Mean shape of interplanetary shocks deduced from in situ observations and its relation with interplanetary CMEs

JANVIER, M.; DEMOULIN, P.; DASSO, S.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2014 vol. 565 p. 99 - 112

0004-6361

Context. Shocks are frequently detected by spacecraft in the interplanetary space. However, the in situ data of a shock do not providedirect information on its overall properties even when a following interplanetary coronal mass ejection (ICME) is detected.Aims. The main aim of this study is to constrain the general shape of ICME shocks with a statistical study of shock orientations.Methods. We first associated a set of shocks detected near Earth over 10 years with a sample of ICMEs over the same period. Wethen analyzed the correlations between shock and ICME parameters and studied the statistical distributions of the local shock normalorientation. Supposing that shocks are uniformly detected all over their surface projected on the 1 AU sphere, we compared the shocknormal distribution with synthetic distributions derived from an analytical shock shape model. Inversely, we derived a direct methodto compute the typical general shape of ICME shocks by integrating observed distributions of the shock normal.Results. We found very similar properties between shocks with and without an in situ detected ICME, so that most of the shocksdetected at 1 AU are ICME-driven even when no ICME is detected. The statistical orientation of shock normals is compatible with amean shape having a rotation symmetry around the Sun-apex line. The analytically modeled shape captures the main characteristicsof the observed shock normal distribution. Next, by directly integrating the observed distribution, we derived the mean shock shape,which is found to be comparable for shocks with and without a detected ICME and weakly affected by the limited statistics of theobserved distribution. We finally found a close correspondence between this statistical result and the leading edge of the ICME sheaththat is observed with STEREO imagers.Conclusions. We have derived a mean shock shape that only depends on one free parameter. This mean shape can be used in variouscontexts, such as studies for high-energy particles or space weather forecasts.