KSK Geomagnetic Research Laboratory

Allahābād, India

KSK Geomagnetic Research Laboratory

Allahābād, India
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Phanikumar D.V.,Aryabhatta Research Institute of Observational science | Kwak Y.-S.,Korea Astronomy and Space Science Institute | Patra A.K.,National Atmospheric Research Laboratory | Maurya A.K.,KSK Geomagnetic Research Laboratory | And 2 more authors.
Advances in Space Research | Year: 2014

In this paper, we analyze VLF signals received at Busan to study the the D-region changes linked with the solar eclipse event of 22 July 2009 for very short (∼390 km) transmitter-receiver great circle path (TRGCP) during local noon time 00:36-03:13 UT (09:36-12:13 KST). The eclipse crossed south of Busan with a maximum obscuration of ∼84%. Observations clearly show a reduction of ∼6.2 dB in the VLF signal strength at the time of maximum solar obscuration (84% at 01:53 UT) as compared to those observed on the control days. Estimated values of change in Wait ionospheric parameters: reflection height (h′) in km and inverse scale height parameter (β) in km-1 from Long Wave Propagation Capability (LWPC) model during the maximum eclipse phase as compared to unperturbed ionosphere are 7 km and 0.055 km-1, respectively. Moreover, the D-region electron density estimated from model computation shows 95% depletion in electron density at the height of ∼71 km. The reflection height is found to increase by ∼7 km in the D-region during the eclipse as compared to those on the control days, implying a depletion in the Lyman-α flux by a factor of ∼7. The present observations are discussed in the light of current understanding on the solar eclipse induced D-region dynamics. © 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.


Selvakumaran R.,Indian Institute of Geomagnetism | Maurya A.K.,KSK Geomagnetic Research Laboratory | Gokani S.A.,Indian Institute of Geomagnetism | Veenadhari B.,Indian Institute of Geomagnetism | And 6 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2015

The D-region ionospheric perturbations caused by solar flares which occurred during January 2010-February 2011, a low solar activity period of current solar cycle 24, have been examined on NWC transmitter signal (19.8 kHz) recorded at an Indian low latitude station, Allahabad (Geographic lat. 25.75°N, long. 81.85°E). A total of 41 solar flares, including 21 C-class, 19 M-class and 01 X-class, occurred during the daylight part of the NWC-Allahabad transmitter receiver great circle path. The local time dependence of solar flare effects on the change in the VLF amplitude, time delay between VLF peak amplitude and X-ray flux peak have been studied during morning, noon and evening periods of local daytime. Using the Long Wave Propagation Capability code V 2.1 the D-region reference height (H/) and sharpness factor (β) for each class of solar flare (C, M and X) have been estimated. It is found that Dregion ionospheric parameters (H/, β) strongly depend on the local time of flare's occurrence and their classes. The flare time electron density estimated by using H/ and β shows maximum increase in the electron density of the order of ~80 times as compared to the normal day values. The electron density was found to increase exponentially with increase in the solar flux intensity. The solar flare effect on horizontal component (H) of the Earth's magnetic field over an equatorial station, Tirunelveli (Geographic lat., 8.7°N, long., 77.8°E, dip lat., 0.4°N), shows a maximum increase in H of ~8.5% for M class solar flares. The increase in H is due to the additional magnetic field produced by the ionospheric electrojet over the equatorial station. © 2015 Elsevier Ltd.


