Interplanetary Scintillation Method Research Articles

Large-Scale Structure of Solar Wind beyond the Earth’s Orbit: Reconstruction Using the Data of Two-Site Measurements of Interplanetary Scintillations in the Decameter Radio Range

Solar wind is a set of flows with different parameters (the speed, the exponent of the spectrum of heterogeneities, the width, etc.). A bimodal character of the speed distribution of the solar wind was determined in spaceborne experiments. The measurements onboard the Ulysses spacecraft confirmed that the bimodal structure of solar wind continues to persist at relatively large distances from the Sun (to several astronomical units). However, there is one more possibility to determine the stream structure of solar wind. This is the method of interplanetary scintillations. The purpose of the paper is to reconstruct the stream structure of solar wind beyond the Earth’s orbit using the data on interplanetary scintillations obtained at two observational sites. The experiments were carried out at decameter wavelengths, since they are rather strongly scattered by the rarefied interplanetary plasma beyond the Earth’s orbit. The experimental data on interplanetary scintillations analyzed in this work were obtained in synchronous observations with the UTR-2 and URAN-2 radio telescopes. The parameters of solar wind and its stream structure were determined by comparison of the characteristics of interplanetary scintillations measured in the experiment (the dependences of the harmonic velocity of the cross-spectrum of scintillations and the power spectra) to those calculated with the models. To separate the interplanetary and ionospheric scintillations, the spectral, spatial, and frequency criteria were used. The results of this analysis show that solar wind beyond the Earth’s orbit consists of several streams that replace each other on the line of sight toward the radio source. These investigations prove the reliability and efficiency of the interplanetary scintillation method for reconstructing the stream structure of solar wind.

Study of compact radio sources using interplanetary scintillations at 111 MHz. Strong gigahertz-peaked spectrum sources

Observations of a sample of gigahertz-peaked spectrum sources have been carried out using the interplanetary-scintillation method. Scintillations were recorded in six of 53 observed sources; upper estimates for the flux density of the compact emission were obtained for the remaining sources. The contribution of a halo to the integrated flux at low frequencies is considered. Three sources with spectral indices close to −2.5 below the spectral cutoff have been found. The synchrotron self-absorption of emission in the studied sources is discussed.

Study of compact radio sources using interplanetary scintillations at 111 MHz. The Pearson-Readhead sample

A complete sample of radio sources has been studied using the interplanetary scintillation method. In total, 32 sources were observed, with scintillations detected in 12 of them. The remaining sources have upper limits for the flux densities of their compact components. Integrated flux densities are estimated for 18 sources.

A study of radio sources using interplanetary scintillations at 111 MHz. Core-dominated sources

A complete sample of core-dominated radio sources has been studied using the interplanetary-scintillation method. In total, 72 sources were observed, with scintillations detected in 28 of them. The remaining sources have upper limits on their flux densities. Integrated flux densities are estimated for 24 sources. Cut-offs have been observed in the spectra of many sources. The thermal-electron densities have been estimated, assuming that these cut-offs are due to free-free absorption of the synchrotron radio emission.

Investigations of physical conditions in AGNs by the radio astronomy method

This is a concise review of investigations of AGNs by the interplanetary scintillation method made in Pushchino Radio Astronomy Observatory.

Investigation of flat spectrum radio sources by the interplanetary scintillation method at 111 MHz

Interplanetary scintillation observations of 48 of the 55 Augusto et al. (1998) flat spectrum radio sources were carried out at 111 MHz using the interplanetary scintillation method on the Large Phased Array (LPA) in Russia. Due to the large size of the LPA beam (1° x 0.5°) a careful inspection of all possible confusion sources was made using extant large radio surveys: 37 of the 48 sources are not confused. We were able to estimate the scintillating flux densities of 13 sources, getting upper limits for the remaining 35. Gathering more or improving extant VLBI data on these sources might significantly improve our results. This proof-of-concept project tells us that compact (<1) flat spectrum radio sources show strong enough scintillations at 11 MHz to establish/constrain their spectra (low-frequency end).

Investigations of AGNs by the interplanetary scintillation method

This is a brief review of investigations of AGNs by the interplanetary scintillation method made in Pushchino Radio Astronomy Observatory.

