Frequency drift rates of powerful decameter Type III bursts
We report on the observations of powerful (fluxes are larger than 10⁻¹⁹ W m⁻² Hz⁻¹) solar Type III bursts at frequencies 10 − 30 MHz. Recordings of 163 bursts, observed in July 2002 and of 231 bursts observed in August 2002 are investigated. The main properties of these Type III bursts (frequency dr...
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| Cite this: | Frequency drift rates of powerful decameter Type III bursts / A.I. Boiko, V.N. Mel'nik, A.A. Konovalenko, H.O. Rucker, E.P. Abranin, V.V. Dorovskyy, A. Lecacheux // Advances in Astronomy and Space Physics. — 2011. — Т. 1., вип. 1-2. — С. 57-60. — Бібліогр.: 5 назв. — англ. |
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irk-123456789-1190852017-06-04T03:02:28Z Frequency drift rates of powerful decameter Type III bursts Boiko, A.I. Mel'nik, V.N. Konovalenko, A.A. Rucker, H.O. Abranin, E.P. Dorovskyy, V.V. Lecacheux, A. We report on the observations of powerful (fluxes are larger than 10⁻¹⁹ W m⁻² Hz⁻¹) solar Type III bursts at frequencies 10 − 30 MHz. Recordings of 163 bursts, observed in July 2002 and of 231 bursts observed in August 2002 are investigated. The main properties of these Type III bursts (frequency drift rate, duration, flux, frequency bandwidth) are analyzed. In present report we pay more attention to consideration of frequency drift rate. A great difference between the observed and the well-known empirical frequency dependencies of Type III bursts drift rate is determined. A linear approximation for the drift rate versus frequency is found. It indicates, that solar corona above active regions has exponential density distribution. We consider that drift rate value depends on the position of an active region on the solar disc. 2011 Article Frequency drift rates of powerful decameter Type III bursts / A.I. Boiko, V.N. Mel'nik, A.A. Konovalenko, H.O. Rucker, E.P. Abranin, V.V. Dorovskyy, A. Lecacheux // Advances in Astronomy and Space Physics. — 2011. — Т. 1., вип. 1-2. — С. 57-60. — Бібліогр.: 5 назв. — англ. 987-966-439-367-3 2227-1481 http://dspace.nbuv.gov.ua/handle/123456789/119085 en Advances in Astronomy and Space Physics Advances in astronomy and space physics |
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We report on the observations of powerful (fluxes are larger than 10⁻¹⁹ W m⁻² Hz⁻¹) solar Type III bursts at frequencies 10 − 30 MHz. Recordings of 163 bursts, observed in July 2002 and of 231 bursts observed in August 2002 are investigated. The main properties of these Type III bursts (frequency drift rate, duration, flux, frequency bandwidth) are analyzed. In present report we pay more attention to consideration of frequency drift rate. A great difference between the observed and the well-known empirical frequency dependencies of Type III bursts drift rate is determined. A linear approximation for the drift rate versus frequency is found. It indicates, that solar corona above active regions has exponential density distribution. We consider that drift rate value depends on the position of an active region on the solar disc. |
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Boiko, A.I. Mel'nik, V.N. Konovalenko, A.A. Rucker, H.O. Abranin, E.P. Dorovskyy, V.V. Lecacheux, A. |
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Boiko, A.I. Mel'nik, V.N. Konovalenko, A.A. Rucker, H.O. Abranin, E.P. Dorovskyy, V.V. Lecacheux, A. Frequency drift rates of powerful decameter Type III bursts Advances in Astronomy and Space Physics |
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Boiko, A.I. Mel'nik, V.N. Konovalenko, A.A. Rucker, H.O. Abranin, E.P. Dorovskyy, V.V. Lecacheux, A. |
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Boiko, A.I. |
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Frequency drift rates of powerful decameter Type III bursts |
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Frequency drift rates of powerful decameter Type III bursts |
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Frequency drift rates of powerful decameter Type III bursts |
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Frequency drift rates of powerful decameter Type III bursts |
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Frequency drift rates of powerful decameter Type III bursts |
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frequency drift rates of powerful decameter type iii bursts |
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Advances in astronomy and space physics |
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2011 |
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Frequency drift rates of powerful decameter Type III bursts / A.I. Boiko, V.N. Mel'nik, A.A. Konovalenko, H.O. Rucker, E.P. Abranin, V.V. Dorovskyy, A. Lecacheux // Advances in Astronomy and Space Physics. — 2011. — Т. 1., вип. 1-2. — С. 57-60. — Бібліогр.: 5 назв. — англ. |
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Advances in Astronomy and Space Physics |
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Frequency drift rates of powerful decameter Type III bursts
A. I. Boiko1, V. N. Mel'nik1, A. A. Konovalenko1,
H. O. Rucker2, E. P. Abranin1, V. V. Dorovskyy1, A. Lecacheux3
1Institute of Radio Astronomy, National Academy of Sciences of Ukraine, Chervonopraporna st., 4, 61002, Kharkiv, Ukraine
2Space Research Institute, Austrian Academy of Sciences, Schmiedlstraÿe 6, A-8042 Graz, Austria
3 Departement de Radioastronomie, Observatoire de Paris, 61, Avenue de l'Observatoire, 75014, Paris, France
boikoana@yandex.ru
We report on the observations of powerful (�uxes are larger than 10−19 W m−2 Hz−1) solar Type III
bursts at frequencies 10 − 30 MHz. Recordings of 163 bursts, observed in July 2002 and of 231 bursts
observed in August 2002 are investigated. The main properties of these Type III bursts (frequency drift rate,
duration, �ux, frequency bandwidth) are analyzed. In present report we pay more attention to consideration
of frequency drift rate. A great di�erence between the observed and the well-known empirical frequency
dependencies of Type III bursts drift rate is determined. A linear approximation for the drift rate versus
frequency is found. It indicates, that solar corona above active regions has exponential density distribution.
