Different times of the year and locations have different frequencies of occurrence. In Northern Australia, the most common times are February to April and August to October, when a plasma bubble is expected every night. Plasma bubbles have dimensions around 100 km. Plasma bubbles form after dark when the sun stops ionising the ionosphere. The ions recombine, forming a lower-density layer. This layer can rise through the more ionized layers above via convection, which makes a plasma bubble. The bubbles are turbulent with irregular edges.