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Operational and Scientific Results Obtained from AWESOME Receivers in India: Setup under IHY/UNBSSI Program. Rajesh Singh , B. Veenadhari, A.K. Maurya, P. Vohat Indian Institute of Geomagnetism New Panvel, Navi Mumbai - India. P. Pant: ARIES, Manora Peak, Nainital – India - PowerPoint PPT Presentation
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Operational and Scientific Results Obtained from AWESOME Receivers in India: Setup
under IHY/UNBSSI Program
Rajesh Singh, B. Veenadhari, A.K. Maurya, P. VohatIndian Institute of GeomagnetismNew Panvel, Navi Mumbai - India
M.B. Cohen, U. S. Inan Stanford University, CA, U.S.A.
P. Pant: ARIES, Manora Peak, Nainital – IndiaA.K. Singh: Physics Department, B.H.U. , Varanasi – India
Outline
A.Installation/operation/science objective of AWESOME receivers in India
B.Scientific results from the AWESOME data collected in India
- 12 May 2008 China Earthquake- 22 July 2009 Total Solar Eclipse
IHY 2007/UNBSSI program
VaranasiLat. 15.41N Long. 156.37E
October, 2007
AllahabadLat.16.49N Long.155.34E
March, 2007
NainitalLat.20.48N Long.153.34E
May, 2007
Stanford University
Location of Indian VLF sites
Experimental Setup
Crossed loop antenna – 10 x 10 meter Frequency response–300Hz to 47.5kHz Sampling – 100 kHz 10-microsecond time resolution
VLF Receiverinstalled
AWESOME VLF Receiver – Stanford University
Capable ofcollecting
Narrowband +
Broadband VLF data
Amplitude and Phase of Transmitter signal
Saves entire VLF signal spectrum
VTX
NWC
JJI3SA
ICVHWU
FTA2
DHQGBR
Allahabad
Nainital
VNS
Lightning discharges Whistlers ELF/VLF emissions Lightning induced electron precipitation (LEP)
Sprites, Elves, Blue jets, etc Solar flares Geomagnetic storms Earthquake precursors etc.
Importance of VLF sites
Allahabd (16.490 N) – multi parameter observatory
Digital flux gate magnetometer
Digital CADI Ionosonde
Air glow optical experiments
VHF Scintillation receivers, TEC measurements
Search coil magnetometer for ULF observations
Nainital (20.290 N) : A high altitude Solar observatory also with lower Atmospheric observations
Varanasi (14.910 N) : The most active group in VLF research in India and very good VLF events were observed in past.
- Also, Scintillation and TEC measurement experiments.
VTX
NWC
JJI3SA
ICVHWU
FTA2
DHQGBR
Allahabad
Nainital
VNS
Monitor natural and sub-ionospheric VLF signals continuously with AWESOME receivers.
Port Blair, Andaman Islands
Multi Parameter Observatory
Essential for EQ studies
Outline of talk
A.Installation and operation of AWESOME receivers in India
B.Scientific results from the AWESOME collected data
- 12 May 2008 China Earthquake- 22 July 2009 Total Solar Eclipse
May 12, 2008 Wenchuan, China earthquake (19th deadliest earthquake of all time)
Depth: 19 kilometres (12 mi)
Epicenter location: 31.021°N 103.367°E
Aftershocks: 149 to 284 major & over 42,719 total
Casualties: ~ 69,000 dead~ 18,000 missing ~ 375,000 injured
Magnitude: 7.9 M
TIME: 06:28:01.42 UT
Japanese and Russian group
Tested all the proposed method of analysis
Primarily two methods of analysis is proposed using sub-ionospheric VLF data to make out precursory effects of ionospheric perturbations
(1) Terminator Time Method
(Hayakawa et al., 1996; Molchanov and Hayakawa, 1998; Hayakawa 2007)
Kobe Earthquake (7.3 M) in 1995
Reported significant shift in the terminator times before the earthquake, inferring daytime felt by VLF signal is elongated for a few days around the earthquake. – Hayakawa et al., 1996
Effective on E-W meridian plane propagation direction and Short paths (~ 1000-2000 km)
(2) Nighttime fluctuation analysis
0 2 4 6 8 10 12 14 16 18 20 22 24-4
-2
0
2
4
6
8
IST(Hours)
Am
pli
tud
e(a
.u.)
