Solar Radio Science Highlights

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 […]

Microwave emission as a proxy of CME speed in ICME forecasting
by Carolina Salas Matamoros, Ludwig Klein and Gerard Trottet

2017-05-09

Coronal Mass Ejections (CMEs) are one type of interplanetary structure that mostly affect the geomagnetic field (e.g. Gonzalez and Tsurutani, 1987; Zhang et al, 2007). These structures are observed and studied through coronagraphic images. The basic limitation of the coronagraph is that it shows the corona only in the plane of the sky, and blocks by necessity the view on the solar disk. Thus, the projection effect in the kinematic […]

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

2017-04-25

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 […]

How Electron Beams Produce Continuous Coherent Plasma Emission
by H. Che, M. Goldstein, P. Diamond, and R. Sagdeev

2017-04-11

It is commonly accepted that energetic electron beams can produce drift frequency radio emission or Type III bursts since Ginzburg and Zhelezniakov first proposed the idea in 1958. However, the electron two-stream instability time (see reference 2) in the corona is fraction of a second, while the duration of coronal Type III bursts lasts several orders of magnitude longer. This problem is called the “Sturrock Dilemma” and remains a subject […]

Radio Diagnostics of Electron Acceleration Sites During the Eruption of a Flux Rope in the Solar Corona
by Eoin Carley et al.*

2017-03-28

Flares and coronal mass ejections (CMEs) are thought to result from magnetic energy release in the solar corona, often involving the destabilisation of a twisted magnetic structure known as a flux rope (Chen et al. 2011, Webb et al. 2012). This activity may be accompanied by the acceleration of electrons (Kahler 2007, Lin et al. 2011). However, there is ongoing debate on exactly where, when and how this particle acceleration occurs […]

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