Over seven decades of solar microwave data obtained with Toyokawa and Nobeyama Radio Polarimeters

Abstract

The Sun is a critical element of the terrestrial environment. As the range of human activities has recently expanded to include space (with, for example, commercial space travel and satellite utilization for ordinary people), the importance of predicting the near-Earth space conditions has rapidly increased. We call such space conditions 'space weather'. Solar activities, especially solar flares, and coronal mass ejections (CMEs), are the highest-priority phenomena for predicting space weather. Research in space weather is crucial not only for research on our environment but also for exoplanet studies. We have already found over 4,800 candidates for exoplanets 1 , mainly from data obtained with the Kepler satellite and the Transiting Exoplanet Survey Satellite (TESS). Studies of exoplanets

A New 6–15 GHz Solar Radio Observation System

“…The famous centimeter-band observation systems are the Expanded Owens Valley Solar Array (E-OVSA), the Solar Broadband Radio Spectrometer (SBRS) in China, the Siberia Solar Radio Telescope (SSRT), the radio spectral heliograph (MUSER), Nobeyama Radio Polarimeters (NoRP), and the Learmonth Solar Radio observation system. Their main parameters are shown in Table 1 (Zhdanov et al 2016;Zucca et al 2017;Tan et al 2019;Yan et al 2021b;Shimojo & Iwai 2023). Their observation frequency is similar to that of the CBScm, both in the centimeter band.…”

Electron Cyclotron Maser Emission and the Brightest Solar Radio Bursts

“…At 2.0 GHz, there are 353 NoRP events over 100 sfu with flux greater than at 3.75 GHz, and 380 events with smaller flux; thus the incidence of dominant coherent emission at 2.0 GHz is significantly smaller than at 1.0 GHz, as inferred previously. Some of the anomalous events in which there is high polarization at 2.0 GHz but less flux than at 3.75 GHz are found to be events in which the 2.0 GHz peak is much larger than the coeval 3.75 GHz flux, but then 3.75 GHz peaks at a very different time; others may be due to radio-frequency interference at either 3.75 GHz or 2.0 GHz (Shimojo & Iwai 2023).…”

“…Note that this is a radio-selected catalog of bursts, not flare selected, so flares in which multiple bursts occurred well separated in time, particularly at 1.0 GHz, may be represented more than once (e.g., the flare of 2006 December 13 discussed further below). Shimojo & Iwai (2023) describe the history of the NoRP data and issues at each frequency over the years that can result in spurious features, and we have tried to take these into account in the analysis. Generally, a clear burst detection at more than one frequency was required for the burst to be included in the list.…”

“…A better understanding of the occurrence of ECM on the Sun may inform broader astrophysical applications. To this end, in this paper we survey the solar radio burst measurements by the Nobeyama Radio Polarimeters (NoRP; Nakajima et al 1985;Shimojo & Iwai 2023, and references therein) at 1.0, 2.0, and 3.75 GHz since 1988. These data are available daily during Japanese daylight hours for essentially the whole period, and importantly provide circular polarization measurements absent in other comparable data sets.…”