On the Fundamental and Harmonic Components of Low-Frequency Type III Solar Radio Bursts

Ground-based observations of Type III bursts made with spectrographs and spectro-polarimeters, at frequencies above the ionospheric cut-off, reveal that most bursts (excluding storm Type IIIs) have fundamental (F) and harmonic (H) structure (Wild et al. 1959; Dulk and Suzuki 1980). An example of F-H bursts is given by Sheridan (1978). Such bursts are produced by streams of electrons travelling along open magnetic field lines and exciting plasma oscillations which are converted to electro-magnetic waves at both the F and H frequencies of the local plasma frequency in the corona.

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On Low‐Frequency Type III Solar Radio Bursts Observed in Interplanetary Space

The Astrophysical Journal ◽

10.1086/382144 ◽

2004 ◽

Vol 605 (1) ◽

pp. 503-510 ◽

Cited By ~ 12

Author(s):

C. S. Wu ◽

M. J. Reiner ◽

P. H. Yoon ◽

H. N. Zheng ◽

S. Wang

Keyword(s):

Solar Radio ◽

Interplanetary Space ◽

Low Frequency ◽

Radio Bursts ◽

Solar Radio Bursts ◽

Type Iii

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First Type III Solar Radio Bursts of Solar Cycle 25

Solar Physics ◽

10.1007/s11207-021-01790-9 ◽

2021 ◽

Vol 296 (4) ◽

Author(s):

Juha Kallunki ◽

Derek McKay ◽

Merja Tornikoski

Keyword(s):

Solar Cycle ◽

Solar Radio ◽

Low Frequency ◽

Radio Bursts ◽

Solar Radio Bursts ◽

Type Iii ◽

Receiver Array ◽

Imaging Receiver ◽

Solar Bursts ◽

Cycle 24

AbstractThe minimum of the previous solar cycle, Solar Cycle 24, occurred in December 2019, which also marked the start of the new Solar Cycle 25. The first radio bursts of the new solar cycle were observed in the spring season 2020. In this work we will present three type III solar bursts which were observed in May and June 2020 at radio frequencies between 18 – 90 MHz. There are two radio observatories in Finland that are capable of doing low-frequency solar radio observations: Aalto University Metsähovi Radio Observatory (MRO) and Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) of the Sodankylä Geophysical Observatory, University of Oulu. The instruments of the two institutes have different design and characteristics, and they operate in rather different radio interference environments. We will compare simultaneous observations from these two instruments and we will also discuss the properties of these type III solar bursts.

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High Resolution Studies of Type III Solar Radio Bursts

Symposium - International Astronomical Union ◽

10.1017/s0074180900234256 ◽

1974 ◽

Vol 57 ◽

pp. 225-226

Author(s):

C. Chiuderi ◽

R. Giachetti ◽

C. Mercier ◽

H. Rosenberg ◽

C. Slottje

Keyword(s):

Solar Radio ◽

Plasma Frequency ◽

Solar Radius ◽

Average Height ◽

Radio Bursts ◽

General Shape ◽

Solar Radio Bursts ◽

Type Iii ◽

Temporal And Spatial ◽

East West

(Solar Phys.). High spectral, temporal and spatial resolution observations were obtained with the 60-channel Utrecht solar radio spectrograph (160–320 MHz) and the 169 MHz Nançay solar radioheliograph. From a large number of type III bursts the average height was found to be 0.37 solar radius above the photosphere, corresponding to approximately the Newkirk streamer density, if the bursts are emitted at the harmonic of the local plasma frequency. No center-to-limb variation, nor east-west asymmetry was observed. All double bursts, double humped bursts, precursor-type III had exactly the same position and general shape for both members of the pair. From this it was concluded that fundamental-harmonic pairs are very rare at frequencies above 160 MHz (Mercier and Rosenberg, 1974).

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Low frequency spectra of type III solar radio bursts

Solar Physics ◽

10.1007/bf00951843 ◽

1978 ◽

Vol 59 (2) ◽

pp. 377-385 ◽

Cited By ~ 16

Author(s):

Richard R. Weber

Keyword(s):

Solar Radio ◽

Low Frequency ◽

Radio Bursts ◽

Solar Radio Bursts ◽

Frequency Spectra ◽

Type Iii

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Exploring the circular polarisation of low-frequency solar radio bursts with LOFAR and estimating the coronal magnetic field

10.5194/egusphere-egu21-9853 ◽

2021 ◽

Author(s):

Diana Morosan ◽

Anshu Kumari ◽

Juska Räsänen ◽

Emilia Kilpua ◽

Pietro Zucca ◽

...

