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.