Convective Cloud Top Height Research Articles

The impacts of shipping emissions on lightning: roles of aerosol-radiation-interactions and aerosol-cloud-interactions

Long-term (2005–2021) observations from the World Wide Lightning Location Network reveal significantly larger flash counts over heavily trafficked shipping lanes in the northeastern Indian Ocean compared to nearby regions. Here, we use the online coupled meteorology-chemistry model WRF-Chem to examine the impact of aerosols from shipping emissions on lightning activity over one of the world’s busiest shipping lanes (5–7° N, 82–92° E). We conduct three case simulations in January 2013, 2015, and 2018 when frequent lightning activities were recorded. The WRF-Chem model with lightning parameterized based on convective cloud-top height captures the temporal evolution of lightning activities but overestimates the magnitude of lightning counts. We find that all three cases consistently show enhanced lightning flash counts due to shipping-induced aerosols by 6.2%–22.3%, accompanied by increased cloud droplet number, cloud water concentration, radar reflectivity, and cloud-top height. Sensitivity simulations show that aerosol-cloud-interactions from shipping aerosols consistently enhance the strength of convection and lightning frequency in all three cases, by increasing cloud condensation nuclei and cloud droplet numbers, delaying precipitation of cloud water, allowing the lift and accumulation of water vapor, increasing release of latent heat, and finally invigorating convections. In comparison, aerosol-radiation-interactions show inconsistent contributions to convection and lightning, which enhance lightning frequency in the 2013 and 2015 cases but decrease lightning frequency in the 2018 case. This inconsistency may be attributed to differences in the number and vertical structure of shipping aerosols and cloud droplet in the three cases. Our study thus approves the certain but complicated anthropogenic impacts on lightning activities through shipping-induced aerosols, which has important implications for understanding future trends in lightning and its impact on atmospheric chemistry and climate.

A Modified Kain–Fritsch Convection Scheme for Extended-Range Prediction

Abstract This paper describes the convection parameterization in the Navy Earth System Prediction Capability (ESPC) system developed at the Naval Research Laboratory, with a focus on the scheme configuration in the v2.0 system. The parameterization is an update of a modification of the Kain–Fritsch convection scheme by Ridout et al. based on an assumed quasi-balance of updraft parcel buoyancy at the cloud-base level. Scheme updates include the treatment of updraft/environment mixing and additional updraft model features, including a parameterized reduction in net detrainment in cases of significant near-cloud upward motion, and a modified cloud-top condition. The scheme includes two convection modes: a turbulence-triggered and a dynamically triggered mode. Hindcast sensitivity with Navy ESPC to features of the scheme is investigated with 45-day integrations from 1 November 2011 for a portion of the Dynamics of the Madden–Julian Oscillation (DYNAMO) research program observational period that overlaps with the occurrence of two episodes of the MJO. The modified updraft mixing is critical in the hindcasts for consistent MJO eastward propagation, whereas the additional updraft updates significantly improve the representation of small-scale rainfall variability, while helping to inhibit development of excessive low-level easterly flow. The added turbulence-triggered convection mode helps to improve the representation of the separation of periods of enhanced MJO convection. The relative occurrence frequency of convective cloud-top height and column water vapor in the equatorial Indo-Pacific is investigated in the hindcasts, showing significant similarities with satellite retrieval results. Significance Statement This study describes the scheme used to represent the effects of convective clouds such as cumulus and cumulonimbus (thunderstorm clouds) in computerized 45-day global forecasts of the Earth system in a forecast model developed at the Naval Research Laboratory, focusing on the version currently undergoing testing for use by the U.S. Navy. Some of the development history and physical basis for the scheme are presented, and results from test simulations are included. The test results investigate potential forecast sensitivity to various features of the scheme and illustrate that the scheme can successfully represent certain effects of convective clouds on large-scale storm systems in the tropics that have global-scale impacts on extended-range (several weeks) prediction of the Earth’s atmosphere/ocean system.

