At 2336:56 UTC on 12 December 2009, a bright gigantic jet (GJ) was recorded by an observer in Italy. Forty‐nine additional sprites, elves, halos and two cases of upward lightning were observed that night. The location of the GJ corresponded to a distinct cloud top (−34°C) west of Ajaccio, Corsica. The GJ reached approximately 91 km altitude, with a “trailing jet” reaching 49–59 km, matching with earlier reported GJs. The duration was short at 120–160 ms. This is the first documented GJ which emerged from a maritime winter thunderstorm only 6.5 km tall, showing high cloud tops are not required for initiation of GJs. In the presence of strong vertical wind shear, the meteorological situation was different from typical outbreaks of fall and winter thunderstorms in the Mediterranean. During the trailing jet phase of the GJ, a sprite with halo triggered by a nearby cloud‐to‐ground lightning flash occurred at a relatively low altitude (<72 km). At the same time, the trailing jet and beads were reilluminated. Electromagnetic waveforms from Hungary, Poland, and the USA revealed this GJ is the first reported to transfer negative charge (approximately 136 C) from the ionosphere to the positively charged origins in the cloud (i.e., a positive cloud‐to‐ionosphere discharge, +CI), with a large total charge moment change of 11600 C km and a maximum current of 3.3 kA. Early VLF transmitter amplitude perturbations detected concurrently with the GJ confirm the production of large conductivity changes due to electron density enhancements in the D‐region of the ionosphere.

Very low frequency (VLF) electromagnetic signals from navigational transmitters propagate worldwide in the Earth‐ionosphere waveguide formed by the Earth and the electrically conducting lower ionosphere. Changes in the signal properties are signatures of variations in the conductivity of the reflecting boundary of the lower ionosphere which is located in the mesosphere and lower thermosphere, and their analysis is, therefore, a way to study processes in these remote regions. Here we present a study on amplitude perturbations of local origin on the VLF transmitter signals (NPM, NLK, NAA, and JJI) observed during tropical cyclone (TC) Evan, 9–16 December 2012 when TC was in the proximity of the transmitter‐receiver links. We observed a maximum amplitude perturbation of 5.7 dB on JJI transmitter during 16 December event. From Long Wave Propagation Capability model applied to three selected events we estimate a maximum decrease in the nighttime D region reference height (H′) by ~5.2 km (13 December, NPM) and maximum increase in the daytime D region H′ by 6.1 km and 7.5 km (14 and 16 December, JJI). The results suggest that the TC caused the neutral densities of the mesosphere and lower thermosphere to lift and sink (bringing the lower ionosphere with it), an effect that may be mediated by gravity waves generated by the TC. The perturbations were observed before the storm was classified as a TC, at a time when it was a tropical depression, suggesting the broader conclusion that severe convective storms, in general, perturb the mesosphere and the stratosphere through which the perturbations propagate.

Two Very Low Frequency (VLF) AWESOME remote sensing systems located at Algiers, Algeria (36.45°N, 3.28°E) and Sebha, Libya (27.02°N, 14.26°E) monitor VLF signal perturbations for evidence of ionospheric disturbances. During the EuroSprite‐2007 campaign a number of Transient Luminous Events (TLEs) were captured over the Mediterranean Sea by cameras at Pic du Midi (42.94°N, 0.14°E) and at Centre de Recherches Atmosphériques (CRA) in southwestern France (43.13°N, 0.37°E). The cameras observations are compared to collected VLF AWESOME data. We consider early VLF perturbations observed on 12–13, 17–18 October and 17–18 December, 2007. The data from the two VLF receivers confirm the association between TLEs and early VLF signal perturbations with the perturbations amplitudes dependent on the observation configuration i.e. whether the TLE is near the receiver, near the transmitter, or far from both and the scattering process. The results also reveal that the early VLF perturbations can occur in the absence of a TLE.

, seventeen distinct sprite events including 3 halos 17 were observed above a storm in northwestern Mediterranean Sea, with a video camera at Pic 18 du Midi (42.93N; 0.14E; 2877 m). The sprites occurred at distances between 280 and 390 km 19 which are estimated based on their parent CG location. The MCS-type storm was 20 characterized by a trailing-stratiform structure and a very circular shape with a size of about 70,000 km 2 (cloud top temperature lower than-35 °C) when the TLEs were observed. The cloud to ground (CG) flash rate was large (45 min-1) one hour before the TLE observation and very low (<5 min-1) during it. Out of the 17 sprite events, 15 parent +CG (P+CG) strokes have been identified and their average peak current is 87 kA (67 kA for the 14 events without halo), while the associated charge moment changes (CMC) that could be determined, range from 424 to 2088±20% C km. Several 2-second videos contain multiple sprite events: one with four events, one with three events and three with two events. Column and carrot type sprites are identified, either together or separately. All P+CG strokes are clearly located within the stratiform region of the storm and the second P+CG stroke of a multiple event is back within 30 the stratiform region. Groups of large and bright carrots reach ~70 km height and ~80 km 31 horizontal extent. These groups are associated with a second pulse of electric field radiation in 32 the ELF range which occur ~5 ms after the P+CG stroke and exhibits the same polarity, which 33 is evidence for current in the sprite body. VLF perturbations associated with the sprite events 1 were recorded with a station in Algiers.

[1] Lightning strokes are capable of initiating disturbances in the lower ionosphere, whose recoveries persist for many minutes. These events are remotely sensed via monitoring subionospherically propagating very low frequency (VLF) transmitter signals, which are perturbed as they pass through the region above the lightning stroke. In this paper we describe the properties and characteristics of the early VLF signal perturbations, which exhibit long recovery times using subionospheric VLF transmitter data from three identical receivers located at Algiers (Algeria), Tunis (Tunisia), and Sebha (Libya). The results indicate that the observation of long recovery events depends strongly on the modal structure of the signal electromagnetic field and the distance from the disturbed region and the receiver or transmitter locations. Comparison of simultaneously collected data at the three sites indicates that the role of the causative lightning stroke properties (e.g., peak current and polarity), or that of transient luminous events may be much less important. The dominant parameter which determines the duration of the recovery time and amplitude appears to be the modal structure of the subionospheric VLF probe signal at the ionospheric disturbance, where scattering occurs, and the subsequent modal structure that propagates to the receiver location.