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Preparations on to study effects of annular solar eclipse

T.S. Subramanian

Experiments to be done by launching sounding rockets from Thumba, Sriharikota

“The January 15 eclipse will last 11 and eight seconds at its longest”
Changes in wind patterns and atmospheric structure will be studied

CHENNAI: Preparations are under way on a “war-footing” at Thumba and Sriharikota to conduct a battery of experiments to study the effects of the annular solar eclipse on equatorial geophysical phenomena in near-earth space. The phenomena are the equatorial electrojet — an intense band of current system at an altitude of about 100 km — and its controlling factors such as winds and composition of the atmosphere. The experiments will be done by launching a series of sounding rockets from Thumba in Thiruvananthapuram and Sriharikota in Andhra Pradesh, tethered balloons, balloon sondes, besides deploying ground-based radars and optical instruments.

P.S. Veeraraghavan, Director, Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram, said the January 15 eclipse would last 11 and eight seconds at its longest. “There will be sounding rocket flights before and after the eclipse to compare the changes in the atmospheric region.”

“Rare occurrence”

“This is purely a scientific pursuit,” said Prof. R. Sridharan, Director, Space Physics Laboratory, VSSC. He called the eclipse “a rare occurrence taking place right over the magnetic equator during noon-time conditions when all the associated geophysical processes are at their peak.” During the eclipse, the sun will be obscured to the tune of 92 per cent. Only its bright rim will be seen at the time of its maximum obscuration. Hence it is called an annular eclipse. The eclipse begins around 11 a.m. and lasts up to 3 p.m. The maximum obscuration will be around 1.05 p.m. The path of maximum obscuration falls very close to Thumba and Sriharikota. The manager of the Thumba Equatorial Rocket Launching Station (TERLS), Koshy Mammen, has mobilised all his resources and moved one of the spare launchers from Sriharikota and set it up at the TERLS.

The Advanced Technology Vehicle Programme group under the direction of Ratnakar Rao is working round-the-clock for releasing the 12 sounding rockets along with other avionics systems.

“It is the investigation of equatorial geophysical phenomena including equatorial electrojet that really led to the setting up of the TERLS, which has grown into the gigantic VSSC,” said Prof. Sridharan.

The electrojet is an intense band of current that flows in the east-west direction at an altitude of about 100 km. It begins to build up in the morning, intensifies at noon and decreases in the evening. It is essentially driven by the solar ultra-violet radiation and the peculiar configuration of the geomagnetic field over the equator and associated electro-dynamical processes.

Radiation

When a solar eclipse occurs, the radiation from the sun is suddenly cut off. “We want to investigate what happens to the electrojet, the winds, the temperature, the composition, the ionospheric densities, etc., in addition to the processes in the stratosphere, troposphere and the lowest part of the atmospheric region. We want to see how they are altered and how the atmospheric system responds to it,” said Prof. Sridharan.

RH-560 mark II sounding rockets with instruments will lift off from Sriharikota and they will reach an altitude of 550 km. Sounding rockets from Thumba will reach an altitude of 75 to 120 km to provide information on the changes in wind patterns and the atmospheric structure.

There will be four flights of sounding rockets from Thumba on January 14 and there will be five flights the next day, said Mr. Veeraraghavan. There will be one RH-560 launch from Sriharikota on January 15 and another on January 17.

Prof. Sridharan called it “one of the largest coordinated experiments to be carried out to investigate the effect of a solar eclipse on the near earth space” up to an altitude of 120 km.

The electrojet extends plus or minus three degrees in latitude with a width of about 600 km. An interesting feature is that Sriharikota falls just outside that belt while Thumba falls within it. Thus, scientists will study the impact of the solar eclipse both within the electro-jet belt and immediately outside it.

A coordinated attempt to study the effects of a solar eclipse was earlier done on February 16, 1980. “Between 1980 and 2010, ISRO in particular has established a variety of ground-based experimental facilities and we are well equipped now to understand the basic geophysical processes,” said Prof. Sridharan.

To perform these experiments, the SPL has developed a new instrument to measure the winds and electron-density irregularities. Another instrument will measure the changes in the Earth’s atmospheric composition when the solar radiation is cut off.

New instrument

The Physical Research Laboratory, Ahmedabad, has devised an instrument to measure the changes in the electric fields and electron densities in the atmosphere, while a specialist group in the VSSC has developed a tri-methyl aluminium cloud release experiment. During this experiment, the released cloud would glow in the atmosphere due to chemiluminescence, enabling photography of the released cloud from ground stations such as Tirunelveli, Thiruvananthapuram, Kanyakumari and Kollam.

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