiency, upper tropospheric NOx lifetime in the near field of convection, and air mass factor biases. Plain Language Summary The high temperatures associated with lightning break apart the bonds of molecular nitrogen and oxygen leading to the production of nitrogen oxides (NOx) and subsequent increases in the concentrations of ozone (O3) and the hydroxyl radical (OH) and subsequent decreases in the concentrations of methane (CH4), thus impacting the climate system. The magnitude of NOx production by lightning is inferred over the tropics using nitrogen dioxide (NO2) columns from the Ozone Monitoring Instrument (OMI) aboard the NASA Aura spacecraft and lightning stroke data from the ground‐based World Wide Lightning Location Network (WWLLN). Overall, it was found that, on average, each lightning flash produces 170 mol of NOx with an uncertainty of approximately 60%. This value is within the commonly cited range of 100 to 400 mol per flash. In addition, it was found that flashes at tropical marine locations produce approximately two times as much NOx per flash as flashes at tropical continental locations and that NOx production per flash is greater in regions with low flash rates than in regions with high flash rates.

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Aura Science Team