IONIZATION HOLE CAMPAIGN - A COORDINATED ROCKET AND GROUND-BASED STUDY AT THE ONSET OF EQUATORIAL SPREAD-F - FIRST RESULTS

A comprehensive multi-technique campaign involving the launch of two h igh altitude RH-560 rockets was carried out from Sriharikota (SHAR), I ndia, a near-equatorial rocket launching station at the onset of equat orial spread-F, along with a host of ground-based complementary experi ments at other locations spread over the country. The main objectives were to obtain the background ionospheric and thermospheric conditions at the onset of equatorial spread-F, and to be able to evaluate the r elative importance of the various agencies, the neutral dynamics in pa rticular. Multiple barium cloud releases, in situ plasma diagnostic me asurements, along with complementary optical and radio probing experim ents were carried out as a part of this campaign. The presence of larg e scale gradients in the ambient electric fields at similar to 185km a ltitude and also of vertical winds of significant magnitudes at higher altitudes were found. The presence of large scale irregularities in t he ion densities at heights above 250 km in a region of negative backg round density gradient is one of the significant new results. The deta ils of the Ionization hole campaign along with the first results are p resented and discussed in the context of the present knowledge of the phenomenon of equatorial spread-F. (C) 1997 Elsevier Science Ltd.