Excitation of large-scale plasma sheets and micropulsations by injected high power radio waves

Abstract

We have conducted several experiments to investigate the simultaneous generation of large plasma sheets and micropulsations by injected high power radio waves via thermal filamentation instabilities [Cohen et al., Phys. Scrip., 2010]. These large plasma sheets generated by HF heater have different configurations, depending upon the polarizations (i.e., O- or X-mode) of the heater waves. It is expected that O-mode heater wave-created parallel-plate waveguides within the meridional plane, and those generated by the X-mode heater waves are orthogonal to the meridional plane. [Lee et al., Geophys. Res Lett., 1998]. One striking feature of thermal filamentation instabilities is the simultaneous excitation of sheet-like plasma density fluctuations (δn) and geomagnetic field fluctuations (δB). The physics can be simply understood as follows. The differential joule heating, resulting from the interactions of HF heater waves and excited high frequency sidebands, yields a thermal pressure force on electrons. Thermal pressure force (denoted by f T ) leads to a f T × B 0 drift motion of electrons and, consequently, induces a net current perpendicular to both the background magnetic field B0 and the wave vector k of the excited plasma density irregularities. Therefore, magnetic field fluctuations (δB) associated with micropulsations are excited along the background magnetic field (B 0 designated as the z-axis) simultaneously with the density irregularities in both O- and X-mode heating processes. The excited magnetic field fluctuations (δB) have three components designated as dδB D , dδB H , and dδB Z . Based on above explanation of the simultaneous excitations of dδn and dδB, we can expect that dδB D and dδB Z (or dδB H and dδB Z ) will be highly correlated in O-mode (or X-mode) heating experiments. Our theoretical predictions are confirmed by GPS satellite measurements, range-time-intensity (RTI) plots of UHF and HF backscatter radars, ionosonde data, as well as magnetometer data analyses. As these plasma sheets experienced E·B drifts, they were intercepted by the HAARP UHF radar and seen as slanted stripes in the RTI plots, as also seen in our earlier Arecibo experiments. Furthermore, based on the GPS satellite measurements, we infer that kilometer-scale plasma sheets can be generated by vertically injected O-mode heater waves.