Ian Whittaker

A solar storm observed from the Sun to Venus using the STEREO, Venus Express, and MESSENGER spacecraft

The suite of SECCHI optical imaging instruments on the STEREO-A spacecraft is used to track a solar storm, consisting of several coronal mass ejections (CMEs) and other coronal loops, as it propagates from the Sun into the heliosphere during May 2007. The 3-D propagation path of the largest interplanetary CME (ICME) is determined from the observations made by the SECCHI Heliospheric Imager (HI) on STEREO-A (HI-1/2A). Two parts of the CME are tracked through the SECCHI images, a bright loop and a V-shaped feature located at the rear of the event. We show that these two structures could be the result of line-of-sight integration of the light scattered by electrons located on a single flux rope. In addition to being imaged by HI, the CME is observed simultaneously by the plasma and magnetic field experiments on the Venus Express and MESSENGER spacecraft. The imaged loop and V-shaped structure bound, as expected, the flux rope observed in situ. The SECCHI images reveal that the leading loop-like structure propagated faster than the V-shaped structure, and a decrease in in situ CME speed occurred during the passage of the flux rope. We interpret this as the result of the continuous radial expansion of the flux rope as it progressed outward through the interplanetary medium. An expansion speed in the radial direction of similar to 30 km s(-1) is obtained directly from the SECCHI-HI images and is in agreement with the difference in speed of the two structures observed in situ. This paper shows that the flux rope location can be determined from white light images, which could have important space weather applications.

Transient Structures and Stream Interaction Regions in the Solar Wind: Results from EISCAT Interplanetary Scintillation, STEREO HI and Venus Express ASPERA-4 Measurements

We discuss the detection and evolution of a complex series of transient and quasi-static solar-wind structures in the days following the well-known comet 2P/Encke tail disconnection event in April 2007. The evolution of transient solar-wind structures ranging in size from <105 km to >106 km was characterised using one-minute time resolution observation of Interplanetary Scintillation (IPS) made using the European Incoherent SCATter (EISCAT) radar system. Simultaneously, the global structure and evolution of these features was characterised by the Heliospheric Imagers (HI) on the Solar TERrestrial RElations Observatory (STEREO) spacecraft, placing the IPS observations in context. Of particular interest was the observation of one transient in the slow wind, apparently being swept up and entrained by a Stream Interaction Region (SIR). The SIR itself was later detected in-situ at Venus by the Analyser of Space Plasma and Energetic Atoms (ASPERA-4) instrument on the Venus Express (VEX) spacecraft. The availability of such diverse data sources over a range of different time resolutions enables us to develop a global picture of these complex events that would not have been possible if these instruments were used in isolation. We suggest that the range of solar-wind transients discussed here may be the interplanetary counterparts of transient structures previously reported from coronagraph observations and are likely to correspond to transient magnetic structures reported in in-situ measurements in interplanetary space. The results reported here also provide the first indication of heliocentric distances at which transients become entrained.