600.20:50:03 · Model Record
Continuity status: Working. Materially developed late-life environmental model; quantitative atmospheric parameters remain open.
The Station contains two different environmental regimes. The inner rim begins with engineered planetary boundary conditions and develops predominantly natural surface ecology and climate. The underrim begins with enclosed artificial architecture: shafts, caverns, galleries, transit volumes, machinery halls, bulkheads, ventilation routes and water systems generate atmospheric conditions which natural ecology subsequently exploits and modifies.
Inner rim: engineered conditions → natural ecological cycles. Underrim: engineered atmospheric cycles → ecology exploiting and modifying them.
Large late-life underrim volumes can behave analogously to terrestrial cave systems. Structural mass supplies thermal inertia; shafts and openings become atmospheric connections; machinery and surviving utilities supply heat; leaks, drains and flooded decks supply moisture; geometry controls circulation. A shaft may act as a chimney, a tunnel as an airflow conduit, a bulkhead as a climatic boundary and a flooded deck as a lake. This is an analogy of system behaviour, not material equivalence with rock.
Major enclosed volumes may be treated provisionally as cave-climate cells coupled through doors, cracks, shafts, tunnels and surviving ventilation. Geometry, connectivity, heat, water and airflow determine local regimes. Deep low-exchange spaces may be stable and humid; ventilated spaces may undergo wet/dry cycles; machinery spaces may sustain convection; hydrological spaces may be dominated by leakage or reservoirs; boundaries may generate fog and recurring condensation.
Condensation geography creates ecological geography. Mosses, fungi, microbial communities and opportunistic plants follow persistent water, light and nutrient pathways and can subsequently modify moisture retention, drainage and airflow locally. This extends 600.20:80:02 and 600.20:80:03; ecology supplements rather than replaces the machinery sustaining the atmosphere.
This is not presently an intended Tribunal Group climate feature. Tribunal engineers designed ventilation, pressure boundaries, drainage and thermal systems; the old Station developed climate as scale, age, partial operation, changed boundaries and ecological colonisation altered those systems.
Underrim weather can become instrumentation. Expected fog, condensation, airflow, temperature or humidity patterns can indirectly indicate pumps, heat exchangers, leaks, ventilation routes and inaccessible connected volumes, extending 600.20:90:04.
A long-sealed bulkhead may also be an atmospheric boundary. Opening it can equalise pressure, reverse airflow, relocate condensation, dry an established wet ecology, wet previously dry machinery or move spores and contaminants. Closing a passage can isolate a volume and establish a new equilibrium.
Pressure zoning, atmospheric connectivity, characteristic cavern dimensions, ventilation-cell scales, thermal gradients, gas composition, breathable extent, exchange with the inner rim and quantitative ecological feedback remain unresolved.
Natural cave climatology supports the mechanism but not Station scale. Terrestrial work on thermally driven airflow, heat and moisture exchange, condensation and cave fog belongs separately in 700. Development provenance belongs in 400; fictional comparisons in 750; in-universe atmospheric documents in 100.