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

We present simulations performed with six lightning parameterizations implemented in the Community Atmosphere Model (CAM5). The amount of lightning-produced nitrogen oxides (LNOx) by the various schemes considered is estimated. We provide some insight on how the lightning NO injected in the atmosphere influences the global concentrations of key chemical species such as OH, HO2, H2O2, NOx, O-3, SO2, CO, and HNO3. The vertical global averaged densities of HO2, H2O2, CO, and SO2 are depleted due to lightning while those of NO, NO2, O-3, OH, and HNO3 increase. Our results indicate that the parameterizations based on the upward ice flux (ICEFLUX) exhibit the largest global and midlatitude spatial correlations (0.73 and 0.632 for ICEFLUX and 0.72 and 0.553 for cloud top height) with respect to satellite global flash rate observations. Five out of the six lightning schemes investigated exhibit larger LNOx per flash in the midlatitudes than in the tropics. In particular, it is found that the ICEFLUX midlatitude LNOx per flash exhibits the largest difference with respect to its predicted tropical LNOx per flash, in agreement with available observations. When using CAM5, the ICEFLUX lightning parameterization could be considered a reliable lightning scheme (within its intrinsic uncertainties) in terms of its geographical distribution. Both ICEFLUX and cloud top height results agree with the enhancements of NO2 and O-3 produced by lightning over tropical Atlantic and Africa and the weaker lightning background over the tropical Pacific reported by Martin et al. (2007) in the periods and locations (upper troposphere) where lightning is expected to dominate the trace gas observations.