The thermal filamentation instability of whistlers that can excite magnetostatic and plasma density fluctuations simultaneously has been investigated for cases in the magnetosphere and in the ionosphere. With the available facilities at Siple. Antarctica, this instability may be excited in the magnetosphere at L=4 within a few minutes by ducted whistler modes whose frequencies are greater than half the local electron cyclotron frequency. No significant ionospheric effects are expected to be produced by the injected Siple VLF waves. However, marked ionospheric perturbations are predicted with employment of envisioned MF transmitters at frequencies slightly less than the electron cyclotron frequency in the ionosphere.