Mid-Latitude Lightning NOx Production from OMI and WWLLN Data

Abstract:

Mid- and upper- tropospheric NO_x (NO + NO₂) is a trace gas important in atmospheric radiative forcing through its regulation of ozone concentrations. Changes in NO_x and ozone result in indirect effects on other greenhouse gases such as methane. Lightning is the dominant source of NO_x in the free troposphere, and most estimates of the concentration of lightning NO_x (LNO_x) require knowledge of the amount of this species produced per lightning flash. We present the largest spatial- and temporal-scale investigation of LNO_x to date that combines satellite-based NO_x estimates and lightning flash data. The data comprise five northern-hemisphere (NH) summers, including much of the mid-latitude regions in North America and Asia and adjacent waters. NO₂ measurements from the Ozone Monitoring Instrument (OMI), selected from cloudy areas, are converted to LNO_x and compared with flashes preceding OMI overpass by 1 – 4 hours. The flash counts are derived from ground-based World Wide Lightning Location Network (WWLLN) data that are adjusted for detection efficiency by comparing them with Optical Transient Detector and Lightning Imaging Sensor satellite data. We find reasonable correlation between the number of lightning flashes and the amount of LNO_x produced and estimate mean efficiencies for the production of LNO_x in various NH regions. Overall results indicate mole/flash values near the low end of those reported in previous LNO_x studies, as well as a possible dependence of production efficiency on flash rate. These findings have potential implications for upper tropospheric trace gases and the global NO_x budget.