Controlled VLF wave injection experiments in the magnetosphere

Whistler-mode waves injected into the magnetosphere from ground sources (e.g., lightning discharge, vlf transmitters) are used to probe the distribution of ions and electrons in the magnetosphere. They also cause wave growth (vlf emissions) and precipitation of electrons. Bursts of X-rays (> 30 keV) and enhancements of D-region ionization are examples of precipitation effects caused by lightning-generated waves. Growing narrowband wave trains are triggered by manmade coherent waves. Growth rates of 100 dB s^-1 and total growths up to 30 dB have been measured using 5.5 kHz signals transmitted from Siple Station, Antarctica. Another source of coherent wave input to the magnetosphere are the harmonics from commercial power line systems. Power line harmonic radiation may suppress triggered emissions or change their frequency-time slope. Exponential growth of narrowband emissions is explained in terms of cyclotron resonance between the waves and trapped energetic electrons, with feedback included. Applications of wave injection experiments include: (1) study of emission mechanisms, (2) control of energetic particle precipitation, (3) diagnostics of cold and hot plasma, and (4) vlf communications.