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 Ă1 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
Ă1) 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 Ă1 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.