Short‐Fractional Hop Whistler Rate Observed by the Low‐Altitude Satellite DEMETER at the End of the Solar Cycle 23

Abstract : For the first time an evaluation of the whistler rate around the Earth is performed using results from the neural network aboard the microsatellite DEMETER. It is shown that the rate of whistlers with low dispersion calculated all around the Earth as a function of longitude vary between 1 and 6 s−1 during nighttime (22.30 LT) and between 0.5 and 0.7 s−1 during daytime (10.30 LT). The whistler rate is anticorrelated with the F10.7‐cm solar flux. A decrease by 25% of the solar flux corresponds to an increase of 62% (26%) of the averaged whistler rate calculated for the entire Earth during nighttime (daytime). Using this averaged whistler rate, the global lightning rate is estimated to be of the order of 123 s−1 (27 s−1) during nighttime (daytime). The main conclusion concerns the precipitation of the electrons in the radiation belt by interaction with the whistlers. It is shown that the decrease of the lightning activity at solar minimum (shown with the help of the Schumann resonances) is largely counterbalanced by the increase of the whistler rates in the upper part of the ionosphere due to the decrease of the ionospheric absorption.