PhD Project

As a graduate student in the space physics group at the University of Washington I worked with Robert Winglee and Erika Harnett. My main research interest is the solar wind interaction with the planetary magnetospheres of Mercury and Saturn.

My thesis research is a study in three-dimensional simulations of the planetary magnetospheres of Mercury and Saturn, elucidating the relative importance of internal conditions (e.g. sources of heavy ions) versus upstream control (e.g. the effects of solar wind or interplanetary magnetic field (IMF)) to plasma processes at both planets. My multi-fluid model includes different heavy ions as multiple fluids. Multi-fluid modeling of these disparate systems is driven by the data and observations of the Mariner 10, Messenger and Cassini spacecraft.

Flux Rope Generation at Mercury

Flux Ropes at Mercury

At Mercury, I have predicted the development of reconnection in association with flux ropes similar to those at Earth, but on a time scale of minutes and a closer radial distance of 3-5 RM. Additionally, with geometry similar to ground-based observations, I show that much of Mercury's dayside magnetic field can be eroded and enhanced plumes of sodium ions outflow at high latitudes into the solar wind during southward interplanetary magnetic field (IMF). This supports the theory that such high latitude enhancements are controlled by IMF-regulated magnetospheric processes.

Modeling the Centrifugal Interchange Cycle at Saturn

Centrifugal Interchange at Saturn

Magnetic and plasma signatures from the Cassini Plasma Spectrometer (CAPS) and magnetometer (MAG) instruments on board the Cassini spacecraft orbiting Saturn motivated my magnetospheric simulations of Saturn. CAPS observed hot, tenuous plasma interchanging with cool, denser plasma. Cassini measurements such as these prompt questions about the extent to which internal or solar wind conditions control these plasma processes.

Saturn is dominated by a source of cold heavy ions: Enceladus, an icy moon deeply embedded in Saturn's inner magnetosphere. A recently discovered plume of ice and water vapor emanates from Enceladus' south pole; this plume creates a torus of particles centered near the moon's orbit. It is believed that the cold Enceladus plasma flows out from Saturn while other sources feed the inner magnetosphere via frequent injections of warm energetic plasma sheet plasma. The cold outwelling plasma interspersed with hot injections, dubbed ‘the centrifugal interchange cycle,’ is similar to a Rayleigh-Taylor instability. I use my multi-fluid model to probe the global geometry of these interchanging fingers of plasma and determine the extent to which their development is influenced by external factors such as the IMF and internal factors such as the concentration of ions in the Enceladus torus.

These simulations demonstrate that interchange finger development can be enhanced by certain internal and external conditions. Increased convection when the IMF is anti-parallel to Saturn's magnetic field allows for growth in the inner magnetospheric plasma that is centrifugally interchanging. In addition, increased densities in the Enceladus ion torus produce an enhancement in plasma interchange.

Saturn-Titan Model

Saturn-Titan Multi-Fluid Model

The Winglee group has recently succeeded in implementing a multifluid/multiscale model which couples the local Titan model of Snowden et al. (2007), embedding it within the framework of the global Saturn model (Kidder et al., 2009).

Here Titan is located in the premidnight sector at 21 SLT. The ions from the solar wind, Saturn's ionosphere, Enceladus torus and Titan's ionosphere are all tracked separately. Titan's ion tail is seen to be affected by its interaction with corotating Kronian magnetospheric plasma – but it is itself of global importance and can influence the inner boundary of the plasma sheet.