High-Resolution Image

Color enhanced images of sprites and an ELVE (an acronym for emissions of light and very low frequency perturbations due to electromagnetic pulse sources) taken during the Mediterranean Israeli Dust Experiment (MEIDEX), on board the space shuttle Columbia on its last and tragic mission. The ELVE in the picture was taken by astronaut Dave Brown on his first attempt to capture sprites.

These short-lived optical flashes are collectively called ÒTransient Luminous Events (TLE)Ó and are associated with strong lightning flashes below. Sprites have lifetimes of tens of milliseconds and seem to be associated with positive cloud-to-ground flashes (positive charge transferred to ground). They are observed at altitudes of 70-85 km above ground. ELVES have a much shorter lifetime (few milliseconds), have a diameter greater than 400 km and are observed higher up at about 90-95 km. Both are red in color. These phenomena occur due to intense electric fields generated in the upper atmosphere by the lightning flash. The high electric fields accelerate and heat free electrons in the mesosphere that collide with Nitrogen molecules, producing the beautiful TLE optical emissions.

There may be a connection to aerosol cloud interactions because aerosols affect cloud development and consequently affect cloud electrification. This may lead to different distributions of charge centers and could modify the type of flashes. Consequently, the frequency of the TLE could also change. It should be pointed out that sprites were first discovered in the late 1980Õs by a group of astronomers from the University of Minnesota while trying to calibrate their camera. Since then, the number of observations has increased dramatically. The MEIDEX measurements are unique because they were carried out from space with a calibrated camera, thus allowing a better estimate of the energies involved, as well as the global distribution of TLEs. In addition to the images taken from space, many research groups from around the world participated in the experiment, using ground-based instruments to detect the electromagnetic waves generated by these phenomena.

The MEIDEX team at Tel Aviv University, Israel prepared the image and the schematic diagram. A list of publications and additional information can be found here.

(Submitted by Zev Levin, Tel Aviv University, visiting the Climate & Radiation Branch as a UMBC/GEST Visiting Fellow)