Low‐mid latitude D region ionospheric perturbations associated with 22 July 2009 total solar eclipse: Wave‐like signatures inferred from VLF observations

Abstract

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.

Changes in the D region associated with three recent solar eclipses in the South Pacific region

“…The wavelet spectra based on the Morlet wavelet analysis of JJI, NWC, and NPM signal filtered amplitude observed during 22 July 2009 total SE [ Maurya et al ., ], 13–14 November 2012 total SE, and 9–10 May 2013 annular SE day for 6 h duration at each station. The black thick contours show 95% confidence line of the period, and the bowel shape contours show the cone of influence; anything below is dubious.…”

“…The total SEs on 22 July 2009 and 13 November 2012 were followed by moderate and intense storms, respectively; however, the geomagnetic disturbances during these SEs were not strong enough to produce any noticeable effect on the low‐latitude D region ionosphere [ Peter et al ., ; Kumar and Kumar , ]. The D region effects of 22 July 2009 SE effects particularly in the Indian and Chinese sectors using ELF‐VLF signals have been studied by several researchers [ Guha et al ., ; Singh et al ., ; Zhang et al ., ; Ohya et al ., ; Pal et al ., ; Phanikumar et al ., ; Maurya et al ., ]. We have primarily used 22 July SE data [ Maurya et al ., ] for modeling the D region ionosphere for JJI‐Suva path and comparing periodic WLS associated with 12 November 2012 and 9 May 2013 SEs.…”

“…The D region effects of 22 July 2009 SE effects particularly in the Indian and Chinese sectors using ELF‐VLF signals have been studied by several researchers [ Guha et al ., ; Singh et al ., ; Zhang et al ., ; Ohya et al ., ; Pal et al ., ; Phanikumar et al ., ; Maurya et al ., ]. We have primarily used 22 July SE data [ Maurya et al ., ] for modeling the D region ionosphere for JJI‐Suva path and comparing periodic WLS associated with 12 November 2012 and 9 May 2013 SEs. The D region ionospheric response time of ~ 4–13 min estimated between the first encounter of three SEs with respective TRGCPs and start of decrease in the amplitude is consistent with observations by Clilverd et al .…”

“…The major portion of solar radiation during the solar eclipses (SEs) is reduced suddenly, which produces temporal changes in the Earth's atmosphere including ionosphere [e.g., Anderson et al ., ; Antonia et al ., ; Chimonas and Hines , ; Chimonas , ; Singh et al ., ; Afraimovich et al ., ; Clilverd et al ., ; Baran et al ., ; Chandra et al ., ; Zhang et al ., ; Chuo , ; Maurya et al ., , and references therein]. Each SE is different from others in terms of their occurrence time, day and year, location of observing station, percentage of the solar disk occultation, and state of the near Earth's environment [ Baran et al ., ]; therefore, continuous investigations on SEs ionospheric effects, mainly in the lower ionosphere, are needed to better establish the SE effects and their variability.…”

“…Maurya et al . [] using Morlet wavelet analysis of JJI, Japan, (22.2 kHz) signal amplitude studied periodic wave‐like signatures (WLS) of period ~16–40 min associated with AGWs during total SE of 22 July 2009. However, no studies on the D region effects of total SE of 13–14 November 2012 and annular SE of 9–10 May 2013 could be found in the literature.…”