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A&A
Volume 686, June 2024
Solar Orbiter First Results (Nominal Mission Phase)
Article Number A279
Number of page(s) 15
Section The Sun and the Heliosphere
DOI https://doi.org/10.1051/0004-6361/202449377
Published online 19 June 2024

© The Authors 2024

Licence Creative CommonsOpen Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication.

1. Introduction

Solar jets are collimated beam-like plasma ejections in the solar atmosphere. They are prevalent and can occur at different scales, and are considered to be an important source of coronal heating and of the solar wind (Raouafi et al. 2016, 2023; Shen 2021; Kumar et al. 2022; Chitta et al. 2023). Solar jets also represent the characteristics of magnetic reconnection, with bidirectional jets strongly supporting this explanation due to their double outflows (Innes et al. 1997; Zheng et al. 2018; Shen et al. 2019). Over the decades, thanks to an improvement in the spatiotemporal resolution of observations, small-scale jets in different layers of the solar atmosphere have been studied in detail. Shibata et al. (2007) investigated the inverted Y-shaped chromospheric anemone jets in active regions, suggesting that the heating of the chromosphere and corona may be related to small-scale ubiquitous reconnection. Ji et al. (2012) reported the ultrafine channels for coronal heating, in which continuous small-scale upward energy flows originate in the photosphere and subsequently light up the corona. Tian et al. (2014) observed the prevalent small-scale jets from the networks of the solar transition region and chromosphere, with speeds on the order of ∼100 km s−1 and temperatures of > 105 K, which are likely the source of the solar wind. There are also some other detailed studies, such as of small-scale jets in coronal plumes (Raouafi & Stenborg 2014; Kumar et al. 2022), chromospheric jets (Wang et al. 2021; Hong et al. 2022), chromospheric spicules (De Pontieu et al. 2007; Samanta et al. 2019), recurrent jets from sunspot light bridges (Tian et al. 2018), small-scale IRIS jets (Li et al. 2018), and coronal nanojets (Antolin et al. 2021).

The high-spatiotemporal-resolution coronal extreme ultraviolet (EUV) images observed by Hi-C 2.1 provided new insights into the study of small-scale jets owing to the discoveries of dot-like, loop-like, and surge- or jet-like EUV brightenings at small spatial scales (Tiwari et al. 2019; Panesar et al. 2019). Recently, observations by the Extreme Ultraviolet Imager (EUI; Rochus et al. 2020) on board the Solar Orbiter (Müller et al. 2020) have revealed transient small-scale brightenings in the quiet solar corona termed campfires (Berghmans et al. 2021; Chen et al. 2021; Panesar et al. 2021), moving structures in ultraviolet bright points (Li 2022), persistent null-point reconnection (Cheng et al. 2023), and small-scale plasma flow and jets (Hou et al. 2021; Chitta et al. 2021b, 2023; Mandal et al. 2022).

The energy of a small-scale jet usually has a nanoflare-like order of magnitude (∼1024 erg, Parker 1988). Hou et al. (2021) estimate the energy of typical coronal microjets, with a thermal energy of ∼3.9 × 1024 erg and kinetic energy of ∼2.9 ×  1023 erg. Antolin et al. (2021) estimate the total energy (“thermal + kinetic”) released by a coronal nanojet to be (7.8–17.3)×1024 erg, and they expect that this range of energies corresponds to the high end of the nanojet distribution, most of which is likely to be unresolved by observations. Additionally, the small-scale EUV brightening or bursts also have an energy of 1024 erg per event (Chitta et al. 2021a). Li et al. (2018) estimate that an upper limit of the thermal energy of the coronal EUV brightening caused by the IRIS jets is around 7 × 1024 erg. Using the observation of EUV brightening, Purkhart & Veronig (2022) study the nanoflare energy distributions in quiet-Sun regions and find that the mean energy flux of (3.7 ± 1.6)×104 erg cm−2 s−1 is one order of magnitude smaller than the coronal heating requirement. They also find that clusters of high energy flux (up to 3 × 105 erg cm−2 s−1) are surrounded by extended regions with lower activity.

