受賞区分：国内学会・会議・シンポジウム等の賞  受賞国：日本国

受賞区分：国内学会・会議・シンポジウム等の賞  受賞国：日本国

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astronomy and Astrophysics  

Context. Recent in situ observations and numerical models indicate that various types of magnetohydrodynamic (MHD) waves contribute to the solar wind acceleration. Among them is an MHD wave decomposition at distances closer than 50 R using data taken by the first perihelion pass of Parker Solar Probe (PSP). However, the underlying physical processes responsible for the formation of the solar wind have not yet been observationally confirmed at distances closer than 10 R . Aims. We aim to infer the mode population of density fluctuations observed by radio occultation, which has all been attributed to slow magnetoacoustic waves. Methods. We compare the radio occultation observations conducted in 2016 using the JAXA’s Venus orbiter Akatsuki with the MHD simulation. The time-frequency analysis was applied to the density fluctuations observed by the radio occultation and those reproduced in the MHD model. Results. The time-spatial spectrum of the density fluctuation in the model exhibits two components that are considered to be fast and slow magnetoacoustic waves. The fast magnetoacoustic waves in the model tend to have periods shorter than the slow magnetoacoustic waves, and the superposition of these modes has a broadened spectrum extending in the range of approximately 20−1000 s, which resembles that of the observed waves. Conclusions. Based on this comparison, it is probable that the density oscillations observed by radio occultation include fast and slow magnetoacoustic waves, and that fast magnetoacoustic waves are predominant at short periods and slow magnetoacoustic waves are prevalent at long periods. This is qualitatively similar to the results of the mode decomposition obtained from the PSP’s first perihelion at more distance regions.

DOI： 10.1051/0004-6361/202449189

Open Access

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

A radio link directly probing the inner solar corona offers the possibility to characterize solar wind properties, including velocity, density, turbulence, and even the axial ratio. In this study, we leveraged radiometric data obtained during a joint superior solar conjunction of the ESA/JAXA BepiColombo mission and the JAXA Akatsuki mission. Our objective is to ascertain the solar wind velocity by analysing Doppler-shift timeseries of radio signals exchanged between the two spacecraft and two distinct ground stations. We conducted a cross-correlation analysis to determine the travel time of large-scale plasma density fluctuations as they intersect with the downlink signals of both spacecraft. This method is applied to the data collected on 2021 March 13 and 2021 March 14. The analysis of the March 13 data has shown that the two Doppler residuals timeseries present a clear correlation at a time-lag of 2910 s. Using the knowledge of the relative distance between the two probe-ground station lines of sight at the closest approach to the Sun, we estimated the solar wind velocity to be 421 ± 21 km s−1. Following the same procedure for the second experiment, we estimated the solar wind speed velocity to be 336 ± 7 km s−1. These results are compatible with the sampling of the slow solar wind at heliographic latitudes of −22◦ and −26◦, respectively.

DOI： 10.1093/mnras/stae1929

Open Access

Web of Science

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s11207-022-01968-9