| Abstract * |
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An impressive variety of dynamic structures permeates the chromosphere above sunspots. Among the most intriguing are penumbral microjets (PMJs). They were first reported in 2007 in time series of Ca II H images observed with the Hinode satellite. PMJs appear as short-lived, bright, small, jet-like transients whose apparent rise speeds are of order 100 km/s. Since their discovery, many studies made significant progress in understanding PMJs by analyzing the distinctive imprints that these features leave in other spectral lines measured using space and ground-based observatories. The brightness, lifetime, and morphology of PMJs point to magnetic reconnections caused by the intricate magnetic field of the underlying photospheric penumbra as their driving mechanism. Furthermore, the progressive heating to transition region temperatures along PMJs revealed by IRIS observations, and the association of some PMJs with downflows in the photosphere found using Hinode data, were interpreted as hints of bi-directional flows produced by the reconnection process. However, an unambiguous confirmation of this scenario requires the clear detection of these magnetic reconnections, which represents a challenge by terms of observing requirements. Recent investigations have reported a discrepancy between their high apparent rise speeds and lower line-of-sight velocities that suggests PMJs may not be entirely related to mass motions induced by magnetic reconnections.
In this talk, I plan to review the current state of knowledge on PMJs, with emphasis on the observational studies that use IRIS and Hinode capabilities, as well as the CRISP and CHROMIS instruments at the SST. |
