Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298
We present the results of the analysis of temporal power spectra of interplanetary scintillation for the strong radio source 3C 298 observed at 111 MHz with radio telescope BSA LPI in the period near the solar activity minimum. The velocity of the solar wind plasma irregularities and the power expon...
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| Zitieren: | Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298 / S.K. Glubokova, I.V. Chashei, S.A. Tyul'bashev, V.I. Shishov // Advances in Astronomy and Space Physics. — 2013. — Т. 3., вип. 2. — С. 94-97. — Бібліогр.: 12 назв. — англ. |
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irk-123456789-1196192017-06-08T03:03:37Z Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298 Glubokova, S.K. Chashei, I.V. Tyul'bashev, S.A. Shishov, V.I. We present the results of the analysis of temporal power spectra of interplanetary scintillation for the strong radio source 3C 298 observed at 111 MHz with radio telescope BSA LPI in the period near the solar activity minimum. The velocity of the solar wind plasma irregularities and the power exponent of the turbulence spatial spectrum are estimated from the measured temporal scintillation spectra. It is shown that some high frequency ffattening of the temporal scintillation power spectra due to the noise influence can bias the estimates of the source angular size and the spectral index of plasma turbulence. The comparison between the turbulence parameters for the sources 3C 48 and 3C 298 have been carried out. The decrease in the turbulence spectral exponent by transit from the high latitude fast solar wind to the low latitude slow solar wind is found from the 3C 298 data that confirms similar dependence found recently for the 3C 48 data. 2013 Article Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298 / S.K. Glubokova, I.V. Chashei, S.A. Tyul'bashev, V.I. Shishov // Advances in Astronomy and Space Physics. — 2013. — Т. 3., вип. 2. — С. 94-97. — Бібліогр.: 12 назв. — англ. 2227-1481 http://dspace.nbuv.gov.ua/handle/123456789/119619 en Advances in Astronomy and Space Physics Головна астрономічна обсерваторія НАН України |
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We present the results of the analysis of temporal power spectra of interplanetary scintillation for the strong radio source 3C 298 observed at 111 MHz with radio telescope BSA LPI in the period near the solar activity minimum. The velocity of the solar wind plasma irregularities and the power exponent of the turbulence spatial spectrum are estimated from the measured temporal scintillation spectra. It is shown that some high frequency ffattening of the temporal scintillation power spectra due to the noise influence can bias the estimates of the source angular size and the spectral index of plasma turbulence. The comparison between the turbulence parameters for the sources 3C 48 and 3C 298 have been carried out. The decrease in the turbulence spectral exponent by transit from the high latitude fast solar wind to the low latitude slow solar wind is found from the 3C 298 data that confirms similar dependence found recently for the 3C 48 data. |
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Article |
| author |
Glubokova, S.K. Chashei, I.V. Tyul'bashev, S.A. Shishov, V.I. |
| spellingShingle |
Glubokova, S.K. Chashei, I.V. Tyul'bashev, S.A. Shishov, V.I. Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298 Advances in Astronomy and Space Physics |
| author_facet |
Glubokova, S.K. Chashei, I.V. Tyul'bashev, S.A. Shishov, V.I. |
| author_sort |
Glubokova, S.K. |
| title |
Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298 |
| title_short |
Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298 |
| title_full |
Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298 |
| title_fullStr |
Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298 |
| title_full_unstemmed |
Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298 |
| title_sort |
changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3c 298 |
| publisher |
Головна астрономічна обсерваторія НАН України |
| publishDate |
2013 |
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http://dspace.nbuv.gov.ua/handle/123456789/119619 |
| citation_txt |
Changes in the spectral index of the interplanetary plasma turbulence in the period of low solar activity from observations of strongly scintillating source 3C 298 / S.K. Glubokova, I.V. Chashei, S.A. Tyul'bashev, V.I. Shishov // Advances in Astronomy and Space Physics. — 2013. — Т. 3., вип. 2. — С. 94-97. — Бібліогр.: 12 назв. — англ. |
| series |
Advances in Astronomy and Space Physics |
| work_keys_str_mv |
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| first_indexed |
2025-07-08T16:16:50Z |
| last_indexed |
2025-07-08T16:16:50Z |
| _version_ |
1837096146510544896 |
| fulltext |
Changes in the spectral index of the interplanetary plasma
turbulence in the period of low solar activity
from observations of strongly scintillating source 3C 298
S. K.Glubokova∗, I. V.Chashei, S. A.Tyul'bashev, V. I. Shishov
Advances in Astronomy and Space Physics, 3, 94-97 (2013)
© S.K.Glubokova, I. V.Chashei, S. A.Tyul'bashev, V. I. Shishov, 2013
Pushchino Radio Astronomy Observatory, Lebedev Physical Institute, Russian Academy of Sciences, Russia
We present the results of the analysis of temporal power spectra of interplanetary scintillation for the strong radio
source 3C 298 observed at 111MHz with radio telescope BSA LPI in the period near the solar activity minimum.
