SpriteLab - 3rd year B.Sc course lab





Introduction
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].

References


Lab instructions
Formulas:
a = 50 [m] (altitude of the station in Tel Aviv).
L Distance to the storm.
R = 6378 [Km] (Radius of Earth).





Electrical field:
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.


Geometric diagram:


Angular coefficients:


Lab instructions: Download this FILE