Interplanetary Scintillation Technique Research Articles

Probing the Plasma Tail of Interstellar Comet 2I/Borisov

We present an occultation study of compact radio sources by the plasma tail of interstellar comet 2I/Borisov (C/2019 Q4) both pre- and near-perihelion using the Arecibo and Green Bank radio telescopes. The interplanetary scintillation technique was used to probe the plasma tail at the P band (302–352 MHz), 820 MHz, and the L band (1120–1730 MHz). The presence and absence of scintillation at different perpendicular distances from the central axis of the plasma tail suggests a narrow tail of less than 6′ at a distance of ∼10′ (∼106 km) from the comet nucleus. Data recorded during the occultation of B1019+083 on 2019 October 31 with the Arecibo Telescope covered the width of the plasma tail from its outer region to the central axis. The systematic increase in scintillation during the occultation provides the plasma properties associated with the tail when the comet was at its pre-perihelion phase. The excess level of L-band scintillation indicates a plasma density enhancement of ∼15–20 times that of the background solar wind. The evolving shape of the observed scintillation power spectra across the tail from its edge to the central axis suggests a density spectrum flatter than Kolmogorov and that the plasma density irregularity scales present in the tail range between 10 and 700 km. The discovery of a high-frequency spectral excess corresponding to irregularity scales much smaller than the Fresnel scale suggests the presence of small-scale density structures in the plasma tail, likely caused by interaction between the solar wind and the plasma environment formed by the comet.

Observations of interplanetary scintillation of the 2005 May 13 coronal mass ejection: numerical models

ABSTRACT The 2005 May 13 eruption was an Earth-directed coronal mass ejection (CME) observed using the Multi-Element Radio-Linked Interferometer Network telescope system in the UK as it traversed the Interplanetary Medium on 2005 May 14. Observations of interplanetary scintillation (IPS) provide information on the solar wind conditions, which include velocities and density. In addition, it is also possible to calculate other parameters related to the turbulence and geometry of density irregularities in the solar wind from observations of IPS. Previous analyses have shown that IPS information can be difficult to interpret when a complex structure is crossing the line of sight since the physical properties of the plasma may change quite drastically with distance from the Sun. In order to compare and relate the internal structure of a CME and its physical changes, with the results from observations of IPS obtained previously, we carried out a numerical simulation of the 2005 May 13 eruptive event as it propagates into the IPM, adapting the geometrical properties derived by IPS analysis. In this work, we give a possible explanation of some signatures of CME sub-structure from the point of view of the IPS technique combined with what the modelling reveals.

Interplanetary scintillation studies with the Murchison Wide-field Array – IV. The hosts of sub-arcsecond compact sources at low radio frequencies

Around 10% of bright low-frequency radio sources observed with the Murchison Widefield Array (MWA) show strong Interplanetary Scintillation (IPS) on timescales of a few seconds, implying that almost all their low-frequency radio emission comes from a compact component less than 0.5 arcsec in angular size. Most of these objects are compact steep-spectrum (CSS) or MHz-peaked spectrum (MPS) radio sources. We have used mid-infrared data from the Wide-field Infrared Survey Explorer (WISE) catalogue to search for the host galaxies of 65 strongly-scintillating MWA sources and compare their properties with those of the overall population of bright low-frequency radio sources. We identified WISE mid-infrared counterparts for 91% of the bright sources in a single 900 square degree MWA field, and found that the hosts of the strongly-scintillating sources were typically at least 1 mag fainter in the WISE W1 (3.4 micron) band than the hosts of weakly-scintillating MWA sources of similar radio flux density. This difference arises mainly because the strongly-scintillating sources are more distant. We estimate that strongly-scintillating MWA sources have a median redshift of z ~ 1.5, and that at least 30% of them are likely to lie at z > 2. The recently-developed wide-field IPS technique therefore has the potential to provide a powerful new tool for identifying high-redshift radio galaxies without the need for radio spectral-index selection.

