Interplanetary Coronal Mass Ejections During Solar Cycles 23 and 24: Sun-Earth Propagation Characteristics and Consequences at the Near-Earth Region

In this article, we present a statistical study probing the relation between interplanetary coronal mass ejections (ICMEs) observed at 1 AU and their corresponding coronal mass ejections at the near-Sun region. The work encompasses the ICME activity that occurred during Solar Cycles 23 and 24 (1996 - 2017) while presenting an overall picture of ICME events during the complete Solar Cycle 24 for the first time. The importance of this study further lies in comparing two subsets of ICMEs, i.e. magnetic clouds (MCs) and ejecta (EJ), to explore how the observed structures of ICMEs at 1 AU could be associated with the properties of CMEs during their launch at the Sun. We find that, although Solar Cycle 24 saw a significant reduction in the number of ICME events compared to the previous cycle, the fraction of MCs was much higher during Cycle 24 than Cycle 23 (60% versus 41%). In general, the ICME transit-time decreases with the increase in the CME initial speed, although a broad range of transit times were observed for a given CME speed. We also find that the high-speed ICMEs (≳500 kms−¹) form a distinct group in terms of the deficit in their transit times when compared with low-speed events (≲500 kms−¹), which means that high-speed ICMEs acquire a much higher internal energy from the source active regions during the initiation process that effectively overcomes the aerodynamic drag force while they transit in the interplanetary medium. The CME propagation from the Sun to the near-Earth environment shows both an overall positive and negative acceleration (i.e. deceleration), although the acceleration is limited to only low-speed CMEs that are launched with a speed comparable with or less than the mean solar wind speed (≈400 -450 kms−¹). Within a given cycle, the similarities of MC and EJ profiles with respect to the CME-ICME speed relation as well as interplanetary acceleration support the hypothesis that all CMEs have a flux rope structure and that the trajectory of the CMEs essentially determines the observed ICME structure at 1 AU.