Now they are simply referred to as sprites, a whimsical term that evokes a sense of their fleeting nature, while at the same time remaining nonjudgemental about physical processes that have yet to be determined. Return to top of page Characteristics of Blue Jets Blue jets are a second high altitude optical phenomenon, distinct from sprites, observed above thunderstorms using low light television systems. As their name implies, blue jets are optical ejections from the top of the electrically active core regions of thunderstorms. Their intensities are on the order of 800 kR near the base, decreasing to about 10 kR near the upper terminus. Blue jets are not aligned with the local magnetic field.
Sprites appear to be elusive for several reasons.
To see them requires visual access to the region above the storm, unobstructed by intervening clouds, and viewing against a dark stellar background. In most locations these conditions occur only rarely. Sprites are dim and can only been seen with the dark adapted eye. On average, their brightness compares to moderately bright aurorae, 10-50 kiloRayleighs. In the human eye, this corresponds approximately to the crossover threshold intensities of cones of the retina, which respond to color, and the somewhat more sensitive but achromatic parfoveal rods, which permit night vision.