Geoeffective Disturbances in the Solar Wind near the Solar Activity Minimum according to the Data of a Two-year Series of Observations of Interplanetary Scintillations with the BSA LPI Radio Telescope

Astronomy Reports - A joint analysis of the monitoring data of interplanetary scintillations with solar and geophysical data showed that at the descending phase of the 24 solar activity cycle, the...     

Corotating and Propagating Disturbances in the Solar Wind Based on Monitoring of Interplanetary Scintillations at the LPA Radio Telescope of the Lebedev Physical Institute in 2017

Monitoring of interplanetary scintillations in 2017 is used as a basis for analyzing the dynamics of scintillation levels in periods preceding the arrival at the Earth of eight large-scale disturbances in the solar wind giving rise to strong geomagnetic storms. In six of the eight events, the dynamics of the scintillation level were mainly determined by the motion of corotating disturbances. In two events, coronal-mass ejections excited in the corona near the western limb of the Sun were observed against the background of corotating disturbances. In one of these cases, a magnetic storm was associated with a corotating flux, and in the other with a powerful propagating disturbance. Comparison with similar data obtained in 2016, also during the descending phase in solar activity, testifies to the existence of corotating disturbances with lifetimes of at least 20 solar rotations. These new results support the earlier conclusion that a weakening of scintillations is observed in the evening sector three to four days before the arrival of the compressed part of a disturbance to the Earth, which could be due to an appreciable lowering of the level of small-scale turbulence in the plasma in an extended region ahead of the frontal part of the disturbance. The interplanetary-scintillation monitoring data for 2017 show that, simultaneously with the associated magnetic storm, there is an enhancement of second-time-scale scintillations, which are most clearly manifest when the storm occurs during the evening or night-time hours. For the events considered, the increase in scintillations accompanying the magnetic storm is associated with an enhancement in the level of small-scale fluctuations in regions of the solar wind adjacent to the Earth when the storm is excited by a corotating disturbance, and with the perturbed ionosphere when the storm is excited by a flare-related disturbance.     

The Coefficient of Asymmetry of Radio-Source Interplanetary Scintillation

It is proposed to use the coefficient of asymmetry of the distribution function of fluctuations of a scintillating source flux density as a parameter that characterizes interplanetary turbulent plasma. It is demonstrated that this parameter can be measured with a differential method and that its informative capacity is equivalent to that of the source scintillation index. A series of test observations of scintillations was performed with the Large Phased Array antenna of the Lebedev Institute of Physics, Russian Academy of Sciences, simultaneously with measurements of the source scintillation indices and coefficients of asymmetry. Comparative analysis of the measured quantities showed that the coefficient of asymmetry within a numerical coefficient equals the source scintillation index, normalized to the flux density of the scintillating component. The coefficient of asymmetry makes it possible to restore scintillation indices when the radio sources are weak and it is difficult to measure their mean flux densities, and, hence, it enlarges the number of observable scintillating sources and makes the exploration of interplanetary plasma by means of the mapping of scintillation indices more efficient.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 4, 2005, pp. 375–380.Original Russian Text Copyright © 2005 by Shishov, Tyul’bashev, Artyukh, Subaev, Chashei, Chernikov.     

Coronal Mass Ejections in September 2017 from Monitoring of Interplanetary Scintillations with the Large Phased Array of the Lebedev Institute of Physics

Results of monitoring of interplanetary scintillations with the Large Phased Array of the Pushchino Radio AstronomyObservatory at 111 MHz during a period of flare activity of the Sun in the first ten days of September 2017 are presented. Enhancements of scintillations associated with interplanetary coronal mass ejections propagating after limb flares have been recorded. The propagation velocities are estimated to be about 2000 km/s for an ejection on September 7 and about 1000 km/s for an ejection on September 6. It is shown that, during the propagation from the Sun, the lateral part of the ejections decelerates faster than its leading part. Night-time enhancements of second-timescale scintillations during periods of high geomagnetic activity have an ionospheric origin.     

