VLF measurements of lightning induced VLF measurements of lightning induced electron precipitations and their effects electron precipitations and their effects on the D on the D - - region electron density profile region electron density profile D. D. Š Š uli uli ć ć 1 , and V. , and V. Srećković 1 1 Institute of Physics, University of Belgrade, Serbia ADVANCING VLF SCIENCE THROUGH THE GLOBAL AWESOME NETWORK 30-May to 01- Jun 2009, Tunis, Tunisia
Transcript
VLF measurements of lightning induced VLF measurements of lightning induced electron precipitations and their effects electron precipitations and their effects on the Don the D--region electron density profileregion electron density profile
D. D. ŠŠuliulićć1, and V. , and V. Srećković1
1 Institute of Physics, University of Belgrade, Serbia
ADVANCING VLF SCIENCE THROUGH THE GLOBAL AWESOME NETWORK 30-May to 01- Jun 2009, Tunis, Tunisia
The response of our space environment to the constantly changing Sun is known as space weather.
When the space environment is disturbed by the variable outputs of the Sun, technologies that we depend on, both in orbit and on the ground can be affected.
Some of the most dramatic space weather effects occur in association with eruptions of material from the solar atmosphere into interplanetary space.
Space weather
Over the last several decades, the monitoring of VLF transmitters has been used to study remote and transient perturbations of the lower ionosphere associated with lightning discharges.
Indeed, these phenomena generate typical amplitude and phase variations of the subionospheric signals, known as the LEP effect.
The perturbation begins by a rapid change in the trans-mission amplitude and/or phase, followed by a relatively slow recovery (<100 s) to the original unperturbed signal.
Introduction
IonosphereIonosphereThe ionosphere is the region extending from about 60 km to several hundreds km, where the motion of free electrons have strong effects on medium and high-frequency radiowave propagation
Ionosphere
60 70 80 90 100 110 12066
68
70
60 80 100 120
-102
-100
-98
-96
40 50 60 70 8066
68
70
40 60 80
-102
-100
-98
-96
Ionosphere Precipitating electrons
Propagation of VLF waves
Belgrade station
AbsPAL (Absolute Phase & Amplitude Logger) receiver was installed at the Institute of Physics, University of Belgrade, in August 2003.
Belgrade (44.85N 20.38E)
0 20 40 60 80 100 12082838485
GQD/22.kHz
Time (s)
Am
p (d
B)
DHO/23.4 kHz
-60-57-54
Phas
e (d
eg)
72
73
74
Am
p (d
B)
-80
-70Ph
ase
(deg
)Ph
ase
(deg
)
636465
NAA/24.0 kHzAm
p (d
B)
Belgrade station May 21, 2008
-30
-20
-10
00 02
Belgrade stationBelgrade station
AWESOME STATION was installed at the Institute of Physics, Belgrade in June 2008.
List of recorded VLF signals
SING FREQ. LOC.
GQDGQD 22.10 kHz22.10 kHz UKUK
NAANAA 24.00 kHz24.00 kHz USAUSA
DHO 23.40 kHz Germany
HWV 20.90 kHz France
ICV 20.27 kHz Italy
NWC 19.80 kHz Australia
Statistical results
During period from 2004 to May 2009 were recorded ~ 5300 of LEP eventsMost of recorded LEP events occurred during local summer and autumn, very rare during winter and springLarge number of LEP events were detected on signal GQD/22.1 kHz – BelgradeAmplitude changed: ΔΑ= < 1(dB)Phase changed: few degrees
Method of numerical modeling
This work is concerned with the numerical simulations of VLF perturbations. The method is based on changing the pair of Wait’s parameter: sharpness β in km-1 and reflection height h’ in km, along segments of GCP.
The aim is to obtain calculated values: ΔAcal = Anonpert - Apert and Δφ =φnonpert - φpert
to be equal or very close with recorded values: ΔArecand Δφrec
The RANGE EXPONENTIAL model (LWPCv21 program) is used to examine a single propagation path. In this model a user specifies a range-dependent ionospheric variation.
Ambient ionospheric condition
Wait and Spies (1964) defined a convenient quantity to describe the characteristics of the lower ionosphere as the conductivity parameter ωρ which is:
ωρ = ωο2/ν = 2.5 x105 s-1,
ωο the plasma frequency of the electrons, and n the electron-neutral collision frequency.
The ionospheric electron density and collision frequency profiles are given by a standard nighttime ionospheric model.
The collision frequency profile is given by:
( ) 11 -11.86 10 exp( 0.15 ) sh hν ⎡ ⎤= ⋅ − ⎣ ⎦
Ambient ionospheric conditionThe unperturbed electron density profile given by:
Under nighttime conditions, the typical ranges for β and h’ are 0.40 to 0.50 km-1 and 80 to 90 km, respectively.
