Dynamics and Electrodynamics of the Mesosphere - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 363

Figure 7.18 shows the variety of mesospheric phenomena that can accompany
cloud-to-ground lightning (CG). The most well studied of these phenomena are
the so-called “sprites” and “elves.” “Blue jets” and “gigantic jets” have recently
come to the forefront, since gigantic jets appear to provide an electrical connec-
tion between cloud tops and the ionosphere. Few observations of gigantic jets
have been made thus far, however, and all known gigantic jets have occurred
above oceanic storms (Pasko et al., 1997, 2002; Su et al., 2003). Elves are expand-
ing rings of luminosity that are directly linked to a causative electromagnetic
pulse (EMP) emanating in a dipole pattern from the cloud-to-ground lightning.
When the EMP encounters the base of the ionosphere (at around 80 km alti-
tude), it heats the ionospheric electrons, and optical emissions are produced.
Elves have been observed with large lightning discharges of either positive or
negative polarity (Inan et al., 1991; Fukunishi et al., 1996; Barrington-Leigh
et al., 2001).
Sprites occur between thundercloud tops and the base of the ionosphere and
are the optical manifestation of upper atmospheric electrical breakdown caused
by cloud-to-ground lightning. They are almost always associated with the more
rare strong positive polarity lightning strikes and generally are thought to be due
to a quasistatic electric field set up above a thundercloud after charge is deposited
to ground by a positive CG strike (Pasko et al., 1997, 2002). Figure 7.19 shows
a schematic diagram of the charge configuration in a sprite-producing cloud as

100

Ionosphere

ELVE
(Expanding disk)

Sprite

Mesosphere

Tendrils

50

Stratosphere

Upward
superbolt
(to be confirmed)

Blue jet

Conventional
cloud-to-air
discharge Stratiform region

Troposphere

Negative cloud-to-ground
flash near convective core

Positive cloud-to-ground
flash with "spider lightning"

0

100 200

Distance (km)

Figure 7.18 Phenomena associated with upward coupling by lightning. (Figure courtesy
of W. Lyons and C. Miralles.) See Color Plate 25.