Broadband electromagnetic field measurements both above and below thunderstorms: the IME-HF instrument for the TARANIS mission and related ground-based instrumentation

Abstract:

The TARANIS (Tool for Analysis of RAdiation from lightNIng and Sprites) micro-satellite of the French space agency CNES carries scientific instruments to study electromagnetic and optical radiation, X-rays and energetic electrons emitted from lightning and optical phenomena (Transient Luminous Events and Terrestrial "Gamma-ray" Flashes) occurring at altitudes between 10 and 100 km, as blue jets, red sprites, halos, and elves.

A broad-band analyzer of the IME-HF instrument (“Instrument de Mesure du champ Electrique Haute Frequence”) records waveform measurements of fluctuating electric fields in the frequency range from a few kHz up to 37 MHz, with the following scientific aims: (i) Identification of possible wave signatures associated with transient luminous phenomena during storms; (ii) Characterization of lightning flashes from their HF electromagnetic signatures; (iii) Identification of possible HF electromagnetic or/and electrostatic signatures of precipitated and accelerated electrons and related wave-particle interactions; (iv) Determination of characteristic frequencies of the medium using natural waves properties; (v) Global mapping of the natural and artificial waves in the HF frequency range, with an emphasis on the transient events.

The instrument is also able to trigger and record interesting intervals of data using a flexible event detection algorithm. Over Europe, these observation from a Sun synchronous polar orbit at 700 km altitude are done together with several ground-based stations operating in the same frequency range, and allowing us therefore to trace the same lightning-related phenomena from below and from above at the same time.