Revisiting the 150 km irregularities: An opportunity for studying weakly ionized plasmas and electromagnetic waves

Equatorial ionospheric radars can observe strong coherent structures at around 150 km altitude with a finite number of layers and gaps vertically organized. Even though the physical mechanism that produces them is still not fully understood, mounting evidence suggests that the gaps occur at heights where the local upper hybrid frequency is a multiple of the gyrofrequency. Recent high-resolution experiments show oscillations with periods ranging from tens of minutes to seconds. In other words, this radar experiment measures weakly ionized plasmas interacting with neutral gravity waves and electromagnetic Alfven waves. In this work, we will describe this radar experiment and present the various waves that have been identified. Moreover, we will show dispersion relations adapted for plasmas from the ionosphere's bottom side and how consistent these are with the spectral analysis of the measurements.