Investigations of AGNS by the Interplanetary Scintillation Method

AbstractThis is a brief review of investigations of AGNs by the interplanetary scintillation method made in Pushchino Radio Astronomy Observatory.

Solar wind speed and its acceleration inferred using the interplanetary scintillation method in carrington rotation 1753

Solar wind speeds (SWSs) estimated by interplanetary scintillation (IPS) observations during Carrington rotation 1753 are projected onto the so-called ‘source-surface’ of 2.5 solar radii along magnetic field lines in interplanetary space. The following two working hypotheses are examined from different points of view: (1) The SWS is a weighted mean along the line of sight to a radio source; the weight for the SWS depends on the distance from theP-point, the closest approach to the Sun on the line of sight. (2) The weighting function has a very sharp peak at theP-point, so that the SWS shows a real solar wind speed at theP-point. In both the two cases, the SWSs projected onto the source surface are further projected onto the photosphere along magnetic field lines in the corona. Footpoints of these field lines are inferred as photospheric source regions of the solar wind. The intensity of the Hei (1083 nm) absorption line (HEI) in the chromosphere corresponding to these photospheric sources is interpolated from observational data. The weighted mean of the HEI is calculated in case 1. The HEI corresponding to theP-point is used in case 2. The SWS is compared with the HEI in both the two cases. It is found that the correlation between the SWS and the HEI is better in case 2 than in case 1. It is further inferred by correlation analysis between the SWS and the HEI that the solar wind is accelerated within ∼27 solar radii on average. Although the data examined in this paper were limited to just one solar rotation, these results suggest that the SWS estimated by the IPS technique corresponds to the solar wind speed near theP-point and the weighting function along the line of sight may have a very sharp peak near theP-point.

Solar cycle dependence of global distribution of solar wind speed

A review is given of observational results concerning the solar cycle dependence of the global structure of solar wind speed distribution during the years from 1973 to 1987. Since observations of solar wind speed in 3-dimensional space can only be made by the interplanetary scintillation method which has been carried out over one sunspot activity cycle since the early 1970's, the review is based on IPS observations. The low-speed regions tend to be distributed along neutral lines which are derived on the source surface, so comparisons between speed distribution and the neutral line are discussed.

Modeling of an interplanetary disturbance event tracked by the interplanetary scintillation method

Using the method which we have developed during the last few years, an interplanetary disturbance event on 25–29 August 1978, was modeled in an attempt to reproduce the corresponding interplanetary scintillation observation (Tappin et al., 1983, Planet. Space Sci. 31, 1171), as well as the simultaneous ISEE-3 satellite data. It is shown that a shock wave generated from the region of a disappearing filament on 23 August can account for the observed shock wave structure and the scintillation sky maps reconstructed by Tappin et al. (1983), but fails to explain the broad high speed stream behind the shock wave, which lasted until about 5 September. On the other hand, it is also shown that a shock wave generated by the sudden activation of the coronal hole on the same day, suggested by Hewish et al. (1985, Nature 314, 137), can account for the high speed stream, but not the observed shock wave. Therefore, an attempt is made to combine the effects of both the filament and the coronal hole. The simulation results reproduce fairly well the major events between 27 August and 5 September 1978. Several specific suggestions are made to improve the scheme for forecasting interplanetary disturbance events.

Solar cycle evolution of solar wind speed structure between 1973 and 1985 observed with the interplanetary scintillation method

The solar cycle evolution of solar wind speed structure was studied for the years from 1973 to 1985 on a basis of interplanetary scintillation observations using a new method for mapping solar wind speed to the source surface. The major minimum‐speed regions are distributed along a neutral line through the whole period of a solar cycle: when solar activity is low, they are distributed on the wavy neutral line along the solar equator; in the active phase they also tend to be distributed along the neutral line, which has a large latitudinal amplitude. The minimum‐speed regions tend to be distributed not only along the neutral line but also at low magnetic intensity regions and/or coronal bright regions which do not correspond to the neutral line. As the polar high‐speed regions extend equatorward around the minimum phase, the latitudinal gradient of speed increases at the boundaries of the low‐speed region, and the width of the low‐speed region decreases. One or two years before the minimum of solar activity, two localized minimum‐speed regions appear on the neutral line, and their locations are longitudinally separated by 180°.