Direct satellite observation of lightning-produced NOx

Comparison of lightning flash data from the National Lightning Detection Network (NLDN) and from the World Wide Lightning Location Network (WWLLN) over the contiguous United States (CONUS) for the 2016-2018 period reveals temporally and spatially varying flash rates that would influence lightning NOx (LNOx) production due to known detection efficiency differences especially during summer months over land (versus over ocean). However, the lightning flash density differences between the two networks show persistent seasonal patterns over geographical regions (e.g., land versus ocean). Since the NLDN data are considered to have higher accuracy (lightning detection with >95% efficiency), we developed scaling factors for the WWLLN flash data based on the ratios of WWLLN to NLDN flash data over time (months of year) and space. In this study, sensitivity simulations using the Community Multiscale Air Quality (CMAQ) model are performed utilizing the original data sets (both NLDN and WWLLN) and the scaled WWLLN flash data for LNOx production over the CONUS. The model performance of using the different lightning flash datasets for ambient O3 and NOx mixing ratios that are directly impacted by LNOx emissions and the wet and dry deposition of oxidized nitrogen species that are indirectly impacted by LNOx emissions is assessed based on comparisons with ground-based observations, vertical profile measurements, and satellite products. During summer months, the original WWLLN data produced less LNOx emissions (due to its lower lightning detection efficiency) compared to the NLDN data, which resulted in less improvement in model performance than the simulation using NLDN data as compared to the simulation without any LNOx emissions. However, the scaled WWLLN data produced LNOx estimates and model performance comparable with the NLDN data, suggesting that scaled WWLLN may be used as a substitute for the NLDN data to provide LNOx estimates in air quality models when the NLDN data are not available (e.g., due to prohibitive cost or lack of spatial coverage).

Production and transport of NOx by convection is critical as it serves as a precursor to tropospheric ozone, an important greenhouse gas. Lightning serves as the largest source of nitrogen oxides (NOx = NO + NO2) to the upper troposphere (UT) and is one of the largest natural sources of NOx. Interest is placed on the vertical advection of NOx because its lifetime increases to several days in the UT compared to roughly 3 hr in the lower troposphere and boundary layer. Thus, lightning can play an important role in ozone production within the UT. However, the amount of NOx produced per flash and NOx advection in storms remain uncertain. This study investigates lightning NOx (LNOx) production and transport processes in anomalous (midlevel positive charge) and normal polarity (midlevel negative charge) thunderstorms by advecting parcels containing LNOx from the flash channels of over 5,600 lightning flashes observed during the Deep Convective Clouds and Chemistry (DC3) field campaign. Results reveal that most flash channels occur near 6‐8 km in the normal polarity thunderstorms and 5‐6 km within anomalous polarity thunderstorms. Larger flash rates and stronger updrafts in anomalous storms result in considerably larger LNOx mixing ratios (peaks of 0.75‐1.75 ppb) in the UT compared to normal polarity storms (peaks < 0.5 ppb). A slightly lower mean flash LNOx production was also found among all five storms in this study (storm mean values of 72‐158 moles per flash) compared to previous estimates, which generally parameterize LNOx by flash rate rather than flash count.

The Ozone Monitoring Instrument (OMI) on board the NASA Aura satellite was launched into sun-synchronous low-earth orbit in 2004. Its hyperspectral measurements have been an invaluable tool in determining trace-gas concentrations in the troposphere and stratosphere. Nitrogen dioxide (NO2) has a particularly prominent absorption signature in the violet and near-UV regions of the OMI spectrum. This signature can be exploited in retrievals of column amounts of NO2 attributable to both natural and anthropogenic sources. We outline the OMI NO2 retrieval algorithm and demonstrate its utility for inferring NOx (NO + NO2) amounts due to lightning. Lightning is the dominant source of NOx in the free troposphere, and most estimates of the concentration of lightning NOx (LNOx) require knowledge of the amount of this species produced per lightning flash. We present the largest spatial- and temporal-scale investigation of LNOx to date that combines satellite-based NOx estimates and lightning flash data. The study comprises five northern-hemisphere (NH) summers, including much of the mid-latitude regions in North America and Asia and adjacent waters. NO2 measurements are converted to LNOx and compared with flashes preceding OMI overpass by 2 hours. The flash counts are derived from ground-based World Wide Lightning Location Network (WWLLN) data that are adjusted for detection efficiency. We find reasonable correlation between the number of lightning flashes and the amount of LNOx produced and estimate mean efficiencies for the production of LNOx in various NH regions. Overall results indicate mole/flash values near the low end of those reported in previous LNOx studies, as well as a possible dependence of production efficiency on flash rate. These findings have potential implications in the chemistry of upper tropospheric trace gases and the global NOx budget.

