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Rajesh Singh , B. Veenadhari, A.K. Maurya, P. Vohat Indian Institute of Geomagnetism

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

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Rajesh Singh , B. Veenadhari, A.K. Maurya, P. Vohat Indian Institute of Geomagnetism

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  1. 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 A.K. Singh: Physics Department, B.H.U. , Varanasi – India M.B. Cohen, U. S. Inan Stanford University, CA, U.S.A.

  2. Outline • Installation/operation/science objective of AWESOME receivers in India • Scientific results from the AWESOME data collected in India - 12 May 2008 China Earthquake - 22 July 2009 Total Solar Eclipse

  3. Location of Indian VLF sites Nainital Lat.20.48N Long.153.34E May, 2007 Allahabad Lat.16.49N Long.155.34E March, 2007 Varanasi Lat. 15.41N Long. 156.37E October, 2007 Stanford University IHY 2007/UNBSSI program

  4. Experimental Setup VLF Receiver installed AWESOME VLF Receiver–Stanford University Narrowband + Broadband VLF data Amplitude and Phase of Transmitter signal Capable of collecting Saves entire VLF signal spectrum Crossed loop antenna – 10 x 10 meter Frequency response–300Hz to 47.5kHz Sampling – 100 kHz 10-microsecond time resolution

  5. DHQ GBR FTA2 HWU ICV Nainital JJI 3SA VNS Allahabad VTX NWC Lightning discharges Whistlers ELF/VLF emissions Lightning induced electron precipitation (LEP) Sprites, Elves, Blue jets, etc Solar flares Geomagnetic storms Earthquake precursors etc.

  6. 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.

  7. DHQ GBR FTA2 HWU ICV Nainital JJI 3SA VNS Allahabad VTX NWC Monitor natural and sub-ionospheric VLF signals continuously with AWESOME receivers. Port Blair, Andaman Islands Multi Parameter Observatory Essential for EQ studies

  8. Outline of talk • Installation and operation of AWESOME receivers in India • Scientific results from the AWESOME collected data - 12 May 2008 China Earthquake - 22 July 2009 Total Solar Eclipse

  9. May 12, 2008 Wenchuan, China earthquake (19th deadliest earthquake of all time) Magnitude: 7.9 M Epicenter location: 31.021°N 103.367°E Depth: 19 kilometres (12 mi) Aftershocks: 149 to 284 major & over 42,719 total Casualties: ~ 69,000 dead ~ 18,000 missing ~ 375,000 injured TIME: 06:28:01.42 UT

  10. Japanese and Russian group Tested all the proposed method of analysis

  11. 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)

  12. 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)

  13. (2) Nighttime fluctuation analysis In this method VLF amplitude corresponding Local night-time is used <A> Estimate Diff : dA = A(t) - <A> A(t) is the amplitude at time ‘t’ <A> is average over one month A(t) Finally, integrate dA2 over the night-time hours and have one data value for one day dA=A(t) - <A>

  14. Sumatra Earthquake – 26 December, 2004 – Hayakawa et al., 2007

  15. – Hayakawa et al., 2007

  16. Terminator -Time not visible Terminator -Time not visible T-T method not applicable

  17. ~5500 km Time Difference ~ 3.5 hrs Difficult to apply T-T method of analysis

  18. Adopted the Nighttime fluctuation analysis method

  19. Kp < 4 So ionospheric perturbation due to solar activity can be ruled out

  20. 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

  21. Response of D-region ionosphere during 22 July 2009 Total Solar Eclipse

  22. 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

  23. Importance VLF waves in study of D-region of the Ionosphere D-regionis lowest part ofionosphereextended from ~ 50-90 km Electron density : ~ 2.5x103 el/ccby dayanddecreases to < 103 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 < 103 cm-3 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

  24. 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.

  25. 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.

  26. 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.

  27. 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

  28. Distance to NWC~ 6700 km 40% Distance to JJI ~ 4750 km Totality at 01:50:00 UT ~ 57 minutes Totality at 00:53:00 UT 40%

  29. Maximum at ~00:57:00 UT to JJI (22.2kHz) Two signals - NWC & JJI (1) Intersecting the totality path (2) Along the totality path Totality at ~00:55:00 UT ~ 45 seconds Totality at ~00:56:00 UT 3 min 12 seconds to NWC (19.8kHz)

  30. 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 - 00:00:17.00 • 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)

  31. Effect on NWC: Intersecting the Path of Totality at: Varanasi 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 • Varanasi: 25.270 N 82.980 E • Eclipse Magnitude = 1.015 • 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) to NWC (19.8kHz)

  32. 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 - 00:03:36 • 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 to NWC (19.8kHz)

  33. 100% 100% 85%

  34. SUMMARY 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 Distance from transmitter to receiver ranged from 6700 km to 4750 km. One path intersecting and other parallel to the movement of totality region Typically negative amplitude changes are seen for the NWC signals whose path intersect the region of totality And positive amplitude changes are seen for the JJI signal, which have its propagation path parallel to

  35. 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.. Thank you for kind attention !

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