1) Ionospheric TEC disturbances were observed in South Korea following the 2011 Tohoku earthquake in Japan. Impulsive TEC enhancements were first observed approximately 16.5 minutes after the earthquake.
2) Small-scale TIDs with a period of around 4 minutes were observed from 6:15-7:10 UT. Medium-scale TIDs with a period of around 15 minutes and duration of 60 minutes were also observed. The amplitude of the medium-scale TIDs was seen to dampen clearly over time.
3) Detailed analysis of GPS data from a station in South Korea found repeated short-period oscillations in TEC variations from 07:15-08:15 UT, indicating regular
Geodetic and seismological analysis of the January 26th, 2014 Cephalonia Isla...Demitris Anastasiou
On January 26, 2014 a strong earthquake of magnitude Mw=5.8 occurred on Cephalonia Island followed by a similar magnitude earthquake Mw=5.7 one week later on February 3, 2014. Extensive structural damages, landslides and many damages on the islands' main roads, harbour and airport caused mainly on the western and central part of the island. The first event located 2km eastern of Lixouri town and was followed five hours later by a strong aftershock of magnitude Mw=5.3. The second strong earthquake located in the north part of Paliki eninsula North-East Cephalonia). Geodetic data of six permanent GNSS stations were available and analysed in this study both in pro and post seismic terms, using 30sec and 1Hz data where available. The time series analysis shows the effect of each event at nearby stations. Seismological data are used to determine the focal mechanisms of the earthquake sequence and an attempt to investigate the homogeneity of the mechanisms and the stress field of the area is presented in the study. Geodetic analysis and seismological results are used to understand the mechanism of the events.
Electromagnetic Phenomena Related to the 2011 Tohoku Earthquake and Tsunami: A Short Review by Stelios M Potirakis, Alexander Schekotov and Masashi Hayakawa in Examines in Marine Biology and Oceanography
First Observation of the Earth’s Permanent FreeOscillation s on Ocean Bottom ...Sérgio Sacani
The Earth’s hum is the permanent free oscillations of the Earth recorded in the absence ofearthquakes, at periods above 30 s. We present the first observations of its fundamental spheroidaleigenmodes on broadband ocean bottom seismometers (OBSs) in the Indian Ocean. At the ocean bottom,the effects of ocean infragravity waves (compliance) and seafloor currents (tilt) overshadow the hum. In ourexperiment, data are also affected by electronic glitches. We remove these signals from the seismic traceby subtracting average glitch signals; performing a linear regression; and using frequency-dependentresponse functions between pressure, horizontal, and vertical seismic components. This reduces the longperiod noise on the OBS to the level of a good land station. Finally, by windowing the autocorrelation toinclude only the direct arrival, the first and second orbits around the Earth, and by calculating its Fouriertransform, we clearly observe the eigenmodes at the ocean bottom.
Geodetic and seismological analysis of the January 26th, 2014 Cephalonia Isla...Demitris Anastasiou
On January 26, 2014 a strong earthquake of magnitude Mw=5.8 occurred on Cephalonia Island followed by a similar magnitude earthquake Mw=5.7 one week later on February 3, 2014. Extensive structural damages, landslides and many damages on the islands' main roads, harbour and airport caused mainly on the western and central part of the island. The first event located 2km eastern of Lixouri town and was followed five hours later by a strong aftershock of magnitude Mw=5.3. The second strong earthquake located in the north part of Paliki eninsula North-East Cephalonia). Geodetic data of six permanent GNSS stations were available and analysed in this study both in pro and post seismic terms, using 30sec and 1Hz data where available. The time series analysis shows the effect of each event at nearby stations. Seismological data are used to determine the focal mechanisms of the earthquake sequence and an attempt to investigate the homogeneity of the mechanisms and the stress field of the area is presented in the study. Geodetic analysis and seismological results are used to understand the mechanism of the events.
Electromagnetic Phenomena Related to the 2011 Tohoku Earthquake and Tsunami: A Short Review by Stelios M Potirakis, Alexander Schekotov and Masashi Hayakawa in Examines in Marine Biology and Oceanography
First Observation of the Earth’s Permanent FreeOscillation s on Ocean Bottom ...Sérgio Sacani
The Earth’s hum is the permanent free oscillations of the Earth recorded in the absence ofearthquakes, at periods above 30 s. We present the first observations of its fundamental spheroidaleigenmodes on broadband ocean bottom seismometers (OBSs) in the Indian Ocean. At the ocean bottom,the effects of ocean infragravity waves (compliance) and seafloor currents (tilt) overshadow the hum. In ourexperiment, data are also affected by electronic glitches. We remove these signals from the seismic traceby subtracting average glitch signals; performing a linear regression; and using frequency-dependentresponse functions between pressure, horizontal, and vertical seismic components. This reduces the longperiod noise on the OBS to the level of a good land station. Finally, by windowing the autocorrelation toinclude only the direct arrival, the first and second orbits around the Earth, and by calculating its Fouriertransform, we clearly observe the eigenmodes at the ocean bottom.
