quiet Sun

Spectroscopic Imaging of the Sun with MeerKAT: Opening a New Frontier in Solar Physics by Kansabanik et al.

2024-04-10

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 […]

Radio Interferometric Observations of the Sun Using Commercial Dish TV Antennas
by G. V. S. Gireesh et al.*

2021-11-09

Commercial dish TV antennas are parabolic structures designed to receive radio waves from a communication satellite. The antennas and the associated front end receiver systems have improved with advances in the TV systems. They operate typically over the frequency range 10.7 – 11.7 GHz (Ku-band) and provide very good signal-to-noise ratio (SNR). It is well known that the Sun emits intense radio emission in the above frequency range with brightness […]

Radio, X-ray and extreme-ultraviolet observations of weak energy releases in the ‘quiet’ Sun
by Ramesh et. al.

2021-10-26

Small scale energy releases on the Sun e.g., flaring bright points, active region transient brightenings, etc. have been studied using X-ray and radio observations. The observations of low frequency radio type III bursts in associated with X-ray bright point flares (Kundu et. al. 1980) and coronal X-ray jets (Aurass et. al. 1994) indicated that the latter are capable of accelerating particles to non-thermal energies, as well as producing the heated […]

Propagation Effects in Quiet Sun Observations at Meter Wavelengths
by R. Sharma and D. Oberoi

2021-02-02

The quiet Sun coronal emission dominantly comes from thermal bremsstrahlung. As this radiation traverses the coronal medium on its way to the Earthbound observer, the coronal optical depth, τ, along typical ray paths is neither low enough to be approximated as optically thin, nor high enough to be treated as optically thick. On its way to the observer, it gets modified substantially due to propagation effects —primarily refraction and scattering—through the […]

Low frequency radio observations of the ‘quiet’ corona during the descending phase of sunspot cycle 24
by R. Ramesh et al.*

2020-10-13

The shape, size and electron density (Ne) of the corona varies with the sunspot cycle, which is now very well established by white-light observations. In our study, we investigated the ‘quiet’ solar corona (i.e., the corona distinct from emission due to transient and long-lasting discrete sources) at radio frequencies during the descending phase of sunspot cycle 24. We used the radio images obtained with the Gauribidanur RAdioheliograPH (GRAPH; Ramesh1998) at […]

First radio evidence of impulsive heating contribution to the quiet solar corona
by Surajit Mondal et al

2020-06-30

The solar community has been trying to understand the mechanism responsible for coronal heating for several decades now. In the past decade, a number of studies have shown that the active regions and the coronal loops are heated impulsively. However, such a consensus is yet to be reached for the quiet sun. Past searches for impulsive events in the EUV and X-ray are yet to provide conclusive evidence in favour […]

Synthetic Radio Imaging in Quiet and Eruptive Solar Cases
by S. P. Moschou et. al.*

2019-01-15

A diverse set of radio production mechanisms makes the radio wavelengths a unique observational window into the universe. Radio emission can be produced by both quiescent and eruptive phenomena, e.g. flares and coronal mass ejections (CMEs). The morphology of the quiet Sun in radio depends on macroscopic MHD quantities, such as the density, the temperature and the magnetic field, and the type of the emission. Lee at al. (2009) showed […]

First high-resolution look at the quiet Sun with ALMA at 3 mm
by A. Nindos et al.*

2018-11-27

Observations of the radio continuum at millimeter (mm) wavelengths provide a unique chromospheric diagnostic. The quiet Sun mm-wavelength emission mechanism is free-free and electrons are almost always in local thermodynamic equilibrium (e.g. Shibasaki et al. 2011 and Wedemeyer et al. 2016). The availability of mm-wavelength solar observations with ALMA can advance our knowledge on the chromosphere because of the instrument’s unique spatial resolution and sensitivity. In a previous study (Alissandrakis […]

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