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Y. Bouderba, S. Naitamor, O. Boumia
Research Center on Astronomy, Astrophysics and Geophysics. CRAAG (Algeria).
International School of Space Science, Frontiers of Space Science: from Solar activity to NEOs.L’Aquila , April 17-22, 2011
E-mail : [email protected]
19 Avril 2011
VLF signals perturbations due to solar flares
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Our vision
I will present in this talk: solar flares, the ionosphere and VLF
signals perturbations recorded till 2010.
Study the disturbances of the D layer of the ionosphere due to the
solar flares.
Understand the behavior of the VLF EM waves in response with
the solar eruptions.
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Solar flares
Northern lights (Norway).
Solar flar and earth size comparison
• Generate enormous flow of waves
emissions at high energies (UV, X-ray,…)
• Radiations from the solar flares affect the terrestrial radioelectric
transmissions, and causes appearance of the polar lights while
entering in interaction with the terrestrial magnetic field.http://img.fotocommunity.com/Landscape/Skies/Aurora-Borealis-over-Trondheim-Norway-a20791924.jpg
• Paramount events of the sun activity .
• Equivalent to gigantic nuclear explosions
which occur on the sun surface.
• Eject an ionized matter (plasma) in the space.
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A : I < 10-7
B : I < 10-6
C : 10-6 < = I < 10-5
M : 10-5 < = I < 10-4
X : I > = 10-4
Solar flare (NASA-2007)
Solar eruptions classes
• They are classified in five categories(A,
B, C, M, X) according to the maximum
intensity of their flow (in Watt/m2) in the
band of X-ray (1 to 8 A°).
• Each category corresponds to a solar eruption of an intensity 10 times more important than the preceding one.
• Each category is divided into 10 subcategories (for example: C1.0 to C1.9).
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The ionosphere
Various layers of the terrestrial atmosphere
It is well known that the solar activity causes disturbances on the earth atmosphere. As the ionosphere is one of the atmosphere layers, it was widely studied using different techniques and instrumentations
The part of the Earth lit by the Sun is then subjected to a bombardment of X-rays and UV radiations. These radiations penetrate to the D layer causing supplementary ionization.
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The ionosphere Layers
Simplified sight of ionosphere layers on 24 h
E layer: (90 to120 km).
We distinguish four principal layers:
D layer: (60 to 90 km)
F layer: (120 to 800 km).
• It disappears quickly after sun lying.
F layerBy night
Ionosphere
E Layer disappearsAlmost at night.
D layer disappears by night
• The lowest layer of the ionosphere.
During the day, F layer is decomposed into to sub-layers F1 and F2
• It is influenced by the solar flares.
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Study of VLF waves
Transmitter
ReceiverEarth
Ionosphere
D layer
Atmosphere
X-rays from solar flares
Wave propagation
The Very low frequencies (VLF) band are used by the naval transmission, and range
between 3 and 30 KHz (wavelength 100 to 10 km), these waves are very sensitive to
small changes in the D layer conductivity, and constitute a powerful tools to study
this low layer density.
VLF waves propagating
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Worldwide VLF receivers
In our case, we used the Very Low Frequencies (VLF) signals coming from naval
transmitters and received by the North African AWESOME network to study the
VLF signal perturbations due to the solar flares.
The VLF signals analysis was carried out during the quite period of the solar activity
i.e. from 2007 to 2010
Data from VLF AWESOME Network
Worldwide VLF Transmitters
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VLF signal without perturbation
During a quite day only the sunrise and sunset effects are observed .
Amp(dB)
Transmitter: GQD (Great Britain)
A typical graph of a quiet day resembles like this
sunrise
sunset
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2007/06/04 at : 05 :05 :00 (Class : M8.9)
Date tonst (min) trecovery (min) Amplitude(dB)
NS NSCNS NRK
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60100
77.5
VLF signal with perturbation
Amp(dB)
A typical graph of an active day with one event (M8.9) resembles like this
The rise of the signal power corresponds to a solar flare.
Transmitters: NSC(Italy), NAA(USA), NRK( Iceland)
M8.9
M8.9
Amp(dB)
Amp(dB)
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2007/07/10 at : 17:50 :00 (Class : C5.2)
Date tonst (min) trec(min) Amp(dB)
NS NAANS NRK
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4563
4.54.1
C1.2C1.4
C2.8
C7.4
VLF signals disturbances due to several solar flares which were happened in the same day
VLF signal with perturbations
Transmitters:NSC(Italy), NAA(USA), NRK( Iceland)
C5.2
C5.2Amp(dB)
Amp(dB)
Amp(dB)
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Example of three AWESOME receivers recorded for the same flare: M4.0
Some transmitters signals showed a decreasing in the amplitude followed by an increasing signal(NSC).
Other transmitters signals showed an increasing one( GQD).
The arrival time of the minimum signal amplitude varies from a receiver to another, so it appears first in Tunis receiver’s, then in Crete and finally in Algiers one.
Transmitters: NSC(Italy), GQD(Great Britain )
VLF signal with perturbation
Amp(dB)
Map of Some transmitters and receivers
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Seasonal dependence of VLF perturbations proprieties for the
same flare C2.3
In May (spring), the perturbation proprieties (amplitudes and duration times) are more important than in January (Winter).
Transmitters: DHO(Germany, GQD(Great Britain ), NSC(Italy), ICV(Italy).
Seasonal VLF signal effects
Amp(dB)
Amp(dB)
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Summary
And finally,following the variation of the D region parameters during the solar cycle by
using the LWPC code.
When a solar flare occurs, the VLF signal is disturbed, and this
perturbation is a function of the flare intensity and the season during
which the flare occurs. The seasonal dependence can be interpreted by the changes in the ionosphere
conductivity during the year.
The shape of the perturbation (increasing or decreasing in the signal amplitude) depends
on the wave modal structure near the receiver or near the transmitter.
It is interesting to continue to analyze more data to determine the lower limit of the flare
class that causes a measurable perturbation.
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