# At what altitudes would clouds form to produce rain on this world and with what general severity?

Planetary surface:

• | 71% Ocean (H2O) | 29% Land |

Atmospheric composition:

• | 2% Trace gases | 58% Nitrogen | 26% Oxygen | 11% Argon | 3% Carbon dioxide |

Average surface temperature:

• 36 degrees Celsius

Planetary rotation:

• 34 hours

Axial tilt:

• 0

Info regarding of altitude, pressure, and atmospheric density:

altitude    pressure    density
(meters)    (atm)       (kg/m^3)
0           17          10
1000        15.3        9
2000        13.8        8.1
3000        12.5        7.3
4000        11.3        6.6
5000        10.1        6
10000        6          3.6
15000        3.6        2.1
20000        2.2        1.3
30000        0.8        0.5
40000        0.3        0.2
50000        0.1        0.06


Keep in mind the oceans are 30% shallower, half the salinity and the surface gravity is 1.36x that of Earths, and the majority of the continents are as big as Australia. At what altitudes would clouds form to produce rain on this world and with what general severity? By general severity I mean how severe would storm systems on a global scale be in contrast to Earths?

• How does rain occur on Earth? The sun heats water, it evaporates, rises, cools, "clumps" together, and when there's enough, it gets too heavy and falls back down. Ocean shallowness is meaningless, I think, but I wonder at what gravity water vapor can no longer rise. – RonJohn Nov 13 '18 at 8:59
• Also, the atmospheric pressure will be so high that I'm dubious as to the atmospheric "carrying capacity" for more gas. – RonJohn Nov 13 '18 at 9:01
• How do you come to the answer that oceans are 30% shallower? – user10645073 Nov 13 '18 at 9:09
• Do you mean ‘how will rain happen’ or ‘what would it be like when it rains’? – Joe Bloggs Nov 13 '18 at 9:34
• @RonJohn Ocean depth can be a factor, really shallow water (where the seabed is illuminated by visible light) heats up more and much faster, but 30% is not shallower enough to have an impact globally; that's still an average depth measured in kilometers. – Ash Nov 13 '18 at 10:39

# How cloud formation occurs

Warm air near the surface of the Earth can rise for many reasons. As it rises, it undergoes adiabatic cooling. Since the pressure drops with rising air, the gas must expand slightly while the temperature drops, as suggested by the ideal gas law ($$PV = nRT$$). As the temperature drops, the relative humidity of the air rises.

If the air rises far enough, and cools enough, then humidity exceeds 100% and moisture precipitates as water droplets. This makes clouds. If enough water precipitates in the clouds, the droplets become big enough that they cannot be suspended in the air and they fall as rain (or snow, depending on temps).

Clouds can form at different altitudes depending on local conditions. Clouds never form above deserts, since there is so little moisture in the air. Clouds form at ground level above wet jungles, since humidity is already 100 %, and any cooling will cause moisture to precipitate. For other climates and conditions, cloud altitude varies.

# How is this affected on your world?

Lets put your pressure to altitude map side by side with Earth's

altitude    Your press  Earth press
(meters)    (atm)       (atm)        ratio
0           17          1             17
1000        15.3        0.89          17
2000        13.8        0.78          18
3000        12.5        0.69          18
4000        11.3        0.61          19
5000        10.1        0.53          19
10000        6.0        0.26          23
15000        3.6        0.12          30
20000        2.2        0.05          44


Air pressure on your planet is relatively higher at altitude, meaning the pressure gradient with increasing altitude is lower than it is on Earth. Since the cooling is driven by pressure changes (again, $$PV = nRT$$), if lower the rate of pressure change with altitude, then we lower the rate of temperature change with altitude.

Therefore, on your planet, cloud formation occurs at slightly higher altitudes than it would on Earth, given similar temperature and humidity conditions at ground level.

• Interesting approach with comparing ratios (and assuming same temp/rel humidity as earth). Not disagreeing with your assumption right now, but you leave out that there is a lot more mass at the higher altitudes (considerably higher densities, presumably due to the argon?). I believe that this would offset a percentage of the pressure changes (being the V part after all). Given that the densities offered by the OP vary considerably from Earth's, I don't think ignoring it as a factor is correct. Would it be safer to include the ratio of volume difference as well? – ColonelPanic Nov 13 '18 at 14:02
• @ColonelPanic The V ratio depends on geometry, namely the radius of the planet. The volume gradient is the same as the derivative of a sphere's volume with respect to changing radius $dV/dr$. Since the OP didn't specify a radius, I assumed it is the same as Earth so it doesn't matter. – kingledion Nov 13 '18 at 14:09
• But he specifies a density which is considerably different than Earth's (I didn't do the math but I assume this is due to different gas makeup). More mass -> faster thermal transfer given all else is constant (as we can only assume right now because OP didn't respond to my earlier comment). Edit: Rereading, yeah, I meant mass, not volume... – ColonelPanic Nov 13 '18 at 14:33
• @ColonelPanic The gas makeup is similar to Earth's. I don't know if the densities are feasible given the stated surface gravity. That is really a separate question, though, I just answered this with what was given. – kingledion Nov 13 '18 at 14:38
• Right, I'm point out that he gave us information which is highly relevant though. Whether the densities are accurate I don't know, but ignoring them all together isn't necessarily correct either. With much more mass, the raising air will cool faster is my point. This would offset at least some of your conclusion that formations would be higher. Just pointing out something that may have been overlooked is all :) – ColonelPanic Nov 13 '18 at 14:49

I think, I see problem here. Atmospheric pressure changes Dew point and at 17 atm it will be around 83°C. How much water vapor air will be able to hold? I dont know. I doubt you can have so clean air to hope supersaturate air to form rains all the time.

So you may have fog and rare rains from high altitude...

*Is not your planet way too hot? Earth is like 14-15°C average, record average temp is 34.5°C. Air density is low, would expect it to be around twice as big or pressure around 8atm.

I may be wrong.

• I spoke with a chemist few days ago in person, he mentioned the air pressure shouldn't be too much of a concern for evaporation to take place, his claim was that... Salinity and temperature play a substantially bigger role for evaporation, however, I'm not exactly sure how my question could be answered ideally since I'm uncertain, I think the clouds would form in much higher altitudes.. but I don't for certain how they would form, I've heard mountains are essential.. but the mountains here would have to be very very very very high to do the same effect.. which can't be done in higher gravity. – Neuryte Nov 18 '18 at 4:58
• Is there a reason why you went with such pressure? For note, humans will die there from oxygen toxicity amd nitrogen narcosis ( Ar makes it worse). – Artemijs Danilovs Nov 18 '18 at 17:03
• I was striving for something really alien, plus there's a lot of volcanic activity present on this world, which fills up the atmosphere, whilst the the higher escape velocity holds the atmosphere better in place. Note, this place is toxic for humans, but the creatures there have adapted to the conditions given, so my humans would require specialized suits when visiting this world. – Neuryte Nov 18 '18 at 20:00