Papers - IWAI Kazumasa

PEAK FLUX DISTRIBUTIONS OF SOLAR RADIO TYPE-I BURSTS FROM HIGHLY RESOLVED SPECTRAL OBSERVATIONS Reviewed

K. Iwai, S. Masuda, Y. Miyoshi, F. Tsuchiya, A. Morioka, H. Misawa

ASTROPHYSICAL JOURNAL LETTERS   Vol. 768 ( 1 ) page： L2   2013.5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Solar radio type-I bursts were observed on 2011 January 26 by high resolution observations with the radio telescope AMATERAS in order to derive their peak flux distributions. We have developed a two-dimensional auto burst detection algorithm that can distinguish each type-I burst element from complex noise storm spectra that include numerous instances of radio frequency interference (RFI). This algorithm removes RFI from the observed radio spectra by applying a moving median filter along the frequency axis. Burst and continuum components are distinguished by a two-dimensional maximum and minimum search of the radio dynamic spectra. The analysis result shows that each type-I burst element has one peak flux without double counts or missed counts. The peak flux distribution of type-I bursts derived using this algorithm follows a power law with a spectral index between 4 and 5.

DOI： 10.1088/2041-8205/768/1/L2

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IPRT/AMATERAS: A New Metric Spectrum Observation System for Solar Radio Bursts Reviewed

K. Iwai, F. Tsuchiya, A. Morioka, H. Misawa

SOLAR PHYSICS   Vol. 277 ( 2 ) page： 447 - 457   2012.4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A new radio spectropolarimeter for solar radio observation has been developed at Tohoku University and installed on the Iitate Planetary Radio Telescope (IPRT) at the Iitate observatory in Fukushima prefecture, Japan. This system, named AMATERAS (the Assembly of Metric-band Aperture TElescope and Real-time Analysis System), enables us to observe solar radio bursts in the frequency range between 150 and 500 MHz. The minimum detectable flux in the observation frequency range is less than 0.7 SFU with an integration time of 10 ms and a bandwidth of 61 kHz. Both left and right polarization components are simultaneously observed in this system. These specifications are accomplished by combining the large aperture of IPRT with a high-speed digital receiver. Observational data are calibrated and archived soon after the daily observation. The database is available online. The high-sensitivity observational data with the high time and frequency resolutions from AMATERAS will be used to analyze spectral fine structures of solar radio bursts.

DOI： 10.1007/s11207-011-9919-y

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SOLAR RADIO TYPE-I NOISE STORM MODULATED BY CORONAL MASS EJECTIONS Reviewed

K. Iwai, Y. Miyoshi, S. Masuda, M. Shimojo, D. Shiota, S. Inoue, F. Tsuchiya, A. Morioka, H. Misawa

ASTROPHYSICAL JOURNAL   Vol. 744 ( 2 ) page： 167   2012.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The first coordinated observations of an active region using ground-based radio telescopes and the Solar Terrestrial Relations Observatory (STEREO) satellites from different heliocentric longitudes were performed to study solar radio type-I noise storms. A type-I noise storm was observed between 100 and 300 MHz during a period from 2010 February 6 to 7. During this period the two STEREO satellites were located approximately 65. (ahead) and -70 degrees (behind) from the Sun-Earth line, which is well suited to observe the earthward propagating coronal mass ejections (CMEs). The radio flux of the type-I noise storm was enhanced after the preceding CME and began to decrease before the subsequent CME. This time variation of the type-I noise storm was directly related to the change of the particle acceleration processes around its source region. Potential-field source-surface extrapolation from the Solar and Heliospheric Observatory/ Michelson Doppler Imager (SOHO/ MDI) magnetograms suggested that there was a multipolar magnetic system around the active region from which the CMEs occurred around the magnetic neutral line of the system. From our observational results, we suggest that the type-I noise storm was activated at a side-lobe reconnection region that was formed after eruption of the preceding CME. This magnetic structure was deformed by a loop expansion that led to the subsequent CME, which then suppressed the radio burst emission.

DOI： 10.1088/0004-637X/744/2/167

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