We consider that drift rate value depends on the position of an active region on the solar disc.
Introduction
Wild in his paper [5] �rst selected Type III bursts as individual type of solar bursts. He found the linear
approximation for frequency drift rate via frequency dependence in the range of 70− 130 MHz. More detail
analysis of Type III bursts was made by Alvarez and Haddock [1]. They determined drift rate dependence
on frequency by equation df/dt = −0.01f1.84 (df/dt is in MHz/s, f is in MHz) in the wide frequency band of
50 kHz � 1 GHz. We report on the analysis of the solar Type III bursts drift rates at frequencies 10−30 MHz.
Observations
Powerful Type III bursts were registered with the radio telescope UTR-2 (Kharkiv, Ukraine) during
summer 2002 observational campaign. Three sections of the radio telescope UTR-2 with a total area of
30 000 m2 were used. It provides a beam of 1◦ × 13◦. Detection was carried out by the 60-channel receiver
with the frequency resolution of 300 kHz, the time resolution of 10 ms, and by the DSP (Digital Spectral
Polarimeter) with the frequency resolution of 12 kHz, the time resolution of 100 ms [2].
Data of powerful solar Type III bursts have been obtained for 163 bursts in July 2002 and for 231 bursts
in August 2002 which are matter of the present investigation. The majority of powerful Type III bursts
are observed, as we discovered, at the days when their occurrence is associated with active regions (see e.g.
http://www.gao.spb.ru/) on the solar disc located near the central meridian or at the medium longitudes
(40◦ − 60◦). The two maxima (Figure 2b) in the burst distribution (on 17 and 26 August 2002) correspond
to the intersection of the central meridian with two active regions. The maximum on 21 August is associated
with 2 active regions located not in the center on the solar disc (60◦ to the East, 50◦ to the West). A similar
situation occurs during the July storm (Figure 2a).
An example of a powerful Type III burst time pro�le against background of usual Type III bursts is
shown in Figure 1. The time pro�les of these bursts are not symmetrical and has fast rise and slow decay,
like usual Type III bursts. In the range of 10− 30 MHz all these bursts have negative frequency drift rates
(burst drift from high to low frequencies), it is true in the most cases for the standard Type III bursts. For
the statistical analysis we divided the whole frequency band from 10 to 30 MHz into the frequency sub-bands
10−13, 13−15, 15−20, 20−25 and 25−30 MHz. We mark all the characteristics on the average frequencies
of these sub-bands.
57
Advances in Astronomy and Space Physics A.I. Boiko, V.N. Mel'nik, A. A. Konovalenko et al.
Figure 1: The powerful Type III burst (10:05:50 UT on August, 17, 2002) time pro�le.
a) b)
Figure 2: Distributions of powerful Type III bursts in July (a) and August (b) 2002.
According to [4] the duration of standard Type III bursts varies from 4 to 10 seconds. The derived
duration value for powerful bursts is within the range of 4− 12 seconds. We obtained di�erent kinds of �ux
dependence on frequency for these bursts. The �ux of these bursts: increases with frequency, decreases with
frequency, or has more complicated dependence. In the most cases powerful bursts have frequency drift rates
in the range of 1−3 MHz/s. In some cases the drift rate can be as small as 0.4 MHz/s and single bursts have
drift rate up to 4 MHz/s. The drift rate histograms for bursts observed on August, 19 are shown in Figure 3.
