Formation of a streamer blob via the merger of multiple plasma clumps below 2 R⊙

Abstract

Context. Propagating streamer blobs could be an important source of disturbances in the solar wind. Direct observations of the formation of streamer blobs could be a proxy for understanding the formation of small-scale structures and disturbances in the solar wind. Aims. We aim to investigate how a streamer blob is formed before it is observed in the outer corona. Methods. Using special coordinated observations from SOHO/LASCO, GOES/SUVI, and SDO/AIA, we studied the precursors of a streamer blob seen in the corona below 2.0 solar radii (R⊙). Results. We find that the streamer blob formed due to the gradual merging of three clumps of brightenings initiated from the lower corona at about 1.8 R⊙, which was likely driven by the expansion of the loop system at the base of the streamer. The acceleration of the blob starts at 1.9 R⊙ or lower. It propagates along the south flank of the streamer, where an expanding elongated brightening occurs coincidentally. Conclusions. Our observations demonstrate that formation of a streamer blob is a complex process. We suggest that the expansion of the loop results in a pinching-off flux-rope-like blob at the loop apex below 2 R⊙. When the blob moves outward, it can be transferred across the overlying loops through interchange or component magnetic reconnection and is then released into the open field system. When the blob moves toward open field lines, interchange magnetic reconnection might also occur, and that can accelerate the plasma blob intermittently, while allowing it to transfer across the open field lines. Such dynamics in a streamer blob might further trigger small-scale disturbances in the solar wind such as switchbacks in the inner heliosphere.