In this study we analyze the discharge morphologies of five confirmed negative sprite‐parent discharges and the associated charge structures of the thunderstorms that produced them. The negative sprite‐parent lightning took place in two thunderstorms that were associated with a tropical disturbance in east central and south Florida. The first thunderstorm, which moved onshore in east central Florida, produced four of the five negative sprite‐parent discharges within a period of 17 min, as it made landfall from the Atlantic Ocean. These negative sprite‐parents were composed of bolt‐from‐the‐blue (BFB), hybrid intracloud‐negative cloud‐to‐ground (IC‐NCG), and multicell IC‐NCGs discharges. The second thunderstorm, which occurred inland over south Florida, produced a negative sprite‐parent that was a probable hybrid IC‐NCG discharge and two negative gigantic jets (GJs). Weakened upper positive charge with very large midlevel negative charge was inferred for both convective cells that initiated the negative‐sprite‐parent discharges. Our study suggests tall, intense convective systems with high wind shear at the middle to upper regions of the cloud accompanied by low cloud‐to‐ground (CG) flash rates promote these charge structures. The excess amount of midlevel negative charge results in these CG discharges transferring much more charge to ground than typical negative CG discharges. We find that BFB discharges prefer an asymmetrical charge structure that brings the negative leader exiting the upper positive charge region closer to the lateral positive screening charge layer. This may be the main factor in determining whether a negative leader exiting the upper positive region of the thundercloud forms a BFB or GJ.

Gigantic jets are atmospheric electrical discharges that propagate from the top of thunderclouds to the lower ionosphere. They begin as lightning leaders inside the thundercloud, and the thundercloud charge structure primarily determines if the leader is able to escape upward and form a gigantic jet. No observationally verified studies have been reported on the thundercloud charge structures of the parent storms of gigantic jets. Here we present meteorological observations and lightning simulation results to identify a probable thundercloud charge structure of those storms. The charge structure features a narrow upper charge region that forms near the end of an intense convective pulse. The convective pulse produces strong storm top divergence and turbulence, as indicated by large values of storm top radial velocity differentials and spectrum width. The simulations show the charge structure produces leader trees closely matching observations. This charge structure may occur at brief intervals during a thunderstorm’s evolution due to the brief nature of convective pulses, which may explain the rarity of gigantic jets compared to other forms of atmospheric electrical discharges.

Here we report the first observations of gigantic jets (GJs) by the Geostationary Lightning Mapper (GLM) on board the Geostationary Operational Environmental Satellite‐R series. Fourteen GJs produced by Tropical Storm Harvey on 19 August 2017 were observed by both GLM and a ground‐based low‐light‐level camera system. The majority of the GJs produced distinguishable signatures in the GLM data, which include long continuous emissions, large peak flash optical energies, and small lateral propagation distances in comparison with other flashes observed by GLM. For two GJs with the best ground‐based images, each have a single pixel that contains the largest optical energy throughout the duration of the GJ and also coincides with the azimuth of the GJ from the video images. The optical energy of the pixel increases as the GJ propagates upward, reaches its peak when the GJ connects to the ionosphere, and then fades away.

This paper reports observation and modeling of five negative sprites occurring above two Florida thunderstorms. The sprites were triggered by unusual types of negative cloud‐to‐ground (CG) lightning discharges with impulse charge moment change ranging from 600 to 1300 C km and charge transfer characterized by a timescale of 0.1–0.2 ms. The negative sprite typically consists of a few generally vertical elements that each contain a bright core and dimmer streamers extending from the core in both downward and upward directions. Modeling results using the measured charge moment change waveforms indicate that the lower ionosphere was significantly modified by the CGs and the lower ionospheric density might have been increased by nearly 4 orders of magnitude due to the most intense CG. Finally, streamer modeling results show that the ionospheric inhomogeneities produced by atmospheric gravity waves can initiate negative sprite streamers, assuming that they can modulate the ionization coefficient.

