I'm envisioning a creature or plant that consumes magical energy, and which produces localized rainfall as a byproduct.

If the consumption of this magical energy produces localized effects related to light and electromagnetic radiation, how might condensation result from that side effect?

Or, to put this another way: What changes to local electromagnetic radiation (such as heavy sunlight, gamma rays, etc) would cause liquid water to condense from a semi-arid atmosphere?

Here's what a sample answer might look like:

[Unobtanium] rapidly cools when exposed to [Alpha particles]. If exposed to heavy concentrations of [Alpha particles], condensation would form on the surface of [Unobtanium deposits], and a plant with high concentrations of [Unobtanium] would drip liquid water if it were being constantly bombarded with [Alpha Particles]

  • $\begingroup$ Your question is confusing. Does consuming magical energy make this creature or plant glow or something? $\endgroup$ – RonJohn Aug 4 '18 at 17:50
  • $\begingroup$ @RonJohn That's not relevant to the question. Why it does this is not important. This is my question: "Under what conditions would changes to local electromagnetic radiation (such as heavy sunlight, gamma rays, etc) condense liquid water from a semi-arid atmosphere?" Hopefully that is less confusing for you. $\endgroup$ – user49466 Aug 4 '18 at 17:51
  • $\begingroup$ No, it's still confusing. If photons cause the rain, what's the purpose of consuming magical energy? $\endgroup$ – RonJohn Aug 4 '18 at 17:53
  • $\begingroup$ @RonJohn The purpose of consuming the magical energy is that its consumption can produce electromagnetic radiation. I'm asking, under what conditions would that radiation condense water. $\endgroup$ – user49466 Aug 4 '18 at 18:13

For rain, a couple of factors are relevant.

  1. Enough moisture in the air.
  2. Nucleation sites, such as dust particles in the air.
  3. The whole thing needs to be cold enough so that water condenses.

So you have a plant that gathers magical energy. But why? Other plants don't need it and except for the rain, it doesn't seem to have any special properties.

It's simple, really, to reproduce.

Once your plant has gathered enough magical energy, it releases millions of spores into the air. The spores will later act as nucleation sites for the rain.

This plant only grows near water sources such as underground lakes and has very deep roots which spread to reach them. Along with the spores, it rapidly releases moisture to get the conditions just right for setting roots. In the process it is known to even drain lakes.

Finally, once the conditions are right and the spores have spread a bit, it releases a pulse of cold magic (which might work similar to laser cooling, if you want to over-explain it and want to stick to the electromagnetic requirement).

So now the conditions are set. There are nucleation sites, there's enough moisture and the air is cold enough for the moisture to condense.

  • $\begingroup$ Another great answer, thanks for your time. Both you and Dan had wonderful responses, but I'm going to give the edge to this one, because you detailed the overall climactic conditions that provide not just a temperature drop, but the corresponding atmospheric conditions that dip would need. I'm likely going to blend both mechanisms and do some more thinking and customization. $\endgroup$ – user49466 Aug 5 '18 at 16:35
  • $\begingroup$ Ok - but this answer barely mentions radiation... thought that was the point of the question. $\endgroup$ – Dan Burden Aug 5 '18 at 20:44

There's Laser Cooling where coherent light is used to force matter to similar velocities thus reducing the velocity variance generally known as temperature. This technique relies on the fact that when atoms absorb and then re-emit photons they are sped up in the direction of the beam of photons, coupled with the fact that at certain wave lengths absorption only occurs when atoms are moving toward the laser source. The end effect of continued laser exposure is that the mass ends up all moving in the direction of the laser beam at the same speed, slightly increased from the speed it was moving at but because all the air is going the same way with no velocity variance the temperature is much lower, down as low as 1 or 2 K.

So an output of coherent green light could cool the atmosphere dramatically causing condensation of any moisture in the immediate area.

  • $\begingroup$ Laser cooling only works in specific laboratory conditions. Everywhere else, shining a laser beam on something heats it up. $\endgroup$ – RonJohn Aug 5 '18 at 14:33
  • $\begingroup$ @RonJohn Laser cooling is only used in laboratory conditions because generating a large enough diameter beam of coherent light to overcome the generally chaotic nature of an open atmosphere. $\endgroup$ – Ash Aug 12 '18 at 19:06

Condensation is a change of phase where a vapor loses energy and becomes liquid.

Photons are quanta of energy, therefore it is impossible that receiving photons a material can lose energy.

The only possible way is to have condensation of water involving photon is to have the vapor (or the air containing it) losing energy by emitting infrared photons, cooling down and condensing.

That's more or less what happens in a night with a clear sky: the atmosphere radiate into space and cools down until the dew point. Once vapor start condensing temperature stop falling and dew begins to form on all available surfaces.

  • $\begingroup$ Thanks @L.Dutch therefore, any solution where the air itself is force to release energy, basically produces the desired effect. That'll help narrow down this mechanism. $\endgroup$ – user49466 Aug 4 '18 at 17:55
  • $\begingroup$ P.s. apparently there ways to nudge an ionized vapor over the point of condensation by introducing radiation. In the case of cloud chambers, photons spark a bonding of hydrogen and oxygen molecules. Its not that they remove energy, so much that they help foment a chemical reaction which produces the liquid water. So energy loss, is, apparently, not the only way to do this. Still trying to think through possible applications of that to this concept. $\endgroup$ – user49466 Aug 4 '18 at 19:13
  • 3
    $\begingroup$ "impossible that receiving photons [cause] a material can lose energy": not really, when we're talking about reducing temperature. See the field of laser cooling $\endgroup$ – user71659 Aug 4 '18 at 21:27
  • $\begingroup$ "the atmosphere radiate into space and cools down until the dew point." Of course, that's many hours after being struck by the photons. $\endgroup$ – RonJohn Aug 5 '18 at 14:32

You could introduce a dormant bacterial spore that only replicated in the presence of a specific wavelength of light. When the plants absorb enough magic, they shine brightly and create a cascade of aerial bacteria growth. In some rare cases, bacterial growth can result in heat uptake (https://www.ncbi.nlm.nih.gov/m/pubmed/11536139/) and these dormant cells would have to be champs at absorbing heat to get the desired effect:

The corresponding temperature drop would cause water condensation in the air and on the plant. This mechanism has a nice symbiosis slant to it, and is technically feasible.

  • $\begingroup$ This is an excellent answer, and mimics the other aspects of how my magical ecologies are set up. It's usually mixtures of magical phenomena and mundane effects piggybacking off of each other, and significant ecological symbiosis. So this would fit perfectly. I'll have to think on this, and specifically, how to incorporate this mechanism. $\endgroup$ – user49466 Aug 5 '18 at 14:29

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