In this study, we investigate 23 small-scale jets emerging from a quiet-Sun region and estimate their energies. Several events show ambiguous inverted Y-shaped structures resembling the standard or blowout jets described by Moore et al. (2010) and Sterling et al. (2015). Most of them exhibit simple, nearly collimated structures similar to coronal microjets (Hou et al. 2021) and picoflare jets (Chitta et al. 2023). This paper is organized as follows: Sect. 2 introduces the observations and data analysis. Section 3 analyzes three examples of small-scale jets. Section 4 is the discussion and conclusions.

2. Observations and data analysis

On March 30 2023, the observation of the 174 Å EUV High-Resolution Imager (HRIEUV) of Solar Orbiter/EUI started at 15:00:15 UT and ended at 16:07:09 UT (Earth time) in a cadence of 6 s (a total of 670 frames). The spacecraft was at a distance of ∼0.379 AU from the Sun, and its position with respect to solar longitude was ∼6.2° west of the Sun-Earth line. The HRIEUV 174 Å plate scale is 0.492 arcsec per pixel, corresponding to a linear scale of ∼134 km per pixel at this distance. This passband is sensitive to emissions from plasma at temperatures of roughly 1 MK. The level-2 calibrated data (Kraaikamp et al. 2023)1 were used and the remaining jitter in the image sequence was removed using the cross-correlation method.

HRIEUV 174 Å had a field of view (FOV) of a quiet-Sun region on the north side of the NOAA active region (AR) 13262, as is outlined by the white box in Fig. 1 (left panel). HRIEUV 174 Å observation is shown in the online movie (movie_hri174.mp4). During this observation period, there were plenty of jet eruptions in this area. A total of twenty two regions were detected and marked by R1–R22 in Fig. 1 (right panel). Some jets ejected matter over long distances, while others ejected it over short distances. We used the white boxes with different scales to cover the jets.

thumbnail Fig. 1.

AIA 171 Å image of the solar disk (left). The white box represents the selected HRIEUV 174 Å FOV (∼136 × 136 Mm2). 22 regions (R1–R22) analyzed in this study are labeled in the HRIEUV 174 Å image (right).

Six EUV channels of the Atmospheric Imaging Assembly (AIA; Lemen et al. 2012) and the line-of-sight (LOS) magnetograms of the Helioseismic and Magnetic Imager (HMI; Scherrer et al. 2012) on board the Solar Dynamics Observatory (SDO; Pesnell et al. 2012) were also used in this study. AIA 94 Å (T ∼ 6 MK), 131 Å (T ∼ 10 MK), 171 Å (T ∼ 0.7 MK), 193 Å (T ∼ 1.6 MK), 211 Å (T ∼ 2 MK), and 335 Å (T ∼ 2.5 MK) mainly reflect the emissions from the corona. The response of the AIA 171 Å passband is similar to the HRIEUV 174 Å. These EUV passbands have a cadence of 12 s and a plate scale of 0.6 arcsec (∼432 km). The HMI LOS magnetograms have a cadence of 45 s and a plate scale of 0.5 arcsec (∼360 km). All of the above data have removed solar rotation by derotating to 15:00:09 UT, as is seen in Fig. 1. The differential emission measure (DEM) analysis (Cheung et al. 2015; Su et al. 2018) was performed on co-aligned AIA images to extract the physical parameters of plasma. In this procedure, we averaged the AIA intensities over two frames; that is, the reconstructed AIA image sequences have a cadence of 24 s. The temperature range of the inversion was set as 5.5 ≤ log10T ≤ 7.6, following previous suggestions (Hannah & Kontar 2012; Cheung et al. 2015; Su et al. 2018).

The DEM function is an instrument-independent function that characterizes the electron and temperature of optically thin plasma in thermal equilibrium. The DEM function (in units of cm−5 K−1) is defined as the squared electron density, n e 2 $ n_{{\rm e}}^2 $, integrated along the LOS depth, z,

DEM ( T ) = n e 2 d z d T , $$ \begin{aligned} \mathrm{DEM}(T) = n_{\mathrm{e}}^2\frac{\mathrm{d}z}{\mathrm{d}T}, \end{aligned} $$(1)

and the emission measure (EM)-weighted temperature is

T ¯ = ∫ DEM ( T ) × T d T ∫ DEM ( T ) d T = ∫ DEM ( T ) × T d T EM . $$ \begin{aligned} \bar{T} = \frac{\int \mathrm{DEM}(T)\times T\mathrm{d}T}{\int \mathrm{DEM}(T)\mathrm{d}T}= \frac{\int \mathrm{DEM}(T)\times T\mathrm{d}T}{\mathrm{EM}}. \end{aligned} $$(2)

