“…The amplitude variations of low‐frequency radio transmissions are also used to monitor the electromagnetic wave propagation in the Earth‐ionosphere cavity (e.g., Inan et al, ; see also Barr et al, , and references therein). Such kind of measurements serve to remote sense the ionized state of the upper atmosphere, that is, the lower D ‐region ionosphere, (e.g., Ohya et al, ; see also Clilverd et al, ; Higginson‐Rollins & Cohen, ; Macotela et al, , and references therein), which responds to space weather, solar variability, and ionospheric modification by lightning discharges (e.g., Shao et al, ; see also Haldoupis et al, ; Kotovsky et al, ; Smith et al, ,, and references therein). The phase of radio transmissions is less often used to determine the ionisation of the lower ionosphere, even though it is an important observation to constrain and enhance the results obtained from amplitude measurements alone (e.g., Thomson et al, ; see also Thomson, ; Thomson et al, , , and references therein).…”