Author name code: lin-yong ADS astronomy entries on 2022-09-14 author:"Lin, Yong" AND aff:"Oslo" ------------------------------------------------------------------------ Title: The Atacama Cosmology Telescope: A Catalog of >4000 Sunyaev-Zel’dovich Galaxy Clusters Authors: Hilton, M.; Sifón, C.; Naess, S.; Madhavacheril, M.; Oguri, M.; Rozo, E.; Rykoff, E.; Abbott, T. M. C.; Adhikari, S.; Aguena, M.; Aiola, S.; Allam, S.; Amodeo, S.; Amon, A.; Annis, J.; Ansarinejad, B.; Aros-Bunster, C.; Austermann, J. E.; Avila, S.; Bacon, D.; Battaglia, N.; Beall, J. A.; Becker, D. T.; Bernstein, G. M.; Bertin, E.; Bhandarkar, T.; Bhargava, S.; Bond, J. R.; Brooks, D.; Burke, D. L.; Calabrese, E.; Carrasco Kind, M.; Carretero, J.; Choi, S. K.; Choi, A.; Conselice, C.; da Costa, L. N.; Costanzi, M.; Crichton, D.; Crowley, K. T.; Dünner, R.; Denison, E. V.; Devlin, M. J.; Dicker, S. R.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Duff, S. M.; Duivenvoorden, A. J.; Dunkley, J.; Everett, S.; Ferraro, S.; Ferrero, I.; Ferté, A.; Flaugher, B.; Frieman, J.; Gallardo, P. A.; García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Giles, P.; Golec, J. E.; Gralla, M. B.; Grandis, S.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gutierrez, G.; Han, D.; Hartley, W. G.; Hasselfield, M.; Hill, J. C.; Hilton, G. C.; Hincks, A. D.; Hinton, S. R.; Ho, S. -P. P.; Honscheid, K.; Hoyle, B.; Hubmayr, J.; Huffenberger, K. M.; Hughes, J. P.; Jaelani, A. T.; Jain, B.; James, D. J.; Jeltema, T.; Kent, S.; Knowles, K.; Koopman, B. J.; Kuehn, K.; Lahav, O.; Lima, M.; Lin, Y. -T.; Lokken, M.; Loubser, S. I.; MacCrann, N.; Maia, M. A. G.; Marriage, T. A.; Martin, J.; McMahon, J.; Melchior, P.; Menanteau, F.; Miquel, R.; Miyatake, H.; Moodley, K.; Morgan, R.; Mroczkowski, T.; Nati, F.; Newburgh, L. B.; Niemack, M. D.; Nishizawa, A. J.; Ogando, R. L. C.; Orlowski-Scherer, J.; Page, L. A.; Palmese, A.; Partridge, B.; Paz-Chinchón, F.; Phakathi, P.; Plazas, A. A.; Robertson, N. C.; Romer, A. K.; Carnero Rosell, A.; Salatino, M.; Sanchez, E.; Schaan, E.; Schillaci, A.; Sehgal, N.; Serrano, S.; Shin, T.; Simon, S. M.; Smith, M.; Soares-Santos, M.; Spergel, D. N.; Staggs, S. T.; Storer, E. R.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; To, C.; Trac, H.; Ullom, J. N.; Vale, L. R.; Van Lanen, J.; Vavagiakis, E. M.; De Vicente, J.; Wilkinson, R. D.; Wollack, E. J.; Xu, Z.; Zhang, Y. Bibcode: 2021ApJS..253....3H Altcode: 2020arXiv200911043H We present a catalog of 4195 optically confirmed Sunyaev-Zel’dovich (SZ) selected galaxy clusters detected with signal-to-noise ratio >4 in 13,211 deg2 of sky surveyed by the Atacama Cosmology Telescope (ACT). Cluster candidates were selected by applying a multifrequency matched filter to 98 and 150 GHz maps constructed from ACT observations obtained from 2008 to 2018 and confirmed using deep, wide-area optical surveys. The clusters span the redshift range 0.04 < z < 1.91 (median z = 0.52). The catalog contains 222 z > 1 clusters, and a total of 868 systems are new discoveries. Assuming an SZ signal versus mass-scaling relation calibrated from X-ray observations, the sample has a 90% completeness mass limit of M 500c > 3.8 × 1014 M , evaluated at z = 0.5, for clusters detected at signal-to-noise ratio >5 in maps filtered at an angular scale of 2.′4. The survey has a large overlap with deep optical weak-lensing surveys that are being used to calibrate the SZ signal mass-scaling relation, such as the Dark Energy Survey (4566 deg2), the Hyper Suprime-Cam Subaru Strategic Program (469 deg2), and the Kilo Degree Survey (825 deg2). We highlight some noteworthy objects in the sample, including potentially projected systems, clusters with strong lensing features, clusters with active central galaxies or star formation, and systems of multiple clusters that may be physically associated. The cluster catalog will be a useful resource for future cosmological analyses and studying the evolution of the intracluster medium and galaxies in massive clusters over the past 10 Gyr. Title: Distinguishing between coronal cloud prominences and channel prominences and their associations with solar and stellar flares Authors: Martin, Sara F.; Engvold, Oddbjorn; Lin, Yong; da Silva, Jacqueline Alves Bibcode: 2016IAUS..320..278M Altcode: To better understand the differences between coronal cloud prominences and channel prominences, we systematically identified and analyzed coronal cloud prominences recorded in SDO/AIA images at 304 Å from 2010 May 20 through 2012 April 28. For the 225 cases identified, their numbers vary directly with the sunspot number. Their durations are typically less than 