Direct Measure of Radiative And Dynamical Properties Of An Exoplanet AtmosphereSérgio Sacani
Two decades after the discovery of 51Pegb, the formation processes and atmospheres of short-period gas giants
remain poorly understood. Observations of eccentric systems provide key insights on those topics as they can
illuminate how a planet’s atmosphere responds to changes in incident flux. We report here the analysis of multi-day
multi-channel photometry of the eccentric (e ~ 0.93) hot Jupiter HD80606b obtained with the Spitzer Space
Telescope. The planet’s extreme eccentricity combined with the long coverage and exquisite precision of new
periastron-passage observations allow us to break the degeneracy between the radiative and dynamical timescales
of HD80606b’s atmosphere and constrain its global thermal response. Our analysis reveals that the atmospheric
layers probed heat rapidly (∼4 hr radiative timescale) from<500 to 1400 K as they absorb ~20% of the incoming
stellar flux during the periastron passage, while the planet’s rotation period is 93 35
85
-
+ hr, which exceeds the predicted
pseudo-synchronous period (40 hr).
Key words: methods: numerical – planet–star interactions – planets and satellites: atmospheres – planets and
satellites: dynamical evolution and stability – planets and satellites: individual (HD 80606 b) – techniques:
photometric
The October 2004 Mw=7.1 Nicaragua earthquake: Rupture process, aftershock loc...Gus Alex Reyes
The subduction zone off the Nicaragua
coastline has been the site of several large
earthquakes in the past decades, including
the 1992 tsunami earthquake that was
anomalous in the size of the tsunami relative
to moment release [Kanamori and
Kikuchi, 1993]. As a focus site for both
the MARGINS-SEIZE and SubFac initiatives,
it is an area of keen interest for
scientists interested in earthquake rupture
and volcanic processes.
The earth�s ionosphere acts as a perturbing medium on satellite-based navigational systems like GPS. Variations in the ionosphere due to weather conditi ons caused by solar flares and coronal mass ejectio n can scatter Trans - Ionosphere radio signals producing fluctuations in both amplitude and phase and GPS cy cle slips disrupting satellite communications and navig ation. The ionosphere delay is one of the fundament al reasons for inaccuracy in GPS positioning and routi ng. The Total Electron Content (TEC) along the radi o wave path from a GPS satellite to the ground receiv er is directly proportional to the ionosphere delay . This paper proposes a method allowing to calculate the T EC with a correctness of about 2�3 TECU and to sens e Travelling Ionosphere Disturbances using GPS measur ements.
Direct Measure of Radiative And Dynamical Properties Of An Exoplanet AtmosphereSérgio Sacani
Two decades after the discovery of 51Pegb, the formation processes and atmospheres of short-period gas giants
remain poorly understood. Observations of eccentric systems provide key insights on those topics as they can
illuminate how a planet’s atmosphere responds to changes in incident flux. We report here the analysis of multi-day
multi-channel photometry of the eccentric (e ~ 0.93) hot Jupiter HD80606b obtained with the Spitzer Space
Telescope. The planet’s extreme eccentricity combined with the long coverage and exquisite precision of new
periastron-passage observations allow us to break the degeneracy between the radiative and dynamical timescales
of HD80606b’s atmosphere and constrain its global thermal response. Our analysis reveals that the atmospheric
layers probed heat rapidly (∼4 hr radiative timescale) from<500 to 1400 K as they absorb ~20% of the incoming
stellar flux during the periastron passage, while the planet’s rotation period is 93 35
85
-
+ hr, which exceeds the predicted
pseudo-synchronous period (40 hr).
Key words: methods: numerical – planet–star interactions – planets and satellites: atmospheres – planets and
satellites: dynamical evolution and stability – planets and satellites: individual (HD 80606 b) – techniques:
photometric
The October 2004 Mw=7.1 Nicaragua earthquake: Rupture process, aftershock loc...Gus Alex Reyes
The subduction zone off the Nicaragua
coastline has been the site of several large
earthquakes in the past decades, including
the 1992 tsunami earthquake that was
anomalous in the size of the tsunami relative
to moment release [Kanamori and
Kikuchi, 1993]. As a focus site for both
the MARGINS-SEIZE and SubFac initiatives,
it is an area of keen interest for
scientists interested in earthquake rupture
and volcanic processes.
The earth�s ionosphere acts as a perturbing medium on satellite-based navigational systems like GPS. Variations in the ionosphere due to weather conditi ons caused by solar flares and coronal mass ejectio n can scatter Trans - Ionosphere radio signals producing fluctuations in both amplitude and phase and GPS cy cle slips disrupting satellite communications and navig ation. The ionosphere delay is one of the fundament al reasons for inaccuracy in GPS positioning and routi ng. The Total Electron Content (TEC) along the radi o wave path from a GPS satellite to the ground receiv er is directly proportional to the ionosphere delay . This paper proposes a method allowing to calculate the T EC with a correctness of about 2�3 TECU and to sens e Travelling Ionosphere Disturbances using GPS measur ements.
Características de los sistemas SCALL y su uso en el Caribe. El Toolbox de GWP Caribe por Natalie Broodman, GWP Caribe, durante el taller regional de intercambio de experiencias sobre SCALL. San Salvador, septiembre 2016.
