The Turbulence Properties of 150-km Echoes in the Lower Ionosphere

The valley region ionosphere spans from approximately 120–200 km in altitude, and hosts a wide range of plasma, neutral, and solar interactions that create and maintain the ionosphere. In this region a ubiquitous and mysterious source of radar echoes called “150-km echoes” has been observed since the 1960s. Recent work has shown these echoes are the result of solar EUV lines creating a bump-on-tail photoelectron distribution, which is unstable to upper hybrid waves. These electron-scale waves couple to ion-acoustic waves through a kinetic turbulence process, which we examine in this work. Range-time-intensity (RTI) plots of 150-km echoes are calculated using a kinetic turbulence theory, producing results that qualitatively match radar observations. Calculation of the echo intensity for different radar frequencies shows that the turbulence has a power-law description for large wavelengths (lower radar frequencies), but the enhancements at smaller wavelengths (sub-meter) are less predictable but observable.