We present a summary of results from ten years of interplanetary scintillation (IPS) observations of stream interaction regions (SIRs) in the solar wind. Previous studies had shown that SIRs were characterized by intermediate-velocity solar wind and – in the case of compressive interactions – higher levels of scintillation. In this study we considered all cases of intermediate velocities in IPS observations from the European Incoherent SCATter (EISCAT) radar facility made at low- and mid-heliographic latitudes between 1994 and 2003. After dismissing intermediate-velocity observations which were associated with solar-wind transients (such as coronal mass ejections) we found that the remaining cases of intermediate velocities lay above coronal structures where stream interaction would be expected. An improved ballistic mapping method (compared to that used in earlier EISCAT studies of interaction regions) was used to identify the regions of raypath in IPS observations which might be expected to include interaction regions and to project these regions out to the distances of in-situ observations. The early stages of developing compression regions, consistent with their development on the leading edges of compressive stream interaction regions, were clearly detected as close to the Sun as 30 R ⊙, and further ballistic projection out to the distances of in-situ observations clearly associated these developing structures with density and velocity features characteristic of developed interaction regions in in-situ data in the cases when such data were available. The same approach was applied to study non-compressive interaction regions (shear layers) between solar-wind streams of different velocities where the stream interface lay at near-constant latitude and the results compared with those from compressive interaction regions. The results confirm that intermediate velocities seen in IPS observations above stream boundaries may arise from either detection of intermediate-velocity flow in compression regions, or from non-compressive shear layers. The variation in velocity about the mean determined from IPS measurements (representing the spread in velocity across that part of the raypath associated with the interaction region in the analysis) was comparable in compressive and non-compressive regions – a potentially interesting result which may contain important information on the geometry of developing SIRs. It is clear from these results that compressive and non-compressive interaction regions belong to the same class of stream – stream interaction, with the dominant mode determined by the latitudinal gradient of the stream interface. Finally, we discuss the results from this survey in the light of new data from the Heliospheric Imagers (HI) on the Solar TErrestrial RElations Observatory (STEREO) spacecraft and other instruments, and suggest possible directions for further work.

The University of California, San Diego (UCSD) three-dimensional (3-D) time-dependent tomography program has been used successfully for a decade to reconstruct and forecast coronal mass ejections from interplanetary scintillation observations. More recently, we have extended this tomography technique to use remote-sensing data from the Solar Mass Ejection Imager (SMEI) on board the Coriolis spacecraft; from the Ootacamund (Ooty) radio telescope in India; and from the European Incoherent SCATter (EISCAT) radar telescopes in northern Scandinavia. Finally, we intend these analyses to be used with observations from the Murchison Widefield Array (MWA), or the LOw Frequency ARray (LOFAR) now being developed respectively in Australia and Europe. In this article we demonstrate how in-situ velocity measurements from the Advanced Composition Explorer (ACE) space-borne instrumentation can be used in addition to remote-sensing data to constrain the time-dependent tomographic solution. Supplementing the remote-sensing observations with in-situ measurements provides additional information to construct an iterated solar-wind parameter that is propagated outward from near the solar surface past the measurement location, and throughout the volume. While the largest changes within the volume are close to the radial directions that incorporate the in-situ measurements, their inclusion significantly reduces the uncertainty in extending these measurements to global 3-D reconstructions that are distant in time and space from the spacecraft. At Earth, this can provide a finely-tuned real-time measurement up to the latest time for which in-situ measurements are available, and enables more-accurate forecasting beyond this than remote-sensing observations alone allow.

We present initial 3D tomographic reconstructions of the inner heliosphere during the Whole Heliosphere Interval (WHI) – Carrington Rotation 2068 (CR2068) – using Solar-Terrestrial Environment Laboratory (STELab) Interplanetary Scintillation (IPS) observations. Such observations have been used for over a decade to visualise and investigate the structure of the solar wind and to study in detail its various features. These features include co-rotating structures as well as transient structures moving out from the Sun. We present global reconstructions of the structure of the inner heliosphere during this time, and compare density and radial velocity with multi-point in situ spacecraft measurements in the ecliptic; namely STEREO and Wind data, as the interplanetary medium passes over the spacecraft locations.

