Wikipedia:Reference desk/Archives/Science/2017 August 28

= August 28 =

Could a non-cooling planet with 100% water clouds rain everywhere at once?
Wouldn't convection prevent 100% the surface area raining at the same time? Could more complex systems like, I don't know, cloud layers of different chemicals allow the surface to always be raining something? Sagittarian Milky Way (talk) 00:40, 28 August 2017 (UTC)


 * Not sure what you mean by a "non-cooling planet". The only problem I see with continuous precipitation everywhere on a planet is that it implies very little sunlight making it below the rain to drive evaporation, which of course is a critical portion of the water cycle.  However, other heat sources could drive the system, such as tidal heating from a large nearby body, radioactive decay, or residual heat from formation.  The last two would require either a somewhat young planet or one somewhat larger than Earth, in order to be significant enough.  The tidal forces could work on a smaller body, though, such as a moon of a Jovian planet.  As to the form of the precip, some might very well be snow, say during night or near the poles.  It would be difficult to imagine a situation where the temp is always in the narrow range for liquid water, throughout the atmosphere.  A planet entirely covered by ocean seems most likely to provide sufficient evaporation to drive planet-wide continuous precipitation.


 * As for convection, you might get a planet covered by hurricanes, and that does imply brief rain-free areas as the eyes pass over. However, sufficient winds like our jet streams might keep them from forming eyes, leaving you with a planet full of continuous tropical depressions.  StuRat (talk) 01:40, 28 August 2017 (UTC)


 * If it's cooling while 100% humidity it could perhaps rain everywhere at once right? i.e. after an asteroid hit so big the hydrosphere boils. Sagittarian Milky Way (talk) 02:13, 28 August 2017 (UTC)


 * Yep, that could do it. I wonder if a supervolcano could, like the ones we've had on Earth. StuRat (talk) 02:49, 28 August 2017 (UTC)


 * Hairy ball theorem prohibits a ball system from having continuous non 0 wind speeds everywhere on the planet . your190 (talk) 19:55, 28 August 2017 (UTC) — Preceding unsigned comment added by 100.35.203.180 (talk)


 * If "everywhere at once" means anything definite, it means that every single point on the planet is being struck by water at every single moment in time. Obviously that isn't going to happen, but equally obviously that isn't what you had in mind.  If you don't give a more precise definition, though, the question has no answer. Looie496 (talk) 02:25, 28 August 2017 (UTC)


 * "The entire surface (non-gaseous planets) or 101.325 kilopascal surface (gas giants and mini-Neptunes) is at one moment in time being hit by a sufficient amount of 0.02+ inch liquid drops per square meter per second that if it was water Earth metrologists of the early 21st century would define it as rain. (or rainier)" This does not imply that said condition continues for tens or hundreds or thousands or millions or billions of years (though that would be really cool). Sagittarian Milky Way (talk) 03:19, 28 August 2017 (UTC)


 * I do not think that it is possible. For rain to form wet air needs to ascend to a height where due to adiabatic cooling its humidity exceeds 100%. However the air also needs to descend somewhere. In these downdrafts the air will warm and its humidity will decrease below 100% thus preventing raining. So, I think it is impossible for more than about 50% of the surface area to have rain at the same time. Ruslik_ Zero 18:49, 28 August 2017 (UTC)


 * There could still be rain, formed at the higher altitudes, falling with the descending air. If the rain evaporates on the way down, then that's virga. StuRat (talk) 20:04, 28 August 2017 (UTC)


 * I immediately thought of the hairy ball theorem, but it's not relevant here. The water is falling through three-dimensional space, not blowing acrost a surface.  The rain will stop when it hits the surface, but in the meantime there is no reason why the motion of any one drop should interfere with another.
 * Visualize a water balloon exploding in free fall, spraying drops in every direction equally. Now run the tape backwards.  Basically, you've got "rain" converging from every direction back onto the original sphere.  Whether the conditions would ever exist to fulfill the OP's thought experiment is one thing, but the hairy ball theorem is not a cucumbrance in this case. μηδείς (talk) 15:31, 29 August 2017 (UTC)

WP:Reference desk/Miscellaneous
What kind of knowledge do I require in order to accomplish the task? A rough step by step guide is sought please. 116.58.200.57 (talk) 08:34, 28 August 2017 (UTC)