Generation of Artificial Acoustic-Gravity Waves and Traveling Ionospheric Disturbances in HF Heating Experiments

We report the results of our ionospheric HF heating experiments to generate artificial acoustic-gravitywaves (AGW) and traveling ionospheric disturbances (TID),whichwere conducted at theHigh-frequencyActiveAuroral Research Program facility inGakona, Alaska. Based on the data from UHF radar, GPS total electron content, and ionosonde measurements, we found that artificialAGW/TID can be generated in ionosphericmodification experiments by sinusoidally modulating the power envelope of the transmitted O-mode HF heater waves. In this case, the modulation frequency needs to be set below the characteristic Brunt–Vaisala frequency at the relevant altitudes. We avoided potential contamination from naturallyoccurring AGW/TID of auroral origin by conducting the experiments during geomagnetically quiet time period. We determine that these artificial AGW/TID propagate away from the edge of the heated region with a horizontal speed of approximately 160 m/s.