Assessing and improving cloud-height-based parameterisations of global lightning flash rate, and their impact on lightning-produced NO<sub><i>x</i></sub> and tropospheric composition in a chemistry–climate model

Abstract. Although lightning-generated oxides of nitrogen (LNOx) account for only approximately 10 % of the global NOx source, they have a disproportionately large impact on tropospheric photochemistry due to the conducive conditions in the tropical upper troposphere where lightning is mostly discharged. In most global composition models, lightning flash rates used to calculate LNOx are expressed in terms of convective cloud-top height via the Price and Rind (1992) (PR92) parameterisations for land and ocean, where the oceanic parameterisation is known to greatly underestimate flash rates. We conduct a critical assessment of flash-rate parameterisations that are based on cloud-top height and validate them within the Australian Community Climate and Earth System Simulator – United Kingdom Chemistry and Aerosol (ACCESS-UKCA) global chemistry–climate model using the Lightning Imaging Sensor and Optical Transient Detector (LIS/OTD) satellite data. While the PR92 parameterisation for land yields satisfactory predictions, the oceanic parameterisation, as expected, underestimates the observed flash-rate density severely, yielding a global average over the ocean of 0.33 flashes s−1 compared to the observed 9.16 flashes s−1 and leading to LNOx being underestimated proportionally. We formulate new flash-rate parameterisations following Boccippio's (2002) scaling relationships between thunderstorm electrical generator power and storm geometry coupled with available data. The new parameterisation for land performs very similarly to the corresponding PR92 one, as would be expected, whereas the new oceanic parameterisation simulates the flash-rate observations much more accurately, giving a global average over the ocean of 8.84 flashes s−1. The use of the improved flash-rate parameterisations in ACCESS-UKCA changes the modelled tropospheric composition – global LNOx increases from 4.8 to 6.6 Tg N yr−1; the ozone (O3) burden increases by 8.5 %; there is an increase in the mid- to upper-tropospheric NOx by as much as 40 pptv, a 13 % increase in the global hydroxyl radical (OH), a decrease in the methane lifetime by 6.7 %, and a decrease in the lower-tropospheric carbon monoxide (CO) by 3 %–7 %. Compared to observations, the modelled tropospheric NOx and ozone in the Southern Hemisphere and over the ocean are improved by this new flash-rate parameterisation.

Convective Influence on the Humidity and Clouds in the Tropical Tropopause Layer During Boreal Summer

AbstractThe impact of convection on the humidity and clouds in the tropical tropopause layer (TTL) during boreal summer 2007 is investigated in simulations of detailed cloud microphysical processes and their effects on the water vapor (H2O) profile along backward trajectories from the 379 K potential temperature (100‐hPa pressure) surface. Convective influence is determined by tracing the trajectories through time‐dependent fields of satellite‐based convective cloud top height. The simulated H2O mixing ratios at the 100‐hPa level and cloud occurrence fractions in the middle to upper (16–18 km) TTL exhibit a pronounced maximum over the Asian monsoon region as in observations; these local enhancements are virtually absent in the simulation without convection, indicating that convection is the dominant driver of the localized H2O and cloud maxima in the Asian summer monsoon region. Convection moistens the 100‐hPa level by 0.6 ppmv (~15%) averaged over the 10°S–50°N domain and increases tropical (10°S–30°N) mean cloud occurrence in the middle to upper TTL by ~170%. Nearly all of the convective enhancements in H2O and clouds are due to the effect of convective saturation; convectively detrained ice crystals have negligible impact. Parcels are most frequently hydrated by deep convection in the southern sector of the Asian monsoon anticyclone and subsequently dehydrated downstream of convection to the west, shifting the locations of final dehydration northwest of the cold temperature region in the northern Tropics. Infrequent, extreme deep convective systems (cloud tops exceeding 380 K) have a disproportionately large effect on TTL humidity and clouds.

Improving the Simulation of Tropical Convective Cloud-Top Heights in CAM5 with CloudSat Observations

Using 4 years of CloudSat data, the simulation of tropical convective cloud-top heights (CCTH) above 6 km simulated by the convection scheme in the Community Atmosphere Model, version 5 (CAM5), is evaluated. Compared to CloudSat observations, CAM5 underestimates CCTH by more than 2 km on average. Further analysis of model results suggests that the dilute CAPE calculation, which has been incorporated into the convective parameterization since CAM4, is a main factor restricting CCTH to much lower levels. After removing this restriction, more convective clouds develop into higher altitudes, although convective clouds with tops above 12 km are still underestimated significantly. The environmental conditions under which convection develops in CAM5 are compared with CloudSat observations for convection with similar CCTHs. It is shown that the model atmosphere is much more unstable compared to CloudSat observations, and there is too much entrainment in CAM5. Since CCTHs are closely associated with cloud radiative forcing, the impacts of CCTH on model simulation are further investigated. Results show that the change of CCTH has important impacts on cloud radiative forcing and precipitation. With increased CCTHs, there is more cloud radiative forcing in tropical Africa and the eastern Pacific, but less cloud radiative forcing in the western Pacific. The contribution to total convective precipitation from convection with cloud tops above 9 km is also increased substantially.

