Controlled study of acoustic gravity waves (AGW) generated by anomalous heat sources

Abstract

We investigate high power radio wave-induced acoustic gravity waves (AGWs) at Gakona, Alaska, using High-frequency Active Aurora Research Program (HAARP) heating facility (i.e., HF heater) and extensive diagnostic instruments. This work is aimed at controlled study of space plasma turbulence, triggered by acoustic gravity waves originating from anomalous heat sources, as observed in our earlier experiments at Arecibo, Puerto Rico [R. Pradipta, MS Thesis, MIT, 2007]. HF heater operated in CW O-mode can heat ionospheric plasmas effectively to yield depleted magnetic flux tube as rising plasma bubbles [Lee et al., Geophys. Res. Lett., 1998]. Two processes responsible for the depletion of magnetic flux tube are (1) thermal expansion and (2) chemical reactions caused by heated ions. The depleted plasmas create large density gradients that can augment spread F processes via generalized Rayleigh-Taylor instabilities [Lee et al., Geophys. Res. Lett., 1999]. It is thus expected that the temperature of neutral particles in the heated ionospheric region can be increased. Such heat source in the neutral atmosphere may potentially generate acoustic gravity waves (AGWs) in the form of traveling ionospheric plasma disturbances (TIPDs). We should point out that these TIPDs have features distinctively different from ExB drifts of HF wave-induced large-scale non-propagating plasma structures. Moreover, it is noted in our recent study of naturally-occurring AGW-induced TIDs that only large-scale AGWs can propagate upward to reach higher altitudes. Thus, in our Gakona experiments we select optimum heating schemes for HF wave-induced AGWs that can be distinguished from the naturally occurring ones. The generation and propagation of AGWs are monitored by Modular UHF Ionospheric Radar (MUIR), digisonde, and GPS/LEO satellites.