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

Dancing sprites:detailed analysis of two case studies

On 29–30 October 2013, a low-light video camera installed at Pic du Midi (2877¿m), recorded transient luminous events above a very active storm over the Mediterranean Sea. The minimum cloud top temperature reached -73°C, while its cloud to ground (CG) flash rate exceeded 30¿fl¿min-1. Some sprite events have long duration and resemble to dancing sprites. We analyze in detail the temporal evolution and estimated location of two series of sprite sequences, as well as the cloud structure, the lightning activity, the electric field radiated in a broad range of low frequencies, and the current moment waveform of the lightning strokes. (i) In each series, successive sprite sequences reflect time and location of corresponding positive lightning strokes across the stratiform region. (ii) The longer time-delayed (>20¿ms) sprite elements correspond to the lower impulsive charge moment changes (iCMC) of the parent strokes (<200¿C¿km), and they are shifted few tens of kilometers from their SP¿+¿CG stroke. However, both short and long time-delayed sprite elements also occur after strokes that produce a large iCMC and that are followed by a continuing current. (iii) The long time-delayed sprite elements during the continuing current correspond to surges in the current moment waveform. They occur sometimes at an altitude apparently lower than the previous short time-delayed sprite elements, possibly because of changes in the local conductivity. (iv) The largest and brightest sprite elements produce significant current signatures, visible when their delay is not too short (~3–5¿ms).Peer ReviewedPreprin

Smelting of high-carbon ferromanganese and silicomanganese with standard phosphorus contents using hydrometallurgical (soda) manganese concentrate

22.00; Translated from Russian (Stal' 1986 (9) p. 40-45)SIGLEAvailable from British Library Document Supply Centre- DSC:9022.06(BISI--25540)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo