arXiv subjects

Sanjiv K. Tiwari

Publications and source records attributed to Sanjiv K. Tiwari.

At least 19 recordsLinked to original sources

arXiv2026

Hbeta Spicules, Small-scale Jets, and Hbeta Microflashes: Sub-arcsecond Dynamic Events and their Magnetic Origins in the Lower Solar Chromosphere Observed by DKIST

We examine an on-disk solar quiet region of enhanced magnetic network using Hbeta images from Daniel K. Inouye Solar Telescopes (DKISTs) Visible Broadband Imager (VBI) and line-of-sight magnetograms from DKISTs Visible Spectro-Polarimeter (ViSP). We also compare the ViSP magnetograms with co-aligned co-temporal line-of-sight magnetograms from the Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI). We find:(i) Two types of chromospheric jet-like features: Hbeta spicules, and small-scale jets. Both are rooted near edges of magnetic network lanes. Several sit close to ViSP-detected tiny islands of either minority-polarity flux or dips in majority-polarity flux. Hence, those several plausibly stem from mixed-polarity magnetic flux, and are caused by chromospheric magnetic reconnection. For H\b{eta} spicules, the average width, length, lifetimes, and speeds are 420$\pm$400 km, 2600$\pm$1600 km, 4.3$\pm$0.25 min, and 12$\pm$4.7 kms. For small-scale jets, those are 385$\pm$100 km, 620$\pm$40 km, 5$\pm$3min, and 4.4$\pm$1.5 kms. (ii) H$β$ microflashes sit in evidently unipolar flux. Their widths, lengths, lifetimes, and speeds are 180$\pm$65 km, 365$\pm$100 km, 4.3$\pm$2.6 min, and 3.1$\pm$0.2 kms. (iii) At the base of a coronal plume, due to its higher spatial resolution than HMI, ViSP shows both some very strong (>800 G) majority-polarity flux not shown by HMI and some sub-arc-second minority-polarity-flux inclusions not shown by HMI. These sub-arcsecond chromospheric transients carry sufficient energy (10^{24}erg) to transiently heat the local chromosphere and corona and potentially contribute to solar-wind acceleration. They may represent the small-scale end of a continuum of magnetic-reconnection-driven activity, highlighting the importance of DKIST's high-resolution magnetic-field measurements for understanding small-scale chromospheric dynamics.

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arXiv2026

Extreme Ultraviolet Microflashes at Plume Bases: A Candidate for Powering the Corona and Solar Wind?

Solar plumes - outflows of bright coronal plasma - are a major component of the open-magnetic-field corona and solar wind, but their driving mechanism remains uncertain. Here we report on network microflashes, fine-scale bright bursts captured by Solar Orbiters Extreme Ultraviolet Imager in 174A images encompassing magnetic network at the base of plumes. Because they sit in evidently unipolar magnetic flux, they are evidently a new, previously unidentified, kind of network event. Approximately 20 microflashes are ongoing within a plume base, with a new microflash starting every second. The energy for an average microflash is 1024 erg, in the range of nanoflares. A 3D data-driven global MHD model yields open magnetic field with fast solar wind for the investigated plumes. From our findings, we suggest that network microflashes result from fine-scale bursts of reconnection of crossed legs of unipolar magnetic field, that the bursts are often triggered by 5-minute p-mode oscillations, and that the bursts are candidates for powering the open-field corona and solar wind. That is, unipolar microflashes such as ours are plausibly from unipolar-network-field reconnection bursts that sustain the heliosphere.

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arXiv2026

The Making of Delta Sunspots

We explore what fraction of delta sunspots in which the polarity inversion line (PIL) is sharp in photospheric magnetograms are made from a writhe kink in an emerging twisted flux rope. We searched simultaneous full-disk magnetograms and continuum images from Helioseismic and Magnetic Imager (HMI) on Solar Dynamics Observatory (SDO) to find 28 random sharp-PIL delta sunspots that are born well on the disk. Only one of these is made from a single newly emerged bipolar magnetic region (BMR) and therefore is a candidate for being made from a single emerging writhe-kinked flux rope. That outcome indicates that few, if any, sharp-PIL delta sunspots are made by a single emerging writhe-kinked flux rope. That is the main new finding of this paper. Each of the other 27 is made by merging of two or more emerging or emerged BMRs. We name delta-sunspot genesis from a single BMR Type I genesis. We identify another three genesis types among the other 27 delta sunspots: Type II, Type III, and Type IV. We present an observed example genesis for each of the four genesis types, and for each example present schematic drawings depicting our scenario(s) for the cause of that example genesis. The core idea of each scenario is that the delta sunspot is made by packing opposite-polarity magnetic flux together by advection into a convection downflow.

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arXiv2025

A sudden fine-scale bright kernel captured by Hi-C Flare in 11 MK emission during an M1.6-class solar flare's post-maximum phase

On April 17, 2024, the third successful Hi-C sounding rocket flight, Hi-C Flare, recorded coronal images in Fe XXI 129 A emission from 11 MK plasma during the post-maximum phase of an M1.6-class solar flare, achieving unprecedented spatial (~300 km) and temporal (1.3 s) resolutions. The flare started at 21:55 UT, peaked at 22:08 UT, and lasted ~40 minutes. Hi-C observed for over five minutes (22:15:45 to 22:21:25), starting roughly eight minutes after flare maximum. A sudden compact bright burst - 875 +/- 25 km wide, lasting 90 +/- 1.3 s, exhibiting a proper motion of ~50 km/s, and splitting into two toward the end - occurs near the foot of some post-flare loops. Its size and brightness are reminiscent of flare-ribbon kernels during a flare's rapid rise phase, kernels marking sites of sudden heating and hot plasma upflow, making its occurrence during the late phase surprising. Such isolated brightenings in a flare's post-maximum phase are rare, and have not been previously reported. The kernel was detected in all SDO/AIA channels. Its 1600 A light curve peaked ~50 s earlier than its 131 A light curve, similar to that of flare-ribbon kernels, albeit with a smaller delay of ~25 s, during the impulsive phase of the flare. In SDO/HMI magnetograms, the kernel sits in unipolar positive magnetic flux near an embedded clump of negative flux. Although localized magnetic reconnection within the kernel (a microflare) cannot be ruled out for its cause, the observations favor the localized brightening being an isolated, exceptionally late flare-ribbon kernel, resulting from an exceptionally late burst of the flare's coronal reconnection.

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arXiv2025

Buildup, Explosion, and Untwisting of a Solar Active Region Jet Observed with Solar Orbiter, IRIS, and SDO

We present detailed analysis of an active region coronal jet accompanying a minifilament eruption that is fully captured and well-resolved in high spatial resolution 174A coronal images from Solar Orbiters Extreme Ultraviolet Imager (EUI). The active region jet is simultaneously observed by the Interface Region Imaging Spectrograph (IRIS) and the Solar Dynamics Observatory (SDO). An erupting minifilament is rooted at the edge of an active region where mixed-polarity magnetic flux is present. Minority-polarity positive flux merges and cancels with the active regions dominant negative flux at an average rate of 1019 Mx/hr, building a minifilament-holding flux rope and triggering its eruption. The eruption shows a slow rise followed by a fast rise, akin to large-scale filament eruptions. EUI images and Mg II k spectra, displaying simultaneously blueshifts and redshifts at the opposite edges of the spire, indicate counterclockwise untwisting of the jet spire. This jet is the clearest, most comprehensively observed active-region jet with this instrument set, displaying striking similarities with quiet Sun and coronal hole jets. Its magnetic, thermal, and kinetic energies suggest a significant contribution to local coronal heating. We conclude that magnetic flux cancelation builds a minifilament-carrying twisted flux rope and also eventually triggers the flux ropes eruption that makes the coronal jet, in line with our recent results on the buildup and explosion of solar coronal jets in quiet Sun and coronal holes. That is, this active region jet clearly works the same way as the vast majority of quiet Sun and coronal hole jets.