DEM(T) also allows us to estimate the unknown electron density, ne, via the measurement of z,

EM = ∫ DEM ( T ) d T = ∫ n e 2 d z = n e 2 z , $$ \begin{aligned} \mathrm{EM} = \int \mathrm{DEM}(T)\mathrm{d}T = \int n_{\mathrm{e}}^2\mathrm{d}z = n_{\mathrm{e}}^2z, \end{aligned} $$(3)

where ne defines a mean electron density that is averaged over the LOS depth, z, with a filling factor of unity (Aschwanden et al. 2000, 2015).

Figure 2a shows the AIA 171 Å map taken at 15:45:21 UT, in which we can see a similar structure to in HRIEUV 174 Å in Fig. 1. Based on the DEM analysis in this region, Figs. 2b,c give the corresponding EM and EM-weighted temperature maps. 22 regions are marked with small boxes.

thumbnail Fig. 2.

(a)–(c) AIA 171 Å map, EM map, and EM-weighted temperature map, respectively. The FOV of the maps covers the R1–R22 regions.

We describe here the assumptions and formulae used to calculate the jet energies. If we assume that these small-scale jets are elongated cylinders and that our LOS is perpendicular to the direction of jet motion, then the depth, z, is equal to the jet width (w). Assuming that the structure of jet is isothermal and homogeneous (with a constant electron density), the total thermal energy can be expressed as (e.g., Aschwanden et al. 2015)

E th = 3 n e k B T e V jet , $$ \begin{aligned} E_{\mathrm{th}} = 3n_{\rm e}k_{\rm B}T_{\rm e}V_{\rm {jet}}, \end{aligned} $$(4)

where n e = Δ EM w $ n_{\mathrm{e}}=\sqrt{\dfrac{\Delta \mathrm{EM}}{\mathit{w}}} $ is the jet density after considering the variation in EM relative to the pre-event value (ΔEM is the increase in EM, e.g., Purkhart & Veronig 2022; Long et al. 2023), kB = 1.38 × 10−16 erg K−1 is the Boltzmann constant, Te is the temperature around the time when the EUV emission peaked, and V jet = π ( w 2 ) 2 l $ V_\mathrm{{jet}}=\pi (\dfrac{\mathit{w}}{2})^2l $ is the volume of jet. The jet width, w, and length, l, can be measured from the HRIEUV 174 Å image.

We can also calculate the mean thermal energy flux, which presumes that the total thermal energy is dissipated through the surface area of the jet throughout its entire lifetime,

F th = 3 n e k B T e V jet τ tot S jet , $$ \begin{aligned} F_{\mathrm{th}} = \frac{3n_{\rm e}k_{\rm B}T_{\rm e}V_{\rm jet}}{\tau _{\rm tot}S_{\rm jet}}, \end{aligned} $$(5)

where τtot is the total lifetime and S jet ≈ π w l ( π w l ≫ π ( w 2 ) 2 ) $ S_{\mathrm{jet}} \approx \pi \mathit{w}l\ (\pi \mathit{w}l \gg \pi (\dfrac{\mathit{w}}{2})^2) $ is the surface area of the jet. The expression of Fth can then be reduced as

F th = 3 n e k B T e w 4 τ tot , $$ \begin{aligned} F_{\mathrm{th}} = \frac{3n_{\rm e}k_{\rm B}T_{\rm e}{ w}}{4\tau _{\rm tot}}, \end{aligned} $$(6)

which is independent of the jet length.

The kinetic energy flux carried by a parcel of fluid moving with velocity v is (e.g., Chitta et al. 2023)

F k = 1 2 ρ v 3 , $$ \begin{aligned} F_{\mathrm{k}} = \frac{1}{2}\rho v^{3}, \end{aligned} $$(7)

where ρ ≈ nemp is the plasma mass density, and mp = 1.67 × 10−26 g is the proton mass. The Fk is the energy per unit area per unit of time on a plane perpendicular to motion. Subsequently, the total kinetic energy can be derived:

E k = ∑ i F k i τ i S bot , $$ \begin{aligned} E_{\rm k} = \sum _{i} F_{\mathrm{k}i}\tau _i S_{\rm bot}, \end{aligned} $$(8)

where the subscript i denotes the ith blob of the jet, τi is its lifetime, and S bot = π ( w 2 ) 2 $ S_{\mathrm{bot}}= \pi \left(\dfrac{\mathit{w}}{2}\right)^2 $ is the bottom area of the jet.

