Celestia Forums

I'm thinking of designing a few textures for hot-Jupiter planets. Would the atmospheric circulation be the usual banded structure seen on the Jovian planets in our solar system or would the bands be radial, moving from the hot pole directly underneath the sun to the cold pole on the dark side?

And would these planets exhibit cloud bands or are the temperatures too high, so you'd get a transparent atmosphere?

Good timing for that question, I spotted just today following abstract:

Changing face of the extrasolar giant planet HD209458B (Cho et al.)

High-resolution, fully-turbulent atmospheric flow simulations of the tidally-locked extrasolar giant planet, HD209458b, show large-scale spatio-temporal variability. This is in contrast to the simple, permanent day/night (i.e., hot/cold) picture. The planet’s global circulation, which emerges from initially random conditions, is characterized by a polar vortex in motion around each pole and a banded structure corresponding to few broad zonal (east-west) jets. These evolved flow structures are generic and robust. For circulations containing very strong (greater than 400 m/s) jets, the flow-induced temperature difference between moving hot and cold regions can reach up to ?1000 K, suggesting that atmospheric variability may be observed in the planet’s spectral and photometric signatures.

So they may have banded atmospheres... Another question is, would those bands be visible and what color would they have. As far as I know, Jupiter's color difference between belts and zones results from gases in different temperatures.

~ Jyri

chaos syndrome wrote:... would the bands be radial, moving from the hot pole directly underneath the sun to the cold pole on the dark side?

Such a pattern is unstable because of the rotation of the planet. Numerical modelling implies strong zonal (parallel to the equator) flow at high altitudes, with cold air coming back from the dark side over the poles in deeper layers. I looked into this when I was doing a big revision of extrasolar.ssc last year, and was influenced by Joshi et al's study of close-in, tidally locked terrestrial planets, together with some 2D modelling of giant planets that showed the same zonal winds, in this case blasting around the planet at >1km/s, particularly at the equator. That's why I modelled all the hot Jupiters in Celestia with a banded structure, and a prominent thermal glow from a broad equatorial band on the night side (because this zone is transporting heat rapidly from day to night).
Since that time I've run into Showman & Guillot's simulation, which shows the same hyperrotating equatorial band, sixty degrees wide, but with a pair of interestingly skewed hemispheric cells at higher latitudes. Their model also implied that bands should be fewer and broader in hot Jupiters, maybe just a couple per planet instead of the 10 or more we see in Jupiter itself.
They also talk a little about cloud formation, pointing out that the mechanism will be different in the hot and cold hemispheres - on the day side, clouds will form in rising air; on the night side they'll form as hot air is transported laterally into darkness and cools.
I think you could produce some interesting textures based on their model - they have nice diagrams of wind direction which you could build on.

Grant

I note the phrase "eddies may grow to hemispheric scale in the atmospheres of Pegasi planets" - does that mean eddies in the sense of the Great Red Spot?

Thanks for the links - some of the circulation patterns look rather extreme...