In this study, we analyze 44 terrestrial gamma‐ray flashes (TGFs) detected by the Fermi Gamma‐ray Burst Monitor (GBM) occurring in 2014–2016 in conjunction with data from the U.S. National Lightning Detection Network (NLDN). We examine the characteristics of magnetic field waveforms measured by NLDN sensors for 61 pulses that occurred within 5 ms of the start‐time of the TGF photon flux. For 21 (out of 44) TGFs, the associated NLDN pulse occurred almost simultaneously with (that is, within 200 μs of) the TGF. One TGF had two NLDN pulses within 200 μs. The median absolute time interval between the beginning of these near‐simultaneous pulses and the TGF flux start‐time is 50 μs. We speculate that these RF pulses are signatures of either TGF‐associated relativistic electron avalanches or currents traveling in conducting paths “preconditioned” by TGF‐associated electron beams. Compared to pulses that were not simultaneous with TGFs (but within 5 ms of one), simultaneous pulses had higher median absolute peak current (26 kA versus 11 kA), longer median threshold‐to‐peak rise time (14 μs versus 2.8 μs), and longer median peak‐to‐zero time (15 μs versus 5.5 μs). A majority (77%) of our simultaneous RF pulses had NLDN‐estimated peak currents less than 50 kA indicating that TGF emissions can be associated with moderate‐peak‐amplitude processes. The lightning flash associated with one of the TGFs in our data set was observed by a Lightning Mapping Array, which reported a relatively high‐power source at an altitude of 25 km occurring 101 μs after the GBM‐reported TGF discovery‐bin start‐time.

Occasionally, lightning will exit the top of a thunderstorm and connect to the lower edge of space, forming a gigantic jet. Here, we report on observations of a negative gigantic jet that transferred an extraordinary amount of charge between the troposphere and ionosphere (∼300 C). It occurred in unusual circumstances, emerging from an area of weak convection. As the discharge ascended from the cloud top, tens of very high frequency (VHF) radio sources were detected from 22 to 45 km altitude, while simultaneous optical emissions (777.4 nm OI emitted from lightning leaders) remained near cloud top (15 to 20 km altitude). This implies that the high-altitude VHF sources were produced by streamers and the streamer discharge activity can extend all the way from near cloud top to the ionosphere. The simultaneous three-dimensional radio and optical data indicate that VHF lightning networks detect emissions from streamer corona rather than the leader channel, which has broad implications to lightning physics beyond that of gigantic jets.

Studies on optical lightning spectroscopy have been performed for over a century. They have focused on cloud-to-ground (CG) discharges, as CG discharges have a vertical orientation and act as their own slit, simplifying the spectrograph design. To create the spectra, prisms, gratings, or a combination of the two (termed 'grisms') are placed in front of a camera or recording device. The optical instruments were assembled to create dispersion in the horizontal direction utilizing the vertical orientation of the CG channel. While optical lightning spectroscopy has been performed since the start of the twentieth century (Salanave, 1961, and references therein), studies seeking to calculate the physical parameters from the spectra were not performed until the

<p>In this presentation we will provide an overview and present preliminary results from a multi-institutional collaborative project, which seeks to detect gigantic jets over hemispheric scales using a combination orbital and ground-based sensors and machine learning. Gigantic jets are a type of transient luminous event (TLE, Pasko 2010, doi: 10.1029/2009JA014860) that escape the cloud top of a thunderstorm and propagate up to the lower ionosphere (80-100 km altitude), transferring tens to hundreds of Coulombs of charge. Our detection methodology primarily uses the Geostationary Lightning Mapper (GLM), which is a staring optical imager in geostationary orbit that detects the 777.4 nm (OI) triplet commonly emitted by lightning (Goodman et al. 2013, doi: 10.1016/j.atmosres.2013.01.006).  Gigantic jets have been shown to have unique signatures in the GLM data from past studies (Boggs et al. 2019, doi: 10.1029/2019GL082278; Boggs et al. 2022, doi: 10.1126/sciadv.abl8731). Thus far, we have built a preliminary, supervised machine learning model that detects potential gigantic jets using GLM, and begun development on a series of vetting techniques to confirm the detections as real gigantic jets. The vetting techniques use a combination of low frequency (LF) and extremely low frequency (ELF) sferic data, in combination with stereo GLM measurements. When our detection methodology grows in maturity, we will deploy it to all past GLM data (2018-present), with the potential to detect thousands of events each year, allowing correlation with other meteorological and atmospheric measurements. We will share the database of gigantic jet detections publicly during and at project conclusion (2025), allowing other researchers to use this data for their own research.</p>