Cool and Cute Fashion Collection is the ultimate simple yet elegant collection to express your positive and charming personalities through your accurate choice. Simply choose to be simple yet elegant to express your positive outlooks about life.
Caso de estudio SCALL en Caribe por Natalie Broodman, GWP Caribe durante el taller regional de intercambio de experiencias sobre SCALL. San Salvador, septiembre 2016.
İstasyon dağılımı çift kanaldan yapılıyor ve bu kanallar AFAD ve KOERI. İlginç olan durum bu istasyonlar 1 YIL içinde yerleştirilmiyor ve YILLARA yayılan bir yerleştirme planı var. İstatistik çalışanlar için iyi özellikle, 'İstasyon Etkilerinin Sismisite Değişimine Muhtemel Etkileri' konusunu çalışmak isteyenler için. Özellikle, 1995 yılında ki çalışmam bununla ilişkili. https://npg.copernicus.org/articles/2/147/1995/
AFAD tarafından DAFZ civarında kurulmuş 28 istasyonu var ve 2006 yılında kurmaya başlamış ve süreç 2017 yılına kadar yükselerek devam etmiş. 2006 yılında 28 istasyonun tamamını 1 DEFA'da kurmuş olsa idi fay zonlarının deprem tehlikesinin araştırılması için önemli bir VERİ toplanması olacaktı ve bugüne kadar 15 yıllık veri üzerinde '0-İnsan Etkisi' olduğundan istatistik çalışmalar ile bulunan sonuçlar anlamlı olacaktı. Sıkça sorulan soru vardır, 'Depremler son yıllarda sayısal olarak artıyor mu?' diye, EVET artıyor çünkü depremi kayıt eden İSTASYON sayısı arttığı için. Bu açıdan, 'İnsana bağlı olarak deprem tehlike verisinde ki değişim' araştırma konusu olur mu? Neden olmasın!
Benzer durum KOERI'de var ve 2006 yılında 5 olan istasyon sayısını 2011 yılına kadar tedrici olarak 10 sayısına yükseltiyor. 2011 yılından sonra sayı 12'de sabit kalıyor.
2006 yılından günümüze DAFZ üzerinde İKİLİ KURUM tarafından kurulan toplam istasyon sayısı 40, fakat bunlar TEK 1 YILDA kurulmadığı için İSTATİSTİK çalışmalara ETKİSİ olumsuz. 2006 yılında 40 istasyon 1 DEFADA kurulsa idi, DAFZ boyunca fayların deprem potansiyelinin araştırılması açısından ÇOK İYİ bir potansiyel olacaktı.
Deprem İstatistiği çalışmalarında DİKKAT edilecek ÇOK noktalar var, bu noktalar bölgede ki VERİ KAPASİTESİ ve VERİ KALİTESİ'nin iyi araştırılması ile mümkün olur. Aslında burada ANLATILANLARI İstatistiksel Sismoloji dersinde detaylı tartıştım. Deprem İstatistiği çalışacak olan ve bu konuda çalışmak isteyenler bu dersler BAŞTAN SONA not alarak 1 KERE daha dinlese İYİ olur. AKSİ taktirde çalışmalarınız İYİ 1 BİLİMSEL TEMELE dayanmazsa çok yararsız olabilir.
Alma observations of_the_transition_from_infall_motion_to_keplerian_rotation_...Sérgio Sacani
We have observed the Class I protostar TMC-1A with Atacama Millimeter/submillimeter
Array (ALMA) in the emissions of 12CO and C18O (J = 2−1),
and 1.3-mm dust continuum. Continuum emission with a deconvolve size of
0.
′′50 × 0.
′′37, perpendicular to the 12CO outflow, is detected. It most likely traces
a circumstellar disk around TMC-1A, as previously reported. In contrast, the
C
18O a more extended structure is detected in C18O although it is still elongated
with a deconvolved size of 3.
′′3 × 2.
′′2, indicating that C18O traces mainly a flattened
envelope surrounding the disk and the central protostar. C
18O shows a
clear velocity gradient perpendicular to the outflow at higher velocities, indicative
of rotation, while an additional velocity gradient along the outflow is found
at lower velocities. The radial profile of the rotational velocity is analyzed in
detail, finding that it is given as a power-law ∝ r
−a with an index of ∼ 0.5 at
higher velocities. This indicates that the rotation at higher velocities can be
explained as Keplerian rotation orbiting a protostar with a dynamical mass of
0.68 M⊙ (inclination corrected). The additional velocity gradient of C18O along
the outflow is considered to be mainly infall motions in the envelope. PositionVelocity
diagrams made from models consisting of an infalling envelope and a
Keplerian disk are compared with the observations, revealing that the observed
infall velocity is ∼0.3 times smaller than free fall velocity yielded by the dynamical
mass of the protostar. Magnetic fields could be responsible for the slow infall
velocity. A possible scenario of Keplerian disk formation is discussed.
