1Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD, USA
2Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
3NCAR Earth System Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
4Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen, Germany
5Department of Physics, University of Munich, Munich, Germany
6Institut für Chemie- und Klimaforschung, Forschungszentrum Jülich, Jülich, Germany
*now at: National Weather Service, Silver Spring, MD, USA
Abstract. Cloud chemistry simulations are performed for a Hector storm observed on 16 November 2005 during the SCOUT-O3/ACTIVE campaigns based in Darwin, Australia, with the primary objective of estimating the average production of NO per lightning flash during the storm which occurred in a tropical environment. The 3-D WRF-AqChem model (Barth et al., 2007a) containing the WRF nonhydrostatic cloud-resolving model, online gas- and aqueous-phase chemistry, and a lightning-NOx production algorithm is used for these calculations. An idealized early morning sounding of temperature, water vapor, and winds is used to initialize the model. Surface heating of the Tiwi Islands is simulated in the model to induce convection. Aircraft observations from air undisturbed by the storm are used to construct composite initial condition chemical profiles. The idealized model storm has many characteristics similar to the observed storm. Convective transport in the idealized simulated storm is evaluated using tracer species, such as CO and O3. The convective transport of CO from the boundary layer to the anvil region was well represented in the model, with a small overestimate of the increase of CO at anvil altitudes. Lightning flashes observed by the LIghtning detection NETwork (LINET) are input to the model and a lightning placement scheme is used to inject the resulting NO into the simulated cloud. We find that a lightning NO production scenario of 500 moles per flash for both CG and IC flashes yields anvil NOx mixing ratios that match aircraft observations well for this storm. These values of NO production nearly match the mean values for CG and IC flashes obtained from similar modeling analyses conducted for several midlatitude and subtropical convective events and are larger than most other estimates for tropical thunderstorms. Approximately 85% of the lightning NOx mass was located at altitudes greater than 7 km in the later stages of the storm, which is an amount greater than found for subtropical and midlatitude storms. Upper tropospheric NO2 partial columns computed from the model output are also considerably greater than observed by satellite for most tropical marine convective events, as tropical island convection, such as Hector, is more vigorous and more productive of lightning NOx.