Geoscience Reference
In-Depth Information
Cummer
1997
) devoted to accumulation of experimental data. The stream of
publications devoted to the further study of phenomenology, and experimental and
theoretical research of high-altitude discharges, proceeds to this day at an increasing
rate. Review of works on this topic can be found in many references, in particular,
in Pasco (
2007
) and Raizer et al. (
2010
).
By the present time, a large volume of observations of discharge processes in
the stratosphere and mesosphere has been collected, and construction of the self-
consistent closed theory of these phenomena is continuing on a wide front.
Among high-altitude discharges one can distinguish the ascending (blue jets)
and the descending (sprites) discharges. This chapter is devoted to constructing a
quantitative theory of the descending discharges of the elves and sprites types.
In brief, observational data of descending discharges observations can be sum-
marized as follows.
On the night side of the Earth above the horizon on a background of the dark
sky, luminescence flashes at altitude about 90 km from a luminous disk
100 km in
radius are observed from time to time. Duration of the flashes is of the order of 0.1-
1 ms. Figure
5.1
shows one of the first photographs of such flashes made from the
Earth's surface in America in 1997 (Barrington-Leigh
2000
)(Fig.
5.1
a) and from
on board the shuttle “Columbia” (19 January 2003) at night above the Pacific Ocean
(Boeck et al.
1998
;Yairetal.
2003
)(Fig.
5.1
b). The photograph in Fig.
5.1
awas
made from a distance of
200 km from the center of a thunderstorm and that in
Fig.
5.1
b from a distance of
1,600 km. In both cases, as well as in all others, the
altitude of the luminous area is estimated in limits of 80-90 km. Such flashes have
acquired the name “elves.”
In some cases, probably at especially strong thunderstorms, large-scale cone-
shaped asperities with a spatial period and amplitude about the depth of the
luminous area develop on the bottom of the elf. Such formations are shown in
Fig.
5.2
(Barrington-Leigh
2000
). From the ends of the cones grow descending
discharge filament structures, falling down to an altitude of
40 km. Development
of cones and branching of the filamentary structure occurs during 10-20 ms at the
already extinguished elf. The speed of the filamentary structure front is usually
10
8
-10
9
cm/s. The cones and filamentary structures have the name “sprites.”
In Fig.
5.3
(Barrington-Leigh et al.
2001
; Cummer et al.
2006
), one can see the
dynamics of the consecutive development of the elf and sprites. It is possible to
see that the elf's bottom border is moving downward by 1-2 km during a time of
1.5 ms, that is, with a speed of
10
8
cm/s. The front of sprites goes downward,
moving with a speed of
10
9
cm/s.
A photograph of one of the powerful sprites is shown in Fig.
5.4
(Stenbaek-
Nielsen et al.
2000
). Temporal evolution of the elf into sprites is seen well in Fig.
5.5
,
where a luminosity waveform of all the discharge area is given.
The first peak of luminosity during a part of a millisecond corresponds to
the elf, and the subsequent luminosity during 30 ms - to the sprites. Research of
high-altitude discharges was executed also from specialized satellites, for example,
from the satellite DEMETR (Błecki et al.
2009
). With the purpose of spectrum
