SpriteLab - 3rd year B.Sc course lab
Until the discovery of the TLEs, the area between the troposphere and the ionosphere was considered
to be an electrical passive area, with no "exciting" electrical phenomena occurring there, although
C.T.R. Wilson had already predicted the existence of a possible breakdown in the upper atmosphere in
1920 [Wilson 1921]. There were stories about strange light sightings in the atmosphere, with the first
documented observation dating back to 1885, but it was only in 1989 that the first TLE was imaged on
video, by chance, when a group of researchers from Minnesota were testing a camera for an astronomical
research project [Franz et al 1990].
There are several types of mesospheric optical emissions that are categorized as TLEs. Some are rare
(Pixies, Trolls, Gnomes, and Gigantic jets) and others are more common (Sprites, Halos, Elves and Blue jets).
The most researched TLEs are sprites and elves. Figure 1-1 illustrates the common types of TLEs. The
common sources of energy driving these processes in the stratosphere and mesosphere are tropospheric
thunderstorms and lightning. The electric field generated by these storms heats ambient electrons which
result in electron impact excitation of the ambient N2 leading to the observed optical emissions. Thus,
these emissions are evidence of rapid transmissions of electromagnetic energy from the troposphere,
across the stratopause, to altitudes as high as the lower thermosphere/ionosphere [Heavner et al 2000].
The three main TLEs are called Sprites (Stratosphere/mesosphere Perturbation Resulting from Intense
Thunderstorm Electricity), Elves (Emissions of Light and VLF perturbations from an EMP Source) and
Blue Jets. Two characteristics separating the common phenomena into the three types are time duration
and altitude. Sprites span the altitude between 40-95 km and last between 10-100 ms. Elves are estimated
to occur between 75-95 km altitudes, lasting less than 1 ms. Blue jets are generated from the cloud
tops (~10km ) and propagate upwards in the shape of an expanding cone to altitudes of over 40 km. The
typical period of blue jets are 200-300 ms [Heavner et al 2000].
- Franz R.C., Nemzek R. J., and Winckler J.R., "Television Image of a large upward electrical discharge
above a thunderstorm system", Science, Vol. 249, 48-50 1990.
- Heavner M.J, Sentman D.D, Moudry D.R, Wescott E.M, Siefring C.L, Morrill J.S, and Bucsela E.J, Sprites
, Blue Jets, and Elves: Optical Evidence of Energy Transport Across the Stratopause, AGU Monograph 123
"Atmospheric Science Across the Stratopause," p 69-82, 2000.
- Wilson C. T. R., Investigations on Lightning Discharges and on the Electric Field of Thunderstorms,
Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a
Mathematical or Physical Character, Vol. 221, pp. 73-115 1921.
a = 50 [m] (altitude of the station in Tel Aviv).
L Distance to the storm.
R = 6378 [Km] (Radius of Earth).
r - distance from the place of charge to altitude Z of the sprite Z=(h1+h2)/2.
Hpos / Hneg - Altitude of Postivie and Negative charges.
Lab instructions: Download this FILE