arXiv subjects

Alphonse C. Sterling

Publications and source records attributed to Alphonse C. Sterling.

At least 55 records · Page 3Linked to original sources

arXiv2020

Coronal-Jet-Producing Minifilament Eruptions as a Possible Source of Parker Solar Probe (PSP) Switchbacks

The Parker Solar Probe (PSP) has observed copious rapid magnetic field direction changes in the near-Sun solar wind. These features have been called "switchbacks," and their origin is a mystery. But their widespread nature suggests that they may be generated by a frequently occurring process in the Sun's atmosphere. We examine the possibility that the switchbacks originate from coronal jets. Recent work suggests that many coronal jets result when photospheric magnetic flux cancels, and forms a small-scale "minifilament" flux rope that erupts and reconnects with coronal field. We argue that the reconnected erupting minifilament flux rope can manifest as an outward propagating Alfvénic fluctuation that steepens into an increasingly compact disturbance as it moves through the solar wind. Using previous observed properties of coronal jets that connect to coronagraph-observed white-light jets (a.k.a. "narrow CMEs"), along with typical solar wind speed values, we expect the coronal-jet-produced disturbances to traverse near-perihelion PSP in ~<25 min, with a velocity of ~400 km/s. To consider further the plausibility of this idea, we show that a previously studied series of equatorial latitude coronal jets, originating from the periphery of an active region, generate white-light jets in the outer corona (seen in STEREO/COR2 coronagraph images; 2.5---15 R_sun), and into the inner heliosphere (seen in STEREO/Hi1 heliospheric imager images; 15---84 R_sun). Thus it is tenable that disturbances put onto open coronal magnetic field lines by coronal-jet-producing erupting minifilament flux ropes can propagate out to PSP space and appear as switchbacks.

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arXiv2020

Network Jets as the Driver of Counter-Streaming Flows in a Solar Filament/Filament Channel

Counter-streaming flows in a small (100" -long) solar filament/filament channel are directly observed in high-resolution SDO/AIA EUV images of a region of enhanced magnetic network. We combine images from SDO/AIA, SDO/HMI and IRIS to investigate the driving mechanism of these flows. We find that: (i) counter-streaming flows are present along adjacent filament/filament channel threads for about 2 hours, (ii) both ends of the filament/filament channel are rooted at the edges of magnetic network flux lanes along which there are impinging fine-scale opposite-polarity flux patches, (iii) recurrent small-scale jets (known as network jets) occur at the edges of the magnetic network flux lanes at the ends of the filament/filament channel, (iv) the recurrent network jet eruptions clearly drive the counter-streaming flows along threads of the filament/filament channel, (v) some of the network jets appear to stem from sites of flux cancelation, between network flux and merging opposite-polarity flux, and (vi) some show brightening at their bases, analogous to the base brightening in coronal jets. The average speed of the counter-streaming flows along the filament/filament channel threads is 70 km/s. The average widths of the AIA filament/filament channel and the Halpha filament are 4" and 2.5", respectively, consistent with the earlier findings that filaments in EUV images are wider than in Halpha images. Thus, our observations show that the continually repeated counter-streaming flows come from network jets, and these driving network-jet eruptions are possibly prepared and triggered by magnetic flux cancelation.

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arXiv2020

Possible Production of Solar Spicules by Microfilament Eruptions

We examine Big Bear Solar Observatory (BBSO) Goode Solar Telescope (GST) high-spatial resolution (0''.06), high-cadence (3.45 s), H-alpha-0.8 Angstrom images of central-disk solar spicules, using data of Samanta et al. (2019). We compare with coronal-jet chromospheric-component observations of Sterling et al. (2010a). Morphologically, bursts of spicules, referred to as "enhanced spicular activities" by Samanta et al. (2019), appear as scaled-down versions of the jet's chromospheric component. Both the jet and the enhanced spicular activities appear as chromospheric-material strands, undergoing twisting-type motions of ~20---50 km/s in the jet and ~20---30 km/s in the enhanced spicular activities. Presumably, the jet resulted from a minifilament-carrying magnetic eruption. For two enhanced spicular activities that we examine in detail, we find tentative candidates for corresponding erupting microfilaments, but not expected corresponding base brightenings. Nonetheless, the enhanced-spicular-activities' interacting mixed-polarity base fields, frequent-apparent-twisting motions, and morphological similarities to the coronal jet's chromospheric-temperature component, suggest that erupting microfilaments might drive the enhanced spicular activities but be hard to detect, perhaps due to H-alpha opacity. Degrading the BBSO/GST-image resolution with a 1''.0-FWHM smoothing function yields enhanced spicular activities resembling the "classical spicules" described by, e.g., Beckers (1968). Thus, a microfilament eruption might be the fundamental driver of many spicules, just as a minifilament eruption is the fundamental driver of many coronal jets. Similarly, a 0".5-FWHM smoothing renders some enhanced spicular activities to resemble previously-reported "twinned" spicules, while the full-resolution features might account for spicules sometimes appearing as 2D-sheet-like structures.

