VLA and Trieste observations of type I storms, type IV and pulsations

Zlobec, P.; Messerotti, M.; Dulk, G. A.; Kucera, T. A.

doi:10.1007/bf00155910

Cited by 26 publications

(15 citation statements)

References 20 publications

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“…Three noise storms were present, and Mercier et al gave results for the most intense storm. Because of the difficult intercalibration between both instruments, the accepted baselines were limited to about 6000 λ. Sizes of ∼50 arcsec were reported, in general agreement with the results of Zlobec et al (1992).…”

Section: Introductionsupporting

confidence: 89%

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The structure of solar radio noise storms

Mercier

Subramanian

Chambe

et al. 2015

A&A

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Context. The Nançay Radioheliograph (NRH) routinely produces snapshot images of the full sun (field of view ∼3 R ) at 6 or 10 frequencies between 150 and 450 MHz, with typical resolution 3 arcmin and time cadence 0.2 s. Combining visibilities from the NRH and from the Giant Meterwave Radio Telescope (GMRT) allows us to produce images of the sun at 236 or 327 MHz, with the same field as the NRH, a resolution as low as 20 arcsec, and a time cadence 2 s. Aims. We seek to investigate the structure of noise storms (the most common non-thermal solar radio emission) which is yet poorly known. We focus on the relation of position and altitude of noise storms with the observing frequency and on the lower limit of their sizes. Methods. We use an improved version of a previously used method for combining NRH and GMRT visibilities to get high-resolution composite images and to investigate the fine structure of noise storms. We also use the NRH data over several consecutive days around the common observation days to derive the altitude of storms at different frequencies.Results. We present results for noise storms on four days. Noise storms consist of an extended halo and of one or several compact cores with relative intensity changing over a few seconds. We found that core sizes can be almost stable over one hour, with a minimum in the range 31-35 arcsec (less than previously reported). The heliocentric distances of noise storms are ∼1.20 and 1.35 R at 432 and 150 MHz, respectively. Regions where storms originate are thus much denser than the ambient corona and their vertical extent is found to be less than expected from hydrostatic equilibrium. Conclusions. The smallest observed sizes impose upper limits on broadening effects due to scattering on density inhomogeneities in the low and medium corona and constrain the level of density turbulence in the solar corona. It is possible that scatter broadening has been overestimated in the past, and that the observed sizes cannot only be attributed to scattering. The vertical structure of the noise storms is difficult to reconcile with the classical columnar model.

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Section: Introductionsupporting

confidence: 89%

“…Zlobec et al (1992) reported sizes ∼50 arcsec for about 20 bursts, with a minimum reliable value of 40 arcsec for two of them. Kerdraon et al (1988) also reported two bursts with size of 40 arsec.…”

Section: Apparent Sizes Of Noise Storm Coresmentioning

confidence: 94%

The structure of solar radio noise storms

Mercier

Subramanian

Chambe

et al. 2015

A&A

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“…However, the observed position of solar radio sources may deviate from the original position because of coronal effects. Coronal scattering was proposed to produce the observed source size of typically between 40 and 90 at 333 MHz (Zlobec et al 1992). Figure 3 suggests that the position differences are not caused by an entirely random process.…”

Section: Discussionmentioning

confidence: 97%

Do solar decimetric spikes originate in coronal X-ray sources?

Battaglia¹,

Benz²

2009

A&A

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Context. In the standard solar flare scenario, a large number of particles are accelerated in the corona. Nonthermal electrons emit both X-rays and radio waves. Thus, correlated signatures of the acceleration process are predicted at both wavelengths, coinciding either close to the footpoints of a magnetic loop or near the coronal X-ray source. Aims. We attempt to study the spatial connection between coronal X-ray emission and decimetric radio spikes to determine the site and geometry of the acceleration process. Methods. The positions of radio-spike sources and coronal X-ray sources are determined and analyzed in a well-observed limb event. Radio spikes are identified in observations from the Phoenix-2 spectrometer. Data from the Nançay radioheliograph are used to determine the position of the radio spikes. RHESSI images in soft and hard X-ray wavelengths are used to determine the X-ray flare geometry. Those observations are complemented by images from GOES/SXI. Results. We find that the radio emission originates at altitudes much higher than the coronal X-ray source, having an offset from the coronal X-ray source amounting to 90 and to 113 and 131 from the two footpoints, averaged over time and frequency. Conclusions. Decimetric spikes do not originate from coronal X-ray flare sources contrary to previous expectations. However, the observations suggest a causal link between the coronal X-ray source, related to the major energy release site, and simultaneous activity in the higher corona.

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“…We therefore adopt the smallest observed source size of 49″ in these maps to be a canonical number for comparison with our model predictions. The only other twodimensional map showing small source sizes that we are aware of is that of Zlobec et al [1992], who observed a source as small as 30″ at 327 MHz. However, the dynamic 1 Indian Institute of Science Education and Research, Pune, India.…”

Section: Introductionmentioning

confidence: 97%

Constraints on coronal turbulence models from source sizes of noise storms at 327 MHz

Subramanian

Cairns

2011

J. Geophys. Res.

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[1] We seek to reconcile observations of small source sizes in the solar corona at 327 MHz with predictions of scattering models that incorporate refractive index effects, inner scale effects, and a spherically diverging wavefront. We use an empirical prescription for the turbulence amplitude C N 2 (R) based on very long baseline interferometry observations by Spangler et al. of compact radio sources against the solar wind for heliocentric distances R ≈ 10-50 R . We use the Coles and Harmon model for the inner scale l i (R), which is presumed to arise from cyclotron damping. In view of the prevalent uncertainty in the power law index that characterizes solar wind turbulence at various heliocentric distances, we retain this index as a free parameter. We find that the inclusion of spherical divergence effects suppresses the predicted source size substantially. We also find that inner scale effects significantly reduce the predicted source size. An important general finding for solar sources is that the calculations substantially underpredict the observed source size. Three possible, nonexclusive, interpretations of this general result are proposed. First and simplest, future observations with better angular resolution will detect much smaller sources. Consistent with this, previous observations of small sources in the corona at metric wavelengths are limited by the instrument resolution. Second, the spatially varying level of turbulence C N 2 (R) is much larger in the inner corona than predicted by straightforward extrapolation sunward of the empirical prescription, which was based on observations between 10 and 50 R . Either the functional form or the constant of proportionality could be different. Third, perhaps the inner scale is smaller than the model, leading to increased scattering. These results and interpretations are discussed and compared with earlier work.

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VLA and Trieste observations of type I storms, type IV and pulsations

Cited by 26 publications

References 20 publications

The structure of solar radio noise storms

The structure of solar radio noise storms

Do solar decimetric spikes originate in coronal X-ray sources?

Constraints on coronal turbulence models from source sizes of noise storms at 327 MHz

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