3D mixing in hot Jupiters atmospheres: I. Application to the day/night cold trap in HD 209458b

Hot Jupiters exhibit atmospheric temperatures ranging from hundreds to thousands of Kelvin. Because of their large day-night temperature differences, condensable species that are stable in the gas phase on the dayside - such as TiO and silicates - may condense and gravitationally settle on the nightside. We investigate the strength of the nightside cold trap in hot Jupiters by investigating the mechanisms and strength of the vertical mixing in these stably stratified atmospheres. We modeled the 3D circulation of HD 209458b including passive tracers that advect with the 3D flow, with a source and sink term on the nightside to represent their condensation into haze particles and their gravitational setting. Finally, we apply our model to the case of TiO in HD 209458b and show that the day-night cold trap would deplete TiO if it condenses into particles bigger than a few microns on the planet's nightside, keeping it from creating the observed stratosphere of the planet.