Probing the Temperature Structure of the Solar Chromosphere with ALMA by C. Alissandrakis et al.*

2017-08-01

Determining the detailed temperature structure of the solar atmosphere from observations is a basic means of constructing and testing atmospheric models. One avenue to address this problem is based on measuring the center-to-limb variation of the intensity in various spectral regions. Observations in the radio domain are particularly suited for such a task since they don’t suffer from a set of complications (e.g., departures from the ionization and local thermodynamic […]

Oscillation of solar radio emission at coronal acoustic cut-off frequency by T. Zaqarashvili et al.

2017-07-25

Recent SECCHI COR2 observations on board the STEREO-A spacecraft have detected density structures at a distance of 2.5-15 R$_{\odot}$ propagating with periodicity of about 90 minutes (Viall and Vourlidas 2015). The authors suggested that the density structures probably formed in the lower corona. We analyzed radio emission at the frequencies of 8–32 MHz, which correspond to a distance of about 1.5–2.5 R$_{\odot}$ according to the Baumbach-Allen model of coronal electron […]

Siberian Radioheliograph: First Results by S.V. Lesovoi et al.*

2017-07-11

Regular observations of the Sun have started at the first stage of the multiwave Siberian Radioheliograph (SRH). It is a T-shaped interferometer currently consisting of 48 antennas observing in a 4-8 GHz operating frequency range with a 10 MHz instantaneous receiving band. The SRH’s antennas are installed on the central antenna posts of the Siberian Solar Radio Telescope (SSRT: Grechnev et al., 2003). The maximum baseline is currently 107.4 m […]

The 30 cm solar radio flux: a new proxy for upper atmosphere specification by Thierry Dudok de Wit and Sean Bruinsma

2017-06-27

The 10.7 cm solar radio flux is a widely (if not the most widely) used proxy for solar activity. However, other centimetric wavelengths have also been monitored, some routinely and for several decades. Such observations provide unique records of long-term solar variability. We find that the radio flux at 30 cm receives relatively stronger contributions from Bremsstrahlung vs gyro-resonance emissions (as compared to the 10.7 cm flux); as a consequence, […]

Particle acceleration and turbulence during a solar flare by E.P. Kontar et al.*

2017-06-13

Particle acceleration during solar flares is a highly efficient process, in terms of both the energy (tens of percent of the released magnetic energy can be transferred to the energetic particles) and the particle number (nearly all electrons in the flaring region are accelerated). So-called stochastic acceleration (e.g., Petrosian 2012 for a review) is one of the most popular mechanisms capable of providing these characteristics. In this scenario, the magnetic […]

Solar wind density turbulence from 10 to 45 solar radii by K. Sasikumar Raja et al.*

2017-06-06

The extended solar corona and the solar wind is a rich testbed for studying the properties of magnetohydrodynamic (MHD) turbulence. While most solar wind turbulence theories only treat incompressible turbulence, density irregularities are present in the solar wind, and are manifested through fluctuations in the refractive index. Knowledge of density turbulence impacts our understanding of the solar wind significantly, and is important for interpreting a variety of observations. It is […]

Multi-Loop Structure of Nonthermal Microwave Sources in a Major Long-Duration Flare by V. Grechnev et al.*

2017-05-23

Hard X-ray (HXR) and microwave observations of flares show only a few nonthermal sources. They are simple and compact, especially in impulsive flares, suggesting involvement of one to two loops. Hanaoka (1996) and Nishio et al. (1997) interpreted these observations in terms of double-loop flares. This view was later extended up to long-duration flares (Tzatzakis, Nindos, and Alissandrakis, 2008). A concept of a simple flare loop became dominant. However, observations […]

Comparison of alternative zebra-structure models in solar radio emission by G.P. Chernov et al.*

2017-05-16

Discussion about the nature of zebra-structure (ZS) in type IV radio bursts continues, despite the ten proposed models. First of all, this is due to the wide variety of stripes in each new phenomenon, making the explanation of all the fine details by any one mechanism becomes impossible. The most widespread explanation is the emission at different levels of double plasma resonance (DPR), sequential on the height surfaces in the magnetic […]

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