Ionospheric Variations Observed by GPSTEC and SuperDARN Hokkaiodo radar following large earthquakes

1
Ionospheric Variations Observed by GPS-TEC and
SuperDARNHokkaiodo radar following large
earthquakes
Y. Otsuka1, N. Kotake1, T. Tsugawa1, K.
Shiokawa1, T. Ogawa1, Y. Yamaya1, N. Nishitani1,
Effendy2, S. Saito3, M. Kawamura3, T.
Maruyama3, N. Hemmakorn4, and T. Komolmis5
1. STEL, Nagoya Univ. 2. LAPAN, Indonesia
3. NICT 4. KMI, Thailand 5. Chiang Mai Univ.,
Thailand

• Sumatra-Andaman Earthquake of
• December 26, 2004 (M9.3)
• Kuril islands earthquake of 13 January 2007 (M8.2)

2
Location of the epicenter and GPS receivers

• GPS receivers
• - Chiang Mai NICT
• - Bangkok NICT
• - Chumphon NICT
• - Padang STEL
• Medan SOPAC
• (Scripps Orbit and
• Permanent Array Center)

3
Total Electron Content (TEC)
TEC increased 1425 min after the eathquake.
0058UT Earthquake
4
(No Transcript)
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Sumatra-Andaman Earthquake(M9.3)Dec. 26, 2004
amplitude of TEC variation
- N of the epicenter large - S
small - E no variation
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Horizontal propagation velocity of TEC variations
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Ray Tracing of Acoustic Wave
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plasma density perturbation caused by neutral
wind perturbation
Hooke, 1968
Plasma moves only along B.
background and perturbation of the electron
density
projection of neutral wind velocity and wave
vector to the geomagnetic field
I dip angle of magnetic field
9
Electron density variations caused by an acoustic
wave (model calculation)
6.5oN, 96.3oE Acoustic wave U130m/s Cs780m/s
T10min
Amplitude of 1.4 TECU
10
TEC variations caused by acoustic wave (model
calculation)
U130m/s Cs780m/s T10min
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Why TEC variation is larger to the north of the
epicenter?
acoustic wave
Plasma moves along B by the collision with
neutrals.
Plasma density variation is large when the
neutrals oscillate parallel to B.
Otsuka et al., 2006
12
Summary

• After the 2004 Sumatra-Andaman earthquake, TEC
  enhancements of 1.6-6.9 TECU were observed at
  Indonesia and Thailand.
• The time delays between the earthquake and rapid
  increases in TEC, which occurred near the
  epicenter, were consistent with the idea that
  acoustic waves generated from the epicenter
  propagated into the ionosphere and caused the TEC
  variations.
• Directivity of the TEC variations with respect
  to the azimuth form the epicenter was seen. This
  could be caused by the directivity in the
  response of electron density variation to the
  acoustic waves in the neutral atmosphere at the
  oblique geomagnetic fields.

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Observations of ionospheric variations following
the 13 January 2007 earthquake using GPS and
Hokkaido HF radar
14
Kuril islands earthquake of 13 January 2007
Magnitude 8.2 time 0423 UT epicenter
46.272N 154.455E
epicenter
Hokkaido HF radar
GPS receivers
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TEC perturbations (Jan.13, 2007)
deviation from 15-min. running average.
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TEC perturbation 25-30 min after the earthquake
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E-W cross-section of the TEC perturbation (41oN)
UT
5
Period 4min.
4
W
E
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• TEC perturbation
• propagated southwestward (azimuth of 220)
• This direction coincides with the direction of
  the epicenter.
• phase velocity of 970 m/s
• (close to the sound velocity
• in the thermosphere)
• period of 4 min.
• 25 min. after the earthquake
• amplitude of 0.03TECU
• (0.4 of the background)
• not seen to the west of the epicenter ?
  directivity of TEC perturbation

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ray tracing of the acoustic wave
TEC perturbation was observed at 960 km far from
the epicenter 28 min. after the earthquake.
20
model calculation
Acoustic wave with an amplitude of 20 m/s cause
TEC perturbation with an amplitude of 0.4 of the
background.
21
model calculation
acoustic wave with an amplitude of 20 m/s
The directivity of TEC perturbation could be
explained by relationship between directions of B
and neutral wind oscillation due to the acoustic
wave.
22
Doppler velocity of ground (sea) scatter echoes
for 04-06 UT (all beams)
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Variation of Doppler velocities of ground scatter
echoes for range 26, beam 0 to 15
earthquake
W
ionosphere
Amplitude of the Doppler velocity perturbation is
10m/s.
E
4
5
7 min.
UT
24
0430UT
0433UT
0436UT
Doppler velocity perturbations propagate westward
at 3-4 km/s.
25
Rayleigh wave
Rayleigh wave
2-3 km/s
Ducic et al., 2003
26
Summary

• GPS-TEC
• TEC perturbation with a period of 4 min.
  propagated from the epicenter with a phase
  velocity of 970 m/s.
• TEC perturbation was observed to the southwest
  of the epicenter, but not observed to the west of
  the epicenter.
• This directivity could be explained in terms of
  relationship between directions of B and neutral
  wind oscillation due to the acoustic wave.
• TEC perturbation could be caused by acoustic
  wave originated at the epicenter and propagate to
  the ionosphere.
• Hokkaido HF radar
• Doppler velocity perturbation propagated from
  the epicenter with a phase velocity of 3-4 km/s.
• This phase velocity corresponds to Rayleigh
  wave on the earths surface.
• Doppler velocity perturbation could be
  caused by acoustic wave originated from Rayleigh
  wave.

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Conclusion

• TEC perturbations were observed after the large
  earthquakes.
• Acoustic waves could be launched at the
  epicenter and propagate into the ionosphere
  causing TEC perturbations.
• Amplitude of TEC perturbation showed directivity
  with respect to the azimuth of the epicenter.
• This directivity could be responsible for
  directivity in the response of electron density
  variation to the acoustic waves in the neutral
  atmosphere.