Interplanetary scintillation studies with the Murchison Widefield Array – II. Properties of sub-arcsecond compact sources at low radio frequencies

We report the first astrophysical application of the technique of wide-field Interplanetary Scintillation (IPS) with the Murchison Widefield Array (MWA). This powerful technique allows us to identify and measure sub-arcsecond compact components in low-frequency radio sources across large areas of sky without the need for long-baseline interferometry or ionospheric calibration. We present the results of a five-minute observation of a 30x30 sq. deg MWA field at 162 MHz with 0.5 second time resolution. Of the 2550 continuum sources detected in this field, 302 (12 per cent) show rapid fluctuations caused by IPS. We find that at least 32% of bright low-frequency radio sources contain a sub-arcsec compact component that contributes over 40% of the total flux density. Perhaps surprisingly, peaked-spectrum radio sources are the dominant population among the strongly-scintillating, low-frequency sources in our sample. While gamma-ray AGN are generally compact, flat-spectrum radio sources at higher frequencies, the 162 MHz properties of many of the Fermi blazars in our field are consistent with a compact component embedded within more extended low-frequency emission. The detection of a known pulsar in our field shows that the wide-field IPS technique is at the threshold of sensitivity needed to detect new pulsars using image plane analysis, and scaling the current MWA sensitivity to that expected for SKA-low implies that large IPS-based pulsar searches will be feasible with SKA. Calibration strategies for the SKA require a better knowledge of the space density of compact sources at low radio frequencies, which IPS observations can now provide.

IPS observations at 140 MHz to study solar wind speeds and density fluctuations by MEXART

The interplanetary scintillation (IPS) technique is a remote-sensing method for monitoring the inner heliosphere. These observations supply information on solar wind conditions covering heliocentric ranges that no other technique can provide. The Mexican Array Radio Telescope (MEXART) is a single-station instrument operating at 140MHz, fully dedicated to performing solar-wind studies employing the IPS technique. We present solar-wind parameters (scintillation indices and solar-wind speeds), using the initial measurements from this array of four IPS sources (3C273, 3C283, 3C286, 3C298) detected during October–December 2014. We report the transit of an IPS radio source (3C298), observed at 140MHz, from weak- to strong-scattering regions at around 0.36 AU, and sky projection maps of solar wind conditions associated presumably with the passing of one or more Coronal Mass Ejections (CMEs). These results show the progress to operate the full array in the near future. The MEXART observations will complement the solar wind IPS studies using other frequencies, and the tracking of solar wind disturbances by other stations located at different longitudes. These solar wind measurements, provided in real time, can have space-weather forecasting applications.

Detection of Solar Wind Disturbances: Mexican Array Radio Telescope IPS Observations at 140 MHz

The interplanetary scintillation (IPS) technique is a remote-sensing method for monitoring solar-wind perturbations. The Mexican Array Radio Telescope (MEXART) is a single-station instrument operating at 140 MHz, fully dedicated to performing solar-wind studies employing the IPS technique. We report MEXART solar-wind measurements (scintillation indices and solar-wind velocities) using data obtained during the 2013 and 2014 campaigns. These solar-wind measurements were calculated employing a new methodology based on the wavelet transform (WT) function. We report the variation of the scintillation indices versus the heliocentric distance for two IPS sources (3C48 and 3C147). We found different average conditions of the solar-wind density fluctuations in 2013 and 2014. We used the fittings of the radial dependence of the scintillation index to calculate g-indices. Based on the g-index value, we identified 17 events that could be associated with strong compression regions in the solar wind. We present the first ICME identifications in our data. We associated 14 IPS events with preceding CME counterparts by employing white-light observations from the Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO) spacecraft. We found that most of the IPS events, detected during the solar maximum of Cycle 24 were associated with complex CME events. For the IPS events associated with single CME counterparts, we found a deceleration tendency of the CMEs as they propagate in the interplanetary medium. These results show that the instrument detects solar-wind disturbances, and the WT methodology provides solar-wind information with good accuracy. The MEXART observations will complement solar-wind IPS studies using other frequencies, and the tracking of solar-wind disturbances by other stations located at different longitudes.

