Quasi-periodic Energy Release and Jets at the Base of Solar Coronal Plumes

Kumar

et al. 2023

ApJ

Plumes are bright structures in coronal holes extending from the solar surface into the corona and are considered as a possible source of the solar wind. Plumes are thought to be rooted in strong unipolar photospheric flux patches (network/plage region). The magnetic activities at the base of plumes may play a crucial role in producing outflows and propagating disturbances (PDs). However, the role of photospheric/chromospheric activities (e.g., jets/spicules) at the base of plumes and their connection to PDs is poorly understood. Using high-resolution observations of a plume taken on 2020 July 23 with the 1.6 m Goode Solar Telescope (GST), Interface Region Imaging Spectrograph (IRIS), and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we analyzed chromospheric/transition region activities at the base of the plume and their connection to outflows/PDs in the plume. The GST Visible Imaging Spectrometer images reveal repetitive spicules with blueshifted emission (pseudo-Doppler maps) at the plume’s footpoint. In addition, the photospheric magnetograms provide evidence of mixed polarities at the base of the plume. The IRIS Mg ii k Dopplergrams show strong blueshifted emission (∼50 km s−1) and a high brightness temperature (Mg ii k2 line) at the footpoint of the plume. The long-period PDs (P ≈ 20–25 minutes) along the plume (AIA 171 Å) match the periodicity of spicules in the chromospheric images, suggesting a close connection between the spicules and the PDs. We suggest that the interchange reconnection between the closed and open flux of the coronal bright point at the plume’s footpoint is the most likely candidate to produce upflows and associated PDs along the plume.

Section: Resultsmentioning

confidence: 54%

Section: Resultsmentioning

confidence: 55%

Section: Summary and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Defining the Middle Corona

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Self Cite

The middle corona, the region roughly spanning heliocentric distances from 1.5 to 6 solar radii, encompasses almost all of the influential physical transitions and processes that govern the behavior of coronal outflow into the heliosphere. The solar wind, eruptions, and flows pass through the region, and they are shaped by it. Importantly, the region also modulates inflow from above that can drive dynamic changes at lower heights in the inner corona. Consequently, the middle corona is essential for comprehensively connecting the corona to the heliosphere and for developing corresponding global models. Nonetheless, because it is challenging to observe, the region has been poorly studied by both major solar remote-sensing and in-situ missions and instruments, extending back to the Solar and Heliospheric Observatory (SOHO) era. Thanks to recent advances in instrumentation, observational processing techniques, and a realization of the importance of the region, interest in the middle corona has increased. Although the region cannot be intrinsically separated from other regions of the solar atmosphere, there has emerged a need to define the region in terms of its location and extension in the solar atmosphere, its composition, the physical transitions that it covers, and the underlying physics believed to shape the region. This article aims to define the middle corona, its physical characteristics, and give an overview of the processes that occur there.

Coronal Holes, Footpoint Reconnection, and the Origin of the Slow (and Fast) Solar Wind

Wang

2024

Sol Phys

The tendency for low-speed solar wind to show greater spatiotemporal variability and different compositional properties from high-speed wind has led to the prevailing idea of a bimodal solar wind, in which fast wind comes from coronal holes and slow wind comes from coronal streamers. We present observational evidence that most of the slow wind originates from small coronal holes or from just inside the boundaries of large holes, with the rest leaking out from coronal streamers and confined to the immediate vicinity of the heliospheric current and plasma sheets. Although this conclusion was suggested earlier by extrapolations of photospheric field maps, additional support comes from (1) observations of slow wind at Earth following the central-meridian passage of small equatorial holes; (2) observations of slow wind with high Alfvénicity at 1 au by Wind, and more recently near the Sun by Parker Solar Probe and Solar Orbiter; and (3) the finding that 80% of the solar wind observed by Helios at 0.3 – 0.4 au during 1974 – 1978 was Alfvénic. We show that compositional properties such as charge-state ratios vary over the solar cycle and may depend on parameters such as the footpoint field strength $B_{0}$ B 0 , and thus cannot be used alone to distinguish between coronal hole and noncoronal-hole wind. Finally, we note that magnetograms greatly underestimate the amount of small-scale flux emerging inside coronal holes and other unipolar regions. If this rate is taken to be the same as in the quiet Sun, the energy flux density resulting from interchange reconnection with open field lines is on the order of $3\times 10^{5}$ 3 × 10 5 erg cm−2 s−1 ($B_{0}$ B 0 /10 G), sufficient to drive the solar wind. The wind speed depends on the rate of flux-tube expansion, with slower expansion leading to more energy deposition at greater heights and faster wind.