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<figure><img src="image_1.png" /></figure>

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# The Magnetic Origin of Solar Campfires

Navdeep K. Panesar<fnref n="1" />,<fnref n="2" /> ID, Sanjiv K. Tiwari<fnref n="1" />,<fnref n="2" /> ID, David Berghmans<fnref n="3" /> ID, Mark C. M. Cheung<fnref n="1" /> ID, Daniel Müller<fnref n="4" /> ID,
Frederic Auchere<fnref n="5" /> ID, and Andrei Zhukov<fnref n="3" />,<fnref n="6" /> ID

Received 2021 August 23; revised 2021 October 5; accepted 2021 October 13; published 2021 November 2

## Abstract

Solar campfires are fine-scale heating events, recently observed by Extreme Ultraviolet Imager (EUI) on board Solar Orbiter. Here we use EUI 174 Å images, together with EUV images from Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), and line-of-sight magnetograms from SDO/Helioseismic and Magnetic Imager (HMI) to investigate the magnetic origin of 52 randomly selected campfires in the quiet solar corona. We find that (i) the campfires are rooted at the edges of photospheric magnetic network lanes; (ii) most of the campfires reside above the neutral line between majority-polarity magnetic flux patch and a merging minority-polarity flux patch, with a flux cancelation rate of ~10¹⁸ Mx hr⁻<fnref n="1" />; (iii) some of the campfires occur repeatedly from the same neutral line; (iv) in the large majority of instances, campfires are preceded by a cool-plasma structure, analogous to minifilaments in coronal jets; and (v) although many campfires have “complex” structure, most campfires resemble small-scale jets, dots, or loops. Thus, “campfire” is a general term that includes different types of small-scale solar dynamic features. They contain sufficient magnetic energy (~10²<fnref n="6" />–10²<fnref n="7" /> erg) to heat the solar atmosphere locally to 0.5–2.5 MK. Their lifetimes range from about 1 minute to over 1 hr, with most of the campfires having a lifetime of <10 minutes. The average lengths and widths of the campfires are 5400 ± 2500 km and 1600 ± 640 km, respectively. Our observations suggest that (a) the presence of magnetic flux ropes may be ubiquitous in the solar atmosphere and not limited to coronal jets and larger-scale eruptions that make CMEs, and (b) magnetic flux cancelation is the fundamental process for the formation and triggering of most campfires.

*Unified Astronomy Thesaurus concepts: Quiet sun (1322); Solar magnetic fields (1503); Solar coronal transients (312); Solar filaments (1495); Solar coronal heating (1989)*

*Supporting material: animations*

## 1. Introduction

The Solar Orbiter mission was launched on 2020 February 10 (Müller et al. 2020). The payload consists of six remote sensing and four in situ instruments. One of its instruments, the Extreme Ultraviolet Imager (EUI; Rochus et al. 2020) has two high-resolution imagers (HRIs): HRI_EUV and HRI_Lya. Both the HRIs observed the quiet solar corona, in the 174 and 1216 Å passbands, during the first perihelion pass of Solar Orbiter. The HRI_EUV captured small-scale brightenings, known as *campfires* (Berghmans et al. 2021), on the solar disk center in 174 Å images.

Solar campfires are small-scale, short-lived, coronal brightenings, and can appear as loop-like, dot-like, or complex structures. They are mostly rooted at the chromospheric network boundaries and their height lies between 1000 and 5000 km above the photosphere (Berghmans et al. 2021; Zhukov et al. 2021). The formation mechanisms of campfires and their connection to the photospheric magnetic field are unknown.

Campfires might be magnetic reconnection events in the quiet-Sun corona, at small scales, in low-lying magnetic structures. Therefore, these could intrinsically be similar to subflares (nanoflares, microflares) and larger-scale solar

eruptions (Parker 1988; Priest & Forbes 2000; Aschwanden 2005). Consistently, Chen et al. (2021) proposed, using an MHD model, that campfires are mostly caused by component magnetic reconnection, heating the quiet-Sun corona to 1 MK or more.

In this Letter, we examine the magnetic field evolution at the base of campfires and investigate what triggers these heating events. We also examine the physical properties of campfires. For this purpose, we combine the HRI_EUV images with images of Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA; Lemen et al. 2012), and investigate the photospheric magnetic field evolution of on-disk campfires using coaligned line-of-sight magnetograms from SDO/Helioseismic and Magnetic Imager (HMI; Scherrer et al. 2012). By studying a total of 52 campfires observed at 44 different locations, we find that (i) 77% (40 out of 52) of campfires appear at sites of magnetic flux cancelation between the majority-polarity flux patch and a merging minority-polarity flux patch, and (ii) 79% (41 out of 52) of campfires are accompanied by structures of cool plasma.

## 2. Data and Methods

In this study, we use L2 EUI data<fnref n="7" /> (calibrated images) from 2020 May 20 and 2020 May 30. The L2 data are the latest

<figure><img src="image_2.png" /></figure>

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<footnote n="1">¹ Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Building 252, Palo Alto, CA 94304, USA; panesar@lmsal.com</footnote>

<footnote n="2">²Bay Area Environmental Research Institute, NASA Research Park, Moffett Field, CA 94035, USA</footnote>

<footnote n="3">³Solar-Terrestrial Centre of Excellence—SIDC, Royal Observatory of Belgium, Ringlaan -3- Av. Circulaire, B-1180 Brussels, Belgium</footnote>

<footnote n="4">⁴European Space Agency, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands</footnote>

<footnote n="5">⁵Université Paris-Saclay, CNRS, Institut d'Astrophysique Spatiale, F-91405, Orsay, France</footnote>

<footnote n="6">⁶Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119992 Moscow, Russia</footnote>

<footnote n="7">⁷ https://doi.org/10.24414/wvj6-nm32</footnote>
calibrated data product, which is suitable for scientific analysis. The observations of these two days were taken when the instrument was in the commissioning phase. The HRI of EUI captured images in the 174 Å channel (centered on the Fe IX and Fe X lines formed around 1 MK) with high spatial resolution (pixel size of 0".492; Rochus et al. 2020) and high temporal cadence (5 to 10 s). All the campfires we studied here were detected in HRI<sub>EUV</sub> 174 Å. None of the campfires were visible in HRI<sub>Lya</sub>.

On 2020 May 20, Solar Orbiter was located at a distance of 0.612 au from the Sun, which means it observed the Sun from that location with a pixel size of 217 km (Figure 1(a)). As part of technical compression tests, HRI<sub>EUV</sub> produced 174 Å images between 21:20 and 22:17 UT, cycling through a 2 minute program that took five images at 10 s cadence plus a sixth image 70 s later. These images have variable settings, but 60 images are well exposed, unbinned, and compressed at high-quality levels. We find that campfires are visible in some binned data as well. Therefore, we have kept in the animations all the EUI frames including binned ones.

Whereas on 2020 May 30, Solar Orbiter was positioned at a distance of 0.556 au from the Sun (a pixel size of 198 km; Figure 1(b)) and it captured the HRI<sub>EUV</sub> images for about 5 minutes at every 5 s. Figures 1(a) and 1(b) show the EUI/Full Sun Imager (FSI) 174 Å images overlaid with HRI field of view, respectively, for 2020 May 20 and 2020 May 30. Both the images were created with the use of JHelioviewer software (Müller et al. 2017).