dA=A(t)-<A>
<A>
A(t)
<A>
A(t)
dA=A(t) - <A>
In this method VLF amplitude corresponding Local night-time is used
Estimate Diff : dA = A(t) - <A> A(t) is the amplitude at time ‘t’ <A> is average over one month
Finally, integrate dA2 over the night-time hours and have one data value for one day
– Hayakawa et al., 2007
Sumatra Earthquake – 26 December, 2004
– Hayakawa et al., 2007
0 2 4 6 8 10 12 14 16 18 20 22 24
JJI-Allahabad: Daily Amplitude Variation
Time in LT
20-April
29-April
11-May
EQ-12-May
16-May
Terminator -Time not visibleTerminator -Time not visibleT-T method not
applicable
~5500 km
Time Difference ~ 3.5 hrsDifficult to apply T-T method of analysis
12 14 16 18 20 22 24
JJI-VNS: Daily Night Time Amlitude Variation
Time in UT
20-April
11-May
EQ-12-May
16-May
12 14 16 18 20 22 24
JJI-NAT: Daily Night Time Amlitude Variation
Time in UT
20-April
11-May
EQ-12-May
20-May
12 14 16 18 20 22 24
JJI-VNS: Daily Night Time Amlitude Variation
Time in UT
20-April
11-May
EQ-12-May
20-May
Adopted the Nighttime fluctuation analysis method
0
200
400
600
800
1000
1200 JJI-ALD: Night Fluctuations
Flu
ctu
atio
n (
a.u
.)
20-April
EQ-12-M
ay
16-May
0
2000
4000
6000
8000
10000 JJI-NAT: Night Fluctuations
Flu
ctu
atio
n (
a.u
.)
20-April
EQ-12-May
20-May
0
1000
2000
3000
4000
5000
6000
7000
8000
9000 JJI-VNS: Night Fluctuations
Flu
ctu
atio
n (
a.u
.)
19-April
EQ-12-May
20-May
Kp < 4
So ionospheric perturbation due to solar activity can be ruled out
So, we clearly see the increase in the VLF amplitude fluctuation for 12 May, 2008 Wenchuan Earthquake
But this is not true for all Earthquakes
Subject of Seismic-Ionospheric perturbations caused by Earthquakes needs more attention and study
Response of D-region ionosphere during
22 July 2009 Total Solar Eclipse
Principle Sources of Ion production in D-region Ionosphere
There are several sources of ion production for ionospheric D region:
Lyman-alpha line of the solar spectrum at 121.5 nm wavelength penetrates below 95 km and ionize the minor species NO
The EUV radiation between 80.0 and 111.8 nm wavelength and X-raya of 02-0.8 nm wavelength ionize O2 and N2 and thus are the main sources of the free electrons in the ionospheric D region
During Total Solar Eclipse, D-region ionosphere of the umbral & penumbral shadow portion of the earth experiences sudden changes.
So solar eclipses provide opportunities to study the physical and chemical processes which determine the behavior of D-region ionosphere
Importance VLF waves in study of D-region of the Ionosphere
The altitude (~70-90 km) of this region are far too high for balloons and too low for satellites to reach, making continuous monitoring of the ionospheric D region difficult
D-regionD-region is lowest part ofis lowest part of ionosphereionosphere extended fromextended from ~ ~ 50-90 km50-90 km Electron density : ~ 2.5x10Electron density : ~ 2.5x103 el/cc el/cc by dayby day andand decreases to < 10decreases to < 103 3 el/cc el/ccat nightat night
It is generally difficult to measure the ionospheric D region on continuous basis because ionosondes and incoherent scatter radars in the HF-VHF range do not receive echos from this region, where electron density is typically < 103 cm-3
Because of the fact that VLF waves are almost completely reflected by the D region makes them as a useful tool for studies in this altitude range
Ground based measurements of ELF/VLF waves makes it possible to monitor the state of the D region ionosphere more routinely
VLF radio remote sensing is the technique suited for detection of disturbances in D-region.
Clilverd et al., 2001: August 11, 1999 Total Solar eclipse effect
• Used both medium and long path VLF signals
• Observed positive amplitude change on path lengths < 2000 km
• Negative amplitude changes on paths > 10,000 km
• Negative phase changes were observed on most paths, independent of path lengths
They further calculated electron concentration values at 77 km altitude throughout the period of solar eclipse, which showed a linear variation in electron production rate with solar ionizing radiation.
