Ionospheric <i>D</i> region remote sensing using VLF radio atmospherics

Cummer, Steven A.; Inan, U. S.; Bell, T. F.

doi:10.1029/98rs02381

Cited by 210 publications

(266 citation statements)

References 31 publications

(11 reference statements)

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“…As most of the electromagnetic (EM) energy generated by lightning discharges (termed "sferics") are radiated within the ELF (extremely low frequency) and VLF bands (peaking between 5-10 kHz) (Cummer, 1997;Rakov and Uman, 2003), and due to the weak attenuation of VLF signals (as mentioned above), sferics originating in the tropics and at mid-to high latitudes can be easily detected at MH or DN. Although lightning pulses are very powerful, their duration is very short (up to the order of 10 −4 s) (Rakov and Uman, 2003).…”

Section: Instrumentation and Methodsologymentioning

confidence: 99%

Semi-annual oscillation (SAO) of the nighttime ionospheric D region as detected through ground-based VLF receivers

2016

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Abstract. Earth's middle and upper atmosphere exhibits several dominant large-scale oscillations in many measured parameters. One of these oscillations is the semi-annual oscillation (SAO). The SAO can be detected in the ionospheric total electron content (TEC), the ionospheric transition height, the wind regime in the mesosphere-lower thermosphere (MLT), and in the MLT temperatures. In addition, as we report for the first time in this study, the SAO is among the most dominant oscillations in nighttime very low frequency (VLF) narrowband (NB) subionospheric measurements. As VLF signals are reflected off the ionospheric D region (at altitudes of ∼ 65 and ∼ 85 km, during the day and night, respectively), this implies that the upper part of the D region is experiencing this oscillation as well, through changes in the dominating electron or ion densities, or by changes in the electron collision frequency, recombination rates, and attachment rates, all of which could be driven by oscillatory MLT temperature changes. We conclude that the main source of the SAO in the nighttime D region is NO x molecule transport from the lower levels of the thermosphere, resulting in enhanced ionization and the creation of free electrons in the nighttime D region, thus modulating the SAO signature in VLF NB measurements. While the cause for the observed SAO is still a subject of debate, this oscillation should be taken into account when modeling the D region in general and VLF wave propagation in particular.

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Section: Instrumentation and Methodsologymentioning

confidence: 99%

Semi-annual oscillation (SAO) of the nighttime ionospheric D region as detected through ground-based VLF receivers

2016

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“…Neither these large antenna dimensions, nor these high peak powers, could be straightforwardly achieved in active radio-sounders ("ionosondes") at VLF. Using opportunistic reception of wideband VLF sferics, the mean D-layer electron-density profile parameters have been obtained (Cummer, 1997;Cummer et al, 1998), and transient D-layer responses to both lightninginduced heating/ionization (Cheng and Cummer, 2005) and energetic-particle precipitation have been observed (Cheng et Published by Copernicus Publications on behalf of the European Geosciences Union. 2176 A. R. Jacobson et al: Low-frequency ionospheric sounding with NBE lightning radio emissions al., 2006).…”

Section: Introductionmentioning

confidence: 99%

“…Another approach retains wideband features, but uses opportunistic reception of the natural VLF emissions ("sferics") from lightning strokes (Cummer, 1997;Cummer et al, 1998). This exploits the large effective antenna dimensions (>1 km) and extremely high peak powers (∼GW) of natural lightning-discharge currents.…”

Section: Introductionmentioning

confidence: 99%

Low-frequency ionospheric sounding with Narrow Bipolar Event lightning radio emissions: regular variabilities and solar-X-ray responses

et al. 2007

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Abstract. We present refinements of a method of ionospheric D-region sounding that makes opportunistic use of powerful (10 9 -10 11 W) broadband lightning radio emissions in the low-frequency (LF; 30-300 kHz) band. Such emissions are from "Narrow Bipolar Event" (NBE) lightning, and they are characterized by a narrow (10-µs), simple emission waveform. These pulses can be used to perform timedelay reflectometry (or "sounding") of the D-region underside, at an effective LF radiated power exceeding by ordersof-magnitude that from man-made sounders. We use this opportunistic sounder to retrieve instantaneous LF ionosphericreflection height whenever a suitable lightning radio pulse from a located NBE is recorded. We show how to correct for three sources of "regular" variability, namely solar zenith angle, radio-propagation range, and radio-propagation azimuth. The residual median magnitude of the noise in reflection height, after applying the regression corrections for the three regular variabilities, is on the order of 1 km. This noise level allows us to retrieve the D-region-reflector-height variation with solar X-ray flux density for intensity levels at and above an M-1 flare. The instantaneous time response is limited by the occurrence rate of NBEs, and the noise level in the height determination is typically in the range ±1 km.

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“…[3] In order to examine the thunderstorm effects on the D-layer, recent work has made use of lightning signals to probe ionospheric properties in the D-region [e.g., Cummer et al, 1998]. Cheng and Cummer [2005] and Cheng et al [2007] reported that intense lightning strokes produced transient (up to 15 s) D-layer disturbances, and, from a waveguidemode model [Pappert and Ferguson, 1986], inferred the possible changes of the electron density profiles.…”

Section: Introductionmentioning

confidence: 99%

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

Lay

Shao

2011

J. Geophys. Res.

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[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.

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Ionospheric D region remote sensing using VLF radio atmospherics

Cited by 210 publications

References 31 publications

Semi-annual oscillation (SAO) of the nighttime ionospheric D region as detected through ground-based VLF receivers

Semi-annual oscillation (SAO) of the nighttime ionospheric D region as detected through ground-based VLF receivers

Low-frequency ionospheric sounding with Narrow Bipolar Event lightning radio emissions: regular variabilities and solar-X-ray responses

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

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