In addition to EUI data, we used EUV images from SDO/AIA. AIA provides full-disk solar images in seven different EUV channels. The AIA images have 0"/6 pixels and 12 s temporal cadence. For our analysis, we mainly used 304, 171, 193, and 211 Å images, because we were able to recognize the EUI events clearly in these four channels. We found that campfires are rarely visible in hotter AIA channels (e.g., 335 and 94 Å). We also checked that they are hardly visible in AIA's UV channels (1600 and 1700 Å). To investigate the photospheric magnetic field setting of campfires, we used line-of-sight magnetograms, of 45 s series, from SDO/HMI. The HMI has 0"/5 pixels, 45 s temporal cadence and a noise level of about 7 G (Schou et al. 2012; Couvidat et al. 2016). Two consecutive magnetograms have been summed at each time step to enhance the visibility of weak field regions.

We downloaded 2 hr of AIA and HMI data for 2020 May 20 and 1 hr of data for 2020 May 30, using the JSOC data cutout service.<fnref n="8" /> The AIA and HMI data sets have been coaligned using SolarSoft routines (Freeland & Handy 1998). It is important to note that EUI and AIA observed the Sun from different heliocentric distances. Solar Orbiter was at 0.612 au and 0.556 au from the Sun on 2020 May 20 and 2020 May 30, respectively. Therefore, the events would appear 3.22 minutes and 3.68 minutes earlier in EUI images than in the AIA images on 2020 May 20 and 2020 May 30, respectively. We have created movies, using EUI, AIA, and HMI data, to follow the evolution of campfires together with their underlying magnetic field. The movies and their corresponding figures display the same field of view. The contours, of ±15 G, of HMI magnetograms are overplotted in the animations and figures. The differential emission measure (DEM; Cheung et al. 2015) has been computed, using six AIA channels (171, 193, 211,

131, 335, and 94 Å), to investigate the emission of campfires in different temperature bins.

We inspected the full-resolution HRI<sub>EUV</sub> data and manually identified 52 campfires (from 44 different locations). We looked for those events that show similarities with the campfires in the Solar Orbiter/EUI press release images.<fnref n="9" /> After selecting the campfires in HRI<sub>EUV</sub> 174 Å, we looked for the same campfires in the AIA 171 Å images. Then we coaligned, using SolarSoft routines, the HMI line-of-sight magnetograms with respect to the AIA images, both on board SDO. Therefore, the alignment between AIA images and HMI magnetograms is accurate in order to study the photospheric magnetic field of the campfires.

Our selected campfires are also consistent with the categories of campfires (loop-like, dot-like, and complex) in Berghmans et al. (2021). In addition, we find several campfires to be jet-like in their appearance. All of our selected events are listed in Table 1. We find that some of the campfires occur more than once from the same location. We mainly obtained the duration, length, and width of the campfires from the HRI<sub>EUV</sub> images. We used AIA data to estimate the duration of those campfires that start/end a few minutes before/after the EUI-time coverage.

In Table 1, the measured length is the integrated distance of each campfire along their longer extension, whereas the estimated width is the cross-sectional distance of the campfire. Both measurements are taken during the peak brightening of the campfires in HRI<sub>EUV</sub> images. To estimate the uncertainty in the length and width, we repeated the measurements three times at three nearby locations and then took the average of the three measurements. The listed uncertainty is the uncertainty of the mean (that is, standard deviation of the three measured lengths/widths from their mean, divided by the square root of 3). The duration of campfires is the estimated time from when each of the campfire turns on until when it fades away in HRI<sub>EUV</sub> images.

In Table 1 we have also listed the visibility of cool plasma that is confirmed from the AIA 304 Å and/or 171 Å images. We also mention the category of campfires in the last column—the events appear as loop-like, dot-like, jet-like, or complex structures.

We created magnetic flux evolution plots to quantitatively assess the changes in magnetic flux as a function of time. We integrate flux inside a box covering those magnetic patches that are usually easier to isolate from the neighboring magnetic flux elements, and make sure no opposite flux flows across the boundary of the box. Furthermore, we also created HMI time-distance flux maps to present a detailed and clear picture of magnetic field evolution (e.g., Figure 3(b)).

## 3. Results

### 3.1. Overview

Figures 1(c) and 1(d) show some of the campfires observed by HRI<sub>EUV</sub> on 2020 May 20 and 2020 May 30, respectively. Figures 1(e) and 1(f) show the same campfires in AIA 171 Å images. Some of the campfires that we have investigated in detail (listed in Table 1) are marked by green arrows.

All these events appear in AIA 171 and 304 Å images, but not as clearly as in HRI<sub>EUV</sub> images (Figure 1). Thus, we likely would not have noticed a few of these features in AIA 171 Å images, without first having them seen in the higher-resolution EUI images. In Section 3.2, we present Campfire-2 of Table 1.

<footnote n="8">⁸ http://jsoc.stanford.edu/apiEXPORTDATA.html</footnote>

<footnote n="9">⁹ https://www.esa.int/Science_Exploration/Space_Science/Solar_Orbiter/Solar_Orbiter_s_first_images_reveal_campfires_on_the_Sun</footnote>
EUI 174 20-May-2020 21:20:12