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arXiv2025

Pivot of the Emerging Bipolar Magnetic Region in the Birth of Sigmoidal Solar Active Regions

We present an augmentation to longstanding evidence from observations and MHD modeling that (1) every solar emerging bipolar magnetic region (BMR) is made by an emerging omega-loop flux rope, and (2) twist in the flux-rope field makes the emerged field sigmoidal. Using co-temporal full-disk coronal EUV images, magnetograms, and continuum images from Solar Dynamics Observatory (SDO), we found and tracked the emergence of 42 emerging single-BMR sigmoidal active regions (ARs) that have sunspots in both polarity domains. Throughout each AR's emergence, we quantified the emerging BMR's tilt angle to the east-west direction (the x-direction in SDO images) by measuring in the continuum images the tilt angle of the line through the (visually located) two centroids of the BMR's opposite-polarity sunspot clusters. As each AR emerges, it becomes either S-shaped (shows net right-handed magnetic twist) or Z-shaped (shows net left-handed magnetic twist) in the coronal EUV images. Nineteen of the ARs become S-shaped and 23 become Z-shaped. For all 42 ARs, in agreement with published MHD simulations of the emergence of a single-BMR sigmoidal AR from a subsurface twisted flux rope, if the AR becomes S-shaped, the emerging BMR pivots counterclockwise, and if the AR becomes Z-shaped, the emerging BMR pivots clockwise. For our 42 ARs, the pivot amount roughly ranges from 10° to 90° and averages about 35°. Thus, at the onset of the emergence of our average emerging omega-loop flux rope, the magnetic field's twist pitch angle at the flux rope's top edge is plausibly about 35°.

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arXiv2025

Bright Dots and Coronal Plume Formation in Sunspot Penumbra

Coronal plumes are narrow, collimated structures that are primarily viewed above the solar poles and in coronal holes in the extreme ultraviolet, but also in sunspots. Open questions remain about plume formation, including the role of small-scale transients and whether plumes embedded in different magnetic field configurations have similar formation mechanisms. We report on coordinated Solar Orbiter/Extreme Ultraviolet Imager (EUI), Interface Region Imaging Spectrograph, and Solar Dynamics Observatory observations of the formation of a plume in sunspot penumbra in 2022 March. During this observation, Solar Orbiter was positioned near the Earth-Sun line and EUI observed at a 5 s cadence with a spatial scale of 185 km pixel$^{-1}$ in the solar corona. We observe fine-scale dots at various locations in the sunspot, but the brightest and highest density of dots is at the plume base. Space-time maps along the plume axis show parabolic and V-shaped patterns, and we conclude that some of these dots are possible signatures of magneto-acoustic shocks. Compared to other radial cuts around the sunspot, along the plume shows the longest periods (~7 minutes) and the most distinct tracks. Bright dots at the plume base are mostly circular and do not show elongations from a fixed origin, in contrast to jetlets and previously reported penumbral dots. We do not find high-speed, repeated downflows along the plume, and the plume appears to brighten coherently along its length. Our analysis suggests that jetlets and downflows are not a necessary component of this plume's formation, and that mechanisms for plume formation could be dependent on magnetic topology and the chromospheric wave field.

