Interplanetary coronal mass ejections (ICMEs) are magnetic structures propagating from the Sun's corona to the interplanetary medium. With over 20 years of observations at the L1 libration point, ACE offers hundreds of ICMEs detected at different times during several solar cycles and with different features such as the propagation speed. We investigate a revisited catalog of more than 400 ICMEs using the superposed epoch method on the mean, median, and the most probable values of the distribution of magnetic and plasma parameters. We also investigate the effects of the speed of ICMEs relative to the solar wind, the solar cycle, and the existence of a magnetic cloud on the generic ICME profile. We find that fast-propagating ICMEs (relatively to the solar wind in front) still show signs of compression at 1 au, as seen by the compressed sheath and the asymmetric profile of the magnetic field. While the solar cycle evolution does not impact the generic features of ICMEs, there are more extreme events during the active part of the cycle, widening the distributions of all parameters. Finally, we find that ICMEs with or without a detected magnetic cloud show similar profiles, which confirms the hypothesis that ICMEs with no detected magnetic clouds are crossed further away from the flux rope core. Such a study provides a generic understanding of processes that shape the overall features of ICMEs in the solar wind and can be extended with future missions at different locations in the solar system. Plain Language Summary Interplanetary coronal mass ejections (ICMEs) are magnetized clouds of solar material expelled from the Sun's atmosphere into the interplanetary medium. In the present article, we use plasma and magnetic data from the NASA ACE mission positioned at the Lagrange 1 point and perform statistical studies over the 400 ICMEs detected over the last 20 years. Such an approach, called a superposed epoch analysis, provides a temporal description of the generic features of ICMEs. In particular, we find that ICMEs that propagate faster than their surrounding solar wind still show compressed regions of plasmas and stronger magnetic field. While we find that the 11-year solar cycle does not affect the generic properties of ICMEs, we observe more extreme events during the active phase. Finally, we also find that a subset of ICMEs, called magnetic clouds and often associated with a stronger and more coherent magnetic field, have the same properties as other ICMEs. This confirms that most ICMEs may be magnetic clouds but which detection is limited by the spacecraft crossing. Such a study, based on long-term heliospheric missions, allows us to probe physical processes that occur during the propagation of ICMEs, which can help better predict space weather and its consequences.

Interplanetary coronal mass ejections (ICMEs) are known to modify the structure of the solar wind as well as interact with the space environment of planetary systems. Their large magnetic structures have been shown to interact with galactic cosmic rays (GCRs), leading to the Forbush decrease (FD) phenomenon. We revisit in the present article the 17 yr of Advanced Composition Explorer spacecraft ICME detection along with two neutron monitors (McMurdo and Oulu) with a superposed epoch analysis to further analyze the role of the magnetic ejecta in driving FDs. We investigate in the following the role of the sheath and the magnetic ejecta in driving FDs, and we further show that for ICMEs without a sheath, a magnetic ejecta only is able to drive significant FDs of comparable intensities. Furthermore, a comparison of samples with and without a sheath with similar speed profiles enable us to show that the magnetic field intensity, rather than its fluctuations, is the main driver for the FD. Finally, the recovery phase of the FD for isolated magnetic ejecta shows an anisotropy in the level of the GCRs. We relate this finding at 1 au to the gradient of the GCR flux found at different heliospheric distances from several interplanetary missions.