Lightning-induced plasma turbulence and ion heating in equatorial ionospheric depletions

A wide range of plasma instabilities exist in various regions of the terrestrial ionosphere, leading to the development of plasma turbulence, in particular close to the lower-hybrid frequency - the frequency of a longitudinal oscillation of ions and electrons in a magnetized plasma that must be near perpendicular to the magnetic field. Most observations have been carried out in the auroral regions, where intense lower-hybrid emissions are frequently observed, possibly producing solitary structures(1) and ion heating(2-4). Lower-hybrid turbulence with a smaller intensity has also been observed at mid- and low latitudes above thunderstorms(5,6) and was shown to be triggered by the electromagnetic whistler wave generated by the lightning current. Here we present observations of equatorial plasma waves that demonstrate the existence of lower-hybrid solitary structures and the simultaneous occurrence of ion heating in deep, large-scale equatorial plasma depletions that form at night during disturbed geomagnetic conditions. These phenomena follow the development of lower-hybrid turbulence triggered by lightning-induced whistlers, revealing a new coupling process between the troposphere and the ionosphere. Since the energy source of the equatorial solitary structures is different from that involved in the auroral processes, our findings support the idea that the formation of lower-hybrid solitary structures may be a universal mechanism operating in inhomogeneous, magnetized plasma and possibly leading to ion heating and acceleration.