We can see the shift of the histograms maxima to small frequency drift values with decreasing frequency.
The drift rates versus frequency dependence for powerful Type III bursts is shown in Figure 4. We draw
attention to the di�erence between derived and generally accepted dependence [1]. Drift rates were almost
the same at frequencies 10 − 15 MHz, but they considerably di�er (by a factor of about 2) at frequencies
20 − 30 MHz and also depend on the location of the active region on the solar disc. We propose a linear
approximation between the drift rate and the frequency df/dt = −A·f +B [3], where A and B are coe�cients
depending on the day and the type of storm. This result is repeatable during all the observational time. For
Figure 3: Drift rate histograms for powerful Type III bursts observed on August, 19, 2002 at di�erent frequencies:
27.5 MHz (a), 17.5 MHz (b), 11.5 MHz (c).
58
Advances in Astronomy and Space Physics A.I. Boiko, V.N. Mel'nik, A. A. Konovalenko et al.
Figure 4: Drift rate dependencies on frequency for July, 19 (a), August, 17 (b) and August, 21 (c) 2002 (the
solid line represents observational curve, the dashed line represents empirical dependence [1]).
the most cases the coe�cient A is in the range of 0.08− 0.09 s−1. The coe�cient B does not exceed 10% of
the measured drift rate. In such case we can use the equation df/dt ≈ −A · f
Our data allow us to �nd the linear velocity of powerful Type III bursts sources. Let us consider in what
way the average drift rate of Type III bursts is changing from 10 to 16 July when the active region N249 got
over the solar disk from the East to the middle of the Sun. The dependence of drift rate on location of the
active region N249 is shown in Figure 5. The drift rate increases with the approach of the active region to
the central meridian. Using known equation
df
dt
=
df
dn
· dn
dr
· c · vs
c− vs · cosβ
, (1)
where n is the plasma density, c is the speed of light, β is the longitude angle, the linear velocity of the
radiation source vs can be derived from observational data. In our case the velocity vs is equal to 0.3c, as
usually supposed. The dashed curve in Figure 5 corresponds to this value of velocity.
Figure 5: The variation of powerful Type III bursts drift rates depending on the active region N249 location on
the solar disk (the solid line represents the drift rate dependence on the position of the active region N249, the
dashed line corresponds to the equation (5) at vs = 0.3c) .
Under the assumption that Type III radio emission is fundamental and occurs at the local plasma fre-
quency f = fpe, we have the equation (df/dt)F = f · 1/(2 · n) · dn/dr · vs. Comparing it with equation for
linear approximation we derive the equation for coe�cient A:
A = − 1
2 · n ·
dn
dr
· vs. (2)
Taking into account that A is a constant value, which does not depend on frequency, and supposing that
the source velocity is also constant, the density dependence on distance can be found as
59
Advances in Astronomy and Space Physics A.I. Boiko, V.N. Mel'nik, A. A. Konovalenko et al.
n = n0 · exp(−2 ·A · r/vs), (3)
where n0 is the normalization factor. We conclude, that the solar corona above active regions has exponential
density distribution.
We estimate the size of inhomogeneity a = n/|dn/dr| for coronal plasma. It is equal to a = 6 · 1010 cm
and a = 5 ·1010 cm above active regions N289 (A = 0.08) and N249 (A = 0.09) correspondingly at vs = 0.3c.
Conclusions
The main result of our analysis of powerful Type III bursts is the discovery of a linear dependence between
the frequency drift rate and frequency in the range of 10 − 30 MHz. It indicates, that solar corona above
active regions has exponential density distribution. We con�rm that drift rate values depend on the position
of an active region on the solar disc.
References
[1] Alvarez H., Haddock F. T. Solar Phys., V. 29, pp. 197-209 (1973)
[2] Kleewein P., Rosolen C., Lecacheux A. Planetary Radio Emission IV, eds.: Rucker H. O., Bauer S. J., Lecacheux A.,
Austrian Academy of Sciences Press, Vienna, pp. 349-358 (1997)
[3] Mel'nik V. N., Konovalenko A. A., Rucker H. O. et. al. Radio Phys. & Radio Astron., V. 15, pp. 129-139 (2010)
[4] Suzuki S., Dulk G. A. Solar Radiophysics, eds.: McLean N. J., Labrum N. R., Cambridge University Press, pp. 289-332
(1985)
[5] Wild J. P. Aust. J. Sci. Res., V. 3, pp. 541-557 (1950)
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