Disturbances in Solar Wind Electrons during the Ascending Half of the Solar C...researchinventy
Ulysses achieved a solar orbit with an inclination of 80.200 , perihelion of 1.34 AU, aphelion of 5.4 AU and a period of 6.2 years. By comparing observations taken over nearly all heliolatitudes and two different intervals covering the same radial distances, we are able to separate the radial and latitudinal variations in the solar wind. This paper describes the detailed results of the studies devoted to the solar activity impact on the Earth’s upper atmosphere and ionosphere. The methods used in this study are based on the data driven from the Ulysses spacecraft. The primary objective of the Ulysses solar wind plasma investigation uses SWOOPS (Solar Wind Observations over the Poles of the Sun) instrument to investigate and establish bulk flow parameters and internal state conditions of the solar wind as a function of solar latitude. The electron temperature Te and the electron density Ne are found to exhibit a sharp enhancement during the ascending half of the solar cycle 23 (1996 – 2004)
X-RAY MEASUREMENTS OF THE PARTICLE ACCELERATION PROPERTIES AT INWARD SHOCKS I...Sérgio Sacani
We present new evidence that the bright non-thermal X-ray emission features in the interior of the Cassiopeia A
supernova remnant (SNR) are caused by inward moving shocks based on Chandra and NuSTAR observations. Several
bright inward-moving filaments were identified using monitoring data taken by Chandra in 2000–2014. These inwardmoving shock locations are nearly coincident with hard X-ray (15–40 keV) hot spots seen by NuSTAR. From proper
motion measurements, the transverse velocities were estimated to be in the range ∼2,100–3,800 km s−1
for a distance of
3.4 kpc. The shock velocities in the frame of the expanding ejecta reach values of ∼5,100–8,700 km s−1
, slightly higher
than the typical speed of the forward shock. Additionally, we find flux variations (both increasing and decreasing) on
timescales of a few years in some of the inward-moving shock filaments. The rapid variability timescales are consistent
with an amplified magnetic field of B ∼ 0.5–1 mG. The high speed and low photon cut-off energy of the inward-moving
shocks are shown to imply a particle diffusion coefficient that departs from the Bohm regime (k0 = D0/D0,Bohm ∼ 3–8)
for the few simple physical configurations we consider in this study. The maximum electron energy at these shocks is
estimated to be ∼8–11 TeV, smaller than the values of ∼15–34 TeV inferred for the forward shock. Cassiopeia A is
dynamically too young for its reverse shock to appear to be moving inward in the observer frame. We propose instead
that the inward-moving shocks are a consequence of the forward shock encountering a density jump of & 5–8 in the
surrounding material.
Similar to Ionospheric TEC Disturbances over South KoreaFollowing the 2011 Great Tohoku Earthquake (20)
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Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
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Ionospheric TEC Disturbances over South KoreaFollowing the 2011 Great Tohoku Earthquake
1. Research Inventy: International Journal of Engineering And Science
Vol.6, Issue 6 (July 2016), PP -35-42
Issn (e): 2278-4721, Issn (p):2319-6483, www.researchinventy.com
35
Ionospheric TEC Disturbances over South KoreaFollowing the
2011 Great Tohoku Earthquake
1
Byung-Kyu Choi, 2
Sang Jeong Lee, 3
Ha Su Yoon
1,3
Space Geodesy Group, Space Science Division, Korea Astronomy and Space Science Institute (KASI)
2
Department of Electronics Engineering, Chungnam National University
Abstract: Ionospheric total electron contents (TEC) disturbances following the 2011 great Tohoku earthquake
on March 11, 2011 were observed by a GPS network in South Korea. The impulsive TEC enhancements were
first observed approximately 16.5 minutes after the beginning of the earthquake. Various types of seismic waves
were also observed over South Korea.To investigate more detailed disturbances in the TEC, we processed the
GPS data with a sampling rate of 1Hz and applied a band-pass filter with corner frequencies of 0.0 and 0.005
Hz. Small-scale traveling ionospheric disturbances (TIDs) with a period of approximately 4minutes (~250
seconds) were observed from 6:15 to 7:10 UT. These variations are considered to be a clear manifestation of the
acoustic resonance oscillations. We also observed medium-scale TIDs with a period of approximately 15
minutes and a duration of approximately 60 minutes. A remarkable finding is that the damping of the amplitude
of the medium-scale TIDs was observed clearly in the time series.
Keywords:ionosphere; earthquake; TEC; disturbance.
I. Introduction
Sudden ionospheric disturbances can be caused by a variety of factors, including solar flares,
geomagnetic storms, space weather and seismic events. Various studies of disturbances of the ionospheric total
electron content (TEC) following seismic eventshave been conducted with the global positioning system (GPS)
have been investigated for two decades (Heki and Ping, 2005; Otsuka et al., 2006, Choosakulet al., 2009).Heki
and Ping (2005) showed directivity and clear velocity of thecoseismic ionospheric disturbance (CID) triggered
by the 2003 Tokachi-Oki earthquake (Mw 8.0) with a GPS network in Japan. Otsuka et al. (2006)detected
ionospheric TEC enhancements induced by large earthquakes. Their report was based on GPS data from
Indonesia and Thailand. They also found the enhancement of ionospheric TEC on the northwards of the
epicenter with cycles of 14 to 40 minutes after the 2004 Sumatra-Andaman earthquake.In particular, Choosakul
et al. (2009) reported a periodic oscillation of ionospheric TEC measured by a GPS network following the 2004
Sumatra earthquake. It lasted for more than three hours in the vicinity of the epicenter and had an obvious
periodicity at 3.7 mHz and 4.4 mHz.