Veenadhari B.,Indian Institute of Geomagnetism | Kumar S.,Indian Institute of Geomagnetism | Tulasi Ram S.,Indian Institute of Geomagnetism | Singh R.,KSK Geomagnetic Research Laboratory | Alex S.,Indian Institute of Geomagnetism
Indian Journal of Radio and Space Physics | Year: 2012

The corotating interaction region (CIR) induced magnetic storms which occurred during solar minimum are investigated to study their effects on equatorial and low-latitude ionosphere and geomagnetic field at Indian sector. This work was a part of Indian CAWSES campaign for the period of March - April 2006. The penetration electric fields play a crucial role in modifying equatorial electric fields during severe magnetic storms and these effects are not studied in detail for moderate magnetic storm originated by CIRs. The present paper investigates the effects of CIR related moderate storms and found that during the moderate magnetic storms, the short lived (duration of 2 - 3 h) penetration of high latitude electric fields to equatorial ionosphere exists during local morning and noon hours during main phase as inferred from changes in EEJ with the response to interplanetary electric field. The variations of EEJ are linearly correlated with the sudden changes in interplanetary electric field (IEFY) around morning to noon hours, which confirms existence of the penetration of electric fields.


Singh A.K.,Banaras Hindu University | Singh R.,KSK Geomagnetic Research Laboratory | Veenadhari B.,Indian Institute of Geomagnetism
Advances in Space Research | Year: 2012

Response of the D-region of the ionosphere to the total solar eclipse of 22 July 2009 at low latitude, Varanasi (Geog lat.; 25.27°N; Geog long.; 82.98°E; Geomag lat = 14°55' N) was investigated using ELF/VLF radio signal Tweeks, a naturally occurring VLF signal and radio signals from various VLF navigational transmitters are first time used simultaneously to study the effect of total solar eclipse (TSE) Tweeks occurrence is a nighttime phenomena but the obscuration of solar disc during TSE in early morning leads to tweek occurrence The changes in D-region ionospheric VLF reflection heights (h) and electron density (n e: 22.6-24.6 cm -3) during eclipse have been estimated from tweek analysis The reflection height increased from ∼89 km from the first occurrence of tweek to about ∼93 km at the totality and then decreased to ∼88 km at the end of the eclipse, suggesting significant increase in tweek reflection height of about 5.5 km during the eclipse The reflection heights at the time of totality during TSE are found to be less by 2-3 km as compared to the usual nighttime tweek reflection heights This is due to partial nighttime condition created by TSE A significant increase of 3 dB in the strength of the amplitude of VLF signal of 22.2 kHz transmitted from JJI-Japan is observed around the time of the total solar eclipse (TSE) as compared to a normal day The modeled electron density height profile of the lower ionosphere depicts linear variation in the electron density with respect to solar radiation as observed by tweek analysis also These low latitude ionospheric perturbations on the eclipse day are discussed and compared with other normal days © 2012 COSPAR Published by Elsevier Ltd All rights reserved.


Maurya A.K.,KSK Geomagnetic Research Laboratory | Singh R.,KSK Geomagnetic Research Laboratory | Veenadhari B.,Indian Institute of Geomagnetism IIG | Kumar S.,University of The South Pacific | Singh A.K.,Banaras Hindu University
Natural Hazards and Earth System Sciences | Year: 2013

The present study reports the VLF (very low frequency) sub-ionospheric perturbations observed on transmitter JJI (22.1 kHz), Japan, received at the Indian low-latitude station, Allahabad ( geographic lat. 25.41 N, long 81.93 E), due to Wenchuan earthquake (EQ) that occurred on 12 May 2008 with the magnitude 7.9 and at the depth of 19 km in Sichuan province of Southwest China, located at 31.0 N, 103.4 E. The nighttime amplitude fluctuation analysis gives a significant increase in fluctuation and dispersion two days before EQ, when it crosses 2σ criterion. However, there was no significant change observed in the amplitude trend. The diurnal amplitude variation shows a significant increase in the amplitude of JJI signal on 11 and 12 May 2008. The gravity wave channel and changes in the electric field associated with this EQ seem to be the potential factors of the observed nighttime amplitude fluctuation, dispersion, and significant increase in the signal strength. © Author(s) 2013. CC Attribution 3.0 License.


