Tatsuhiro Yokoyama

Tatsuhiro Yokoyama
Kyoto University | Kyodai · Research Institute for Sustainable Humanosphere

PhD

About

109
Publications
11,126
Reads
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1,735
Citations
Additional affiliations
November 2018 - present
Kyoto University
Position
  • Professor (Associate)
April 2016 - November 2018
National Institute of Information and Communications Technology
Position
  • Senior Researcher
April 2014 - March 2016
National Institute of Information and Communications Technology
Position
  • Senior Researcher
Education
April 1995 - March 2004
Kyoto University
Field of study
  • Electrical and Electronic Engineering, Ionospheric Physics

Publications

Publications (109)
Article
Full-text available
Equatorial plasma bubbles (EPBs) have been a longstanding and increasingly important subject because they cause severe scintillations in radio waves from Global Navigation Satellite System satellites. The phenomenon was found in the 1930s as irregular ionosonde observations and was termed equatorial spread F (ESF). ESF is interpreted as plasma dens...
Article
Full-text available
Earth’s magnetic field results from various internal and external sources. The electric currents in the ionosphere are major external sources of the magnetic field in the daytime. High-resolution magnetometers onboard low-Earth-orbit satellites such as CHAMP and Swarm can detect small-scale currents in the nighttime ionosphere, where plasma density...
Article
Plasma density depletions in the equatorial ionosphere, or so-called equatorial plasma bubbles (EPBs), are generated in the postsunset period and tend to have a very complex spatial structure. Especially, the east-west asymmetry of EPBs has been reported by various observations. Using a high-resolution bubble (HIRB) model, which is a newly develope...
Article
A detailed comparison between the observations of the Communication/Navigation Outage Forecasting System (C/NOFS) satellite and the 47 MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36°S dip latitude) on the postmidnight irregularities is presented. The zonal and meridional E × B drift velocities measured by the vector electri...
Article
Plasma density structures and associated irregularities in the nighttime midlatitude ionospheric E and F regions are frequently observed as frontal structures elongated from northwest to southeast (NW-SE) in the northern hemisphere. The frontal structures and the coupling process between the E and F regions are studied with a three-dimensional nume...
Article
Full-text available
Observations and theoretical analysis on the night-time mid-latitude ionospheric irregularities support the postulation of frequently coupled E and F regions. In this paper, we attempt at asserting this notion while using total electron content (TEC) measurements. The TECs are from a dense GNSS receiver network over Japan with more than 1200 statio...
Article
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Investigations of upwelling backscatter plumes are mostly from observations of VHF radars. In this study, we report the first observation of upwelling backscatter plumes (backscatter echoes beyond the critical frequency of the F2 layer, foF2) recorded by ionosondes at low latitudes on 13 March, 2015. With a pair of ionosondes (Puer, 22.7o N, 101.05...
Article
Full-text available
A novel two‐step three‐dimensional (3‐D) computerized ionospheric tomography (CIT) technique has been developed to image the structure of daytime midlatitude sporadic‐E (Es). The CIT relies on total electron content (TEC) from a dense ground‐based Global Navigation Satellite System (GNSS) receiver network over the Japan area. First, on a coarse gri...
Article
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Plain Language Summary A new type of terrestrial line spectra found by the Arase (ERG) satellite was reported. They primarily consist of constant frequency narrowband emissions at frequencies between 525 kHz and 1,700 kHz (hectometric wavelength) and additional emissions with changing frequencies. The former emissions originate and are amplified fr...
Article
Full-text available
The F‐region observations of field aligned irregularities (FAI) by the Equatorial Atmosphere Radar (EAR) at Kototabang (0.2°S, 100.3°E, 10.36°S dip latitude) show maximum percentage of occurrence (PO) of post‐midnight echoes due to spread F during boreal summer of solar minimum years. However, the PO is observed to be anomalously high during Septem...
Article
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Motivated by the observations and linear theory analysis of ionospheric irregularities at Mars, we performed numerical simulations of the nonlinear evolution of the electromagnetic gradient drift instability in the Martian ionospheric dynamo region. The seeding source of ionospheric irregularities is perturbation zonal neutral wind. We found that t...
Article
Full-text available
An unseasonal equatorial plasma bubble (EPB) event over South‐East Asia was observed on July 22, 2014 that has not been studied before. An investigation into this event is presented with the 26th July, 2014 as a comparison, non‐bubble day. The 22nd July EPB event occurred in the late post‐sunset sector and was associated with a small upward plasma...
Article
Full-text available
Plain Language Summary Two rockets with scientific instruments were launched in the middle of the day to study the upper atmosphere and how it interacts with the ionosphere. The rockets ascended to altitudes of about 140 km—just high enough to gather the necessary data—before coming back down along parabolic trajectories. A vapor trail released by...