Recently,a massive earthquake with a magnitude of 9.0 occurred in the Tohoku area, on the east coast
of Honshu, Japan (38.322°N, 142.369°E, depth 32km) at 05:46:23 UT (universal time) on 11 March 2011. The
ionospheric disturbances generated by this large earthquakeand tsunami have been analyzed by many
investigators (Maruyama et al., 2011; Matsumura et al., 2011; Saito et al., 2011; Tsugawaet al., 2011; Tsai et al.,
2001; Liu et al., 2011; Rolland et al., 2011). Maruyama et al. (2011) observed ionospheric disturbances in
ionograms obtained at the four ionosondes in Japan. Matsumura et al. (2011)reported that ionospheric TEC
oscillations induced by the Tohoku earthquake show a good agreement with simulated atmospheric
perturbations. This result indicates that ionospheric oscillations are associated with the motion of the neutral
atmosphere. Saito et al. (2011) revealed that a displacement of the sea surface caused by the earthquake
inducedatmospheric waves, which propagated upwards to the thermosphere. Tsugawaet al. (2011) detected
ionospheric TEC disturbances following the Tohoku earthquake with a dense GPS network in Japan. They
calculated the vertical TECfrom data recorded at a GPS station and also found that the sudden depletions of the
TEC and the short-period oscillations after the earthquake were observed in the signals of some GPS satellites.
Tsai et al. (2011) studied the ionospheric signature induced by the Tohoku earthquake with a network of several
GPS facilities, including GEONET in Japan, 7 IGS sites, and Taiwan stations. These authors indicated that the
ionospheric perturbations are primarilyproduced by the earthquake. Liu et al. (2011) observed remarkable
signatures, including Rayleigh waves, acoustic gravity waves, and tsunami waves triggered by the M9.0 Tohoku
earthquake. These phenomena were observed from the ground-based GPS networks in Japan and Taiwan.
Rolland et al. (2011) analyzed the ionosphere TEC variations associated with the Tohoku earthquake. They also
observed three different types of wave: the Rayleigh surface waves, acoustic waves and gravity waves. These
observations show good agreement with the observations of Liu et al. (2011).
GPS data can be used to observe the ionospheric disturbances recorded following large earthquakes.
Ground-based GPS dataallow the detection of anomalies in the ionospheric TEC.In this paper, we processedGPS
2. Ionospheric TEC Disturbances Over South Korea Following The 2011 Great Tohoku Earthquake
36
data from 9 ground-based GPS reference stations in the Korean GPS network (KGN)to detect various types of
the ionospheric TEC disturbances induced by the 2011 great Tohoku earthquake.
This paper also focuses ona detailed investigation of a periodic oscillation and the high-resolution
observation of the TEC disturbancesinduced by the Tohoku earthquake. For this purpose, we used GPS data
with two different sampling parameters: a sampling interval of 30 sec and a sampling rate of 1Hz.
II. GPS Data And Method
To investigate ionospheric disturbances over South Korea following the Tohoku earthquake, we
processed the GPS data obtained from the KGN in South Korea (9 GPS stations designated as ‘daej’, ‘bhao’,
‘jeju’, ‘kohg’, ‘mlyn’, ‘mkpo’, ‘sbao’, ‘skch’ and‘skma’).The estimation methods used to extract TEC
information from GPS signals have beendescribed by several investigators (Klobuchar et al., 1994; Klobuchar,
1996; Jakowskiet al., 1996).
The fundamental equations for the code and carrier phase measurements can be expressed as follows
(Schaer, 1999).
P = ρ + c ∙ 𝑑𝑡 𝑠
− 𝑑𝑡 𝑟 + c ∙ 𝑑 𝑠
+ 𝑑 𝑟 + 𝑑𝑖𝑜𝑛 + 𝑑𝑡𝑟𝑜𝑝 + εP (1)
Φ = ρ + c ∙ 𝑑𝑡 𝑠
− 𝑑𝑡 𝑟 − 𝑑𝑖𝑜𝑛 + 𝑑𝑡𝑟𝑜𝑝 + λ ∙ N + εΦ(2)
Where,
ρtrue geometric range from satellite to receiver (m)
𝑑𝑡 𝑠
satellite clock error (s)
𝑑𝑡 𝑟receiver clock error (s)
𝑑 𝑠
satellite hardware bias (s)
𝑑 𝑟receiver hardware bias (s)
cspeed of light in a vacuum (m/s)
𝑑𝑖𝑜𝑛 ionospheric delay (m)
𝑑𝑡𝑟𝑜𝑝 tropospheric delay (m)
λwavelength of frequency (m)
N carrier phase integer ambiguity (cycle)
εmeasurement noises (m)
The estimated TEC values derived from the code measurements have a large uncertainty due to the
high noise. The carrier phase measurements are much more accurate than the code measurements, but carrier
phase measurements require the resolution of phase ambiguity and consideration of infrequent cycle slips. To
obtain better accuracy for the derived GPS-TEC, a smoothing technique is employed with the code and carrier
phase measurements. The smoothed code with the carrier phase is described as follows:
𝑃(𝑡) 𝑠𝑚 = ω ∙ P t + 1 − ω ∙ {𝑃 𝑡 − 1 𝑠𝑚 + λ ∙ Φ t − Φ t − 1 } (3)
WhereP(t)and Φ(t)are the pseudo-range and carrier phase measurements. The term ω is the
smoothing factor. The term𝑃(𝑡) 𝑠𝑚 is the smoothed code. To calculate the ionospheric TEC, we adopted the
common model in which the ionosphere consists of a thin shell at a fixed height, usually 350 km. Slant TEC is a
measure of the total electron content of the ionosphere along the ray path. It can be easily computed from the
following Eq.(4).
