This study uses Fast On-Orbit Detection of Transient Events (FORTE)
satellite observations to identify superbolt-class optical lightning
events and evaluate their origins. Superbolts have been defined by
Turman (1977) as lightning pulses whose peak power exceeds 10 W.
However, it has been unclear whether superbolts resulted from particular
types of high-energy lightning process or whether they were the result
of measurement bias. In the latter case, any decently-bright lightning
process could be recorded as a superbolt if the sensor had a
particularly clear sight line to the hot channel without thick clouds
diluting the optical signals.
Our 12-year analysis of FORTE superbolt detections indicates that the
lower superbolt energy range (~100 GW) is dominated by
normal lightning, but brighter cases up to or exceeding the terawatt
scale are predominantly strong +CG strokes that originate from specific
types of storms. Oceanic storm systems, particularly during the winter,
and especially those located around Japan are shown to produce these
intense superbolts. We suggest that both interpretations of superbolt
origins are correct: that some result from favorable viewing conditions
and would not be identified as such by another instrument located
elsewhere, and that others are associated with a unique set of physics
that may merit the “superbolt” distinction.