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Sun-to-Earth Observations and Characteristics of Isolated Earth- Impacting Interplanetary Coronal Mass Ejections During 2008 - 2014

A sample of isolated Earth-impacting interplanetary coronal mass ejections (ICMEs) that occurred in the period January 2008 to August 2014 is analyzed to study in detail the ICME in situ signatures, with respect to the type of filament eruption related to the corresponding CME. Observations from different vantage points provided by the Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory Ahead and Behind (STEREO-A and B) are used to determine whether each CME under study is Earth directed or not. For Earth-directed CMEs, a kinematical study was performed using the STEREO-A and B COR1 and COR2 coronagraphs and the Heliospheric Imagers (HI1), to estimate the CME arrival time at 1 AU and to link the CMEs with the corresponding in situ solar wind counterparts. Based on the extrapolated CME kinematics, we identified interacting CMEs, which were excluded from further analysis. Applying this approach, a set of 31 isolated Earth-impacting CMEs was unambiguously identified and related to the in situ measurements recorded by the Wind spacecraft. We classified the events into subsets with respect to the CME source location, as well as with respect to the type of the associated filament eruption. Hence, the events are divided into three subsamples: active region (AR) CMEs, disappearing filament (DSF) CMEs, and stealthy CMEs. The related three groups of ICMEs were further divided into two subsets: magnetic obstacle (MO) events (out of which four were stealthy), covering ICMEs that at least partly showed characteristics of flux ropes, and ejecta (EJ) events, not showing such characteristics. In this way, 14 MO-ICMEs and 17 EJ-ICMES were identified. The solar source regions of the non-stealthy MO-ICMEs are found to be located predominantly (9/10, 90%) within ±30∘ from the solar central meridian, whereas EJ-ICMEs originate predominantly (16/17, 94%) from source regions that are outside ±30∘. In the next step, MO-events were analyzed in more detail, considering the magnetic field strength and the plasma characteristics in three different segments, defined as the turbulent sheath (TS), the frontal region (FR), and the MO itself. The analysis revealed various well- defined correlations for AR, DSF, and stealthy ICMEs, which we interpreted considering basic physical concepts. Our results support the hypothesis that ICMEs show different signatures depending on the in situ spacecraft trajectory, in terms of apex versus flank hits.

Coronal mass ejection ; Solar wind ; Filament

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