3 days. Their most frequent maximum height is 90,000 + and - 10,000 km. We offer our hypothesis that many coronal cloud prominences originate from some of the mass of previously erupted filaments ejected high out of their filament channels; subsequently part of this mass falls and collects in leaky magnetic troughs among coronal magnetic fields which constrain the leaked mass to slowly drain downward along curved trajectories where it appears as coronal rain. Currently there is inadequate evidence for a convincing correspondence between either coronal cloud prominences or channel prominences with stellar prominences detected to date. Title: Observing Cascades of Solar Bullets at High Resolution. II. Authors: Scullion, E.; Engvold, O.; Lin, Y.; Rouppe van der Voort, L. Bibcode: 2015ApJ...814..123S Altcode: High resolution observations from the Swedish 1-m Solar Telescope revealed bright, discrete, blob-like structures (which we refer to as solar bullets) in the Hα 656.28 nm line core that appear to propagate laterally across the solar atmosphere as clusters in active regions (ARs). These small-scale structures appear to be field aligned and many bullets become triggered simultaneously and traverse collectively as a cluster. Here, we conduct a follow-up study on these rapidly evolving structures with coincident observations from the Solar Dynamics Observatory/Atmospheric Imaging Assembly. With the co-aligned data sets, we reveal (a) an evolving multithermal structure in the bullet cluster ranging from chromospheric to at least transition region temperatures, (b) evidence for cascade-like behavior and corresponding bidirectional motions in bullets within the cluster, which indicate that there is a common source of the initial instability leading to bullet formation, and (c) a direct relationship between co-incident bullet velocities observed in Hα and He ii 30.4 nm and an inverse relationship with respect to bullet intensity in these channels. We find evidence supporting that bullets are typically composed of a cooler, higher density core detectable in Hα with a less dense, hotter, and fainter co-moving outer sheath. Bullets unequivocally demonstrate the finely structured nature of the AR corona. We have no clear evidence for bullets being associated with locally heated (or cooled), fast flowing plasma. Fast MHD pulses (such as solitons) could best describe the dynamic properties of bullets whereas the presence of a multithermal structure is new. Title: Distinguishing Between Different Types of Prominences Associated with Solar Flares Authors: Martin, Sara F.; Engvold, Oddbjorn; Lin, Yong Bibcode: 2015IAUGA..2255962M Altcode: In the early days of solar astronomy, any feature that extended above the solar limb was called a prominence. However, many such coronal features have been sufficiently studied to justify more specific names such as flare loops, surges, and flaring arches. Each of these named phenomena has different properties and involves different physical processes from other solar prominences. If we exclude these well-identified phenomena, we find that the majority of the remaining prominences can be grouped into only two categories that are distinctly different from each other. The main two types are (1) channel prominences or channel filaments when seen against the solar disk and (2) coronal cloud prominences, including narrow, down-flows named coronal rain. We illustrate the many significant differences between channel prominences and coronal cloud prominences. One of the fundamental differences is that channel prominences often have patterns of mass motions useful in anticipating many flares while coronal cloud prominences tend to occur hours after major solar flares. We also raise the question of whether the much taller coronal cloud prominences could have a counterpart in prominences on solar-like stars with magnetic fields of greater magnitude than the Sun. Title: Prominence seismology using ground- and space-based observations Authors: Ballester, J. L.; Arregui, I.; Oliver, R.; Terradas, J.; Soler, R.; Lin, Y.; Engvold, O.; Langagen, O.; Rouppe van der Voort, L. H. M. Bibcode: 2012EAS....55..169B Altcode: Ground- and space-based observations have confirmed the presence of oscillatory motions in prominences and they have been interpreted in terms of magnetohydrodynamic (MHD) waves. This interpretation opens the door to perform prominence seismology, whose main aim is to determine physical parameters in magnetic and plasma structures (prominences) that are difficult to measure by direct means. Here, two prominence seismology applications are presented. Title: