Estimates of energy fluxes associated with sprites in the mesosphere

Abstract

We present calibrated estimates of photon flux, lightning peak Poynting flux and Joule heating associated with the brightest region of sprites observed in the mesosphere over South Africa. The sprites' photon fluxes were estimated using 28 sprites events (observed during the 2019 sprites campaign) calibrated by stars in the sprite's image background. The lightning driven background electric field associated with the brightest region of sprites were found to vary from 0.1 to 6.7 Ek (local air breakdown field). The lightning return stroke at lower frequencies (4 Hz - 2 kHz) has more influence in carrot sprites than in column sprites formation processes. The lightning peak Poynting flux and Joule heating were estimated from calibrated electromagnetic field measurements made in parallel with eight sprites events (observed during the 2020 sprites campaign). The photon flux, peak Poynting flux, and peak Joule heating associated with the brightest region of sprites were found to be 1.1 × 10−7 W/m2, 12.7 W/m2, and 4.7 × 10−3 W/m2 on average, respectively. The altitude/distance-normalised lightning peak Poynting flux decreases with increasing atmospheric altitude. The photon flux from column sprites decreased with increased altitude of the brightest region. Column sprites have a shorter time delay (<30 ms) from their parent lightning strokes than carrot sprites (up to 145 ms).