LONG-DISTANCE DETECTION OF ELF MODULATED BY HAARP
- LONG-DISTANCE DETECTION OF ELF WAVES GENERATED
VIA MODULATED HF HEATING OF THE AURORAL ELECTRO-JET
The High-frequency Active Auroral Research Program (HAARP) HF
transmitter in Gakona, Alaska robustly generates electromagnetic
ELF/VLF signals via modulated heating of the lower ionosphere.
ELF/VLF signals produced in this manner propagate to large distances
in the Earth-ionosphere waveguide with relatively low attenuation.
Between 0800 and 1200 UT on February 11, 2005, the HAARP HF
transmitter modulated the auroral electrojet currents, generating ELF
waves alternately at 575 and 2125 Hz, each for 60 minutes at a time.
Each of the ELF signals produced were detected at an ELF/VLF receiver
35 km from the HAARP facility. The ELF/VLF receiver at Midway Atoll,
located in the middle of the Pacific Ocean at a distance of 4500 km
from the HAARP facility, detected the 2125 Hz transmission between
1100 and 1200 UT.
This 4500 km ground distance separation between the ELF signal source
and the receiver constitutes the largest distance at which HAARP-
generated ELF/VLF waves have been detected to date. In this paper, we
quantitatively assess the characteristics of the ELF/VLF source
region using an Earth-ionosphere waveguide propagation model with
realistic electromagnetic parameters together with the observed
properties of the ELF signals detected both in the near field and in
the far field.
Near field measurements are used to calculate the relative excitation
magnitudes and phases of a set of effective Hall and Pedersen
dipoles, the radiation from which is shown to be consistent with far
field observations for radiated power levels on the order of several
tens of Watts.
In addition, our results suggest that a single dipole located between
60 and 85 km altitude cannot accurately model the polarization
ellipse observed in the far field at Midway Atoll, despite the 4500
km distance between the signal source and the receiver. This
observation underscores the importance of the Earth-ionosphere
waveguide mode-excitation process as it relates to a distributed body
of radiating currents such as that present above the HAARP HF heater