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arXiv2019

Coronal Jets, and the Jet-CME Connection

Solar coronal jets have been observed in detail since the early 1990s. While it is clear that these jets are magnetically driven, the details of the driving process has recently been updated. Previously it was suspected that the jets were a consequence of magnetic flux emergence interacting with ambient coronal field. New evidence however indicates that often the direct driver of the jets is erupting field, often carrying cool material (a "minifilament"), that undergoes interchange magnetic reconnection with preexisting field ([1]). More recent work indicates that the trigger for eruption of the minifilament is frequently cancelation of photospheric magnetic fields at the base of the minifilament. These erupting minifilaments are analogous to the better-known larger-scale filament eruptions that produce solar flares and, frequently, coronal mass ejections (CMEs). A subset of coronal jets drive narrow "white-light jets," which are very narrow CME-like features, and apparently a few jets can drive wider, although relatively weak, "streamer-puff" CMEs. Here we summarize these recent findings.

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arXiv2019

Hi-C 2.1 Observations of Small-Scale Miniature-Filament-Eruption-Like Cool Ejections in Active Region Plage

We examine 172 Ang ultra-high-resolution images of a solar plage region from the Hi-C 2.1 ("Hi-C") rocket flight of 2018 May 29. Over its five-minute flight, Hi-C resolves a plethora of small-scale dynamic features that appear near noise level in concurrent Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) 171 Ang images. For ten selected events, comparisons with AIA images at other wavelengths and with the Interface Region Imaging Spectrograph (IRIS) images indicate that these features are cool (compared to the corona) ejections. Combining Hi-C 172 Ang, AIA 171 Ang, IRIS 1400 Ang, and H$α$, we see that these ten cool ejections are similar to the H$α$ "dynamic fibrils" and Ca ii "anemone jets" found in earlier studies. The front of some of our cool ejections are likely heated, showing emission in IRIS 1400 Ang. On average, these cool ejections have approximate widths: $3''.2 \pm 2''.1$, (projected) maximum heights and velocities: $4''.3 \pm 2''.5$ and $23 \pm 6$ km/s, and lifetimes: $6.5 \pm 2.4$ min. We consider whether these Hi-C features might result from eruptions of sub-minifilaments (smaller than the minifilaments that erupt to produce coronal jets). Comparisons with SDO's Helioseismic and Magnetic Imager (HMI) magnetograms do not show magnetic mixed-polarity neutral lines at these events' bases, as would be expected for true scaled-down versions of solar filaments/minifilaments. But the features' bases are all close to single-polarity strong-flux-edge locations, suggesting possible local opposite-polarity flux unresolved by HMI. Or, it may be that our Hi-C ejections instead operate via the shock-wave mechanism that is suggested to drive dynamic fibrils and the so-called type I spicules.

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arXiv2019

Hi-C 2.1 Observations of Jetlet-like Events at Edges of Solar Magnetic Network Lane

We present high-resolution, high-cadence observations of six, fine-scale, on-disk jet-like events observed by the High-resolution Coronal Imager 2.1 (Hi-C 2.1) during its sounding-rocket flight. We combine the Hi-C 2.1 images with images from SDO/AIA, and IRIS, and investigate each event's magnetic setting with co-aligned line-of-sight magnetograms from SDO/HMI. We find that: (i) all six events are jetlet-like (having apparent properties of jetlets), (ii) all six are rooted at edges of magnetic network lanes, (iii) four of the jetlet-like events stem from sites of flux cancelation between majority-polarity network flux and merging minority-polarity flux, and (iv) four of the jetlet-like events show brightenings at their bases reminiscent of the base brightenings in coronal jets. The average spire length of the six jetlet-like events (9,000$\pm$3000km) is three times shorter than that for IRIS jetlets (27,000$\pm$8000km). While not ruling out other generation mechanisms, the observations suggest that at least four of these events may be miniature versions of both larger-scale coronal jets that are driven by minifilament eruptions and still-larger-scale solar eruptions that are driven by filament eruptions. Therefore, we propose that our Hi-C events are driven by the eruption of a tiny sheared-field flux rope, and that the flux-rope field is built and triggered to erupt by flux cancelation.

