We report ground based, low frequency heliograph (80 MHz), spectral MHz) and polarimeter (80 and 40 MHz) observations of drifting, non-thermal radio continuum associated with the 'halo' coronal mass ejection (CME) that occurred in the solar atmosphere on 2013 March 15. The magnetic field strengths (B) near the radio source were estimated to be B ≈ 2.2 ± 0.4 G at 80 MHz and B ≈ 1.4±0.2 G at 40 MHz. The corresponding radial distances (r) are r ≈ 1.9 R ⊙ (80 MHz) and r ≈ 2.2 R ⊙ (40 MHz). Subject headings: Sun -activity: Sun -flares: Sun -corona: Sun -radio radiation: Sun: coronal mass ejections (CMEs): Sun -magnetic topologythe referee for his/her comments that helped to bring out the results more clearly. The SOHO data are produced by a consortium of the Naval Research Laboratory (USA),

We report low-frequency (80 MHz) radio observations of circularly polarized non-thermal type I radio bursts ("noise storms") in the solar corona whose estimated energy is ∼10 21 erg. These are the weakest energy release events reported to date in the solar atmosphere. The plot of the distribution of the number of bursts (dN) versus their corresponding peak flux density in the range S to S + dS shows a power-law behavior, i.e., dN ∝ S γ dS. The power-law index γ is in the range −2.2 to −2.7 for the events reported in the present work. The present results provide independent observational evidence for the existence of picoflare category energy releases in the solar atmosphere which are yet to be explored.

We report on the amplitude of the density turbulence spectrum ( CN2) and the density modulation index (δN/N) in the solar wind between 10 and 45R⊙. We derive these quantities using a structure function that is observationally constrained by occultation observations of the Crab nebula made in 2011 and 2013 and similar observations published earlier. We use the most general form of the structure function, together with currently used prescriptions for the inner/dissipation scale of the turbulence spectrum. Our work yields a comprehensive picture (a) of the manner in which CN2 and δN/N vary with heliocentric distance in the solar wind and (b) of the solar cycle dependence of these quantities.

Eruptive activity in the solar corona can often lead to the propagation of shock waves. In the radio domain the primary signature of such shocks are type II radio bursts, observed in dynamic spectra as bands of emission slowly drifting toward lower frequencies over time. These radio bursts can sometimes have an inhomogeneous and fragmented fine structure, but the cause of this fine structure is currently unclear. Here we observe a type II radio burst on 2019 March 20th using the New Extension in Nançay Upgrading LOFAR, a radio interferometer observing between 10-85 MHz. We show that the distribution of size scales of density perturbations associated with the type II fine structure follows a power law with a spectral index in the range of α = −1.7 to −2.0, which closely matches the value of −5/3 expected of fully developed turbulence. We determine this turbulence to be upstream of the shock, in background coronal plasma at a heliocentric distance of ∼2 R e . The observed inertial size scales of the turbulent density inhomogeneities range from ∼62 Mm to ∼209 km. This shows that type II fine structure and fragmentation can be due to shock propagation through an inhomogeneous and turbulent coronal plasma, and we discuss the implications of this on electron acceleration in the coronal shock.Unified Astronomy Thesaurus concepts: Solar physics (1476); Solar coronal mass ejections (310); Solar coronal mass ejection shocks (1997); Solar particle emission (1517)