Sensitivity of tropical tropospheric composition to lightning NO_x production as determined by replay simulations with GEOS‐5

Abstract

The sensitivity of tropical tropospheric composition to the source strength of nitrogen oxides (NO x ) produced by lightning (LNO x ) is analyzed for September through November 2007 using the NASA GEOS-5 model constrained by MERRA fields, with full GMI stratospheric-tropospheric chemistry and an LNO x algorithm that is appropriate for use in a climate modeling setting; satellite retrievals from OMI, TES, and OMI/MLS; and in situ measurements from SHADOZ ozonesondes. Global mean LNO x production rates of 0 to 492 mol NO flash À1 and the subsequent responses of NO x , ozone (O 3 ), hydroxyl radical (OH), nitric acid (HNO 3 ), peroxyacetyl nitrate (PAN), and NO y (NO x + HNO 3 + PAN) are investigated. The radiative implications associated with LNO x -induced changes in tropospheric O 3 are assessed. Increasing the LNO x production rate by a factor of 4 (from 123 to 492 mol flash À1) leads to tropical upper tropospheric enhancements of greater than 100% in NO x , OH, HNO 3 , and PAN. This increase in LNO x production also leads to O 3 enhancements of up to 60%, which subsequently yields a factor-of-three increase in the mean net radiative flux at the tropopause. An LNO x source of 246 mol flash À1 agrees reasonably well with measurements, with an approximate factor-of-two uncertainty due to the short length of the study, inconsistencies in the observational data sets, and systematic biases in modeled LNO x production. Further research into the regional dependencies of lightning flash rates and LNO x production per flash, along with improvements in satellite retrievals, should help resolve the discrepancies that currently exist between the model and observations.

The impact of lightning on tropospheric ozone chemistry using a new global lightning parametrisation

“…In Wild (2007) and Liaskos et al (2015) the ozone burden and mean tropospheric column ozone, respectively, scaled approximately linearly with increases in lightning emissions. Using the mean bias data in Table 1 we can calculate the mean increase in ozone column associated with each TgN emission from lightning.…”

“…The solid line shows the mean annual tropopause as diagnosed using the modelled meteorology. Liaskos et al (2015) identified that, even with the same total global emissions, the magnitude and distribution of radiative forcing resulting from lightning emissions is dependent on the method for distributing the emissions horizontally and vertically. The changes in zonal-altitudinal distribution discussed in this section show that these changes could be expected as a result of changes in ozone in the upper troposphere.…”

“…Ozone acts as a greenhouse gas in the atmosphere and is most potent in the upper troposphere where temperature differences between the atmosphere and ground are greatest (Lacis et al, 1990;Dahlmann et al, 2011). Understanding lightning NO production and ozone formation in this region is important for de-D. L. Finney et al: Modelling lightning and ozone termining changes in radiative flux resulting from changes in ozone (Liaskos et al, 2015).…”

“…However, this and other existing approaches have been shown to lead to large errors in the distribution of flashes compared to lightning observations (Tost et al, 2007). Several studies have shown that the global magnitude of lightning NO x emissions is an important contributor to ozone and other trace gases, especially in the upper tropical troposphere (Labrador et al, 2005;Wild, 2007;Liaskos et al, 2015). Each of these studies uses a single horizontal distribution of lightning, so the impact of varying the lightning emission distribution is unknown.…”

Key drivers of ozone change and its radiative forcing over the 21st century

“…Hegglin and Shepherd, 2009;Zeng et al, 2010) and lightning-produced ozone (e.g. Liaskos et al, 2015).…”