Coronal Condensation at Preferential Topological Locations: The Birth of Solar Prominences and Coronal Rain

The million-degree hot and tenuous solar coronal plasma, under certain conditions, can enigmatically undergo a radiative cooling instability and condense into material of 100 times cooler in the form of prominences or coronal rain. Where, when, and how such cooling condensation takes place remain poorly understood. Answers to these questions are not only of scientific importance in their own right, but also bear implications for the fundamental question of coronal heating and the chromosphere-corona mass cycle. Magnetic fields in the magnetized corona undoubtedly play a crucial role (e.g., by trapping the plasma), but where and how? We report recent imaging and spectroscopic observations from SDO/AIA/HMI and IRIS that can shed light on these puzzles. Through a systematic survey, we found that a large fraction of quiet-Sun condensations preferentially occur at the dips of coronal loops or funnels. Such dips are located at/near magnetic topological features, such as null points and quasi-separatrix layers (QSLs), which are regions characterized by high values of the squashing factor. We also identified evidence of magnetic reconnection at such locations, which can produce favorable conditions, e.g., density enhancement by compression and/or mass trapping in plasmoids, that can trigger run-away radiative cooling. We will discuss the significance and broader implications of these novel observations.