Radio echo and sporadic radiation scattering in the solar corona

Abranin, E. P.; Bazelyan, L. L.; Зайцев, В. В.; Rapoport, V. O.; Tsybko, Ya. G.

doi:10.1007/bf00151152

Cited by 11 publications

(10 citation statements)

References 10 publications

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“…Neglecting the group velocity slowing factor and the corrections associated with the small angle between the observa, tion direction and the source radius, we can write AR = _C (AT1)max = 1.6Re, 2 where c = 3 x 105 km s-1 is the velocity of light and R e = 7 x 105 km is the radius of the Sun. An account of the group delay results in AR = 0.87R e (Abranin et al, 1982). The value AR ~ 1R e for the range 12.5 to 25.0 MHz is not in conflict with the current knowledge on the dimensions of the corona.…”

Section: Discussionmentioning

confidence: 92%

“…As the source of the harmonic is moved away from the central meridian, the echo delay decreases to merge with the 'main' signal at heliolongitudes above 30 to 45 ~ where they form a single, slowly decaying burst. Riddle's results are of particular interest in connection with decameter echo events and related diffuse stria-bursts observed with a UTR-2 radio telescope (Bazelyan et al, 1974;Abranin et aL, 1982). With regard to the heliolongitude dependence of intensity profiles, the narrow-band decameter echoes and the signals from a second harmonic source analysed by Riddle in the meter range are very much alike.…”

Section: Introductionmentioning

confidence: 79%

“…Two five-beam records of echo events on that day are presented as an example in Figure 3 (the two left-hand columns). The corresponding dynamic spectra of the echo events, similar to type IIIb stria chains or type III bursts, have the form of inclined tracks (Abranin et aL, 1982). However, in these peculiar events, the first series of narrow-band bursts is followed several seconds later at the same frequencies by another series of weaker but longer, echo-like radio bursts.…”

Section: Observationsmentioning

confidence: 99%

“…Within the operating range of the spectrograph (i.e., 24 to 26 MHz) the denser chains contain up to 12 narrow-band, almost simultaneous echo events. Very important data were obtained in July 1974 when a lot of echo events were observed in the 24-26 MHz range (Abranin et al, 1982), during the passage across the solar disc of active region McMath 13057 (Solar-Geophysical Data, 1974). The central meridian was crossed by McMath 13057 oh 14 July, 1974.…”

Section: Observationsmentioning

confidence: 99%

“…Active region McMath 13057 with which the echo events were associated, was located in the southern hemisphere at a heliolatitude of -8.5 ~ with the solar axis inclined by 4 ~ and with the north pole towards the Earth. Diffuse stria-bursts (i.e., the limb variety of decameter echo events) were observed with the 25 MHz two-dimensional radio-heliograph at a considerable distance from the Sun and it turned out that the direction of radiation arrival at the end of the burst corresponds to deeper coronal layers (Abranin et aL, 1982). Noting the relation of the echo events with optically active regions near the central meridian, it should be pointed out that at two-dimensional 25 MHz heliograms, the echo sources lie in the central part of the corona as well.…”

Section: Observationsmentioning

confidence: 99%

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Multiple radio echoes in the solar corona

Abranin¹,

Bazelyan²,

Зайцев³

et al. 1984

Sol Phys

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Echo-type solar radio bursts are associated with preceding short-lived bursts in double events. The peculiar and rather rare decameter echoes are observed with a UTR-2 antenna. The initial narrow-band burst is followed, some 5 to 10 s later, by an echo-like burst at the same frequency. The observational data obtained for decameter echo evens are, on the whole, consistent with the model of a pulsed source emitting radio signals at the plasma-frequency harmonic, which is placed in a non-uniform corona and rotates together with the Sun.Intensity-time profiles of 25 MHz echo bursts are of an unusual shape, featuring an extended leading edge and an abrupt decay at the trailing edge and also showing some fine structures in the form of an additional, weakly pronounced maximum or a 'step' at the final stage of the burst. Time parameters characterizing the profiles are evaluated. The 'step' is delayed with respect to the main pulse at about two times longer than the principal echo maximum. At the same time, the time delays depend essentially on the heliolongitude of the active region and achieve their maximum values at the meridian. The 'step' height does not exceed 0.5 of the echo maximum. At this level, the echo-decay time almost coincides with the initial burst duration but is about 1.7 times less than the echo-rise time. The feature at the echo tail can be interpreted as a result of a repeated reflection of the burst from the source region. The causes and conditions for the formation of multiple echoes are discussed. The extended leading edge of the echo permit s us to assume a quasi-radial fibrous structure of the corona, capable of back-scattering the incident radiation.