EUI 174 30-May-2020 14:54:15

<figure><img src="image_3.png" /><figcaption>**Figure 1.** Examples of campfires observed on 2020 May 20 and 2020 May 30. Panels (a) and (b) show the EUI/Full Sun Imager (FSI) 174 Å images overlaid with the high-resolution imager (HRI) field of view. The intersections of the two solid yellow circles in (a) and (b) indicate the SDO subsolar points. Panels (c) and (d) show the HRI_EUV images of the same region that is overlaid in panels (a) and (b), respectively. Panels (e) and (f) display AIA 171 Å images of the same field of view shown in panels (c) and (d). The green arrows (in (c) and (d)) point to some of the campfires that we have studied. The green arrows in the AIA images point to the same campfires. The white box in HRI_EUV image (shown in (c); also displayed in (e)) shows the location of the campfires that is presented in detail in Figure 2.</figcaption></figure>
<table><caption>Table 1
Measured Parameters of the Observed Campfires</caption><thead><tr><th>Event No.<br>2020 May 20</th><th>Time<sup>a</sup><br>(UT)</th><th>Location<sup>b</sup><br>(x,y) arcsec</th><th>No. of<sup>c</sup><br>CFs</th><th>Duration<sup>d</sup><br>(minutes)</th><th>Length<sup>e</sup><br>(km)</th><th>Width<sup>f</sup><br>(km)</th><th>Visibility of<sup>g</sup><br>Cool Plasma</th><th>Discernible<sup>h</sup><br>Flux Cancel.</th><th>Category<sup>i</sup><br>of CFs</th></tr></thead><tbody><tr><td>1</td><td>21:20:52<br>21:54:22</td><td>-230, -270</td><td>3<sup>s</sup></td><td>2.1 ± 10 s<br>6.0 ± 12s<sup>t</sup></td><td>7100 ± 330<br>7800 ± 350</td><td>1400 ± 40<br>1350 ± 100</td><td>Y<br>Y</td><td>A<sup>l</sup><br>A</td><td>loop-like</td></tr><tr><td>2</td><td>21:26:12<br>21:58:22<sup>g</sup></td><td>-235, -305</td><td>2</td><td>7.0 ± 10 s<br>4.0 ± 12s<sup>t</sup></td><td>5700 ± 340<br>6900 ± 730</td><td>1500 ± 160<br>2700 ± 900</td><td>Y<br>Y</td><td>Y<br>Y</td><td>loop-like</td></tr><tr><td>3</td><td>21:35:02<br>21:44:52<br>22:00:52</td><td>-20, -250</td><td>3</td><td>2.0 ± 10 s<br>1.5 ± 10 s<br>4.5 ± 12 s</td><td>7600 ± 50<br>5500 ± 150<br>9300 ± 900</td><td>1600 ± 360<br>1300 ± 100<br>2100 ± 300</td><td>Y<br>Y<br>Y</td><td>A<br>A<br>A</td><td>loop-like</td></tr><tr><td>4</td><td>21:48:22<br>22:10:32</td><td>-580,380</td><td>2</td><td>7.0 ± 10 s<br>2.0 ± 10 s</td><td>8700 ± 550<br>7000 ± 640</td><td>1700 ± 670<br>1300 ± 50</td><td>Y<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>5</td><td>21:26:52<br>22:22:42</td><td>285,55</td><td>1</td><td>17.0 ± 20 s<br>8.0 ± 1m<sup>l</sup></td><td>5500 ± 920<br>9600 ± 430</td><td>2200 ± 280<br>1900 ± 220</td><td>Y<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>6</td><td>21:32:42</td><td>225,445</td><td>1</td><td>6.0 ± 10 s<br>129 ± 24s<sup>l</sup></td><td>7300 ± 350<br>7000 ± 550</td><td>2700 ± 260<br>2400 ± 300</td><td>Y<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>7</td><td>22:08:12</td><td>-40, -370</td><td>2</td><td>17.0 ± 10 s<br>13.0 ± 10 s<br>26.0 ± 20 s</td><td>4900 ± 60<br>9500 ± 280<br>10400 ± 810</td><td>1600 ± 235<br>2600 ± 295<br>1900 ± 780</td><td>Y<br>Y<br>Y</td><td>Y<br>Y<br>Y</td><td>complex</td></tr><tr><td>8</td><td>21:37:02</td><td>-80,150</td><td>1</td><td>17.0 ± 10 s</td><td>4900 ± 60</td><td>1900 ± 225</td><td>Y<br>Y</td><td>Y<br>Y</td><td>loop-like</td></tr><tr><td>9</td><td>22:10:22</td><td>-600,580</td><td>1</td><td>12.0 ± 30s<sup>l</sup></td><td>9500 ± 280</td><td>2000 ± 225</td><td>Y<br>Y</td><td>Y<sup>m</sup><br>Y</td><td>complex</td></tr><tr><td>10</td><td>22:13:02</td><td>-530,570</td><td>1</td><td>13.0 ± 10 s</td><td>1000 ± 810</td><td>1900 ± 780</td><td>Y<br>Y</td><td>Y<sup>m</sup><br>Y</td><td>jet-like</td></tr><tr><td>11</td><td>22:08:12</td><td>-590,500</td><td>1</td><td>8.0 ± 10 s</td><td>5000 ± 160</td><td>2000 ± 225</td><td>Y<br>Y</td><td>Y<br>Y</td><td>jet-like</td></tr><tr><td>12</td><td>22:04:52</td><td>-520,510</td><td>1</td><td>26.0 ± 20 s</td><td>8100 ± 340</td><td>1300 ± 430</td><td>Y<br>Y</td><td>Y<br>Y</td><td>dot-like</td></tr><tr><td>13</td><td>22:11:02</td><td>280,43</td><td>1</td><td>6.5 ± 10 s</td><td>6000 ± 440</td><td>3800 ± 225</td><td>Y<br>Y</td><td>Y<br>Y</td><td>jet-like</td></tr><tr><td>14</td><td>22:16:22</td><td>-45, -380</td><td>1</td><td>9.0 ± 12 s</td><td>2900 ± 150</td><td>1400 ± 250</td><td>Y<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>15</td><td>21:38:22</td><td>-600,510</td><td>1</td><td>3.0 ± 10 s</td><td>3300 ± 350</td><td>1500 ± 240</td><td>Y<br>Y</td><td>Y<br>Y</td><td>jet-like</td></tr><tr><td>16</td><td>22:14:52</td><td>-580,365</td><td>1</td><td>8.0 ± 10 s</td><td>2700 ± 350</td><td>1800 ± 160</td><td>Y<br>Y</td><td>Y<br>Y</td><td>loop-like</td></tr><tr><td>17</td><td>22:08:22<br>22:14:32</td><td>-605,395</td><td>2</td><td>5.5 ± 10 s<br>2.0 ± 10 s</td><td>3700 ± 100<br>1300 ± 150</td><td>1200 ± 400<br>1100 ± 100</td><td>Y<br>Y</td><td>Y<br>Y</td><td>jet-like</td></tr><tr><td>18</td><td>22:00:22</td><td>-400, -20</td><td>1</td><td>1.0 ± 10 s</td><td>4900 ± 570</td><td>2800 ± 150</td><td>Y<br>Y</td><td>Y<br>Y</td><td>jet-like</td></tr><tr><td>19</td><td>22:16:22</td><td>-400,0</td><td>1</td><td>8.0 ± 12s<sup>t</sup></td><td>2400 ± 200</td><td>2100 ± 130</td><td>Y<br>Y</td><td>Y<sup>m</sup><br>Y<sup>m</sup></td><td>dot-like</td></tr><tr><td>20</td><td>22:11:22</td><td>-380,0</td><td>1</td><td>4.0 ± 10 s</td><td>1000 ± 10</td><td>960 ± 40</td><td>Y<br>Y</td><td>Y<sup>m</sup><br>Y<sup>m</sup></td><td>dot-like</td></tr><tr><td colspan="10"><strong>2020 May 30</strong></td></tr><tr><td>21</td><td>14:54:40</td><td>-450,330</td><td>1</td><td>7.0 ± 12 s</td><td>9600 ± 670</td><td>1100 ± 315</td><td>Y<br>Y</td><td>Y<sup>n</sup><br>Y</td><td>complex</td></tr><tr><td>22</td><td>14:54:30</td><td>-440,220</td><td>2<sup>s</sup></td><td>11.0 ± 12s<sup>t</sup></td><td>8400 ± 85</td><td>1700 ± 690</td><td>Y<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>23</td><td>14:57:50</td><td>-335,145</td><td>1</td><td>4.0 ± 5 s</td><td>4700 ± 185</td><td>1000 ± 90</td><td>Y<br>Y</td><td>A<sup>o</sup><br>Y</td><td>complex</td></tr><tr><td>24</td><td>15:04:03</td><td>-175,154</td><td>1</td><td>3.0 ± 15 s</td><td>7400 ± 250</td><td>750 ± 10</td><td>Y<br>Y</td><td>Y<br>Y</td><td>loop-like</td></tr><tr><td>25</td><td>14:56:10</td><td>-100,370</td><td>1</td><td>20.5 ± 24 s</td><td>5500 ± 420</td><td>1600 ± 370</td><td>Y<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>26</td><td>14:55:50<br>15:04:00</td><td>-305,350</td><td>3<sup>s</sup></td><td>5.0 ± 12s<sup>t</sup><br>3.0 ± 12s<sup>t</sup></td><td>4700 ± 470<br>5800 ± 450</td><td>1000 ± 220<br>1200 ± 100</td><td>Y<br>Y</td><td>Y<br>Y</td><td>jet-like</td></tr><tr><td>27</td><td>14:55:00</td><td>135,47</td><td>1</td><td>1.5 ± 5 s</td><td>4100 ± 160</td><td>900 ± 75</td><td>N<br>Y</td><td>Y<br>Y</td><td>loop-like</td></tr><tr><td>28</td><td>14:55:55</td><td>20, -70</td><td>1</td><td>3.5 ± 10 s</td><td>4300 ± 140</td><td>1000 ± 120</td><td>Y<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>29</td><td>14:54:00</td><td>-190,50</td><td>1</td><td>3.5 ± 5 s</td><td>6600 ± 350</td><td>2000 ± 200</td><td>Y<sup>q</sup><br>Y<sup>m</sup></td><td>Y<br>Y<sup>m</sup></td><td>complex</td></tr><tr><td>30</td><td>14:55:10</td><td>-220, -100</td><td>1</td><td>198 ± 10m<sup>l</sup></td><td>6600 ± 350</td><td>2000 ± 200</td><td>A<sup>l</sup><br>A</td><td>Y<br>A</td><td>complex</td></tr><tr><td>31</td><td>14:54:25</td><td>105, -180</td><td>1</td><td>22 ± 12 s</td><td>6700 ± 1300</td><td>2100 ± 340</td><td>A<br>Y</td><td>A<br>Y</td><td>complex</td></tr><tr><td>32</td><td>14:57:30</td><td>265, -180</td><td>1</td><td>2.0 ± 5 s</td><td>3600 ± 160</td><td>1200 ± 35</td><td>Y<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>33</td><td>14:54:45</td><td>95, -235</td><td>1</td><td>7.0 ± 12s<sup>t</sup></td><td>3600 ± 135</td><td>1200 ± 190</td><td>Y<br>Y<sup>m</sup></td><td>Y<br>Y</td><td>jet-like</td></tr><tr><td>34</td><td>14:56:05</td><td>-615,140</td><td>1</td><td>18 ± 24s<sup>l</sup></td><td>3500 ± 55</td><td>1600 ± 155</td><td>A<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>35</td><td>14:57:20</td><td>-575,170</td><td>3<sup>s</sup></td><td>4.5 ± 5 s</td><td>6300 ± 530</td><td>1100 ± 155</td><td>A<br>Y</td><td>Y<br>Y</td><td>loop-like</td></tr><tr><td>36</td><td>14:57:55</td><td>326,16</td><td>1</td><td>7.0 ± 5 s</td><td>3400 ± 90</td><td>1200 ± 130</td><td>A<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>37</td><td>14:54:30</td><td>-500,590</td><td>1</td><td>30 ± 24 s</td><td>7700 ± 380</td><td>2700 ± 250</td><td>Y<br>Y</td><td>Y<br>Y<sup>m</sup></td><td>jet-like</td></tr><tr><td>38</td><td>14:55:10</td><td>-190,353</td><td>1</td><td>7.0 ± 10 s</td><td>6300 ± 245</td><td>1800 ± 35</td><td>Y<br>Y</td><td>Y<sup>m</sup><br>Y</td><td>complex</td></tr><tr><td>39</td><td>14:56:50</td><td>-410, -235</td><td>1</td><td>3.0 ± 5 s</td><td>5300 ± 285</td><td>1500 ± 180</td><td>A<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>40</td><td>14:54:25</td><td>-154,335</td><td>1</td><td>3.0 ± 5 s</td><td>3000 ± 255</td><td>1000 ± 140</td><td>A<br>Y</td><td>A<br>Y</td><td>dot-like</td></tr><tr><td>41</td><td>14:57:15</td><td>-192,160</td><td>1</td><td>1.5 ± 5 s</td><td>2000 ± 400</td><td>1150 ± 270</td><td>Y<br>Y</td><td>Y<br>Y</td><td>complex</td></tr><tr><td>42</td><td>14:54:45</td><td>-148,320</td><td>1</td><td>1.0 ± 5 s</td><td>2100 ± 140</td><td>700 ± 100</td><td>A<br>Y</td><td>A<br>A</td><td>loop-like</td></tr><tr><td>43</td><td>14:54:35</td><td>-158,300</td><td>1</td><td>1.3 ± 5 s</td><td>1400 ± 140</td><td>800 ± 160</td><td>N<br>Y<sup>r</sup></td><td>A<br>Y</td><td>dot-like</td></tr><tr><td>44</td><td>14:57:20</td><td>-195, -340</td><td>1</td><td>1.3 ± 10 s</td><td>750 ± 20</td><td>700 ± 70</td><td>Y<sup>r</sup></td><td>Y<sup>r</sup></td><td>dot-like</td></tr><tr><td colspan="10">average ± 1σ<sub>ave</sub> 13.2 ± 30 5400 ± 2500 1600 ± 640</td></tr></tbody></table>

