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

Abstract

We estimate D region changes due to 22 July 2009 total solar eclipse (SE), 13–14 November 2012 total SE, and 9–10 May 2013 annular SE, using VLF navigational transmitters signal observations at Suva, Fiji. The North West Cape (NWC) signal (19.8 kHz) showed an amplitude and phase decrease of 0.70 dB and 23° during November SE and 2.0 dB and 90° during May SE. The modeling using Long Wave Propagation Capability code for NWC‐Suva path during November and May SEs showed an increase in average D region reflection height (H′) and sharpness factor (β) by 0.6 and 0.5 km and 0.012 and 0.015 km−1, respectively. The July total SE for JJI‐Suva path showed an increase in H′ of 1.5 km and a decrease in β of 0.055 km−1. The decrease in the electron density calculated using SE time H′ and β is maximum for July total SE and minimum for May annular SE. The effective recombination coefficient estimated from the decay and recovery of signal phase associated with May annular SE was higher (27%) than normal daytime value 5.0 × 10−7 cm−3 s−1 and varied between 1.47 × 10−6 and 1.15 × 10−7 cm−3 s−1 in the altitude 70 to 80 km. Morlet wavelet analysis of signals amplitude shows strong wave‐like signatures (WLS) associated with three SEs with period ranging 24–66 min, but the intensity and duration of WLS show no clear dependence on SE magnitude and type. Apart from the cooling spot, the eclipse shadow can also generate WLS associated with atmospheric gravity waves.

The 22 July 2009 Total Solar Eclipse: Modeling D Region Ionosphere Using Narrowband VLF Observations

“…In above equation , H ′ and β are the key parameters, which give altitude N e (z) profile and have been used by many workers to calculate D region electron density height profile using LWPC modeling of narrowband VLF observations (e.g., Clilverd et al, ; Guha et al, ; Han & Cummer, , ; Kumar et al, ; Thomson et al, ). In the modeling process first, we model control day amplitude and phase of the VLF signal, which in this case is the NWC signal (19.8 kHz).…”

“…In above equation (1), H 0 and β are the key parameters, which give altitude N e (z) profile and have been used by many workers to calculate D region electron density height profile using LWPC modeling of narrowband VLF observations (e.g., Clilverd et al, 2001;Guha et al, 2010;Han & Cummer, 2010a, 2010bKumar et al, 2016;Thomson et al, 2007). In the modeling process first, we model control day amplitude and phase of the VLF signal, which in this case is the NWC signal ( As shown in Figure 1, the TRGCPs of NWC signal to five stations of (1) Allahabad, (2) Varanasi, (3) Nainital, (4) Busan, and (5) Suva cover regions from no-eclipse to partiality to totality region in low and equatorial sectors.…”

“…Since past several decades, TSEs' studies using VLF waves have given episodically chances to study D region ionosphere. There are reports on the D region studies by using VLF observations during several TSEs (e.g., Clilverd et al, 2001;Guha et al, 2010Guha et al, , 2012Kumar et al, 2016;Maurya et al, 2014;Ohya et al, 2012;Phanikumar et al, 2014;Reeve & Rycroft, 1972;Singh et al, 2012Singh et al, , 2011. But still, studies are limited because of the rare occurrence of TSEs.…”

“…Prior to this report, an extensive modeling of the D region during 11 August 1999 TSE using VLF observations at multiple sites was carried out by Clilverd et al () in the European sector, which covered midlatitude to high‐latitude region. There are some studies on 22 July 2009 TSE effects using both broadband (300 Hz to 30 kHz) and narrowband (fixed frequency) VLF signal observations (e.g., Guha et al, ; Kumar et al, ; Ohya et al, ; Phanikumar et al, ; Singh et al, ; Zhang et al, ). But none of these studies was focused on modeling of D region ionosphere using a comprehensive data set from multiple sites covering whole eclipse region from the start of eclipse totality in India to its end in the Pacific Ocean.…”

The D Region Response to the August 2017 Total Solar Eclipse and Coincident Solar Flare

“…Very little such activity is observed after the solar eclipse, however, and this includes delayed effects of the solar eclipse, such as atmospheric gravity waves (Dang et al, ). (Atmospheric gravity waves have apparently been observed using VLF sensing during previous solar eclipses; Kumar et al, ; Maurya et al, . The observational geometry for the 2017 eclipse was not ideal to detect the traveling atmospheric disturbances predicted by Dang et al, , however, at least in part due to the NAA transmitter being off on the day of the eclipse.…”