Transcript Реферат (новембар 2000. године)

ADVANCING VLF SCIENCE THROUGH
THE GLOBAL AWESOME NETWORK
30-May to 01- Jun 2009, Tunis, Tunisia
VLF measurements of lightning induced
electron precipitations and their effects
on the D-region electron density profile
D. Šulić1, and V. Srećković1
1 Institute of Physics, University of Belgrade, Serbia
Space weather
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.
Introduction

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 transmission amplitude and/or phase, followed by a relatively
slow recovery (<100 s) to the original unperturbed
signal.
Ionosphere
The 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
Propagation of VLF waves
Ionosphere
-96
-98
-100
-102
60
80
100
120
70
68
66
60
Ionosphere
70
80
90
100
110
120
Precipitating electrons
-96
-98
-100
-102
40
60
80
70
68
66
40
50
60
70
80
Belgrade station
Belgrade
AbsPAL (Absolute Phase & Amplitude Logger) receiver was
installed at the Institute of Physics, University of Belgrade,
in August 2003.
Phase (deg)
Belgrade station May 21, 2008
-10
Amp (dB) Phase (deg) Amp (dB) Phase (deg) Amp (dB)

(44.85N 20.38E)
65
-20
-30
64
NAA/24.0 kHz
63
-70
-80
74
73
GQD/22.kHz
72
-54
-57
-60
85
84
83
82
00 02 0
DHO/23.4 kHz
20
40
60
Time (s)
80
100
120
Belgrade station
AWESOME STATION was installed at the
Institute of Physics, Belgrade in June 2008.
List of recorded VLF signals
SING
FREQ.
LOC.
GQD
22.10 kHz UK
NAA
24.00 kHz USA
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 events
 Most of recorded LEP events occurred
during local summer and autumn, very rare
during winter and spring
 Large number of LEP events were detected
on signal GQD/22.1 kHz – Belgrade
 Amplitude changed: DA= < 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 b in
km-1 and reflection height h’ in km, along segments of
GCP.

The aim is to obtain calculated values:
DAcal = Anonpert - Apert and Df =fnonpert - fpert
to be equal or very close with recorded values: DArec
and Dfrec

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 wr which is:
wr = wo2/n = 2.5 x105 s-1,
wo the plasma frequency of the electrons, and n the electronneutral 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:
n  h  = 1.86 1011 exp(0.15h) s-1 
Ambient ionospheric condition

The unperturbed electron density profile given
by:
NWait (h, h ', b ) = 78.57 n  h   exp( b (h  h ')) m-3 
where the pair of Wait's parameters are: sharpness b in
km-1, reflection height h’ in km. The height above the
Earth’s surface is h in km .