Notes.

a Approximate time of peak brightening in EUI 174 Å images.

b Approximate location of the campfires in EUI 174 Å images.

c Total No. of campfires (CFs) from the same neutral line.

d Duration of the campfires in EUI 174 Å images.

e Integrated length of the campfires during its peak brightening in EUI 174 Å images.

f Cross-sectional width of the campfires during its peak brightening in EUI 174 Å images.

g Whether or not a cool-plasma structure is present at the base of the campfires in AIA 304 and/or 171 Å images.

h Whether a discernible flux cancelation occurs at the base of the campfire.

i Category of the campfires.

j Canceling minority-polarity flux is far from the PIL.

k EUI 174 Å images are binned during the second event.

l Multiple structures brighten at the PIL even after the end of the campfire.

m Cancelation between “weak” flux elements.

n Flux coalescence can be seen at 14:53 UT in the negative flux clump during the event.

o Weak flux elements cancel 10 minutes before the rise of cool plasma.

p Ambiguous, there are many substructures making it difficult to estimate.

q Cool plasma appears and disappears.

r Barely visible in AIA images.

s Only those campfires are characterized here that are covered by EUI (e.g., in Event No. 1, the third campfire is not covered by EUI, thus it is not characterized).

t Duration estimated from AIA 171 Å images.
in detail, and show six additional campfire examples (Figures 5–10), including their DEMs (Figures 11 and 12), in the Appendix.

## 3.2. Presence of Cool Plasma at the Campfire's Base

Figure 2 shows an example of a campfire observed on 2020 May 20. As noted in Table 1, there are two campfires from the same location (Campfire-2 of Table 1). Here, we present the first campfire from this location in detail.

Figures 2(a)–(d) and 2(e)–(t) show the evolution of the campfire in HRI<sub>EUV</sub> and AIA images, respectively. The campfire starts to brighten at 21:24:12 in HRI<sub>EUV</sub> images (Figure 2(a)), reaching at its peak intensity at ~21:26:12. The campfire lasts for about 7 minutes. Before and during the progression of the campfire, a small-scale cool-plasma structure appears at the same location of the campfire (see the white arrow in Figures 2(a) and (b)). As the campfire grows with time, the cool-plasma structure also expands upward (from 21:24:12 to 21:25:02 in the left panel of the Figure 2 animation) from the base of the campfire. The cool structure has a length of 8000 ± 280 km and a width of 1300 ± 140 km during the rise phase.

The campfire and the cool-plasma structure are also visible in AIA 171, 304, 193, and 211 Å images (Figure 2). However, in 193 and 211 Å images the cool plasma is not as clearly visible as in 171 and 304 Å images. We notice that the cool-plasma structure starts to rise at 21:24:57 in AIA 171 Å (right panel of the Figure 2 animation). After the rise of the cool-plasma structure a brightening appears (at 21:26:57) turning into a campfire, at the location where the cool-plasma structure was rooted prior to its rise (see Figures 2(b), (f)).