Study of 11 August, 1999 Solar eclipse in Indian Longitude(Sridharan et al., 2002, Ann. Geophy.)
Electrodynamics of the equatorial E- and F- region was studies with observations from ionosondes, VHF and HF radars at Trivandrum
Reported sudden intensification of weak blanketing type Es-layer irregularities, which was pushed down by ~ 8 km during the eclipse.
Naturally occurring VLF signals during Total Solar Eclipse The observation of natural VLF signals during eclipse are rare The only example of ionospheric study during eclipse with VLF signal is by Rycroft and Reeve, 1970, Nature, 226, 1126; 1972, JATP, 34, 667
Estimated increase in ionospheric reflection height by 7 km during eclipse of March 7, 1970 from the measurements of tweeks
40%
40%
Totality at 01:50:00 UT
~ 57 minutes
Totality at 00:53:00 UT
Distance to NWC~ 6700 km
Distance to JJI ~ 4750 km
to JJI(22.2kHz)
to NWC(19.8kHz)
Totality at ~00:55:00 UT~ 45 seconds Totality at ~00:56:00 UT
3 min 12 seconds
Maximum at ~00:57:00 UT
Two signals - NWC & JJI Two signals - NWC & JJI (1) Intersecting the totality path(1) Intersecting the totality path(2) Along the totality path(2) Along the totality path
to NWC(19.8kHz)
Effect on NWC:Intersecting the Path of Totality at: Allahabad
Allahabad: 25.400 N 81.930 E Eclipse Magnitude = 1 Totality Duration = 45.6 sec
Start of Partial Eclipse - 00:00:17.00Start of Total Eclipse - 00:55:08.9Maximum Eclipse - 00:55:31.4End of Total Eclipse - 00:55:54.3End of Partial Eclipse - 01:56:46.1
(Time in UT)
Decrease in Amplitude of signal as the eclipse progresses Maximum depression around the period of TOTALITY ( ~ 45 sec) A significant decrease in amplitude of 1.5 dB is observed Reaching minimum close to time of totality on the ~ 6700 km path between NWC VLF transmitter and Allahabad Also shift in Morning terminator time is seen from ~ 00:30 UT to time in eclipse totality
to NWC(19.8kHz)
Effect on NWC: Intersecting the Path of Totality at: Varanasi
Varanasi: 25.270 N 82.980 E
Eclipse Magnitude = 1.015TotalityDuration= 3 min 11.5 sec
Start of Partial Eclipse: 00:00:03Start of Total Eclipse: 00:54:08Maximum Eclipse: 00:55:42.6End of Total Eclipse: 00:57:17.1End of Partial Eclipse: 01:56:46
(Time in UT)
Decrease in Amplitude, Minimum depression around the period of TOTALITY
A significant decrease in amplitude of 2.5 dB is observed
Extended period of depression is observed because totality period is ~ 3 min 12 sec
Reaching minimum close to time of totality on the ~ 6700 km path between NWC VLF transmitter and Varanasi
Here again shift in Morning terminator time from ~ 00:30 UT to time in eclipse totality
to NWC(19.8kHz)
Effect on NWC: Intersecting the Path of Totality at: Nainital
Nainital: 29.350 N 79.450 E Eclipse Magnitude = 0.845 NO Totality
Start of Partial Eclipse - 00:03:36Maximum Eclipse - 00:57:18End of Partial Eclipse - 01:56:19
(Time in UT)
First increase in amplitude is seen with the start of eclipse
Then a significant decrease in amplitude of is observed around the time of maximum eclipse
Difference in amplitude variation when propagation path ends in totality region
100% 100% 85%
During the total solar eclipse of 22 July 2009 measurements of NWC(19.8 kHz) and JJI(221.2 kHz) VLF transmitter signals where made in India at three sites
Typically negative amplitude changes are seen for the NWC signals whose path intersect the region of totality
SUMMARY
Distance from transmitter to receiver ranged from 6700 km to 4750 km. One path intersecting and other parallel to the movement of totality region
And positive amplitude changes are seen for the JJI signal, which have its propagation path parallel to
Thank you for kind attention !
The positive and negative changes in amplitude of the VLF signals throughout the whole solar eclipse period shows the chnges in the dynamic process of the D-region ionosphere during eclipse
Further D region ionosphere modeling for earth-ionosphere waveguide propagation is in process to quantitatively infer the information during eclipse period – changes in the ionosphere height, relation between ion production rate and solar ionization, etc..