Lightning NOx Production in the Midlatitudes and Tropics as Determined Using OMI NO2 Retrievals and WWLLN Stroke Data (Invited Presentation)

Deep convective clouds affect atmospheric chemistry in a variety of ways. Lightning is the primary source of NO_x (NO + NO₂) in the mid-to-upper troposphere, where lightning-produced NO_x has been shown to cause increases in ozone and OH and decreases in methane. Global production of NO_x from lightning is uncertain by a factor of four. In this study, the amount of NO_x produced per lightning flash is examined using 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. Estimates of LNO_x PE are obtained for six regions (tropical Americas, tropical Africa, tropical Pacific, Gulf of Mexico, eastern North America, Europe, and eastern Asia) using two approaches. In the summation approach, the mean vertical column of tropospheric NO_x due to recent lightning over flashing grid boxes is divided by mean flashes during a one-to-six hour accumulation period prior to the time of the OMI overpass. In the regression approach, mean daily columns of tropospheric NO_x values over a region are regressed against mean daily flashes during the accumulation period. Overall, the mean LNO_x PE for the continental subtropical/midlatitude regions is found to be 180 ± 100 moles NO_x produced per flash, a value that is roughly similar to the values for the entire tropics (157 ± 72 moles per flash) but larger than the value for continental locations in the tropics (113 ± 56 moles per flash). The PE is observed to depend strongly on flash rate, with higher flash rates producing less NO_x per flash. For example, PE is larger over the tropical Pacific (a low flash rate region with a high percentage of energetic marine flashes) than tropical Africa (a high flash rate region with a high percentage of less energetic continental flashes). The non-linear dependence is evident not only in the derived NO_x amounts but in the initial OMI NO₂ columns, themselves. It is most apparent over lower cloud tops and less so above storms with high anvils, where the PE becomes nearly constant.The main contributors to uncertainty are examined and shown to be uncertainties in WWLLN detection efficiency and upper tropospheric NO_x lifetime in the near field of convection.