STEC =
1
40.3
(
𝑓1
2∙𝑓2
2
𝑓1
2−𝑓2
2)(𝑃2 − 𝑃1 + 𝐷 𝑠
+ 𝐷𝑟 ) (4)
Where,𝐷 𝑠
= 𝑑2
𝑠
− 𝑑1
𝑠
and 𝐷𝑟 = 𝑑2𝑟 − 𝑑1𝑟are the differential code bias (DCB) of the satellite and the
receiver, respectively. It is well known that these biases significantly affect the ionospheric TEC value (Ma and
Maruyama, 2003; Choi et al., 2011).The DCB values were obtained with weighted least squares and applied to
the daily averaged estimates.
In this study, we obtained TEC values from ground-based GPS data with a 30 secondsampling interval.
In addition, we processed GPS data with a 1Hz sampling rate from the ‘daej’GPS stationto allow more detailed
investigation of the TEC disturbances.The time-differenced vertical TEC for each GPS receiver-satellite pair
was considered to reveal the variation in the TEC due to the earthquake and the tsunami.To enhance the
coherence of the characteristics of seismic-wave propagation, aband-pass filter was also applied tothe TEC time
series.
3. Ionospheric TEC Disturbances Over South Korea Following The 2011 Great Tohoku Earthquake
37
Figure1 The locations of 9 GPS reference stations in South Korea (green dots). The IPPs for the PRN 26 (red
line) and PRN 27 (blue line) satellite-receiver pairs on March 11, 2011. The digits represent the corresponding
UT hours.
Figure 2 The vertical TEC variations of the PRN 26 satellite observed from 9 GPS stations in South Korea on
March 11, 2011.
III. Results
To study the ionospheric disturbances over South Korea following the 2011 Tohoku earthquake, we
processed GPS data from the KGN in South Korea.
Figure 1 shows the IPPs for the PRN 26 and PRN 27 satellites. The IPPs for the PRN 26 satellite are
approaching the epicenter across the Korean Peninsula. The IPPs for the PRN 27 satellite resemble those of
PRN 26. They remained in the vicinity of South Korea for almost three hours after the onset of the earthquake.
The digits represent the corresponding time.
Figure 2shows the time series of the vertical TEC of the PRN 26 satellite observed by 9 GPS reference
stations in South Korea. The vertical TEC estimated from all GPS sites showed impulsive enhancements with
amplitudes of 0.5~1 TECU at 06:02 UT. After the impulsive TEC enhancements, sudden decreases in the
vertical TEC were observed. Compared with the TEC before the impulsive enhancements, the average
amplitude of the TEC decreases was approximately 1 TEC. Small-scale TEC perturbations, weaker than 0.5
TEC,appeared during short periods from 06:00 UT to 06:30 UT. Tsugawa et al. (2011) reported a decrease of 20%
in the TEC measurements relative to the previous TEC value (before the depletions occurred) over Japan.
Figure 3represents the time series of the time-differenced vertical TEC (TECU/30sec) of the PRN 26
satellite at 9 GPS stations. We considered the distance from the GPS stations to the epicenter.The ‘bhao’ station
in South Korea was closest to the epicenterand the ‘jeju’ station wasthe farthest from the epicenter. The
4. Ionospheric TEC Disturbances Over South Korea Following The 2011 Great Tohoku Earthquake
38
Figure 3 The time-differenced vertical TEC of the PRN 26 satellite at 9 GPS stations on March 11, 2011. The y-
axis shows the 4 characters used to represent the site name. The red line indicates the beginning of the
earthquake.
Figure 4 The vertical TEC variations of the PRN 27 satellite observed from 9 GPS stations in South Korea on
March 11, 2011.
behaviours of the time-differenced TEC (TEC/30 sec) before the earthquake were very quiet. No remarkable
variations in the TEC were observed over South Koreafor approximately16minutes after the earthquake.
