DIX Planetary Science Seminar
Weather Report from Distant Worlds: Spatially Resolved Atmospheric Retrievals of Variable Brown Dwarfs
Brown dwarfs provide a laboratory for studying cloudy, rotating atmospheres under conditions similar to those of directly imaged giant exoplanets. Time-resolved spectroscopy reveals rotational variability, but converting disk-integrated light curves into physical atmospheric structure is an ill-posed inverse problem. I will present a Bayesian framework that turns spectroscopic rotational monitoring into spatially resolved spectra with propagated mapping uncertainties. The method uses analytic spherical-harmonic light-curve inversion, evidence-optimized regularization, and Bayesian model averaging over map complexity and viewing geometry, allowing hundreds of wavelength channels to be mapped without Monte Carlo sampling. We then identify a small number of spectrally distinct regions and perform atmospheric retrievals on those regional spectra rather than on phase-averaged observations. Applied to JWST/NIRSpec monitoring of Luhman 16B and SIMP 0136, the retrievals reveal spatial variations in cloud structure and thermal profiles caused by radiative feedback in both objects. These results provide a statistically controlled route from unresolved rotational variability to atmospheric heterogeneity. I will also discuss extensions to eclipse mapping of exoplanets with phase curves and to measuring wind speeds on brown dwarfs with time-resolved high-resolution spectroscopy.
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Polar vortex crystals on Jupiter: Simulating Jupiter's atmosphere using a Quasi-Geostrophic model.
Juno spacecraft observed persistent polygonal patterns of large cyclones at both the north and south poles. These patterns have been studied by plasma physics, but they represent the first of their kind on a planet. Siegelman utilized a one-layer quasi-geostrophic (QG) model with initial turbulence to investigate the formation of vortex crystals. Li employed a one-layer shallow water (SW) model with initial large-scale vortices to demonstrate the significance of vortex shielding. Chen et al. employed the SW equations, commencing with initial turbulence, to study the vertical structure of the layer. However, these simulations commenced with an initial disturbance and did not incorporate continuous forcing balanced by dissipation, which is more representative of the actual situation on Jupiter. We intend to employ a QG model at the pole of a rotating planet to study the evolution of vortices under the influence of forcing and dissipation. A crucial parameter of the models is the radius of deformation, ), where g is the gravitational acceleration, h is the thickness of the weather layer, ∆ρ/ρ is the fractional density difference between the weather layer and the abyssal layer beneath, and is the planetary rotation. To generate vortex crystals, the models starting with initial turbulence necessitate substantial values of , implying stable stratification and a substantial weather layer penetrating into the abyssal layer. Whether this requirement holds true when the flow is continuously forced and balanced by dissipation constitutes a significant outcome of this study.