Under nighttime conditions, the typical ranges
for b and h’ are 0.40 to 0.50 km-1 and 80 to 90
km, respectively.
SOLAR FLARE
The intense radiation from a solar
flare travels to Earth in eight minutes.
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
NAA/24.0 kHz
72
66
60
54
48
42
36
1440
2880
4320
5760
1440
2880
4320
5760
GQD/22.1 kHz
75
70
65
60
55
Sep 06, 12:00 UT
Sep 10, 12:00 UT
•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
7
6.0x10
7
5.5x10
Sep 08 2005
7
Sep 08 2005
5.0x10
Electron density
Belgrade station
80
7580
7075
6570
6065
60
DPhase
7
4.5x10
7
4.0x10
)
(deg
66
0
5
Longitu
DA
15
)
20
NAA/24.0 kHz
36
6x10
7
34
7
DA
7
3x10
0
60
120
180
240
300
360
Time from 03:36:20 to 03:37:00
Time from 03:33:00 to 03:38:00
420
7
2x10
7
7
1x10 -5
56
54
52
50
48
46
44
g)
4x10
( de
5x10
tude
32
74.2
74.2
74.0
74.0
73.8
73.8
73.6
73.6
73.4
73.4
73.2
73.2
0
5
10
Longitu
de (deg
)
15
20
Lati
32
10
de (deg
38
3)
electron density (m
NAA/22.1 kHz
NAA/22.1 kHz
34
tu d e
7
3.0x10 -5
66
64
4064
3840
36
56
54
52
50
48
46
44
7
3.5x10
Lati
NAA/24.0 kHz
NAA/24.0 kHz
Belgrade station
Location of electron density enhancement
Belgrade station Sep 08, 2005
110
100
GQD/22.1 kHz
90
70
80
70
60
60
0
500
1000
1500
2000
50
Distance over the GCP path (km)
Belgrade station NAA/24.0 kHz
120
40
Amplitude (db)
110
100
standard value for Sep.
after flare
LEP
90
80
70
60
0
1000
2000
3000
4000
5000
Distance along path over great circle
6000
30
-20
0
20
40
CORONAL MASS
EJECTION
One of the most important solar
events from Earth's perspective
is the coronal mass ejection, the
solar equivalent of a hurricane.
A CME is an eruption of a huge bubble of energized plasma
from the Sun's outer atmosphere, or corona
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.
December 04/05 2004
70
60
50
Bel
40
30
20
ICV/20.27 kHz
Phase (deg)
112
110
108
106
104
30
40
50
60
75
74
73
21:59:
30
40
Time (UT)
50
60
40
18
-28
-30
-32
16
GQD/22.1 kHz
Dec 04 2994
114
0
72.0
71.7
-45
-50
-55
57.5
57.0
56.5
100
80
60
14
12
10
71.8
71.6
71.4
71.2
71.0
NAA/24.0 kHz
-20
HWU/18.3 kHz NAA/24.0 kHzGQD/22.1 kHz
-40
ICV/20.27 kHz
-60
Amplitude (dB)
-80
•In the night Dec 04/05 (from 17 U
to 06 UT) more than 300 LEP even
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
71.5
71.0
10
0
-10
-20
68
-10
-12
-14
-16
-18
62.0
61.6
61.2
66
0
20
40
60
80
2:26:00.00 5/12/04
100
120
0 10 20 30 40 50 60 70 80 90 100 110 120
5:37:00.00 5/12/04
HWU/18.3 kHz NAA/24.0 kHzGQD/22.1 kHz
-28
-30
-32
72.0
71.7
-45
-50
-55
57.5
57.0
56.5
100
80
60
71.5
ICV/20.27 kHz
71.0
10
0
-10
-20
68
-26
-28
-30
-32
Path
(km)
DA
(dB)
DF
(deg)
D
(km)
DNmax
GQD/22.1kHz
1983
-0.39
8.54
740
1.22E7
NAA/ 24.0 kHz
6548
-0.566
11
940
0.8E7
HWU/18.3 kHz
1493
-0.343
8
860
1.03E7
ICV/20.27 kHz
970
-0.74
-4
460
0.51E7
Transmitter
72.0
71.7
-45
-50
-55
57.5
57.0
56.5
100
80
60
71.5
71.0
10
0
-10
-20
68
66
40
66
50
60
2:26:00.00 5/12/04
60
80
100
120
2:26:00.00 5/12/04
Dec 05 2004 HWU/18.3 kHz
Dec 05 2004 ICV/20.27 kHz
3.7E7
Dec 05 2004
Dec 05 2004 NAA/24.0 kHz
4.4E7
4.2E7
4E7
4.2E7
4E7
R
de
10
(de
46
44
15
g)
20
42
40
it
Lat
ude
3.2E7
50
48
-5
g)
(de
0
5
10
Longitu
de (deg
)
R
15
20
54
52
3.2E7
50
48
46
44
-5
0
5
10
longitu
de (deg
)
R
15
20
54
52
50
48
46
tude
itu
T
5
3.4E7
44
Lati
ng
0
3.6E7
(deg
)
3.1E7
-5
3.4E7
tude
3.2E7
T
3.6E7
Lati
3.6E7
3.3E7
4E7
3.8E7
-3
(m )
Electron density
(m-3 )
3.8E7
-3
(deg Electron density (m )
)
3.8E7
3.5E7
Electron density
(m-3 )
Electron density
3.6E7
3.4E7
GQD/22.1 kHz
T
3.4E7
3.2E7
3E7-5
54
52
50
48
46
)
40
(deg
20
0
R
5
10
Longitu
de (deg
15
)
20
tude
0
Lo
-3
(m )
44
Lati
ICV/20.27 kHz
HWU/18.3 kHz NAA/24.0 kHzGQD/22.1 kHz
Calculated electron density
Location of electron enhancement
70
December 05 2004
4.4E7
60
(m-3 )
4.2E7
3.8E7
Electron density
50
4E7
3.6E7
3.2E7
30
-20
-10
0
10
20
30
40
0
5
10
Long
itude
(deg
)
Ax
is
3E7-5
56
54
52
50
48
46
44
42
40
15
Y
40
3.4E7
20
LEP events observed simultaneously on the four VLF paths
ware the pointer to the geographical location of the region of
enhancement density, over Europe.
Solar eclipse on October 03, 2005
GQD/22,1 kHz
Phase (deg)
-100
-120
Amplitude [dB]
5:18:00.00
10:18:00.00
15:18:00.00
64
09:09:00 UT
62
60
5:18:00.00
10:18:00.00
Oct. 03 2005
15:18:00.00
We would like ….
Summary
1. 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.