Irregular fluctuations in the TEC were firstobserved at 06:02 UT over almost all of South Korea.However,few
time differences in the arrival of the disturbances were observed. It is known that the seismic perturbations
triggered by the earthquake affected the ionospheric TEC over South Korea. Liu et al. (2011) reported that these
perturbations are described as seismo-traveling ionospheric disturbances (STIDs). A remarkable finding is that
the impulsive variations in the TEC estimated by the ‘jeju’ station were relatively higher than those estimated by
the other stations. This difference could be associated with the direction of propagation of the first large-scale
circular waves triggered by the earthquake.According to Heki and Ping (2005), a CID is only detected in a
magnetic equatorward direction due to magnetic field inclination. Tohoku earthquake observations showed clear
north-south asymmetry of the CID exited by the Rayleigh wave (Yoshihoet al., 2013). Therefore our result is
related to an asymmetry of the CID.
Figure 4 shows thetime series of the vertical TECof the PRN 27 satellite observed by 9 GPS stations
from 05:00 UT to 09:00 UT. The TEC variations showed no remarkable features before 07:15 UT. Weak
fluctuations in the TEC variations with a period of approximately 15 min were just observable from 07:15to
08:15 UT.These fluctuations were identified as the slower CID propagated in all direction from the tsunami
source.
5. Ionospheric TEC Disturbances Over South Korea Following The 2011 Great Tohoku Earthquake
39
Figure 5 The time-differenced vertical TEC of the PRN 27 satellite at 9 GPS stations on March 11, 2011. The y-
axis shows the 4 characters used to represent the site name.
Figure 5shows the time series of the time-differenced vertical TEC(TEC/30 sec) of the PRN 27 satellite.
As shown in Figure 5(a), the initial ionospheric TEC disturbances appeared at 06:02 UT. The absolute amplitude
of the TEC variations in the short period wasapproximately0.3 TEC. Following the impulsive perturbations, no
further features of the TEC variations were observed until 07:15 UT. However, remarkable small TEC
fluctuations, not shown by Figure 6, were observed after 07:15 UT all over South Korea. As shown in Figure
5(b), our results indicate that regular wave patterns in the TEC variationswere clearly observed for one hour
from 07:15 UT to 08:15 UT. These waves, shown in Figure 5(b),also exhibited repeatedshort-period
oscillationsover a period of one hour.
Tsugawaet al. (2011) reported that medium-scale concentric waves with a wavelength of 200-300
kmwere observed until after 08:00 UT in western Japan after the propagation of the first large-scale circular
waves triggered by the Tohoku earthquake. Our findings are in good agreement with thisresult.
To investigate more detailed variations in the TEC over South Korea following the Tohoku earthquake,
we processed the GPS data with a sampling rate of 1Hz obtained from the ‘daej’ station and examined the
temporal variation of the TEC data. A band-pass filter with corner frequencies of 0.0 and 0.005 Hz was also
applied to enhance the coherence of the characteristics of seismic-wave propagation.
Figure 6 shows the TEC time series for satellite 26 at the ‘daej’station in South Korea. The behavior of
the vertical TEC decreased linearly approximately 15 minutesafter the beginning of the earthquake. A small
impulsive enhancement with an amplitude of 0.3 TECthen occurred at 06:02 UT.Following the impulsive
enhancement, the TEC showed rapid decreases until 06:07 UT. The amount of the depletion of TEC was
approximately 1.3 TECU relative to the TEC before the impulsive enhancement. The lower image in Figure 6
shows the time series of the time-differenced TEC (dTEC=TEC/1sec).The blue dotted line in Figure 6 represents
the time series of the dTEC obtained from 1Hz data at the‘daej’GPS station. The amplitude of the time-
differenced TEC for the PRN 26 satellite showed a maximum of ~0.03 TEC. From these results, we do not
observe coseismic signatures clearly. However, the application ofa band-pass filter to the TEC variations
allowed us to observe, the features in TEC fluctuations induced by the earthquake. The red line in Figure 6
represents the time series of the band-pass filtered TEC variations. The sudden disturbances of the TEC
variations at 06:02 UT are assumed to result fromthe main shock produced by the earthquake.After the main
shock, small-scale periodic oscillation with a period of about 4 minute was observed continuously. It is
explained that an acoustic wave triggered by a propagating Rayleigh wave shows an atmospheric resonance.
We could also observe remarkable features of theTEC variationsfor a longer time,as shown in Figure
7.Figure 7 presents the time series of the band-pass filtered TEC variationsfrom the PRN 27 satellite. We
observed two types of perturbations in the TEC variations followingthe Tohoku earthquake. Sudden
disturbances in the TEC variations are clearly visible at 06:02 UT. Small amplitude TEC variationswere
observed from 6:15 to 7:15 UT.We detected variations in TEC with a time period of approximately4minutes
(~250 seconds) and a duration of approximately1 hour.To calculate a period of the oscillation, an averaging time
of the consecutive peak-to-peak amplitude was used.The period was kept constant. These variations are
considered to represent a clear instance ofthe acoustic waves. Using 1 Hz sampling TEC data, we have found
that the short-period oscillations (4 minutes) caused by the acoustic resonanceare detected continuously for one
6. Ionospheric TEC Disturbances Over South Korea Following The 2011 Great Tohoku Earthquake
40
Figure 6 TEC time series for satellite 26 calculated with high-resolution GPS data (the sampling rate is 1Hz)
from 05:30-06:45 UT.The upper panelrepresents the TEC time series. The lower panel represents the time series
of the corresponding TEC variations. The red line representsthe band-pass filtered TEC variations, analyzed
using corner frequencies of 0.0 and 0.005 Hz.
