I was thinking something more along the lines of a living organism, so far as we can tell it was injured in a great battle (also described as having died by several characters) perhaps the itensity refers to some sort of shield erected as a defence mechanism while healing perhaps as part of a self induced coma (similar to how we treat head injuries). The intensity of which varying as it shifts resources between protection and healing? Of course this is only a theory.

I think it might actually float a little bit up and down over the city.