Spatial and Dynamical Relations between Spicules and Network Bright Points

TL;DR

This study investigates how network bright points (NBPs) influence chromospheric spicules and their connection to coronal emission. Using high-resolution Hα data from the GST/VIS instrument, along with NIRIS magnetograms and SWAMIS-based NBPs tracking, the authors derive Doppler maps and time–distance diagnostics to characterize spicule motions, including torsional components, and correlate these with NBPs and EUV brightness. They find that blueshifted spicules and NBPs show peaked speed distributions, torsional spicules move much faster than NBPs, and high-speed spicules tend to occur above NBPs in EUV-bright regions, consistent with a scenario in which NBPs generate Alfvén waves that drive bidirectional spicule motions and contribute to coronal heating. The results favor NBPs as an energy source and Alfvén waves as the primary energy carrier, with spicules acting as byproducts, pointing to a chromosphere–corona energy-transfer pathway that warrants future multi-line, high-cadence observations with next-generation solar telescopes.

Abstract

Spicules are among the most ubiquitous small-scale, jet-like features in the solar chromosphere and are widely believed to play a significant role in transporting mass and energy into the solar corona with their mechanisms not fully understood. We utilize high-resolution H$α$ images acquired from the 1.6-meter Goode Solar Telescope (GST) at Big Bear Solar Observatory (BBSO) to investigate spatial and the dynamical properties of both spicules and network bright points (NBPs) and, for the first time, incorporated NBP motions in the analyses of spicules. Our main results are as follows: (1) The speed distributions of blueshifted spicules and NBPs both exhibit distinct peaks, whereas that of redshifted spicules is monotonically decreasing. (2) Torsional motions of spicules inferred from alternating signs of Dopplershifts are faster than the NBPs' transversal motions by a factor of $10-10^2$, which may imply the mass density ratio in two different heights as $10^2-10^4$. (3) Blueshifted spicules are found to be more abundant than redshifted spicules in general, but their relative population difference reduces to ~10% at Doppler speeds above 35 km s$^{-1}$. (4) Redshifted spicules lying at higher heights share morphological and dynamical similarity with the blueshifted spicules, which implies the same driving mechanism operating in both directions. (5) These two populations appear above NBPs concentrated under the AIA 193 A bright region. We interpret these results in favor of a scenario that Alfven waves generated by NBPs motions impart their energies to spicules in both torsional and field-aligned motions, and also contribute to the coronal heating and possibly the acceleration of the solar wind.

Figures (8)

• Figure 1: EUV and H$\alpha$ images. (a) SDO/AIA EUV 193 Å shows the target region near a coronal hole. The NIRIS magnetogram is overplotted as contours at the levels of +50 G (pink) and $-$50 G (green). The white box is plotted to denote the FOV of the other panels, and it has the ordinate in the solar radius direction (named $R$) and the abscissa in the azimuthal direction ($T$). The rest are GST/VIS H$\alpha$ composite images constructed by adding the blue/red wing images in the H$\alpha$$\pm$0.6 Å (b) and those in $\pm$1.0 Å (c). Both images are inverted in intensity so that the bright straw-like features are spicules and the dark points underneath are NBPs.
• Figure 2: Blueshifted and redshifted spicules maps and NBPs. (a) A wing difference image obtained by subtracting H$\alpha$$-1.0$Å and H$\alpha$$+1.0$Å images. (b) A pseudo-Dopplergram of the H$\alpha$ line constructed using images in the 11 wavelengths between H$\alpha$$\pm1.0$Å with a scale bar. The vertical dotted lines divide the FOV into 3 sections, A--C. (c) The sub-region within the white box in (b) is shown with only Doppler signals above 25 km s$^{-1}$. The apparent height of a tall blueshifted spicules and a redshifted spicules are $h_B\approx$8.4$"$ and $h_R\approx$2.7$"$. (d) Another sub-region, the yellow box in (b), is shown to be filled with thin and long redshifted spicules and blueshifted spicules. $d_R\approx$0.65$"$ is the interval between two adjacent thin redshifted spicules.
• Figure 3: Spicules and NBPs in motion. Both panels use the Dopplergrams from the GST/VIS H$\alpha$ line data at 16:45:09 UT a the background image. (a) Spicules of interest and seemingly associated NBPs are marked with the green trapeziums. The red circles mark the location of active (moving) NBPs with area-equivalent diameter. (b) Blue arrows are added representing the velocity of NBPs determined using SWAMIS. The three half circles with arrowhead represents inferred rotational sense of NBPs color-coded to mimic blue-red shifts. The half circle denoted A$_3$ is the inferred rotational motion of the footpoint of the spicule in box A$_3$, and those denoted A$_4^{\rm L,R}$, the leftmost and rightmost spicules in box A$_4$.
• Figure 4: Speed distributions in the chromosphere and photosphere. The number of pixels per speed interval counted for (a) blueshifted spicules, (b) redshifted spicules, and (c) NBPs. The dotted lines in (a) and (b) are identical and indicate that in the particular speed interval and region, the count of redshifted spicules pixels agrees to that of blueshifted spicules, while blueshifted spicules usually outnumber redshifted spicules in other speeds. The speed distribution of NBPs in (c) is constructed from 3429 data points from total 141 frames. (d) is the frame used in the calculation of the speed distributions in (a,b), in which the blueshifted/redshifted spicules are marked in the blue/red color shades, and NBPs, in mixed colored contours. The vertical dashed lines divide the whole region into 3 sub-regions denoted as A--C.
• Figure 5: TD maps for spicules and NBPs. (a--d) TD maps for spicules calculated for the different speed threshold as denoted in each panel. See text for the construction method. (e) TD map for NBPs obtained by adding up the number of pixels occupied by NBPs along the vertical direction ($R$-axis) to result in the one-dimensional distribution in the $T$-axis at each time. (f) blueshifted spicules/redshifted spicules shown as color shades over the H$\alpha$--1.0 Å inverse image as a guide. The vertical dashed lines divide the FOV into three regions as defined in previous figures.