Figure 7 TEC time series of satellite 27 calculated with the GPS data with a sampling rate of 1 Hz from 05:00-
09:00 UT.The upper panel represents the TEC time series. The lower panel represents the time series of the
corresponding TEC variations. The red line representsthe band-pass filtered TEC variations.
hours over South Korea. TheseTEC responses agreed with the results of earlier studies (Calais and Minster,
1995; Afraimovichet al., 2006). Moreover, we observed medium-scale TIDs with a period of 15 minutesand a
duration of 60 minutes. These perturbation structures appeared at approximately 07:30 UT and gradually
disappeared after 08:30 UT.They formedintensive quasi-periodic TEC variations. An interesting feature of these
structures is that the amplitude of medium-scale TIDs was clearly observed on the time series.The amplitude of
wave showed a gradual decrease. After 8:30UT, the amplitude became small. This is coincident with the report
by Saito et al. (2011). The amplitude change would be generated by the coupling of acoustic resonance between
the ground surface and the lower thermosphere. Further detailed analysis is necessary to discuss the relationship
between the amplitude change and the TEC variations.The GPS data with a 1 Hz sampling rate enables us to
obtain detailed observations ofthe propagation and attenuation of medium-scale TIDs. Such ionospheric
disturbances were observed for four hours at the northwest of the epicenter, tothe east of South Korea.
IV. Discussion And Summary
Ionospheric TEC disturbances induced by the 2011 Tohoku earthquake on March 11, 2011
wereinvestigated using a GPS network in South Korea. Impulsive TEC enhancements were first observed
7. Ionospheric TEC Disturbances Over South Korea Following The 2011 Great Tohoku Earthquake
41
approximately 16.5 minutes after the beginning of the earthquake. The CID associated with the Rayleigh wave
was observed in west direction (over South Korea) from the epicenter. Astafyevaand Heki(2009) explained that
the shape of the response depends on the location of sub-ionospheric points (SIPs) relative to the epicenter. In
our results, the amplitude of the waves reached the maximum value of 0.9 TECat the ‘jeju’ station and then
decreased to 0.1-0.2 TEC. The SIPsrecorded from the GPS stations in South Korea are located approximately
1,250 km away from the ionospheric epicenter. TheCID propagated with the velocity 1.26km/s from the
epicenter to South Korea. If it is assumed that the STIDs induced on the Earth’s surface reach the ionosphere at
approximately 05:53 UT, the wave speed is 2.31 km/s (1250km/540 seconds), which is within the range of
Rayleigh surface wave speeds.These features are also consistent with previous observations (Astafyevaet al.,
2009; Rolland et al., 2011).
Short-period TEC oscillations were observed more than one hour over South Korea after the
earthquake. Tsugawaet al. (2011) reported that medium-scale concentric waves were observed until after 08:30
UT in western Japan.Large earthquakes can generate acoustic waves and gravity waves which propagate into the
ionosphere and interact with the ionized gases. The oscillation of seismic-waves such as Rayleigh waves,
acoustic waves, gravity waves and tsunami waves triggered by Tohoku earthquakecontinued for four hours
above the epicenter.This implies that the resonance of the acoustic waves was lasted for four hours after
earthquake onset.
To investigate more detailed features of the TEC perturbations, the GPS data from the‘daej’ site with a
sampling rate of 1Hz were processed. We observedclear features of small-scale and medium-scale waves in the
TEC variations in the time series,as shown in Figure 6 and 7. In Figure 6, we could observe signatures of
Rayleigh surface waves and the acoustic gravity waves. The distance of the SIPs of the PRN 26 satelliteand the
ionospheric epicenter was approximately 510km. Therefore the velocity of wave can be easily calculated using
time difference in any direction. Its wave speed was about 1.05 km/s. Heki and Ping (2005) showed that the
acoustic wave speed is about0.6-1.1 km/s at 300 km altitude in the ionosphere. Using numerical simulations,
Matsumura et al. (2011) indicated that the atmospheric waves were generated by a sea surface displacement
induced from the large earthquake, not by a propagting tsunami.
As shown in Figure 7, the acoustic waves with a period of approximately 250 seconds (about 4 minutes)
and a duration of approximately 60 minutes were the first detailed aspects of the TEC variations found in 1 Hz
TEC data. They are considered to represent a manifestation of the acoustic resonance oscillations. These waves
were not seen in 30 seconds data.
We also observed medium-scale TIDs with a period of approximately 15 minutes and a duration of one
hour. These medium-scale TIDs structures appeared at approximately 07:30 UT over eastern South Korea. The
amplitude of the medium-scale waves tended to decrease with time. It is assumed that these waves are induced
by the tsunami due to the slow speed. These waves propagated for more than horizontal distance of 1,000 km
from the ionospheric epicenter.
The use of the GPS data with a 1 Hz sampling rate enabled us to observe clearly the seismic
wavesexpanding as far as horizontal distance of 1,000 km from the epicenter. This approach also enabled us
toobserve the details of the propagation and attenuation of the acoustic waveover South Korea.
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