Estimates of Lightning NOx Production Based on OMI NO2 Observations over the Gulf of Mexico
Thursday, 17 December 2015
Poster Hall (Moscone South)
Radiative forcing of climate due to tropospheric O3 is very sensitive to the amount of O3 that is produced in the upper troposphere resulting from lightning NOx (LNOx). Therefore, global chemistry and climate models require accurate specification of LNOx production per flash. As part of a global investigation, in this study we evaluate LNOX production in convective storms over the Gulf of Mexico region for all summer months during the 2007 to 2011 time period. We use data from the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite along with detection efficiency-adjusted lightning data from the World Wide Lightning Location Network (WWLLN). A special algorithm was developed to retrieve the LNOx signal from OMI. The algorithm takes the total slant column NO2 from OMI and removes the stratospheric contribution and tropospheric background (NO2 from sources other than lightning) and includes an air mass factor appropriate for the profile of lightning NOX to convert the slant column LNO2 to a vertical column of LNOx. WWLLN flashes are totaled over a time period (based on climatological winds) in which an air parcel is expected to remain in a 1o x 1o grid box prior to OMI overpass. The analysis is conducted using pixels with cloud radiance fraction (CRF) greater than 0.9, indicative of deep, highly reflective clouds. Therefore, the method discussed in this presentation is appropriate over regions of active or recently active convection. With this criterion, the tropospheric background is minimal. We use summation and regression methods to estimate the monthly mean LNOx production per flash over the region. Averaging over summer months during 2007 – 2011 yields a monthly mean LNOx production of 267±73 moles per flash for the summation method and 196±63 moles per flash for the regression method. These results are consistent with literature estimates and more robust than many prior estimates of LNOx production due to the large number of storms considered.