33 citations · 425 across the 25 of their papers we have counts for
25 papers
Application of Novel Interplanetary Scintillation Visualisations using LOFAR: A Case Study of Merged CMEs from September 2017
R. A. Fallows, K. Iwai, B. V. Jackson +3
Observations of interplanetary scintillation (IPS - the scintillation of compact radio sources due to density variations in the solar wind) enable the velocity of the solar wind to…
Magnetohydrodynamic simulation of coronal mass ejections using interplanetary scintillation data observed from radio sites ISEE and LOFAR
Kazumasa Iwai, Richard A. Fallows, Mario M. Bisi +4
Interplanetary scintillation (IPS) is a useful tool for detecting coronal mass ejections (CMEs) throughout interplanetary space. Global magnetohydrodynamic (MHD) simulations of the…
Solar Observing with the Atacama Large Millimeter-Submillimeter Array
Timothy Bastian, Masumi Shimojo, Miroslav Barta +2
The Atacama Large Millimeter-submillimeter Array (ALMA), sited on the high desert plains of Chajnantor in Chile, has opened a new window onto solar physics in 2016 by providing con…
Over seven decades of solar microwave data obtained with Toyokawa and Nobeyama Radio Polarimeters
Masumi Shimojo, Kazumasa Iwai
Monitoring observations of solar microwave fluxes and their polarization began in Japan during the 1950s at Toyokawa and Mitaka. At present (April 2022), monitoring observations co…
Testing the Alfvén-wave model of the solar wind with interplanetary scintillation
Munehito Shoda, Kazumasa Iwai, Daikou Shiota
Understanding the mechanism(s) of the solar wind acceleration is important in astrophysics and geophysics. A promising model of the solar wind acceleration is known as the wave/tur…
Validation of Coronal Mass Ejection Arrival-Time Forecasts by Magnetohydrodynamic Simulations based on Interplanetary Scintillation Observations
Kazumasa Iwai, Daikou Shiota, Munetoshi Tokumaru +3
Coronal mass ejections (CMEs) cause various disturbances of the space environment; therefore, forecasting their arrival time is very important. However, forecasting accuracy is hin…
Estimating the temperature and density of a spicule from 100 GHz data obtained with ALMA
Masumi Shimojo, Tomoko Kawate, Takenori J. Okamoto +6
We succeeded in observing two large spicules simultaneously with the Atacama Large Millimeter/submillimeter Array (ALMA), the Interface Region Imaging Spectrograph (IRIS), and the…
Spectral Structures of Type II Solar Radio Bursts and Solar Energetic Particles
Kazumasa Iwai, Seiji Yashiro, Nariaki V. Nitta +1
We investigated the relationship between the spectral structures of type II solar radio bursts in the hectometric and kilometric wavelength ranges and solar energetic particles (SE…
Development of a coronal mass ejection arrival time forecasting system using interplanetary scintillation observations
Kazumasa Iwai, Daikou Shiota, Munetoshi Tokumaru +3
Coronal mass ejections (CMEs) cause disturbances in the environment of the Earth when they arrive at the Earth. However, the prediction of the arrival of CMEs still remains a chall…
Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind Over the Solar Poles
Ken'ichi Fujiki, Kiyoto Shibasaki, Seiji Yashiro +3
We comparatively studied the long-term variation (1992-2017) in polar brightening observed with the Nobeyama Radioheliograph, the polar solar wind velocity with interplanetary scin…
Solar polar brightening and radius at 100 and 230 GHz observed by ALMA
Caius L. Selhorst, Paulo J. A. Simões, Roman Brajša +8
Polar brightening of the Sun at radio frequencies has been studied for almost fifty years and yet a disagreement persists between solar atmospheric models and observations. Some ob…
Solar ALMA observations: constraining the chromosphere above sunspots
Maria Loukitcheva, Kazumasa Iwai, Sami K. Solanki +2
We present the first high-resolution Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a sunspot at wavelengths of 1.3 mm and 3 mm, obtained during the solar ALMA…
Variation of Solar Microwave Spectrum in the Last Half Century
M. Shimojo, K. Iwai, A. Asai +3
The total solar fluxes at 1, 2, 3.75, and 9.4 GHz were observed continuously from 1957 to 1994 at Toyokawa, and from 1994 until now at Nobeyama, Japan with the current Nobeyama Rad…
Polarization Characteristics of Zebra Patterns in Type IV Solar Radio Bursts
Kazutaka Kaneda, H. Misawa, K. Iwai +4
The polarization characteristics of zebra patterns (ZPs) in type IV solar bursts were studied. We analyzed 21 ZP events observed by the Assembly of Metric-band Aperture Telescope a…
OCTAD-S: Digital Fast Fourier Transform Spectrometers by FPGA
Kazumasa Iwai, Yûki Kubo, Hiromitsu Ishibashi +5
We have developed a digital fast Fourier transform (FFT) spectrometer made of an analog-to-digital converter (ADC) and a field-programmable gate array (FPGA). The base instrument h…
ALMA Discovery of Solar Umbral Brightness Enhancement at λ=3 mm
Kazumasa Iwai, Maria Loukitcheva, Masumi Shimojo +2
We report the discovery of a brightness enhancement in the center of a large sunspot umbra at a wavelength of 3 mm using the Atacama Large Millimeter/sub-millimeter Array (ALMA). S…
First ALMA Observation of a Solar Plasmoid Ejection from an X-ray Bright Point
M. Shimojo, H. S. Hudson, S. M. White +2
Eruptive phenomena such as plasmoid ejections or jets are an important feature of solar activity with the potential for improving our understanding of the dynamics of the solar atm…
The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm
Kazumasa Iwai, Masumi Shimojo, Shinichiro Asayama +4
The absolute brightness temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this pro…
Chromospheric sunspots in the millimeter range as observed by the Nobeyama Radioheliograph
Kazumasa Iwai, Hideki Koshiishi, Kiyoto Shibasaki +3
We investigate the upper chromosphere and the transition region of the sunspot umbra using the radio brightness temperature at 34 GHz (corresponding to 8.8-mm observations) as obse…
Coronal Magnetic Fields Derived from Simultaneous Microwave and EUV Observations and Comparison with the Potential Field Model
Shun Miyawaki, Kazumasa Iwai, Kiyoto Shibasaki +2
We estimated the accuracy of coronal magnetic fields derived from radio observations by comparing them to potential field calculations and the DEM measurements using EUV observatio…
Frequency Dependence of Polarization of Zebra Pattern in Type-IV Solar Radio Bursts
Kazutaka Kaneda, Hiroaki Misawa, Kazumasa Iwai +2
We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the gen…
Observation of Chromospheric Sunspot at Millimeter Range with the Nobeyama 45 m Telescope
Kazumasa Iwai, Masumi Shimojo
The brightness temperature of the radio free-free emission at millimeter range is an effective tool for characterizing the vertical structure of the solar chromosphere. In this pap…
Coronal magnetic field and the plasma beta determined from radio and multiple satellite observations
Kazumasa Iwai, Kiyoto Shibasaki, Satoshi Nozawa +5
We derived the coronal magnetic field, plasma density, and temperature from the observation of polarization and intensity of radio thermal free-free emission using the Nobeyama Rad…
Spectral Structures and Their Generation Mechanisms for Solar Radio Type-I Bursts
Kazumasa Iwai, Yoshizumi Miyoshi, Satoshi Masuda +3
The fine spectral structures of solar radio type-I bursts were observed by the solar radio telescope AMATERAS. The spectral characteristics, such as the peak flux, duration, and ba…