Wending Skies
Aerography Overview
The air disk around Mundus stretches outwards for hundreds of thousands of kilometers, though over most of this is it only a few thousand kilometers thick, with the low-pressure thin disk being roughly double that in thickness. The overall structure is that of a lazy, poorly-defined spiral and most truly large-scale structures such as the Great Wall, the Sky Rivers and even the general relative density of islands and gulfs can be seen to form long, lightly curved scimitar-esque shapes. It is hardly homogeneous however; the air disk is distinctly 'lumpy' due to the unseen but not unfelt effects of the invisible dark ether disk of Mundus as well as the lesser but still important effects of local gravity by the larger shells.
Thus areas around shells and other concentrations have thick, breathable air while large gulfs tend to be much thinner; corridors and streams of comfortable air have shaped humanity's great trade routes and expansions for untold thousands of years. The largest air deserts also act as conduits for solar radiation and shells near their bottoms tend to have above-average temperatures. The density of luminous ether likewise varies, though the swings between ether deserts and thick ether (taking the form of nebula) is much more pronounced than that of atmospheric density and less correlated to shells.
Aerographic Zones
Mundus
Mundus is a gas giant with an equatorial radius of roughly 70,000 kilometers. Its complicated cloud systems are varying pastel shades of white, peach and violet, with the occasional break in the cloud decks revealing rich colors deeper down. Having no solid surface and a gravity almost three times standard at cloud tops it has been visited only rarely on some mission of science or publicity.
The Abyss
The zone lowest and closest to Mundus, the Abyss stretches upwards for roughly a hundred thousand kilometers from the cloud surface of Mundus to the stormy jet streams at the bottom of the Bathics. The Abyss is mostly clear and thin air, though a handful of islands sparsely dot it and an equally small number of sluggish skycurrents wind their way through it. The most defining factor of the Abyss is that it is normally (effectively) lightless with only the seasonal tilt providing a modicum of twilight during the heights of summer, what light that does reach the Bathic's basal storms being completely blocked by these nigh-continuous cloud bands. Less obvious but no less notable is the paucity of ether in the Abyss, the entire zone being mostly an ether desert save in the wake of diapirs rising from Mundus. The depth of the Abyss in the sky disk also means it is cold, though this is mitigated somewhat by the overal calmness and the flow of heat from Mundus below; the upper Abyss is actually colder than the lower Abyss.
All this said, life does exist here, such as vast and slow migrations of Sundogs from their spawning grounds on Mundus spending years making the trip up through the Abyss. Even civilization of a sort, the lantern-eyed Umbroc make their lairs in the Abyss, shunned by all.
For centuries worthwhile routes through the Abyss have been sought to cut down on the time taken to reach Wildspace but despite these efforts, none have been found. A few intrepid traders (or more commonly, lowlifes) do follow the winding paths through the darkness but such a crossing is not for the faint-hearted.
The Bathic Zone
The deepest of the illuminated photic air ring, the Bathics makes up roughly the inner quarter of the thick ring. This depth means that is tends to be cooler, with shorter days (generally 8-10 hours long) between long extinction nights and drawn-out twilight. The Bathics also tends to be stormy, particularly along the inner edge of the thick ring where a number of jet streams spawn icy cyclones that can sprawl across entire shells. The upper edge, by contrast, is typicaly taken as the limit of the Low-Lattitude Shear which is not as violent as the Basal Streams but can still regularly unleashes days or weeks of grey clouds and rain. As the Low-Lattitude Shear can sometimes oscillate up to ten thousand kilometers over the span of several years this is a relatively arbitrary deliniation. Finally, being deep in the air disk, the Bathics are known for their orange and red skies though diffuse, low contrast white skies with no visible sun are equally common if much less photogenic. Likewise the immense air depth regularly results in sun colorations and optical effects that would be considered exotic and rare further from Mundus.
