Transient Upper Atmospheric Plasmas:Sprites and Halos

Sprites and halos are two types of the so-called transient luminous events occurring in the upper layers (40-90 km) of the earth atmosphere. Their spectacular appearance is due to the optical emissions from mesospheric plasmas caused by the electric breakdown of the high-altitude rarified air. While halos look like flattened diffuse flashes of light appearing between 80 and 85 km, sprites exhibit a sharp transition between the upper diffuse and lower plasma streamer regions, as observed in one of the images shown here.