Observations of the Solar Wind Interaction with Venus using the ASPERA-4 Ion Mass Analyser and Magnetometers onboard the Venus Express Spacecraft

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Student thesis: Doctoral ThesisDoctor of Philosophy

Original languageEnglish
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  • SUFFOLK COUNTY COUNCIL
Award date26 Jan 2015
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Abstract

Venus Express is the first European mission to Venus and will help to answer questions such as: What governs the escape processes of the atmosphere? How did it end up with the atmospheric state it’s currently in? What role does the green-house effect play on Venus? These are important questions for the evolution of Earth.
The solar minimum in 2009 was one of the lowest on record, and by 2006 minimum conditions were already in place. Utilising the Analyser of Space Plasma and Energetic Ions (ASPERA-4) Ion Mass Analyser (IMA) and the paired magnetometers on board Venus Express the relation between the ions and flux ropes are examined. First, by using the magnetometer to identify the flux rope in the ionosphere and then by using the IMA to point out interesting coincidences. The altitude of ropes are dependent on the time spent in the ionosphere; the ropes which had been in the ionosphere longer had an increased weight. However, the occurrence of flux ropes and a high and low energy populations of ions is coincidental.
Venus has no substantial magnetic field and thus it currently it has no barrier to solar wind scavenging of the atmosphere, despite which the atmosphere on Venus is dense. Flux ropes are investigated to determine whether they a part of the replenishment or loss of atmosphere. Venus boundaries are examined during 2007, and 2011 / 2012 going toward solar maximum. A new use of the transition parameter is put forward; to aid with boundary placement. The bow shock is located with an automatic algorithm and this is then compared with previous models, giving a sense of Venus reaction to solar activity. It is shown that the bow shock position is largely unchanged. The ion composition boundary and the magnetic pile-up boundary are also located. They coincide to within one IMA accumulation period, but the Ion Composition Boundary (ICB) is in general inside the Magnetic Pile-up Boundary (MPB).
Finally, solar transients at both solar minimum and solar maximum are investigated to see whether they increase the loss rate. During solar minimum the passage of comet 2P/Encke, and of two Coronal Mass Ejections (CME) and a co-rotating interaction region were investigated. In solar maximum three potential CMEs are selected using the WSA-Enlil solar wind prediction model and then the real data are compared to Enlil predictions. It is found that when the comet 2P/Encke was in the vicinity the concentration of high energy ions, especially oxygen, was raised. CMEs interacts with the Venus magnetosphere to add heavier ions to the solar wind.