[Amps] article in Nature, modified Aurora via HF tspa

[John T. M. Lyles]

There is an Interesting paper in Nature (#433, 
page 498-500, 3 Feb, 2005) in which high power HF 
radio transmissions from HAARP were used to cause 
visible changes in the aurora, where speckles 
appeared. They were using the full 960 kW beam, 
from 4 -6  MHz, with 7.5 seconds on and then 7.5 
second off time. Operating QRO. Look it up, its 
pretty neat. I have a text version I can forward 
upon request.
73
John
K5PRO
-----------------------------------------

Nature 433, 498 - 500 (03 February 2005); doi:10.1038/nature03243

Creation of visible artificial optical emissions 
in the aurora by high-power radio waves

TODD. R. PEDERSEN1 AND ELIZABETH A. GERKEN2

1 Space Vehicles Directorate, Air Force Research 
Laboratory, Hanscom Air Force Base, Massachusetts 
01731, USA

2 Department of Electrical and Computer 
Engineering, Cornell University, Ithaca, New York 
14853, USA



Correspondence and requests for materials should 
be addressed to T.R.P. 
(todd.pedersen at hanscom.af.mil).

Generation of artificial light in the sky by 
means of high-power radio waves interacting with 
the ionospheric plasma has been envisaged since 
the early days of radio exploration of the upper 
atmosphere, with proposed applications ranging 
from regional night-time street lighting to 
atmospheric measurements1. Weak optical emissions 
have been produced for decades in such 
ionospheric 'heating' experiments, where they 
serve as key indicators of electron acceleration, 
thermal heating, and other effects of 
incompletely understood waveñparticle 
interactions in the plasma under conditions 
difficult to replicate in the laboratory2. The 
extremely low intensities produced previously 
have, however, required sensitive instrumentation 
for detection, preventing applications beyond 
scientific research. Here we report observations 
of radio-induced optical emissions bright enough 
to be seen by the naked eye, and produced not in 
the quiet mid-latitude ionosphere, but in the 
midst of a pulsating natural aurora. This may 
open the door to visual applications of 
ionospheric heating technology or provide a way 
to probe the dynamics of the natural aurora and 
magnetosphere.



The most readily observed emissions produced in 
ionospheric heating are the 'forbidden' red and 
green lines from atomic oxygen at 630.0 and 557.7 
nm, both common components of the natural aurora 
and airglow3. In almost all past experiments, 
artificial emissions have been produced by the 
interaction of radio waves with the ionospheric F 
region, the long-lived primary ionospheric layer 
composed of atomic ions at an altitude of several 
hundred kilometres4. Only rarely have optical 
effects been reported from the ionospheric E 
region5, an ephemeral layer created from 
occasional meteoric ions or continuous solar 
illumination or auroral precipitation near an 
altitude of 100 km (ref. 4), where increased 
collisions with neutral molecules alter the 
behaviour of the plasma, and the proximity to the 
transmitter provides a large inverse-square 
increase in power density5. Emission intensities 
achieved previously have typically ranged up to 
several hundred Rayleighs (1 R = 106 photons cm-2 
s-1 integrated along a line of sight) for the 
more easily excited red line and tens of 
Rayleighs for the higher-energy green line. In 
all cases, intensities have remained far below 
the threshold for detection by the human eye, 
which is given as 20 kR at 630 nm (ref. 2) 
towards the red end of the visible wavelength 
range, and 1 kR for 558 nm (ref. 6) near the peak 
sensitivity of the eye.



We recently produced dramatically stronger 
artificial optical emissions bright enough to be 
visible to the naked eye in an experiment 
targeting the ionospheric E layer created by the 
natural aurora. The experiment was conducted on 
10 March 2004, between approx6ñ7 UT, using the 
960-kW transmitter array at the High Frequency 
Active Auroral Research Program (HAARP) facility 
near Gakona, Alaska (62.4ƒ N, 145.15ƒ W). The 
HAARP transmitter was run in a 15-s cycle 
alternating between 7.5 s of full power and 7.5 s 
off. Four filtered optical imaging systems 
ranging from all-sky to telescopic were operated 
in synchronization with the transmitter on and 
off intervals. Background conditions during the 
experiment period were characterized by aurora 
pulsating with apparent periods of approx10 s in 
longitudinal bands running in the magnetic 
eastñwest direction over most of the sky, 
including the region within the transmitter beam 
(Fig. 1). The auroral precipitation created a 
blanketing E layer near an altitude of 100 km 
with critical frequencies ranging from 4ñ6 MHz.