Despite the colder and less pleasant conditions typical of the Bathics, there is great mineral and etheric resources to be found among the dense archipelagos and more than one exiled despot has fled to the mines and factories of the deep Bathics to plot their revenge from snow-encrusted redoubts.
The Bathics are also the most direct route to Wildspace on the far side of Mundus and several rich trading empires have called it their home over the millenia.
The Pelasic Zone
The broad temperate zone of Mundus' sky disk, the Pelasic Zone stretches from roughly 250 latitude (the Low-Lattitude Shear) up to 400 latitude (the Stratic Convergence Zone). Hosting the original cradles of civilization, there are hundreds of significantly-populated shells scattered through just the Known Triangle and uncountable lesser ones. With a favorable climate overall and reliable ether flows the Pelasics are densely populated.
These millennia of technic civilization does not mean that the Pelasics are fully civilized or empty of mysteries. A number of planet-sized nebula dot the Pelasics, their obscuring clouds never properly mapped and concealing all manner of enigmas.
The Stratic Zone
The outermost of the three main climatic zones of the photic ring, the Stratics extend from the Stratic Convergence Zone at 400 latitude to the outer edge of the photic ring at ~470 latitude. This outer position means it gets the most direct light and it is characterized by both generally warm to hot conditions and long days of up 14 hours with sudden, rapid nightfall.
Some parts of the Stratics are parched sky-deserts host to desolate, rocky shells while others are sodden under near-constant monsoons. The former are home to some of the most tenacious fauna while the latter are incredibly productive and often inhabited by teeming masses of voracious predators and vast aerojungles. The skies themselves are also thickly inhabited by various aerofauna, the abundant ether and solar energy both providing a feast for living beings.
Mostly abandoned during the Fall and the Great Roar, the last few centuries have seen a return of 'civilization' to the outer limits of the sky as a number of empires both formal and informal have begun to plumb its limits.
The Coronic Zone
The fringe of the air disk, the Coronics take the shape of a ring that is slightly skewed relative to the main disk. The Coronics can be divided into four main segments; the two antipodal spokes where the inclined ring intersects/emerges from the outer air disk and the two arcuate ring segments, the Upper and Lower Coronics (the Coronic Arches). The latter are mostly not masked by the main body of the air disk and so even on the far side of Mundus they are illuminated; for much of the Coronics night only lasts one or two hours though morning and evening semi-twilight. As a result they have been nicknamed the Skies of the Midnight Sun. The incessant sunlight makes the Coronics exceptionally productive, a veritable feast of light and energy, much like the Stratics but even moreso.
The Coronics are particularly dotted with small nebulae as well as various complex currents and cloudbanks, but this reaches its zenith at the intersection spokes. These are both host to massive nebular complexes; the Great Wall and the Drakenwalds each trace the invisible dark ether structure at the spokes. The large complexities of both of these extend all the way to the Stratic Convergence Zone and the excess air masses has a general cooling effect, with the Spoke Effect adjusting photo- and thermoclines more than 50,000 km outwards.
Like the Stratics, the Coronics have been mostly abandoned as of the Fall and even today are a true frontier where thousand year old structures are slowly being consumed by jungle. One hinderance to exploration of the Coronics is the almost complete lack of etheric clathrates to be found. As shells generally do not have a permanently shaded Mundus-facing side there is none of the chilly mesoclimate that allow for the deposition and growth of nightside ices.
The Flachmeers
Two elongated, arcuate areas of near-space that lie between the Coronic Arches and the nearby Stratics, the Flachmeers are long zones of low pressure (generally between 0.2 and 0.4 standard pressure) that are one of the main cometary accretion zones. The temperature inversion from greatly reduced pressure gives the Flachmeers frigid air temperatures and even with almost perpetual sunlight it will normally range from -30 to -60. Many atmospheric rivers will terminate in the Flachmeers where the moisture will crystalize out in the low pressure and temperature; this collects into comets which expand over time. Most will tumble out of the Flachmeers by the time they have reached several kilometers in size though a few, such as Murdo Island, have exceeded five hundred kilometers in diameter and are essentially static. Some will fall fairly rapidly into the thick disk and melt - air temperatures going from -30 to +30 in a couple dozen kilometers - while many will slowly migrate inward inside the boundaries of the thin disk. Some comets - albeit very few - have been tracked falling all the way to the low-altitude shear.