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arXiv2019

Magnetic Flux Cancellation as the Trigger Mechanism of Solar Coronal Jets

Coronal jets are transient narrow features in the solar corona that originate from all regions of the solar disk: active regions, quiet sun, and coronal holes. Recent studies indicate that at least some coronal jets in quiet regions and coronal holes are driven by the eruption of a minifilament following flux cancellation at a magnetic neutral line. We have tested the veracity of that view by examining 60 random jets in quiet regions and coronal holes using multithermal (304 A, 171 A, 193 A, and 211 A) extreme ultraviolet (EUV) images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and line-of-sight magnetograms from the SDO/Helioseismic and Magnetic Imager (HMI). By examining the structure and changes in the magnetic field before, during, and after jet onset, we found that 85% of these jets resulted from a minifilament eruption triggered by flux cancellation at the neutral line. The 60 jets have a mean base diameter of 8800 +/- 3100 km and a mean duration of 9 +/-3.6 minutes. These observations confirm that minifilament eruption is the driver and magnetic flux cancellation is the primary trigger mechanism for most coronal hole and quiet region coronal jets.

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arXiv2018

Evidence of Twisting and Mixed-polarity Solar Photospheric Magnetic Field in Large Penumbral Jets: IRIS and Hinode Observations

A recent study using {\it Hinode} (SOT/FG) data of a sunspot revealed some unusually large penumbral jets that often repeatedly occurred at the same locations in the penumbra, namely at the tail of a penumbral filament or where the tails of multiple penumbral filaments converged. These locations had obvious photospheric mixed-polarity magnetic flux in \NaI\ 5896 Stokes-V images obtained with SOT/FG. Several other recent investigations have found that extreme ultraviolet (EUV)/X-ray coronal jets in quiet Sun regions (QRs), coronal holes (CHs) and near active regions (ARs) have obvious mixed-polarity fluxes at their base, and that magnetic flux cancellation prepares and triggers a minifilament flux-rope eruption that drives the jet. Typical QR, CH, and AR coronal jets are up to a hundred times bigger than large penumbral jets, and in EUV/X-ray images show clear twisting motion in their spires. Here, using IRIS \MgII\ k 2796 Å SJ images and spectra in the penumbrae of two sunspots we characterize large penumbral jets. We find redshift and blueshift next to each other across several large penumbral jets, and interpret these as untwisting of the magnetic field in the jet spire. Using Hinode/SOT (FG and SP) data, we also find mixed-polarity magnetic flux at the base of these jets. Because large penumbral jets have mixed-polarity field at their base and have twisting motion in their spires, they might be driven the same way as QR, CH and AR coronal jets.

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arXiv2018

A Two-Sided-Loop X-Ray Solar Coronal Jet Driven by a Minifilament Eruption

Most of the commonly discussed solar coronal jets are of the type consisting of a single spire extending approximately vertically from near the solar surface into the corona. Recent research supports that eruption of a miniature filament (minifilament) drives many such single-spire jets, and concurrently generates a miniflare at the eruption site. A different type of coronal jet, identified in X-ray images during the Yohkoh era, are two-sided-loop jets, which extend from a central excitation location in opposite directions, along low-lying coronal loops more-or-less horizontal to the surface. We observe such a two-sided-loop jet from the edge of active region (AR) 12473, using data from Hinode XRT and EIS, and SDO AIA and HMI. Similar to single-spire jets, this two-sided-loop jet results from eruption of a minifilament, which accelerates to over 140 km/s before abruptly stopping after striking overlying nearly-horizontal loop field at about 30,000 km altitude and producing the two-sided-loop jet. Analysis of EIS raster scans show that a hot brightening, consistent with a small flare, develops in the aftermath of the eruption, and that Doppler motions (approx 40 km/s) occur near the jet-formation region. As with many single-spire jets, the magnetic trigger here is apparently flux cancelation, which occurs at a rate of approx 4x10^18 Mx/hr, comparable to the rate observed in some single-spire AR jets. An apparent increase in the (line-of-sight) flux occurs within minutes of onset of the minifilament eruption, consistent with the apparent increase being due to a rapid reconfiguration of low-lying field during and soon after minifilament-eruption onset.