Oxides of nitrogen are critical trace gases in the troposphere and are precursors for nitrate aerosol and ozone, which is an important pollutant and greenhouse gas. Lightning is the major source of NOx (NO + NO2) in the middle to upper troposphere. We estimate the production efficiency (PE) of lightning NOx (LNOx) using satellite data from the Ozone Monitoring Instrument and the ground‐based World Wide Lightning Location Network in three northern midlatitudes, primarily continental regions that include much of North America, Europe, and East Asia. Data were obtained over five boreal summers, 2007–2011, and comprise the largest number of midlatitude convective events to date for estimating the LNOx PE with satellite NO2 and ground‐based lightning measurements. In contrast to some previous studies, the algorithm assumes no minimum flash‐rate threshold and estimates freshly produced LNOx by subtracting a background of aged NOx estimated from the Ozone Monitoring Instrument data set itself. We infer an average value of 180 ± 100 moles LNOx produced per lightning flash. We also show evidence of a dependence of PE on lightning flash rate and find an approximate empirical power function relating moles LNOx to flashes. PE decreases by an order of magnitude for a 2 orders of magnitude increase in flash rate. This phenomenon has not been reported in previous satellite LNOx studies but is consistent with ground‐based observations suggesting an inverse relationship between flash rate and size.

Lightning is thought to represent an important source of tropospheric reactive nitrogen species NOx (NO + NO2), but estimates of global production of NOx by lightning vary considerably. We evaluate the production of NOx by lightning using a global chemical/transport model, satellite lightning observations, and airborne NOx measurements. Various model calculations are conducted to assess the global NOx production rate of lightning by comparing the model calculations with airborne measurements. The results show that the simulated NOx in the tropical middle and upper troposphere are very sensitive to the amount and altitude of the lightning NOx used in the model. A global lightning NOx production of 7 Tg N yr −1 uniformly distributed in convective clouds or 3.5 Tg Ny r −1 distributed in the upper cloud regions produces good agreement between calculated and measured NOx concentrations in the tropics.

Daily zenith scattered light intensity observations were carried out in the morning twilight hours using home-made UV-visible spectrometer over the tropical station Pune (18‡31′, 73‡51′) for the years 2000–2003. These observations are obtained in the spectral range 462–498 nm for the solar zenith angles (SZAs) varying from 87‡ to 91.5‡. An algorithm has been developed to retrieve vertical profiles of ozone (O3) and nitrogen dioxide (NO2) from ground-based measurements using the Chahine iteration method. This retrieval method has been checked using measured and recalculated slant column densities (SCDs) and they are found to be well matching. O3 and NO2 vertical profiles have been retrieved using a set of their air mass factors (AMFs) and SCDs measured over a range of 87–91.5‡ SZA during the morning. The vertical profiles obtained by this method are compared with Umkehr profiles and ozonesondes and they are found to be in good agreement. The bulk of the column density is found near layer 20–25 km. Daily total column densities (TCDs) of O3 and NO2 along with their stratospheric and tropospheric counterparts are derived using their vertical profiles for the period 2000–2003. The total column, stratospheric column and tropospheric column amounts of both trace gases are found to be maximum in summer and minimum in the winter season. Increasing trend is found in column density of NO2 in stratospheric, tropospheric and surface layers, but no trend is observed in O3 columns for above layers during the period 2000–2003

Thunderstorm activity is indirectly taken into account when using statistics on forest fires. Another way is to use the data of the lightning discharge finding sensors. This chapter proposes using the data of the World Wide Lightning Location Network (WWLLN). To assess the probability of forest fire occurrence, it is necessary to know the energy and the spatial distribution of lightning discharges. For the analysis of the data of the storm-direction-finding WWLLN, it is proposed to use clustering algorithms. For the computational experiment, the region covering the Timiryazevskiy forestry of the Tomsk region (55.93 - 56.86) on the north, (83.94 - 85.07), and the data on lightning discharges registered by the WWLLN network in this region in July 2014. The sample data were 273 lightning discharges. The results of clustering are presented, as well as the image of the silhouette index for each object, the average value of the ASW index for grouping solutions obtained using the complete, kmeans, and dbscan algorithms.

