1. WITH LOW FREQUENCY UKRAINIAN RADIO TELESCOPES UTR-2, URAN and GURT
STREAM STRUCTURE OF SOLAR WIND BEYOND EARTH’s ORBIT BY IPS OBSERVATIONS
WITH LOW FREQUENCY UKRAINIAN RADIO TELESCOPES UTR-2, URAN and GURT
N. Kalinichenko*(1), M. Olyak (1), A. Konovalenko (1), H. Rucker (2), R. Fallows (3), P. Zarka (4), A. Lecacheux, I. Bubnov(1), S. Yerin(1), A. Brazhenko(5), O. Ivantishin (6), V. Koshovy (6), O. Lytvynenko(1),
(1) Radio Astronomy institute of NAS of Ukraine, Kharkiv, Ukraine (2) Space Research Institute, Austrian Academy of Science, Graz, Austria.
(3) ASTRON – the Netherlands institute for Radio Astronomy, the Netherlands (4) LESIA– Observatore de Paris, CNRS, France.
(5) Gravimetrical observatory of Geophysical institute, Poltava, Ukraine (6) Institute of Physics and Mechanics of NAS of Ukraine, Lviv, Ukraine
1. Observations.
UTR-2 – URAN- GURT is European radio telescope systems that allows us to carry out the interplanetary scintillation (IPS) observations in the frequency range from 8 to 32 MHz. This is the lowest frequency IPS facility in Europe (among LOFAR ( MHz), EISCAT (900 and 1400 MHz), MERLIN (several frequency bands ranging from 151 MHz to 22 MHz)). Low frequencies (lower than 100 MHz) allow us to obtain the solar wind parameters both at small (less than 90 degrees) and large (more than 90 degrees) elongations. The last ones correspond to the solar wind beyond Earth's orbit where high frequencies are only slightly scattered by the rarefied interplanetary plasma.
Fig. 2. Dynamic spectrum of IPS at a small elongation (40 degree). (Radio telescope UTR-2)
Fig. 3. Dynamic spectrum of IPS at a large elongation (170 degree).
(Radio telescope UTR-2)
Fig.1. A map of the locations of UTR-2 and
URAN radio telescopes throughout Ukraine
The purpose of this report is to describe and test a new method for reconstruction of solar wind stream structure beyond Earth’s orbit.
2. The model
The method is based on the analysis of IPS data which are obtained from the simultaneous two-site observations at decameter wavelengths. To derive the stream structure of the solar wind, the theoretical model characteristics are fitted to the observed ones. We assume that the line of sight (axis ) crosses solar wind flows extending radially from the Sun. We use the multi-flow models of the solar wind.
Equations (1 - 2) obtained by using Feynman path-integral technique describe well the interplanetary scintillations at decameter wavelengths and allow us to estimate the width of the solar wind streams beyond Earth’s orbit.
During modeling it has been found that the presence of several solar wind streams significantly influences the shape of the scintillation spectrum and dispersion curve. If more than one flow exists on the line of sight to the radio source, additional "knees" appear in the scintillation spectrum. In this case the high-frequency parts of the scintillation spectrum correspond to the solar wind flows which pass near the Earth. The shape of the dispersion curve strongly depends on the width of the stream passing close to the Earth. The slope of the dispersion curves only weakly depends on the spectral index of the interplanetary turbulence spectrum. The maximum slope angle of the dispersion curve is during the passage of the high-speed solar wind stream near the Earth. If a slow stream crosses the line of sight near the Earth, the slope of the dispersion curve decreases.
3. The stream structure of the solar wind for 6 successive days (January 12 – January 17, 2016
The next six Figures illustrate the reconstructed stream structure of the solar wind for 6 successive days. The different streams are marked by the different colors. It is seen that on the first day, January 12, only one powerful flow (marked A) is detected on the line of sight to the radio source. The next day, January 13, the stream A becomes weaker and it becomes possible to see the stream B, which is situated ahead of the stream A. The next day, January 14, the streams A and B are pushed by the next stream C. The situation remains analogous on January 15. There are three streams (A, B and C) on the line of sight to the radio source. On January 16, only one stream C remains on the line of sight to the radio source. On the last day (January 17), we detect three streams which are possible the parts of the one low speed stream D observed on the previous day.
v=540 км/с, n=3.8, a=2.8, l=0.7 а. е.
v1=400 км/с, n1=3.8, a1=2.8, l1=0.2 а.е.,
v2=540 км/с, n2=3.7, a2=2.8, l2=0.3 а.е.,
v3=480 км/с, n3=3.8, a3=2.5, l2=0.5 а.е.
v1=450 км/с, n1=3.9, a1=2.5, l1=0.4 а.е.
v2=560 км/с, n2=3.8, a2=2.8, l2=0.6 а.е.
v3=290 км/с, n3=3.8, a3=2.0
v1=260 км/с, n1=3.7, a1=2.7, l1=0.2 а.е.
v2=230 км/с, n2=3.9, a2=2.5, l2=0.2 а.е.
v3=300 км/с, n3=3.7, a3=2.8, l2=2.0 а.е.
v1=530 км/с, n1=3.9, a1=2.6, l1=0.4 а.е.,
v2=400 км/с, n2=3.9, a2=2.2, l2=2 а.е.
v1=280 км/с, n1=3.7, a1=2.5, l1=0.3 а.е.
v2=400 км/с, n2=3.7, a2=2.5, l2≥1.0 а.е.
4. Perspectives.
Additional observations with the use of more radio sources are needed to develop this method. As the ability of the observation to resolve streams of solar wind with different velocities increases as the parallel baseline increases, the use of another URAN radio telescopes and LOFAR radio telescopes for observations of the same radio sources are desirable. This way is good also from the point of view of the different ionospheric impact and interference immunity.