[1] We present the first global distribution of the average estimated peak currents in negative lightning flashes using 1 year of continuous data from the Vaisala global lightning data set GLD360. The data set, composed of 353 million flashes, was compared with the National Lightning Detection Network TM for peak current accuracy, location accuracy, and detection efficiency. The validation results demonstrated a mean (geometric mean) peak current magnitude error of 21% (6%), a median location accuracy of 2.5 km, and a relative ground flash detection efficiency of 57% averaged over all positive and negative reference flashes, and 67% for all reference flashes above 15 kA. The distribution of peak currents for negative flashes shifts to higher magnitudes over the ocean. Three case study 10 ı 10 ı regions are analyzed, in which the peak current enhancement is extremely sharp at the coastline, suggesting that the higher peak currents for oceanic lightning cannot be solely attributable to network artifacts such as detection efficiency and peak current estimation error. In these regions, the geometric mean and 95th percentile of the peak current distribution for negative cloud to ocean flashes is 22%-88% and 65%-121% higher, respectively, compared to cloud to ground flashes in nearby land regions. Globally, the majority of all negative flashes with estimated peak current magnitude above 75 kA occur over the ocean.Citation: Said, R. K., M. B. Cohen, and U. S. Inan (2013), Highly intense lightning over the oceans: Estimated peak currents from global GLD360 observations,

[1] Lightning discharges generate broadband electromagnetic pulses with a peak component in the very low frequency (VLF; 3-30 kHz) range. VLF waves propagate through the Earth-ionosphere waveguide with relatively low attenuation, enabling the detection of these radio atmospherics at great distances from the lightning discharge. A new technique of long-range (≤6000 km) global lightning geolocation via sferic detection is presented. This new technique catalogs the dominant variation in expected received waveforms in a set of waveform banks, which are then used to estimate the propagation distance and accurately determine the arrival time. Using three sensors in a trial network, this new technique is used to demonstrate a median accuracy of 1-4 km, depending on the time of day. An overall cloud-to-ground (CG) stroke detection efficiency between ∼40 and 60% is estimated by correlating individual lightning stroke events to data from the National Lightning Detection Network (NLDN). Additional events reported by the trial network are shown to have a tight spatial clustering to storm clusters identified by NLDN, suggesting that many of the unmatched events correspond to weak cloud-toground strokes, M components, or cloud pulses. Exploiting an empirical correlation between peak VLF field strength and peak current values reported by NLDN, we also provide unvalidated estimates of the peak current and lightning channel polarity. The trial network does not distinguish between cloud and ground discharges, so these peak current estimates only relate to an Earth-referenced channel current for the subset of reported events that are return strokes.

[1] Analysis of ELF/VLF broadband data from Palmer Station, Antarctica indicates that 76% Terrestrial Gammaray Flashes (TGFs) detected on the RHESSI spacecraft occur in association with lightning-generated radio atmospherics arriving from near the footprint of RHESSI and within a few ms of the TGF. The remaining TGFs are not associated with any radio atmospheric, thus by implication CG lightning. The peak currents of TGFassociated lightning discharges are often among the most intense from a given storm, with the degree of this association apparently varying between oceanic and land regions. The time-integrated ELF energy of the associated sferics (and thus the lightning charge moment) exhibit much less tendency to be large. Statistical analysis of the spread in arrival time suggests a $2 ms variance due to factors other than geometry and measurement error.

Terrestrial gamma‐ray flashes (TGFs) are impulsive (∼1 ms) but intense sources of gamma‐rays associated with lightning activity and typically detected via low orbiting spacecrafts. We present the first catalog of precise (<30 km error) TGF source locations, determined via ground‐based detection of ELF/VLF radio atmospherics (or sferics) from lightning discharges, which enables precise geolocation of lightning locations. We present the distribution of source‐to‐nadir distances, established due to effects of Compton scattering on the escaping photons. We find that TGFs occur in coincidence with the lightning discharge, but with a few ms variance, and that a detectable sferic at long distances is nearly always present. The properties of TGF‐associated sferics and their connection to multiple‐peak TGFs are highly variable and inconsistent, and are classified into two categories.

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