Transcript Loop antenna preamplifier transfer function

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 Xrays 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%
Distance to NWC~ 6700 km
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
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 NWC:Intersecting the Path of Totality at: Allahabad
to NWC
(19.8kHz)
0 N 81.93of
0 Esignal
 Allahabad:
Decrease in
25.40
Amplitude
 Eclipse
as
the eclipse
Magnitude
progresses
=1
 Maximum
Totality Duration
depression
= 45.6around
sec
the
period of TOTALITY ( ~ 45 sec)
A
significant
decrease
in
Start of Partial
amplitude
of 1.5Eclipse
dB is observed
- 00:00:17.00
Start

Reaching
of Totalminimum
Eclipse - 00:55:08.9
close to time
Maximum
of
totality on
Eclipse
the -~00:55:31.4
6700 km path
End of Total
between
NWC
Eclipse
VLF transmitter
- 00:55:54.3 and
End of Partial Eclipse - 01:56:46.1
Allahabad
 Also shift in(Time
Morning
in UT)terminator
time is seen from ~ 00:30 UT to time
in eclipse totality
Effect on NWC: Intersecting the Path of Totality at: Varanasi
 Decrease in Amplitude, Minimum
depression around the period of
TOTALITY
A
significant 0 decrease
in
0
Varanasi:
25.27
N observed
82.98 E
amplitude
of 2.5
dB is
Eclipse Magnitude = 1.015
min 11.5 secis
 TotalityDuration=
Extended period of3 depression
observed because totality period is
~ 3 min 12 sec
Start of Partial Eclipse: 00:00:03
of Total
Eclipse:close
00:54:08
 Start
Reaching
minimum
to time
ofMaximum
totality onEclipse:
the ~ 00:55:42.6
6700 km path
End ofNWC
Total Eclipse:
00:57:17.1and
between
VLF transmitter
End of Partial Eclipse: 01:56:46
Varanasi
(Time in UT)
 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

in = amplitude
is
 First
Eclipseincrease
Magnitude
0.845
seen
with
start of eclipse

NOthe
Totality
 Then a significant decrease in
amplitude
of is observed
around the
Start of Partial
Eclipse - 00:03:36
time
of maximum
Maximum
Eclipseeclipse
- 00:57:18
End of Partial Eclipse - 01:56:19
(Time in UT)
to NWC
(19.8kHz)
100%
100%
85%
Observations from SID: Bushan, S. Korea
Bushan
Y-Sil Kwak:KASI, Daejeon - South Korea
S Park: KAIST, Bushan - South Korea
Observations from Tashkent
21 July
22 July
 figure: courtesy Yusuf and Boboamurat
Observations from
Azerbaijan
Modeling is REQUIRED!
 figure: courtesy Elchin Babayev
Continuous Broadband Observations
- Tweek Radio Atmospherics
By analyzing the dispersive part of tweeks we
can estimate :
A. Reflection height (h) of lower region (D-region) of
ionosphere
B. Night time Electron density (N)
C. 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
~ 30 min before Totality
~ around 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
Thank you for kind attention !
Importance VLF waves in study of D-region of the Ionosphere
D-region is lowest part of ionosphere extended from ~ 50-90 km
Electron density : ~ 2.5x103 el/cc by day and decreases 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
(Sridharan et al., 2002, Ann. Geophy.)
Electrodynamics of the equatorial E- and Fregion 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
 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