The campfire reaches its peak intensity at about 21:29:45 (right panel of the Figure 2 animation). (Note that the campfire appears earlier in EUI images than in AIA images because of the different heliocentric distances of both the instruments from the Sun; see Section 2.) The cool plasma continues to rise and it erupts at 21:29:45. The appearance of the cool-plasma structure is very similar to the minifilaments that are seen to drive typical coronal jets (see, e.g., Sterling et al. 2015; Panesar et al. 2016). The average length and width of the cool structure (estimated using AIA 171 Å images) are 11,000 ± 1500 km and 2300 ± 100 km, respectively, which are also similar to the lengths and widths of the pre-jet minifilaments (Panesar et al. 2016).

Similarly, the majority of campfires are accompanied by a cool-plasma structure (Table 1). See the Appendix for six more examples of campfires (Figures 5, 6, 7, 8, 9, and 10).

## 3.3. Magnetic Field Evolution at the Campfire's Base

Figures 2(u)–(x) display the photospheric line-of-sight magnetic field at the base of the campfire. The campfire occurs at the edge of the negative-polarity magnetic flux lane (Figure 2(i)). In this region, the negative magnetic flux is in the majority and the positive flux is in the minority. Both the campfire and cool plasma reside above the same neutral line, between the majority-polarity magnetic flux patch (negative) and a merging minority-polarity flux patch (positive; Figure 2(i)). We followed these flux patches for about 2 hr and noticed that there is flux cancelation going on between the positive and negative flux patches (Figures 2(u)–(x)).

We carefully isolated the minority-polarity (positive) magnetic flux patch of the campfire base and made a plot to show the magnetic flux evolution quantitatively (Figure 3(a)). The area of integrated flux is bounded by a white box in Figure 2(v). Figure 3(a) shows that there is a decrease in the positive magnetic flux, which is due to the continuous flux cancelation between the negative flux patch and a merging positive flux patch. We interpret that the flux cancelation triggers the cool-plasma eruption and that cool plasma drives the campfire. Another campfire appears at the same neutral line (see the red dashed line in Figure 3) apparently caused by the continuous flux cancelation. We estimate the average rate of flux decrease using the best-fit line in Figure 3(a) to be $1.0 \times 10^{18} \text{ Mx hr}^{-1}$.

Figure 3(b) shows the time-distance map along the red dashed line of Figure 2(u). The magnetic flux patches converge and cancel, and trigger the cool-plasma eruption accompanied by the campfire. This scenario is similar to pre-jet minifilaments that are seen to form and erupt multiple times due to flux cancelation at the magnetic neutral line (Panesar et al. 2017; Sterling et al. 2017; Panesar et al. 2018a). Furthermore, the magnetic setup of campfires is also similar to the magnetic environment of small-scale events (e.g., jetlets, explosive events, and coronal bright points) that are also seen to occur due to flux cancelation (e.g., Panesar et al. 2018b; Madjarska 2019; Panesar et al. 2019; Tiwari et al. 2019).

Analogous to this example, we find that all the campfires, of Table 1, reside above magnetic neutral lines and most of them are accompanied by magnetic flux cancelation (Figures 5, 6, 7, 9, and 10).

## 3.4. DEM

We use images from six EUV AIA channels (171, 193, 211, 131, 335, and 94 Å) to compute the DEM distributions of our campfires. Figures 11(a), (b), and (c) show the total EM of the campfire region presented in Figure 2 (campfire-2 of Table 1) that is contained within the temperature range of $log_{10} T$ [5.7,6.0], [6.1,6.4], and [6.5,6.8], respectively. Evidently the campfire contains high coronal temperatures. Most of the EM lies in the $log_{10} T$ bins of 6 to 6.6 (~1 to 4 MK). This particular campfire shows EM signals for low- to high-temperature ranges (from log $T_{10}$ = [5.7,6.0] to [6.5,6.8]).

Figures 11(d)–(f) and 11(g)–(i) show the DEM maps for campfires-8 and-13, from 2020 May 20. Both of these campfires are nicely visible in the temperature range of ~0.5 to 2.5 MK but these do not show EM in 3 MK temperatures or above (in Figures 11(f) and (i)).

Similarly, Figure 12 shows the DEM distributions of campfires shown in Figures 7, 8, 9, and 10. All these campfires have large EM in the temperature range of ~0.5 to 2.5 MK. Overall, all of these campfires appear to have emission in coronal temperatures—this is consistent with the findings of Berghmans et al. (2021).

## 3.5. Statistical Physical Properties

Different physical properties of 52 campfires are listed in Table 1. We find that all the campfires reside above the magnetic neutral lines. Most of the campfires (40 out of 52; exceptions are indicated in Table 1) are accompanied by a cool-plasma structure. Only in two events we did not find any evidence of cool plasma—these events are relatively smaller. In 40 out of 52 events, we observe discernible flux cancelation. In
<figure><img src="image_4.png" /></figure>

**Figure 2.** An example of a campfire observed on 2020 May 20. Panels (a)–(d) show 174 Å HRI<sub>EUV</sub> images of the campfire and display the same field of view as inside the white box of Figure 1(c). A white horizontal bar in (d) scales 5" distance for reference. For HRI<sub>EUV</sub> on 2020 May 20 1" is equal to 443 km. Panels (e)–(h), (i)–(l), (m)–(p), and (q)–(t) show, respectively, the AIA 171, 304, 193, and 211 Å images of the same campfire, and have the same field of view as in the white box of Figure 1(e). Panels (u)–(x) show the HMI line-of-sight magnetograms of the same region. The diagonal red dashed line in panel (u) show the location of the line along which the time-distance map is created and shown in Figure 3(b). The white box in (v) shows the area that is used to calculate the positive magnetic flux plot shown in Figure 3(a). The white arrows point to the cool-plasma structure, and the green arrows point to the campfire itself. In panel (i), HMI contours, of levels ±15 G (at 21:26:06) are overlaid, where cyan and yellow contours represent the positive and negative magnetic polarities, respectively. An animation of this figure is available. The left panel shows the EUI animation from 21:20 to 21:32 UT. It is unannotated and its real-time duration is 3 s. The right side contains the AIA images in a 3 × 2 grid of panels. Its annotations and FOV are same as in the figure and it runs from 21:20 to 22:20 UT. The real-time duration of the right side is 12 s. The events in the EUI animation appear 3.2 minutes earlier than in the AIA images.

(An animation of this figure is available.)
<figure><img src="image_5.png" /><figcaption>**Figure 3.** Magnetic field evolution at the base of the campfire presented in Figure 2. Panel (a) shows the integrated positive magnetic flux plot as a function of time computed inside the box shown in Figure 2(v). Panel (b) shows the HMI time-distance maps along the red dashed lines in Figure 2(u). The solid red lines show the peak time of the campfire. The red dashed lines mark the time of the second campfire that occurs at the same neutral line due to ongoing flux cancelation. The blue line is the least-squares fit of the flux evolution.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>**Figure 4.** Histograms of the physical parameters of 52 campfires listed in Table 1. Panels (a), (b), and (c) show the histograms of the length, width, and duration of the campfires, respectively. In panel (c) the x-axis is displayed in logarithm scale. The mean (median) values of the length, width, and duration are 5400 ± 2500 km (5500 km), 1600 ± 640 km (1500 km), and 13.2 ± 30 minutes (6 minutes), respectively.</figcaption></figure>

a few cases, which are listed as ambiguous, campfires reside above very weak flux patches—even in those cases HMI animations show visible flux cancelation before and/or during the events. We find that in the majority of events, the cool-plasma structures are formed and triggered by flux cancelation.

