“The Weather Will Be Dry … Unless It Rains”


Mobile Suit Gundam: High Frontier

Life In The Universal Century

“The Weather Will Be Dry … Unless It Rains”

Even the most idyllic “temperate” colony has a distinctive weather cycle. The port end of the colony, facing the Sun, becomes hotter than the starboard end, facing away from the Sun. The air at the center, in zero-gravity and unaffected at first by the radial acceleration, expands outward toward the colony wall, where it picks up the radial acceleration and veers downspin as it moves starboard along the axis. It eventually reaches the end cap, where it wraps around to the outer wall, again accelerating and increasing its downspin veer as it moves toward port along the wall. As it accelerates, it moves in toward the center of the cylinder, creating what would’ve been a circular rise-and-fall cycle were it not for the starboard flow along the axis and corresponding port flow along the wall.

The net result is a downspin, corkscrew spiral running from starboard to port (south to north) along the wall—perceived as a prevailing “southwester” by the inhabitants—and a helical cyclonic stream running port to starboard (north to south) along the axis. Buildings, bodies of water and other landscaped “natural” features and variations in heat distribution will disrupt these prevailing winds, of course, resulting in unpredictably variable cross-winds. Occasional small, gusting whirlwinds (“dust devils” or “Will o’ the Wisps”) may also be common.

Tornado Lamp

You can see a good approximation of the airflow within a cylindrical space colony inside one of those “tornado lamps” that have become the “lava lamps” of the 1990s. Picture the stripes on a barber pole, substituting azure for red, and you’ll have a pretty good idea of the prevailing wind pattern—the white stripe is the cloud formation, the blue is clear sky.

The thermodynamics of the air in the rotating cylinder parallel the classical orbital dynamics of the “Smoke Ring” gas torus described in Larry Niven’s novels The Integral Trees (1983, Ballantine Del Rey, ISBN 0-345-32065-4) and The Smoke Ring (1987, Ballantine Del Rey, ISBN 0-345-30275-5). “East takes you out, out takes you west, west takes you in and in takes you east.” This can be paraphrased as “downspin takes you down, down takes you upspin, upspin takes you up and up takes you downspin.” Moving with the spin increases weight and speed. Moving against it decreases them.

The dynamics of temperature, humidity and rotation are such that the “island effect” seen on the Earth is also duplicated in the “islands” of space. A heavy rainfall occurs every “day” at 10:00, 13:00 and 16:00 UTC, lasting no more than five minutes per shower, as evaporated ground water reaches the saturation point and condenses spontaneously. (This is why Chris MacKenzie and Al Izuruha get soaked in a sudden downpour in the first episode of Gundam 0080.)


Although Tomino refers to the sky panels as “river” areas in his novels, there is one consequence of precipitation within an O’Neill Cylinder that seems to have been overlooked to date. Anything that falls onto a ground panel falls onto a sky panel as well, so, when it rains, the sky panel will fill with water!

This accumulation of water may never evaporate completely, which may change the index of refraction of the glass and disrupt the reflection of sunlight into the colony. The conductivity of quartz glass is such that the ambient temperature of the sky panels may even be low enough to form a layer of permafrost on the inner surface.

One solution would be to permanently fill the sky panels with water, such that they double as “lakes” or “reservoirs” between the ground panels. Water has the same refractive index as glass, so clarity and focus be unaffected, but it will never be mottled by wet and dry areas as would plain glass. This scheme has the added benefit of freeing up areas of the ground panels that would’ve been used for lakes and streams for use as dry land. It also opens up the possibility of a unique tourist attraction: a glass-bottomed boat across a sky/lake panel, with a view of space “below” and scenic landscape arching high overhead. (Unless, of course, it’s raining…) Please note that the water level on the downspin side might be as much as 20% lower than on the upspin side, due to the aforementioned Coriolis forces, friction and inertia.

While most colonies regulate their weather in some fashion, others purposely randomize it to maintain a more “natural” and unpredictable environment. Storms and even blizzards are not only possible but in some cases promoted, usually on a “seasonal” basis, though even the most carefully regulated weather system occasionally goes awry. Colonies that follow the Terrestrial seasons are synchronized with the Northern Hemisphere. (This explains why Zeon infiltrator Bernard Wiseman’s claim to be from Sydney, Australia backfires in third episode of Gundam 0080.)

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Last Update: 01 January 2020

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2 thoughts on ““The Weather Will Be Dry … Unless It Rains””

  1. The weather thing was really cool. I never thought of that, and I haven’t read of anyone else who’s thought of it, either. Congratulations, be proud! I may refer to this on my website. I’m legitimately impressed.

    Anyway: The way to get stuff off the window panels is pretty easy: make them slightly-less-curved than the land panels. Even making them just one degree shallower would mean that the water would (Eventually) run to the edges, where you could have a rain gutter pick it up.

    1. Or even slightly concave where they are shown as being convex to match the curve of the “ground” panels. Even so, I still envision an army of window washers, even if the actual work is performed by Roombas. In fact, landscaping and gardening might be a lucrative full-time profession in the habitats, if only to keep pesky Mother Nature from gumming up the sterile Works of Man.

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