3. Results

3.1. Unidirectional jets

Each blob (plasmoid; Zhang & Ji 2014; Ni et al. 2017) of small-scale jets recognized and analyzed in this study lasts for at least three frames (i.e., 18 s), which enabled the motion identification from HRIEUV 174 Å images. Figure 3a shows the R12 jet in the HRIEUV 174 Å image, which presents a simple linear motion along a straight line. The blue slit is outlined to obtain the time–distance stacks, and the “end” represents the end of the slit. The dashed black line is the position used to calculate the jet width. Figure 3b shows the estimation of the jet width. The black profile is the reconstructed intensity along the black slit in Fig. 3a, and the blue profile represents the singe Gaussian fitting with a linear background. The full width at half maximum (FWHM) of the fitting result is considered to be the width, which corresponds to a linear scale of ∼0.32 Mm. Figure 3c shows the time–distance diagram derived from the blue slit. To make it easier to show the variability, we also give the corresponding smooth-subtracted images for all of the time–distance diagrams in this study. Figure 3d is the smooth-subtracted image of panel e; that is, after subtracting the slowly varying component, which is a 4-frame (24 s) running average of the original intensity. The smoothing window was chosen individually for each event, and its size can be seen through the blank frames on both sides of the smooth-subtracted image. In Fig. 3d, there is a slanted bright stripe spanning five frames, which outlines the blob motion with a velocity of ∼98 km s−1. The jet lifetime is defined as the time interval between the beginning and end of the moving blob; that is 30 s.

thumbnail Fig. 3.

(a) HRIEUV 174 Å image of the R12 jet. (b) The estimation of the jet width. (c) Time-distance diagram in the position of the blue slit. (d) Smooth-subtracted image of panel c. (e) AIA 171 Å image of the R12 jet. The contour level represents 90% of the peak intensity of AIA 171 Å. (f) The EM map. (g) The EM-weighted temperature map. The mean EM and temperature are averaged over the 90% area. ΔEM is the net increase in EM relative to the pre-jet value.

Figures 3e–f is a zoom-in of the R12 region labeled in Fig. 2. It is obvious that the moving blob is only several bright pixels in the FOV of AIA 171 Å. We chose 90% of the peak intensity as the contour of the jet, which is a good representation due to its elongated structure. Therefore, the mean EM and EM-weighted temperature can be obtained within the 90% area; their values are 4.25 × 1026 cm−5 and 1.78 MK, respectively. As is noted in Sect. 2, the variation in EM relative to the pre-jet value should be considered to estimate the jet density. The ΔEM below Fig. 3f is the net increase that is calculated over the same area as the EM. These EMs and EM-weighted temperatures are computed over the temperature range of 5.6 ≤ log10T ≤ 6.5, where the DEM solution is well constrained. This range is almost the same as in previous literature about coronal microjets (Hou et al. 2021). All other jets also exhibit emissions originating from a similar temperature range and lack higher-temperature components, and thus we can apply the same range to EM analysis of all jets.

Using the ΔEM = 0.36 × 1026 cm−5 and w = 0.32 Mm in Eq. (3), the ne is 1.06 × 109 cm−3, which is a reasonable value for the coronal condition. The jet length, l ∼ 1.5 Mm, can be roughly measured from the HRIEUV 174 Å image. Substituting these known quantities into Eq. (4), the estimated total thermal energy is 9.43 × 1022 erg, which is one order of magnitude smaller than the energy of typical nanoflares (∼1024 erg, Parker 1988; Chitta et al. 2021a). Thus, the thermal energy flux of the R12 jet is 2.08 × 105 erg cm−2 s−1, contributing 2/3 of the canonical amount of energy required to heat the quiet-Sun corona (3 × 105 erg cm−2 s−1, Withbroe & Noyes 1977).