Evaluation of Lightning Forecasting Based on One Lightning Parameterization Scheme and Two Diagnostic Methods

Lightning forecasting is a vital item in server convective system short-time forecasting. However, lightning parameterization in mesoscale numerical prediction models is still in its early stages of development. Several lightning parameterization schemes are implemented in the Weather Research and Forecasting (WRF) model. Data assimilation can provide a more accurate initial field, which could be useful for subsequent lightning forecasting. To evaluate its effect on lightning forecasting, a severe convective case that influenced Jiangsu and Anhui Province on 5 June 2009 is utilized and a series of experiments are conducted including assimilating radar reflectivity and lightning location network data via the three-dimensional variational (3DVar) method. Results show that data assimilation can effectively improve reflectivity forecasting and subsequent lightning forecasting. Lightning forecasting based on the PR92 lightning parameterization scheme, which is based on the convective cloud top height, offers a weaker magnitude forecast. The diagnostic method based on reflectivity and temperature has some spatial displacement. The potential forecast provided by lightning threat indexes produced an improvement in Anhui Province, while in other regions, it is located further east than the observation.

Using CloudSat observations to evaluate cloud top heights from convection parameterization

How high convective clouds can go is of great importance to climate. Cloud ice and liquid water that detrain nearthe top of convective cores are important for the formation of anvil clouds and thus impact cloud radiative forcing and theEarth’s radiation budget. This study uses CloudSat observations to evaluate convective cloud top heights in the NationalCenter for Atmospheric Research (NCAR) Community Atmosphere Model (CAM5). Results show that convective cloud topheights in the tropics are much lower than observed by CloudSat, by more than 2 km on average. Temperature and moistureanomalies from climatological means are composited for convective clouds of different heights for both observations andmodel simulation. It is found that convective environment is warmer and moister, and the anomalies are larger for clouds ofhigher tops. For a given convective cloud top height, the corresponding atmosphere in CAM5 is more convectively unstablethan what the CloudSat observations indicate, suggesting that there is too much entrainment into convective clouds in themodel.

Development of a self‐consistent lightning NOx simulation in large‐scale 3‐D models

AbstractWe seek to develop a self‐consistent representation of lightning NOx (LNOx) simulation in a large‐scale 3‐D model. Lightning flash rates are parameterized functions of meteorological variables related to convection. We examine a suite of such variables and find that convective available potential energy and cloud top height give the best estimates compared to July 2010 observations from ground‐based lightning observation networks. Previous models often use lightning NOx vertical profiles derived from cloud‐resolving model simulations. An implicit assumption of such an approach is that the postconvection lightning NOx vertical distribution is the same for all deep convection, regardless of geographic location, time of year, or meteorological environment. Detailed observations of the lightning channel segment altitude distribution derived from the NASA Lightning Nitrogen Oxides Model can be used to obtain the LNOx emission profile. Coupling such a profile with model convective transport leads to a more self‐consistent lightning distribution compared to using prescribed postconvection profiles. We find that convective redistribution appears to be a more important factor than preconvection LNOx profile selection, providing another reason for linking the strength of convective transport to LNOx distribution.

Dynamical, convective, and microphysical control on wintertime distributions of water vapor and clouds in the tropical tropopause layer

AbstractProcesses that influence the humidity and cirrus cloud abundance in the Tropical Tropopause Layer (TTL) during boreal winter 2006–2007 are investigated in simulations of clouds along backward trajectories of parcels ending at the 372 K potential temperature (100 hPa) level in the tropics. Trajectories are calculated using offline calculations of seasonal mean tropical radiative heating rates along with reanalysis temperature and wind data with enhanced wave‐driven variability in the TTL. The one‐dimensional (vertical) time‐dependent cloud microphysical model is initialized with water vapor measurements from the Microwave Limb Sounder and the evolution of clouds along each trajectory is simulated using temperature profiles extracted from reanalysis data and convective cloud top heights estimated from 3‐hourly geostationary satellite imagery. Averaged over the tropics, waves dehydrate the 100 hPa level by 0.5 ppmv, while convection and cloud microphysical processes moisten by 0.3 and 0.7 ppmv, respectively. The tropical mean cloud occurrence frequencies in the middle to upper TTL agree well with those based on satellite observations (spatial correlation of 0.8). Waves and convection enhance cloud occurrence at the cold point tropopause by 4% and 2%, respectively. Temporal variability of the heating rates as indicated by the ERA‐Interim 6‐hourly heating rate fields dehydrates the TTL by 0.4 ppmv and decreases the cloud occurrence by 4% because parcels are more likely to encounter the coldest temperatures and dehydrate near the cold point, limiting cloud formation above. The final dehydration locations of parcels, concentrated near the dateline in the tropical Pacific, are insensitive to various model parameters.

