Weather in a Dysonish sphere

[Dalillama]

Picture a sphere ~500 AU in diameter, filled with air (oxynitro mix at approximately 1.25 atm of pressure). The material of the sphere has no gravitational masd. Knots of dirt, rock, and water drift with the winds, as do cohesive balls of flaming gas (assume butane). In the center 9f the sphere is a ring of fire .5 au in diameter which burns and goes out on a 20 hour cycle, 10 hours on, 10 hours off. Assuming physics like real life on a macro scale except as specified, what kind of weather is to be expected?

[RogerBW]

Originally Posted by Dalillama

Picture a sphere ~500 AU in diameter, filled with air (oxynitro mix at approximately 1.25 atm of pressure). The material of the sphere has no gravitational masd. Knots of dirt, rock, and water drift with the winds, as do cohesive balls of flaming gas (assume butane). In the center 9f the sphere is a ring of fire .5 au in diameter which burns and goes out on a 20 hour cycle, 10 hours on, 10 hours off. Assuming physics like real life on a macro scale except as specified, what kind of weather is to be expected?

The mass or otherwise of the sphere doesn't matter - if it's uniform there's zero gravitational force from the sphere inside it.

Does the central ring of fire have any mass, in which case things will drift towards it, or is the whole space effectively in zero-G, in which case the flaming gas will soon run out of oxygen to burn due to lack of convection?

[Anaraxes]

Weather is a way for planets to move heat around. Hot air rises only because there's gravity. Winds occur mostly because hot air rises (needed that low pressure to get filled in at ground level from somewhere else), and rotate direction mostly because the planet spins (Coriolis effect). Rain comes from evaporating water (absorbing heat where it's warmer) condensing again (releasing heat where it's cooler).

So the weather is all going to be driven by that central fire and the drifting balls. But with no gravity, there's no wind, and little way other than conduction and radiation to move the heat away from the fires. Warmer and colder as the drifting balls of fire get closer or further, warmer near the center and cooler toward the outer rim, in a pretty smooth gradient.

Are the "knots of dirt, rock, and water" large enough to have their own gravity?

[Dalillama]

Does the central ring of fire have any mass, in which case things will drift towards it, or is the whole space effectively in zero-G, in which case the flaming gas will soon run out of oxygen to burn due to lack of convection?

I was envisioning zero G except where the rocks or globules are big enough to have gravity.

Are the "knots of dirt, rock, and water" large enough to have their own gravity?

Many of them. The blazing gasballs might have some as well.

[RogerBW]

The blazing gasballs need some propulsive force to keep them moving into oxygenated air, or they'll go out.

At which point I suspect you basically end up saying "magic physics", and you might as well choose the weather system you fancy. This isn't necessarily a bad thing; it's just that making painstaking physics solutions to problem A when problem B is solved by magic seems like wasted effort.

[Dalillama]

Originally Posted by RogerBW

The blazing gasballs need some propulsive force to keep them moving into oxygenated air, or they'll go out.

Would setting the ring to spinning like a coin on its edge get me some decent winds going?

At which point I suspect you basically end up saying "magic physics", and you might as well choose the weather system you fancy. This isn't necessarily a bad thing; it's just that making painstaking physics solutions to problem A when problem B is solved by magic seems like wasted effort.

Probably it is, but since I'm doing Larry Niven's setting into Spelljammer, it feels like I ought to have at least some idea of what should be happening in a setup like this.

[Agemegos]

Originally Posted by Dalillama

I was envisioning zero G except where the rocks or globules are big enough to have gravity.

Then you are overlooking the gravity of the atmosphere. The gravity of the shell is zero inside the shell, but even if the 1.25 bar of breathemix is magically prevented from self-gravitating towards the centre its mass is about 1.25 × 0.029 kg/mol × 44.5 mol/m^3 × 4π/3 × (3.65 × 10^13 m)^3 = 3.29 × 10^41 kg = 1.6 × 10^11 solar masses. Assuming standard temperature and pressure throughout.

Surface gravity of the uniform sphere of breathemix would be about 16.5 × 10^4 m/s^2 = 1 682 gees.

[malloyd]

Originally Posted by Dalillama

I was envisioning zero G except where the rocks or globules are big enough to have gravity.


Many of them. The blazing gasballs might have some as well.

Probably not if they are actually blazing - if they were big enough to have much gravity, the oxygen would presumably probably sink down below the butane pretty quickly, any burning still happening is *way* below the cloud tops. Of course the whole system is probably much too recent for that, or the chemistry would have run to equilibrium long ago anyway.

Seriously I don't think this is a sustainable natural system - it's either being maintained by god-like power (in which case the "weather" is whatever said power wants it to be) or a very recent (like thousands of years tops) creation that hasn't quite had enough time to fall apart yet.

[Irish Wolf]

Which of Niven's settings? The Ringworld spins for effective gravity - its rotational speed of 770 m/s gives it slightly under one Earth gravity. The air is held aboard by massive walls around the edges.

The Smoke Ring is in fact a ring of gases, with low gravity throughout, spun off of a gas giant orbiting a binary pair where one star is a yellow dwarf and the other is a neutron star. Maneuvering through the Ring is... tricky; most people never leave the Integral Trees they grew up on.

The disc he conceived (but never wrote stories on) is a flat disc like a record, with a star in the middle, and air once again held in place by walls. Gravity would be perpendicular to the plane of the disc, and the area would be in a perpetual twilight (although a day/night cycle could be approximated by "bobbing" the disc "up" and "down").

However, if you decide to solve any issues using magic, make sure you don't also use his magic system. You wouldn't want to be living in, say, the sphere discussed earlier, with things kept from falling into the sun with magic, when the mana fails...

[Agemegos]

Originally Posted by RogerBW

The mass or otherwise of the sphere doesn't matter - if it's uniform there's zero gravitational force from the sphere inside it.

Does the central ring of fire have any mass, in which case things will drift towards it, or is the whole space effectively in zero-G, in which case the flaming gas will soon run out of oxygen to burn due to lack of convection?

The atmosphere inside the sphere, though, will self-gravitate towards the centre, unless a uniform pressure of 1.25 bar is part of the exception to physics. So where is this 1.25 bar we're told about? At the shell? In that case the central pressure is enormous and the mass of the internal atmosphere is huge. Or is 1.25 bar at the centre? In that case the pressure at the shell is negligible. Or is 1.25 bar maintained throughout in defiance of physics?

Somebody ought to look up the physics of Jeans Collapse. Bags not me.