Gravity wave modulation of gradient drift instabilities in mid-latitude sporadic E irregularities

摘要: Recent E region VHF backscatter echoes observed by the MU radar at mid-latitudes show quasi-periodic striations with a fairly constant range vs. time tilt in RTI display. These features are explained terms of gravity waves frequencies close to Brunt-Vaisala frequency which modulate shape sporadic layers. The conditions instability, when magnetic field has significant dip angle, is revised. Differing from previous work, we argue that local gradient drift instability not sufficient and one consider integrated properties each filed tube. Stratified layers stable using this new criteria, unless they distorted produce unstable gradients. Gravity phase fronts parallel angle capable producing such distortion, imposing its own temporal spatial periodicity on echoes.