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arXiv2025

Quantifying Suppression of Solar Surface Magnetic Flux Advection with Increasing Field Strength

One of the main theories for heating of the solar corona is based on the idea that solar convection shuffles and tangles magnetic field lines to make many small-scale current sheets that, via reconnection, heat coronal loops. Tiwari et al 2017 present evidence that, besides depending on loop length and other factors, the brightness of a coronal loop depends on the field strength in the loop feet and the freedom of convection in the feet. While it is known that strong solar magnetic fields suppress convection, the decrease in the speed of horizontal advection of magnetic flux with increasing field strength has not been quantified before. We quantify that trend by analyzing 24hours of HMI SHARP vector magnetograms of each of six sunspot active regions and their surroundings. Using Fourier Local Correlation Tracking, we estimate the horizontal advection speed of the magnetic flux at each pixel in which the vertical component of the magnetic field strength (Bz) is well above (greater than or equal to 150 G) noise level. We find that the average horizontal advection speed of magnetic flux steadily decreases as Bz increases, from 110 pm 3 meters per sec for 150 G (in network and plage) to 10 pm 4 meters per sec for 2500 G (in sunspot umbra). The trend is well fit by a fourth degree polynomial. These results quantitatively confirm the expectation that magnetic flux advection is suppressed by increasing magnetic field strength. The presented quantitative relation should be useful for future MHD simulations of coronal heating.

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arXiv2024

Magnetic diffusion in Solar atmosphere produces measurable electric fields

The efficient release of magnetic energy in astrophysical plasmas, such as during solar flares, can in principle be achieved through magnetic diffusion, at a rate determined by the associated electric field. However, attempts at measuring electric fields in the solar atmosphere are scarce, and none exist for sites where the magnetic energy is presumably released. Here, we present observations of an energetic event using the National Science Foundation's Daniel K. Inouye Solar Telescope, where we detect the polarization signature of electric fields associated with magnetic diffusion. We measure the linear and circular polarization across the hydrogen H-epsilon Balmer line at 397 nm at the site of a brightening event in the solar chromosphere. Our spectro-polarimetric modeling demonstrates that the observed polarization signals can only be explained by the presence of electric fields, providing conclusive evidence of magnetic diffusion, and opening a new window for the quantitative study of this mechanism in space plasmas.

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arXiv2024

Stealth Non-standard-model Confined Flare Eruptions: Sudden Reconnection Events in Ostensibly Inert Magnetic Arches from Sunspots

We report seven examples of a long-ignored type of confined solar flare eruption that does not fit the standard model for confined flare eruptions. Because they are confined eruptions, do not fit the standard model, and unexpectedly erupt in ostensibly inert magnetic arches, we have named them stealth non-standard-model confined flare eruptions. Each of our flaring magnetic arches stems from a big sunspot. We tracked each eruption in full-cadence UV and EUV images from the Atmospheric Imaging Assembly (AIA) of Solar Dynamics Observatory (SDO) in combination with magnetograms from SDO's Helioseismic and Magnetic Imager (HMI). We present the onset and evolution of two eruptions in detail: one of six that each make two side-by-side main flare loops, and one that makes two crossed main flare loops. For these two cases, we present cartoons of the proposed pre-eruption field configuration and how sudden reconnection makes the flare ribbons and flare loops. Each of the seven eruptions is consistent with being made by sudden reconnection at an interface between two internal field strands of the magnetic arch, where they cross at a small (10 - 20 degrees) angle. These stealth non-standard-model confined flare eruptions therefore plausibly support the idea of E. N. Parker for coronal heating in solar coronal magnetic loops by nanoflare bursts of reconnection at interfaces of internal field strands that cross at angles of 10 - 20 degrees.