Observations of Rapid Velocity Variations in the Slow Solar Wind

The technique of interplanetary scintillation (IPS) is the observation of rapid fluctuations of the radio signal from an astronomical compact source as the signal passes through the ever-changing density of the solar wind. Cross-correlation of simultaneous observations of IPS from a single radio source, received at multiple sites of the European Incoherent SCATter (EISCAT) radio antenna network, is used to determine the velocity of the solar wind material passing over the lines of sight of the antennas. Calculated velocities reveal the slow solar wind to contain rapid velocity variations when viewed on a time-scale of several minutes. Solar TErrestrial RElations Observatory (STEREO) Heliospheric Imager (HI) observations of white-light intensity have been compared with EISCAT observations of IPS to identify common density structures that may relate to the rapid velocity variations in the slow solar wind. We have surveyed a one-year period, starting in April 2007, of the EISCAT IPS observing campaigns beginning shortly after the commencement of full science operations of the STEREO mission in a bid to identify common density structures in both EISCAT and STEREO HI datasets. We provide a detailed investigation and presentation of joint IPS/HI observations from two specific intervals on 23 April 2007 and 19 May 2007 for which the IPS P-Point (point of closest approach of the line of sight to the Sun) was between 72 and 87 solar radii out from the Sun’s centre. During the 23 April interval, a meso-scale (of the order of 105 km or larger) transient structure was observed by HI-1A to pass over the IPS ray path near the P-Point; the observations of IPS showed a micro-scale structure (of the order of 102 km) within the meso-scale transient. Observations of IPS from the second interval, on 19 May, revealed similar micro-scale velocity changes, however, no transient structures were detected by the HIs during that period. We also pose some fundamental thoughts on the slow solar wind structure itself.

A search for compact decametric radio sources in supernova remnants using the interplanetary scintillation technique

Interplanetary scintillation observations of eleven supernova remnants and the pulsar J1939+2134, around which the existence of a supernova remnant remains obscure, were carried out with the largest in the world decameter radio telescope UTR-2 at 20, 25 and 30 MHz to determine if any of them contain compact radio sources with the angular size θ<5″. The sample included the young Galactic remnants and the other powerful SNRs. The interplanetary scintillations of the compact radio source in the Crab Nebula associated with the well-known pulsar J0534+2200 and the pulsar J1939+2134 were observed. Apart from the Crab Nebula, we have not detected a compact radio source in supernova remnants with the angular size θ<5″ and the flux density more than 10 Jy. The observations do not confirm the existence of the low frequency compact source in Cassiopeia A that has remained controversial.

Veso: virtual earth-sun observatory

We present the Virtual Earth-Sun Observatory (VESO) at the web site http://www.veso.unam.mx. This site shows a real time integrated database obtained from four instruments of the Instituto de Geofisica-UNAM studying Sun-Earth connection phenomena. (1) The Solar Radio Interferometer (RIS, Radio Interferometro Solar) measures the lower solar atmosphere radiation at 7.5 GHz, revealing microwave bursts associated with solar activity. (2) The Mexican Array Radio Telescope (MEXART, Observatorio de Centelleo Interplanetario de Coeneo) will detect solar wind large-scale disturbances between Sun and Earth (e.g., Interplanetary counterparts of Coronal Mass Ejections (ICMES) and Stream Interaction Regions (SIR)) employing the interplanetary scintillation technique (IPS) operating at 140 MHz. (3) The Cosmic Ray Observatory (RC) detects high energy galactic particles, whose flow is affected by magnetic disturbances in the solar wind, and (4) the Teoloyucan Geomagnetic Observatory (TEO) measures the variations in the Earths magnetic field. The VESO instruments provide data from four different points of the complex chain of the solar terrestrial relations and will allow the study of intense solar events causing geomagnetic activity. The VESO project is part of the celebration of the International Heliophysical Year (IHY) and the Electronic Geophysical Year (EGY) in Mexico.

