First Type III Solar Radio Bursts of Solar Cycle 25

The minimum of the previous solar cycle, Solar Cycle 24, occurred in December 2019, which also marked the start of the new Solar Cycle 25. The first radio bursts of the new solar cycle were observed in the spring season 2020. In this work we will present three type III solar bursts which were observed in May and June 2020 at radio frequencies between 18 – 90 MHz. There are two radio observatories in Finland that are capable of doing low-frequency solar radio observations: Aalto University Metsähovi Radio Observatory (MRO) and Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) of the Sodankylä Geophysical Observatory, University of Oulu. The instruments of the two institutes have different design and characteristics, and they operate in rather different radio interference environments. We will compare simultaneous observations from these two instruments and we will also discuss the properties of these type III solar bursts.

Observations of Solar Type III radio bursts by Cassini/RPWS experiment

In this study, we report on the occurrence of solar Type III radio bursts recorded by radio and plasma wave experiment (RPWS) experiment onboard Cassini spacecraft. This instrument is designed to investigate the Saturn's plasma environment and sub-auroral radio missions. RPWS/Cassini experiment allows to measure electric field over a frequency range from 1 Hz to 16 MHz (Gurnett et al., 2004). The essential observed emission is associated to the Saturnian Kilometric Radiation (SKR) which is generated in the sub-auroral regions of the magnetosphere. The capability of this experiment leads to detect Solar Type III radio bursts recorded during the increase phase of the solar activity, i.e. January 2008 to December 2014. Hence we have found more than 300 Type III solar bursts when the distance of Cassini to the Sun was about 10 AU. Observational parameters like the time occurrence, the emission frequency and the relative intensity are considered in this analysis. Those features lead us to characterize the detection conditions and to estimate the occurrence variabilities of Type III bursts.

Solar Type III radio bursts at Saturn’s orbit: Case study of stereoscopic observations by Cassini/RPWS and Wind/WAVES experiments

<p>Type III radio bursts are produced by electron beams accelerated in active regions and following open magnetic field lines. Type III observed frequency is found to be nearly equal to the plasma frequency directly linked to the local electron density. The source regions of such solar bursts are the solar corona and the interplanetary medium where, respectively, higher and lower frequencies are generated. In this work, we consider specific Type III solar bursts simultaneously observed by Cassini/RPWS and Wind/WAVES experiments. Despite the distance of Cassini spacecraft to the Sun such Type III bursts have been detected at Saturn’s orbit, i.e. at about 10AU. Those considered bursts are covering a frequency bandwidth from about 10 MHz down to 100 kHz. We attempt in this study to characterize the spectral pattern, i.e. the flux density versus the observation time and the frequency range, and the visibility of the source regions to the observer (i.e. Wind and Cassini spacecraft). In this context, we analyze the evolution of the Type III bursts from the solar corona and up to Saturn’s orbit taking into consideration the Archimedean spiral which is the geometrical configuration of the solar magnetic field extension in the interplanetary medium. We principally discuss the physical parameters, i.e. solar wind speed and the electron density, which lead to constraint the location of the source region and its visibility to both spacecraft.</p>

The RPW Time Domain Sampler (TDS) on Solar Orbiter: In-flight performance and first data

<p>The Radio and Plasma Wave instrument (RPW) for Solar Orbiter includes a Time Domain Sampler sub-unit (TDS) designed to capture electromagnetic waveform measurements of high-frequency plasma waves and antenna voltage spikes associated with dust impacts. TDS will digitize three components of the electric field and one magnetic component at 524 kHz sampling rate and scan the obtained signal for plasma waves and dust impact signatures. The main science target of TDS are Langmuir waves observed in the solar wind in association with Type II and Type III solar bursts, interplanetary shocks, magnetic holes, and other phenomena. In this poster, we present the scientific data products provided by the TDS instrument and discuss the first data obtained during the commissioning phase. The first data will be used to evaluate the actual performance of the RPW TDS instrument.</p>