On the Contribution of Coronal Mass Ejections to the Heliospheric Magnetic Flux Budget on Different Time Scales

Coronal mass ejections (CMEs) contribute closed magnetic flux to the heliosphere while they are connected at both ends to the Sun and play a key role in adding magnetic flux to the heliosphere. Here, we discuss an outstanding question in heliophysics: how the type of magnetic reconnection that opens CME field lines in the inner heliosphere, i.e. interchange (IC) reconnection (below the Alfvén surface) and/or interplanetary (IP) reconnection (above the Alfvén surface), determines the length of time CMEs contribute to the heliospheric flux budget. Although IP reconnection does not alter the total amount of magnetic flux in the heliosphere, it matters in this context because it prevents the efficient opening of CME closed magnetic flux through IC reconnection, thereby prolonging the length of time that CMEs contribute closed magnetic flux to the heliosphere. We suggest that there is a varying timescale of contribution of individual CMEs to the heliospheric flux budget, with some CMEs contributing for considerably longer than others, depending on their interactions in IP space (i.e., depending on the fraction of the CME magnetic field lines opened up through IP reconnection vs. IC reconnection, or both). Such a distinction has not been taken into account in past studies that estimate the CME flux opening timescale. We outline key criteria to aid in distinguishing IC reconnection from IP reconnection based on in situ spacecraft data and highlight these through two example events. Studying the manner in which CMEs reconnect and open in the inner heliosphere has implications for a broad range of solar and heliospheric physics research areas and yields important insights not only into CMEs' role in the heliospheric flux budget but also the evolution of CME complexity, connectivity, and topology.