We present the results from modeling the coronal mass ejection (CME) properties that have an effect on the Faraday rotation (FR) signatures that may be measured with an imaging radio antenna array such as the Murchison Widefield Array (MWA). These include the magnetic flux rope orientation, handedness, magnetic-field magnitude, velocity, radius, expansion rate, electron density, and the presence of a shock/sheath region. We find that simultaneous multiple radio source observations (FR imaging) can be used to uniquely determine the orientation of the magnetic field in a CME, increase the advance warning time on the geoeffectiveness of a CME by an order of magnitude from the warning time possible from in-situ observations at L 1, and investigate the extent and structure of the shock/sheath region at the leading edge of fast CMEs. The magnetic field of the heliosphere is largely “invisible” with only a fraction of the interplanetary magnetic-field lines convecting past the Earth; remote sensing the heliospheric magnetic field through FR imaging from the MWA will advance solar physics investigations into CME evolution and dynamics.

The zodiacal-light photometers on the twin Helios spacecraft, the Solar Mass Ejection Imager (SMEI) on the Coriolis spacecraft, and the Heliospheric Imagers (HIs) on the Solar-TErrestrial RElations Observatory (STEREO) twin spacecraft all point the way to optimizing future remote-sensing Thomson-scattering observations from deep space. Such data could be provided by wide-angle viewing instruments on Solar Orbiter, Solar Probe, or other deep-space probes. Here, we present instrument specifications required for a successful heliospheric imager, and the measurements and data-processing steps that make the best use of this remote-sensing system. When this type of instrument is properly designed and calibrated, its data are capable of determining zodiacal-dust properties, and of three-dimensional reconstructions of heliospheric electron density over large volumes of the inner heliosphere. Such systems can measure fundamental properties of the inner heliospheric plasma, provide context for the in-situ monitors on board spacecraft, and enable physics-based analyses of this important segment of the Sun-spacecraft connection.

The European Incoherent SCATter (EISCAT) radar has been used for remote-sensing observations of interplanetary scintillation (IPS) for a quarter of a century. During the April/May 2007 observing campaign, a large number of observations of IPS using EISCAT took place to give a reasonable spatial and temporal coverage of solar wind velocity structure throughout this time during the declining phase of Solar Cycle 23. Many co-rotating and transient features were observed during this period. Using the University of California, San Diego three-dimensional (3-D) time-dependent computer assisted tomography (C.A.T.) solar-wind reconstruction analysis, we show the velocity structure of the inner heliosphere in three dimensions throughout the time interval of 20 April through 20 May 2007. We also compare to white-light remote-sensing observations of an interplanetary coronal mass ejection (ICME) seen by the STEREO Ahead spacecraft inner Heliospheric Imager on 16 May 2007, as well as to in-situ solar-wind measurements taken with near-Earth spacebourne instrumentation throughout this interval. The reconstructions show clear co-rotating regions during this period, and the time-series extraction at spacecraft locations compares well with measurements made by the STEREO, Wind, and ACE spacecraft. This is the first time such clear structures have been revealed using this 3-D technique with EISCAT IPS data as input.

We report the results of a multi-instrument, multi-technique, coordinated study of the solar eruptive event of 13 May 2005. We discuss the resultant Earth-directed (halo) coronal mass ejection (CME), and the effects on the terrestrial space environment and upper Earth atmosphere. The interplanetary CME (ICME) impacted the Earth’s magnetosphere and caused the most-intense geomagnetic storm of 2005 with a Disturbed Storm Time (Dst) index reaching −263 nT at its peak. The terrestrial environment responded to the storm on a global scale. We have combined observations and measurements from coronal and interplanetary remote-sensing instruments, interplanetary and near-Earth in-situ measurements, remote-sensing observations and in-situ measurements of the terrestrial magnetosphere and ionosphere, along with coronal and heliospheric modelling. These analyses are used to trace the origin, development, propagation, terrestrial impact, and subsequent consequences of this event to obtain the most comprehensive view of a geo-effective solar eruption to date. This particular event is also part of a NASA-sponsored Living With a Star (LWS) study and an on-going US NSF-sponsored Solar, Heliospheric, and INterplanetary Environment (SHINE) community investigation.