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.

22 July, 2009 Total Solar Eclipse: Effect on D-region Ionosphere Dynamics as Studied from AWESOME VLF Observations

Rajesh SinghB. Veenadhari, A.K. Maurya

Indian Institute of Geomagnetism

P. Pant: ARIES, Manora Peak, Nainital – IndiaA.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 Ionosphereduring: 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)

AWESOME sites in observation on 22 July 2009 TSE

SID in Bhusan, Korea

Narrowband Observations

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.

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

Indian Stations

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

100% 100% 85%

Observations from SID: Bushan, S. Korea

Bushan

Y-Sil Kwak:KASI, Daejeon - South KoreaS Park: KAIST, Bushan - South Korea

Observations from Tashkent

22 July

21 July

figure: courtesy Yusuf and Boboamurat

Observations from Azerbaijan

figure: courtesy Elchin Babayev

Modeling is REQUIRED!

Continuous Broadband Observations- Tweek Radio Atmospherics

By analyzing the dispersive part of tweeks we By analyzing the dispersive part of tweeks we can estimate :can estimate :

A.A. Reflection height (h) of lower region (D-region) of Reflection height (h) of lower region (D-region) of ionosphereionosphere

B.B. Night time Electron density (N)Night time Electron density (N)

C.C. Propagation distance (d) in Earth-Ionosphere Propagation distance (d) in Earth-Ionosphere wave-guide 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

~ 30 min before Totality

~ 30 min After Totality

~ around Totality

~ around Totality

Tweek Examples during TSE Observed ~ 40 Tweeks

TSE Period

Ionospheric Reflection Height and Electron Density Variation during TSE

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 (NWC) & 4750 km (JJI). 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

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

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..

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

Thank you for kind attention !

Total Solar Eclipse- view from Allahabad

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

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.

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

Importance VLF waves in study of D-region of the Ionosphere

Carried out both Narrowband and Broadband (Continuous) measurements