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Tidally locked climate models
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| jmoran582 | Date: Tuesday, 07.01.2014, 19:27 | Message # 1 |
 Observer
Group: Newbies
United States
Messages: 4
Status: Offline
| Hi folks, new poster here. I want to start off by saying that I enjoy SE a great deal as a successor of sorts to Celestia, and I have donated so I'm not a complete freeloader.  I'd like to offer some suggestions for improving tidally locked terras in SE, with some links to current research on model climates and circulation patterns for these worlds.
In versions 0.9.7 and 0.9.7.1, tidally locked terras, oceanias, and deserts can show up with two types of cloud patterns, Venus-like chevrons and giant subsolar cyclones ("eyeball" storms). Venus isn't tidally locked, but its days are so long that its atmosphere acts as if it were. In this respect using Venus chevrons is a good rough approximation, and it would be nice if SE used it in all cases. Instead it seems to make a random choice between chevrons and "eyeball" storms.
The problem with the "eyeball" storm idea is that it overlooks the fact that a tidally locked world still rotates, in some cases as quickly as Earth does, and Coriolis effects are still in play. Remember how cyclones spin counterclockwise in our Northern hemisphere and clockwise in the South. A cyclone never crosses the Equator, because there the Coriolis spin would cancel out and the storm would dissipate. It's the same on a tidally locked world, and while there could be regular cyclones in the North or the South, there couldn't be a giant one sitting on the equator. For the same reason, the overall cloud rotation would be from West to East (or East to West if retrograde), not spinning around the subsolar point. I'd really like to see "eyeball" storms go away.
Venus chevrons are a decent approximation for a desert planet with a thick atmosphere, but what about locked worlds more like our own with oceans? Some new research models with oceans included produce "lobster" cloud patterns on the dayside, with two large cyclones forming the "claws" (one in each hemisphere and spinning in opposite directions), and a long body and tail following the prevailing winds toward the nightside. This is fairly consistent with older circulation models that show two different patterns depending on altitude. At high altitudes, the entire atmosphere would superrotate just like on Venus. At low altitudes, warm air would tend to spread around the equator toward the nightside, and cold air would tend to flow over the poles toward the dayside.
This leads to my other suggestion, concerning the surface textures when a planet shows a clearly warm dayside and cool nightside (covered in ice). Currently the warm/cold transition is always shown perfectly aligned with the day/night terminator. A better approximation to current models would be something more like the stitch pattern on the skin of a baseball. On a "baseball" world, the warm half would be centered on the dayside but with two lobes extending East and West around the equator and dipping slightly into the nightside (more so in the direction of prevailing winds, less in the opposite direction). The cold half would be centered on the nightside but extending North and South over the poles. The dayside would end up looking somewhat familiar in this scenario, with cold polar regions and a warm equator. And while most of the nightside would be cold, there would be dark but warmer twilight regions on the equator near the terminator. I think this would be really interesting to explore in SpaceEngine.
Now for the links, they should all be public and free to access.
Simulations of the Atmospheres of Synchronously Rotating Terrestrial Planets (Joshi, et al 1997).
http://crack.seismo.unr.edu/ftp/pub/gillett/joshi.pdf
Clouds Extend the Habitable Zone of Alien Planets (Yang, et al 2013).
http://www.sen.com/news....planets
http://inspirehep.net/record/1241299/plots
Researchers Extend Capabilities of Computer Simulation of Tidally Locked Exoplanets (Hu, 2013).
http://phys.org/news....ts.html
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| Irigi | Date: Wednesday, 08.01.2014, 12:20 | Message # 2 |
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Observer
Group: Users
Czech Republic
Messages: 18
Status: Offline
| Thank you for interesting post and for the links! The tidally-locked planets of red dwarfs are really cool stuff!
Quote Instead it seems to make a random choice between chevrons and "eyeball" storms.
Btw. here is interesting post from the Forum of Speculative Evolution, where Oceaniis did a model of atmospheric circulation depending on the rotation rate and atmosphere density. (I think the more dense the lower in the diagrams and the same for the rotation rate.)
Edited by Irigi - Saturday, 18.01.2014, 17:10 |
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| ZalgoWaits | Date: Thursday, 05.06.2014, 03:00 | Message # 3 |
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Observer
Group: Newbies
United States
Messages: 6
Status: Offline
| I realize this is quite a bit of a necro, but I have to echo the request for a reexamination of the current tidally-locked climate model regarding a frozen night side. I actually just typed up a post on the subject before I went looking to see if anyone else had brought it up already. Turns out, someone had! So I guess I'll just post it here so it doesn't go to waste.
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Good evening. I don't normally make feature requests in programs, especially not free ones that are done as a labour of love, but I do have one to make.
In my readings, I've found journal articles that suggest that with planets that are tidally-locked to their stars, the presence of a significant amount of liquid water on the surface (Hu & Yang, 2014) as well as the presence of a reasonably-thick—about 75 kPa minimum, if I interpreted it right—atmosphere with a decent amount of CO2 (Merlis & Schneider, 2010) may both contribute to a significant amount of temperature transfer between the day and night sides, serving to even things out between them and reducing the difference between the two from the commonly-held belief of several hundred Kelvins to only about 50-60.
Thus, I would like to request that in a future version of Space Engine—definitely not 0.98, and probably not 0.99 either, given the amount of work that's likely to be involved, but some future version nonetheless—the presence or absence of a hemisphere-wide icecap on the night side of a tidally-locked planet be determined by a combination of surface water coverage, atmospheric density, and atmospheric greenhouse effect. Plus mean global temperature, of course.
Thank you for your time and your consideration. Namaste.
References
Hu, Y., & Yang, J. (2014). Role of ocean heat transport in climates of tidally locked exoplanets around M dwarf stars. Proceedings Of The National Academy Of Sciences, 111(2), 629-634. doi:10.1073/pnas.1315215111
Merlis, T., & Schneider, T. (2010). Atmospheric Dynamics of Earth-Like Tidally Locked Aquaplanets (1st ed., pp. 9, 15). Pasadena, CA: California Institute of Technology. Retrieved from http://www.clidyn.ethz.ch/papers/tidally_locked.pdf
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