The velocity of the solar wind plasma irregularities and the power exponent of the turbulence spatial spectrum are
estimated from the measured temporal scintillation spectra. It is shown that some high frequency �attening of the
temporal scintillation power spectra due to the noise in�uence can bias the estimates of the source angular size
and the spectral index of plasma turbulence. The comparison between the turbulence parameters for the sources
3C 48 and 3C298 have been carried out. The decrease in the turbulence spectral exponent by transit from the high
latitude fast solar wind to the low latitude slow solar wind is found from the 3C 298 data that con�rms similar
dependence found recently for the 3C 48 data.
Key words: solar wind, interplanetary scintillation
introduction
The interplanetary scintillation (IPS) was discov-
ered in 1964 by Hewish et al. [7]. This scintillation
e�ect is caused by the di�raction of radio waves prop-
agating from a distant compact radio source on the
density irregularities of the interplanetary plasma
(IPP) with the scales of about Fresnel scale (sev-
eral hundred kilometres for the meter wave length).
Therefore, IPS is widely used to investigate proper-
ties of the IPP and parameters of scintillating radio
sources. Compact (< 1′′) radio sources, such as ac-
tive galactic nuclei (AGN), are usually used in IPS
observations.
There are several methods of IPP and scintillat-
ing sources investigation using IPS measurements.
One of them is based on the analysis of IPS tem-
poral power spectra. This method was developed
by Shishov [11, 12]. The possibility to estimate the
solar wind speed using IPS temporal spectra were
demonstrated in [3, 8].
The method of simultaneous estimates of the
spectral power exponent of small-scale plasma tur-
bulence, the source angular sizes and the solar wind
speed from temporal scintillation spectra was devel-
oped in [4, 9]. The evidences of the dependence of
the turbulence spectral index on heliolatitude con-
nected with solar wind bimodal structure during the
minimum of solar activity were obtained. In order to
con�rm the results of [4], the IPS observations data
for the quasar 3C 298 in the period of solar activity
minimum are analysed in this paper.
observations
The scintillation observations were carried out in
monitoring mode by the radio telescope BSA (Big
Scanning Array) of Lebedev Physical Institute from
2007 to 2011. The radio telescope allows to observe
scintillating sources simultaneously in 16 beams.
BSA LPI beam system covers about eight degrees
in declination. The frequency of observations was
111.5MHz, bandwidth was 600 kHz, the sampling
rate was 10Hz. The radio telescope e�ective area
toward the zenith was 20000�25000m2. The sizes of
individual beam are approximately 1◦ × 0.5◦ (along
the east-west and north-south directions).
Since the solar declination varies from −23◦ (in
winter) to 23◦ (in summer) the optimal elongations
(the angular distance between the line of sight and
the direction to the Sun, ε) for observations of scin-
tillating sources are reached in di�erent regions of
the sky. Therefore two declination bands with coor-
dinates of 3.5◦ − 12.5◦ from October to March and
28.5◦− 35◦ from March to October were selected for
monitoring. Radio sources 3C 298 (right ascension
14h17m, declination 6◦41′) and 3C48 (right ascen-
sion 1h35m, declination 32◦53′′) are the strongest
scintillating sources in the lower and upper bands,
respectively. These sources are the strongest in our
observations.