	Figure 1 A pair of all-sky images taken 5 
s apart showing the dynamic natural background 
aurora pulsating in long bands over most of the 
sky.   Full legend



High resolution image and legend (37k)



For a period of approximately 10 min between 
about 06:40 and 06:50, a number of small speckles 
of enhanced green emission were observed with the 
HAARP telescope wide-field camera, which provided 
high-resolution images of the region within the 
transmitter beam near magnetic zenith (Fig. 2). 
The speckles were present only during the image 
frames when the transmitter was on and were 
absent from exposures taken during the off 
periods. There is evidence of dynamic pulsations 
in the background aurora within this narrower 
field of view as well, such as the auroral bands 
that appear and disappear in the lower left 
corner of the images. The largest speckles are 
approximately one degree across.



	Figure 2 Images from the HAARP telescope 
wide field camera showing speckle-like artificial 
optical emissions superimposed on the background 
aurora only during frames when the transmitter 
was on.   Full legend



High resolution image and legend (48k)



Within a given frame the speckles appear to be 
randomly distributed, but upon closer examination 
of successive 'on' frames, some of the speckles 
often appear to be correlated with but displaced 
from those seen in the previous 'on' period. This 
suggests that some speckle features are in motion 
but may still retain coherence across multiple 
onñoff cycles of the transmitter.



Calibrated average intensities for the background 
aurora within the transmitter beam were obtained 
from another imager, which made measurements at 
several different wavelengths once each minute 
(Fig. 3). In spite of the rapid pulsations in 
narrow bands and on 10-s timescales, the average 
auroral brightness at 557.7 nm remained near 4 
kR, with an increase to approx5 kR near the time 
the speckles were observed. This intensity 
calibration, applied to the high-resolution data 
in Fig. 2, indicates that the brightest speckles 
were approximately 4 kR in total intensity, well 
above the threshold for visibility and 1 kR or 
more above the darker auroral regions.



	Figure 3 Calibrated measurements from the 
HAARP imager showing the intensities of various 
auroral emissions including the oxygen green 
line, which was well above the threshold for 
detection by the naked eye during the experiment. 
Full legend



High resolution image and legend (57k)



Given the unprecedented brightness of the 
speckles, we carried out a number of tests to 
rule out potential artefacts, including: 
repeating the transmission pattern at a different 
time to rule out radio-frequency (r.f.) 
interference with the camera electronics, 
verifying from radar records that no aircraft 
were in the area, and measuring the periods of 
white-light sources such as nearby communications 
towers and airport beacons. We attempted to 
reproduce the results whenever an aurora moved 
into range, but auroral events later in the 
experiment window never produced E layers of 
sufficient density to support significant 
transmissions at the original frequency again. 
More detailed analysis of the data revealed 
additional weak speckles earlier in the original 
6-UT hour, at about 06:20 UT, when the 
transmitter was operated at a lower frequency 
(and lower effective power), and some of the 
brightest speckles were also identified in data 
from one of the other lower-resolution camera 
systems operated from a separate building, 
eliminating any doubt that the speckles represent 
actual light from the sky.



Although visible levels of artificial optical 
emissions have not been reported previously, 
there have been other attempts made to stimulate 
the auroral E layer with radio waves. A similar 
experiment that used low-light television cameras 
and a 2-s onñoff cycle but different polarization 
reported an estimated modulation of less than 10 
R, interpreted as radio-induced decreases in the 
green line emission7. Large-scale structural 
changes in the overhead aurora have been reported 
in conjunction with E-layer heating8, but the 
extremely small number of cases and the close 
similarity of the observed effects to naturally 
occurring processes make it difficult to assess 
the true influence of the radio waves on the 
auroral events. In contrast, the recent HAARP 
observations demonstrate clear on-off control of 
the speckles over 50 or more complete cycles.



Potential sources of the observed bright speckles 
fall into two categories: production in the local 
E-region ionosphere by the transmitter beam, or 
indirect creation by modification of the auroral 
particle precipitation, which then produces the 
optical speckles in the same way as the 
background aurora. If the speckles are locally 
generated, the role of the natural aurora would 
probably be limited to creation of the E layer 
for the radio waves to interact with, and it 
might be possible to generate similar phenomena 
in non-auroral E layers independent of any 
specific on-off cycling, a potentially desirable 
condition for creation of visible artificial 
light. If, on the other hand, the speckles result 
from modification of the auroral particle 
population, perhaps through perturbations to 
currents flowing in the E layer or a wave 
resonance, we expect that the specific frequency 
of the onñoff cycling relative to the natural 
pulsation frequencies might be a critical 
parameter, and experiments of this type could 
potentially become a new tool for exploration of 
time-dependent processes in the aurora and 
magnetosphere.



Received 13 September 2004;accepted 6 December 2004

------------------



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Acknowledgements. HAARP is a Department of 
Defense programme operated jointly by the US Air 
Force and US Navy. We thank E. Mishin for his 
contributions to the experiment planning and P. 
Ning for operating the all-sky imager.



Competing interests statement. The authors 
declare that they have no competing financial 
interests.