Observation‐constrained modeling of the ionospheric impact of negative sprites

Abstract

This paper reports observation and modeling of five negative sprites occurring above two Florida thunderstorms. The sprites were triggered by unusual types of negative cloud‐to‐ground (CG) lightning discharges with impulse charge moment change ranging from 600 to 1300 C km and charge transfer characterized by a timescale of 0.1–0.2 ms. The negative sprite typically consists of a few generally vertical elements that each contain a bright core and dimmer streamers extending from the core in both downward and upward directions. Modeling results using the measured charge moment change waveforms indicate that the lower ionosphere was significantly modified by the CGs and the lower ionospheric density might have been increased by nearly 4 orders of magnitude due to the most intense CG. Finally, streamer modeling results show that the ionospheric inhomogeneities produced by atmospheric gravity waves can initiate negative sprite streamers, assuming that they can modulate the ionization coefficient.

Observations of Red Sprites Above Hurricane Matthew

“…Although the minimum iCMC for triggering negative sprites is estimated to be −320 C‐km (Qin et al, ), the iCMC produced by negative sprite‐producing CG strokes usually exceeds −450 C‐km (Boggs et al, ; Li et al, ), which is much higher than the typical threshold (around +300 C‐km) for positive sprite‐producing iCMCs (e.g., Lu et al, ). The streamers of negative sprites are usually dim and terminate at relatively high altitude (Li et al, ), indicating the excitation by a lightning current with relatively short timescale (<0.5 ms for the cases examined by Li et al, , and Liu et al, ). Therefore, it is possible that for the negative CGs in Figure a with iCMCs exceeding the threshold of sprite production, the timescale of charge transfer after the return stroke was not sufficiently long to initiate streamers.…”

On negative Sprites and the Polarity Paradox

“…Negative CG flashes typically outnumber positive ones by 10 to 1; however, the vast majority of documented sprites were observed during ground observations and found by a margin of at least 1,000 to 1 to be triggered by positive CG lightning (Williams et al, 2007). So far, only 22 sprites have been linked to negative ground flashes unambiguously (Barrington-Leigh & Inan, 1999;Boggs et al, 2016;Lang et al, 2013;Li et al, 2012;Liu et al, 2016;Lu et al, 2012;Lu et al, 2016;Lyons, 2011;Taylor et al, 2008). This sprite polarity paradox was further deepened by reports that exceptional, strong negative CG flashes generally failed to produce sprites (Williams, 2001;Williams et al, 2007).…”

Determination of sprite streamers altitude based on N2 spectroscopic analysis

“…Because of the restrictions imposed by the model, the method developed in the present paper is based on separate local streamer simulations conducted at different altitudes under similar conditions [e.g., Pasko , ; Qin and Pasko , ] and reasonable values of the ambient electric field needed for the propagation of sprite streamers and 0.9 [e.g., Hu et al , ; Li et al , ; N. Y. Liu et al , ; Qin et al , ]. It will be very interesting to push the simulation beyond and compare with simulations of streamers initiated under more realistic conditions of ambient electric field, charges species, and ionospheric inhomogeneities [e.g., Liu et al , , ] and to study the application of the method introduced in the present paper.…”

“…Y. Liu et al, 2009;Qin et al, 2013b]. It will be very interesting to push the simulation beyond and compare with simulations of streamers initiated under more realistic conditions of ambient electric field, charges species, and ionospheric inhomogeneities [e.g., Liu et al, 2015Liu et al, , 2016 and to study the application of the method introduced in the present paper.…”