Estimating Lightning NOx Production Using NO2 Columns from the TROPOMI Instrument and Flashes from the Geostationary Lightning Mappers
Authors: Pickering Kenneth , Allen Dale , Bucsela Eric , van Geffen Jos , Eskes Henk , Veefkind Pepijn , Koshak William , Krotkov Nickolay 
Published: March 2020

&lt;p&gt;Nitric oxide (NO) is produced in lightning channels and quickly comes into equilibrium with nitrogen dioxide (NO&lt;sub&gt;2&lt;/sub&gt;)&amp;#160;in the atmosphere.&amp;#160; The production of NO&lt;sub&gt;x&lt;/sub&gt; (NO + NO&lt;sub&gt;2&lt;/sub&gt;) leads to subsequent increases in the concentrations of ozone (O&lt;sub&gt;3&lt;/sub&gt;) and the hydroxyl radical (OH) and decreases in the concentration of methane (CH&lt;sub&gt;4&lt;/sub&gt;), thus impacting the climate system.&amp;#160; Global production of NO&lt;sub&gt;x&lt;/sub&gt;&amp;#160;from lightning is uncertain by a factor of four. &amp;#160;NO&lt;sub&gt;x&lt;/sub&gt; production by lightning will be examined using NO&lt;sub&gt;2&lt;/sub&gt; columns from the TROPOspheric Monitoring Instrument (TROPOMI) on board the Copernicus Sentinel-5 Precursor Satellite with an overpass time of approximately 1330 LT and flash rates from the Geostationary Lightning Mapper (GLM) on board the NOAA GOES-16 (75.2&amp;#176; W) and GOES-17 (137.2&amp;#176; W) satellites.&amp;#160; Where there is overlap in coverage of the two GLM instruments, the greater of the two flash counts is used.&amp;#160; Two approaches have been undertaken for this analysis:&amp;#160; a series of case studies of storm systems over the United States, and a gridded analysis over the entire contiguous United States, Central America, northern South America, and surrounding oceans.&amp;#160; A modified Copernicus Sentinel 5P TROPOMI NO&lt;sub&gt;2&lt;/sub&gt; data set is used here for the case-study analysis to improve data coverage over deep convective clouds.&amp;#160; In both approaches, only TROPOMI pixels with cloud fraction &gt; 0.95 and cloud pressure &lt; 500 hPa are used.&amp;#160; The stratospheric column is removed from the total slant column, and the result is divided by air mass factors appropriate for deep convective clouds containing lightning NO&lt;sub&gt;x&lt;/sub&gt; (LNO&lt;sub&gt;x&lt;/sub&gt;).&amp;#160; Case studies have been selected from deep convective systems over and near the United States during the warm seasons of 2018 and 2019.&amp;#160; For each of these systems, NO&lt;sub&gt;x&lt;/sub&gt; production per flash is determined by multiplying a TROPOMI-based estimate of the mean tropospheric column of LNO&lt;sub&gt;x&lt;/sub&gt; over each system by the storm area and then dividing by a GLM-based estimate of the flashes that contribute to the column.&amp;#160; In the large temporal and spatial scale analysis, the TROPOMI data are aggregated on a 0.5 x 0.5 degree grid and converted to moles LNO&lt;sub&gt;x&lt;/sub&gt;*. &amp;#160;GLM flash counts during the one-hour period before TROPOMI overpass are similarly binned. A tropospheric background of LNO&lt;sub&gt;x&lt;/sub&gt;* is estimated from grid cells without lightning and subtracted from LNO&lt;sub&gt;x&lt;/sub&gt;* in cells with lightning to yield an estimate of freshly produced lightning NO&lt;sub&gt;x&lt;/sub&gt;, designated LNO&lt;sub&gt;x&lt;/sub&gt;. &amp;#160;Results of the two approaches are compared and discussed with respect to previous LNO&lt;sub&gt;x&lt;/sub&gt; per flash estimates.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;