We use the Regional chEmical trAnsport Model (REAM) to investigate the impacts of lightning NOx production and anthropogenic NOx emissions on outgoing longwave radiation (OLR) over the United States and the western North Atlantic Ocean from June to August 2005. Tropospheric column O3 estimates based on data from the OMI and MLS instruments onboard the Aura satellite and the OLR data from NOAA polar orbiting satellites are also used in the study.

The REAM-simulated OLR fields on the basis of MM5-derived meteorology capture the spatial distribution of the remotely sensed OLR fields reasonably (R?0.85) with relatively small mean biases. In the convective outflow regions over North America and the western North Atlantic Ocean, the contribution of lightning NOx production on the summertime tropospheric O3 is comparable to that of anthropogenic sources. The NOx production due to significant lightning during the North Atlantic Monsoon in July resulted in large enhancements in the upper tropospheric O3 concentration. Results in this study reveal that the contribution of lightning-generated NOx on OLR variations via enhancements in tropospheric O3 is significantly larger than the corresponding effects of surface NOx emissions. The model results also show similar increases in OLR over the southwestern United States region after the onset of North American Monsoon in July. We will also discuss the heating rate changes associated with the two NOx sources. The radiative impact of NOx produced by lightning over North America is becoming larger as fossil-fuel combustion NOx emissions decrease in recent years.