Detection of Strong Photospheric Downflows Accompanying Magnetic Cancellation in Collisional Polarity Inversion Lines of Flare- and CME-Productive Active Regions

Individual events of cancellation of small magnetic features in the quiet Sun seen in photospheric magnetogram observations can be attributed to either the submergence of Ω-loops or the emergence of U-loop structures through the solar photosphere. As the opposite polarities of these small features converge and cancel, they form very compact polarity inversion lines (PILs). In Active Regions (ARs) cancellation of such small opposite polarity features is typically seen to occur during the decay phase of ARs. However, compact PILs can form earlier in an AR’s lifetime, e.g. in complex and developing multipolar ARs, as a result of the collision between at least two emerging flux tubes nested within the same AR. This process is called "collisional shearing" as to emphasize that the shearing and flux cancellation develop owing to the collision. High spatial and temporal resolution observations from the Solar Dynamics Observatory for two emerging ARs, AR 11158 and AR 12017, show the continuous cancellation at the collisional PIL for as long as the collision persists. The flux cancellation is accompanied by a succession of solar flares and CMEs, products of magnetic reconnection along the collisional PIL. Here, we use high spatial resolution magnetograms and Doppler observations from HINODE/SP to confirm that the cancellation is consistent with the submergence of Ω-loops, also resulting to a twisted magnetic flux rope in the corona. Such confirmation with HINODE/SP is important to elucidate the role of the collisional shearing process on the formation of magnetic flux ropes. This finding has implications in our understanding of extreme solar activity.