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arXiv2023

Prospective Implications of EUV Coronal Plumes for Magnetic-network Genesis of Coronal Heating, Coronal-hole Solar Wind, and Solar-wind Magnetic-field Switchbacks

We propose that coronal heating in EUV coronal plumes is weaker, not stronger, than in adjacent non-plume coronal magnetic funnels. This expectation stems from (i) the observation that an EUV plume is born as the magnetic flux at the foot of the plume's magnetic funnel becomes tightly packed together, and (ii) the observation that coronal heating in quiet regions increases in proportion to the coast-line length of the underlying magnetic network. We do not rule out the possibility that coronal heating in EUV plumes might be stronger, not weaker, but we point out how the opposite is plausible. We reason that increasing coronal heating during plume birth would cause co-temporal increasing net upward mass flux in the plume, whereas decreasing coronal heating during plume birth would cause co-temporal net downward mass flux in quiet-region plumes and co-temporal decrease in net upward mass flux or even net downward mass flux in coronal-hole plumes. We further reason that conclusive evidence of weaker coronal heating in EUV plumes would strengthen the possibility that magnetic twist waves from fine-scale magnetic explosions at the edges of the magnetic network (1) power much of the coronal heating in quiet regions, and (2) power most of the coronal heating and solar wind acceleration in coronal holes, with many twist waves surviving to become magnetic-field switchbacks in the solar wind from coronal holes.

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arXiv2023

Future High-Resolution and High-Cadence Observations for Unraveling Small-Scale Explosive Solar Features

Solar coronal jets are frequently occurring collimated ejections of solar plasma, originating from magnetically mixed polarity locations on the Sun of size scale comparable to that of a supergranule. Many, if not most, coronal jets are produced by eruptions of small-scale filaments, or minifilaments, whose magnetic field reconnects both with itself and also with surrounding coronal field. There is evidence that minifilament eruptions are a scaled-down version of typical filament eruptions that produce solar flares and coronal mass ejections (CMEs). Moreover, the magnetic processes building up to and triggering minifilament eruptions, which is often flux cancelation, might similarly build up and trigger the larger filaments to erupt. Thus, detailed study of coronal jets will inform us of the physics leading to, triggering, and driving the larger eruptions. Additionally, such studies potentially can inform us of smaller-scale coronal-jet-like features, such as jetlets and perhaps some spicules, that might work the same way as coronal jets. We propose a high-resolution (~0.1 pixels), high-cadence (~5 seconds) EUV-solar-imaging mission for the upcoming decades, that would be dedicated to observations of features of the coronal-jet size scale, and smaller-scale solar features produced by similar physics. Such a mission could provide invaluable insight into the operation of larger features such as CMEs that produce significant Space Weather disturbances, and also smaller-scale features that could be important for coronal heating, solar wind acceleration, and heliospheric features such as the magnetic switchbacks that are frequently observed in the solar wind.

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arXiv2022

Dominance of Bursty over Steady Heating of the 4--8 MK Coronal Plasma in a Solar Active Region: Quantification using Maps of Minimum, Maximum, and Average Brightness

A challenge in characterizing active region (AR) coronal heating is in separating transient (bursty) loop heating from the diffuse background (steady) heating. We present a method of quantifying coronal heating's bursty and steady components in ARs, applying it to FeXVIII (hot94) emission of an AR observed by SDO/AIA. The maximum, minimum, and average brightness values for each pixel, over a 24 hour period, yield a maximum-brightness map, a minimum-brightness map, and an average-brightness map of the AR. Running sets of such three maps come from repeating this process for each time step of running windows of 20, 16, 12, 8, 5, 3, 1 and 0.5 hours. From each running window's set of three maps, we obtain the AR's three corresponding luminosity light curves. We find: (1) The time-averaged ratio of minimum-brightness-map luminosity to average-brightness-map luminosity increases as the time window decreases, and the time-averaged ratio of maximum-brightness-map luminosity to average-brightness-map luminosity decreases as the window decreases. (2) For the 24-hour window, the minimum-brightness map's luminosity is 5% of the average-brightness map's luminosity, indicating that at most 5% of the AR's hot94 luminosity is from heating that is steady for 24 hours. (3) This upper limit on the fraction of the hot94 luminosity from steady heating increases to 33% for the 30-minute running window. This requires that the heating of the 4--8 MK plasma in this AR is mostly in bursts lasting less than 30 minutes: at most a third of the heating is steady for 30 minutes.

