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

Jacobson, A. R.; Holzworth, R. H.; Lay, E. H.; Heavner, M.; Smith, David A.

doi:10.5194/angeo-25-2175-2007

Cited by 15 publications

(34 citation statements)

References 23 publications

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“… Cheng et al [2006] measured electron density profile variations of 16 nights in 2004 by fitting the Long Wave Propagation Capability (LWPC) modeled spectra to measured sferic spectra. Jacobson et al [2007] retrieved the D region reflection height variations in 3 years by comparing the arrival time of ground waves and ionospheric echoes. However, systematic measurements of D region variations showing time and spatial scales are lacking.…”

Section: Introductionmentioning

confidence: 99%

Midlatitude nighttime D region ionosphere variability on hourly to monthly time scales

2010

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[1] Significant temporal variability of the nighttime D region is well known, but its inaccessibility means that the time scales, magnitudes, and sources for that variability are not well understood. We probed the ionospheric D region by measuring the high-power broadband very low frequency (VLF) signals launched by lightning and propagating in the Earth-ionosphere waveguide. We analyzed broadband sferic data of July and August 2005 recorded by our sensors located near Duke University by comparing measured sferic spectra to model results and extracted the height of an assumed exponential electron density profile for each measurement. The measured nighttime D region electron density profile heights showed large temporal variations of several kilometers on some nights and relatively stable behaviors on others. The measured hourly average heights in 260 h ranged between 82.0 and 87.2 km, with a mean value of 84.9 km and a standard deviation of 1.1 km. The maximum variation in the 5 h period was around just above 4.0 km and the maximum variation in the 1 h period was around 1.3 km, with sharper gradients observed over shorter time periods. We also observed spatial variability as large as 2.0 km over 5°latitudes on some nights and no spatial variability on others. On some nights, the temporal variability exhibited a close correlation with the occurrence rate of lightning discharges under the probed region. This suggests that the direct energy coupling between lightning discharges and lower ionosphere can be a significant source of the D region variability. However, on other nights, the measured height temporal variability showed weak to no correlation with local lightning, displaced lightning (as would be expected for lightning-induced electron precipitation), or geomagnetic activities. These measurements suggest that nighttime D region variability may be driven by many sources.Citation: Han, F., and S. A. Cummer (2010), Midlatitude nighttime D region ionosphere variability on hourly to monthly time scales,

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Section: Introductionmentioning

confidence: 99%

Midlatitude nighttime D region ionosphere variability on hourly to monthly time scales

2010

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“…Notwithstanding the low probability that LASA with its bandwidth limit could even observe the bouncing-wave phenomenon, we have combed through an extensive and welldocumented LASA sferic-waveform NBP data set (Jacobson et al, 2007) but have found no multi-period oscillations suggestive of the bouncing-wave signature. We note however that a single secondary peak has been reported in some LASA waveforms of NBPs (Hamlin et al, 2007), without ringing oscillations, but it is not evident that this secondary peak and the phenomena reported by Nag et al are the same process.…”

Section: Quasi-repetitive Burstsmentioning

confidence: 99%

Observations of multi-microsecond VHF pulsetrains in energetic intracloud lightning discharges

2011

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Abstract. Certain intracloud lightning discharges emit energetic, multi-microsecond pulsetrains of radio noise. Observations of this distinctive form of lightning date from 1980 and have involved both ground-based and satellite-based radio recording systems. The underlying intracloud lightning discharges have been referred to as "Narrow Bipolar Pulses", "Narrow Bipolar Events", and "Compact Intracloud Discharges". An important discriminant for this species of radio emission is that, in the range above ∼30 MHz, it consists of several microseconds of intense radio noise.When the intracloud emission is viewed from a satellite, each radio pulsetrain is received both from a direct lightning-to-satellite path, and after some delay, from a path via ground. Thus one recording of the radio emission, if of sufficient length, contains the "view" of the intracloud emission from two different angles. One view is of radiation exiting the emitter into the upper hemisphere, the other for radiation exiting into the lower hemisphere. However, the propagation conditions are similar, except that one path includes a ground reflection, while the other does not.One would normally expect a stereoscopic double view of the "same" emission process to provide two almost congruent time series, one delayed from the other, and also differing due to the different propagation effects along the two signal paths, namely, the ground reflection. We present somewhat unexpected results on this matter, using recordings from the FORTE satellite at a passband 118-141 MHz, with simultaneous data at 26-49 MHz. We find that the 118-141 MHz pulsetrain's detailed time-dependence is completely uncorrelated between the two views of the process. We examine statistics of the 118-141 MHz pulsetrain's integrated power and show that the power emitted into the lower hemisphere, on average, exceeds the power emitted into the upper hemiCorrespondence to: A. R. Jacobson (abramj@u.washington.edu) sphere. Finally, we examine statistical measures of the amplitude distribution and show that the 118-141 MHz signal emitted downward is slightly more dominated by discrete, temporally-narrow impulses than is the signal emitted upward.

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“…The NBE is a special type of incloud discharge process that produces intense and narrow VLF/LF pulses [Smith et al, 1999], and the ionospheric reflections can be readily identified in the time waveforms in the LASA record. However, due to infrequent occurrence of NBEs in thunderstorms, an ensemble of many storms were needed to derive the general diurnal variations [Jacobson et al, 2007[Jacobson et al, , 2010 and, therefore, spatially resolved measurements were difficult to achieve.…”

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

Cited by 15 publications

References 23 publications

Midlatitude nighttime D region ionosphere variability on hourly to monthly time scales

Midlatitude nighttime D region ionosphere variability on hourly to monthly time scales

Observations of multi-microsecond VHF pulsetrains in energetic intracloud lightning discharges

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

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