( ) -3( , ', ) 78.57 exp( ( ')) mWaitN h h h h hβ ν β ⎡ ⎤= ⋅ ⋅ − ⎣ ⎦
where the pair of Wait's parameters are: sharpness β in km-1, reflection height h’ in km. The height above the Earth’s surface is h in km .
The intense radiation from a solar flare travels to Earth in eight minutes.
SOLAR FLARE
The Earth’s upper atmosphere becomes more ionized and expands.
Long distance radio signals can be disrupted by the resulting change in the Earth’s ionosphere.
A satellite’s orbit around the Earth can be disturbed from the expand atmosphere.
Satellites electronic components can be damaged.
Sunspot 798 in September 2005
Hyperactive sunspot 798 unleashed nine X-class solar flares including a colossal X17-flare (Sept. 07, 2005)
This colossal spot made September 2005 the most active month on the Sun in almost 15 years.
06 – 10 September 2005
•In the period 06 – 10 Sep 2005 more than 50 LEP events were recorded each night.
•Most of them were recorded on signals: GQD/22.10 kHz and NAA/24.0kHz.
Calculated electron density on height of reflection over path
-5 0 5 10 15 20
1x107
2x107
3x107
4x107
5x107
6x107
44464850525456
elec
tron
dens
ity (m
3 )
Latit
ude
(deg
)
Longitude (deg)
NAA/24.0 kHz
Location of electron density enhancement
-20 0 20 4030
40
50
60
70
0 500 1000 1500 200060
70
80
90
100
110
Distance over the GCP path (km)
GQD/22.1 kHz
Belgrade station Sep 08, 2005
0 1000 2000 3000 4000 5000 6000
60
70
80
90
100
110
120
Am
plitu
de (d
b)
Distance along path over great circle
standard value for Sep. after flare LEP
Belgrade station NAA/24.0 kHz
One of the most important solar One of the most important solar events from Earth's perspective events from Earth's perspective is the coronal mass ejection, the is the coronal mass ejection, the solar equivalent of a hurricanesolar equivalent of a hurricane.
CORONAL MASS EJECTION
Having escaped the Sun's gravity, a CME speeds across the gulf of space at velocities of some 400 km/s. They reach the Earth in 2.5 to 5 days.
A CME is an eruption of a huge bubble of energized plasma from the Sun's outer atmosphere, or corona
Bel
December 04/05 2004
0 20 40 60 80 100 120
6668
2:26:00.00 5/12/04
ICV
/20.
27 k
Hz
-20-10010
71.0
71.5
HW
U/1
8.3
kHz
6080
10056.557.057.5
NA
A/2
4.0
kHz
-55-50-45
71.772.0
GQ
D/2
2.1
kHz
-32-30-28
0 10 20 30 40 50 60 70 80 90 100 110 120
61.2
61.6
62.0
5:37:00.00 5/12/04N
AA
/24.
0 kH
z
-18-16-14-12-10
71.071.271.471.671.8
GQ
D/2
2.1
kHz
1012141618
•In the night Dec 04/05 (from 17 Uto 06 UT) more than 300 LEP events were recorded.•Most of them on signals: GQD/22.10 kHz and ICV/20.27kH• Sporadically during that night LEPs were recorded on four signals-80 -60 -40 -20 0 20 40
LEP events observed simultaneously on the four VLF paths ware the pointer to the geographical location of the region of enhancement density, over Europe.
-5 0 510
1520
3E7
3.2E7
3.4E7
3.6E7
3.8E7
4E7
4.2E7
4.4E7
4042
4446
4850525456Elec
tron
dens
ity (m
-3)
Y Axis
Longitude (deg)
December 05 2004
Location of electron enhancement
Solar eclipse on October 03, 2005
5:18:00.00 10:18:00.00 15:18:00.0060
62
64A
mpl
itude
[dB
]
Oct. 03 2005
09:09:00 UT
5:18:00.00 10:18:00.00 15:18:00.00
-120
-100
Phas
e (d
eg)
GQD/22,1 kHz
We would like ….
Summary1. The use of VLF transmissions propagating inside the waveguide
Earth – ionosphere is well developed technique for probing conditions inside the ionospheric D-region.
2. For daytime propagation conditions, the D-region is particularly stable, with reflections heights occurring at about 70-75 km.
3. Additional perturbations are driven by solar flares and total solar eclipses. Variations in the D-region lead to changes in the propagation conditions for VLF waves inside the waveguide.
4. LEP events observed simultaneously on the several VLF paths can be used as the pointer to the geographical location of the region of enhancement density, over Europe
5. Recorded data at the Belgrade station are used to study global and local conditions in the D-region in order to make relevant models.