Article
Full-text available
The equatorial plasma bubbles, once developed, grow nonlinearly into topside ionosphere, and simultaneous secondary instabilities lead to the development of shorter scale irregularities. The altitudinal growth and generation of smaller scale irregularities determine the spatio‐temporal occurrence and the intensity of ionospheric scintillations at w...
Article
Full-text available
Spatio‐temporal characteristics of equatorial plasma bubble (EPB) have been studied based on Equatorial Atmosphere Radar (EAR) fan sector observations from Kototabang. EPBs were characterized as either locally generated (whose genesis and subsequent evolution was observed in the fan sector maps) or drifted type (which drifted into fan sector scans...
Article
Full-text available
A comparative study of the equatorial spread F occurrence was conducted at different longitudes during 2010 and 2013 representing the low (LSA) and moderate (MSA) solar activity periods respectively. The ionogram data were recorded at low-latitude stations including Jicamarca (JIC;75.76∘ W, 8.17∘ S), Fortaleza (FZA; 38.52∘ W, 3.73∘ S), Ilorin (ILR;...
Article
Full-text available
An all‐sky imager at El Leoncito Observatory (−31.8°, 69.3°W, 18.2° magnetic latitude) is used to study 630.0‐nm airglow emissions related to medium‐scale traveling ionospheric disturbances (MSTIDs). On the night of 6 December 2007 an unusual event consisting of bright bands propagating northwestward was observed. Enhancements in total electron con...
Article
Full-text available
The seeding mechanism of equatorial plasma bubbles (EPBs) in the ionosphere has not been fully understood for several decades. Before investigating the complex seeding process by atmospheric gravity waves, which have been considered as a possible candidate, we investigate the vertical neutral wind effect on the EPB seeding by making the numerical s...
Article
Full-text available
A comparative study of the equatorial spread F occurrence was conducted at different longitudes during 2009 or 2010 and 2011 or 2013 which represents the low (LSA) and moderate (MSA) solar activity periods respectively. The ionogram data were recorded at low latitude stations including Jicamarca (JIC; 75.76° W, 8.17° S), Peru; Fortaleza (FZA; 38.52...
Article
Full-text available
Analysis of the ionospheric parameters on the ionogram is important for the study of ionospheric physics and related field. This paper introduces an application program tool used for extracting ionospheric profile parameters on the ionogram from the South East Asia Low-latitude Ionospheric Network FMCW ionosonde measurement. The software runs under...
Article
Full-text available
Abstract An unseasonal development of Equatorial Plasma Bubble (EPB)/Equatorial Spread-F (ESF) activity in a wide longitudinal sector over India and Southeast Asia during the post-sunset hours of 28 July 2014 has been investigated in detail using the multiple independent observations in this paper and a companion paper by (Prog Earth Planet Sci 5:1...
Article
Full-text available
Abstract Manifestations of severe nighttime equatorial ionospheric disturbances have been observed for decades. It is generally accepted that the phenomena are caused by large depletions, referred to as equatorial plasma bubbles (EPBs), which are initiated on the rising unstable bottom side of the nighttime F layer. Physics-based simulations have e...
Article
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Stochastic ionospheric structure is characterized by spectral density functions (SDFs), which are formally the average intensity of Fourier transformations of the electron density structure. Structure elongation along magnetic field lines is typically accommodated by constraining contours of constant spatial correlation to field-aligned ellipsoidal...
Article
The nature and extent of the irregularities causing L-band nighttime scintillations at a group of five stations Dibrugarh (27.5°N, 95°E, 43° dip), Kohima (25.6°N, 94.1°E, 39° dip), Aizawl (23.7°N, 92.8°E, 36° dip), Port Blair (11.6°N, 92.7°E, 9° dip), and Cocos Islands (12.2°S, 96.8°E, 43° dip) from the northern low midlatitudes to southern midlati...
Article
Full-text available
We present long overdue statistical analysis of the 150-km echoes based on 10 years of observations made using the Equatorial Atmosphere Radar located at Kototabang, Indonesia. Analysis shows that while the basic features of the echoes are very similar to those observed from other equatorial/low-latitude stations, occurrence and power/signal-to-noi...
Article
Full-text available
The linear growth rates of the Rayleigh-Taylor (R-T) instability in the ionosphere from 2011 to 2013 were obtained with a whole atmosphere-ionosphere coupled model GAIA (ground-to-topside model of atmosphere and ionosphere for aeronomy). The effects of thermospheric dynamics driven by atmospheric waves propagating from below on the R-T growth rate...
