W. Dietrich, J. Wicht, S. Kumar, R. Redmer, M. French, A. J. Poser
Among the striking properties of Hot Jupiters are the extreme surface temperatures of up to 3000 K, the often anomalously large radii and their brightness patterns. The diverse day-to-night-side brightness contrast and the displacement of the hottest spot indicate the action of fierce atmospheric flows. We have performed an extensive numerical campaign modelling the irradiation driven flows in the radiative atmospheric layer of a Hot Jupiter. The models typically develop a strong, super-rotating (eastward) equatorial jet and a pair of sub-rotating jets at higher latitudes. This basic flow can be significantly modified or even destroyed by turbulent Kelvin-Helmholtz instabilities and subsequent chaotic fluctuations. Its amplitude reaches typical values of U = 1-10 R Ω, where R is the radius und Ω the rotation frequency. Moreover, our models reveal a complex 3D structure of the flow and the entropy (temperature) distribution. This makes the prediction of the resulting hot spot displacement and day-to-night-side brightness contrast and thus the interpretation of observed infrared phase curves quite challenging.
If the temperatures exceed ca. 2000 K, the thermal ionisation of alkali metals becomes significant as it generates ions and electrons. Thus, the resulting electrical conductivity combined with the strong winds induce electromagnetic currents, which in turn generate heat by ohmic dissipation – a mechanism to heat and inflate Hot Jupiters.