The NASA Lightning Nitrogen Oxides Model (LNOM): Application to air quality modeling

Abstract. Lightning activity detected by the World Wide Lightning Location Network (WWLLN) over oceanic regions adjacent to Mexico is often as high as that observed over the continent. In order to explore the possible causes of the observed high flash density over those regions, the relationships between lightning, rainfall, vertical hydrometeor profiles, latent heating, wind variability and aerosol optical depth are analyzed. The characteristics of lightning and precipitation over four oceanic zones adjacent to Mexican coastlines are contrasted against those over the continent. The number of flashes per rainfall over some coastal maritime regions is found to be higher than over the continent. The largest number of flashes per rainfall is observed during the biomass burning season. In addition, we compare two smaller areas of the Tropical Pacific Ocean: one located within the Inter-Tropical Convergence Zone and characterized by high rainfall and weak lightning activity and the other one influenced by a continental wind jet and characterized by high rainfall and strong lightning activity. During the rainy season, the monthly distribution of lightning within the region influenced by the continental wind jet is contrary to that of rainfall. Moreover, the monthly variability of lightning is very similar to the variability of the meridional wind component and it is also related to the variability of aerosol optical depth. The analysis suggests that the high lightning activity observed over coastal Pacific region is linked to the continental cloud condensation nuclei advected over the ocean. Analysis of daily observations indicates that the greatest lightning density is observed for moderate values of the aerosol optical depth, between 0.2 and 0.35.

We analyze variations of lightning activity presented by the lightning stroke number obtained by the World Wide Lightning Location Network (WWLLN) within the territory with boundaries 40–80° N and 60–180° E in 2009–2016. There are two regions with high lightning activity: western (48–60° N, 60–90° E) and eastern (40–55° N, 110–140° E). The lightning stroke density in these regions is 10–100 times higher than that in surrounding areas. The comparison between daily variations of lightning stroke number and the 10.7 cm solar radio flux shows no correlation: the linear cor-relation coefficient varied from –0.55 to 0.86 in the western region and from –0.78 to 0.39 in the eastern region during all summer seasons. During the ascending phase of solar cycle 24, there was a spatial lightning redistribution between the western and eastern regions of high lightning activity. During peaks of the solar cy-cle and its descending phase, the redistribution was not so pronounced as that during the ascending

Lightning is the dominant source of nitrogen oxides (NOx) in the free troposphere. Yet, its representation in models is highly parameterised, limiting our ability to determine past and future changes in lightning NOx and causing errors in model representation of tropospheric ozone and NOx. Models such as GEOS-Chem use fixed lightning NOx production rates constrained with historic satellite instrument observations of ozone. A new approach is to model NOx production per flash (mol N fl-1) using lightning energy dependent NOx yields and lightning flash radiant energy data from the space-based lightning imaging sensor (LIS) aboard both the Tropical Rainfall Measuring Mission (TRMM) satellite and the International Space Station (ISS). This updated approach is then used in GEOS-Chem to compute total lightning NOx yields through the Harmonized Emissions Component (HEMCO), rather than using fixed values. The updated annual lightning NOx emissions total 6.5 Tg N, similar to the original parameterised representation (5.8 Tg N), but with much greater variability in NOx production rates. The original implementation uses 260 mol N fl-1 everywhere except the northern extratropics that are at 500 mol fl-1. In the updated implementation, values range from 27 to 632 mol N fl-1 over the ocean and from 66 to 482 mol N fl-1 over land. Greater values over the ocean are due to oft-reported much more energetic maritime lightning. To test the effect on tropospheric ozone and NOx, we are currently comparing seasonal mean GEOS-Chem and TROPOMI-derived vertical profiles of ozone and NO2. The TROPOMI-derived values, obtained by cloud-slicing partial columns over optically thick clouds, we have previously evaluated to be consistent with NASA DC-8 aircraft measurements in the free troposphere for cloud-sliced NO2 (differences < 20 pptv) and the global ozonesonde network for cloud-sliced ozone across the whole troposphere (differences < 35 ppbv). This offers the means to assess the representation of lightning NOx and better understand its influence on tropospheric NOx and ozone.

