Changes in VLF radiowaves in ionosphere observed during TSE

The scientists from the Indian Institute of Geomagnetism (IIG) monitored Very Low Frequency (VLF) radiowaves covering long distances through the earth-ionosphere and found increase in its signal strength during TSE at around 50 to 60 kms above the earth.

IIG scientists conducted simultaneous experiments to record at Allahabad, Varanasi, and Nainital, the VLF radio wave signals transmitted from Japan, Australia and a place near Tirunelveli in Tamil Nadu, using special receivers, its Director Dr Archana Bhattacharya said.
"The VLF signals that were monitored had frequencies around 20 kHz, and covered long distance through the earth-ionosphere, underwent reflections from the lowest part of the ionosphere, the D region," Bhattacharya said.

VLF radio wave signals are also used for facilitating communication techniques of submarines whose frequency radiowaves get attenuated while being deep in the sea.

The three stations -- Allahabad, Varanasi and Nainital -- are also part of a global network of VLF recording stations with AWESOME (Atmospheric Weather Electromagnetic System for Observation, Modeling, and Education) receivers, a collaboration started by USA's Stanford University.
IIG scientists also found that during the TSE, there was no production of ionization in the ionosphere and the ions and electrons in the lowest part of it recombined at a rapid rate causing the electron density in the 'D' region to decrease significantly, she said.

"The scientists found that the VLF signal amplitude was very much enhanced because there was no production of ionisation during TSE and at the same time the existing electrons and ions recombined rapidly," Bhattacharya said.
For the signal from Japan to Allahabad and Varanasi, the propagation paths were largely along the solar eclipse totality path. At these two stations huge increase in the strength of the signal were observed around the time of the TSE as compared to a control day, Bhattacharya said.
This is attributed to the significant decrease in the electron density in the 'D' region of the ionosphere and the simultaneous increase in the width of the earth-ionosphere during the TSE.
This is only preliminary analysis and further modelling is being done with the data collected during the TSE, she said.

"Observations of ultra-low frequency (ULF) variations in the magnetic field carried out by the IIG scientists at Bhagalpur using an induction coil magnetometer showed a decrease in the amplitude of the so-called Schumann resonance," she said.

Schumann resonance is a global phenomenon witnessed at a frequency of about 8 Hz caused by lightning discharges in the electromagnetic resonant cavity formed by the surface of the earth and ionosphere, Bhattacharya added.

This is the first time Indian scientists have conducted these types of experiments during this rare celestial event, she said, adding, a team of scientists from Banaras Hindu University in Varanasi and ARIES in Nainital were also engaged in conducting the simultaneous experiments regarding effects of total solar eclipse on VLF electromagnetic waves.

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