The semidiurnal (12.42 h) and semimonthly (14.76 days) lunar tides have been well-known by fishermen for several centuries. The gravitational force of the relative positions between the Sun, the ...Moon, and the Earth results in two symmetrical tidal bulges (double bulges) appearing at equatorial latitudes directly under and opposite the Moon. We utilize ionospheric GNSS (Global Navigation Satellite System) radio occultation soundings to show the global three-dimensional structures and dynamics of the double bulges of ionospheric lunar tides for the first time. The double-bulge amplitude of ionospheric F2-peak height hmF2, lagging the sublunar or antipodal point by about 2-3 h, is about 3-5 km at the equator and 1.5-2.0 km at ± 35° magnetic latitude. The electron density further depicts global three-dimensional plasma flows in the ionosphere.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
FORMOSAT-3/COSMIC (F3/C) constellation of six micro-satellites was launched into the circular low-earth orbit at 800 km altitude with a 72-degree inclination angle on 15 April 2006, uniformly ...monitoring the ionosphere by the GPS (Global Positioning System) Radio Occultation (RO). Each F3/C satellite is equipped with a TIP (Tiny Ionospheric Photometer) observing 135.6 nm emissions and a TBB (Tri-Band Beacon) for conducting ionospheric tomography. More than 2000 RO profiles per day for the first time allows us globally studying three-dimensional ionospheric electron density structures and formation mechanisms of the equatorial ionization anomaly, middle-latitude trough, Weddell/Okhotsk Sea anomaly, etc. In addition, several new findings, such as plasma caves, plasma depletion bays, etc., have been reported. F3/C electron density profiles together with ground-based GPS total electron contents can be used to monitor, nowcast, and forecast ionospheric space weather. The S4 index of GPS signal scintillations recorded by F3/C is useful for ionospheric irregularities monitoring as well as for positioning, navigation, and communication applications. F3/C was officially decommissioned on 1 May 2020 and replaced by FORMOSAT-7/COSMIC-2 (F7/C2). F7/C2 constellation of six small satellites was launched into the circular low-Earth orbit at 550 km altitude with a 24-degree inclination angle on 25 June 2019. F7/C2 carries an advanced TGRS (Tri Gnss (global navigation satellite system) Radio occultation System) instrument, which tracks more than 4000 RO profiles per day. Each F7/C2 satellite also has a RFB (Radio Reference Beacon) on board for ionospheric tomography and an IVM (Ion Velocity Meter) for measuring ion temperature, velocity, and density. F7/C2 TGRS, IVM, and RFB shall continue to expand the F3/C success in the ionospheric space weather forecasting.
Key Points
FORMOSAT-3/COSMIC and FORMOSAT-7/COSMIC-2 uniformly observe 3D electron density.
FORMOSAT-3 and FORMOSAT-7 enable ionospheric weather forecasting.
FORMOSAT-7/COSMIC-2 TGRS and IVM have a better understanding of the electrodynamics of ionospheric plasma.
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FFLJ, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UL, UM, UPUK
A newly developed cost-effective fiber-optic gyroscope (FOG) and an existing seismometer co-locating at the campus of National Central University (NCU) recorded seismic waves of a M6.6 Yilan ...earthquake and aftershock events occurring at around 24.74° N 122.03° E (88 km away from NCU) during 10–11 December 2020. Two nearest accessible broadband seismographs located in Hsinchu have also been employed as measurement references for facilitating the analysis of the detected seismic signals. Conventional seismometers usually detect the translational components of the seismic waves, while the FOG observes the rotational component. The recorded FOG data exhibit high-resolution details of the rotational component of shockwaves, which provides additional information of seismic waves. The shock waveforms of the translational and rotational components, analyzed under the conservation of the shock wave energy density received by FOG and seismograph, are found to be significantly correlated. The correlation coefficients of 60-s data are > 0.85 for the main shock and > 0.86 for the aftershock, while those of the 10-s peak periods are as high as 0.9064 and 0.8953, respectively. The highly correlated data imply that the energy registered by the two devices are equivalent. The optical interference-based rotation senor of the cost-effective FOG provides a high sensitivity of better than 3.6 deg/h and an extended dynamic sensing range as high as 55 dB with the fully sensing ability from
±
3.6 deg/h to
±
720,000 deg/h. The FOG seismometer sheds some light on building an earthquake six-degree-of-freedom observation array to have a bettering on the understanding of the seismicity.
