Atmospheric Circulation of Hot Jupiters: Dayside–Nightside Temperature Differences. II. Comparison with Observations

Abstract

The full-phase infrared light curves of low-eccentricity hot Jupiters show a trend of increasing fractional daysidenightside brightness temperature difference with increasing incident stellar flux, both averaged across the infrared and in each individual wavelength band. The analytic theory of Komacek & Showman shows that this trend is due to the decreasing ability with increasing incident stellar flux of waves to propagate from day to night and erase temperature differences. Here, we compare the predictions of this theory with observations, showing that it explains well the shape of the trend of increasing dayside-nightside temperature difference with increasing equilibrium temperature. Applied to individual planets, the theory matches well with observations at high equilibrium temperatures but, for a fixed photosphere pressure of 100 mbar, systematically underpredicts the dayside-nightside brightness temperature differences at equilibrium temperatures less than 2000 K. We interpret this as being due to the effects of a process that moves the infrared photospheres of these cooler hot Jupiters to lower pressures. We also utilize general circulation modeling with double-gray radiative transfer to explore how the circulation changes with equilibrium temperature and drag strengths. As expected from our theory, the dayside-nightside temperature differences from our numerical simulations increase with increasing incident stellar flux and drag strengths. We calculate model phase curves using our general circulation models, from which we compare the broadband infrared offset from the substellar point and dayside-nightside brightness temperature differences against observations, finding that strong drag or additional effects (e.g., clouds and/or supersolar metallicities) are necessary to explain many observed phase curves.

Demarcating Circulation Regimes of Synchronously Rotating Terrestrial Planets within the Habitable Zone

“…The decreasing trend of day-night surface temperature contrast with increasing equilibrium temperature from our terrestrial simulations is opposite for synchronously rotating gas giant planets, where observations show that an increase in heating leads to an increase in the day-night temperature contrast (Perez-Becker & Showman 2013;Komacek & Showman 2016;Komacek et al 2017). The day-night temperature contrast observed on an optically thick gas giant atmosphere occurs at the emission level in the free atmosphere, whereas the flux emitted by an optically thin terrestrial atmosphere primarily emerges from the surface.…”

“…For both of these regimes, the day-night heat transport in the free atmosphere of synchronously rotating planets is strongly influenced by radiation and zonally propagating waves Perez-Becker & Showman 2013;Wordsworth 2015;Koll & Abbot 2015Komacek & Showman 2016;Komacek et al 2017;Zhang & Showman 2017). The free-atmosphere day-night temperature contrast can be predicted based on a scaling theory developed by Komacek & Showman (2016); Komacek et al (2017) and Zhang & Showman (2017),…”

“…The free-atmosphere day-night temperature contrast can be predicted based on a scaling theory developed by Komacek & Showman (2016); Komacek et al (2017) and Zhang & Showman (2017),…”

Observing transiting planets with JWST

“…This advection seems to be most effective for cool, low-mass planets (Perez-Becker & Showman 2013;Kammer et al 2015;Komacek et al 2016). Therefore, for cool, low-mass planets, not all of the energy absorbed in a given region of the atmosphere is reradiated immediately, which would in turn mean that the (Morley et al 2014) treatment may still be valid.…”

“…As shown in Perez-Becker & Showman (2013), Komacek et al (2016) this process depends on the equilibrium temperature of the planet: the hotter the equilibrium temperature, the weaker the redistribution becomes, meaning that radiative cooling increasingly dominates over advection.…”