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arXiv2022

Solar Orbiter and SDO Observations, and Bifrost MHD Simulations of Small-scale Coronal Jets

We report high-resolution, high-cadence observations of five small-scale coronal jets in an on-disk quiet Sun region observed with Solar Orbiter's EUI/\hri\ in 174 Å. We combine the \hri\ images with the EUV images of SDO/AIA and investigate magnetic setting of the jets using co-aligned line-of-sight magnetograms from SDO/HMI. The \hri\ jets are miniature versions of typical coronal jets as they show narrow collimated spires with a base brightening. Three out of five jets result from a detectable minifilament eruption following flux cancelation at the neutral line under the minifilament, analogous to coronal jets. To better understand the physics of jets, we also analyze five small-scale jets from a high-resolution Bifrost MHD simulation in synthetic \FeIX/\FeX\ emissions. The jets in the simulation reside above neutral lines and four out of five jets are triggered by magnetic flux cancelation. The temperature maps show the evidence of cool gas in the same four jets. Our simulation also shows the signatures of opposite Doppler shifts (of the order of $\pm$10s of \kms) in the jet spire, which is evidence of untwisting motion of the magnetic field in the jet spire. The average jet duration, spire length, base width, and speed in our observations (and in synthetic \FeIX/\FeX\ images) are 6.5$\pm$4.0 min (9.0$\pm$4.0 min), 6050$\pm$2900 km (6500$\pm$6500 km), 2200$\pm$850 km, (3900$\pm$2100 km), and 60$\pm$8 \kms\ (42$\pm$20 \kms), respectively. Our observation and simulation results provide a unified picture of small-scale solar coronal jets driven by magnetic reconnection accompanying flux cancelation. This picture also aligns well with the most recent reports of the formation and eruption mechanisms of larger coronal jets.

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arXiv2022

Genesis and Coronal-jet-generating Eruption of a Solar Minifilament Captured by IRIS Slit-raster Spectra

We present the first IRIS Mg II slit-raster spectra that fully capture the genesis and coronal-jet-generating eruption of a central-disk solar minifilament. The minifilament arose in a negative-magnetic-polarity coronal hole. The Mg II spectroheliograms verify that the minifilament plasma temperature is chromospheric. The Mg II spectra show that the erupting minifilament's plasma has blueshifted upflow in the jet spire's onset and simultaneous redshifted downflow at the location of the compact jet bright point (JBP). From the Mg II spectra together with AIA EUV images and HMI magnetograms, we find: (i) the minifilament forms above a flux cancelation neutral line at an edge of a negative-polarity network flux clump; (ii) during the minifilament's fast-eruption onset and jet-spire onset, the JBP begins brightening over the flux-cancelation neutral line. From IRIS2 inversion of the Mg II spectra, the JBP's Mg II bright plasma has electron density, temperature, and downward (red-shift) Doppler speed of 1012 cm^-3, 6000 K, and 10 kms, respectively, and the growing spire shows clockwise spin. We speculate: (i) during the slow rise of the erupting minifilament-carrying twisted flux rope, the top of the erupting flux-rope loop, by writhing, makes its field direction opposite that of encountered ambient far-reaching field; (ii) the erupting kink then can reconnect with the far-reaching field to make the spire and reconnect internally to make the JBP. We conclude that this coronal jet is normal in that magnetic flux cancelation builds a minifilament-carrying twisted flux rope and triggers the JBP-generating and jet-spire-generating eruption of the flux rope.