Small-scale, Dynamic Bright Blobs in Solar Filaments and Active Regions Authors: Lin, Y.; Engvold, O.; Rouppe van der Voort, L. H. M. Bibcode: 2012ApJ...747..129L Altcode: 2012arXiv1201.0406L High-cadence high spatial resolution observations in Hα with the Swedish 1 m Solar Telescope on La Palma have revealed the existence of small-scale highly dynamic bright blobs. A fast wavelength tuning spectropolarimeter provides spectral information of these structures. The blobs slide along thin magnetic threads at speeds in the range from 45 km s-1 to 111 km s-1. The blobs have a slightly elongated shape and their lengths increase by a factor of three from close to half an arcsecond when they first appear until they disappear one to two minutes later. The brightest blobs show the highest speed. The widths of the Hα line emission of the blobs correspond to non-thermal velocities in the plasma less than 10 km s-1, which implies that they are not the result of shock-driven heating. The dynamic character of the bright blobs is similar to what can be expected from an MHD fast-mode pulse. Title: Filament Thread-like Structures and Their Small-amplitude Oscillations Authors: Lin, Yong Bibcode: 2011SSRv..158..237L Altcode: 2010SSRv..tmp..176L Thanks to gradually improving observational capabilities, both from space and ground-based observatories, it is now generally accepted that thin threads (width ∼200 km) constitute the building blocks of solar filaments and prominences. At ultra-small scales, high quality image sequences show a non-static picture of filaments and reveal that their oscillatory behavior is an important dynamic feature of these structures. Filament seismology sheds light on the internal magnetic structures of filaments and their interactions with surrounding solar regions. Understanding the overall magnetic topology of solar filaments and prominences including their small-scale thread-like structures is essential in interpretation and understanding of their oscillations. For this reason we aim here to present an update of the dynamic and spatial structures of prominences and filaments as inferred from high resolution observations in the past decennia. Some constraints in high resolution observations are addressed. Our review focuses mainly on the observational aspects and aims to summarize recent oscillation studies of individual filament threads and groups of threads. Finally, some theoretical interpretations of oscillations of filament threads and the inferred physical conditions of filament plasma are also discussed. Title: Swaying Threads of a Solar Filament Authors: Lin, Y.; Soler, R.; Engvold, O.; Ballester, J. L.; Langangen, Ø.; Oliver, R.; Rouppe van der Voort, L. H. M. Bibcode: 2009ApJ...704..870L Altcode: 2009arXiv0909.2792L From recent high-resolution observations obtained with the Swedish 1 m Solar Telescope in La Palma, we detect swaying motions of individual filament threads in the plane of the sky. The oscillatory characters of these motions are comparable with oscillatory Doppler signals obtained from corresponding filament threads. Simultaneous recordings of motions in the line of sight and in the plane of the sky give information about the orientation of the oscillatory plane. These oscillations are interpreted in the context of the magnetohydrodynamic (MHD) theory. Kink MHD waves supported by the thread body are proposed as an explanation of the observed thread oscillations. On the basis of this interpretation and by means of seismological arguments, we give an estimation of the thread Alfvén speed and magnetic field strength by means of seismological arguments. Title: On small active region filaments, fibrils and surges Authors: Lin, Y.; Martin, S. F.; Engvold, O.; Rouppe van der Voort, L. H. M.; van Noort, M. Bibcode: 2008AdSpR..42..803L Altcode: High resolution Hα images and magnetograms (0.2 arc s) of an active region were obtained in alternating time series at 42 s cadences using the Swedish 1-m Solar Telescope on 2004 August 21. The Hα filtergrams reveal an active region filament and surges consisting of thread-like structures which have widths similar to the widths of chromospheric fibrils, both recorded down to the resolution limit in the best images. All observed structures in the active region appear highly dynamic. Fibrils show counterstreaming strongly resembling the counterstreaming threads in filaments. Streaming, along the threads of surges extending more than 10 arc s, is higher in speed (∼20 km s-1) than in the filament and fibrils and appears to flow independently over and above the chromospheric fibrils. Blue shifts seen in the Hα