On 29–30 May 2012, the Deep Convective Clouds and Chemistry experiment observed a supercell thunderstorm on the southern end of a broken line of severe storms in Oklahoma. This study focuses on an approximately 70 min period during which three mobile Doppler radars operated and a balloon‐borne electric field meter, radiosonde, and particle imager flew through the storm. An overview of the relationships among flash rates, very high frequency (VHF) source densities, and Doppler‐radar‐derived storm parameters is presented. Furthermore, the evolution of the flash distribution relative to the midlevel storm's kinematics and microphysics is examined at two times during a period of rapid storm intensification. The timing of increases in VHF counts in the 8–10 km above ground level (agl) layer, which contained the largest VHF source counts, is similar to the timing of increases in updraft mass flux, in updraft volume, and in graupel volume at approximately 5–9 km agl. Although some increases in VHF source counts had little or no corresponding increase in one or more of the other storm parameters, at least one other parameter had an increase near the time of every VHF increase, a pattern which suggests a common dependence on updraft pulses, as expected from the noninductive graupel‐ice electrification mechanism. A classic bounded weak lightning region was observed initially during storm intensification, but late in the period it appeared to be due to a wake in the flow around the updraft, rather than due to a precipitation cascade around the updraft core as is usually observed.

Previous studies have found that the vertical distribution of sources of very high frequency (VHF) signals from discharges mapped by Lightning Mapping Arrays typically have a secondary maximum in a storm's overshooting top. Low rates of these sources tend to occur continually throughout the lifetime of the overshooting top (OT), rather than sources occurring in the episodic distinct flashes observed at lower altitudes. This study examines the evolution of the VHF OT signature (VHF OT, defined here as a sustained period of ≥4 VHF sources per minute per 200 m layer above a storm's level of neutral buoyancy (LNB)) relative to the evolution of radar reflectivity and IR imagery of overshooting tops in three supercell and two multicell storms. The VHF OT began before OTs were detected in IR satellite imagery of the supercell storms. No OT was observed in IR imagery for either multicell storm, but this lack may have been due to the spatial and temporal resolution of the current IR imager. The VHF OT began near the time the 18 or 30 dBZ echo top rose above the LNB and ended near the time it fell below the LNB. There were too few radar volume scans of OTs in the multicell storms for a correlation analysis. In the supercell storms, however, the maximum altitude of VHF sources typically was less than or equal to the altitude of 18 dBZ echo tops and was correlated with these echo tops (linear correlation coefficient ≥0.86) during the period of the VHF OT.

The Earth Networks Total Lightning Network (ENTLN) launched a new processor (P2021) in December 2021. Some major upgrades were made in the new processor, including a new classification algorithm, a new propagation model, and regional data processing architecture. Ground-truth datasets of natural and rocket-triggered lightning acquired in Florida were used to evaluate the performance characteristics of the new processor. Compared to the last processor launched in 2015 (P2015), the stroke classification accuracy increased from 91% to 94% for natural lightning and from 86% to 88% for rocket-triggered lightning. The location accuracy improved significantly with the median location error decreasing from 215 m to 92 m. On a global scale, we found the number of pulses detected by the ENLTN increased in all regions with an overall detection gain of 149%. One can see modest gains in detection in regions with a fairly dense network of sensors and significant gains in regions where sensor density is much lower. Each of the major upgrades as well as their influences on the performance characteristics of the ENLTN are discussed.

Previous studies have shown that subsequent leaders in positive cloud‐to‐ground lightning (+CG) flashes rarely traverse pre‐existing channels to ground. In this paper, we present evidence that this actually can be common, at least for some thunderstorms. Observations of +CG flashes in a supercell storm in Argentina by Córdoba Argentina Marx Meter Array (CAMMA) are presented, in which 54 (64%) of 84 multiple‐stroke +CG flashes had subsequent leaders following a pre‐existing channel to ground. These subsequent positive leaders are found to behave similarly to their negative counterparts, including propagation speeds along pre‐existing channels with a median of 8 × 106 m/s, which is comparable to that of negative dart leaders. Two representative multiple‐stroke +CG flashes are presented and discussed in detail. The observations reported herein call for an update to the traditional explanation of the disparity between positive and negative lightning.

