Wednesday, 14 January 2009: 11:30 AM
Lightning NOx production during the NASA TC4 experiment as observed by Aura/OMI
Room 126A (Phoenix Convention Center)
Lightning is responsible for an estimated 10-15 percent of total NOx emissions, and is one of the most prominent sources in the upper troposphere, especially in the tropics. In this study, we present estimates of lightning-generated NO2 (LNO2) using data from the Ozone Monitoring Instrument (OMI), which observed tropospheric column NO2 during NASA's Tropical Composition, Cloud and Climate Coupling Experiment (TC4) based in Costa Rica in July and August, 2007. NO2 was also measured on the DC-8 aircraft during the experiment. Profiles from the DC-8 were used to estimate background column NO2 amounts that were subtracted from the OMI data for the vicinity of observed deep convective events with lightning. DC-8 profiles characteristic of convective outflow were used in estimating appropriate air mass factors to be applied in the OMI NO2 retrieval yielding tropospheric column amounts (LNO2) for the regions influenced by the lightning NOx production. Lightning flash data (primarily CG) observed by the surface network operated by the Instituto Costarricense de Electricidad were examined for the region upwind of regions of enhanced OMI LNO2. The observed flash data were adjusted for total flash detection efficiency using factors estimated from comparisons of network data with observations from the LIS instrument onboard the TRMM satellite. Estimates of average NOx production per flash were made using the OMI LNO2 retrievals, the number of upwind flashes, and an estimate of the NO/NO2 ratio from the DC-8 observations. The magnitudes of lightning-caused NO2 enhancements in the TC4 region are compared with those observed by the DC-8 and with those observed in midlatitude experiments.