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Elves have been described by models as heating from the EMP from
tropospheric lightning (Pasko et al.(1998),Inan et al.(1997)).
The optical emissions of elves have been identified as originating
from N2(1PG) (Heavner(2000)). The short duration of elves suggests
that individual elves are less important energetically than sprites or
jets. However, elves (optical emissions) may represent only the high
energy component of the effect of
lightning discharges transferring energy to the middle atmosphere.
Lower energy
lightning discharges may not cause optical emissions, but the majority
of tropospheric lightning discharges can still cause neutral heating
in the middle and upper atmosphere but do not stimulate optical
emissions. Before the documentation of elves, the neutral heating of
the upper atmosphere by lightning was proposed as a mechanism for
creating a long-term (hour time scale) infrared glow above
thunderstorms (Picard et al.(1997),Inan et al.(1991)). The mechanism described the
vibrational excitation of ground state N2 by electron impact
followed by energy transfer via
N2(X1Su+) -> CO2.
Because elves
are observed to occur above both positive and negative CG's they may
occur more frequently than sprites.
Matt Heavner
2002-02-13