. The knowledge of the lightning-induced nitrogen oxides (LNOx) source is important for understanding and predicting the nitrogen oxides and ozone distributions in the troposphere and their trends, the oxidising capacity of the atmosphere, and the lifetime of trace gases destroyed by reactions with OH. This knowledge is further required for the assessment of other important NOx sources, in particular from aviation emissions, the stratosphere, and from surface sources, and for understanding the possible feedback between climate changes and lightning. This paper reviews more than 3 decades of research. The review includes laboratory studies as well as surface, airborne and satellite-based observations of lightning and of NOx and related species in the atmosphere. Relevant data available from measurements in regions with strong LNOx influence are identified, including recent observations at midlatitudes and over tropical continents where most lightning occurs. Various methods to model LNOx at cloud scales or globally are described. Previous estimates are re-evaluated using the global annual mean flash frequency of 44±5 s−1 reported from OTD satellite data. From the review, mainly of airborne measurements near thunderstorms and cloud-resolving models, we conclude that a "typical" thunderstorm flash produces 15 (2–40)×1025 NO molecules per flash, equivalent to 250 mol NOx or 3.5 kg of N mass per flash with uncertainty factor from 0.13 to 2.7. Mainly as a result of global model studies for various LNOx parameterisations tested with related observations, the best estimate of the annual global LNOx nitrogen mass source and its uncertainty range is (5±3) Tg a−1 in this study. In spite of a smaller global flash rate, the best estimate is essentially the same as in some earlier reviews, implying larger flash-specific NOx emissions. The paper estimates the LNOx accuracy required for various applications and lays out strategies for improving estimates in the future. An accuracy of about 1 Tg a−1 or 20%, as necessary in particular for understanding tropical tropospheric chemistry, is still a challenging goal.

/pdf/the-global-lightning-induced-nitrogen-oxides-source-4n884kbcha.pdf

The global lightning-induced nitrogen oxides source

Four years of observations from the NASA Optical Transient Detector (OTD) and Global Atmospherics National Lightning Detection Network (NLDN) are combined to determine the geographic distribution of the intracloud/cloud to ground lightning ratio over the continental United States. The mean ratio over this region is 2.64-2.94, with a standard deviation of 1.1-1.3 and anomalies as low as 1.0 or less over the Rocky and Appalachian mountains and as high as 8-10 in the central-upper midwest. There is some indication that the ratio covaries with ground elevation, although the relationship is nonunique. Little evidence is found to support a latitudinal covariance, despite significant variation in the climatological mean tropopause pressure over the latitudes considered. The dynamic range of local variability is comparable to the range of values cited by previous studies for latitudinal variation from the deep tropics to midlatitudes. Local high anomalies of this ratio in the midwest are coincident with anomalies in the climatological percentage of positive CG occurrence, as well as in the occurrence of large positive CGs characteristic of MCS convective and trailing stratiform regions. This suggests that storm type, morphology and level of organization may dominate over environmental cofactors in the local determination of this ratio.

Combined Satellite- and Surface-Based Estimation of the Intracloud Cloud-to-Ground Lightning Ratio over the Continental United States

Ratios of area mean rainfall and cloud-to-ground lightning flash count (termed rain yields) were computed for several different locations around the globe, over temporal and spatial scales of 1 month and 10 4 -10 5 km 2 , respectively. Values of the rain yield clustered near 10 8 kg/fl for a large portion of the midcontinental United States. Rain yields were slightly lower over the arid southwestern United States, averaging ∼6 × 10 7 kg/fl. In tropical locations the rain yields increased systematically from a tropical continental value of 4 × 10 8 kg/fl to a value of 10 10 kg/fl for the tropical western Pacific Ocean. The observed stability of the rain yield, coupled with demonstrated positive correlations between cloud-to-ground flash density and rainfall amount, suggests that cloud-to-ground lightning data may be useful for inferring monthly convective rainfall statistics in certain rainfall regimes.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JD02064

On the relationship between cloud‐to‐ground lightning and convective rainfall

DUNDEE (Down Under Doppler and Electricity Experiment) is described. DUNDEE was carded out in the vicinity of Darwin, Northern Territory, Australia, during the wet seasons of November 1988 through February 1989, and November 1989 through February 1990. The general goal of DUNDEE was to investigate the dynamical and electrical properties of tropical mesoscale convective systems and isolated deep convective storms. Darwin, situated at the southern tip of the “maritime continent,” experiences both monsoon and “break” period conditions during the wet season. We discuss the observational network deployed for DUNDEE and present preliminary scientific results. One particularly interesting observation is a large contrast in the frequency of total lightning between break period convection (high lightning rates) and convection in the monsoon trough (low lightning rates). A relationship between CAPE (convective available potentional energy) and total flash rate is presented and discussed to explain this obs...

The Down Under Doppler and Electricity Experiment (DUNDEE): Overview and Preliminary Results

The ratio of intracloud lightning (IC) to cloud-to-ground lightning (CG) in thunderstorms is observed to vary with latitude. The reason frequently given for this behavior is that the height of the freezing level, and hence the negative charge center in thunderstorms, varies with latitude, resulting in higher ratios in the tropics compared with those in midlatitudes. This study shows that this hypothesis could well be incorrect. Analysis of cloud and lightning data indicates that the IC/CG ratio is linked to the thickness of the cold cloud region in thunderstorms (0 C to cloud top), rather than to the freezing level height.

What determines the cloud-to-ground lightning fraction in thunderstorms?

Observations of the ratio of cloud to cloud-ground lightning flashes in thunderstorms have been reviewed, and used to obtain empirical relationships between this ratio (z), latitude (λ) and annual thunder-days (T). The 29 observations, covering a latitude range 69°N to 37°S, gave a mean value of z of 3.35. The empirical relationship proposed between z and λ is z(λ) = 4.16 + 2.16 cos3λ, 0 ≤ λ ≤ 60°. From 26 pairs of values of z and T, covering the range 5 to 81 thunderdays per year, the proposed relationship is z(T) = 1.0 + 0.063T, 10 ≤ T ≤ 84 z = 6.3, T > 84. Information on z for high latitudes is sparse. It is probable that z lies between 1 and 2 for λ > 60° and T < 10. The existence of a relationship between z and T is attributed to the fact that both are related to latitude. The relationship between z and λ probably depends on the variation of freezing level height with latitude, and a possible relationship between z and freezing level height is examined. Where both λ and T are known, the prop...

The Ratio of Cloud to Cloud-Ground Lightning Flashes in Thunderstorms

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The Ratio of Cloud to Cloud-Ground Lightning Flashes in Thunderstorms