Coronal Structure of a Flaring Region and Associated Coronal Mass Ejection

We report the multiwavelength investigations of an eruptive flare event that occurred on 2001 April 2 at about 11 UT. The manifestations associated with this flare event have been studied from the near-Sun region to about 0.5 AU. The H-alpha images from the Meudon Spectroheliograph reveal a fast spectacular eruption of plasmoids from the flare site to the west and a Moreton wave disturbance propagating toward the south, A bright, fast, wide coronal mass ejection (CME) associated with this eruptive event was imaged by SOHO/LASCO and the remote-sensing interplanetary scintillation technique. The timings and positions of the Type II radio bursts, H-alpha eruption, and CME onset as well as the magnetic field configuration suggest a release of energy at the null point. The results seem to support the breakout scenario proposed by Antiochos and coworkers, and they are also suggestive that the energy release is followed by magnetic reconnection between the low-lying loops near the separatrix and the loop system above them.

&amp;lt;i&amp;gt;Foreword by the Chairman of the EISCAT Council&amp;lt;/i&amp;gt;

This volume contains papers presented at the 10th biennial International EISCAT workshop, held in Tokyo, Japan, in July 2001. The quality and excitement of the papers clearly demonstrate that the vitality and diversity of the science made possible by these radars is stronger than ever and that the facilities have maintained their pre-eminence in the field. For more than 20 years, the EISCAT radars have been producing world-leading data for research into space plasmas. The majority of the observations are of the ionosphere; however, because the behaviour of the ionospheric plasma is strongly linked by collisions to the upper neutral atmosphere and, via electomagnetic coupling and auroral particle precipitation, to the magnetosphere, EISCAT is able to study both these regions of geospace as well. The location of the EISCAT Svalbard Radar under the cusp allows studies of how Earth’s magnetosphere-ionosphere system interacts with the solar wind; the locations of the mainland systems are ideal for studying the internal dynamics of the magnetospheric tail. In addition, EISCAT is unique in having a high-power HF modification (“heater”) facility supported by an incoherent scatter radar. In fact, in addition to having both the UHF and VHF radars as diagnostics, the heater field-of-view is also monitored by a digital ionosonde and the CUTLASS HF radar system as well as optical instrumentation and an imaging riometer. This combination really does turn the ionosphere over Tromso into a natural laboratory for studying the mechanisms and behaviour of large-scale plasma. As an example, studies of “artificial aurora” induced by the heater have given new insights into plasma-wave interactions. In addition to this broad diversity of science, the interplanetary scintillation technique has been applied to EISCAT with great success, making it possible to observe uniquely close to the Sun and, consequently, to study the acceleration of the solar wind. Further developments will allow yet more diversification into areas such as space debris and interplanetary particles.

Synoptic Maps of Solar Wind: Comparison of IPS Data and the NOAA/SEC Version of the Wang and Sheeley Model

Since the 1970s, the Solar-Terrestrial Environment Laboratory, Japan, has been publishing synoptic maps of solar wind velocity prepared using the technique of interplanetary scintillation. These maps, known as V-maps, are useful to study the global distribution of solar wind in the heliosphere. As the Earth-orbiting satellites are unable to probe regions outside the ecliptic, it is important to exploit the scope of interplanetary scintillation to study the solar wind properties at these regions and their relation with coronal features. It has been shown by Wang and Sheeley that there exists an inverse correlation between rate of magnetic flux expansion and the solar wind velocity. The NOAA/Space Environment Center daily updated version of the Wang and Sheeley model has been used to produce synoptic maps of solar wind velocity and magnetic field polarity for individual Carrington rotations. The predictions of the model at 1 AU have been found to be in good agreement with the observed values of the same. The present work is a comparison of the synoptic maps on the source surface using the interplanetary scintillation measurements from Japan and the NOAA/SEC version of the Wang and Sheeley model. The two results agree near the equatorial regions and the slow solar wind locations are consistent most of the times. However, at higher latitudes within ±60°, the wind velocities differ considerably. In the Wang and Sheeley model the highest speed obtained is ∼ 600 km s−1 whereas in the IPS results velocities as high as 800 km s−1 have been detected. The paper discusses the possible causes for this discrepancy and suggestion to improve the agreement between the two results.