Synoptic and mesoscale cyclonic systems over the ocean and seas are often accompanied by thunderstorm activity, the intensity and spatial distribution of which is modulated by the dynamic structure of these systems. Lightning discharges are sources of electromagnetic radiation in the range of very low frequencies (VLF) and are detected by VLF location finders. Using the World Wide Lightning Location Network (WWLLN), relations between characteristics of fields of detected lightning discharges in the north-western part of the Pacific Ocean and those of fields of meteorological elements of weather formations estimated by data of remote sensing of the Earth by satellites are studied by an example of tropical cyclones. We illustrate a technique permitting one to connect thunderstorm activity parameters (frequency and intensity, as well as spatial distribution of lightning discharges) with the structure of weather systems over oceans and seas and with the intensity and forms of mesoscale formations distinguished in these systems by fields of the near-water wind vortex (the fields are obtained using a scatterometer) and by satellite images in the visible and infrared ranges. The relations between the frequency and density of lightning discharges in the range of influence of a tropical cyclone (TC) and spatial distribution of the near-water wind vortex are demonstrated by an example of individual TCs of 2005–2013.

On Aug. 29, 2016, the tropical cyclone Lionrock was reported to turn into an extra-tropical storm and go to the shore of the Primorsky Region as monitoring shows, which brought about significant precipitation growth recorded in the north of the coast. Many surveys show the tropical cyclones in this area to transform into extra-tropical ones and become powerful mid-latitude storms with significant damage to coastal and maritime areas. The paper uses WWLLN (World Wide Lightning Location Network) data to study the thunderstorm activity while the tropical cyclone reaches the typhoon level with the maximum wind velocity. This made it possible to identify parameters’ variations of thunderstorm activity during atmospheric vortex phenomena. It also enabled us to determine the emergency probability due to a thunderstorm.

In the free troposphere, injection from the stratosphere, emissions at the surface transported upward by dynamic processes, aircraft emissions and production in lightning strokes are the main sources of oxides of nitrogen (NOx). The global source of NOx production by lightning is not well known and estimates vary from 3 to 650 Mt NO2/yr. In this paper the role of regional and episodic emissions of NOx from lightning is examined with a three‐dimensional chemistry transport model, and a parameterization of the emissions is proposed, linking it to the intensity of latent heat generation in convection calculated in a numerical weather prediction model. The parameterization is scaled to give an annual global emission of 16 MtNO2/yr. The resulting distribution of the concentration of NOx, ozone, OH and nonmethane hydrocarbons is compared for the free troposphere over the northern hemisphere with the results of a calculation where the total NOx emissions from lightning were about the same but were fixed in time and space over the 18 days' calculation (June 18 to July 5, 1995). The maximum differences in the free tropospheric concentrations are significant: for NOx, OH and nonmethane hydrocarbon of the same order of magnitude as the concentrations themselves, for ozone 1 order of magnitude less than the ozone concentration. This means that NOx emissions from lightning may cause a variability in free tropospheric composition which makes it quite difficult to distinguish the importance of other sources of free tropospheric NOx from that of lightning in periods when lightning occurs.

The Free Tropospheric Experiment (FREETEX’98) was conducted at the Jungfraujoch Observatory in the Swiss Alps (3580 in above sea level) during the well‐documented spring maximum in ozone. In spring the Jungfraujoch frequently lies in the free troposphere but can also be influenced by air from the planetary boundary layer. Measurements of NOx, NOy, peroxy‐acetylnitrate (PAN), HCHO, O3, CO, nonmethane hydrocarbons, peroxy radicals, j(O1D), j(NO2), and a variety of other tropospheric constituents crucial to ozone photochemical cycles were made over a 1‐month period. Two independent measurements of NOx, NOy, and PAN showed good agreement. Average free tropospheric daytime NO levels were about 50 pptv, sufficient to sustain photochemical ozone formation. Although high mixing ratios were encountered, PAN decomposition did not contribute to NOx production during FREETEX’98. Ozone production efficiencies (E N) derived from observed ΔO3/(NOz) ratios in free tropospheric air were 20–30 molecules of O3 produced per NOx molecule oxidized and agreed well with a photochemical model. A much lower ozone production efficiency of 4 was determined in a photochemically aged air mass arriving from southern Europe, in line with other measurements and calculations in regimes containing high levels of oxidized nitrogen. Model simulations indicated that by sequestering NOx and HO2, low‐temperature formation of peroxynitric acid (PNA) decreased ozone production by 20% and instantaneous ozone production efficiencies by 40%, whereas PAN formation had little effect. The model reproduced well the observed sharp transformation from ozone production to ozone destruction (defined as ΔO3/Delta;(NOz) = 0) at 20–25 pptv NO. The observed and calculated strong dependence of EN on NOx concentration in the low‐NOx regime highlights the difficulty in assigning a single O3 production efficiency value to remote regions, where most of the CO and CH4 in the atmosphere are oxidized.