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arXiv2018

IRIS and SDO Observations of Solar Jetlets Resulting from Network-Edge Flux Cancelation

Recent observations show that the buildup and triggering of minifilament eruptions that drive coronal jets result from magnetic flux cancelation at the neutral line between merging majority- and minority-polarity magnetic flux patches. We investigate the magnetic setting of ten on-disk small-scale UV/EUV jets (jetlets), smaller than coronal X-ray jets but larger than chromospheric spicules) in a coronal hole by using IRIS UV images and SDOAIA EUV images and line-of-sight magnetograms from SDO/HMI. We observe recurring jetlets at the edges of magnetic network flux lanes in the coronal hole. From magnetograms co-aligned with the IRIS and AIA images, we find, clearly visible in nine cases, that the jetlets stem from sites of flux cancelation proceeding at an average rate of 1.5 X 10^18 Mx hr^{-1}, and show brightenings at their bases reminiscent of the base brightenings in larger-scale coronal jets. We find that jetlets happen at many locations along the edges of network lanes (not limited to the base of plumes) with average lifetimes of 3 min and speeds of 70 kms. The average jetlet-base width (4000 km) is three to four times smaller than for coronal jets (18,000 km). Based on these observations of ten obvious jetlets, and our previous observations of larger-scale coronal jets in quiet regions and coronal holes, we infer that flux cancelation is an essential process in the buildup and triggering of jetlets. Our observations suggest that network jetlet eruptions might be small-scale analogs of both larger-scale coronal jets and the still-larger-scale eruptions producing CMEs.

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arXiv2018

Magnetic Flux Cancelation as the Buildup and Trigger Mechanism for CME-Producing Eruptions in two Small Active Regions

We follow two small, magnetically isolated CME-producing solar active regions (ARs) from the time of their emergence until several days later, when their core regions erupt to produce the CMEs. In both cases, magnetograms show: (a) following an initial period where the poles of the emerging regions separate from each other, the poles then reverse direction and start to retract inward; (b) during the retraction period, flux cancelation occurs along the main neutral line of the regions; (c) this cancelation builds the sheared core field/flux rope that eventually erupts to make the CME. In the two cases, respectively 30% and 50% of the maximum flux of the region cancels prior to the eruption. Recent studies indicate that solar coronal jets frequently result from small-scale filaments eruptions, with those "minifilament" eruptions also being built up and triggered by cancelation of magnetic flux. Together, the small-AR eruptions here and the coronal jet results suggest that isolated bipolar regions tend to erupt when some threshold fraction, perhaps in the range of 50%, of the region's maximum flux has canceled. Our observed erupting filaments/flux ropes form at sites of flux cancelation, in agreement with previous observations. Thus, the recent finding that minifilaments that erupt to form jets also form via flux cancelation is further evidence that minifilaments are small-scale versions of the long-studied full-sized filaments.

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arXiv2018

Onset of the magnetic explosion in solar polar coronal X-ray jets

We follow up on the Sterling et al (2015) discovery that nearly all polar coronal X-ray jets are made by an explosive eruption of closed magnetic field carrying a miniature filament in its core. In the same X-ray and EUV movies used by Sterling et al (2015), we examine the onset and growth of the driving magnetic explosion in 15 of the 20 jets that they studied. We find evidence that: (1) in a large majority of polar X-ray jets, the runaway internal/tether-cutting reconnection under the erupting minifilament flux rope starts after both the minifilaments rise and the spire-producing external/breakout reconnection have started and (2) in a large minority, (a) before the eruption starts there is a current sheet between the explosive closed field and the ambient open field, and (b) the eruption starts with breakout reconnection at that current sheet. The variety of event sequences in the eruptions supports the idea that the magnetic explosions that make polar X-ray jets work the same way as the much larger magnetic explosions that make a flare and coronal mass ejection (CME). That idea, and recent observations indicating that magnetic flux cancelation is the fundamental process that builds the field in and around the pre-jet mininfilament and triggers that fields jet-driving explosion, together suggest that flux cancelation inside the magnetic arcade that explodes in a flare/CME eruption is usually the fundamental process that builds the explosive field in the core of the arcade and triggers that fields explosion.

