Abstract
Nitrogen oxides (NOx ≡ NO + NO2) produced by lightning make a major contribution to the global production of tropospheric ozone and OH. Lightning distributions inferred from standard convective parameterizations in global chemical transport models (CTMs) fail to reproduce observations from the Lightning Imaging Sensor (LIS) and the Optical Transient Detector (OTD) satellite instruments. We present an optimal regional scaling algorithm for CTMs to fit the lightning NOxsource to the satellite lightning data in a way that preserves the coupling to deep convective transport. We show that applying monthly scaling factors over ∼37 regions globally significantly improves the tropical ozone simulation in the GEOS‐Chem CTM as compared to a simulation unconstrained by the satellite data and performs equally well to a simulation with local scaling. The coarse regional scaling preserves sufficient statistics in the satellite data to constrain the interannual variability (IAV) of lightning. After processing the LIS data to remove their diurnal sampling bias, we construct a monthly time series of lightning flash rates for 1998–2010 and 35°S–35°N. We find a correlation of IAV in total tropical lightning with El Niño but not with the solar cycle or the quasi‐biennial oscillation. The global lightning NOxsource ± IAV standard deviation in GEOS‐Chem is 6.0 ± 0.5 Tg N yr−1, compared to 5.5 ± 0.8 Tg N yr−1 for the biomass burning source. Lightning NOx could have a large influence on the IAV of tropospheric ozone because it is released in the upper troposphere where ozone production is most efficient.
Highlights
The extreme heat in a lightning flash channel converts atmospheric N2 and O2 to nitrogen oxide radicals (NOx ≡ NO + NO2) that drive the formation of tropospheric ozone and influence OH, the principal tropospheric oxidant [Chameides et al, 1977; Logan et al, 1981; Labrador et al, 2004]
We show that adequate fidelity to lightning observations can be achieved with regions sufficiently coarse to constrain the interannual variability in lightning and investigate the resulting impact on atmospheric chemistry
We have explored and compared different approaches for using Lightning Imaging Sensor (LIS)/Optical Transient Detector (OTD) satellite observations to constrain the lightning NOx source in global chemical transport models, with focus on enabling simulation of interannual variability (IAV) and its implications for tropospheric chemistry
Summary
The extreme heat in a lightning flash channel converts atmospheric N2 and O2 to nitrogen oxide radicals (NOx ≡ NO + NO2) that drive the formation of tropospheric ozone and influence OH, the principal tropospheric oxidant [Chameides et al, 1977; Logan et al, 1981; Labrador et al, 2004]. Parameterizations used in global chemical transport models (CTMs) show little skill in reproducing observed lightning distributions [Tost et al, 2007; Sauvage et al, 2007b]. We develop a method for using satellite observations to constrain the lightning source in global CTMs in a way that preserves the coupling to convective transport and allows investigation of interannual variability of lightning influence. Climatological LIS/OTD data have been used previously in CTMs to apply correction factors on various scales to the lightning flash rate parameterizations. We develop an optimal algorithm for selecting coherent lightning regions over which to apply correction factors, and we use an improved LIS/OTD data set to examine the sensitivity of CTM results to the scales over which the correction factors are applied. We show that adequate fidelity to lightning observations can be achieved with regions sufficiently coarse to constrain the interannual variability in lightning and investigate the resulting impact on atmospheric chemistry
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