Using Eqs. (7) and (8), the kinetic energy flux of R12 jet is estimated to be 8.34 × 105 erg cm−2 s−1, and the kinetic energy is 2.01 × 1022 erg. We note that the velocity calculated above is a projected velocity and may depend on the viewing angle. The kinetic energy estimation can be heavily affected by the projection effect and may not be accurate, and, based on the calculation, the kinetic energy is very small compared to the thermal energy. It may not be accurate to represent the total energy of the jet simply as “Ek + Eth”, and hence we do not present the total energy in this study.

3.2. Bidirectional jets

Figure 4 gives an example of bidirectional jets in R13. Similar to the analysis for jet R12, Figs. 4a–d show the HRIEUV 174 Å image, the estimation of the jet width, the time–distance diagram, and the smooth-subtracted image, respectively. In this event, two blobs have different velocities (∼80 km s−1 and ∼38 km s−1), but their lifetimes are the same as the total lifetime: 30 s. The jet length has a rough value of ∼3 Mm. Figure 4e shows the AIA 171 Å image of the R13 jets, which just exhibits a few bright pixels. The 90% contour level is also marked. The EM and EM-weighted temperature maps are shown in Figs. 4f,g.

thumbnail Fig. 4.

(a)–(g) Similar to Fig. 3, the results for the R13 jets.

According to the above procedures, the electron density, thermal energy flux, and total thermal energy, are estimated to be 1.25 × 109 cm−3, 2.56 × 105 erg cm−2 s−1, and 2.46 × 1023 erg, respectively. The derived thermal energy flux almost satisfies the energy demand for coronal heating in the quiet-Sun region. The total thermal energy is in the range of 1023–1024 erg. As for the kinetic energy flux, two blobs should be calculated individually: 5.34 × 105 and 0.57 × 105 erg cm−2 s−1. Therefore, the total kinetic energy is 1.61 × 1022 erg, which is one order of magnitude smaller than the total thermal energy.

3.3. Hybrid jets

Besides unidirectional and bidirectional jets, a third type of jet was also detected. In this study, we refer to it as a hybrid jet, which is a mixture of the former two types. Figures 5 and 6 give an example of the third type that is taken in R15. Figures 5a–f present the temporal evolution of jets. The first eruption is bidirectional, followed by a unidirectional propagation, as is indicated by the black arrows. Figure 5g gives the HMI LOS magnetogram, and the red and blue contours represent the magnetic field strength with levels of ±10 G, respectively. Figure 5h shows the AIA 171 Å map with overplotted HMI contours. From this we can see that the jet base is located in a weak opposite-polarity region, which is surrounded by several patches with a magnetic field strength greater than 10 G. The magnetic flux cancellation in opposite-polarity regions is usually the trigger of quiet-region coronal jet eruptions (Panesar et al. 2016). The phenomenon of hybrid jets may be caused by changes in the magnetic field configuration during the first reconnection, which result in the subsequent unidirectional jet.

thumbnail Fig. 5.

(a)–(f) Temporal evolution of the R15 jets. The black arrows indicate the propagation directions of the jets. (g) HMI LOS magnetogram. The red and blue contours represent magnetic field strengths with levels of ±10 G, respectively. (h) AIA 171 Å map with overplotted HMI contours.

thumbnail Fig. 6.

(a)–(g) Similar to Fig. 3, the results for the R15 jets.

The total lifetime of hybrid jets is defined as the time interval between the initiation of the first blob and the termination of the last blob; it is 96 s in this event. The jet length is around 2 Mm, based on Fig. 6a. Using Eqs. (3), (4), and (6), the electron density, thermal energy flux, and total thermal energy are 1.81 × 109 cm−3, 1.06 × 105 erg cm−2 s−1, and 1.98 × 1023 erg, respectively. The thermal energy flux accounts for 1/3 of the energy required to heat the quiet-Sun corona. The total thermal energy is also in the range of 1023–1024 erg.

The respective lifetimes of the three blobs are 78, 60, and 48 s, with speeds of ∼19, ∼21, and ∼21 km s−1. Using Eqs. (7) and (8), the kinetic energy fluxes are 0.10 × 105, 0.14 × 105, and 0.14 × 105 erg cm−2 s−1, and the total kinetic energy is 1.76 × 1021 erg.

Using the same method, the jets in another 19 regions were analyzed and are shown in Appendix A. In order to display the jet contour appropriately, the contour level was chosen individually for every jet within the intensity range of 50–90%. Their parameters and energies are listed in Table 1.

