[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,

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We report observations of two negative polarity gigantic jets sufficiently near very high‐frequency (VHF) lightning mapping networks that the associated lightning characteristics and charge transfer could be investigated. In both cases the gigantic jet‐producing flash began as ordinary intracloud lightning with upper level channels attempting to exit the cloud, and then produced the upward gigantic jet. Neither flash had developed channels to ground, confirming that the major charge transfer during gigantic jets occurred between the cloud and ionosphere. The leader progression of one event was detected at altitudes above 20 km, demonstrating the possibility of detecting and tracking the propagation of negative jets above the cloud with VHF techniques.

ELF/VLF radio waves (300 Hz–30 kHz) are difficult to generate with practical antennae, because of their extraordinarily long (10–1000 km) wavelengths, and the lossy nature of the Earth's surface at these frequencies. ELF/VLF waves have been successfully generated via amplitude modulated (AM) HF (2–10 MHz) heating of the lower ionosphere. Through the temperature‐dependent conductivity of the lower ionospheric plasma, a patch of the ionospheric current becomes a large radiating ‘antenna’. We implement a new method of ELF/VLF wave generation, herein named ‘geometric modulation’, involving scanning the HF heating beam in a geometric pattern without modulating its power. Utilizing results from the upgraded 3.6 MW radiated HAARP HF antenna array, we show that geometric modulation can enhance ELF/VLF wave generation by up to ∼11 dB over the conventional AM method. Geometric modulation also allows directional launching of the signal into the Earth‐ionosphere waveguide, forming an unprecedented steerable large‐element ELF/VLF ionospheric phased array.