Evaluation of cloud convection and tracer transport in a three-dimensional chemical transport model

Abstract. We investigate the performance of cloud convection and tracer transport in a global off-line 3-D chemical transport model. Various model simulations are performed using different meteorological (re)analyses (ERA-40, ECMWF operational and ECMWF Interim) to diagnose the updraft mass flux, convective precipitation and cloud top height. The diagnosed upward mass flux distribution from TOMCAT agrees quite well with the ECMWF reanalysis data (ERA-40 and ERA-Interim) below 200 hPa. Inclusion of midlevel convection improves the agreement at mid-high latitudes. However, the reanalyses show strong convective transport up to 100 hPa, well into the tropical tropopause layer (TTL), which is not captured by TOMCAT. Similarly, the model captures the spatial and seasonal variation of convective cloud top height although the mean modelled value is about 2 km lower than observed. The ERA-Interim reanalyses have smaller archived upward convective mass fluxes than ERA-40, and smaller convective precipitation, which is in better agreement with satellite-based data. TOMCAT captures these relative differences when diagnosing convection from the large-scale fields. The model also shows differences in diagnosed convection with the version of the operational analyses used, which cautions against using results of the model from one specific time period as a general evaluation. We have tested the effect of resolution on the diagnosed modelled convection with simulations ranging from 5.6° × 5.6° to 1° × 1°. Overall, in the off-line model, the higher model resolution gives stronger vertical tracer transport, however, it does not make a large change to the diagnosed convective updraft mass flux (i.e., the model results using the convection scheme fail to capture the strong convection transport up to 100 hPa as seen in the archived convective mass fluxes). Similarly, the resolution of the forcing winds in the higher resolution CTM does not make a large improvement compared to the archived mass fluxes. Including a radon tracer in the model confirms the importance of convection for reproducing observed midlatitude profiles. The model run using archived mass fluxes transports significantly more radon to the upper troposphere but the available data does not strongly discriminate between the different model versions.

A model study of smoke-haze influence on clouds and warm precipitation formation in Indonesia 1997/1998

In the last few decades, fire and smoke-haze occurrence increased in Indonesia by intentionally set land clearing fires and higher fire susceptibility of disturbed forests. Particularly, during El Niño years with prolonged droughts in Indonesia, land clearing fires become uncontrolled wildfires and produce large amounts of gaseous and particulate emissions. This paper investigates the influence of smoke-haze aerosols from such fires on clouds and precipitation over Indonesia during the El Niño event 1997/1998 by numerical modelling. Warm precipitation formation in both layered and convective clouds is calculated dependent on the atmospheric aerosol concentration. In the smoke-haze affected regions of Indonesia, aerosol–cloud interactions induce events with both precipitation suppression and increase compared to a reference simulation without aerosol–cloud interactions. The effect of precipitation suppression is found to dominate with about 2/3 of all precipitation modification events pointing to a prolongation of smoke-haze episodes. The corresponding convective cloud top height of shallow clouds is increased whereas distinct lower deep convective cloud top heights are found. The remaining about 1/3 events are characterised by increased precipitation and cloud liquid water content, accompanied by lower convective cloud top heights of shallow clouds and higher deep convective clouds.

Extreme weather condition for aviation over the Donets Ridge on August 22, 2006

Synoptic, aerological, satellite, and radar data are analyzed to detect space and time evolution of aviation-hazardous weather in Donbass on August 22, 2006. The forecasts of dangerous convective activity, of convective cloud top heights, and of convective cloud location within the frontal zone, produced with an operational forecasting technology at the Hydrometeorological Center of Russia, suggest extremely hazardous conditions in Donbass; mesoscale analysis, based on classical rules, gives additional information. Special conditions favoring the convective activity were a wave disturbance at the polar front, convective instability at the time of its maximum development, and effects of upland and of proximity of the sea.

