Vlasov Simulations of Ionospheric Turbulence near the Upper Hybrid Resonance and Fourth Gyroharmonic

Abstract:

High-frequency, ordinary (O) mode electromagnetic waves incident on a magnetized plasma near the upper hybrid resonance can excite magnetic field aligned density striations associated with both turbulence and electron heating. We have used Vlasov simulations, which combine low noise and high resolution of all areas of phase space, in one spatial and two velocity dimensions to study the induced turbulence in the presence of striations near the upper hybrid resonance, where the O-mode pump is mode converted to large amplitude upper hybrid oscillations trapped in a striation. We were able to correlate the evolution of stationary electron and ion oscillations with the onset of turbulence, and the heating of electrons in the striation with large amplitude, short wavelength electron Bernstein waves. These Bernstein waves excite stochastic electron heating when the normalized gradients of their electric field exceed the electron gyroradius, breaking the drift approximation, and causing particle orbits in phase space to diverge exponentially, rapidly increasing the electron temperature by several thousand Kelvin. Our most recent results include simulations where the frequency of the pump wave is close to the double resonance, both the upper hybrid and the fourth gyroharmonic. These results are relevant to ongoing high-latitude heating experiments and specifically, to the theory of the formation of descending artificial ionized layers.