MIT Department of Electrical Engineering & Computer Science

SPECIAL SEMINAR

Wednesday, February 8, 1995
RLE Conference Room, 36-428

Refreshments at 1:45 PM
Talk at 2:00 PM

Probing the D-Region of the Lower Ionosphere Using Very Low Frequency Electromagnetic Waves

Dr. Juan Rodriguez
Phillips Laboratory, Hanscom AFB

The Earth's surface and the lowest region of the ionosphere, also known as the D-region (50-90 km altitude), form a concentric spherical waveguide that permits long distance propagation at very low frequencies (VLF, 3-30 kHz). The amplitudes and phases of VLF waves propagating in the Earth-ionosphere waveguide are sensitive to small fluctuations in the D region electron number density and temperature. This sensitivity permits continuous waves radiated by VLF transmitters to be used to probe the D region, which is typically too tenuous at night for standard ionospheric sounders or incoherent scatter radars to sense. This technique has been used successfully to investigate disturbances in the nighttime D region electron density and temperature caused by electromagnetic radiation from lightning discharges as well as by signals radiated continuously by VLF communications transmitters. Observations are interpreted using models of wave propagation and absorption in a magnetized, weakly ionized plasma.