Keyword(s):

Magnetic Field ◽

Solar Radio ◽

Low Frequency ◽

Coronal Magnetic Field ◽

Plasma Emission ◽

The Sun ◽

Radio Bursts ◽

Solar Radio Bursts ◽

Circular Polarisation ◽

Type Iii

<p>The Sun is an active star that often produces numerous bursts of electromagnetic radiation at radio wavelengths. In particular, low frequency (< 150 MHz) &#160;radio bursts have recently been brought back to light with the advancement of novel radio interferometric arrays. However, the polarisation properties of solar radio bursts have not yet been explored in detail, especially with the Low Frequency Array (LOFAR). Here, we explore the circular polarisation of type III radio bursts and a type I noise storm and present the first Stokes V low frequency radio images of the Sun with LOFAR in tied array mode observations. We find that the degree of circular polarisation for each of the selected bursts increases with frequency for fundamental plasma emission, while this trend is either not clear or absent for harmonic plasma emission. In the case of type III bursts, we also find that the sense of circular polarisation varies with each burst, most likely due to their different propagation directions, despite all of these bursts being part of a long-lasting type III storm. Furthermore, we use the degree of circular polarisation of the harmonic emission of type III bursts to estimate the coronal magnetic field at distances of 1.4 to 4 solar radii from the centre of the Sun. We found that the magnetic field has a power law variation with a power index in the range 2.4-3.6, depending on the individual type III burst observed.</p>

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Solar Radio Bursts at Low Frequencies

Symposium - International Astronomical Union ◽

10.1017/s0074180900234232 ◽

1974 ◽

Vol 57 ◽

pp. 183-200 ◽

Cited By ~ 1

Author(s):

J. Fainberg

Keyword(s):

Solar Radio ◽

Low Frequency ◽

Leading Edge ◽

Emission Region ◽

The Sun ◽

Radio Bursts ◽

Solar Radio Bursts ◽

Low Frequencies ◽

Type Iii ◽

Radio Measurements

Properties of solar radio bursts observed by spacecraft at frequencies below several MHz are reviewed. In this frequency range most of the observed bursts are type III events (associated with particles) but several cases of type II emission (associated with shocks) have been reported. The analyses which lead to emission levels of type III solar bursts out to beyond 1 AU from the Sun also indicate that the low frequency radiation is observed at the harmonic of the emission region plasma frequency. Simultaneous particle and radio measurements imply that the bursts are generated near the leading edge of impulsive streams of solar electrons with energies extending from several hundred keV to several keV. Recent experiments measuring the direction of arrival of the radio emission allow the exciter particles to be tracked along the interplanetary magnetic field from regions near the Sun out to 1 AU.

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The Mechanism Responsible for 'Shadow' Type III Solar Radio Bursts. II. Absorption due to Ion Sound Turbulence

Australian Journal of Physics ◽

10.1071/ph740271 ◽

1974 ◽

Vol 27 (2) ◽

pp. 271 ◽

Cited By ~ 10

Author(s):

DB Melrose

Keyword(s):

Energy Density ◽

Solar Radio ◽

Plasma Frequency ◽

Radio Bursts ◽

Sound Waves ◽

Solar Radio Bursts ◽

Langmuir Waves ◽

Transverse Waves ◽

Type Iii ◽

Ion Plasma

The hypothesis is explored that ion sound turbulence generated by the exciting agency for type III bursts is responsible for shadow type III events. The possible absorption mechanisms are listed: the most favourable are the coalescence of transverse waves and ion sound waves into Langmuir waves or the decay of transverse waves into Langmuir waves and ion sound waves. These mechanisms can operate only if the background source emits at the fundamental plasma frequency and the absorbing region is directly above it (;$ 3 x 104 km). It is found that the event discussed by Kai (1973) can be explained in terms of such absorption with reasonable parameters, e.g. with an energy density in ion sound turbulence W' ~ 10-12 ergcm- 3 at frequencies co' ~ O�3cop! (where cop! is the ion plasma frequency).

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