Since the discovery of solar radio emission in the late 1940s, the Sun has been studied in great detail across a wide range of frequencies from a few tens of kHz to several hundreds of GHz. Solar radio emissions provide several unique diagnostics of the solar corona, which are otherwise simply inaccessible. Despite this long history of observations and studies, the Sun still harbors several mysteries. Improved observations from the new telescopes enabled by technological advances help solve these mysteries. At the same time, these new advancements probe the Sun in ways not possible earlier ..read more

The study of solar wind acceleration and coronal heating has been a major challenge in solar physics. The main difficulty is that the collisionless characteristic of high-temperature, thin, and fully ionized coronal plasmas lead to the heating and acceleration of the coronal plasmas to be dominated by wave particle interactions, which are the “elementary processes” of the plasma collective interaction at the kinetic scales of plasma particles. Radio observation becomes main information sources of the coronal plasmas, instead of the spectral line observation, which is a main method of inferri ..read more

The turbulent heliosphere has a significant effect on the observed characteristics of radio emission produced in, or viewed through, the solar atmosphere. In particular, radio-wave scattering on density irregularities can broaden the observed decay times and source sizes, and shift the apparent source position. Both radio burst observations and simulations have demonstrated that the turbulence is anisotropic, which can explain both the observed decay times and source sizes simultaneously. Considering that the same density turbulence modifies extra solar and solar sources, and the density flu ..read more

Recent years, several new generation solar radio telescopes operating in the centimeter decimeter (dm-cm) wavelengths have emerged in the world, including the Mingantu Spectral Radioheliograph (MUSER, 0.4-15GHz) (Yan et al. 2021), the Expanded Owens Valley Solar Array (EOVSA, 1-18GHz) (Gary et al. 2018), and the Siberian Radio Heliograph (SRH, 3-24GHz) (Altyntsev et al. 2020). Due to the fact that the solar radio emission in dm-cm wavelengths mainly originates from the solar burst source region and the primary propagation region of released energy and accelerated high-energy particles, the o ..read more

Density turbulence in the solar corona and solar wind is evident via the properties of solar radio bursts; angular scattering-broadening of extra-solar radio sources observed through the solar atmosphere, and can be measured in-situ in the solar wind. A viable density turbulence model should simultaneously explain all three types of density fluctuation observations. Solar radio bursts (e.g. Type I, II, III) observed below ~1 GHz are produced predominantly via plasma mechanisms at frequencies that are close to either the local plasma frequency or its double (harmonic), and are thus particular ..read more

Coronal mass ejections (CMEs) are large-scale expulsion of plasma and magnetic fields from the solar corona into the heliosphere. Magnetic field entrained in the CME plasma is crucial to understand their propagation, evolution, and geo-effectiveness. Among the different observables at radio wavelengths, spectral modeling of faint gyrosynchrotron (GS) emission from CME plasma has been regarded as one of the most promising remote observing techniques for estimating spatially resolved CME magnetic fields. Imaging the very low flux density CME GS emission in close proximity to the Sun with order ..read more

Type II solar bursts are radio signatures of shock waves in the solar corona driven by solar flares or coronal mass ejections. Therefore, these bursts present complex spectral morphologies in solar dynamic spectra. In particular, the radio emission lane may separate into two thinner bands that is known as band-splitting (Vršnak et al., 2002). “Fractured” type II bursts, exhibiting spectrally indented shapes in the form of bumps or breaks, are attributed to the collisions of shock waves with coronal density structures (Koval et al., 2021). Furthermore, type II burst can have a herringbone app ..read more

A long-standing problem in solar energetic particle (SEP) studies is to pinpoint their source regions at the Sun. Potential contributions by both the flare and CME-driven shocks complicate the analysis. A certain type of SEP events shows very wide particle spreads up to all around the Sun. The mechanisms proposed so far to generate these widespread events are a very wide SEP injection region, likely a shock, or strong perpendicular diffusion in the interplanetary medium (e.g., Dresing et al. 2014). Our exhaustive multi-spacecraft analysis of the 17 April 2021 widespread SEP event revealed a ..read more

Solar radio emission can be significantly influenced by Earth’s atmosphere when transmitting towards the Earth’s surface, due to atmospheric turbulence and the absorption of vapor and oxygen molecules etc. Consequently, antennas receive signals with a ‘dither’ component, indicating a noise signal exhibiting random variations. As a result, the sensitivity of observing systems distorts severely , especially for weaker radio bursts in the millimeter passband. Weak bursts can be usually observed in three ways: (1) Utilizing large antennas with a narrow beam-width at half power, (2) Compensating ..read more

Solar accelerated electron beams interact with the background plasma of the solar wind to locally generate Langmuir waves and subsequently produce radio emission (Ginzburg and Zhelezniakov 1958). Numerous observations at different distances from the Sun by spacecrafts like Solar Orbiter (0.5AU) and ACE (1AU) show different energy ranges of electrons interacting with the plasma to produce Langmuir oscillations. At 0.5AU, non-thermal electrons in the deca-keV range arrive co-temporal to the Langmuir oscillations (Gomez-Herrero et al, 2021). At 1AU, there are no associated plasma waves observed ..read more