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arXiv2018

Magnetic Flux Cancelation as the Trigger of Solar Coronal-Hole Coronal Jets

We investigate in detail the magnetic cause of minifilament eruptions that drive coronal-hole jets. We study 13 random on-disk coronal hole jet eruptions, using high resolution X-ray images from Hinode/XRT, EUV images from SDO/AIA, and magnetograms from SDO/HMI. For all 13 events, we track the evolution of the jet-base region and find that a minifilament of cool (transition-region-temperature) plasma is present prior to each jet eruption. HMI magnetograms show that the minifilaments reside along a magnetic neutral line between majority-polarity and minority-polarity magnetic flux patches. These patches converge and cancel with each other, with an average cancelation rate of ~0.6 X 10$^18 Mx hr^{-1} for all 13 jets. Persistent flux cancelation at the neutral line eventually destabilizes the minifilament field, which erupts outward and produces the jet spire. Thus, we find that all 13 coronal-hole-jet-driving minifilament eruptions are triggered by flux cancelation at the neutral line. These results are in agreement with our recent findings Panesar et al 2016b for quiet-region jets, where flux cancelation at the underlying neutral line triggers the minifilament eruption that drives each jet. Thus from that study of quiet-Sun jets and this study of coronal hole jets, we conclude that flux cancelation is the main candidate for triggering quiet region and coronal hole jets

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arXiv2017

Magnetic Flux Cancelation as the Origin of Solar Quiet Region Pre-Jet Minifilaments

We investigate the origin of ten solar quiet region pre-jet minifilaments, using EUV images from SDO/AIA and magnetograms from SDO/HMI. We recently found panesar16b that quiet region coronal jets are driven by minifilament eruptions, where those eruptions result from flux cancelation at the magnetic neutral line under the minifilament. Here, we study the longer-term origin of the pre-jet minifilaments themselves. We find that they result from flux cancelation between minority-polarity and majority-polarity flux patches. In each of ten pre-jet regions, we find that opposite-polarity patches of magnetic flux converge and cancel, with a flux reduction of 10--40% from before to after the minifilament appears. For our ten events, the minifilaments exist for periods ranging from 1.5 hr to two days before erupting to make a jet. Apparently, the flux cancelation builds highly sheared field that runs above and traces the neutral line, and the cool-transition-region-plasma minifilament forms in this field and is suspended in it. We infer that the convergence of the opposite-polarity patches results in reconnection in the low corona that builds a magnetic arcade enveloping the minifilament in its core, and that the continuing flux cancelation at the neutral line finally destabilizes the minifilament field so that it erupts and drives the production of a coronal jet. Thus our observations strongly support that quiet region magnetic flux cancelation results in both the formation of the pre-jet minifilament and its jet-driving eruption.

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arXiv2017

Onset of a Large Ejective Solar Eruption from a Typical Coronal-Jet-Base Field Configuration

Utilizing multiwavelength observations and magnetic field data from SDO/AIA, SDO/HMI, GOES and RHESSI, we investigate a large-scale ejective solar eruption of 2014 December 18 from active region NOAA 12241. This event produced a distinctive three-ribbon flare, having two parallel ribbons corresponding to the ribbons of a standard two-ribbon flare, and a larger-scale third quasi-circular ribbon offset from the other two ribbons. There are two components to this eruptive event. First, a flux rope forms above a strong-field polarity-inversion line and erupts and grows as the parallel ribbons turn on, grow, and spread part from that polarity-inversion line; this evolution is consistent with the tether-cutting-reconnection mechanism for eruptions. Second, the eruption of the arcade that has the erupting flux rope in its core under goes magnetic reconnection at the null point of a fan dome that envelops the erupting arcade, resulting in formation of the quasi-circular ribbon; this is consistent with the breakout reconnection mechanism for eruptions. We find that the parallel ribbons begin well before (12 min) circular ribbon onset, indicating that tether-cutting reconnection (or a non-ideal MHD instability) initiated this event, rather than breakout reconnection. The overall setup for this large-scale (circular-ribbon diameter 100000 km) eruption is analogous to that of coronal jets (base size 10000 km), many of which, according to recent findings, result from eruptions of small-scale minifilaments. Thus these findings confirm that eruptions of sheared-core magnetic arcades seated in fan-spine null-point magnetic topology happen on a wide range of size scales on the Sun.

