[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] A three-dimensional cloud-scale chemical transport model has been used to simulate trace gas transport, lightning NO production, and photochemical ozone production in the 12 July 1996 storm observed during the Stratosphere-Troposphere Experiment: Radiation, Aerosols and Ozone (STERAO-A) field experiment. The model is driven by meteorological fields from a nonhydrostatic cloud-resolving model (see Stenchikov et al., 2005). An assumption that both cloud-to-ground and intracloud flashes produce 460 moles NO/flash on average yielded the best comparison with the profile of NO observed in the storm anvil. Scenarios in which the NO production of an intracloud flash was 75 to 100% of the production of a cloud-to-ground flash best matched the column NO x mass computed from observations. Additional ozone production attributable to lightning NO within the storm cloud during the lifetime of the storm was very small ($2 ppbv). However, simulations of the photochemistry over the 24 hours following the storm show that an additional 10 ppbv of ozone production can be attributed to lightning NO production in the upper troposphere. Convective transport of HO x precursors led to the generation of a HO x plume, which substantially aided the downstream ozone production. Soluble species mixing ratios in the simulated cloud were all within a factor of two of observations. Citation: DeCaria, A. J., K. E. Pickering, G. L. Stenchikov, and L. E. Ott (2005), Lightning-generated NO X and its impact on tropospheric ozone production: A three-dimensional modeling study of a Stratosphere-Troposphere Experiment: Radiation, Aerosols and Ozone (STERAO-A) thunderstorm,

Abstract. Understanding lightning NO x (NO + NO2) production on the cloud scale is key for developing better parameterizations of lightning NOx for use in regional and global chemical transport models. This paper attempts to further the understanding of lightning NOx production on the cloud scale using a cloud model simulation of an observed thunderstorm. Objectives are (1) to infer from the model simulations and in situ measurements the relative production rates of NOx by cloud-to-ground (CG) and intracloud (IC) lightning for the storm; (2) to assess the relative contributions in the storm anvil of convective transport of NOx from the boundary layer and NOx production by lightning; and (3) to simulate the effects of the lightning-generated NOx on subsequent photochemical ozone production. We use a two-dimensional cloud model that includes a parameterized source of lightning-generated NOx to study the production and advection of NO x associated with a developing northeast Colorado thunderstorm observed on July 12, 1996, during the Stratosphere-Troposphere Experiment--Radiation, Aerosols, Ozone

Abstract. Analysis of chemical transport on Flight 10 of the 1999 Pacific ExploratoryMission (PEM) Tropics B mission clarifies the role of the South Pacific Convergence Zone (SPCZ) in establishing ozone and other trace gas distributions in the southwestern tropical Pacific. The SPCZ is found to be a barrier to mixing in the lower troposphere but a mechanism for convective mixing of tropical boundary layer air from northeast of the SPCZ with upper tropospheric air arriving from the west. A two-dimensional cloudresolving model is used to quantify three critical processes in global and regional transport: convective mixing, lightning NO x production, and wet scavenging of soluble species. Very low NO and 03 tropical boundary layer air from the northeastern side of the SPCZ entered the convective updrafts and was transported to the upper troposphere where it mixed with subtropical upper tropospheric air containing much larger NO and 03 mixing ratios that had arrived from Australia. Aircraft observations show that very little NO appears to have been produced by electrical discharges within the SPCZ convection. We estimate that at least 90% of the HNO 3 and H20 2 that would have been in upper tropospheric cloud outflow had been removed during transport through the cloud. Lesser percentages are estimated for less soluble species (e.g., <50% for CH3OOH ). Net ozone production rates were decreased in the upper troposphere by -60% due to the upward transport and outflow of low-NO boundary layer air. However, this outflow mixed with much higher NO air parcels on the southwest edge of the cloud, and the mixture ultimately possessed a net ozone production potential intermediate between those of the air masses on either side of the SPCZ. A large, persistent convective system such as the SPCZ is likely to have substantial effects on tropospheric chemistry. 32,591

[1] Vertical mixing of chemical tracers and optically active constituents by deep convection affects regional and global chemical balances in the troposphere and lower stratosphere. This important process is not explicitly resolved in global and regional models and has to be parameterized. However, mixing depends strongly on the spatial structure, strength, and temporal evolution of the particular storm, complicating parameterization of this important effect in the large-scale models. To better quantify dynamic fields and associated mixing processes, we simulate a thunderstorm observed on 12 July 1996 during the STERAO-A (Stratosphere-Troposphere Experiment: Radiation, Aerosols, and Ozone) Deep Convection field project using the Goddard Cloud Ensemble (GCE) model. The 12 July STERAO-A storm had very complex temporal and spatial structure. The meteorological environment and evolution of the storm were significantly different than those of the 10 July STERAO-A storm extensively discussed in previous studies. Our 2-D and 3-D GCE model runs with uniform one-sounding initialization were unable to reproduce the full life cycle of the 12 July storm observed by the CHILL radar system. To describe the storm evolution, we modified the 3-D GCE model to include the effects of terrain and the capability of using nonuniform initial fields. We conducted a series of numerical experiments and reproduced the observed life cycle and fine spatial structure of the storm. The main characteristics of the 3-D simulation of the 12 July storm were compared with observations, with 2-D simulations of the same storm, and with the evolution of the 10 July storm. The simulated 3-D convection appears to be stronger and more realistic than in our 2-D simulations. Having developed in a less unstable environment than the 10 July 1996 STERAO-A storm, our simulation of the 12 July storm produced weaker but sustainable convection that was significantly fed by wind shear instability in the lower troposphere. The time evolution, direction, and speed of propagation of the storm were determined by interaction with the nonuniform background mesoscale flow. For example, storm intensity decreased drastically when the storm left the region with large convective available potential energy. The model appears to be successful in reproducing the rectangular four-cell structure of the convection. The distributions of convergence, vertical vorticity, and position of the inflow level in the later single-cell regime compare favorably with the airborne Doppler radar observations. This analysis allowed us to better understand the role of terrain and mesoscale circulation in the development of a midlatitude deep convective system and associated convective mixing. Wind, temperature, hydrometeor, and turbulent diffusion coefficient data from the cloud model simulations were provided for off-line 3-D cloud-scale chemical transport simulations discussed in the companion paper by DeCaria et al. (2005).

The relationship between dry static energy and potential temperature, c p ϭ c p T ϩ gz, is exact for an adiabatic temperature profile, and extremely close to exact for an isothermal profile. Even though it is extremely accurate, its use in atmospheres with nonadiabatic temperature profiles can lead to significant errors when comparing the entropies of isolated atmospheric layers. Use of the relation in this context leads to the incorrect conclusion that an adiabatic temperature profile has greater entropy than an isothermal profile for the same static energy. The relation fails in this application because of the extreme sensitivity of the column-integrated entropy to temperature.

The confusion and ambiguity in the literature regarding the notation (V Á $)V versus V Á $V is discussed, and the equivalence of the two expressions is demonstrated. The invariance of this notation in any coordinate system is also shown.Corresponding author address: Alex J.

Attempts to calculate the area to specific work equivalence on a skew T-log p diagram for a Carnot cycle can lead to large errors if the pressures of the nodes of the cycle are estimated from the diagram. The cause is the extreme sensitivity of the calculation to the pressures of the nodes. To keep errors within 10%, the pressures of the nodes must be known to within 0.1 hPa, a precision that is not practical by direct reading from the diagram. To avoid these errors the pressures of the nodes should be calculated directly from Poisson's equation, which relates temperature, potential temperature, and pressure.