Experimental constraints on pulsed and steady state models of the solar wind near the Sun

Ulysses observations of the high‐latitude solar wind were combined with Spartan 201 observations of the corona to investigate the nature and extent of uncertainties in our knowledge of solar wind structure near the Sun. In addition to uncertainties stemming from the propagation of errors in density profiles inferred from coronagraph observations [see, e.g., Lallement et al., 1986], an assessment of the consequences of choosing different analysis assumptions reveals very large, fundamental uncertainties in our knowledge of even the basics of coronal structure near the Sun. In the spirit of demonstrating the nature and extent of these uncertainties we develop just one of a generic class of explicitly time‐dependent and filamentary models of the corona that is consistent with the Ulysses and Spartan 201 data. This model provides a natural explanation for the radial profiles of both the axial ratios and apparent radial speeds of density irregularities measured at radial distances less than 10 Rs using the interplanetary scintillation technique.

Interplanetary scintillation observations of the high-latitude solar wind

Until the ULYSSES spacecraft reached the polar regions of the solar wind, the only high-latitude measurements available were from indirect techniques. The most productive observations in regions of the solar wind between 5 R⊙ and 200 R⊙ have been the family of radio scattering techniques loosely referred to as Interplanetary Scintillation (IPS) (Coles, 1978). Useful observations can be obtained using a variety of radio sources, for example spacecraft beacons, planetary radar echoes and compact cosmic sources (quasars, active galactic nuclei, pulsars, galactic masers, etc.). However for measurement of the high-latitude solar wind cosmic sources provide the widest coverage and this review will be confined to such observations. IPS observations played a very important role in establishing that polar coronal holes (first observed in soft x-ray emission) were sources of fast solar wind streams which occasionally extend down to the equatorial region and are observed by spacecraft. Here I will review the IPS technique and show the variation of both the velocity and the turbulence level with latitude over the last solar cycle. I will also outline recent work and discuss comparisons that we hope to make between IPS and ULYSSES observations.

Multi-Station System for Solar Wind Observations Using the Interplanetary Scintillation Method.

We describe a multi-station system dedicated to measurements of the solar wind plasma using the interplanetary scintillation technique. The observation system, which is operated at a frequency of 327 MHz, consists of four stations located at Toyokawa, Fuji, Sugadaira and Kiso. The newest station was constructed at Kiso in 1993 to make a four-station system. The present system, however, has insufficient sensitivity to measure enough IPS sources for observing the solar wind with good spatial and temporal resolution. As a result, for example, one synoptic map of solar wind speeds requires the superposition of data for three solar rotations. Therefore we have begun the project to upgrade the antenna system at each station. To start with, the Fuji antenna has successfully been improved with an optimum design of the primary feed system and the development of a low noise preamplifier. The Fuji antenna system after the improvement achieved the minimum detectable flux density of 0.3 Jy (bandwidth: 10 MHz, time constant: 100 ms) which is nearly five times better than the previous system. This upgrade project is expected to be fruitful during the coming decade for solar wind study.

