A solar type N burst at decametric wavelengths
by Karl-Ludwig Klein

2007-03-12 273 views

Electron beams travelling through the solar corona excite Langmuir waves near the local electron plasma frequency. When these Langmuir waves are converted into electromagnetic waves, the radiation can be detected by radio telescopes as bursts with very specific spectral signatures that depend on the magnetic structure which guides the beams. E.g., an electron beam that propagates upward along open magnetic fields produces a short pulse of emission at systematically decreasing […]

Radio-quiet Fast and Wide Coronal Mass Ejections
by Nat Gopalswamy

2007-02-07 75 views

Radio-quiet coronal mass ejections (CMEs) are those with no detectable type II radio emission in the metric and decameter-hectometric (DH) wavelengths. (The CMEs may be associated with other types of radio emission such as type III bursts, see definitions for the different types of bursts or the diagram of burst classification). The radio-loud CMEs are those with identifiable type II burst in the DH domain from Wind/WAVES data, irrespective of […]

Are there Radio-quiet Solar Flares?
by Arnold Benz

2007-01-04 93 views

Solar flares accelerate particles, and their distribution is usually non-thermal. Non-thermal electrons are prone to velocity space instabilities driving various plasma waves which, in turn, couple into observable radio waves. Such coherent emissions are the result of the combined action of many electrons organized by kinetic plasma waves and can therefore be extremely efficient. Small coherent radio bursts at the limit of present routine observations emit an energy of some […]

High dynamic range solar radio images by combining visibilities from the Giant Meterwave Radio Telescope and the Nancay Radioheliograph
by Claude Mercier

2006-12-07 127 views

We present first results from an ongoing program of combining data from the Nancay Radioheliograph NRH and the Giant Meterwave Radio Telescope GMRT, to produce snapshot images of the Sun at meter wavelengths. The data processing includes a superposition of complex visibilities from NRH and GMRT, a Fourier Transform and a cleaning multi-scale algorithm. We show results from a simulation and an observation of a complex noise storm at 327 […]

Particle acceleration during flares – the part played by an outflow termination shock
by Gottfried Mann

2006-10-11 62 views

During solar flares energetic nonthermal electromagnetic radiation up to the gamma-ray range is emitted from the solar atmosphere, implying the generation of accelerated electrons and ions. Particle acceleration in cosmic plasma is of fundamental physical interest. The solar corona offers detailed remote sounding of these processes. A fine example An interesting example is the X17-flare of 28 October 2003, one of the strongest events of the last activity cycle. Figure 1 […]

Coronal shock waves: tracking down the drivers for radio emission
by Silja Pohjolainen

2006-09-21 144 views

In the solar corona, shocks are formed when the speed of a disturbance exceeds the local magnetosonic (Alfvén) speed. At low atmospheric heights, above high-density active regions, the Alfvén velocity can drop down to a few hundred km/s, but it then rises steadily to a global maximum of about 1000 km/s near the heliocentric height of 3.5 R (see calculations in Warmuth & Mann 2005). At heights above 1.5 R […]

Radio “crystallography” of the solar corona
by Miroslav Bárta and Marian Karlický

2006-05-10 154 views

We suggest a new method for the analysis of fine structures in the cosmic plasma and investigate its applicability for the diagnostics of the solar atmosphere on scales that are not accessible by current observational techniques. The method is based on coherent interaction (diffraction) of radio waves with regular structures – as an example one can consider plasma waves of various kinds, periodic oscillations in the shock-fronts, or even stationary […]

Combining radio and optical observations for coronal magnetic field determination
by Henry Aurass

2006-02-15 181 views

We present a method newly developed at the Astrophysikalisches Institut Potsdam (AIP) for determining the structure and the strength of coronal magnetic fields during the late phase of solar flares. Fiber bursts Fiber bursts are a spectral fine structure occuring in some type IV radio burst continua. Here we assume that the fiber bursts are excited by whistler waves and their interaction with nonthermal electrons trapped in a magnetic loop. […]

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