High temporal and spatial-resolution detection of D-layer fluctuations by using time-domain lightning waveforms

Abstract

[1] This paper presents a new method for probing ionospheric D-layer fluctuations with time-domain very-low and low-frequency (VLF/LF) lightning waveforms detected several hundred kilometers away from lightning storms. The technique compares the amplitude and the time delay between the direct ground wave and the first-hop ionospheric reflection of the lightning signal to measure the apparent D-layer reflectivity and height. This time-domain technique allows a higher time and spatial resolution measurement of the D-layer fluctuations compared to previously reported frequency-domain techniques. For a region near a nighttime thunderstorm, results demonstrate that the apparent reflectivity and height exhibit significant variation on spatial scales of tens of kilometers and over time periods of hours. The range of the reflectivity variation was observed as large as 100% away from the averaged reflectivity for some localized regions, and the height varies by as much as 5% (4 km). The time scales and propagation velocities of the fluctuations appear to be consistent with signatures of atmospheric gravity waves at D-layer altitudes, and the direction of the fluctuation propagation suggests that the gravity waves are originated from the storm. Superimposed on the fluctuations, a general decreasing trend (by ∼4-8 km) in reflection height over the nighttime is observed. In some localized ionosphere regions, apparent splitting of the D-layer by 2-4 km is observed to last a short time period of about 10 min.

Revisiting "Narrow Bipolar Event" intracloud lightning using the FORTE satellite

“…In fact it is an exceptionally uncluttered negative cloud-toground stroke, such as those used in a recent study of Dregion VLF/LF reflection (Lay and Shao, 2011). Figure 5 is similar to Fig.…”

Ionospheric response to infrasonic‐acoustic waves generated by natural hazard events

“…Waves above the Brunt-Väisälä frequency (>3.3 mHz, periods <5 min) have also been detected in mesospheric airglow spectral data [Pilger et al, 2013a[Pilger et al, , 2013b, consistent with acoustic or evanescent waves near the acoustic cutoff frequency; remote sensing of the D region likewise reveals short acoustic and gravity wave periods [Lay and Shao, 2011;Marshall and Snively, 2014]. Recent GPS observations of ionospheric TEC following the Moore, Oklahoma EF5 tornado-producing storm revealed ∼4 min periodicities southward of the storm center [Nishioka et al, 2013], illustrating clearly the direct spatial and temporal connections between tropospheric weather and localized periodic disturbances of the F region ionosphere.…”

Plasma irregularities in the D-region ionosphere in association with sprite streamer initiation

“…Tropospheric thunderstorms are well known to be able to disturb the lower ionosphere by convective atmospheric gravity waves and by lightning electric fields, leading to conductivity enhancement, electron density depletions and D-layer reflection height splitting 1,2,7,20 . However, most of those are large spatial scale processes.…”

“…For tropospheric thunderstorms, low electron density in this transition region enables the penetration of lightning electric fields, leading to many not yet well-understood thunderstorm effects such as electron density fluctuations and depletions 1,2 , as well as occasionally the formation of spectacular sprite discharges 3 . Moreover, for meteor events, the D-region is usually the lowest altitude region that meteoroids can reach owing to significant friction caused by the rapid increase of air density, resulting in plasma irregularities observed as low-altitude meteor trail echoes in radar observations 4 .…”