Ultra low frequency waves at Venus: Observations by the Venus Express spacecraft. (15th October 2017)

• Record Type: Journal Article
• Authors: Fränz, M.; Echer, E.; Marques de Souza, A.; Dubinin, E.; Zhang, T.L.
• Is Part Of: Planetary and space science. Volume 146(2017)
• Page Start: 55
• Page End: 65
• Publication Date: 2017-10-15
• Subjects: Solar wind-Venus interaction -- Planetary magnetosheaths -- Plasma waves -- Induced magnetospheres; Space sciences -- Periodicals; Atmosphere, Upper -- Periodicals; Sciences spatiales -- Périodiques; Haute atmosphère -- Périodiques; 523
• DOI: 10.1016/j.pss.2017.08.011
• Languages: English
• ISSNs: 0032-0633

Abstract

Abstract: The generation of waves with low frequencies (below 100 mHz) has been observed in the environment of most bodies in the solar system and well studied at Earth. These waves can be generated either upstream of the body in the solar wind by ionization of planetary exospheres or ions reflected from a bow shock or in the magnetosheath closer to the magnetic barrier. For Mars and Venus the waves may have special importance since they can contribute to the erosion of the ionopause and by that enhance atmospheric escape. While over the past years many case studies on wave phenomena observed at Venus have been published most statistical studies have been based on magnetic observations only. On the other hand the generation mechanisms and transport of these waves through the magnetosphere can only be quantified using both magnetic and particle observations. We use the long time observations of Venus Express (2006–2014) to determine the predominant processes and transport parameters. First we demonstrate the analysis methods in four case studies, then we present a statistical analysis by determining transport ratios from the complete Venus Express dataset. We find that Alfvenic waves are very dominant (>80%) in the solar wind and in the core magnetosheath. Fast waves are observed mainly at the bow shock (around 40%) but also at the magnetic barrier where they may be most important for the energy transfer into the ionosphere. Their occurrence in the magnetotail may be an artifact of the detection of individual plasma jets in this region. Slow mode waves are rarely dominating but occur with probability of about 10% at the bow shock and in the pile-up-region. Mirror mode waves have probability <20% in the magnetosheath slightly increasing towards the pile-up-boundary. Highlights: First statistical analysis of plasma wave modes observed at Venus. Covering 8 years of observation by Venus Express. Both magnetic field and particle data are analyzed. Four observational cases discussed in detail. Compressional fast mode waves are most important for energy transfer into ionosphere.