Monitoring of interplanetary and ionospheric scintillation of an ensemble of radio sources

The results of a series of 24-hour observations of radio-source interplanetary and ionospheric scintillation performed on April 4–10, 2006, at the Pushchino Radio Astronomy Observatory are presented. The observations were carried out with the Large Phased Array radio telescope of the Lebedev Institute of Physics, Russian Academy of Sciences, at a frequency of 110 MHz. The scintillating fluxes of all radio sources that fall within a field of sky between declinations +28° and +31° were automatically recorded applying eight beams of the reception pattern operating simultaneously. All of the sources with flux densities of 0.2 Jy or higher were detected. The structure functions of the flux fluctuations were measured for time shifts 1 and 10 s, which characterize the interplanetary (1 s) and ionospheric (10 s) scintillation, respectively. The mean scintillation index m _IPP (on a characteristic time scale of 1 s) of an ensemble of radio sources located within a sky band 4° wide in declination and 1 h wide in right ascension was measured as the parameter that characterizes the interplanetary plasma. Diurnal variations of the interplanetary scintillation index were determined. The maximum m _IPP value at daytime equals 0.3, and the minimum value at nighttime equals 0.10. Weak interday variations of the mean daytime and nighttime scintillation indices were detected. The ionospheric scintillation indices m _Ion are small compared to m _IPP at daytime, but m _Ion ? m _IPP at nighttime. On the whole, both the interplanetary plasma and ionosphere were quiet during the observations.     

Observations of Corotating Streams of the Solar Wind with the Large Phased Array of the Lebedev Physical Institute in 2016

Astronomy Reports - Solar and geomagnetic data demonstrate that, at the decay phase of solar activity in 2016, the dominating role in strong geomagnetic perturations was played by long-lived...     

Results of IPS Observations in the Period Near Solar Activity Minimum

IPS observations with the Big Scanning Array of Lebedev Physical Institute (BSA LPI) radio telescope at the frequency 111 MHz have been monitored since 2006. All the sources, about several hundred daily, with a scintillating flux greater than 0.2 Jy are recorded for 24 hours in the 16 beams of the radio telescope covering a sky strip of 8^° declination width. We present some results of IPS observations for the recent period of low solar activity considering a statistical ensemble of scintillating radio sources. The dependences of the averaged over ensemble scintillation index on heliocentric distance are considerably weaker than the dependence expected for a spherically symmetric geometry. The difference is especially pronounced in the year 2008 during the very deep solar activity minimum period. These features are explained by the influence of the heliospheric current sheet that is seen as a strong concentration of turbulent solar wind plasma aligned with the solar equatorial plane. A local maximum of the scintillation index is found in the anti-solar direction. Future prospects of IPS observations using BSA LPI are briefly discussed.     

Reproducible characteristics of the solar wind acceleration

In experiments that were regularly carried out in 1999–2002 with Pushchino radio telescopes (Russian Academy of Sciences), the study of the radial dependence of the scattering of radio emission from compact natural sources was extended to regions of circumsolar plasma farther from the Sun. Based on a large body of data, we show that, apart from the standard transonic acceleration region located at distances of 10–40 R_⊙ from the Sun, there is a region of repeated acceleration at distances of 34–60 R_⊙ attributable to the equality between the solar wind velocity and the Alfvénic velocity. The repetition in the trans-Alfvénic region of the characteristic features of the radial stream structure observed in the transonic region (the existence of a precursor, a narrow region of reduced scattering that precedes a wide region of enhanced scattering) suggests that the main characteristic features of the resonant acceleration of solar wind streams are preserved up to distances of the order of 60 R_⊙.     

Monitoring of the turbulent solar wind with the upgraded Large Phased Array of the Lebedev Institute of Physics: First results

The design properties and technical characteristics of the upgraded Large Phased Array (LPA) are briefly described. The results of an annual cycle of observations of interplanetary scintillations of radio sources on the LPA with the new 96-beam BEAM 3 system are presented. Within a day, about 5000 radio sources displaying second-timescale fluctuations in their flux densities due to interplanetary scintillations were observed. At present, the parameters of many of these radio sources are unknown. Therefore, the number of sources with root-mean-square flux-density fluctuations greater than 0.2 Jy in a 3° × 3° area of sky was used to characterize the scintillation level. The observational data obtained during the period of the maximum of solar cycle 24 can be interpreted using a three-component model for the spatial structure of the solar wind, consisting of a stable global component, propagating disturbances, and corotating structures. The global component corresponds to the spherically symmetric structure of the distribution of the turbulent interplanetary plasma. Disturbances propagating from the Sun are observed against the background of the global structure. Propagating disturbances recorded at heliocentric distances of 0.4–1 AU and at all heliolatitudes reach the Earth’s orbit one to two days after the scintillation enhancement. Enhancements of ionospheric scintillations are observed during night-time. Corotating disturbances have a recurrence period of 27^d. Disturbances of the ionosphere are observed as the coronal base of a corotating structure approaches the western edge of the solar limb.