Stars are filled with sound. Turbulent convection within a star makes a broadband hum, but certain frequencies get amplified because they are resonant. For example, the Sun’s surface throbs and rings under the combined influence of several million resonant acoustic modes. Thus, stars act like really bad-sounding musical instruments. Helioseismology is the field of study where the sound waves observed at the surface of the Sun are used to image the Sun’s interior, where we view directly. In asteroseismology, the same techniques are applied to more distant stars. Both fields are analogous to how sound waves are used to image a baby, view a bum knee, or monitor blood flow in a heart during an ultrasound. In star’s we have been able to use the frequencies of the resonant acoustic oscillations to measure the radial profiles of mass density and temperature throughout a star’s interior. Further, we have been able to measure flow fields in the interior, including the star’s rotation rate, meridional circulation, and subsurface convective motions. In this seminar, I will present an overview of the topic. In particular, I’ll discuss how the sound waves are generated and why they are resonant. Further, I will examine the integral inversion problem that must be performed in order to obtain estimates of the star’s interior properties from measurements of the resonant frequencies. Finally, I will present a brief historical survey of the major discoveries of helioseismology (and asteroseismology) and how those discoveries have changed our understanding of the fluid dynamics that is going on inside stars.

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Jhett Bordwell - Chemical Transport in Giant Planets and Brown Dwarfs

Abstract Pending

Ryan Orvedahl - Polarity Reversals in Stars and Planets

Abstract Pending

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Condensate, fluctuations and symmetries — a tale of 2D turbulence

Earth's jet streams, Jupiters Great Red Spot and its zonal winds are all examples of persistent large scale flows,  whose dynamics is to a good approximation two-dimensional. These flows are also highly turbulent, and the interaction  between the turbulence and these coherent structures remains poorly understood. Apart from its geophysical relevance,  2Dturbulence is a rich and beautiful fundamental system — where turbulence takes a counter-intuitive role.Indeed, in 2D, energy is transferred to progressively larger scales, which can terminate in the self organization of the turbulence into a large scale coherent structure, a so called condensate, on top of small scale fluctuations.

I will describe a recent theoretical framework in which the profile of this coherent mean flow can be obtained, along with the mean momentum flux of the fluctuations. I will explain how and when the relation between the two can be deduced from dimensional analysis and symmetry considerations, and how it can be derived. Finally, I will show that, to leading order, the velocity two-point correlation function solves a scale invariant advection equation. The solution determines the average energy of the fluctuations, but does not contribute at this order to the momentum flux, due to parity + time reversal symmetry. Using analytic expressions for the solutions, matched to data from extensive numerical simulations, it is then possible to determine the main characteristics of the average energy. This is the first-ever self-consistent theory of turbulence-flow interaction.

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