UNDERSTANDING INTERPLANETARY CORONAL MASS EJECTION SIGNATURES Report of Working Group B R. F. WIMMER-SCHWEINGRUBER 1,∗ , N. U. CROOKER 2 , A. BALOGH 3 , V. BOTHMER 4 , R. J. FORSYTH 3 , P. GAZIS 5 , J. T. GOSLING 6 , T. HORBURY 3 , A. KILCHENMANN 7 , I. G. RICHARDSON 8 , J. D. RICHARDSON 9 , P. RILEY 10 , L. RODRIGUEZ 4 , R. VON STEIGER 7 , P. WURZ 11 , and T. H. ZURBUCHEN 12 1 Institut f ¨ ur Experimentelle und Angewandte Physik, Extraterrestrische Physik, Christian-Albrechts-University¨ at zu Kiel, Germany 2 Center for Space Physics, Boston University, Boston, MA, USA 3 The Blackett Laboratory, Imperial College London, United Kingdom 4 Max-Planck-Institut f¨ ur Sonnensystemforschung, Lindau, Germany 5 San Jose State University Foundation, NASA Ames Research Center, Moffett Field, CA, USA 6 Laboratory for Atmospheric and Space Physicsm University of Colorado, Boulder, CO, USA 7 International Space Science Institute, Bern, Switzerland 8 NASA Goddard Space Flight Center, Greenbelt, MD, USA 9 Massachusets Institute of Technology, Cambridge, MA, USA 10 Science Applications International Corporation, San Diego, CA, USA 11 Physikalisches Institut, Universit¨ at Bern, Switzerland 12 Dept. of Atmosph. ,Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI, USA ( ∗ Author for correspondence: E-mail: wimmer@physik.uni-kiel.de) (Received 30 November 2005; Accepted in final form 24 May 2006) Abstract. While interplanetary coronal mass ejections (ICMEs) are understood to be the heliospheric counterparts of CMEs, with signatures undeniably linked to the CME process, the variability of these signatures and questions about mapping to observed CME features raise issues that remain on the cutting edge of ICME research. These issues are discussed in the context of traditional understanding, and recent results using innovative analysis techniques are reviewed. Keywords: coronal mass ejections, interplanetary physics, solar wind 1. Introduction Coronal mass ejections (CMEs) and their interplanetary manifestations, interplane- tary coronal mass injections (ICMEs,) are still poorly understood entities. A decade ago, Schwenn (1996) gave an extensive list of unsolved problems and questions. Since then, the Solar and Heliospheric Observatory (SOHO) has much improved and to some extent revolutionized our understanding of CMEs and ICMEs. Our current knowledge of the relation of solar observables with ICMEs is discussed by Crooker and Horbury (2006) and Forsyth et al. (2006) in this volume. This paper focuses on recent progress in understanding in-situ signatures of ICMEs, building upon the introductory paper by Zurbuchen and Richardson (2006, this volume). Space Science Reviews (2006) 123: 177–216 DOI: 10.1007/s11214-006-9017-x C  Springer 2006