The edge of the Flachmeers is a favored habitat of skywhales, with many comets lingering on the border and providing both food and habitat to vast ecologies from airkrill to the skywhales themselves.
Aerographic Features
Nebula
While luminifous ether is normally not harmfull to life (in fact, it is often beneficial); it is understood that at a critical density it thickens greatly in process that is essentially self-sustaining. Known as miasma, the high etheric density leads to the formation of all manner of exotic chemistry and to most living things (including humans) miasma is no more breathable than the effluent of an industrial plant. That said, there are entire orders of life that breathe miasma the way humans breathe air with some going between air and miasma in different stages of life. Misma can sometimes be found collected around shells or in drifting clouds but most grandly it can be found forming immense nebulae, thousands of kilometers on even their shortest dimension.
Some of these nebula contain shells inside their gaseous envelope, while others are bereft of anything larger than random rubble and ponds. The thick miasma of nebula tend to block light very effectively, and while they sometimes glow softly in various shades they inevitably cast long shadows through the air disk. Their high ether concentration also results in continous lightning discharges and often unpredictable weather in the neighboring skies while inside the nebula proper the air - the miasma - is commonly stagnant. With all navigation methods save dead reckoning useless inside these opaque masses getting trapped inside one can be a death sentence.
Of course the ether and the miasma is equally valuable; it is a great source of gaseous ether in high concentration and all manner of industrially useful chemicals. An extremely short list would include Promethium R and Promethium S compound families, aerosolized Sakuradite, Merculite precursors, Polydichloric euthimal and Iotimoline particulates, not to mention more common etheric thiolins and hydrocarbons. Thus the edges of nebulae are often sites of extractive industries.
The largest nebulae often extend out of the air disk to quite significant distances, often also wrapping themselves in an envelope of breathable air. The latter often also host habitable shells which, due to their position above or below the main air disk can have strange climates relative to their neighbors. Of particular note for this is the aforementioned Great Wall and the nearby Tiamat's Shroud, the Pillars of Creation and the Greater and Lesser Drakenwalds. A few are even haunted by weapons of ages past, with the aptly-named Gunpowder Nebula thick with millenia-old shock mines, their corroded metal shells still protecting a payload of metastable merculite.
A far more benign relative of the nebula are fogwalls. Benign, that is, until your ship smashes into a rock concealed inside the fluffy white mists. Consisting (mostly) of innocuous water clouds, fogwalls are readily distinguishable from nebula by their clean white color as opposed to various rich shades. Generally found at the intersection of multiple air masses, the main difference between a fogwall and a simple large cloudbank is that fogwalls are - within the bounds of seasonal variance - essentially permanent features. Like nebula, the shade side of fogwalls often creates significant mesoclimates with the most famous of this being Quahog Sound bordering the Nanket archipelago.
Comets
Comets are one of the main sources of etheric clathrates over much of the air disk, these dirty snowballs growing over time in the thin, low-pressure disk before eventually falling towards the denser and warmer inner disk. The two most productive sources of comets are the Flachmeers but they can coalesce almost anywhere along the upper or lower side of the disk; a number of fairly regular upwellings result in some regions of active cometary formation all across the disk and curled-off vortices from both the Low-Lattitude Shear and the Stratic Convergence Zone likewise continually support cometary growth centered around 250 and 400 latitude.
In all cases the growth cycle is the same; humid air from the thick disk enters the colder, thinner thin disk and begins to expel moisture in the form of ice crystals. These, along with miscellaneous other aerial detritus, dust and ether nucleates and coalesces into ever-larger cometary bodies.