A global three-dimensional time-dependent lightning source of tropospheric NOx

The spatial and temporal distribution for a global three-dimensional, time-dependent lightning source of NOx is constructed from a general circulation model's (GCM) deep moist convection statistics [Manabe et al,, 1974; Manabe and Holloway, 1975], observations of cloud-to-cloud and intracloud lightning fractions and the vertical distribution of lightning discharge [Proctor, 1991], and empirical/theoretical estimates of relative lightning frequency resulting from deep moist convection over ocean and over land [Price and Rind, 1992]. We then bracket the annual global emission of NOx from lightning between 2 and 6 Tg N/yr, with a most probable range of 3 to 5 Tg N/yr, by comparing tropospheric NOx simulations from the Geophysical Fluid Dynamics Laboratory Global Chemical Transport Model with measurements of NOx and/or NOy in the mid and upper troposphere where lightning is a major, if not the dominant, source. With this approach, the global magnitude of the lightning source is constrained by observed levels of NOx, while the temporal and spatial distributions of the source are under the control of the parent GCM. Although our lightning source is smaller than many previous estimates, it is still the major source of NOx and NOy in the mid and upper troposphere for a latitude belt running from 30 degrees N to 30 degrees S, an important contributor to summertime free tropospheric levels over the midlatitudes, and a major contributor, even in the lower troposphere,to the low NOx and NOy levels over the remote oceans.