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arXiv2022

Parallel plasma loops and the energization of the solar corona

The outer atmosphere of the Sun is composed of plasma heated to temperatures well in excess of the visible surface. We investigate short cool and warm (<1 MK) loops seen in the core of an active region to address the role of field-line braiding in energising these structures. We report observations from the High-resolution Coronal imager (Hi-C) that have been acquired in a coordinated campaign with the Interface Region Imaging Spectrograph (IRIS). In the core of the active region, the 172 A band of Hi-C and the 1400 A channel of IRIS show plasma loops at different temperatures that run in parallel. There is a small but detectable spatial offset of less than 1 arcsec between the loops seen in the two bands. Most importantly, we do not see observational signatures that these loops might be twisted around each other. Considering the scenario of magnetic braiding, our observations of parallel loops imply that the stresses put into the magnetic field have to relax while the braiding is applied: the magnetic field never reaches a highly braided state on these length-scales comparable to the separation of the loops. This supports recent numerical 3D models of loop braiding in which the effective dissipation is sufficiently large that it keeps the magnetic field from getting highly twisted within a loop.

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arXiv2022

Bipolar Ephemeral Active Regions, Magnetic Flux Cancellation, and Solar Magnetic Explosions

We examine the cradle-to-grave magnetic evolution of 10 bipolar ephemeral active regions (BEARs) in solar coronal holes, especially aspects of the magnetic evolution leading to each of 43 obvious microflare events. The data are from Solar Dynamics Observatory: 211 A coronal EUV images and line-of-sight photospheric magnetograms. We find evidence that (1) each microflare event is a magnetic explosion that results in a miniature flare arcade astride the polarity inversion line (PIL) of the explosive lobe of the BEARs anemone magnetic field; (2) relative to the BEAR's emerged flux-rope omega loop, the anemone's explosive lobe can be an inside lobe, an outside lobe, or an inside & outside lobe; (3) 5 events are confined explosions, 20 events are mostly-confined explosions, and 18 events are blowout explosions, which are miniatures of the magnetic explosions that make coronal mass ejections (CMEs); (4) contrary to the expectation of Moore et al (2010), none of the 18 blowout events explode from inside the BEARs omega loop during the omega loops emergence; (5) before and during each of the 43 microflare events there is magnetic flux cancellation at the PIL of the anemone's explosive lobe. From finding evident flux cancellation at the underlying PIL before and during all 43 microflare events - together with BEARs evidently being miniatures of all larger solar bipolar active regions - we expect that in essentially the same way, flux cancellation in sunspot active regions prepares and triggers the magnetic explosions for many major flares and CMEs.

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arXiv2022

SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation

We report on the presence of numerous tiny bright dots in and around an emerging flux region (an X-ray/coronal bright point) observed with SolO's EUI/\hri\ in 174 Å. These dots are roundish, have a diameter of 675$\pm$300 km, a lifetime of 50$\pm$35 seconds, and an intensity enhancement of 30\% $\pm$10\% above their immediate surroundings. About half of the dots remain isolated during their evolution and move randomly and slowly ($<$10 \kms). The other half show extensions, appearing as a small loop or surge/jet, with intensity propagations below 30\,\kms. Many of the bigger and brighter \hri\ dots are discernible in SDO/AIA 171 Å channel, have significant emissivity in the temperature range of 1--2 MK, and are often located at polarity inversion lines observed in HMI LOS magnetograms. Although not as pervasive as in observations, Bifrost MHD simulation of an emerging flux region do show dots in synthetic \fe\ images. These dots in simulation show distinct Doppler signatures -- blueshifts and redshifts coexist, or a redshift of the order of 10 \kms\ is followed by a blueshift of similar or higher magnitude. The synthetic images of \oxy\ and \siiv\ lines, which represent transition region radiation, also show the dots that are observed in \fe\ images, often expanded in size, or extended as a loop, and always with stronger Doppler velocities (up to 100 \kms) than that in \fe\ lines. Our observation and simulation results, together with the field geometry of dots in the simulation, suggest that most dots in emerging flux regions form in the lower solar atmosphere (at $\approx$1 Mm) by magnetic reconnection between emerging and pre-existing/emerged magnetic field. Some dots might be manifestations of magneto-acoustic shocks through the line formation region of \fe\ emission.

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