Water droplet forms from a pool of water and gradually rise or accelerate upward to the sky, my question is how can I explain such an phenomenon in a convincing way? kindly use magic sparingly and setting can be on any celestial body not neccessarily have to be on Earth! definitely no technology of any kind allowed.
If the air was heavier than water, it would not be just drops that rose up. All the water would float above it.
If you picture the inside of a gas giant or ice giant planet, different layers will have possibilities of rain moving in one direction or another, or some of each.
In the depths of a waterworld you could have ice under different pressures and temperatures that rises or sinks depending. If it's not pure water but water-ammonia, methane, or something, you could have droplets of some kind rise upwards.
Maybe something in the pool make the water to became strongly magnetic and a near moon with a high magnetic field attract them.
As the pool is what make the water to became magnetic, only the water in the pool will raise. You also need that the main body don't have a magnetic field by itself and don't have an strong gravity (for example a big asteroid or minor planet would be good).
this physics question would appear to be relevant:
It is possible to have a mixture of xenon and oxygen under high pressure which is a gas but which has a density higher than that of water.
It would require extreme pressure and I'm guessing it would require high temperature as well. Humans are unlikely to survive the conditions but you could have some aliens which could.
Then of course the question becomes how the water gets to the bottom so that it can fall up again.
there's an interesting side effect: gas compresses, liquid doesn't very much and as a result you could have a layer of gas like this where above a certain point the water bubbles downwards and bellow that the water bubbles upwards leading to a floating ocean with the same gas above and bellow it.
Hugely powerful, well bounded magnetic fields might do the trick, but I'm not sure it would classify as rain or be survivable.
As PhoneixS notes in his comment to his own answer, water is diamagnetic. This means that it creates an opposing magnetic field to a magnetic field that is applied to it. In the link he's posted this effect causes a frog to float, but it can also be used to levitate all sorts of materials (water included; in fact the high water content of the frog was essential in levitating it). This effect could cause water to rise away from a surface without it needing to have anything clever done to it.
Now the problems: This wouldn't cause rain. Rather the whole mass of water would rise as one monolithic drop. If it rose fast enough then interactions with the air might cause it to turn into spray, but I'm not sure the classic 'rain is water condensing in the sky' applies.
Secondly: We're talking huge magnetic fields here. Seriously huge. The field used to levitate the frog had a magnetic flux of 16 Tesla. The record is 33 Tesla (with a supercooled superconducting electromagnet in a lab). The really strong neodymium magnets that are almost impossible to take off fridges are just over 1 tesla. This is some serious power we're playing with, and in order to make water float upwards on any sort of scale you'll have to ramp it up something fierce. Not only that, but you'll have to apply some funky boundary conditions to whatever's making the field in order to make sure that it can't tear itself apart.
Oh, by the way, it'll probably also do very bad things to your physiology, along with making you float too. Unless your belt buckle is made of steel, in which case... ouch...
Maybe something biological in nature. An aquatic insect type creature lays its eggs (or transports itself) in water encased in a thin bubble membrane, it inflates the bubble with lifting gas, and when these creatures are in full breeding (or migration) season the surface of lakes "bubble off" into the sky. The creatures do this to spread themselves far and wide, wafted by the wind.
The most effective lifting gas is hydrogen, helium seems unlikely for biological reasons, methane is also a lifting gas in our atmosphere. Hydrogen and Methane can both be produced by organisms. The buoyancy of any gas is improved by heating it.
In a CO2 atmosphere, which is denser than our atmosphere, oxygen and nitrogen are also lifting gases (but poor ones), other lifting gases (such as hydrogen and methane) are made more effective.
I would probably go with a creature which produces methane, in a CO2 atmosphere, with additional heat provided to the bubble from biological activity and sunlight.
I think you could pull this off with very high heat and humidity. It wouldn't exactly be rain in the conventional sense, but I believe with the right balance of heat and humidity you could get the water to condense quickly while still rising. This can be seen to a certain degree in the real world. In places where summer storms are common and after a storm you can often see clouds of steam rising off of the concrete.