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22 July, 2009 Total Solar Eclipse: Effect on D-region Ionosphere Dynamics as Studied from AWESOME VLF Observations. Rajesh Singh B. Veenadhari, A.K. Maurya Indian Institute of Geomagnetism. P. Pant: ARIES, Manora Peak, Nainital – India

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22 July, 2009 Total Solar Eclipse:

Effect on D-region Ionosphere Dynamics as Studied from AWESOME VLF Observations

Rajesh Singh

B. Veenadhari, A.K. Maurya

Indian Institute of Geomagnetism

P. Pant: ARIES, Manora Peak, Nainital – India

A.K. Singh: Physics Department, B.H.U. , Varanasi – India


~ 03.50 Hrs

~ 200 – 260 Km

~ 3 – 5 minuets

~ 15,150 Km: 71% Earth Area


Principle Sources of Ion production in D-region Ionosphere

during: Daily usual Sun

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-rays 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: Eclipsed Sun

  • 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


Carried out both measurements:

Narrowband & Broadband (Continuous)




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.


Distance to NWC~ 6700 km effect

40%

Distance to JJI ~ 4750 km

Totality at 01:50:00 UT

~ 57 minutes

Totality at 00:53:00 UT

40%

Indian Stations


Maximum at ~00:57:00 UT effect

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)


Effect on effect 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)


Effect on effect 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)


Effect on effect 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

to NWC

(19.8kHz)


100% effect

100%

85%


Observations from SID: Bushan, S. Korea effect

Bushan

Y-Sil Kwak:KASI, Daejeon - South Korea

S Park: KAIST, Bushan - South Korea


Observations from Tashkent effect

21 July

22 July

figure: courtesy Yusuf and Boboamurat


Observations from effect

Azerbaijan

Modeling is REQUIRED!

figure: courtesy Elchin Babayev


Continuous effect Broadband Observations

- Tweek Radio Atmospherics


By analyzing the dispersive part of tweeks we can estimate :

  • Reflection height (h) of lower region (D-region) of ionosphere

  • Night time Electron density (N)

  • Propagation distance (d) in Earth-Ionosphere wave-guide


Broadband signals during Total Solar Eclipse: only ONE case :

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


Tweek Examples during TSE :

Observed ~ 40 Tweeks

~ around Totality

~ 30 min before Totality

~ around Totality

~ 30 min After Totality


Ionospheric Reflection Height and :

Electron Density Variation during TSE

TSE Period


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 (NWC) & 4750 km (JJI). 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


The positive and negative changes in amplitude of the VLF signals throughout the whole solar eclipse period shows the changes in D-region ionosphere during eclipse

Broad band observations of Tweek radio atmospherics shows the lower boundary of ionosphere and electron density moving to the levels of night

Further D region ionosphere modeling for earth-ionosphere waveguide propagation NEEDS TO BE DONE to quantitatively infer the information during eclipse period – changes in the ionosphere height, relation between ion production rate and solar ionization, etc..


Total Solar Eclipse- view from Allahabad signals throughout the whole solar eclipse period shows the changes in D-region ionosphere during eclipse

Thank you for kind attention !


Importance VLF waves in study of D-region of the Ionosphere signals throughout the whole solar eclipse period shows the changes in D-region ionosphere during eclipse

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


Study of 11 August, 1999 Solar eclipse in Indian Longitude signals throughout the whole solar eclipse period shows the changes in D-region ionosphere during eclipse

(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.


Importance VLF waves in study of D-region of the Ionosphere signals throughout the whole solar eclipse period shows the changes in D-region ionosphere during eclipse

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

Carried out both Narrowband and Broadband (Continuous) measurements


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