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

2021-02-02 187 views

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.*

2020-10-13 303 views

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

2020-06-30 174 views

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.*

2019-01-15 378 views

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.*

2018-11-27 497 views

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 […]

The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm
by Kazumasa Iwai et al

2017-04-25 1,015 views

The brightness temperature of the Sun constitutes a basic property of the solar atmosphere. The main emission mechanism of the Sun at millimeter and submillimeter wavelengths is thermal free–free emission from the chromosphere, which is an atmospheric layer with a temperature ranging between 6000 to 20,000 K. The opacity of thermal free–free emission depends on the temperature and density in the emission region. In addition, the Rayleigh– Jeans law is applicable […]