Community of European Solar Radio Astronomers – Page 23

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 […]

Solar Science with the Atacama Large Millimeter/Submillimeter Array — A New View of Our Sun
by S. Wedemeyer

2017-03-14

The Atacama Large Millimeter/submillimeter Array (ALMA), which consists of 66 antennas placed on the Chajnantor plateau in the Chilean Andes, has already produced impressive results for a large range of astronomical objects. Regular observations of the Sun have been carried out for the first time in December 2016 and exciting results can be expected soon. ALMA combines high spatial, temporal, and spectral resolution with the diagnostic advantages of radiation at […]

Quasi-periodic acceleration of electrons in the flare on 2012 July 19
by Jing Huang et al.*

2017-02-28

We study the quasi-periodic pulsations (QPPs) of nonthermal emission in an M7.7 class flare on 2012 July 19 with spatially resolved observations at microwave and HXR bands and with spectral observations at decimetric, metric waves. Microwave emission at 17 GHz of two footpoints, HXR emission at 20–50 keV of the north footpoint and loop top, and type III bursts at 0.7–3 GHz show prominent in-phase oscillations at 270$\,$s. Through the […]

Large-scale simulations of Langmuir Wave Distributions Induced by Electron Beams
by H. Reid and E. Kontar

2017-02-14

Langmuir waves that generate type III radio bursts are excited by high-energy electron beams streaming out from the corona through interplanetary space. Despite a smooth temporal distribution of electrons, the Langmuir waves are measured to occur in discrete clumps, commonly attributed to the turbulent nature of the solar wind electron density (e.g. Smith and Sime 1979, Melrose et al 1986). But how do fluctuations in the background plasma shape the […]

Emission of radiation by plasmas with counter-streaming electron beams
by L. F. Ziebell et al.*

2017-01-31

The phenomena of emission of radiation by the Sun, which are known as type II and type III solar radio bursts, have been known and investigated for more than sixty years. The bursts of radiation occur at a frequency corresponding to the plasma frequency at the source region, and harmonics are frequently observed. It is commonly accepted that the radiation is generated by a nonlinear mechanism, proposed by Ginzburg and […]

Simultaneous near-Sun observations of a moving type IV radio burst and the associated white-light CME
by K. Hariharan et al.*

2017-01-17

Quasi-continuum radio emissions of duration ~10-60 min that occur along with flares and coronal mass ejections (CMEs) in the solar atmosphere are termed as type IV bursts. The bursts are non-thermal in nature and can be classified into two categories, i.e. moving type IV (type IVm) bursts and stationary type IV (type IVs) bursts, depending on their time-frequency characteristics in the dynamic spectrum. Amongst the two, the former has a […]

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