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..