Evolution of interacting coronal mass ejections driving the great geomagnetic storm on 10 May 2024

Abstract: The arrival of a series of coronal mass ejections (CMEs) at the Earth resulted in a great geomagnetic storm on 10 May 2024, the strongest storm in the last two decades. We investigate the kinematic and thermal evolution of the successive CMEs to understand their interaction en route to Earth. We attempt to find the dynamics, thermodynamics, and magnetic field signatures of CME-CME interactions. Our focus is to compare the thermal state of CMEs near the Sun and in their post-interaction phase at 1 AU. The 3D kinematics of six identified Earth-directed CMEs were determined using the GCS model. The flux rope internal state (FRIS) model is implemented to estimate the CMEs' polytropic index and temperature evolution from their measured kinematics. The thermal states of the interacting CMEs are examined using in-situ at 1 AU. Our study determined the interaction heights of selected CMEs and confirmed their interaction that led to the formation of complex ejecta identified at 1 AU. The plasma, magnetic field, and thermal characteristics of magnetic ejecta (ME) within the complex ejecta and other substructures, such as interaction regions (IRs) within two ME and double flux rope-like structures within a single ME, show the possible signatures of CME-CME interaction in in-situ observations. The FRIS-model-derived thermal states for individual CMEs reveal their diverse thermal evolution near the Sun, with most CMEs transitioning to an isothermal state at 6-9 Rsun, except for CME4, which exhibits an adiabatic state due to a slower expansion rate. The complex ejecta at 1 AU shows a predominant heat-release state in electrons, while the ions show a bimodal distribution of thermal states. On comparing the characteristics of CMEs near the Sun and at 1 AU, we suggest that such one-to-one comparison is difficult due to CME-CME interactions significantly influencing their post-interaction characteristics.