Heavy Ion Flows in the Upper Ionosphere of the Venusian North Pole

M. Persson , Y. Futaana , H. Nilsson , G. Stenberg Wieser , M. Hamrin , A. Fedorov (1) , T. L. Zhang , S. Barabash

1 IRAP - Institut de recherche en astrophysique et planétologie

We investigate the heavy ion density and velocity in the Venusian upper ionosphere near the North Pole, using the Ion Mass Analyzer, a part of the Analyzer of Space Plasmas and Energetic Atoms 4, together with the magnetic field instruments on Venus Express. The measurements were made during June-July 2014, covering the aerobraking campaign with lowered altitude measurements ( 130 km). The plasma scale heights are 15 km below 150-km altitude and 200 km at 150-400-km altitude. A clear trend of dusk-to-dawn heavy ion flow across the polar ionosphere was found, with speeds of 2-10 km/s. In addition, the flow has a significant downward radial velocity component. The flow pattern does not depend on the interplanetary magnetic field directions nor the ionospheric magnetization states. Instead, we suggest a thermal pressure gradient between the equatorial and polar terminator regions, induced by the decrease in density between the regions, as the dominant mechanism driving the ion flow.

Mots clés: Venus ionosphere nightward flow; trans-terminator flow; ion dynamics; dusk-to-dawn flow pattern; Venus North Pole

Domaines: Planète et Univers [physics]

M. Persson, Y. Futaana, H. Nilsson, G. Stenberg Wieser, M. Hamrin, et al.. Heavy Ion Flows in the Upper Ionosphere of the Venusian North Pole. Journal of Geophysical Research Space Physics, 2019, 124, pp.4597-4607. ⟨10.1029/2018JA026271⟩. ⟨insu-03674435⟩