Radio astronomical studies of solar activity and its effects on the Solar Corona and the heliosphere

The radio astronomical studies of solar activity are powerful complementary tools to the studies in the other parts of the electromagnetic spectrum and of the corpuscular emissions. We can either observe the Solar radio emission directly or resort to the occultation techniques. The solar radio emission is monitored world wide in all the radio bands, both as the quiet Sun and the bursty solar radio events which can reach levels up to about one million times over the quiet Sun radio emission level. The solar cycle is very much more pronounced in the bursty than it is in the quiet solar emission. The four decades of solar coronal scattering observations have given us extensive information about the varying conditions in the solar outer corona as well as in the remote regions of the heliosphere (by means of the interplanetary scintillation technique). In addition the radio observations have the important advantage which permits us to study the Jovian magnetosphere at the decimetre wavelength all the time from the ground based radio observatories, where it was first discovered more than a decade before the first independent Pioneer and later by the Voyager spacecraft confirmations. Due to the effect of the 22 year solar magnetic cycle which reverses the magnetic polarity of the Sun an unexpected decline has been observed in the late 60-ties and early 70-ties of the scattering of radio waves in the Solar Corona. During the same time there was also a marked decline of the radio emission from the Jovian magnetosphere. This 30% fall of the Jovian decimetric radio emission recovered within several years.

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.

Design of a 74-MHz antenna for radio astronomy

Describes the design and construction of an 8000 m/sup 2/ 74-MHz phased array dedicated to measurement of the solar-wind velocity using the interplanetary scintillation (IPS) technique, and a simple and novel autocalibration system that measures and connects phase and amplitude errors to a level of 1/spl deg/ and 0.2 dB rms. In the IPS technique, intensity fluctuations of compact radio sources caused by plasma turbulence in the solar wind are observed with multiple antennas. The time lag between the antennas is estimated using a cross-correlation analysis. The primary requirement of such a system is sensitivity so that one may observe a large number of compact sources. A secondary requirement is high beam efficiency so that one may observe near the Sun. The scan angle was limited to allow the largest possible array element and thus the simplest feed system. The feed was designed to have independent phase and amplitude control of each element. Although this is not strictly necessary it permits the use of the feed as a phase switched interferometer with which any element can be correlated against any other group of elements. This provides a simple and accurate calibration of the entire array. The antenna was completely prefabricated, the site preparation was minimal, and the installation was quick and accurate. The system is remotely operated. The control information, system diagnostics, and data are transmitted over a leased telephone line. The entire system is powered by storage batteries charged by solar cells. In addition to IFS it has been used extensively for pulsar observations which have similar requirements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evolution of the solar wind structure over a solar cycle: Interplanetary scintillation velocity measurements compared with coronal observations

Sixteen years of solar wind observations via the technique of interplanetary scintillation (IPS) are presented. By an ecliptic comparison with in situ spacecraft observations, these data are shown to be valuable estimates of the large‐scale slowly evolving structures in the solar wind speed, but to underestimate the speed in small‐scale or rapidly evolving structures. These IPS observations allow the large structures to be studied over solar latitudes from 60° north to 60° south over more than a solar cycle. The observations are presented as half‐yearly averages in Carrington longitude and latitude. These are compared with plots of coronal density estimated from coronameter observations and radial magnetic field estimated from solar magnetograph observations and the potential field method. In low and declining solar activity, there is the expected relationship between fast wind and low‐density open‐field regions, and between slow wind, dense corona and proximity to the neutral sheet. The dipolar field component wanders up to 30° from the rotation axis and is followed by dipolar distributions of density and velocity. Near solar maximum, average wind speeds are uniformly slow over the entire range of latitudes covered, the coronal density becomes more spherically distributed (though it retains a somewhat lower density over the solar poles), and the neutral sheet ranges over all latitudes and sometimes forms disconnected surfaces. The relationship between wind speed, density and angular separation from the neutral sheet are then broken. The results confirm the controlling influence of the coronal magnetic field in determining the three‐dimensional structure of the solar wind.

New observations of the angular diameter-redshift relation for radio sources

Measurements of the angular sizes of radio source components in the range 0.1″–1.0″, using the technique of interplanetary scintillation, reveal an absence of small–diameter sources at the largest redshifts. The cosmological implications of this result are discussed.