Equatorial retrograde flow in WASP-43b elicited by deep wind jets?

Abstract

<jats:title>ABSTRACT</jats:title> <jats:p>We present WASP-43b climate simulations with deep wind jets (down to 700 bar) that are linked to retrograde (westward) flow at the equatorial day side for p &amp;lt; 0.1 bar. Retrograde flow inhibits efficient eastward heat transport and naturally explains the small hotspot shift and large day-night-side gradient of WASP-43b (Porb = Prot = 0.8135 d) observed with Spitzer. We find that deep wind jets are mainly associated with very fast rotations (Prot = Porb ≤ 1.5 d) which correspond to the Rhines length smaller than 2 planetary radii. We also diagnose wave activity that likely gives rise to deviations from superrotation. Further, we show that we can achieve full steady state in our climate simulations by imposing a deep forcing regime for p &amp;gt; 10 bar: convergence time-scale τconv = 106–108 s to a common adiabat, as well as linear drag at depth (p ≥ 200 bar), which mimics to first-order magnetic drag. Lower boundary stability and the deep forcing assumptions were also tested with climate simulations for HD 209458b (Porb = Prot = 3.5 d). HD 209458b simulations always show shallow wind jets (never deeper than 100 bar) and unperturbed superrotation. If we impose a fast rotation (Porb = Prot = 0.8135 d), also the HD 209458b-like simulation shows equatorial retrograde flow at the day side. We conclude that the placement of the lower boundary at p = 200 bar is justified for slow rotators like HD 209458b, but we suggest that it has to be placed deeper for fast-rotating, dense hot Jupiters (Porb ≤ 1.5 d) like WASP-43b. Our study highlights that the deep atmosphere may have a strong influence on the observable atmospheric flow in some hot Jupiters.</jats:p>

Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: effects of rotation

“…Note that this form of drag has been used in previous studies of hot Jupiters (e.g., Liu & Showman 2013;Tan & Komacek 2019;Carone et al 2020). The strength of this drag could influence the qualitative dynamics in the cloud-forming region as will be shown in Section 3.4.…”

Atmospheric Dynamics of Hot Giant Planets and Brown Dwarfs

“…Compared to the shallow hot Jupiter simulations with a bottom pressure of about 1 bar (e.g., Heng et al 2011b;, flows in the "deep" simulations are typically more time-invariant. Recently, Carone et al (2020) proposed that for rapidly rotating hot Jupiters like WASP-43b, the simulated domain should extend to a deeper pressure (∼ 700 bars) to properly capture dynamics in the observable layers.…”

“…Convection leads to a nearly barotropic state of the interior, witch together with the slower winds (which implies a small global Rossby number) may result in a Taylor-Proudman effects (Pedlosky 2013) that tends to drag down winds in the deep GCM layers (e.g., Schneider and Liu 2009). To crudely represent this effect, some GCMs adopted a frictional drag near the bottom boundary that relax winds towards zero over characteristic drag timescales (e.g., Liu and Showman 2013;Tan and Komacek 2019;Carone et al 2020). Although easy to implement, the choice of drag timescale and the exact form of the drag are rather loosely chosen.…”

Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: global and equatorial dynamics

“…Yet no theoretical study systematically investigate how such interactions should be parameterized in GCMs of gaseous planets. Nevertheless, this simple drag serves to dissipate flows in our bottom model layers, and similar drag schemes have been used in previous studies of Jupiter (Schneider & Liu 2009) and hot Jupiters (e.g., Liu & Showman 2013;Tan & Komacek 2019;Carone et al 2020).…”