In Figures 4(a), (b), and (c), we show histograms of the length, width, and duration of the 52 campfires (of Table 1), respectively. Evidently, most of the campfires have lengths between 4000 to 6000 km, but they can be as small as 750 km and as long as 10,400 km. The width of the most campfires ranges between 1000 to 1600 km, but they can be as narrow as 700 km and as wide as 3800 km. The sizes of these events are evidently larger than the spatial resolution of the HRI<sub>EUV</sub> data

(~400 km). The average lengths of the campfires are smaller than the average lengths of Hi-C 2.1 jet-like events (Panesar et al. 2020a) and EUI microjets (Hou et al. 2021). The sizes of dot-like campfires are similar or smaller than the sizes of Hi-C 2.1 dot-like events (Tiwari et al. 2019). The majority of campfires (40) have durations of less than 10 minutes. But they can live as long as 198 minutes (Figure 4).

We estimated free magnetic energy ($B^2 \times V/8\pi$) of the campfires based on their sizes and approximated coronal magnetic field of 20 G, and found them to range in the order of $10^{26}$ to $10^{27}$ erg. For estimating the volumes of dot-like campfires, we considered spherical geometry ($V = 4 \pi r^3/3$), and took the average of their length and width as radius r.
Whereas for the loop-like, jet-like, and complex campfires, we assumed a cylindrical geometry ($V = \pi r^2 h$), and took lengths of the campfires as height $h$ and their widths as radius $r$. In the absence of true measured coronal magnetic field, and due to the fact that we use the projected lengths and widths of campfires, our evaluated free magnetic energies are only crude estimates.

## 4. Discussion

We have examined the evolution of 52 solar campfires using HRI<sub>EUV</sub> images from Solar Orbiter and EUV images from SDO/AIA, and investigated their magnetic origin using line-of-sight magnetograms from SDO/HMI. We find that (i) all the campfires are located above magnetic neutral lines; (ii) in the majority of instances (79%), campfires are accompanied by a cool-plasma structure; (iii) 77% of campfires come from the sites of magnetic flux cancelation, analogous to coronal jets and jetlets; (iv) the cool-plasma structures are anchored at sites of flux cancelation, reminiscent of pre-jet minifilaments; (v) the campfires appear at coronal temperatures (~0.5 to 2.5 MK); (vi) their estimated free magnetic energies are in the order of $10^{26}$ to $10^{27}$ erg; and (vii) while many of the campfires are complex in their structure (previously unexplored), most of them appear as a small-scale loop, a dot, or a coronal jet. In the following we discuss our findings:

*Magnetic flux cancelation.* We find that all our campfires (in Table 1) are rooted at the edges of photospheric magnetic network flux lanes. Most of them occur, at neutral lines, at evident sites of magnetic flux cancelation (40 out of 52 show clear flux cancelation). In a few cases (listed as “ambiguous” in the second to last column of Table 1) (a) either magnetic flux cancelation occurs between the weak flux patches, or (b) the canceling minority flux is a few pixels away from the base of the campfire. However, the minority-polarity flux patches are present at or around the base of each campfire, suggestive of magnetic flux cancelation being involved in generating all campfires.

The flux cancelation rate of ~$10^{18}$ Mx hr$^{-1}$, at the campfire's base, is similar to the flux cancelation rates found for coronal jets in the quiet-Sun regions and coronal holes ($10^{18}$ Mx hr$^{-1}$; Panesar et al. 2016, 2018a), and in large penumbral jets ($10^{18}$ Mx hr$^{-1}$; Tiwari et al. 2018), but are lower than the flux cancelation rates found for active region jets ($10^{19}$ Mx hr$^{-1}$; Sterling et al. 2017), and surges in the core of active regions ($10^{19}$ Mx hr$^{-1}$; Tiwari et al. 2019).

*Presence of cool plasma.* Most of the campfires (41 out of 52; exceptions are indicated in Table 1) are accompanied by a cool-plasma structure, which is present along the neutral line, at the base of the campfire. Only in two events we did not find any evidence of cool plasma. These events are relatively smaller—therefore, the cool plasma might not be discernible. Furthermore, in some cases the campfires occur multiple times from the same neutral line, similar to jets, jetlets, and network jets (Raouafi & Stenborg 2014; Tian et al. 2014; Panesar et al. 2016, 2020b), and each time they are accompanied with a cool-plasma structure.

We infer that the presence of cool-plasma structure might be an indicator of the presence of a magnetic flux rope, probably created by flux cancelation in the same way as observed for pre-jet minifilaments (Panesar et al. 2017) and for typical solar filaments (van Ballegooijen & Martens 1989; Moore & Roumeliotis 1992). We conjecture that the visible flux cancelation is a result of the submergence of the lower

reconnected loops into the photosphere (van Ballegooijen & Martens 1989; Priest & Syntelis 2021; Syntelis & Priest 2021).

Alternatively, magnetic reconnection can directly lead to generation of campfires (without flux ropes) as proposed in some analytical theories and numerical simulations for coronal jets (e.g., Yokoyama & Shibata 1995; Shibata & Magara 2011). This could be the case for a few campfires that do not show clear presence of a cool-plasma structure marked as “ambiguous/no” in the third to last column of Table 1). However, there are some simulations that do show flux rope formation in coronal jets (e.g., Wyper et al. 2018; Doyle et al. 2019).

*Free magnetic energy.* Our estimated free magnetic energies for campfires ($10^{26}$ to $10^{27}$ erg, as discussed earlier) are in agreement with that estimated for campfires in a numerical model by Chen et al. (2021). Our estimated free magnetic energies are also in the range of that of coronal hole jets (Pucci et al. 2013) and coronal X-ray bright points (e.g., Priest et al. 1994). The campfires' free magnetic energies are about an order of magnitude lower in magnitude than the free magnetic energies of active region jets (Sterling et al. 2017), and of active region loops and subflares (Cirtain et al. 2013; Tiwari et al. 2014). Thus, campfires contain sufficient energy to heat the quiet-Sun corona, locally, which is consistent with their emission measure (EM) distributions.

*Similarities with other events.* Based on their appearances in HRI<sub>EUV</sub> images, we have categorized campfires as small loop-like, dot-like, jet-like, or complex structures (as listed in Table 1). Our loop-like, jet-like/surge and dot-like events show similarities with the explosive events in the core of an active region observed by Hi-C 2.1 (Tiwari et al. 2019). The Hi-C explosive events also appeared at sites of opposite-polarity magnetic flux patches, and are confined, thus are reminiscent of campfires, albeit they are located in a different magnetic environment. The loop-like campfires also look similar to the low-lying loop nanoflare events in the moss region observed by Hi-C (Winebarger et al. 2013). The sizes of our jet-like campfires are smaller than the sizes of Hi-C 2.1 jet-like events (Panesar et al. 2019) and EUI microjets (Hou et al. 2021). Further, these two studies did not find any evidence of cool-plasma structure at the jet-base regions.

Some of the campfires might have similarities with coronal X-ray bright points—bright points are also seen to occur at the sites of magnetic flux cancelation (e.g., Longcope 1998). However, coronal bright points might be hotter than campfires because they are visible in hotter wavelengths, e.g., in X-rays (Golub et al. 1974) and/or in AIA 94 Å (Madjarska 2019), whereas our campfires are barely discernible in AIA 94 Å.