The results and details of techniques for the radio
∗glubokovask@yandex.ru
94
Advances in Astronomy and Space Physics S.K.Glubokova, I. V.Chashei, S. A.Tyul'bashev, V. I. Shishov
source 3C 48 observed in April�May 2007�2009 are
described in [2, 4]. In this paper we analyse the IPS
observations for the source 3C 298 during the long
quiet period November 2007�2009.
During the observation series for 3C 48 and
3C298 elongations were within the limits ε = 20◦ −
40◦, when IPS reaches its maximum value. The state
of the interplanetary plasma was relatively quiet1.
The examples of initial records of the sources 3C 48
and 3C298 are presented in Fig. 1 which shows that
the source 3C 48 is much stronger than the source
3C 298. In our previous paper [4] 157 IPS power
spectra were used for analysis with signal-to-noise
ratio greater than 30. In this paper we analyse only
52 IPS spectra selected from the criteria that signal-
to-noise ratio is above 15.
Fig. 1: The examples of typical IPS records for the
sources 3C 48 and 3C298.
influence of noise on the
turbulence index and the
source angular sizes estimates
The ideal IPS temporal power spectrum shown
in Fig. 2 has typical shape with approximately con-
stant level at low frequencies and exponential de-
crease to higher frequencies (3D spectral index is
about n ≈ 3.6)
In real observations the received signal has a �-
nite duration and a power spectrum is distorted by
noise. Noises are revealed in the power spectra as a
�at part at highest frequencies. The noise in�uence
on the shape of power spectrum is shown in Fig. 2.
At the highest frequencies power spectrum �attens.
So the source angular size and the turbulence spec-
tral index can be distorted by the noise. Qualita-
tively it is clear that the weaker is the source (the
lower signal-to-noise ratio), the greater is the con-
tribution of noise. However, quantitative estimates
of the noise contribution to the change in the esti-
mates of the source angular size and the turbulence
spectral index are not known. Fig. 3 shows the real
power spectrum of the source 3C 298 in comparison
with schematic representation.
Fig. 2: Schematic representation of the power spectrum
in the absence of noise (ideal case) and in the case when
noises are included.
Fig. 3: The example of the power spectrum of the source
3C 298.
In Fig. 2: f0 is the frequency of the power spec-
1http://www.lmsal.com/solarsoft/last_events/
95
Advances in Astronomy and Space Physics S.K.Glubokova, I. V.Chashei, S. A.Tyul'bashev, V. I. Shishov
trum break, N is the average noise level, f1 is the last
point where the power spectrum is above the noise
level (up to this point we compare the experimental
spectrum with a set of theoretical power spectra).
The details of the reduction are presented in [4].
In the absence of noise (ideal case) the IPS power
spectrum is power law, M0(f) = Af−α. The spec-
tral index of IPS temporal power spectrum α is
connected with the turbulence 3D spectral index n
by the simple relation n = α + 1. In the case
with noise the power spectrum becomes more �at,
Ms(f) = Af−α +N = Bf−β , where β < α.
In the case without noise we have:
M0(f0) = Af−α
0 , M0(f1) = Af−α
1 . (1)
From (1) one can obtain the temporal IPS spectral
index:
α =
lg
(
M0(f0)
M0(f1)
)
lg
(
f1
f0
) . (2)
If the noise is included the spectral index is shifted
to lower values:
Ms0(f0) = Af−α
0 +N = f−β
0 ,
Ms1(f1) = Af−α
1 +N = f−β
1 , (3)
where β is the temporal IPS spectral index in the
presence of noise. Taking into account relations (1)-
(3) one can found:
β =
lg
(
Ms0
Ms1
)
lg
(
f1
f0
) =
lg
(
Af−α
0 +N
Af−α
1 +N
)
lg
(
f1
f0
) =
= α−
lg
(
1 +
Nfα
1
A
)
lg
(
f1
f0
) =
{
M(f1) = Af−α
1
}
=
= α−
lg
(
1 +
N
M(f1)
)
lg
(
f1
f0
) = α−∆α, (4)
∆α =
lg
(
1 +
N
M(f1)
)
lg
(
f1
f0
) . (5)
Equation (5) describes the dependence of the spec-
tral exponent shift ∆α on the signal-to-noise ratio
and can be used for systematical correction of the
power exponent if this ratio is measured. When the
signal-to-noise ratio q � 1, then ∆α = 0. In case
q � 1 equation (4) does not make sense.
