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

Abstract

Abstract. A lightning parametrisation based on upward cloud ice flux is implemented in a chemistry-climate model (CCM) for the first time. The UK Chemistry and Aerosols model is used to study the impact of these lightning nitric oxide (NO) emissions on ozone. Comparisons are then made between the new ice flux parametrisation and the commonly used, cloud-top height parametrisation. The ice flux approach improves the simulation of lightning and the temporal correlations with ozone sonde measurements in the middle and upper troposphere. Peak values of ozone in these regions are attributed to high lightning NO emissions. The ice flux approach reduces the overestimation of tropical lightning apparent in this CCM when using the cloud-top approach. This results in less NO emission in the tropical upper troposphere and more in the extratropics when using the ice flux scheme. In the tropical upper troposphere the reduction in ozone concentration is around 5-10 %. Surprisingly, there is only a small reduction in tropospheric ozone burden when using the ice flux approach. The greatest absolute change in ozone burden is found in the lower stratosphere, suggesting that much of the ozone produced in the upper troposphere is transported to higher altitudes. Major differences in the frequency distribution of flash rates for the two approaches are found. The cloud-top height scheme has lower maximum flash rates and more mid-range flash rates than the ice flux scheme. The initial O x (odd oxygen species) production associated with the frequency distribution of continental lightning is analysed to show that higher flash rates are less efficient at producing O x ; low flash rates initially produce around 10 times more O x per flash than high-end flash rates. We find that the newly implemented lightning scheme performs favourably compared to the cloud-top scheme with respect to simulation of lightning and tropospheric ozone. This alternative lightning scheme shows spatial and temporal differences in ozone chemistry which may have implications for comparison between models and observations, as well as for simulation of future changes in tropospheric ozone.

Comparison of Six Lightning Parameterizations in CAM5 and the Impact on Global Atmospheric Chemistry

“…Our calculations indicate that lightning (through the production of NO x ) promotes an enhancement in the concentration of tropospheric ozone (O 3 ) that ranges between 32% and 45% with respect to ambient values with no lightning and with the maximum relative enhancement at ∼7.5 km in agreement with modeling results by Finney et al (2016). The calculated global average vertical profiles for O 3 follow the measured values (approximately doubles between ground level and 8 km) of different available observations (Martini et al, 2011).…”

“…Finally, the ICEFLUX scheme predicts an enhancement of ∼38% (at ∼7.5 km) in the concentration of tropospheric ozone (O 3 ) with respect to ambient values with no lightning and provides close agreement with ozone sonde measurements at 500 and 250 hPa (Finney et al, 2016). Based on the ICEFLUX global and midlatitude spatial correlations of, respectively, 0.732 (the largest one) and 0.632 (well above 0.553 of CTH), it could be considered that ICEFLUX is the most reliable (with respect to OTD/LIS geographical distribution) lightning scheme among the tested ones in this study.…”

“…This might be connected to advection of tropospheric ozone and precursors from intense lightning regions of Africa (in the lower and middle troposphere) and South America (in the upper troposhere) (Finney et al, 2016;Grewe, 2007;Murray, 2016). All the parameterizations show nonnegligible O 3 increase at ∼10 • S over the Atlantic Ocean where lightning density and NO enhancement are small (with respect to the maxima in central Africa).…”

“…The superscripts in the first column stand for the reference of the lightning scheme: (1) Price and Rind (1992), (2) Michalon et al (1999), (3) and (4) Allen and Pickering (2002), (5) the scaling needed for the ICEFLUX parameterization in the UKCA model is similar (1.12) (Finney et al, 2016) to one earlier reported (1.09) when using ERA-Interim global atmospheric reanalysis data (Finney et al, 2014), there is a nonnegligible difference in the global flash rate scaling factors for the CTH parameterization when implemented in the UKCA, the ECHAM5/MESSy models and the present study (scale factor of 2.05). The predicted lightning flash rates range between 44 (CP) and 51 (CTH-M) flashes s −1 , and they were scaled to match the observations by OTD/LIS.…”

Response of lightning NOx emissions and ozone production to climate change: Insights from the Atmospheric Chemistry and Climate Model Intercomparison Project

“…The impacts of LNO x on atmospheric chemistry and radiative forcing are dependent on the spatial distribution of emissions as well as the global total [ Liaskos et al , ; Finney et al , ]. We consider here the spatial distribution of LNO x and change in LNO x between present day and future, and whether there is anomalous behavior underlying the distributions.…”