When magical energy has been used to power spells often in an area, the magical energy is left in a constant swirl that is easy to shape, but that might collapse into a chaos zone more easily. When the magical energy is still, it is slow moving and resilient, difficult to shape in a spell pattern, but reality remains more stable.
Note that this is not the same as GURPS Magic mana levels. Virtually all of Ymirea is a normal mana area, allowing only wizards to cast spells. However, aether ambience makes it easier or harder to cast and control spells
The great majority of the civilized lands of Ymirea have normal ambience (hence the name "normal" for this level). However, in the north, where sorcery is more rare, there is less ambient movement. Such places are defined as having a slow ambience, and include the Dwarven lands, the Naamlands, Rogheimr and the Savage Lands.
Similarly, certain areas have a greater ambient movement, most notably the Elven lands, and much of the Confederacy of Sorcerers. Here, the ambient movement is quick.
However, these are only general trends, and the variations in ambient movement form a complex patchwork. In thaumatological terms, any place where there is significantly greater movement than the surrounding area, is a peak, and any area with notably lesser movement than the surrounding area is a sink.
In general, the use of magic, or even the presence of magical beings and spirits creates changes in the ambient movement. If a place is kept free of sorcerers for years, it will gradually become a sink, whereas traditional sites of magic, such as covens, stone circles and wizard’s towers become peaks.
There are great lines of power running across most worlds, known as ley lines, aether lines, magic rivers, etc. Their proper name is one aetherpotamos (meaning "river of aether), several aetherpotamoi. Aetherpotamoi carry torrents of magical energy. Being magical, they run in both directions at once, non-wizards tend to find this paradox phenomenon hard to comprehend. It must be seen to be understood.
Aetherpotamoi often cause iron and other metals and alloys affected by magnetism to become magnetized, skip around, hover etc. Aetherpotamoi also tend to make sentient creatures dream strange and vivid dreams. Elves are immune to this effect.
Aetherpotamoi have a Frothing aether ambience (+4 to casting, -4 to control, -2 to cost), or one step greater than the surrounding area, whichever is higher. An enterprising sorcerer may harness the energy of aetherpotamoi in several more indirect ways.
Aetheranemoi are magical winds/weather: Aether moves in mysterious ways. Moving across the local patterns of ebbs and flows of energy are large, mobile patterns of aether agitation known as aetheranemoi (singular aetheranemos). Aetheranemoi are most powerful at high altitudes, less powerful at sea level, and somewhat weak in submarine and subterran areas. Some wizards build their towers at high altitudes to take advantage of occational gluts of magical energy, others prefer a more predicable and stable supply.
The aetheranemoi are best imagined as clusters of dust devils and whirlwinds, though more spherical than conical.
Aetheranemoi are classed in strength by sorcerers, ranging from dead aether to aether storms. The stronger the local aetheranemos is, the easier a spell will be to cast, but the harder it will be to control, and vice versa.
Occationally, the entire world is massively energized with magic, the aether of earth moving like fire, and the aether of fire moving blindingly fast. This causes mana levels to surge worldwide, and causes freaky occurences and fluxations of chance. The Annals of the Ashuku dynasty record 11 theophlatoi over the last 364 years, which indicates that there has been an average of one theophlatos per 33 years. They have struck at intervals ranging from 3 to 78 years.