Lightning data are often used to measure the location and intensity of thunderstorms. This study presents 5 years of data from the Earth Networks Global Lightning Detection Network (ENGLN) in the form of thunder hours. A thunder hour is defined as an hour during which thunder can be heard from a given location, and thunder hours can be calculated for the entire globe. Thunder hours are an intuitive measure of thunderstorm frequency where the 1-h interval corresponds to the life-span of most thunderstorms, and the hourly temporal resolution of the data also represents long-lived systems well. Flash-density-observing systems are incredibly useful, but they have some drawbacks that limit how they can be used to quantify global thunderstorm activity on a climatological scale: flash density distributions derived from satellite observations must sacrifice a great deal of their spatial resolution in order to capture the diurnal convective cycle, and the detection efficiencies of ground-based lightning detection systems are not uniform in space or constant in time. Examining convective patterns in the context of thunder hours lends insight into thunderstorm activity without being heavily influenced by network performance, making thunder hours particularly useful for studying thunderstorm climatology. The ENGLN thunder hour dataset offers powerful utility to climatological studies involving lightning and thunderstorms. This study first shows that the ENGLN thunder hours dataset is very consistent with past measurements of global thunderstorm activity and the global electric circuit using only 5 years of data. Then, this study showcases thunder anomaly fields, designed to be analogous to temperature anomalies, which can be used to diagnose changes in thunderstorm frequency relative to the long-term mean in both time and space.

Abstract. As city governments take steps towards establishing emissions reduction targets, the atmospheric research community is increasingly able to assist in tracking emissions reductions. Researchers have established systems for observing atmospheric greenhouse gases in urban areas with the aim of attributing greenhouse gas concentration enhancements (and thus emissions) to the region in question. However, to attribute enhancements to a particular region, one must isolate the component of the observed concentration attributable to fluxes inside the region by removing the background, which is the component due to fluxes outside. In this study, we demonstrate methods to construct several versions of a background for our carbon dioxide and methane observing network in the Washington, DC, and Baltimore, MD, metropolitan region. Some of these versions rely on transport and flux models, while others are based on observations upwind of the domain. First, we evaluate the backgrounds in a synthetic data framework, and then we evaluate against real observations from our urban network. We find that backgrounds based on upwind observations capture the variability better than model-based backgrounds, although care must be taken to avoid bias from biospheric carbon dioxide fluxes near background stations in summer. Model-based backgrounds also perform well when upwind fluxes can be modeled accurately. Our study evaluates different background methods and provides guidance in determining background methodology that can impact the design of urban monitoring networks.

We provide evidence that Terrestrial Gamma‐Ray Flashes (TGFs), in well isolated thunderstorms, tend to occur during periods of low and declining flash rates, and when the flash amplitudes are larger than average. This conclusion comes from examining the results of 371 manually tracked TGF‐producing thunderstorms. Fermi‐GBM identified TGFs are used for this analysis and lightning data come from both World Wide Lightning Location Network and Earth Networks Total Lightning Network. The data from these storms suggest that TGFs are likely to occur in almost every phase of storms that last longer than an hour, but tend to occur later on in shorter storms. We also note that, in short storms, TGFs are more likely to accompany a flash when the flash rates of the storm are lower than average, and they are less likely per flash during the peak flash rate periods of the storms. We find that the tendency for TGFs to occur while the flash rate is falling and when the amplitudes of flashes (the sum of the absolute values of peak currents of all constituent sferics in the flash) are larger than average, does not depend strongly on the duration of the storms. This implies that not just any lightning flash can or even will produce a TGF, but that the electrical conditions of the storm play a crucial role in TGF production.

Lightning activity is invigorated with the exacerbation of anthropogenic aerosol emission (Westcott, 1995). Deep convective cloud systems produce numerous lightning discharges by the main mechanism of non-inductive charge separation via rebounding collisions between graupel/hail and ice crystals in the presence of supercooled liquid water (