Article
Full-text available
This contribution is the first of a two-part investigation into an unseasonal post-sunset equatorial F-region irregularity (EFI) event over the Southeast Asian region on the evening of 28 July 2014. Ground-based GPS scintillation data, space-based GPS radio occultation (RO) data, and ionosonde data show the existence of EFIs shortly after sunset ov...
Article
Full-text available
We conducted geomagnetically conjugate observations of 630-nm airglow for a midnight brightness wave (MBW) at Kototabang, Indonesia [geomagnetic latitude (MLAT): 10.0°S], and Chiang Mai, Thailand (MLAT: 8.9°N), which are geomagnetically conjugate points at low latitudes. An airglow enhancement that was considered to be an MBW was observed in OI (63...
Article
Full-text available
After publication of this work (Fukushima et al. 2017) some errors were noticed. In Figures 2b, 2c and 2f the letters ‘N’, ‘N’ and ‘S’ appear in the images, respectively. The original article was corrected. The publisher apologises for these errors.
Article
Full-text available
Radar echoes from the daytime equatorial ionospheric F1 region, popularly known as "150 km echoes," have challenged ionospheric plasma physicists for several decades. Recent theoretical simulations showed that enhanced photoelectron fluxes can amplify the amplitude of plasma waves, generating spectra similar to those of the radar echoes, implying t...
Article
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Multi-beam observations of the 150-km echoes made using the Equatorial Atmosphere Radar (EAR), located at Kototabang, Indonesia provide unique opportunity to study both vertical and zonal ExB plasma drifts in the equatorial ionosphere. In this paper, we focus on estimating daytime zonal drifts at the 150 km (140-160 km) and E (100-110 km) regions u...
Article
We present the development of physics-based models of solar-terrestrial regions from the solar surface to the Earth’s atmosphere at NICT. Our models consist of three regions: (1) the solar surface and solar wind, (2) the Earth’s magnetosphere-ionosphere, and (3) a model of the whole atmosphere from the troposphere to the ionosphere, called the Grou...
Article
Full-text available
The vertical rise velocity (Vr) and maximum altitude (Hm) of equatorial plasma bubbles (EPBs) were estimated using the two-dimensional fan sector maps of 47 MHz Equatorial Atmosphere Radar (EAR), Kototabang, during May 2010 to April 2013. A total of 86 EPBs were observed out of which 68 were postsunset EPBs and remaining 18 EPBs were observed aroun...
Article
Full-text available
This study mainly investigates equatorial and low-latitude ionospheric response to a great geomagnetic storm occurred on the 17 March 2015. We found that there were some interesting ionospheric phenomena, e.g. short-term ionospheric positive effect, daytime spread F, and morning Equatorial Ionization Anomaly (EIA) in the topside ionosphere, emerged...
Article
Full-text available
Hainan coherent scatter phased array radar (HCOPAR) located at low-latitude of China has recorded the extremely rare daytime F-region irregularities at noon of 22 July 2013 and 23 May 2016. The two field-aligned irregularities (FAIs) appeared in the topside F2-layer and presented small Doppler velocities and narrow spectral widths. The fan sector m...
Article
The occurrence rate of the equatorial plasma bubble (EPB) with season, solar activity, and geomagnetic conditions are investigated using long-term data sets of Malaysia Real-Time Kinematics Network (MyRTKnet) from 2008 to 2013. The rate of TEC (total electron content) change index (ROTI) in 5 min was derived from MyRTKnet data to detect the EPB wit...
Article
This paper proposes a new expression for computing the bottomside thickness parameter at equatorial latitude station, Chumphon (10.72°N, 99.37°E), Thailand. Its diurnal variations from 2004 to 2006 at this location are then studied. The proposed expression is derived based on two experimental data sources: FMCW ionosonde and dual-frequency GPS syst...
Article
Full-text available
Spread F on ionograms has been considered to be a phenomenon mainly occurred at nighttime. This study presented a case study of daytime spread F observed by the ionosonde installed at Puer (PUR, 22.7o N, 101.05o E, Dip Latitude 12.9o N), where daytime spread F that lasted for more than 2 hours (about 08:30 LT ~ 10:45 LT) was observed on 14 November...
Article
The effects of the St. Patrick's Day geomagnetic storms of 2013 and 2015 in the equatorial and low latitude regions of both hemispheres in the 100°E longitude sector is investigated and compared with the response in the Indian sector at 77°E. The data from a chain of ionosondes and GPS/GNSS receivers at magnetic conjugate locations in the 100°E sec...
Article
There is considerable evidence that plasma structure in nighttime equatorial F layer develops from large-scale wave structure (LSWS) in bottomside F layer. However, crucial details of how this process proceeds, from LSWS to equatorial plasma bubbles (EPBs), remain to be sorted out. A major obstacle to success is the paucity of measurements that pro...
