Blue Jets and Blue Starters

On July 1, 1994 University of Alaska scientists aboard aircraft were observing a thunderstorm over Arkansas as part of a three week sprite campaign. Because of the storm/aircraft geometry (the cameras were viewing away from the sunset), the observations began about one hour earlier than most other nights. Fifty-nine examples of luminous columns of light propagating up from the storm tops were recorded during a 22 minute period. At the time of observation, these new phenomena were obviously different from sprites in two ways: (1) the propagation speed was such that the upward motion was easily apparent at video rates and (2) the emissions were blue, as observed by an intensified color camera. Due to the upward motion and the color of the phenomena, they were given the name blue jets. Triangulation analysis of 34 blue jets observed simultaneously by both aircraft found an upper altitude of 37.2 +/- 5.3 km and an upward velocity of 112 +/- 24 km/s (Wescott et al.(1995)). The blue jets do not occur in association with either positive or negative cloud-to-ground lightning as reported by the National Lightning Detection Network. The blue jets do occur over regions of storms actively producing negative cloud-to-ground discharges and heavy hail activity, but the jets are not temporally coincident with a single discharge.

A similar phenomena, blue starters, propagate up from the top of the thunderstorm (Wescott et al.(1996)). However, starters terminate at an average altitude of ~25.5 km and have a velocity range of 27-153 km/s. Intensified color camera observations record starters as the same color as blue jets. Thirty starters were observed in the same region of the storm as the blue jets, during the same 22 minute interval. On several other nights starters were observed over the active convective core of storms (but no blue jets were recorded). Blue starters were also observed during the EXL98 mission (described in the Energetics section). The starters were observed in blue filtered images and also in the near infrared. The implications of these observations will be discussed below.