Table 1.

Parameters and calculated energies of the small-scale jets.

4. Discussion and conclusions

Using the high-spatiotemporal-resolution observation of HRIEUV 174 Å of Solar Orbiter/EUI, 23 small-scale jets were identified in a quiet-Sun region that was observed at 15:00:15–16:07:09 UT on March 30, 2023. Three types can be classified based on their motion behaviors: unidirectional, bidirectional, and hybrid jets. The third type may be caused by changes in the magnetic field configuration during the first reconnection, which affects the subsequent eruption. Most of these jets also show repeated blobs, which could arise from the quasi-periodic reconnection that has been observed in some solar flares (Shi et al. 2022a,b; Li et al. 2022). By combining the Solar Orbiter/EUI observation with a simultaneous observation from SDO/AIA, the jets’ physical parameters and energies were measured. According to Table 1, Figs. 7a–c plot the histograms of width, temperature, and velocity, with average values of 0.37 Mm, 1.69 MK, and 70 km s−1, respectively. These jets typically have a width of ∼0.3 Mm and temperature of ∼1.7 MK, with velocities in a wide range between ∼20 and 170 km s−1.

thumbnail Fig. 7.

(a)–(c) Histograms of width, temperature, and velocity, respectively. The average values are given. (d) Jet frequency distribution and the fitting results on a normalized scale in units of 10−50 jets per unit of time (s−1), unit of area (cm−2), and unit of energy (erg−1). The power-law distributions, N(E)∝E−α (red for thermal energy and blue for kinetic energy), are also given.

Most of these jets have an energy of 1023–1024 erg, which is marginally smaller than the energy of typical nanoflares (∼1024 erg, e.g., Parker 1988; Chitta et al. 2021a). We also find that the kinetic energy of small-scale jets is usually one to two orders of magnitude lower than the thermal energy, except for several relatively intense jets such as R5, R7, and R8, which show ambiguous inverted Y-shaped structures similar to standard or blowouts jets (Moore et al. 2010; Sterling et al. 2015). As is shown in Table 1, the thermal energy fluxes of 23 jets are estimated to be (0.74–2.96)×105 erg cm−2 s−1, which is almost on the same order as the energy flow required to heat the quiet-Sun corona (3 × 105 erg cm−2 s−1, Withbroe & Noyes 1977), although the kinetic energy fluxes change over a wide range due to their strong dependence on velocity. Additionally, based on the current 23 samples, we do not find significant discrepancies in energetics between the different jet types.

Figure 7d plots the jet frequency distribution and fitting results on a normalized scale in units of 10−50 jets per unit of time (s−1), unit of area (cm−2), and unit of energy (erg−1). The thermal energy (red) and kinetic energy (blue) both follow the power-law distribution N(E)∝E−α, with slopes of −1.57 and −1.20, respectively. The distribution shown here comes from a relatively small sample size of 23 jets; thus, the distribution only shows a rough approximation. Our results are roughly consistent with the composite flare frequency distribution, as is shown by Aschwanden et al. (2000), who integrated multiple studies over the energy domain of 1024–1032 erg (Crosby et al. 1993; Shimizu & Tsuneta 1997; Krucker & Benz 1998; Parnell & Jupp 2000).

As is shown by Withbroe & Noyes (1977), the coronal energy losses in the quiet-Sun region consist of three components: conduction flux (2 × 105 erg cm−2 s−1), radiative flux (105 erg cm−2 s−1), and solar wind flux (≲5 × 104 erg cm−2 s−1). The area of the quiet-Sun region investigated in this study is 136 × 136 Mm2, as is seen in Fig. 1, and thus the total energy required to sustain the heating of the whole region from 15:00:15 to 16:07:09 UT is around 2 × 1029 erg. Summing the total energy of the 23 events in Table 1, we can obtain a value of about 3 × 1025 erg, which means that the 23 events only account for a very small portion of the total energy demand during this observation. Considering that the 23 events are only a part of all the jets, there are still substantial jets in the image sequence of HRIEUV 174 Å (online movie_hri174.mp4) that are difficult to recognize because of relative strong background emissions or transient properties, or several jets occurring in the same region (such as R4_a and R4_b) that are not listed. It is reasonable to infer that those jets have similar thermal energy fluxes to those calculated here (comparable to 3 × 105 erg cm−2 s−1), contributing to the heating of the local corona. Thus, the contribution of small-scale jets to coronal heating will actually become greater. Besides the energy input into the corona, the dissipation mechanisms of energy are also important. The relevant dissipation mechanisms need to be investigated in future studies. In our observations, although these jets cannot provide sufficient energy to heat the whole quiet-Sun coronal region, they are likely to account for a significant portion of the energy demand in the local regions where the jets occur.

