LARGE-SCALE REDUCTIONS IN THE ELECTRON DENSITY OF IONOSPHERIC F-REGION, OBSERVABLE ALONG ROCKET TRAJECTORIES AT LAUNCH

Purpose. The object of the study are electron density depletions (‘holes’) occurring in the ionospheric F-region under the action of rocket exhaust products. The purpose is to present and discuss the results of observations concerning the ionospheric holes that were detected in the course of a number of launches of medium-lift Kosmos vehicles from the Kapustin Yar spaceport. Nei- ther that cosmodrome, nor the rocket type had been subjects of similar analysis before. Design/methodology/approach. The observations at the Kapustin Yar cosmodrome were performed with a portable vertical Doppler sounder. The beats between a reference signal and the one reflected from the ionosphere were subjected to spectral analysis, which allowed identifying the principal mode of the Doppler frequency shift and establishing time dependences of that frequency shift. An ionosonde located nearby was used for monitoring the underlying state of the ionosphere. Findings. The measurements performed with the vertical Doppler sounder near the launch site of the medium-lift Kosmos rocket have allowed obtaining first estimates for the principal parameters of the ionospheric holes arising in the F-region along the vehicle trajectory, as well as for the accompanying quasi-periodic variations in the electron density. The spatial scale sizes of the holes have been found to be in excess of 300 km, while the electron density reductions may attain » 50 %. These results are in agreement with the data obtained by international researchers for effects from heavy- and super heavy-lift launch vehicles. Also, note that the types of propellant differed significantly. The propagation velocity of the hole’s front edge was estimated to be » 140 m/s. The hole formation was accompanied by quasi-periodic variations in the Doppler frequency shift as a result of radar signal scattering from the electron density fluctuations produced by propagating atmospheric gravity- and infrasonic waves. The atmospheric gravity waves showed periods in the range from 7 to 20 minutes, and the infrasonic waves had a period close to 2 min. The amplitudes of quasi-periodic electron density variations were estimated for the two modes to be » 0.3 ¸1.5 % and » 0.02 ¸ 0.03 %, respectively. Conclusions. Medium-lift launch vehicles (mass of a few hundred tons) are capable of forming ionospheric ‘holes’ of several hundred kilometers in size and of reducing the electron density in the F-region by a factor greater than 2.