Soumyaranjan Dash

Knowledge of the global magnetic field distribution and its evolution on the Sun’s surface is crucial for modeling the coronal magnetic field, understanding the solar wind dynamics, computing the heliospheric open flux distribution, and predicting the solar cycle strength. As the far side of the Sun cannot be observed directly and high-latitude observations always suffer from projection effects, we often rely on surface flux transport (SFT) simulations to model the long-term global magnetic field distribution. Meridional circulation, the large-scale north–south component of the surface flow profile, is one of the key components of the SFT simulation that requires further constraints near high latitudes. Prediction of the photospheric magnetic field distribution requires knowledge of the flow profile in the future, which demands reconstruction of that same flow at the current time so that it can be estimated at a later time. By performing Observing System Simulation Experiments, we demonstrate how the ensemble Kalman filter technique, when used with an SFT model, can be utilized to make "posterior" estimates of flow profiles into the future that can be used to drive the model forward to forecast the photospheric magnetic field distribution.

Magnetic clouds (MCs) are flux rope magnetic structures forming a subset of solar coronal mass ejections, which have significant space weather impacts. The geoeffectiveness of MCs depends on their properties, which evolve during their interplanetary passage. Based on an analysis of observations spanning two solar cycles, we establish that MCs interacting with the ambient solar wind magnetic field (i.e., heliospheric open flux) lose a substantial amount of their initial magnetic flux via magnetic reconnection, which, in some cases, reduce their geoeffectiveness. We find a linear correlation between the eroded flux of MCs and solar open flux which is consistent with the scenario that MC erosion is mediated via the local heliospheric magnetic field draping around an MC during its interplanetary propagation. The solar open flux is governed by the sunspot cycle. This work therefore uncovers a hitherto unknown pathway for solar cycle modulation of the properties of MCs.