Dopplergrams confirm the outward mass motion of the surges. However, in at least one case, we also see simultaneous downflows from the same site but in the opposite direction and downward toward the chromosphere. We suggest that the site between these two outward and downward flows identifies the place where magnetic reconnection could occur and thereby cause of the surge. This appears to imply that the reconnection site is in the high chromosphere or low corona. Title: A Method of Resolving the 180-Degree Ambiguity by Employing the Chirality of Solar Features Authors: Martin, S. F.; Lin, Y.; Engvold, O. Bibcode: 2008SoPh..250...31M Altcode: 2008SoPh..tmp..105M The 180-degree ambiguity in magnetic field direction along polarity reversal boundaries can be resolved often and reliably by the chiral method. The chiral method requires (1) identification of the chirality of at least one solar feature related to a polarity reversal boundary along which the field direction is sought and (2) knowledge of the polarity of the network magnetic field on at least one side of the polarity reversal boundary. In the context of the Sun, chirality is an observable signature of the handedness of the magnetic field of a solar feature. We concentrate on how to determine magnetic field direction from chirality definitions and illustrate the technique in eight examples. The examples cover the spectrum of polarity boundaries associated with filament channels and filaments ranging from those connected with active regions to those on the quiet Sun. The applicability of the chiral method to all categories of filaments supports the view that active region filaments and quiescent filaments are the extreme ends in a continuous spectrum of filaments. Title: The Unique 3D Magnetic Structure of Filaments Authors: Lin, Y.; Engvold, O.; Martin, S.; Panasenco, O. Bibcode: 2008AGUSMSH23A..05L Altcode: Filaments in active regions most clearly have the form of long thin ribbons as seen in Hα. The ribbon structure is also readily demonstrated for quiescent filaments when seen from an end view as a filament is transported across the east or west limb due to solar rotation. In addition to the primary ribbon structure, filaments also have shorter, secondary structures called barbs which connect some threads of the main ribbon structure to the chromosphere; these are also seen in the end view of filaments at the limb. This connection with the chromosphere is corroborated in high resolution images of filaments recorded against the disk at the 1-meter Swedish Solar Telescope (SST). In these high resolution Hα movies, the lower parts of all threads are recognizable because they move less freely than the higher parts. The connection of the ends of the threads of the main filament ribbon and the ends of the filament barbs to the chromosphere/photosphere is strong evidence alone that filaments have their own magnetic fields separate from surrounding coronal magnetic fields. The chirality (handedness) of filaments provides further evidence that filaments have their own magnetic fields. The two forms of dextral and sinistral chirality are generally manifest in the relative direction of the deviation of barbs from the main ribbon. However, the sign of chirality is most clear in the thread structure of all barbs seen in Hα images from the SST. From a number of characteristics of the observed mass motions of filament threads of the order of several to tens of kilometers per second, we have previously concluded that filament threads are field-aligned. Therefore we use the threads and their mass motions to construct the 3D configuration of filament magnetic fields. We end this presentation with movies of filaments from STEREO/SECCHI/EUVI consistent with our thread model of filaments. Title: Measurements of Plasma Motions in Dynamic Fibrils Authors: Langangen, Øystein; Rouppe van der Voort, Luc; Lin, Yong Bibcode: 2008ApJ...673.1201L Altcode: 2007arXiv0710.1011L We present a 40 minute time series of filtergrams from the red and blue wings of the Hα line in an active region near the solar disk center. From these filtergrams we construct both Dopplergrams and summed "line center" images. Several dynamic fibrils (DFs) are identified in the summed images. The data are used to simultaneously measure the proper motion and the Doppler signals in DFs. For calibration of the Doppler signals, we use spatially resolved spectrograms of a similar active region. Significant variations in the calibration constant for different solar features are observed, and only regions containing DFs have been used in order to reduce calibration errors. We find a