Information on the source angular size is needed
to obtain the correct estimates of turbulence spec-
tral index. Accuracy of the estimates of the source
angular size from IPS data is not better than 0.1′′
at 100MHz [1]. In addition the interstellar medium
scatters the signal, and the degree of scattering varies
with the direction in the Galaxy that gives its own
limits on the angular size of the observed sources.
We have taken the source angular size from orig-
inal papers in order to separate the contributions
to temporal scintillation spectra from the source an-
gular size and from the turbulence spectral index.
Radio source 3C 298 is a bright quasar. A lot of
interferometric observations of this source are avail-
able. The observations of the source at frequencies
of 327MHz, 608MHz, 1.7GHz, 5GHz are given in
[5, 6, 10]. These observations suggest that the source
at low frequencies is a three-component, the compo-
nents are aligned along the straight line. The �ux
density of the middle component is a few times less
than from the outer components. The total distance
between the outermost components is about 1.5′′,
and the angular sizes of each of the three compo-
nents are approximately equal to 0.25′′ × 0.1′′.
results
We analysed the calculated IPS power spectra in
order to de�ne the model which describes adequately
the IPP turbulence. Fig. 4 shows the dependencies
of the spectral index of the turbulence on the elon-
gation without (A) and with correction ∆n (B). We
assumed the angular size of the source to be equal to
0.25′′ in our model. We can see that the turbulence
index decreases with increasing the elongation angle.
The source 3C 298 has several components, they
are aligned and the distance between the components
is such that it is di�cult to describe the source by a
simple model. We can put additional parameters on
the applied model [4]: the elongation of the details,
the distance between the components, the angular
size of each component, taking into account the rel-
ative details position of the source relative to the di-
rection of the solar wind. However, using such model
one cannot obtain a unique solution. We supposed
that the obtained values of the turbulence spectral
index which are lower than those of the source 3C 48
are connected with a complex angular structure of
the source 3C 298.
The dependence of the plasma turbulence spec-
tral index on the observed speed of the solar wind is
presented in Fig. 5. We see that the turbulence spec-
tral index decreases with transit from fast high lati-
tude to slow low latitude solar wind. Fitting the line
n = n0 + kv by least-squares method to the result-
ing dependence gives the following results: n0 = 2.6,
96
Advances in Astronomy and Space Physics S.K.Glubokova, I. V.Chashei, S. A.Tyul'bashev, V. I. Shishov
k = 0.002.
Fig. 4: Dependence of the turbulence spectral index on
elongation. On the x-axis in logarithmic scale: initial
results (A); results corrected for the noise in�uence (B).
The tendency of the turbulence spectral index in-
crease with increasing of the solar wind speed is the
same as previously found from IPS observations of
the source 3C 48 [4]. The results can be explained
by bimodal structure of the solar wind, that is typi-
cal for the period of solar activity minimum.
conclusions
1. The values of the solar wind plasma turbu-
lence spectral index estimated from IPS data should
be corrected for the noise in�uence if the signal-to-
noise ratio is not very high.
2. The dependence of the turbulence spectral in-
dex on the speed of the solar wind during the period
of solar activity minimum is con�rmed by the IPS
data for the source 3C 298.
3. The last conclusion can be useful for develop-
ing of new models of the solar wind turbulence.
Fig. 5: The dependence of the plasma turbulence spec-
tral index on the speed of the solar wind for the source
3C 298.
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Chashei I. V. & ShishovV. I. 2011, Geomagnetism and
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[4] Glubokova S.K., Tyul'bashev S.A., Chashei I. V. &
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