Long‐duration geomagnetic storm effects on the <i>D</i> region of the ionosphere: Some case studies using VLF signal

Choudhury, Abhijit; De, B. K.; Guha, Anirban; Roy, R.

doi:10.1002/2014ja020738

Cited by 18 publications

(12 citation statements)

References 33 publications

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“…The ~100‐s LF oscillations occurred during the main phase of the storm at 05:51–05:56 UT on 11 March 2011. “Primary storm” and “afterstorm/poststorm” effects have been reported in previous studies of VLF/LF waves during magnetic storms (e.g., Araki, ; Belrose & Thomas, ; Choudhury et al, ; Clilverd et al, ; Peter et al, ). The primary storm effects occur during the main phase and show rapid variations in amplitude and phase, whereas the “afterstorm” effects occur several days after the storm, and strong absorption of signals is observed.…”

Section: Resultsmentioning

confidence: 57%

Periodic Oscillations in the D Region Ionosphere After the 2011 Tohoku Earthquake Using LF Standard Radio Waves

et al. 2018

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We report the first observations of~100-s periodic oscillations of intensity in low-frequency (LF) standard radio waves over Japan at 05:51-05:56 UT, which was about 4 min and 42 s after mainshock onset of "the 2011 off the Pacific coast of Tohoku earthquake" on 11 March 2011 (Mw 9.0). The LF radio wave propagation paths used in this study were JJY (Japan, 60 kHz)-Rikubetsu (RKB, Japan), and BPC (China, 68.5 kHz)-RKB, where the minimum distances between the epicenter and the LF propagation paths were 413.6 and 561.5 km, respectively. The observed modulations in intensity and phase were about 0.1 dB and 0.5°, respectively. Based on a numerical simulation of the neutral atmosphere and the wave-hop method, the occurrence time of the~100-s periodic oscillations was in good agreement with the total propagation time of the Rayleigh wave that spread concentrically from the epicenter to the LF propagation paths and acoustic waves propagating vertically from the Earth's surface to the bottom of the ionosphere. Variations in synthesized electric field intensity of ground waves and sky waves, calculated by the wave hop method up to 10 hops, reproduced similar~100-s periodic oscillations that were caused by the difference in arrival time of the acoustic waves excited by the Rayleigh waves at each hop point. The amplitude of the D region electron density variations at 70 km altitude during the~100-s periodic oscillation was estimated to be about 1% compared to the background electron density, based on the numerical simulation.

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Section: Resultsmentioning

confidence: 57%

Periodic Oscillations in the D Region Ionosphere After the 2011 Tohoku Earthquake Using LF Standard Radio Waves

et al. 2018

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“…The D region response to solar flares has been well studied by several previous workers (e.g., Thomson et al, 2005;Grubor et al, 2005;Selvakumaran et al, 2015), which increases sudden ionization, but the geomagnetic storm effect mainly occurs in the high and midlatitude D region due to energetic electron precipitation (EEP) that causes localized electron density enhancements (Clilverd et al, 2010;Kikuchi & Evans, 1983;Peter et al, 2006;Rodger et al, 2007). The geomagnetic storm effect on the D region particularly at low and equatorial latitudes still remains not well known despite few recent efforts (e.g., Choudhury et al, 2015;Kumar et al, 2015). In the past, few attempts were made to study storm effects on the D region by using VLF observations at middle-and high-latitude stations (Araki, 1974; amplitude changes (also called negative storm effect on VLF subionospheric propagation) in the day and more pronounced effect at the night for low and midlatitudes (Australia-Kamchatka radio path).…”

Section: Introductionmentioning

confidence: 99%

“…In the past, few attempts were made to study storm effects on the D region by using VLF observations at middle-and high-latitude stations (Araki, 1974; amplitude changes (also called negative storm effect on VLF subionospheric propagation) in the day and more pronounced effect at the night for low and midlatitudes (Australia-Kamchatka radio path). Choudhury et al (2015) analyzed D-layer preparation time depth during long-duration (>20 hr) geomagnetic storms on the NWC signal recorded at Agartala (23.75°N, 91.25°E), India, during November 2008 to November 2011. They found negative correlation between D-layer preparation time depth and geomagnetic disturbance index (A P ) based on eight cases of long duration geomagnetic storms.…”

Section: Introductionmentioning

confidence: 99%

Effects of St. Patrick's Day Geomagnetic Storm of March 2015 and of June 2015 on Low‐Equatorial D Region Ionosphere

