ADVANCEMENT TO CANIDIDACY: Magnetohydrodynamics of the Solar Tachocline: Modeling the sharp transition of rotational shear detected in the interior of the Sun.

Luis Antonio Acevedo-Arreguin
Tuesday, October 27, 2009, 2:00 pm, Engineering 2 Room 280
Hosted by Pascale Garaud
Applied Mathematics & Statistics

Abstract

Solar physics has seen a remarkable progress since the mid-90s thanks to the valuable
information provided by helioseismology. Detailed observations of the solar surface have been
statistically analyzed to infer the structure of the solar interior. There are two important
regions in the Sun: a quiet, radiative, inner zone and a turbulent, convective, outer zone.
Helioseismic determinations of their angular velocity show that the convection zone is differentially rotating while the radiative zone is rotating almost uniformly (Schou et al.,1998).
The tachocline is the very thin layer where these sharp changes in angular velocity occur.
The phenomena underlying this rotational behavior have put the tachocline in the center of
a quite a few scientific endeavors in modern times.

The importance of the tachocline cannot be understood without looking at the solar
magnetic cycle. Since Galileo’s time, dark spots on the solar surface have captured the
attention of astronomers, and NASA currently keeps a daily record of their appearance,
number, and location. Approximately every eleven years, sunspots start emerging at latitudes
around 30 degrees N, and throughout the cycle their peak location moves toward the
equator. The current paradigm explains that this fluctuating magnetic field is generated by
a solar dynamo, a mechanism in which electrical currents driven by plasma in motion create
a magnetic field, and prevent it from Ohmic dissipation over time (Brummell, personal
communication, 2009). The analysis of the records of the solar magnetic cycle, combined
with mathematical models, suggests the location of the solar dynamo at the base of the
convection zone, with the tachocline playing a primary role in the dynamics of the magnetic
field (Tobias and Weiss, 2007).

The magnetic activity associated with sunspots affects anything beyond the protective
terrestrial atmosphere. Astronauts performing maneuvers in space, and electronic equipment
carried by communication satellites are examples of possible targets vulnerable to solar magnetic storms. Hence, the study of the dynamics of the tachocline is important to understand solar weather, which in turn impacts human activity on and around Earth.

Based on models developed by Garaud and Garaud (2008), as well as by Garaud and
Acevedo-Arreguin (2009), this research project aims to mathematically simulate the magnetohydrodynamics of the solar tachocline to explain the rotational behavior of the interior
of the Sun. Predictions of the solar rotation profile from this model will be compared to
current helioseismic determinations. Once refined, this model might serve to validate existing
theories of the internal rotation of the Sun (i.e. Gough and McIntyre, 1998), to improve
predictions of standard solar models on chemical abundances, and to simulate the dynamics
of the tachocline at different stages during the evolution of the Sun.