Key Points
A NCU fiber-optic gyroscopy station detects the earthquake rotational motion.
The bias stability of the fiber-optic gyroscope reaches 0.034 deg/h.
The correlation of translational and rotational shockwave components is > 0.85.
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FFLJ, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UL, UM, UPUK
Historical records truthfully document human life and environment associated with climate changes. We quantify official historical records of China dating back last 2000 years to examine the ...disasters due to anomalous temperatures of cold or hot, irregular precipitations of wet or dry, and floods in inland/coastal or Northern/Southern areas in four seasons that possibly linked to solar activities during 1-1825 CE (Common Era). It is found that the proportion of disaster years is positively associated with the time periods, and therefore, both the cases with high and low solar activity (HSA and LSA) leading are under study. Statistical results show that extreme cold weather occurs particularly in the Winter and Spring during LSA periods. Irregularities precipitations, including heavy rain/hail/snow and severe drought are significantly frequent during LSA periods, while floods on inland and coastal river basins tend to occur more frequently in LSA and HSA periods, respectively. The disasters owing to irregularities precipitations and floods frequently happen in Summer and Autumn, which suggests that the irregular precipitations could cause the floods. All the disasters occur significantly in the Northern China, which suggests the climate boundary of the Qinling–Huaihe Line along at about 33°N being essential. In total, all the disasters due to the anomalously cold temperatures, irregular precipitations, and floods tend to occur during the LSA periods.
More than 1.4 million S4-index profiles sounded by FORMOSAT-3/COSMIC (F3/C) radio occultation during 2007-2014 are used to construct a global scintillation occurrence model for the ground-based GNSS ...(Global Navigation Satellite System) users. The local maximums of each F3/C S4-index profile at every 10 km altitude window are integrated to simulate the worst-case L-band S4-index (S4conv) on the ground. The S4conv mega-data bind into 3° × 3° in latitude × longitude allows us computing the occurrence probability of the globe for a given S4-index threshold. The occurrence probability of S4 of the developed model agree well with those of ground-based GNSS receivers of the SCINDA (SCIntillation Network Decision Aid) network. Global patterns in the occurrence probability of the model are similar to that of in-situ plasma measurements probed by ROCSAT and FORMOSAT-7/ COSMIC-2 satellites in various solar activities. These agreements and similarities indicate that the constructed empirical model can be employed to calculate and predict L-band S4-index and its occurrence probability in the ionosphere.
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FFLJ, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UL, UM, UPUK
We investigate ionospheric disturbances using the total electron content (TEC) data obtained from the radio signals emitted from three satellites after the foreshock of the 2011 Tohoku Earthquake on ...March 9, 2011. Co‐seismic ionospheric disturbances (CIDs) appeared to extend from an onset point concentrically in all of the satellite data. We have found, however, that the geographic coordinates of the onset points did not coincide if the observed CIDs were assumed to occur at one altitude. Admitting that the altitudes of the onset points are different, we searched for coinciding geographic coordinates of the onset points by changing the altitudes and identified the altitude of the three onset points to be 107.8, 131.8, and 133.3 km and the onset time at these altitudes. As a result, the vertical velocity of an acoustic‐gravity wave is estimated to be 448 m/s from the travel time between the altitudes of 107.8 and 131.8 km and 370 m/s between the altitude of 107.8 and 133.3 km. This is comparable to the speed of sound calculated using the empirical model NRLMSISE‐00. The present study provides a method of determining the altitude and geographic coordinates of the onset point from the ionospheric TEC analysis independently of the seismic data. Furthermore, the source location of the acoustic‐gravity wave is simultaneously determined because its wavefront propagating vertically arrives earliest at an altitude that TEC disturbance is detectable.