Small-scale transient brightenings in the quiet Sun are reportedly located in the magnetic network lanes at the boundaries of supergranule cells (Porter et al. 1987; Porter & Dere 1991; Falconer et al. 1998; Gošić et al. 2014; Attie et al. 2016), similar to our findings for campfires. Some of the campfires have similar sizes and lifetimes of explosive events found in the quiet-Sun regions (Dere et al. 1989). However, the explosive events in the above-mentioned study are found to have lower temperatures and thus most probably are transition region events (e.g., Chae et al. 1998; Innes & Teriaca 2013; Gupta & Tripathi 2015; Huang et al. 2019).

The physical properties of most campfires are in agreement with the above-mentioned events (i.e., loops, dots, coronal jets, and coronal bright points). Therefore the term “campfire” includes different varieties of small-scale solar features/events.
The presence of cool-plasma structure in most of our campfires provides evidence that tiny flux ropes are plausibly present in many solar features, everywhere on the Sun. The magnetic flux cancelation seems to build and trigger tiny flux rope eruptions in campfires, similar to the pre-jet minifilaments (Adams et al. 2014; Young & Muglach 2014; Panesar et al. 2016, 2017, 2018a; McGlasson et al. 2019; Muglach 2021; Shen 2021) and typical solar filaments (that drive CMEs e.g., Sterling et al. 2018). The only major difference lies in that the cool-plasma eruptions in jets occur along far-reaching field lines, whereas in campfires the cool-plasma eruptions are mostly confined and seem to occur at the base of closed-field lines. That is plausibly why most campfires are not seen to erupt outward.

Our results support the simulations of campfires (Chen et al. 2021)—these are at coronal temperature and show evidence of magnetic flux ropes. However, our observations show that the presence of cool structures is much more common than inferred in the simulation (Chen et al. 2021) where only one out of the seven campfires showed a flux rope.

Our observational results provide new insights into the understanding of coronal heating by small-scale campfires, and elucidate that cool-plasma structures might accompany most solar eruptions (ejective or confined). These tiny flux ropes are most probably created by small-scale magnetic flux cancelation, plausibly driven by photospheric random convective flows.

## 5. Conclusions

We investigate the magnetic origin of solar campfires by using Solar Orbiter/EUI, SDO/AIA, and SDO/HMI observations. Although many campfires are “complex,” the term *campfire* encompasses a wide variety of small-scale coronal events (e.g., small-scale loops, dots, and coronal jets). They occur at the edges of photospheric magnetic network flux lanes. The majority of the campfires are accompanied by a

cool-plasma structure, which resides above the magnetic neutral line, where evidently magnetic flux cancelation takes place. Thus, campfires bear similarities with solar eruptions such as coronal jets and CME-producing filament eruptions. Our observations suggest that the presence of cool plasma, i.e., magnetic flux ropes in the solar atmosphere, is more common than previously thought. The campfires contain coronal temperatures and plausibly are small-scale magnetic reconnection events.

We thank an anonymous referee for constructive comments. N.K.P. acknowledges support from NASA's SDO/AIA (NNG04EA00C) and HGI grant (80NSSC20K0720). S.K.T. gratefully acknowledges support by NASA HGI grant (80NSSC21K0520) and NASA contract NNM07AA01C. We acknowledge the use of Solar Orbiter/EUI and SDO/AIA/HMI data. Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. The EUI instrument was built by CSL, IAS, MPS, MSSL/UCL, PMOD/WRC, ROB, LCF/IO with funding from the Belgian Federal Science Policy Office (BELSPO/PRODEX); the Centre National d'Etudes Spatiales (CNES); the UK Space Agency (UKSA); the Bundesministerium für Wirtschaft und Energie (BMWi) through the Deutsches Zentrum für Luft- und Raumfahrt (DLR); and the Swiss Space Office (SSO). AIA is an instrument on board the Solar Dynamics Observatory, a mission for NASA's Living With a Star program. This work has made use of NASA ADSABS.

# Appendix
## Appendix Information

Six additional examples of campfires are shown in Figures 5–10, and their DEMs are shown in Figures 11 and 12.
<figure><img src="image_7.png" /><figcaption>**Figure 5.** Campfire-8 observed on 2020 May 20 (Table 1). Panel (a) shows the 174 Å HRI<sub>EUV</sub> image of the campfire. Panels (b), (c), (d), and (e) show the AIA 171, 304, 193, and 211 Å images of the campfire, respectively. The white arrows point to the cool-plasma structure, and the green arrows point to the campfire. Panel (f) shows the HMI magnetogram of the same region. The red dashed line in (f) shows the cut for the time-distance map in panel (h). The white box in (f) shows the area that is used to calculate the negative magnetic flux plot shown in panel (g). Panels (g) and (h), respectively, show the negative flux plot versus time and the HMI time-distance map. The peak in (g) at 21:45 is due to flux coalescence. The rate of magnetic flux cancelation is $0.4 \times 10^{18} \text{ m} \times \text{hr}^{-1}$. The red line marks the start time of the campfire. In panel (c), HMI contours, of levels ±15 G, of 21:38:06 are overlaid, where cyan and yellow contours represent the positive and negative polarities, respectively. An animation of panels (a)–(f) in this figure is available. The left panel shows the EUI animation from 21:32 to 21:49 UT. It is unannotated and its real-time duration is 4 s. The right side contains the AIA images in a 3 × 2 grid of panels. Its annotations and FOV are same as in the figure and it runs from 21:00 to 22:08 UT. The real-time duration of the right side is 17 s. The events in the EUI animation appear 3.2 minutes earlier than in the AIA images.</figcaption></figure>

(An animation of this figure is available.)
<figure><img src="image_8.png" /><figcaption>**Figure 6.** Campfire-13 observed on 2020 May 20 (Table 1). Panel (a) shows the 174 Å HRI<sub>EUV</sub> image of the campfire. Panels (b), (c), (d), and (e) show the AIA 171, 304, 193, and 211 Å images of the campfire, respectively. The white arrows point to the cool-plasma structure, and the green arrows point to the campfire. Panel (f) shows the HMI magnetogram of the same region. The white box in (f) shows the area that is used to calculate the positive magnetic flux plot shown in panel (g). The red dashed line in (f) shows the east-west cut for the time-distance map in panel (h). Panels (g) and (h) show the positive flux plot versus time and the HMI time-distance map, respectively. Flux cancelation rate is 1.0 × 10<sup>18</sup> mx hr<sup>-1</sup>. The red line marks the start time of the campfire in (g) and (h). In panel (b), HMI contours, of levels ±15 G, of 21:14:06 are overlaid, where cyan and yellow contours represents the positive and negative magnetic polarities, respectively. An animation of panels (a)–(f) in this figure is available. The left panel shows the EUI animation from 22:08 to 22:17 UT. It is unannotated and its real-time duration is 2 s. The right side contains the AIA images in a 3 × 2 grid of panels. Its annotations and FOV are same as in the figure and it runs from 21:47 to 22:24 UT. The real-time duration of the right side is 7 s. The events in the EUI animation appear 3.2 minutes earlier than in the AIA images.</figcaption></figure>