Movie

Movie 1 (movie_hri174) Access here

Acknowledgments

We thank the referee for valuable comments. This work is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, Grant No. XDB0560000. This work is also funded by the National Key R&D Program of China2022YFF0503002 (2022YFF0503000), NSFC under grants 12073081. Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. We appreciate the teams of SDO for their open data-use policy.

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Appendix A: The remaining small-scale jets

thumbnail Fig. A.1.

Similar to Fig. 3, the results for R1, R2, and R3.

thumbnail Fig. A.2.

Similar to Fig. 3, the results for R4_a, R4_b, and R5.

thumbnail Fig. A.3.

Similar to Fig. 3, the results for R6, R7, and R8.

thumbnail Fig. A.4.

Similar to Fig. 3, the results for R9, R10, and R11.

thumbnail Fig. A.5.

Similar to Fig. 3, the results for R14, R16, and R17.

thumbnail Fig. A.6.

Similar to Fig. 3, the results for R18, R19, and R20.

thumbnail Fig. A.7.

Similar to Fig. 3, the results for R21 and R22.

All Tables

Table 1.

Parameters and calculated energies of the small-scale jets.

In the text

All Figures

thumbnail Fig. 1.

AIA 171 Å image of the solar disk (left). The white box represents the selected HRIEUV 174 Å FOV (∼136 × 136 Mm2). 22 regions (R1–R22) analyzed in this study are labeled in the HRIEUV 174 Å image (right).
In the text
thumbnail Fig. 2.

(a)–(c) AIA 171 Å map, EM map, and EM-weighted temperature map, respectively. The FOV of the maps covers the R1–R22 regions.
In the text
thumbnail Fig. 3.

(a) HRIEUV 174 Å image of the R12 jet. (b) The estimation of the jet width. (c) Time-distance diagram in the position of the blue slit. (d) Smooth-subtracted image of panel c. (e) AIA 171 Å image of the R12 jet. The contour level represents 90% of the peak intensity of AIA 171 Å. (f) The EM map. (g) The EM-weighted temperature map. The mean EM and temperature are averaged over the 90% area. ΔEM is the net increase in EM relative to the pre-jet value.
In the text
thumbnail Fig. 4.

(a)–(g) Similar to Fig. 3, the results for the R13 jets.
In the text
thumbnail Fig. 5.

(a)–(f) Temporal evolution of the R15 jets. The black arrows indicate the propagation directions of the jets. (g) HMI LOS magnetogram. The red and blue contours represent magnetic field strengths with levels of ±10 G, respectively. (h) AIA 171 Å map with overplotted HMI contours.
In the text
thumbnail Fig. 6.

(a)–(g) Similar to Fig. 3, the results for the R15 jets.
In the text
thumbnail Fig. 7.

(a)–(c) Histograms of width, temperature, and velocity, respectively. The average values are given. (d) Jet frequency distribution and the fitting results on a normalized scale in units of 10−50 jets per unit of time (s−1), unit of area (cm−2), and unit of energy (erg−1). The power-law distributions, N(E)∝E−α (red for thermal energy and blue for kinetic energy), are also given.
In the text
thumbnail Fig. A.1.

Similar to Fig. 3, the results for R1, R2, and R3.
In the text
thumbnail Fig. A.2.

Similar to Fig. 3, the results for R4_a, R4_b, and R5.
In the text
thumbnail Fig. A.3.

Similar to Fig. 3, the results for R6, R7, and R8.
In the text
thumbnail Fig. A.4.

Similar to Fig. 3, the results for R9, R10, and R11.
In the text
thumbnail Fig. A.5.

Similar to Fig. 3, the results for R14, R16, and R17.
In the text
thumbnail Fig. A.6.

Similar to Fig. 3, the results for R18, R19, and R20.
In the text
thumbnail Fig. A.7.

Similar to Fig. 3, the results for R21 and R22.
In the text

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