Model study on production and transport of lightning‐produced NO_x in a EULINOX supercell storm

Abstract

The production of nitrogen oxides (NO x ) by lightning has been investigated with a three‐dimensional cloud model. For the study of the NO x transport, the lightning NO x emissions are represented by a Lagrangian particle model instead of volume emissions. The advantages of this approach are (1) the transport of NO x inside the thunderstorm can be analyzed in great detail, (2) the NO x emissions can be represented as a line source instead of a volume emission, and (3) the comparison with high‐resolution aircraft measurements can be conducted. This approach is applied to the 21 July 1998 supercell storm observed during the European Lightning Nitrogen Oxides project (EULINOX). Both, parameterized and observed cloud‐to‐ground and intracloud flash frequencies are used in the simulation and two different lightning NO x production rates are tested. The analysis shows that the parameterization using instantaneous cloud properties can approximately reproduce the lightning activity during the early mature phase of the intensifying storm but cannot be used for the complete life cycle. The comparison of the model results with aircraft NO x measurements indicate that the NO x production rate for intracloud lightning is equivalent or higher than that for cloud‐to‐ground flashes. Experimentally deduced values for the cloud‐to‐ground lightning NO x production of 4.9 kg(N), or equivalent 2.1 × 10 26 molecules NO, and a ratio between the intracloud and cloud‐to‐ground NO x production of 1.4 are confirmed by the model leading to an intracloud contribution to the total NO x production of up to 93%. For the applied production parameters 50% to 80% of the total lightning NO x is transported into the anvil, leading to a very pronounced “C”‐shape profile. The estimated total NO x production by lightning during the lifetime of the storm is 22 t(N).