(An animation of this figure is available.)
<figure><img src="image_9.png" /><figcaption>**Figure 7.** Campfire-22 observed on 2020 May 30 (Table 1). Panel (a) shows the 174 Å HRI<sub>EUV</sub> image of the campfire. Panels (b), (c), (d), and (e) show the AIA 171, 304, 193, and 211 Å images of the campfire, respectively. The white arrows point to the cool-plasma structure that is accompanied by the campfire. Panel (f) shows the HMI magnetogram of the same region. The white box region in (f) shows the area that is used to calculate the negative magnetic flux plot shown in panel (g). The red dashed line in (f) shows the east-west cut for the time-distance map in panel (h). Panels (g) and (h) show, respectively, the negative flux plot versus time and the HMI time-distance map along the red dashed line in (f). The peak in panel (g) at 14:48 is due to flux coalescence. Flux cancelation rate is 1.7 × 10<sup>18</sup> mx hr<sup>-1</sup>. The vertical red lines show the start time of both the campfires from the same location. In panel (e), HMI contours, of levels ±15 G, of 14:44:07 are overlaid, where cyan and yellow contours represents the positive and negative magnetic polarities, respectively. This campfire is same as that shown in Figure C5/C6 in Berghmans et al. (2021). An animation of panels (a)–(f) in this figure is available. The left panel shows the EUI animation from 14:54 to 15:04 UT. It is unannotated and its real-time duration is 4 s. The right side contains the AIA images in a 3 × 2 grid of panels. Its annotations and FOV are same as in the figure and it runs from 14:30 to 15:28 UT. The real-time duration of the right side is 15 s. The events in the EUI animation appear 3.6 minutes earlier than in the AIA images.</figcaption></figure>

(An animation of this figure is available.)
<figure><img src="image_10.png" /></figure>

**Figure 8.** Campfire-23 observed on 2020 May 30 (Table 1). Panel (a) shows the 174 Å HRI_EUV image of the campfire. Panels (b), (c), (d), and (e) show the AIA 171, 304, 193, and 211 Å images of the campfire, respectively. The white arrows point to the cool-plasma structure that is accompanied by the campfire. The green arrows show the campfire. Panels (f) and (g) show the HMI magnetograms of the same region. Panel (f) shows the weak magnetic flux patches that cancel 10 minutes before the rise of cool plasma. In panel (e), HMI contours, of levels ±15 G, of 14:58:22 are overlaid on AIA 304 Å image, where cyan and yellow contours represents the positive and negative magnetic polarities, respectively. An animation of this figure is available. The left panel shows the EUI animation from 14:54 to 15:04 UT. It is unannotated and its real-time duration is 4 s. The right side contains the AIA images in a 3 × 2 grid of panels. Its annotations and FOV are same as in the figure and it runs from 14:35 to 15:09 UT. The real-time duration of the right side is 7 s. The events in the EUI animation appear 3.6 minutes earlier than in the AIA images.

(An animation of this figure is available.)
<figure><img src="image_11.png" /><figcaption>**Figure 9.** Campfire-25 observed on 2020 May 30 (Table 1). Panel (a) shows the 174 Å HRI<sub>EUV</sub> image of the campfire. Panels (b), (c), (d), and (e) show the AIA 171, 304, 193, and 211 Å images of the campfire, respectively. The white arrow in (b) points to the possible structure of the cool plasma; the cool plasma is not visible in any other AIA channel. Panel (f) shows the HMI magnetogram of the same region. The white box in (f) shows the area that is used to calculate the positive magnetic flux plot shown in panel (g). The red dashed line in (f) shows the north-south cut for the time-distance map in panel (h). Panels (g) and (h) show the positive flux plot versus time and the HMI time-distance map. Flux cancelation rate is $3.6 \times 10^{18} \text{ mx hr}^{-1}$. The red line marks the start time of the campfire in (g) and (h). In panel (c), HMI contours, of levels ± 15 G, of 14:59:52 are overlaid, where cyan and yellow contours represent the positive and negative magnetic polarities, respectively. An animation of panels (a)–(f) in this figure is available. The left panel shows the EUI animation from 14:54 to 15:04 UT. It is unannotated and its real-time duration is 4 s. The right side contains the AIA images in a 3 × 2 grid of panels. Its annotations and FOV are same as in the figure and it runs from 14:41 to 15:17 UT. The real-time duration of the right side is 8 s. The events in the EUI animation appear 3.6 minutes earlier than in the AIA images.</figcaption></figure>

(An animation of this figure is available.)
<figure><img src="image_12.png" /><figcaption>**Figure 10.** Campfire-26 observed on 2020 May 30 (Table 1). Panel (a) shows the 174 Å HRI<sub>EUV</sub> images of the campfire. Panels (b), (c), (d), and (e) show the AIA 171, 304, 193, and 211 Å images of the same campfire, respectively. The white and green arrows point to the cool-plasma structure and campfire, respectively. Panel (f) shows the HMI magnetogram of the same region. The white box in (f) shows the area that is used to calculate the positive magnetic flux plot shown in panel (g). The red dashed line in (f) shows the east-west cut for the time-distance map in panel (h). Panels (g) and (h) show the positive flux plot versus time and the HMI time-distance map, respectively. Flux cancelation rate is $0.95 \times 10^{18} \text{ mx hr}^{-1}$. The solid red lines show the peak time of the first campfire. The red dashed lines mark the times of the second campfire that occurs at the same neutral line due to ongoing flux cancelation. The blue line in (g) is the least-squares fit of the flux evolution. In panel (e), HMI contours, of levels ± 15 G, of 14:56:52 are overlaid, where cyan and yellow contours represent the positive and negative magnetic polarities, respectively. An animation of panels (a)–(f) in this figure is available. The left panel shows the EUI animation from 14:54 to 15:04 UT. It is unannotated and its real-time duration is 4 s. The right side contains the AIA images in a 3 × 2 grid of panels. Its annotations and FOV are same as in the figure and it runs from 14:30 to 15:29 UT. The real-time duration of the right side is 12 s. The events in the EUI animation appear 3.6 minutes earlier than in the AIA images.</figcaption></figure>

(An animation of this figure is available.)
<figure><img src="image_13.png" /><figcaption>**Figure 11.** DEM distribution of campfires observed on 2020 May 20. Panels (a)–(c), (d)–(f), and (g)–(i) display the DEM maps of campfires shown in Figures 2, 5, and 6, respectively. The EM for each campfire is displayed in three different temperature bins. The color bar on the top of the image indicates the total EM included within each log<sub>10</sub> T range mentioned in the upper left corner of each panel. The DEM maps show that these campfires have significant EM at coronal temperatures in panels (a)–(e), (g), and (h). However, in panels (f) and (i) there is barely any emission at temperatures above log<sub>10</sub> T(K) = 6.5.</figcaption></figure>
<figure><img src="image_14.png" /><figcaption>**Figure 12.** DEM distribution of campfires observed on 2020 May 30. Panels (a)–(c), (d)–(f), (g)–(i), and (j)–(l) show the DEM maps of campfires shown in Figures 7, 8, 9, and 10, respectively. The color bar indicates the total EM included within a log T range shown in the upper left corner of each panel. The DEM maps show that campfires are visible at coronal temperatures in panels (a)–(e), (g), (h), (j), and (k). However, in panels (c), (f), (i), and (l) there is barely any emission at temperatures above log₁₀ T(K) = 6.5.</figcaption></figure>
ORCID iDs

Navdeep K. Panesar https://orcid.org/0000-0001-7620-362X

Sanjiv K. Tiwari https://orcid.org/0000-0001-7817-2978

David Berghmans https://orcid.org/0000-0003-4052-9462

Mark C. M. Cheung https://orcid.org/0000-0003-2110-9753

Daniel Müller https://orcid.org/0000-0001-9027-9954

Frederic Auchere https://orcid.org/0000-0003-0972-7022

Andrei Zhukov https://orcid.org/0000-0002-2542-9810

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