Lightning NOx Production per Flash in the Midlatitudes and Tropics Derived from OMI NO2, and WWLLN Observations

This presentation will review our work to date on use of OMI NO₂ slant columns and lightning observations from the World-Wide Lightning Location Network (WWLLN) in estimating mean NO_x production per lightning flash (LNO_x Production Efficiency, PE) for various regions of the globe. We will first review the retrieval algorithm and summarize the results from our initial study of LNO_x PE for the Gulf of Mexico (Pickering et al., 2016). The general algorithm takes the NO₂ slant columns and subtracts the stratospheric component which comes from the NASA standard NO₂ product. The difference is then converted to a vertical column of convectively-perturbed NO_x using an airmass factor appropriate for deep convective clouds containing lightning. A tropospheric background NO_x is then subtracted from the resulting vertical column amount. Only OMI pixels representing deep convective clouds (cloud radiance fraction > 0.9 or more and optical centroid pressure < 500 hPa). The results for the Gulf of Mexico yielded mean LNO_x PE of 80 ± 45 moles NOx per flash. The work has been expanded to cover the mid-latitude continental regions and three major high lightning density regions of the tropics. Variations on the formulation of the method for determining the tropospheric background and on the cloud radiance fraction criterion have been employed for the various regions. The WWLLN lightning stroke data are converted to flashes using detection efficiency values derived from comparisons with the OTD/LIS satellite climatology. The mid-latitude analysis results suggest a possible nonlinear relationship between LNO_x and flash rate, yielding LNO_x PE values that range from >300 moles per flash for very low flash rate storms to <50 moles per flash for very high flash rates. The tropical PE values range from ~150 moles per flash for the low flash rate Western Pacific to ~50 moles per flash for the high flash rate Africa region. Uncertainties will be discussed, which are roughly 50%. Future analyses will be conducted using NO₂ column data from the ESA Sentinel 5 Precursor TROPOMI instrument and lightning flashes from the new GOES-16 Geostationary Lightning Mapper.