SA43A-1885
Extended heating of the nighttime D region by very low frequency transmitters: Subionospheric observations & modeling
Kevin L. Graf1, Maria Spasojevic1, Umran S. Inan2,1, Robert A. Marshall1, Forrest Foust1, Nikolai G. Lehtinen1
1. Electrical Engineering, Stanford University, Stanford, CA, USA, 2. Koc University, Istanbul, Turkey
Very low frequency (VLF, 3-30 kHz) signals propagating in the
Earth-ionosphere waveguide are used to probe the heated nighttime D
region over three keyed U.S. Navy VLF transmitters. The keyed VLF
transmitters are turned on-off in periodic formats for thirty to sixty
minutes each day over the course of several months each, providing
sensitive measurements of their heating effect on the surrounding
ionosphere. On several occasions, the heating effect is observed on
probe signal pathways at distances greater than 1500 km from the keyed
transmitter. It is proposed that the heating effect of VLF transmitters
extends over very large distances through the subionospheric propagation
of its radiated signal. General statistics are presented on the
observed extent of the heating region over the course of the
experiments, and a combination of propagation, heating, and scattering
models are used to analyze the results.