Maurya A.K.,KSK Geomagnetic Research Laboratory | Singh R.,KSK Geomagnetic Research Laboratory | Kumar S.,University of The South Pacific | Kumar D.V.P.,Aryabhatta Research Institute of Observational science | Veenadhari B.,Indian Institute of Geomagnetism IIG
2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014 | Year: 2014

The present study reports presence of periodic Wave-Like Signatures (WLS) in the D-region ionosphere detected using NWC, Australia, VLF navigational transmitter signal (19.8 kHz) observed at Allahabad, an Indian low latitude station. The observed WLS are associated with series of solar flares which includes 12 C, 3 M and 2 X class flares occurred during the month of May 2013. Significant variations are observed on NWC-VLF amplitude and phase due to different classes of flares which occurred at different solar zenith angles. The wavelet analysis of VLF amplitude on control day reveals presence of WLS with periods 40-180 minutes during day/night and night/day transition times which are probably generated due to passage of dusk and dawn solar terminator. Flare day WLS are observed with period varying 90-200 minutes and are remarkably different in their period, occurrence duration/time and amplitude depending on the class and occurrence time of flare and are more prominent during morning and evening times when D-region is in developing stage. The WLS on flare day are probably generated by solar flare induced gravity waves which may cause periodic changes in temperature, electron density, and plasma conductivity in the ionosphere. The present observations seem to shed additional light on the current understanding of gravity wave induced D-region dynamics. © 2014 IEEE.


Maurya A.K.,KSK Geomagnetic Research Laboratory | Phanikumar D.V.,Aryabhatta Research Institute of Observational science | Singh R.,KSK Geomagnetic Research Laboratory | Kumar S.,University of The South Pacific | And 5 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2014

We present first report on the periodic wave-like signatures (WLS) in the D region ionosphere during 22 July 2009 total solar eclipse using JJI, Japan, very low frequency (VLF) navigational transmitter signal (22.2 kHz) observations at stations, Allahabad, Varanasi and Nainital in Indian Sector, Busan in Korea, and Suva in Fiji. The signal amplitude increased on 22 July by about 6 and 7 dB at Allahabad and Varanasi and decreased by about 2.7, 3.5, and 0.5 dB at Nainital, Busan, and Suva, respectively, as compared to 24 July 2009 (normal day). The increase/decrease in the amplitude can be understood in terms of modal interference at the sites of modes converted at the discontinuity created by the eclipse intercepting the different transmitter-receiver great circle paths. The wavelet analysis shows the presence of WLS of period ~16-40 min at stations under total eclipse and of period ~30-80 min at stations under partial eclipse (~85-54% totality) with delay times between ~50 and 100 min at different stations. The intensity of WLS was maximum for paths in the partially eclipsed region and minimum in the fully eclipsed region. The features of WLS on eclipse day seem almost similar to WLS observed in the nighttime of normal days (e.g., 24 July 2009). The WLS could be generated by sudden cutoff of the photo-ionization creating nighttime like conditions in the D region ionosphere and solar eclipse induced gravity waves coming to ionosphere from below and above. The present observations shed additional light on the current understanding of gravity waves induced D region ionospheric perturbations. © 2014. American Geophysical Union. All Rights Reserved.


Singh A.K.,Banaras Hindu University | Singh R.,KSK Geomagnetic Research Laboratory | Singh R.P.,Banaras Hindu University | Adams K.,New Hill | Dowden R.L.,New Hill
Advances in Space Research | Year: 2015

Initial results of subionospheric very low frequency (VLF) perturbations observed on NWC (19.8 kHz) and NPM (21.4 kHz) transmitter signals at low latitude ground station Varanasi, India, during the period January-June 2010, are presented. Characteristics and occurrence rates of these events mainly observed during nighttime are studied. Most of the early VLF events had slow recovery with amplitude perturbations of 0.5-4.5 dB and phase changes of 3-12°. Temporal variation of the events is studied. World Wide Lightning Location Network data along with the broadband VLF data are analyzed to find the location of causative lightning discharge and/or the sferics associated with these early VLF events. Lightning induced changes in D-region ionospheric conductivity are attributed to the perturbations in the VLF signals. © 2014 COSPAR.


