Prediction of the In Situ Coronal Mass Ejection Rate for Solar Cycle 25: Implications for Parker Solar Probe In Situ Observations

Abstract:

The Parker Solar Probe (PSP) and Solar Orbiter missions are designed to make groundbreaking observations of the Sun and interplanetary space within this decade. We show that a particularly interesting possible in situ observation of an interplanetary coronal mass ejection (ICME) by PSP may arise when PSP shortly resides at distances $< 0.1$~AU to the Sun. During these close encounters, the same ICME flux rope could be observed in situ by PSP twice, by impacting its frontal part as well as its leg. Investigating the odds of this situation, we forecast the yearly and monthly rate of ICME observations in solar cycle 25 (up to the year 2032) based on 2 models for the sunspot number (SSN): (1) the consensus prediction of an expert panel in 2019 (maximum SSN=115), and (2) a prediction by McIntosh et al. (2020, maximum SSN = 232). We link the SSN to the observed ICME rates in solar cycles 23 and 24 with the Richardson and Cane list and our own ICME catalog with a linear fit. This allows us to include several sources of uncertainties, and the average ICME rate results in 3 to 5 events per month at any in situ location near the solar equatorial plane during solar maximum in 2025. Based on these results, we calculate the number of ICMEs to be observed by PSP at distances $< 0.1$ AU as between 2 and 7 until the nominal end of the mission in 2025, including 1~$\sigma$ uncertainties, making a double encounter of an ICME flux rope by PSP indeed possible. We model the potential flux rope signatures of such a double crossing with the semi-empirical 3DCORE flux rope model, showing a telltale elevation of the radial magnetic field component $B_R$, a sign reversal in the component $B_N$ normal to the solar equator, and an otherwise almost constant field during the second encounter, which is in contrast to the classic field rotation in the first encounter. This holds considerable promise to determine the structure of CMEs close to their origin in the solar corona.