Maurya

Venkatesham²,

Kumar

et al. 2018

JGR Space Physics

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D region effects of the 17–19 March 2015, a St Patrick's Day super geomagnetic storm (Dst = −223 nT), using a navigational transmitter very low frequency (VLF) signal (NWC, 19.8 kHz) recorded at a low‐latitude Indian station, Allahabad (geomag. lat., 16.45°N), have been analyzed and compared with similar strength of the 22–25 June 2015 storm (Dst = −204 nT). During the March storm, NWC signal amplitude decreased on 17 March (main phase of the storm) and recovered on 27 March, which is 1 day after the recovery of the storm, whereas for the June storm, VLF amplitude decreased for 2 days only during its recovery phase. The decrease in the amplitude was pronounced during evening terminator for both the storms. The modeling of VLF signal anomaly on 17 March and on 25 June using Long‐Wave Propagation Capability code shows an increase in the D region reference height (h′) by ~2.6 km and ~2.5 km, for March and June storms, respectively. The D region electron density (Ne) determined using storm time h′ and sharpness factor β shows a decrease in the Ne during the main phase followed by a slow recovery during the recovery phase of the March storm, whereas June 2015 storm showed a decrease in the Ne only on 25 and 26 June. Morlet Wavelet analysis of the amplitude for both the storms shows a presence of strong wave‐like signatures, suggesting propagation of atmospheric gravity waves/traveling ionosphere disturbances to the low latitude D region due to the Joule heating at high latitudes.

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“…Periods of high geomagnetic activity (D st < -50nT) are known to strongly disturb the ionosphere at middle-and low-latitudes (Huang et al, 2005;Qian et al, 2019) and have been observed to signi cantly perturb VLF signals (eg. Choudhury et al, 2015). Hence, data from the World Data Centre has been used to recognize and remove such periods in our analysis to minimize the in uence of high geomagnetic activity in the VLF signal variability.…”

Section: Data and Analysismentioning

confidence: 99%

Lightning Evolution and VLF Perturbations Associated With Category 5 TC Yasa in the South Pacific Region

Redoblado

kumar

Kumar³

et al. 2021

Preprint

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In this paper, we present the D-region ionospheric response during the lifespan (10–19 December 2020) of a severe category 5 tropical cyclone (TC) Yasa in the South Pacific by using the very low frequency (VLF, 3-30 kHz) signals from NPM, NLK, and JJI transmitters recorded at Suva, Fiji. Results indicate enhanced lightning and convective activity in all three regions (eyewall, inner rainbands, and outer rainbands) during the TC Yasa that are also linked to the wave sensitive zones of these transmitter-receiver great circle paths. Of the three regions, the outer rainbands showed the maximum lightning occurrence; hence convective activity. Prominent eyewall lightning was observed just before the TC started to weaken following its peak intensity. Analysis of VLF signal amplitudes showed both negative and positive perturbations (amplitudes exceeding ±3σ mark) lasting for more than 2 hours with maximum change in the daytime and nighttime signal amplitudes of -4.9 dB (NPM) and -19.8 dB (NLK), respectively. The signal perturbations were wave-like, exhibiting periods of oscillations between ~2.2-5.5 hours as revealed by the Morlet wavelet analysis. Additionally, the LWPC modeling of the signal perturbations indicated a 10 km increase in daytime D-region reference height, H¢, and a 12 km decrease in nighttime D-region H¢ during TC Yasa. The D-region density gradients (sharpness), b, showed small perturbations of 0.01–0.14 km-1 from its normal values. We suggest that the observed changes to the D-region parameters are due to the enhanced convection during TC Yasa which excites atmospheric gravity waves producing travelling ionospheric disturbances to the D-region.

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Long‐duration geomagnetic storm effects on the D region of the ionosphere: Some case studies using VLF signal

Cited by 18 publications

References 33 publications

Periodic Oscillations in the D Region Ionosphere After the 2011 Tohoku Earthquake Using LF Standard Radio Waves

Periodic Oscillations in the D Region Ionosphere After the 2011 Tohoku Earthquake Using LF Standard Radio Waves

Effects of St. Patrick's Day Geomagnetic Storm of March 2015 and of June 2015 on Low‐Equatorial D Region Ionosphere

Lightning Evolution and VLF Perturbations Associated With Category 5 TC Yasa in the South Pacific Region

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