Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session L13: Astrophysical Fluid Dynamics |
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Chair: Philip Marcus, U.C. Berkeley Room: 304 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L13.00001: The Shedding of Jupiter’s Red Flakes Does Not Mean It Is Dying Philip Marcus, Pedram Hassanzahdeh, Michael Wong, Imke de Pater, Aidi Zhang, Joseph Barranco, David Lee During 2019 the Great Red Spot (GRS) of Jupiter repeatedly shed large (100,000 km$^2$) chunks of itself as red “flakes”. Rather than the GRS "dying" as report in the popular press, we have a more benign hypothesis tested with 3D numerical simulations. There are 2 distinct boundaries of the GRS (n.b., neither of which is coincident with the boundary of its cloud cover): (1) the boundary of its potential vorticity (PV) anomaly, and (2) its last "closed streamline". An isolated vortex has nested closed streamlines, both interior to it and exterior it. The latter circumscribe the vortex. However, an anti-cyclone embedded in an anti-cyclonic zonal shear only has exterior closed streamlines near the PV boundary. Farther from its PV boundary, it has "open streamlines" that circumscribe the planet, not the vortex. The last close streamline contains at least one stagnation point. We show that when there is large area between the last closed streamline and the PV boundary, vortices "fed" to the GRS merge with it. However, when that area is small, vortices fed to the GRS will be expelled at or near a stagnation point. Thus, our explanation of the of recent Red Flakes is that area between the PV boundary of the GRS and its last closed streamline has shrunk. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L13.00002: Nonlinear Magnetosonic Periodic and Solitary Waves in a Magnetized Dusty Plasma Nimardeep Kaur, Nareshpal Singh Saini An investigation of magnetosonic nonlinear periodic (cnoidal) waves is presented in a magnetized electron-ion-dust plasma having cold dust fluid with inertialess warm ions and electrons. The reductive perturbation method is employed to derive the Korteweg-de Vries equation. The magnetosonic cnoidal wave solution is derived using the Sagdeev pseudopotential approach under the specific boundary conditions. There is the formation of only positive potential magnetosonic cnoidal waves and solitary structures in the high plasma-b limit. The findings of the present investigation may be helpful in describing the characteristics of various nonlinear excitations in Earth's magnetosphere, solar wind, Saturn's magnetosphere, and space/astrophysical environments, where many space observations by various satellites confirm the existence of dust grains, highly energetic electrons, and high plasma-$\beta $. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L13.00003: Quantitative Flow Field Measurements of Astrophysical Relevance on the Blast-Driven Instability (RMI & RTI) Samuel Petter, Benjamin Musci, Gokul Pathikonda, Devesh Ranjan The presented work focuses on the implementation of Particle Image Velocimetry (PIV) to study the Blast-Driven Instability (BDI) in cylindrical geometry at the Georgia Tech Shock Tube and Advanced Mixing Laboratory. The facility uses detonators to generate a blast wave that accelerates the flow through a diverging test-chamber. The blast wave then interacts with a gaseous, membrane-less, interface of differing density, causing the occurrence of the combined Richtmyer-Meshkov (RMI) and Rayleigh-Taylor Instabilities (RTI); the two instabilities comprising the BDI. Previous validation of the facility was completed using high speed Mie Scattering and demonstrated faithful reproduction of the BDI phenomena. This validation garnered information about the qualitative development of the instability and identified aspects of improvement within the facility, both of which will be covered in this presentation. Preliminary PIV results are shown to corroborate the earlier Mie Scattering findings as well as predictions made by Taylor-Sedov theory derived from experimental pressure data. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L13.00004: Horizontal shear instabilities in stellar radiative zones Junho Park, Vincent Prat, Stéphane Mathis Shear flows in stratified-rotating fluids have been a popular research topic in astrophysics due to their applications for stellar evolution modeling. In stellar radiative zones, the thermal diffusivity is high with small Prandtl number of order 10\textasciicircum (-6). Also, the horizontal rotation component in latitudinal direction has not been generally considered with the traditional f-plane approximation, but recent research has revealed that it modifies significantly dynamics of inertia-gravity waves in the radiative zones. In this presentation, we revisit the horizontal shear instability problem by considering two components: the thermal diffusivity and the complete Coriolis acceleration rotation (i.e. the non-traditional f-plane approximation). And we study their impacts on hydrodynamic instabilities: inflection-point and inertial instabilities. With numerical and asymptotic stability analyses, we will present new results with mathematical formulations how the thermal diffusivity and horizontal modify these instabilities. For instance, a fast thermal diffusion destabilizes the inertial instability due to the suppression of the stratification effect while the horizontal rotation promotes instabilities and broadens the unstable regime. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L13.00005: Dynamics in the Ball: Models for Fully Convective, Rotating M-Dwarf Stars Benjamin Brown, Jeffrey Oishi, Daniel Lecoanet, Keaton Burns, Geoffrey Vasil M-dwarf stars are smaller and less luminous than our Sun. In their interiors, convection dominates energy transport from the center of the star to their surface. This ball-like geometry is unique among all the stars on the main-sequence; in our Sun, solar convection is bounded from below by regions of stable stratification, creating a shell-like geometry instead. Within stellar convection zones, the turbulent plasma motions act as a dynamo, stretching and amplifying magnetic fields. M-dwarf stars have abundant and strong magnetic fields at their surfaces, but at a fundamental level we do not know whether these ball-like stars are similar to or different from our shell-like Sun. Here, using the novel spherical Dedalus pseudospectral framework, we consider the properties of convection and magnetic dynamo action in rotating, stratified simulations within global ball domains that capture the coordinate singularity at the center ($r=0$), as well as the north and south pole. We find that global shearing flows are built by the convection, and these amplify global magnetic fields. Many ingredients in the fully convective M-dwarf simulations are similar to those found in simulations of the solar dynamo; this implies that these dissimilar stars may have similar internal processes. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L13.00006: Radiative damping of convectively-driven gravity waves in the atmospheres of hot Jupiters Jhett Bordwell, Benjamin Brown, Jeffrey Oishi, Whitney Powers Jovian atmospheres consist of a substantial, deep convection zone underlying a stably stratified region populated by convectively driven waves at many scales. These waves are significant to the pumping of large scale atmospheric jets, upper atmosphere heating, and chemical transport. To understand the role that radiation plays in the propagation of these waves, we perform numerical experiments with Dedalus at small scales studying wave driving and chemical transport in an atmosphere with radiative diffusion (appropriate for a hot Jupiter). We find that assuming an opacity structure appropriate for a Jovian atmosphere, all but the largest scale waves are damped out by radiation. We further compare our results with those of a Reynold's stress forcing model of wave driving, and explore the transport of reactive passive tracers through a simple Newtonian relaxation model. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L13.00007: Nonlinear dynamics of forced baroclinic critical layers Chen Wang, Neil Balmforth Baroclinic critical levels are singularities of waves propagating in inviscid stratified shear flow, and they play a crucial role in the self-replication of `zombie vortices'. Our previous work has shown that for baroclinic critical layers under continuous forcing, the linear evolution features secular growth of density and decreasing thickness, and the following nonlinear evolution is characterized by a jet-like mean flow, which is focused exponentially at later times. In the present work, we show that thermal diffusion can arrest the focussing. A coherent structure of density is formed instead, which drifts in the cross-stream direction and leaves behind a growing defect in the mean-flow velocity. We explore detailed properties of the drifting coherent structure, and conjecture that it could be responsible for the expansion of critical layers as observed in the zombie vortices. [Preview Abstract] |
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