Cross field instability and ionization irregularities in the equatorial E region

Abstract

FOUR Nike Apache rockets with Langmuir probe and plasma noise probe payloads were flown from Thumba (dip latitude 0° 47′ S) to measure the electron density, electron temperature and ionization irregularities in the E region. The measurements revealed the presence of irregularities in electron density with amplitudes of 5 to 20% in the scale size range of 30–300 m, and with amplitudes of 1 to 2% in the scale size range 1–15 m (refs. 1–3). The irregularities were observed in several discrete height ranges. The observations near rocket apogee of the irregularities with scale sizes of a few metres or less were found to be due to rocket motion in the medium1,2. The rest of the irregularities observed on these flights represent genuine ionization irregularities actually present in the ambient medium. Most of these were found to occur in regions where the background electron density exhibits a definite type of gradient. Their positions of occurrence lead us to believe that, depending on the time of the day at which observations are made, electron density gradients of a given sign promote the generation of these irregularities while gradients with the opposite sign inhibit their growth. Results from all the four flights lead us to the same conclusion. For the sake of brevity, only results from two representative flights are presented here. These are typical results and full details are being published elsewhere.