Article
There is mounting evidence that plasma structure in nighttime equatorial F layer evolves from large-scale wave structure (LSWS) in the bottomside F layer. This process cannot be ignored because equatorial plasma bubbles (EPBs), arise from large-amplitude LSWS; and, because intense radiowave scintillations are associated with EPBs, understanding the...
Conference Paper
It is increasing to measure the ionosphere over the ocean, since it occupies 70% of whole ionosphere and it is necessary for improving the precision of empirical/numerical models. Especially, as the operational aviation requires the precise ionospheric information, it is indispensable to develop the methods of measurement of ionosphere over the oce...
Article
Predawn plasma bubble was detected as deep plasma depletion by GNU Radio Beacon Receiver (GRBR) network and in situ measurement onboard Defense Meteorological Satellite Program F15 (DMSPF15) satellite and was confirmed by sparse GPS network in Southeast Asia. In addition to the deep depletion, the GPS network revealed the coexisting submesoscale ir...
Article
Ionospheric nighttime enhancements are manifested in an increase of the electron density at nighttime. This paper studies the latitudinal variation of the specific local time of post-midnight enhancement peaks using ionosondes distributed at low latitudes. To obtain the parameters of the ionosphere, we manually extracted ionograms recorded by ionos...
Article
Full-text available
This paper presents a new method to reconstruct the vertical electron density profile based on vertical Total Electron Content (TEC) using the simulated annealing algorithm. The present technique used the Quasi-parabolic segments (QPS) to model the bottomside ionosphere. The initial parameters of the ionosphere model were determined from both Inter...
Article
Full-text available
The equatorial zonal electric field responses to prompt penetration of eastward convection electric fields (PPEF) were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 March 2015. At dusk sector (Indian longitudes), a rapid uplift of equatorial F layer to >550km and developm...
Article
Simultaneous observations of F2 layer stratification and spread F at postmidnight (00:00 LT to 05:00 LT) were carried out on 22, 23, and 28 November 2013, using ionosondes distributed over a northern equatorial anomaly region at three specific locations, i.e., Puer (PUR, 22.7°N, 101.05°E, dip latitude 12.9°N), Chiang Mai (CMU, 18.8°N, 98.9°E, dip l...
Conference Paper
Malaysia Real-Time Kinematics GNSS Network (MyRTKnet) which consists of 78 GPS receivers was used to investigate the occurrence of equatorial plasma bubble (EPB) along 96°E–120°E longitude. In this study, we present the monthly occurrence rate of EPB along the geographical longitudes of 96°E–120°E for a half of solar cycle period (2008–2013). A 2D...
Article
The unusual evolution of fresh and intense field-aligned irregularities (FAI) near sunrise terminator which further sustained for more than 90 min of postsunrise period was observed by Equatorial Atmosphere Radar at Kototabang during a minor geomagnetic storm period. These FAI echoes were initially observed around 250–350 km altitudes, growing upwa...
Article
Full-text available
To reveal the temporal change of the equatorial ionization anomaly (EIA) asymmetry, a multipoint satellite-ground beacon experiment was conducted along the meridional plane of the Thailand–Indonesia sector. The observation includes one station near the magnetic equator and four stations at off-equator latitudes. This is the first EIA asymmetry stud...
Article
Using the fan sector backscatter maps of 47 MHz Equatorial Atmosphere Radar (EAR) at Kototabang (0.2oS geog. lat, 100.3oE geog. long and 10.4oS geomag. lat), Indonesia, the spatial and temporal evolution of equatorial plasma bubbles (EPBs) were examined to classify the evolutionary type EPBs from those which formed elsewhere and drifting into the f...
Article
A new three-dimensional high-resolution numerical model to study equatorial plasma bubble (EPB) has been developed. The High-Resolution Bubble (HIRB) model is developed in a magnetic dipole coordinate system for the equatorial and low-latitude ionosphere with a spatial resolution of as fine as 1 km. Adopting a higher-order numerical scheme than tho...
Article
High-density GPS receivers located in Southeast Asia (SEA) were utilized to study the two-dimensional structure of ionospheric plasma irregularities in the equatorial region. The longitudinal and latitudinal variations of tens of kilometer-scale irregularities associated with equatorial plasma bubbles (EPBs) were investigated using two-dimensional...
Article
Total electron content (TEC) is an important parameter for revealing latitudinal ionospheric structures, such as the equatorial ionization anomaly (EIA) in Southeast Asia. Understanding the EIA is beneficial for studying equatorial spread F. To reveal the structures, the absolute TEC as a function of latitude must be accurately determined. In early...