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 M.B. Cohen, U. S. Inan Stanford University, CA, U.S.A. P. Pant: ARIES, Manora Peak, Nainital – India A.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 Varanasi Lat N Long E October, 2007 Allahabad Lat.16.49N Long E March, 2007 Nainital Lat.20.48N Long E 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 Receiver installed AWESOME VLF Receiver – Stanford University Capable of collecting Narrowband + Broadband VLF data Amplitude and Phase of Transmitter signal Saves entire VLF signal spectrum

VTX NWC JJI 3SA ICV HWU FTA2 DHQ GBR 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 ( 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 ( N) : A high altitude Solar observatory also with lower Atmospheric observations Varanasi ( 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 JJI 3SA ICV HWU FTA2 DHQ GBR 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: °N °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 (~ km)

(2) Nighttime fluctuation analysis A(t) dA=A(t) -  In this method VLF amplitude corresponding Local night-time is used  Estimate Diff : dA = A(t) - A(t) is the amplitude at time ‘t’ is average over one month  Finally, integrate dA 2 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

Terminator -Time not visible T-T method not applicable

~5500 km Time Difference ~ 3.5 hrs Difficult to apply T-T method of analysis

Adopted the Nighttime fluctuation analysis method

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 nm wavelength penetrates below 95 km and ionize the minor species NO  The EUV radiation between 80.0 and nm wavelength and X- raya of nm wavelength ionize O 2 and N 2 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-region is lowest part of ionosphere extended from ~ km Electron density : ~ 2.5x10 el/cc by day and decreases to < 10 3 el/cc Electron density : ~ 2.5x10 3 el/cc by day and decreases to < 10 3 el/cc at 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 < 10 3 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 E s -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% 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 (1) Intersecting the totality path (2) Along the totality path

to NWC (19.8kHz) Effect on NWC:Intersecting the Path of Totality at: Allahabad  Allahabad: N E  Eclipse Magnitude = 1  Totality Duration = 45.6 sec  Start of Partial Eclipse - 00:00:17.00  Start of Total Eclipse - 00:55:08.9  Maximum Eclipse - 00:55:31.4  End of Total Eclipse - 00:55:54.3  End 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: N E  Eclipse Magnitude =  TotalityDuration= 3 min 11.5 sec  Start of Partial Eclipse: 00:00:03  Start of Total Eclipse: 00:54:08  Maximum Eclipse: 00:55:42.6  End of Total Eclipse: 00:57:17.1  End 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: N E  Eclipse Magnitude =  NO Totality  Start of Partial Eclipse - 00:03:36  Maximum Eclipse - 00:57:18  End 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% 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..