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arXiv2017

Small-scale filament eruptions as the driver of solar coronal hole X-ray jets

Solar X-ray jets are evidently made by a burst of reconnection of closed magnetic field in a jet's base with ambient "open" field (1,2). In the widely-accepted version of the "emerging-flux" model, that reconnection occurs at a current sheet between the open field and emerging closed field and also makes a compact hot brightening that is usually observed at the edge of the jet's base (1,3). Here we report on high-resolution X-ray and EUV observations of 20 randomly-selected X-ray jets in polar coronal holes. In each jet, contrary to the emerging-flux model, a miniature version of the filament eruptions that initiate coronal mass ejections (CMEs) (4-7) drives the jet-producing reconnection, and the compact hot brightening is made by internal reconnection of the legs of the minifilament-carrying erupting closed field, analogous to solar flares of larger-scale eruptions. Previous observations have found that some jets are driven by base-field eruptions (8-10,12), but only one such study, of only one jet, provisionally questioned the emerging-flux model (13). Our observations support the view that solar filament eruptions are made by a fundamental explosive magnetic process that occurs on a vast range of scales, from the biggest CME/flare eruptions down to X-ray jets, and perhaps down to even smaller jets that are candidates for powering coronal heating (10,14,15). A picture similar to that suggested by our observations was drawn before, inferred from different observations and based on a different origin of the erupting minifilament flux rope (11) (see Methods).

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arXiv2017

Solar Active Region Coronal Jets II: Triggering and Evolution of Violent Jets

We study a series of X-ray-bright, rapidly-evolving active-region coronal jets outside the leading sunspot of AR 12259, using Hinode/XRT, SDO/AIA and HMI, and IRIS data. The detailed evolution of such rapidly evolving "violent" jets remained a mystery after our previous investigation of active region jets (Sterling et al. 2016, Paper 1). The jets we investigate here erupt from three localized subregions, each containing a rapidly evolving (positive) minority-polarity magnetic-flux patch bathed in a (majority) negative-polarity magnetic-flux background. At least several of the jets begin with eruptions of what appear to be thin (thickness <~2") miniature-filament (minifilament) "strands" from a magnetic neutral line where magnetic flux cancelation is ongoing, consistent with the magnetic configuration presented for coronal-hole jets in Sterling et al. (2015). Some jets strands are difficult/impossible to detect, perhaps due to, e.g. their thinness, obscuration by surrounding bright or dark features, or the absence of erupting cool-material minifilaments in those jets. Tracing in detail the flux evolution in one of the subregions, we find bursts of strong jetting occurring only during times of strong flux cancelation. Averaged over seven jetting episodes, the cancelation rate was ~1.5x10^19 Mx/hr. An average flux of ~5x10^18 Mx canceled prior to each episode, arguably building up ~10^28 - 10^29 ergs of free magnetic energy per jet. From these and previous observations, we infer that flux cancelation is the fundamental process responsible for the pre-eruption buildup and triggering of at least many jets in active regions, quiet regions, and coronal holes.

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arXiv2016

A Microfilament-Eruption Mechanism for Solar Spicules

Recent investigations indicate that solar coronal jets result from eruptions of small-scale chromospheric filaments, called minifilaments; that is, the jets are produced by scaled-down versions of typical-sized filament eruptions. We consider whether solar spicules might in turn be scaled-down versions of coronal jets, being driven by eruptions of "microfilaments." Assuming a microfilament's size is about a spicule's width ($\sim$300~km), the estimated occurrence number plotted against the estimated size of erupting filaments, minifilaments, and microfilaments approximately follows a power-law distribution (based on counts of CMEs, coronal jets, and spicules), suggesting that many or most spicules could result from microfilament eruptions. Observed spicule-base Ca II brightenings plausibly result from such microfilament eruptions. By analogy with coronal jets, microfilament eruptions might produce spicules with many of their observed characteristics, including smooth rise profiles, twisting motions, and EUV counterparts. The postulated microfilament eruptions are presumably eruptions of twisted-core micro magnetic bipoles that are $\sim$1$".0$ wide. These explosive bipoles might be built and destabilized by merging and cancelation of magnetic-flux elements of $\sim$few$\times 100$~G and of size <~$0".5$---$1".0$. If however spicules are relatively more numerous than indicated by our extrapolated distribution, then only a fraction of spicules might result from this proposed mechanism.

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