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Solar-cycle dependence of the heliospheric magnetic field

Our sun is a rotating gaseous body of which the atmosphere is constantly blown away from its surface, forming a stellar wind. The resulting bubble in interstellar space is called the heliosphere. The solar wind is a highly conducting plasma into which the solar magnetic field is imbedded. Consequently, the field is drawn away from the Sun and the combination with rotation lead to a spiral structure for heliospheric magnetic field (HMF). The HMF changes with solar activity. A measure of this activity is the number of sunspots, which are cooler and therefore darker regions on the Sun through which magnetic flux escapes. The number of sunspots increases with solar activity, with a period of approximately 11 years, and has been documented since the 1600s. The transport of charged particles inside the heliosphere depends, amongst other things, on the structure and the magnitude of the HMF. Since we don’t have in situ measurements throughout the heliosphere, it is vital that models be tested against the available data. If they do well, we can assume that they will also give at least reasonable results in regions of the heliosphere where no measurements are available. Spacecraft measurements of the HMF are available from the 1960s to date. Moreover, the theory to derive the spiral magnetic field is easily understood with undergraduate knowledge of Electromagnetism. The project consists of four parts: 1. Gaining a basic understanding of how the magnetic properties of the Sun changes with solar activity. 2. Derivation of the so-called Parker spiral field from first principles. 3. Analysis of spacecraft data to study the solar-cycle dependence of the magnitude and the direction of the HMF. This is the main part of the project. 4. Comparison of the predictions of the Parker spiral field with observations.
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Research Area: 
Space Physics

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