Discovery of correlated evolution in noise storm source parameters: Insights on $\vec{B}$ dynamics during a microflare
by A. Mohan

2021-04-13 269 views

Solar noise storms are known to be related to small and large scale magnetic field enhancements at active regions (Elgaroy 1977, Li et al.,2017). However, the mechanism still remain unclear. Their high spectro-temporal variability and ubiquity of weak events demanded sub-second and sub-MHz scale imaging with high dynamic ranges (DRs) to reliably study emission from individual sources. Using high DR snapshot spectroscopic images from the Murchison Widefield Array, this work […]

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

2021-02-02 197 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 […]

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

2020-06-30 177 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 […]

A microflare associated with periodic particle acceleration
by A. Mohan et al.*

2019-10-29 444 views

Microflares are weaker cousins of large flares with 103 to 106 times less energies. They are also much more ubiquitous and frequent than larger flares. A very common phenomena of the Extreme Ultra-Violet (EUV) corona, namely the Active Region Transient Brightening (ARTB; Shimizu, 1996) event is known to be associated with microflares. The ARTBs are associated with active coronal loops of length ranging from 5 – 40 Mm and often […]

Unsupervised Generation of High Dynamic Range Solar Images: A Novel Algorithm for Self-calibration of Interferometry Data
by Surajit Mondal et al.*

2019-07-16 256 views

Imaging the sun at radio wavelengths with high fidelity is an intrinsically hard problem. This stems from: a) the large range of angular scales on which the emission is present; b) the huge difference in brightness temperature associated with the various emission mechanisms which are responsible for radio emission; and c) high variability of solar emission on small temporal (<1s) and spectral (~kHz) scales. These together imply that the uv […]

Coronal Densities Probed by Type III Radio Burst Imaging
by P. McCauley et al.*

2018-11-13 335 views

Type III solar radio bursts are caused by electron beams accelerated to modest fractions of light speed by magnetic reconnection, the process that drives solar flares. The beams stimulate oscillations in the ambient plasma, which in turn produce short periods of intense radio emission. The standard theory predicts emission at either the fundamental electron plasma frequency (fp) or its harmonic (2fp). These values are proportional to the square root of […]

Wavelet-based characterization of small-scale solar emission features at low radio frequencies
by A. Suresh et al.*

2017-08-15 662 views

The improved sensitivity provided by new-generation radio arrays has unveiled an enormous diversity of previously under-appreciated solar radio bursts. Observations in the 100-240 MHz band using the Murchison Widefield Array (MWA) have highlighted the presence of a myriad of weak, short-lived, narrow-band solar emission features (Fig. 1), even during calm solar periods. Their appearance in the MWA solar dynamic spectrum (DS) comes closest to miniature versions of type-III bursts with […]