DEMETER satellite observations of man-made and natural processes in the auroral ionosphere over
the HAARP HF heater
D. Piddyachiy1, U. S. Inan1, T. F. Bell1, M. Parrot2 and J.-J. Berthelier3
1
STAR Laboratory, Stanford University, Stanford, California, USA
Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, CNRS, Orléans, France
3
Laboratoire Atmosphères, Milieux, Observations Spatiales, IPSL, CNRS, Saint-Maur, France
2
Recently there have been several attempts to demonstrate the modification of ionospheric plasma densities
by powerful High Frequency (HF) heaters situated in high-latitude regions [Milikh et al., 2008; Wong et al.,
2009]. Such facilities illuminate the ionosphere with a powerful HF beam (in case of HAARP: fcarrier is from
2.7 to 10 MHz, continuous power is 3.6 MW) and can generally modify various ionospheric parameters. The
detection of density modifications is a complicated problem at high latitudes because the ionosphere there is
directly affected by the solar wind and energetic particles from the magnetosphere. As a consequence, the
ionospheric parameters are more variable than at lower latitudes [Hunsucker, 2003]. One important feature
of the ionosphere above the HAARP HF heater which can introduce significant variability is the main
ionospheric trough [Hunsucker, 2003].
An important ability of HAARP HF heater is to generate Extremely and Very Low Frequency (ELF/VLF)
waves via modulation of the natural auroral electrojet current. These waves are used for the study of waveparticle interaction in the Earth’s magnetosphere.
The DEMETER satellite is suitable for observations of both ELF waves injected in space with an HF heater
and ionospheric parameters above a heater that exist naturally and can be modified by heater operation.
DEMETER is a low-earth orbit satellite (altitude of 660 km, horizontal velocity of 7.6 km/s) capable of
simultaneous measurements of electron and ion densities, electron and ion temperatures, and electromagnetic
emissions in ULF, ELF, VLF and HF bands from 0 to 3.3 MHz.
In this work we present
DEMETER observations of the
ionospheric trough consisting of
more than 100 analyzed passes
over HAARP, when the HF
transmitter was in both the
transmitting
and
nontransmitting
modes.
These
observations show that the
ionospheric trough is often
observed near HAARP and
constitutes
the
dominant
component of density variations
in this region. Figure 1 shows
DEMETER observations of the
HAARP HF signal at 3.3 MHz
(top
spectrogram).
The
ionospheric trough in electron
and ion densities was also
recorded at the same region by
DEMETER. This case initially
triggered the discussion that
such density depletions might be
Figure 1. Recordings of DEMETER satellite over operating HAARP HF heater. created by HAARP HF heating,
but further investigations showed
that such depletions occur also in the HAARP region when the transmitter is non-operating. The position and
behavior of such depletion suggest that it is indeed the trough. Figure 2 shows DEMETER observations of
similar density depletions over HAARP when the HF heater is not operating.
Another important phenomenon
observed in the region above
HAARP is the presence of
Broadband Electrostatic Noise
(BEN). BEN often disrupts
satellite observations of ELF
waves and therefore should be
taken into account during the
analysis of ELF waves produced
by active experiments. It was
revealed that the occurrence of
BEN correlates well with density
irregularities
inside
the
ionospheric trough. In most
cases the particle density is
irregular within the trough
region and in those cases BEN is
recorded by DEMETER VLF
receiver in the frequency range
up to about 1 kHz, as is shown in
Figure 1 and 2. It is supposed
that density irregularities are the
main factor of BEN occurrence
in satellite measurements not
Figure 2. Recordings of DEMETER satellite over non-operating HAARP.
only in high latitudes but also in
other regions. To prove this fact
DEMETER observations over the NPM VLF transmitter (f = 21.4 kHz, L = 1.2) are also presented. Bell et
al., 2008 showed that the bandwidth of VLF signal increases when satellite passes through regions with
density fluctuations. In this work we demonstrate the occurrence of BEN in the same regions where density
fluctuations and VLF bandwidth increase are observed.
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