Bangalore/Thiruvananthapuram, Jan 15 (IANS) India Friday launched six 'sounding' rockets - rockets carrying instruments to measure the physical parameters of the upper atmosphere - to study the millennium's longest annular solar eclipse and its effect on the earth's atmosphere, a senior space scientist said.

'The various instruments onboard the six rockets observed the solar eclipse and collected voluminous data the eclipse had on the earth's atmosphere, wind, electric and magnetic fields and plasma,' Indian Space Research Organisation (ISRO) project director P. Ratnakar Rao told IANS from Thiruvananthapuram.

The state-run Indian space agency launched five sounding rockets, including three Rohini 300 series and two Rohini 200 series from the Thumba Equatorial Rocket Launch Station (TERLS) at the Vikram Sarabhai Space Centre (VSSC) in Kerala between 12.20 p.m. and 4 p.m.

The three Rohini 300 rockets, weighing 500 kg each and measuring six metres, were fired up to 125 km as programmed between 1-3 p.m. and Rohini 200, weighing 100 kg and measuring three metres, up to 65 km.

The sixth rocket (Rohini 560), weighing 1550 kg and measuring 10 metres, was launched around 4.30 p.m. from ISRO's spaceport at Sriharikota in Andhra Pradesh, to an altitude of 525 km over the Bay of Bengal.

'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 ionisation and temperature,' Rao said.

Friday's 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 data from the rockets was relayed to our stations at the respective space centres before the rockets plunged into the sea as programmed along with the instruments,' Rao said.

The space agency's Physical Research Laboratory at Ahmedabad and VSSC will compare the data during the eclipse with that of three rockets launched Thursday from VSSC and analyse its effect on the lower atmosphere before and after the celestial spectacle.

'The eclipse passed close to TERLS with 91 percent obscuration of Sun during the event. The maximum obscuration occurred around 1.15 p.m. IST. All the rockets conducted the study of the effects of the annular solar eclipse on the atmospheric structure and dynamics,' Rao noted.

Many scientifically interesting phenomena occur in the diurnal equatorial atmosphere. Equatorial electrojet, equatorial ionization anomaly and equatorial temperature and wind anomaly are examples of such phenomena.

'Interpretation of eclipse data together with space data is expected to give new insights to the earlier eclipse observations,' Rao added.

This was the first ISRO effort to realise sounding rocket systems for a record 11 flights during a short period of two days from its space centres at Thiruvananthapuram and Sriharikota.