The longest annular solar eclipse of this millennium occurred on January 15, 2010. The eclipse was well visible in the southern parts of the India. On this unique occasion, Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram successfully launched a total of eleven Rohini series of indigenous Sounding Rockets from TERLS, Thumba and Satish Dhawan Space Centre (SDSC), Sriharikota, to investigate the effects of the solar eclipse on the atmosphere. All the payloads (scientific instruments) of the rockets were developed in-house by VSSC.

.Many scientifically interesting phenomena occur in the diurnal equatorial atmosphere. Equatorial Electrojet (EEJ), Equatorial Ionization Anomaly (EIA) and Equatorial Temperature and Wind Anomaly (ETWA) are examples of such phenomena. When solar eclipse occurs, there will be a sudden cut-off of solar radiation. This cut-off will affect the atmospheric structure and dynamics and there will be a large reduction in ionization and temperature. Todays eclipse offered a unique opportunity to scientists to investigate the effects of fast varying solar flux on the photochemistry and electrodynamics of the different atmospheric regions, especially the equatorial mesopause and ionosphere-thermosphere regions.

The main payload instruments that flew in the sounding rockets during these experiments are:

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 were taken in a scanning mode during the ascent and descent of the rocket flights during and after the eclipse.

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

Results of these experiments will coordinate ground-based eclipse observations with in situ space measurements. Interpretation of eclipse data together with space data is expected to give new insights to the earlier eclipse observations.

This was the first ISRO effort to realise sounding rocket systems for a record 11 flights during a short period of two days from TERLS and SDSC.

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