coherent behavior of the Doppler velocity and the proper motion that clearly demonstrates that the evolution of DFs involves plasma motion. The Doppler velocities are found to be a factor of 2-3 smaller than velocities derived from proper motions in the image plane. The difference can be explained by the radiative processes involved, as the Doppler velocity is a result of the local atmospheric velocity weighted with the response function. As a result, the Doppler velocity originates from a wide range of heights in the atmosphere. This is contrasted with the proper-motion velocity, which is measured from the sharply defined bright tops of the DFs and is therefore a very local velocity measure. The Doppler signal originates from well below the top of the DF. Finally, we discuss how this difference, together with the lower spatial resolution of older observations, has contributed to some of the confusion about the identity of DFs, spicules, and mottles. Title: Evidence of Traveling Waves in Filament Threads Authors: Lin, Y.; Engvold, O.; Rouppe van der Voort, L. H. M.; van Noort, M. Bibcode: 2007SoPh..246...65L Altcode: High-resolution Hα filtergrams (0.2″) obtained with the Swedish 1-m Solar Telescope resolve numerous very thin, thread-like structures in solar filaments. The threads are believed to represent thin magnetic flux tubes that must be longer than the observable threads. We report on evidence for small-amplitude (1 - 2 km s−1) waves propagating along a number of threads with an average phase velocity of 12 km s−1 and a wavelength of 4″. The oscillatory period of individual threads vary from 3 to 9 minutes. Temporal variation of the Doppler velocities averaged over a small area containing a number of individual threads shows a short-period (3.6 minutes) wave pattern. These short-period oscillations could possibly represent fast modes in accordance with numerical fibril models proposed by Díaz et al. (Astron. Astrophys.379, 1083, 2001). In some cases, it is clear that the propagating waves are moving in the same direction as the mass flows. Title: Solar Filaments and Photospheric Network Authors: Lin, Yong; Wiik, Jun Elin; Engvold, Oddbjørn; Van Der Voort, Luc Rouppe; Frank, Zoe A. Bibcode: 2005SoPh..227..283L Altcode: The locations of barbs of quiescent solar filaments are compared with the photospheric/chromospheric network, which thereby serves as a proxy of regions with enhanced concentrations of magnetic flux. The study covers quiet regions, where also the photospheric network as represented by flow converging regions, i.e., supergranular cell boundaries, contain largely weak magnetic fields. It is shown that close to 65% of the observed end points of barbs falls within the network boundaries. The remaining fraction points into the inner areas of the network cells. This confirms earlier findings (Lin et al., Solar Physics, 2004) that quiescent filaments are basically connected with weaker magnetic fields in the photosphere below. Title: Thin Threads of Solar Filaments Authors: Lin, Yong; Engvold, OddbjØrn; der Voort, Luc Rouppe van; Wiik, Jun Elin; Berger, Thomas E. Bibcode: 2005SoPh..226..239L Altcode: High-resolution images obtained in Hα with the new Swedish Solar Telescope at La Palma, Spain, have been used for studies of fine-scale threads in solar filaments. The widths of the thin threads are ≤0.3 arcsec. The fact that the width of the thinnest threads is comparable to the diffraction limit of the telescope of about 0.14 arcsec, at the wavelength of Hα, suggests that even thinner threads may exist. Assuming that the threads represent thin magnetic strings, we conclude that only a small fraction of these are filled with observable absorbing plasma, at a given time. The absorbing plasma is continuously flowing along the thread structures at velocities 15± 10 kms−1, which suggests that the flows must be field-aligned. In one case where a bundle of thin threads appears to be rooted in the nearby photosphere, we find that the individual threads connects with intergranular, dark lanes in the photosphere. We do not find signs of typical network fields at the `roots' of the fine threads, as normally evidenced by bright points in associated G-band images. It is suggested that filament threads are rooted in relatively weak magnetic fields. Title: Multi-wavelength study of a high-latitude EUV filament Authors: Schmieder, Brigitte; Lin, Yong; Heinzel, Petr; Schwartz, Pavol Bibcode: 2004SoPh..221..297S Altcode: A large filament was observed during a multi-wavelength coordinated campaign on June 19, 1998 in the Hα line with the Swedish Vacuum Solar Telescope (SVST) at La