No abstract

[1] A three-dimensional (3-D) cloud-scale chemical transport model that includes a parameterized source of lightning NO x on the basis of observed flash rates has been used to simulate six midlatitude and subtropical thunderstorms observed during four field projects. Production per intracloud (P IC ) and cloud-to-ground (P CG ) flash is estimated by assuming various values of P IC and P CG for each storm and determining which production scenario yields NO x mixing ratios that compare most favorably with in-cloud aircraft observations. We obtain a mean P CG value of 500 moles NO (7 kg N) per flash. The results of this analysis also suggest that on average, P IC may be nearly equal to P CG , which is contrary to the common assumption that intracloud flashes are significantly less productive of NO than are cloud-to-ground flashes. This study also presents vertical profiles of the mass of lightning NO x after convection based on 3-D cloud-scale model simulations. The results suggest that following convection, a large percentage of lightning NO x remains in the middle and upper troposphere where it originated, while only a small percentage is found near the surface. The results of this work differ from profiles calculated from 2-D cloud-scale model simulations with a simpler lightning parameterization that were peaked near the surface and in the upper troposphere (referred to as a ''C-shaped'' profile). The new model results (a backward C-shaped profile) suggest that chemical transport models that assume a C-shaped vertical profile of lightning NO x mass may place too much mass near the surface and too little in the middle troposphere.

[1] Model simulations of tropospheric O 3 require an accurate specification of the reactive odd nitrogen (NO x ) source from lightning that is consistent in time and space with convective transport of O 3 precursors. Lightning NO x production in global models is often parameterized in terms of convective cloud top heights (CLDHT). However, a closer relationship may exist between flash rate and other measures of convective intensity. In this study, flash rates are parameterized in terms of CLDHT, convective precipitation (PRECON), and upward convective mass flux (MFLUX) from the Goddard Earth Observing System Data Assimilation System (GEOS DAS). GEOS-based flash rates are compared to flash rates from the National Lightning Detection Network (NLDN) and Long Range Flash (LRF) network and the Optical Transient Detector (OTD). Overall, MFLUX-based flash rates are most realistic. PRECON-and CLDHTbased flash rates are too large in the tropics. The MFLUX-and PRECON-based flash rates are a factor of 3 too high (low) over the equatorial western Pacific (central and southern Africa), while CLDHT-based flash rates are much too low at nearly all marine locations. In many cases, biases in the flash rate distributions can be traced to biases in the GEOS DAS convective fields. Improvements in flash rate parameterizations will be tied closely to improvements in model physics as well as to increases in the amount of tropical data that are available for assimilation. Flash rates calculated from the 6-hour averaged CLDHTs are much less variable than observed, and O 3 production rates calculated using the NO x produced from these flash rates are likely to be larger than observed.

We evaluate nitrogen oxide (NO x = NO + NO 2 ) production from lightning over the Gulf of Mexico region using data from the Ozone Monitoring Instrument (OMI) aboard NASA's Aura satellite along with detection efficiency-adjusted lightning data from the World Wide Lightning Location Network (WWLLN). A special algorithm was developed to retrieve the lightning NO x (LNO x ) signal from OMI. The algorithm in its general form takes the total slant column NO 2 from OMI and removes the stratospheric contribution and tropospheric background and includes an air mass factor appropriate for the profile of lightning NO x to convert the slant column LNO 2 to a vertical column of LNO x . WWLLN flashes are totaled over a period of 3 h prior to OMI overpass, which is the time an air parcel is expected to remain in a 1°× 1°grid box. The analysis is conducted for grid cells containing flash counts greater than a threshold value of 3000 flashes that yields an expected LNO x signal greater than the background. Pixels with cloud radiance fraction greater than a criterion value (0.9) indicative of highly reflective clouds are used. Results for the summer seasons during 2007-2011 yield mean LNO x production of~80 ± 45 mol per flash over the region for the two analysis methods after accounting for biases and uncertainties in the estimation method. These results are consistent with literature estimates and more robust than many prior estimates due to the large number of storms considered but are sensitive to several substantial sources of uncertainty.