Maurya A.K.,KSK Geomagnetic Research Laboratory | Veenadhari B.,Indian Institute of Geomagnetism | Singh R.,KSK Geomagnetic Research Laboratory | Kumar S.,University of The South Pacific | And 7 more authors.
Journal of Geophysical Research: Space Physics | Year: 2012

Dispersive atmospherics (tweeks) observed during 2010 simultaneously at two low-latitude stations, Allahabad (geomagnetic latitude, 16.05N) and Nainital (geomagnetic latitude, 20.48N), have been used to estimate the nighttime D region electron density at the ionospheric reflection height under the local nighttime propagation (21:00-02:00 LT or 15:30-20:30 UT). The analysis of simultaneously recorded tweeks at both the stations on five international quiet days during one month each from summer (June), winter (January), and equinox (March) seasons shows that the D region electron density varies 21.5-24.5 cm-3 over the ionospheric reflection height of 85-95 km. The average values of Wait lower ionospheric parameters: ionospheric reference height h and sharpness factor are almost same during winter (85.9-86.1 km, 0.51-0.52 km -1) and equinox (85.6-85.7 km, 0.54 km-1) seasons. The values of h and during summer season are about 83.5 km and 0.60 km-1 at both stations. Overall, equivalent electron density profile obtained using tweek method shows lower values of electron density by about 5-60% than those obtained using the International Reference Ionosphere (IRI-2007) model and lower/higher by 2-68% than those obtained using rocket technique. The electron density estimated using all three techniques (tweek, IRI-2007, and rocket) is consistent in the altitude range of 82-98 km. The estimated geographic locations of causative lightnings of tweeks were matched with the locations and times of lightnings detected by the World-Wide Lightning Location Network (WWLLN). The WWLLN detected about 27.5% of causative lightnings of tweeks simultaneously observed at both the stations. © 2012. American Geophysical Union. All Rights Reserved.


Maurya A.K.,Indian Institute of Geomagnetism | Singh R.,KSK Geomagnetic Research Laboratory | Singh R.,Stanford University | Veenadhari B.,Indian Institute of Geomagnetism | And 8 more authors.
Journal of Geophysical Research: Space Physics | Year: 2012

A total of 19,308 tweeks recorded during April 2007 to March 2008, at Allahabad, a low-latitude station in the Indian sector, has been used to study seasonal occurrence which shows maximum tweek occurrence of about 63% during summer season and about 19% and 18% occurrences during equinox and winter seasons. Maximum occurrence of tweeks during summer season is consistent with the larger number of lightnings detected by World Wide Lightning Location Network in the Indian and Asia Oceania regions during summer as compared to that during equinox and winter. Seasonally, tweek (ionospheric) reflection height in the premidnight (18:00-00:00 LT) during winter is less as compared to that during equinox and summer. Annual (seasonal average) variation of the mean ionospheric reflection height shows a gradual increase in the reflection height from about 19:30 to 04:30 LT. The annual average of postmidnight (00:00-06:00 LT) reflection height is about 5 km higher as compared to that in the premidnight. Our initial results on the variability in the ionospheric reflection height under pure nighttime propagation (21:00-03:00 LT) on magnetically quiet days show a day-to-day variability of up to 8 km. Theoretically calculated attenuation of the Earth-ionosphere waveguide for first six tweek modes in the early and late night periods (21:00-00:00 LT; 00:00-03:00 LT) is less compared to that in the dusk (18:00-21:00 LT) period. The higher attenuation in the dusk period and most of the tweeks in the dawn period traveling partially under daytime conditions explain the lower occurrence of tweeks in these periods. Copyright 2012 by the American Geophysical Union.

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