Palma, in the coronal lines Fe ix/x 171 Å and Fe xi 195 Å with the Transition Region and Coronal Explorer (TRACE) and in EUV lines with the SOHO/CDS spectrometer and the hydrogen Lyman series with the SOHO/SUMER spectrometer. Because of its high-latitude location, it is possible to disentangle the physical properties of the Hα filament and the filament channel seen in EUV lines. TRACE images point out a dark region fitting the Hα fine-structure threads and a dark corridor (filament channel), well extended south of the magnetic inversion line. A similar pattern is observed in the CDS EUV-line images. The opacity of the hydrogen and helium resonance continua at 171 Å is almost two orders of magnitude lower than that at the Hi head (912 Å) and thus similar to the opacity of the Hα line. Since we do not see the filament channel in Hα, this would imply that it should also be invisible in TRACE lines. Thus, the diffuse dark corridor is interpreted as due to the coronal `volume blocking' by a cool plasma which extends to large altitudes. Such extensions were also confirmed by computing the heights from the projection geometry and by simulations of the CDS and TRACE line intensities using the spectroscopic model of EUV filaments (Heinzel, Anzer, and Schmieder, 2003). Finally, our NLTE analysis of selected hydrogen Lyman lines observed by SUMER also leads to a conclusion that the dark filament channel is due to a presence of relatively cool plasma having low densities and being distributed at altitudes reaching the Hα filament. Title: Magnetic field topology inferred from studies of fine threads in solar filaments Authors: Lin, Yong Bibcode: 2004PhDT.......255L Altcode: No abstract at ADS Title: Counterstreaming in a Large Polar Crown Filament Authors: Lin, Yong; Engvold, OddbjØ rn; Wiik, Jun Elin Bibcode: 2003SoPh..216..109L Altcode: The motion of small-scale structures is well resolved in high-resolution filament images that were observed on 19 June 1998 with the Swedish Vacuum Solar Telescope, La Palma. The filament was between 80 000 and 100 000 km high. The study is based on two hours of narrow-band observations at three wavelength positions in Hα. Velocities along the line of sight and in the transverse direction, respectively, Vlos and Vtr, were measured for a large number of individual small-scale filament structures. Small features are all moving along nearly parallel threads, some in one direction along the threads and the remainder in the other direction, a pattern of motion known as counterstreaming. The net flow velocities in the two directions are about 8 km s−1 and both are tilted by an angle δ≃16° relative to the plane of the sky. This angle is less than expected, by factors between 2.0 and 2.5, relative to the local horizontal plane. We believe that Vlos is underestimated by these factors due to a line-shift reducing effect by the underlying Hα absorption line of the chromosphere. Title: Filament activation and magnetic reconnection Authors: Deng, Yuanyong; Lin, Yong; Schmieder, Brigitte; Engvold, OddbjØrn Bibcode: 2002SoPh..209..153D Altcode: A curved filament in a decaying active region (AR 8329) was observed on 9 September 1998 with a combination of several instruments. The main data base is a 4-hour long time series of 1 min cadence using the Lockheed tunable filter mounted in the Swedish Vacuum Solar Tower in La Palma (SVST). Filtergrams obtained at several wavelength positions in Hα images are used to derive Doppler images. Interleaved images in the magnetic sensitive Fe i 6302.5 Å line yield corresponding magnetograms. Supplementing observations are collected from TRACE and the French Multi-Channel Double Pass spectrograph (MSDP) mounted in the German VTT in Tenerife. The filament, which consists of several discrete fragments with nearly horizontal fine structures, undergoes activity and counter-streaming bulk flow, but without erupting. The magnetic field inversion line of this active region is complex and strongly influenced by intrusion of a positive polarity area in a following negative polarity of the region. The positive polarity area contains a small sunspot surrounded by moving magnetic features (MMFs). The MMFs interact directly with the parasitic polarities in the filament channel, and thereby gives rise to merging and canceling magnetic flux. When the interaction occurs at the location of the feet (`barbs') of the filament notable activations are observed (ejection of `blobs'). The ejections of `blobs' are preceded by twist of filament threads and the `blobs' move along downward bending field lines towards the photosphere close to the sound speed.