Characteristics and conditions of production of transient luminous events observed over a maritime storm

International audienceOn the night of 15/16 November 2007, cameras in southern France detected 30 transient luminous events (TLEs) over a storm located in the Corsican region (France). Among these TLEs, 19 were sprites, 6 were halos, and 5 were elves. For 26 of them, a positive “parent” cloud‐to‐ground lightning (P+CG) flash was identified. The peak current of the P+CG flashes for the sprites had an average value of 63 kA and had a maximum value of 125 kA. The flashes for the halos and the elves had average values of 272 and 351 kA, respectively, and they had maximum values of 312 and 384 kA, respectively. No TLEs were detected after negative CG flashes with very large peak currents. Among the 26 P+CG flashes, 23 were located in a stratiform region with reflectivity values lower than 45 dBZ. The CG flashes in this region were classified into two groups according to the time interval separating them from the following flash: one group with values less than 2 s and one with values greater than 2 s. About 79% of all CGs were produced in a sequence of at least two flashes less than 2 s apart. For 65.5% of the sequences, the first flash was positive with an average peak current of 73 kA, while the later +CG flashes in a sequence had much lower peak currents. Several triangulated sprites were found to be shifted from their P+CG flashes by about 10 to 50 km and preferentially downstream. The observations suggest that the P+CG flashes can initiate both sprites and other CG flashes in a storm

Illumination of mesospheric irregularity by lightning discharge

International audienceTheoretical model calculations recently predicted the existence of mesospheric irregularities which assist the initiation of sprites. Here we report the experimental detection of a ∼3–19 km3 large mesospheric irregularity at ∼80–85 km height which is illuminated by the electromagnetic field of an intense positive cloud-to-ground lightning discharge. While the lightning discharge causes a prompt group of four sprites above the lightning discharge, the mesospheric irregularity is found at a horizontal distance at least ∼15–20 km away from the sprite group and it rebrightens ∼40–60 ms after the sprite group occurrence. This rebrightening is driven by a local quasi-static electric field enhancement with a charge moment ∼4–20 Ckm which causes the irregularity to develop a downward descending luminous column from ∼75–85 km height. The quasi-static electric field enhancement is caused by the reorganization of residual charge inside the thundercloud during a high-level activity of intracloud discharges with ∼10–20 pulses per ms. Such mesospheric irregularities might have an effect on the wave propagation of 100 kHz radio waves which are used for atomic time transfer and marine navigation