Tropospheric Adumbrans monitor a developing cloud cell on Darwin
Adumbrans (sometimes known as Cloud-Vecs) are the sophont descendants of robot clouds formed out of utility fog that were originally created during the First Federation period to act as a means of weather control and atmospheric regulation. Originally mere non-sophont devices, the complexities of the weather and its chaotic nature, as well as the necessity to deal with the unexpected and natural disasters, and the effects of the Adumbrans themselves on the atmosphere, forced upgrades of the original designs. This first gave them idiot savant levels of cognition where atmospheric physics was concerned, and then later upgraded them to full sophoncy. In most types of Adumbran they still retain a level of cognition relating to atmospheric physics and management over and above their intelligence in other areas.
As utility fog, the Adumbrans are very large and light, with a sufficiently low density that they float in the air. They drift with the wind and have a shape that shifts and flows with it. By controlling their surface configuration, they can create or remove nucleation centres and so control the condensation of water into clouds. They can control their albedo to regulate temperature, as well as store and re-radiate heat as required. By controlling their shape and creating barriers and channels for air flow, they can regulate air flow and control their movement through the air; although they normally drift with the wind they can move against it if they need to, using their foglets as motors. Controlling their density (how closely packed their foglets are) and using stored heat also allows them to control their altitude. Many Adumbrans can also remove pollutants of various kinds from the air, concentrating them until they can be safely disposed of. They are mainly powered by solar energy, but can also extract energy from the air that passes through them if that is what is required at a given moment, and from atmospheric thermal and electrical gradients.
The smallest Adumbrans are hundreds of metres across, and individually influence the weather only in an area somewhat bigger than themselves; these are sometime employed to protect individual facilities on a planetary surface. The largest form a single entity extending throughout and thus influencing an entire planetary atmosphere. They can all pack down into much smaller and denser forms if necessary, such as for transport to other locations. All Adumbrans are hard to damage or dissipate, by their very nature, and their foglets are designed to be resistant to hostile atmospheric phenomena such as lightning.
In terms of senses, Adumbrans have extraordinarily acute vision and hearing, their widely spread foglet units giving them eyes and ears as large as they are with sensitivity into the infra-red and ultraviolet. From the air passing around and through them they can feel atmospheric pressure, temperature, composition and wind speed and direction. Most Adumbrans communicate via subtle variations in their surface reflectivity (albedo), though some types use laser emitters in their foglets to talk to one another. Some have radio communications abilities, although this requires the Adumbran to have thread antennae longer then their foglets running through them.
Because of their original raison d'être, many Adumbrans form part of an angelnet.
In addition to their size there is a great deal of variation among Adumbran types. Some have clearly defined borders and while they can meet and make contact with others they remain definite individuals. Others have no such defined borders, and should the wind take them they blow through one another, merging and splitting off again, sharing thought processes and foglets as they do so. These latter types tend not to have much in the way of individual personalities, as their mergings tend to erase any variations between them.
There are various different Adumbran civilisations. Some are an integral part of the ground-bound civilisations of the worlds they inhabit; this is particularly the case when the entire planetary atmosphere is inhabited by a single Adumbran. Others live in isolation from them, or on worlds that they inhabit alone. Many of them have a culture based on wind and energy transactions between individual Adumbrans.
Adumbrans are capable of reproduction. In many cases they create new utility foglets out of dust and other elements found in the atmosphere they inhabit. In others these have to be supplied externally, or the Adumbrans extract them from the ground of their world. Some grow to the point where they split into a number of new individuals by a process of fission. Others create new children that grow and develop as biont children do.
Adumbrans ascend to higher toposophic status at approximately the same rate as other modosophonts. Transapient Adumbrans are generally larger than modosophont examples, and tend to radiate more waste heat, an effect that can have profound effects on their local microclimate.
Over the centuries most types of Adumbran have acquired very good protection against viruses, mental intrusion and hacking. This has arisen from the desire of planetary populations not to have their atmospheres taken under the control of hostile outsiders.