Space Centre is getting ready for a rare celestial event - Dated : January 12, 2010
A rare and longest annular solar eclipse of this millennium will occur on January 15, 2010 visible in the southern part of the country. An annular eclipse occurs when the Moon covers the centre of the Sun, but not its edges. This leaves a ring (or annulus) of the Sun, which will be visible around its edges with the Moon darkening its centre.

Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram will launch a series of Rohini Sounding Rockets from TERLS, Thumba to investigate the effects of the solar eclipse on the atmosphere. Four sounding rockets of series RH 200 and RH300MK II with peak altitudes of about 70km and 116 km respectively will be launched on 14th January to collect data. This will be followed by another five launches on the next day, the eclipse day. Two larger Rohini rockets of the series RH 560 MK II will also be launched from the Satish Dhawan Space Centre (SDSC), Sriharikota, one each 14th and 15th January, which will have a peak altitude of 548 km.

The occurrence of eclipse will result in a sudden cut-off of solar radiation. This affects the atmospheric structure and dynamics. There will be a large reduction in ionization and temperature. On January 15th, at around IST 1:14 pm, the eclipse will pass close to TERLS with 91% obscuration and the edges will touch SDSC, Sriharikota, with an obscuration of 85%. Although the centre line just misses the main land, the path being 323 km wide, this should still be a unique opportunity to investigate the effects of the fast varying solar flux on the photochemistry and electrodynamics of the different atmospheric regions, especially the equatorial mesopause and ionosphere-thermosphere regions.

The uniqueness of this eclipse is that it occurs during the noontime, when the incoming solar radiation is in its maximum, Sun being at its zenith. Further, the obscuration of Sun during this eclipse is exceptionally long, about 11 min 08 sec. The maximum obscuration occurs during noon hours (13:15 1ST). As a consequence, it provides an opportunity to study, perhaps for the first time, the solar eclipse induced effects in the noontime Equatorial Region.

The ionosphere above 120 km becomes turbulent on certain days in the post sunset period with structures or eddies appearing in ionization. It would be an interesting problem to look into the possible generation of these turbulent structures during the peak eclipse period when the geophysical conditions are likely to resemble those of the post sunset period. Such a study would certainly give more insights into the generation mechanism of these structures that pose a major threat to modern day GPS based navigation systems.

The main payload instruments that will fly in the Rohini rockets during these experiments are given below.

Langmuir Probes and Electric Field Probes to study the characteristics of E-region plasma waves and generation process associated with sub-meter waves in relation to plasma temperature.

Trimethyl Aluminum Experiment (TMA) to derive neutral winds using TMA trails, ground based photography and a chain of magnetometers.

Electron density and Neutral Wind (ENWi) Probe consisting of a velocity probe and a Langmuir probe, for measurement of ionospheric E-region neutral winds, electron density and irregularity strength.

Earths Atmospheric Composition Explorer (EACE) - to make very fast measurements on the neutral atmospheric composition. The measurements will be taken in a scanning mode during the ascent and descent of the proposed rocket flights during and after the eclipse.

Chaff Experiment to investigate the temperature and horizontal wind perturbations in the middle atmosphere.

These experiments will coordinate modern ground-based eclipse observations with in situ space measurements. Interpretation of eclipse data together with space data will give new insights to the earlier eclipse observations. With so many atmospheric-ionospheric parameters being analysed, this is going to be one of the most comprehensive campaigns, ever attempted, during a solar eclipse anywhere in the world.
 
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