The Implications of 3D Thermal Structure on 1D Atmospheric Retrieval

TL;DR

This study compares 1D atmospheric retrievals with 3D simulation data for exoplanet HD 189733b, highlighting how instrument resolution and data coverage influence the accuracy of thermal structure recovery.

Contribution

It demonstrates how 1D retrievals can approximate 3D thermal structures and explores the effects of spectral resolution and parametrization on retrieval accuracy.

Findings

Higher spectral resolution improves retrieval accuracy.

More data points lead to better thermal profile estimates.

Flexible temperature parametrizations enhance model fitting.

Abstract

Using the atmospheric structure from a 3D global radiation-hydrodynamic simulation of HD 189733b and the open-source BART code, we investigate the difference between the secondary-eclipse temperature structure produced with a 3D simulation and the best-fit 1D retrieved model. Synthetic data are generated by integrating the 3D models over the Spitzer, HST, and JWST bandpasses, covering the wavelength range between 1 and 11 um. Using the data from different observing instruments, we present detailed comparisons between the temperature-pressure profiles recovered by BART and those from the 3D simulations. We calculate several averages of the 3D thermal structure and implement two temperature parameterizations to investigate different thermal profile shapes. To assess which part of the thermal structure is best constrained by the data, we generate contribution functions for both our theoretical model and each of our retrieved models. Our conclusions are strongly affected by the spectral resolution of the instruments included, their wavelength coverage, and the number of data points combined. We also see some limitations in each of the temperature parametrizations. The results show that our 1D retrieval is recovering a temperature and pressure profile that most closely matches the arithmetic average of the 3D thermal structure. When we use a higher resolution, more data points, and a parametrized temperature profile that allows more flexibility in the middle part of the atmosphere, we find a better match between the retrieved temperature and pressure profile and the arithmetic average.