Factors Limiting Convective Cloud-Top Height at the ARM Nauru Island Climate Research Facility

Abstract Cumulus congestus clouds, with moderate shortwave albedos and cloud-top temperatures near freezing, occur fairly often in the Tropics. These clouds may play an important role in the evolution of the Madden–Julian oscillation and the regulation of relative humidity in the midtroposphere. Despite this importance they are not necessarily simulated very well in global climate models. Surface remote sensing observations and soundings from the Atmospheric Radiation Measurement (ARM) climate research facility at Nauru Island are coupled with a simple parcel model in order to address the following questions about these cloud types: 1) Which environmental factors play a role in determining the depth of tropical convective clouds? 2) What environmental parameters are related to entrainment rate in cumulus congestus clouds? The results presented herein suggest that at Nauru Island a drying of the midtroposphere is more likely to be responsible for limiting congestus cloud-top heights than is a stabilizing of the freezing level. It is also found that low-level CAPE and the RH profile account for the largest portion of the variance in cumulus congestus entrainment rates, consistent with the idea that entrainment rate depends on the buoyant production of turbulent kinetic energy. If the analysis is limited to cases where there is a sounding during the hour preceding the cumulus congestus observations, it is found that the low-level CAPE accounts for 85% of the total variance in entrainment rate.

Evaluation of lightning flash rate parameterizations for use in a global chemical transport model

Model simulations of tropospheric O3 require an accurate specification of the reactive odd nitrogen (NOx) source from lightning that is consistent in time and space with convective transport of O3 precursors. Lightning NOx 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 CLDHT‐based 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 O3 production rates calculated using the NOx produced from these flash rates are likely to be larger than observed.

Improvement and evaluation of the parameterisation of nitrogen oxide production by lightning

In order to describe the production of nitrogen oxides (NOx) by lightning in chemistry-transport models the spatial and temporal distribution of this NOx source needs to be specified. Various meteorological model parameters can be used as a proxy for specifying this distribution. In order to determine the most suitable parameter as a proxy for lightning, we have correlated different meteorological quantities from the ECMWF model, such as convective precipitation and cloud top height, with ground-based lightning observations made during the EULINOX project. Convective precipitation gave the best correlation for summer conditions over Europe. Using the established relationship between convective precipitation and lightning intensity, we have tested different vertical distributions of the NOx lightning source in the global chemistry-transport model TM3. The model simulated NO fields have been compared with the NO observations made during the 1998 EULINOX and the 1997 POLINAT/SONEX campaigns. We found that a prescribed lightning NOx profile gave the best agreement with the observations. The observations covered various conditions: typical background situations, inside thunderstorms, and the outflow of thunderstorms of various ages. The model underestimated the NO concentrations in cases of fresh lightning NOx, likely due to its insufficient spatial and temporal resolution, but under most other circumstances the new parameterisation performed reasonably well, and is a clear improvement over the previously used parameterisation based on cloud top heights.

Modelling NO x from lightning and its impact on global chemical fields

We have used a three-dimensional off-line chemical transport model (CTM) to assess the impact of lightning emissions in the free troposphere both on NO x itself and on other chemical species such as O 3 and OH. We have investigated these effects using two lightning emission scenarios. In the first, lightning emissions are coupled in space and time to the convective cloud top height calculated every 6 h by the CTM's moist convection scheme. In the second, lightning emissions are calculated as a constant, monthly mean field. The model's performance against observed profiles of NO x and O 3 in the Atlantic and Pacific ocean improves significantly when lightning emissions are included. With the inclusion of these emissions, the CTM produces a significant increase in the NO x concentrations in the upper troposphere, where the NO x lifetime is long, and a smaller increase in the lower free troposphere, where the surface NO x sources dominate. These changes cause a significant increase in the O 3 production in the upper troposphere and hence higher calculated O 3 there. The model indicates that lightning emissions cause local increases of over 50 parts per 10 12 by volume (pptv) in NO x , 200 pptv in HNO 3 and 20 parts per 10 9 by volume (ppbv) (>40%) in O 3. In addition, a smaller increase of O 3 in the lower troposphere occurs due to an increase in the downward transport of O 3. The O 3 change is accompanied by an increase in OH which is more pronounced in the upper troposphere with a corresponding reduction in CO. The method of emission employed in the model does not appear to have a significant effect globally. In the upper troposphere (above about 300 hPa) NO x concentrations are generally lower with monthly mean emissions, because of the de-coupling of emissions from the model's convection scheme, which vents NO x aloft more efficiently in the coupled scheme. Below the local convective outflow altitude, NO x concentrations are larger when using the monthly mean emissions than when coupled to the convection scheme, because the more dilute emissions, and nighttime emissions, lead to a slower NO x destruction rate. Only minor changes are predicted in the monthly average fields of O 3 if we emit lightning as a monthly constant field. However, the method of emission becomes important when we make a direct comparison of model results with time varying data. These differences should be taken into account when a direct comparison of O 3 with measurements collected at particular times and locations is attempted.

