On 2010 August 1, the northern solar hemisphere underwent significant activity that involved a complex set of active regions near central meridian with, nearby, two large prominences and other more distant active regions. This activity culminated in the eruption of four major coronal mass ejections (CMEs), effects of which were detected at Earth and other solar system bodies. Recognizing the unprecedented wealth of data from the wide range of spacecraft that were available-providing the potential for us to explore methods for CME identification and tracking, and to assess issues regarding onset and planetary impact-we present a comprehensive analysis of this sequence of CMEs. We show that, for three of the four major CMEs, onset is associated with prominence eruption, while the remaining CME appears to be closely associated with a flare. Using instrumentation on board the Solar Terrestrial Relations Observatory spacecraft, three of the CMEs could be tracked out to elongations beyond 50 • ; their directions and speeds have been determined by various methods, not least to assess their potential for Earth impact. The analysis techniques that can be applied to the other CME, the first to erupt, are more limited since that CME was obscured by the subsequent, much faster event before it had propagated far from the Sun; we discuss the speculation that these two CMEs interact. The consistency of the results, derived from the wide variety of methods applied to such an extraordinarily complete data set, has allowed us to converge on robust interpretations of the CME onsets and their arrivals at 1 AU.

We present multi-point in situ observations of a complex sequence of coronal mass ejections (CMEs) which may serve as a benchmark event for numerical and empirical space weather prediction models. On 2010 August 1, instruments on various space missions (Solar Dynamics Observatory/ Solar and Heliospheric Observatory/Solar-TErrestrial-RElations-Observatory) monitored several CMEs originating within tens of degrees from solar disk center. We compare their imprints on four widely separated locations, spanning 120 • in heliospheric longitude, with radial distances from the Sun ranging from MESSENGER (0.38 AU) to Venus Express (VEX, at 0.72 AU) to Wind, ACE and ARTEMIS near Earth and STEREO-B close to 1 AU. Calculating shock and flux rope parameters at each location points to a non-spherical shape of the shock, and shows the global configuration of the interplanetary coronal mass ejections (ICMEs), which have interacted, but do not seem to have merged. VEX and STEREO-B observed similar magnetic flux ropes (MFRs), in contrast to structures at Wind. The geomagnetic storm was intense, reaching two minima in the Dst index (≈ −100 nT), caused by the sheath region behind the shock and one of two observed MFRs. MESSENGER received a glancing blow of the ICMEs, and the events missed STEREO-A entirely. The observations demonstrate how sympathetic solar eruptions may immerse at least 1/3 of the heliosphere in the ecliptic with their distinct plasma and magnetic field signatures. We also emphasize the difficulties in linking the local views derived from single-spacecraft observations to a consistent global picture, pointing to possible alterations from the classical picture of ICMEs.

[1] Simultaneous observations obtained by the Solwind coronagraph and Faraday rotation of the Helios radio frequency carrier signal in 1979 showed that CMEs produce characteristic 'W' or sigmoid transients in Faraday rotation observations similar to those observed by Pioneer 6 and 9 in 1968 and 1970. We demonstrate that a relaxed flux-rope model is capable of reproducing these observations. Through fitting the model to the observations, we can obtain information on the flux rope orientation, position, size, velocity, rate of change of rope radius and pitch angle. With electron density measurements, we can also obtain a measure of the magnetic field strength. These fits demonstrate that Faraday rotation observations can provide information on the magnetic field of a CME shortly after it erupts.

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.

Fluctuations in plasma electron density may play a role in solar coronal energy transport and dissipation of wave energy. Transcoronal spacecraft radio sounding observations reveal frequency fluctuations (FF) that encode the electron number density disturbances, allowing exploration of coronal compressive wave and advected inhomogeneity models. Primary FF observations from MESSENGER 2009 and published FF residuals from HELIOS 1975-1976 superior conjunctions were combined to produce a composite view of equatorial region FF near solar minimum over solar o↵set range 1.4-25R. Methods to estimate the electron number density fluctuation variance from the observed FF were developed. We created a simple stacked flux tube model that incorporated both propagating slow density waves and advected spatial density variations to explain the observed FF. Slow density waves accounted for most of the FF at low solar o↵set, while spatial density inhomogeneities advected at solar wind speed dominated above the sonic point at 6R. Corresponding spatial scales ranged 1-38 Mm, with scales above 10 Mm contributing most to FF variance. Flux-tube structuring of the model introduced radial elongation anistropy at lower solar o↵sets, but geometric conditions for isotropy were achieved as the the flux tube widths increased further out in the corona. The model produced agreement with the FF observations up to 12R. FF analysis provides information on electron density fluctuations in the solar corona, and should take into account the background compressive slow waves and solar wind-related advection of quasi-static spatial density variations.