Key Points
We propose a new method of determining the location of ionospheric disturbance detected in total electron content (TEC) independent of the seismic data
The ionospheric disturbances in TEC were found to be below the F2‐peak at the foreshock of the 2011 Tohoku Earthquake on March 9, 2011
Source location of an acoustic‐gravity wave can be determined by analyzing TEC disturbances
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In this work, we assessed the possible relation of ionospheric perturbations observed by Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER), Global Positioning ...System total electron content (GPS TEC), National Oceanic and Atmospheric Administration (NOAA)-derived outgoing longwave-Earth radiation (OLR), and atmospheric chemical potential (ACP) measurements, with volcanic and Saharan dust events identified by ground and satellite-based medium infrared/thermal infrared (MIR/TIR) observations. The results indicated that the Mt. Etna (Italy) volcanic activity of 2006 was probably responsible for the ionospheric perturbations revealed by DEMETER on 4 November and 6 December and by GPS TEC observations on 4 November and 12 December. This activity also affected the OLR (on 26 October; 6 and 23 November; and 2, 6, and 14 December) and ACP (on 31 October–1 November) analyses. Similarly, two massive Saharan dust episodes, detected by Robust Satellite Techniques (RST) using Spinning Enhanced Visible and Infrared Imager (SEVIRI) optical data, probably caused the ionospheric anomalies recorded, based on DEMETER and GPS TEC observations, over the Mediterranean basin in May 2008. The study confirmed the perturbing effects of volcanic and dust events on tropospheric and ionospheric parameters. Further, it demonstrated the advantages of using independent satellite observations to investigate atmospheric phenomena, which may not always be well documented. The impact of this increased detection capacity in reducing false positives, in the framework of a short-term seismic hazard forecast based on the study of ionospheric and tropospheric anomalies, is also addressed.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
This study uses the Hilbert‐Huang transform to compute the instantaneous (daily) phase shift between temperature signals at the ground surface and at a depth of 5 m. This approach is not restricted ...to the stationary harmonic surface temperature assumptions invoked by analytical solutions. The annual cycles are extracted from the ground surface temperatures and the shallow subsurface temperatures at 5 m depth recorded at the Hualien (23.98°N, 121.61°E) and Ilan (24.77°N, 121.75°E) meteorology stations of Central Weather Bureau in Taiwan from 1952 to 2008. Significant reductions in the phase shift and increases in the estimated thermal diffusivity from 1980s to 1990s are found and suggest that the recent warming of the Pacific Decadal Oscillation may affect heat transport in the subsurface environment. The marginal spectra of the instantaneous phase shifts and the precipitation intensity records at Hualien and Ilan reveal that precipitation may play a role in the evolution of seasonal variation in shallow subsurface heat transport.
Key Points
Using HHT to derive phase shifts of annual subsurface temperature cycles
Relationship between PDO and heat transport in subsurface
Relationship between precipitation and heat transport in subsurface
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Modern society relies heavily on the Global Navigation Satellite System (GNSS) technology for applications such as satellite communication, navigation, and positioning on the ground and/or aviation ...in the troposphere/stratosphere. However, ionospheric scintillations can severely impact GNSS systems and their related applications. In this study, a global empirical ionospheric scintillation model is constructed with S4-index data obtained by the FORMOSAT-3/COSMIC (F3/C) satellites during 2007–2014 (hereafter referred to as the F3CGS4 model). This model describes the S4-index as a function of local time, day of year, dip-latitude, and solar activity using the index PF10.7. The model reproduces the F3/C S4-index observations well, and yields good agreement with ground-based reception of satellite signals. This confirms that the constructed model can be used to forecast global L-band scintillations on the ground and in the near surface atmosphere.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This paper presents a near real-time evaluation of earthquake hazard after the shallow M_L 6.2 Hualien shock of depth 10.6 km occurred 2350 LT, 6 February 2018 at epicenter (24.10°N, 121.73°E). Since ...a large aftershock intends to bring up a new aftershock sequence, we develop a time-magnitude hazard function for the double aftershock sequences. Note that the double-sequence aftershock hazard model can be regarded as a generalization of the Reasenberg-Jones (RJ) model and hence is denoted by DSRJ. For a near real-time evaluation of the aftershock hazard in the golden window particularly for emergent rescue work, the DSRJ or RJ model is estimated based on early aftershock sequence and then the occurrence rate and number of the forthcoming aftershocks in 3 days after the Hualien main shock are forecasted. Results of a data analysis show that the DSRJ model is better than the RJ model on near real-time assessment of short-term aftershock hazard. This provides an evidence that the aftershocks occurred in a short time after the Hualien main shock may not be a single aftershock sequence.
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FFLJ, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UL, UM, UPUK
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