Validation of an off‐line three‐dimensional chemical transport model using observed radon profiles: 2. Model results

We parameterize radon emissions in the TOMCAT global off‐line three‐dimensional chemical transport model (CTM) and compare modeled radon profiles with spatially and temporally matched observations obtained near Moffett Field, California, in June 1994. The CTM was forced using European Centre for Medium‐Range Weather Forecasts analyses for April‐August 1994. To identify the origin of modeled radon, we divided the radon sources into three regions. We performed CTM sensitivity experiments at horizontal resolutions of 2.8° × 2.8° (latitude × longitude) and 7.5° × 7.5°, and with and without moist convection and/or vertical diffusion. At the higher resolution the full CTM (i.e., including convection and vertical diffusion) generally agrees well with the observations in the free troposphere. The observations exhibit free‐tropospheric radon peaks at altitudes where zonal wind speeds in the Pacific jet stream are greatest (generally at ≥7 km). In this region the modeled radon originates from Asia, and the observed variability in the radon concentration is reproduced. Thus, the model reproduces the position and strength of the jet. We identify observed radon peaks that may originate from convective lifting, as they do in the model results. If these observed peaks do originate from convection, then the full CTM captures the correct temporal variability in convection over Asia and the Pacific for the observation period. Quantitative comparison shows that the model‐data agreement is degraded if we decrease the model resolution to 7.5° × 7.5°, or remove the parameterizations of convection and/or vertical diffusion. This suggests a resolution of near 2.8° × 2.8° is needed in global models for realistic simulations of short‐lived species. We have identified certain shortcomings with TOMCAT: the model underestimates the amount of convective cloud, the convective cloud top height, and the amount of vertical diffusion. We identify improvements to ameliorate these problems.

Estimations of global no, emissions and their uncertainties

The AERONOX programme investigated the impact of NO x emissions from aircraft on the atmosphere and included an extensive modelling programme. In the model comparisons undertaken within the AERONOX programme, a “standard” set of emissions of NO x from both aviation and non-aviation sources was required so that differences between the models could be examined. This paper describes the data sets used in the study. These were: fossil fuel combustion from stationary and mobile sources at Earth's surface (22 Tg N yr −1), tropical biomass burning (5 Tg N yr −1), soil microbial production of NO (4 Tg N yr −1), lightning (5 Tg N yr −1), and the stratospheric decomposition of nitrous oxide (0.6 Tg N yr −1), ). However, global emission inventories of trace gases are developing rapidly: this paper also presents some emission estimates updated since the AERONOX study and also attempts to quantify uncertainties. The lightning source was constructed using convective cloud-top height from a GCM and differential rates of NO production calculated for cloud-to-cloud, and cloud-to-ground strikes. A revised biomass inventory including deforestation, savanna burning, agricultural waste burning and biofuel combustion results in approximately 8 Tg Nyr −1. This estimate includes sources beyond the tropics. Both extrapolation of measurements of soil NO fluxes by biome type, and a further refinement of the AERONOX soils emission model resulted in an emission of approximately 7 Tg Nyr −1. Ammonia oxidation as a source of NO x is calculated to be 0.9 N Tg yr −1), with a range of 0-l.6 Tg N yr −1), which shows that this is a relatively unimportant source of NO x in the troposphere. Uncertainty estimates for all sources have been given and discussed. The global source term for NO x for all sources (including the revisions) is estimated to be 44 Tg N yr −1), with an uncertainty range of 23–81 Tg N yr −1), A future scenario for fossil fuel combustion is given for 2025 resulting in an emission term of 46.5 Tg N for this source, showing a pronounced shift in distribution to Asia and the Far-East.

A simple lightning parameterization for calculating global lightning distributions

A simple parameterization has been developed to simulate global lightning distributions. Convective cloud top height is used as the variable in the parameterization, with different formulations for continental and marine thunderstorms. The parameterization has been validated using two lightning data sets: one global and one regional. In both cases the simulated lightning distributions and frequencies are in very good agreement with the observed lightning data. This parameterization could be used for global studies of lightning climatology; the Earth's electric circuit; in general circulation models for modeling global lightning activity, atmospheric NOx concentrations, and perhaps forest fire distributions for both the present and future climate; and, possibly, even as a short‐term forecasting aid.