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Section: Discussionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 79%

Section: Observationsmentioning

confidence: 99%

Section: Observationsmentioning

confidence: 99%

Section: Observationsmentioning

confidence: 99%

See 3 more Smart Citations

Multiple radio echoes in the solar corona

Abranin¹,

Bazelyan²,

Зайцев³

et al. 1984

Sol Phys

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Low‐frequency heliographic observations of the quiet Sun corona

2013

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We present new results of heliographic observations of quiet-Sun radio emission fulfilled by the UTR-2 radio telescope. The solar corona investigations have been made close to the last solar minimum (Cycle 23) in the late August and early September of 2010 by means of the two-dimensional heliograph within 16.5-33 MHz. Moreover, the UTR-2 radio telescope was used also as an 1-D heliograph for one-dimensional scanning of the Sun at the beginning of September 2010 as well as in short-time observational campaigns in April and August of 2012. The average values of integral flux density of the undisturbed Sun continuum emission at different frequencies have been found. Using the data, we have determined the spectral index of quiet-Sun radio emission in the range 16.5-200 MHz. It is equal to -2.1±0.1. The brightness distribution maps of outer solar corona at frequencies 20.0 MHz and 26.0 MHz have been obtained. The angular sizes of radio Sun were estimated. It is found that the solar corona at these frequencies is stretched-out along equatorial direction. The coefficient of corona ellipticity varies slightly during above period. Its mean magnitudes are equal to ≈ 0.75 and ≈ 0.73 at 20.0 MHz and 26.0 MHz, respectively. The presented results for continuum emission of solar corona conform with being ones at higher frequencies.

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Harmonic components of decametric solar radio bursts

Tsybko

1984

Sol Phys

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Type-lIIb, l lid, and III solar decametric radio bursts, being distinguished by the typical negative drift rate of their dynamic spectra, are compared. Observational data were obtained with a UTR-2 antenna during the period 1973-1982. During the analysis of the bursts of all these spectral varieties, the frequency drift time (drift delay) was measured in the ranges 25 to 12.5 MHz, 25 to 20 Mliz, and 12.5 to 10 MHz. Durations of type-lll bursts were determined at the harmonically-related frequencies of 25 and 12.5 Mttz; radio source locations were also used.It is shown that these decametric bursts arc distinctly divided into two groups: (1)type-lllb chains of simple stria bursts and also normal type-Ill storm bursts observed at central regions constitute a group of events with a fast drifting spectrum; (2)type-Ill bursts from type-Illb-lll pairs and the limb variant of normal III bursts, as well as peculiar type-llld chains of diffuse striae and related chains with an echo component, constitute a second group of events with comparatively slow drift rates.The first group of the phenomena is associated with the fundamental F frequency and the second one, with the harmonic H of the coronal plasma frequency. The results of the present investigation agree well with earlier conclusions on the harmonic origin of decametric chains and type-Ill bursts. Measurements of drift delays in narrow fi'equency ranges, an octave apart, as well as type-I I I burst durations at harmonically-related fi'equencies confirm the existence of both F and H components in the solar radiation. The essential result of 10 years ofdecametric observations is that the ti-cquency drift rates and durations arc rather stable parameters for the various type-III bursts and stria-burst chains. The stability characterizes some unspecified conditions of burst generation in the middle corona.

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Radio echo and sporadic radiation scattering in the solar corona

Cited by 11 publications

References 10 publications

Multiple radio echoes in the solar corona

Multiple radio echoes in the solar corona

Low‐frequency heliographic observations of the quiet Sun corona

Harmonic components of decametric solar radio bursts

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