Based on the image, it seems that the picture is of the layers of the atmosphere. Now the B layer is the thermosphere. It is found in between the mesosphere (layer below) and the ionosphere (layer above). It extends up to 600 km high and you can find satellites and the aurora here. Temperature here is higher as the height increases and it is because of this trait, its name thermosphere was based on on. "Thermo," in Greek means heat. It overlaps with the ionosphere.