Naval Research Laboratory
Comparing White Light Images from STEREO with in Situ Measurements of the Solar Wind during the Recent Solar Minimum
The STEREO mission allows detailed comparisons of white light images of the solar wind (SECCHI experiment) with in situ measurements (ACE, WIND or STEREO) to be performed. We will review the recent results of such comparisons. They confirm that the location, orientation and topology of the magnetic field inside Coronal Mass Ejections (CMEs) largely dictate the aspect of CMEs in white light images. The standard solar indices such as the sunspot number and the flare indices suggest that there was remarkably little solar activity during the recent solar minimum. However, the eruption of CMEs never ceased during the last three years; in particular several formations of Merged Interaction Regions (MIRs) have been detected in SECCHI images and in situ measurements of the solar wind. Many solar transients in the form of CMEs, streamer blowouts, pinch-offs, or blobs can erupt successively and interact before they reach 1 AU. This continual streamer activity, albeit largely reduced compared to solar maximum years, manifests itself in white light images and in situ measurements as the frequent entrainment of transients by fast solar wind streams and the coalescence of complex ejecta. These STEREO observations provide new insights into the variability of the slow solar wind, the evolution of the coronal magnetic field and the modulation of galactic comic rays during an extended period of very low solar activity.