Image of the Month

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Research Illustrations

Every month, an image (or video) related to the WaLSA Team’s activities is showcased on this page. For greater details, please visit the original source given at the bottom of each image's caption.

Select month/year for previous images/videos:


Solar inertial modes: Observations, identification, and diagnostic promise

The oscillations of a slowly rotating star have long been classified into spheroidal and toroidal modes. The spheroidal modes include the well-known 5-min acoustic modes used in helioseismology. Observations of the Sun's toroidal modes, for which the restoring force is the Coriolis force and whose periods are on the order of the solar rotation period, are reported in this article. By comparing the observations with the normal modes of a differentially rotating spherical shell, the authors were able to identify many of the observed modes. These are the high-latitude inertial modes, the critical-latitude inertial modes, and the equatorial Rossby modes.
Observed and model eigenfunctions for the modes are shown in the figure above. The left column shows the observed velocity (u-φ for the m=1 and m=2 modes, u+θ for the m=3 mode). The middle columns show the corresponding eigenfunctions of the 2D model for νt=100 km2 s-1 and δ=0, at the surface and through the central meridian, together with the kinetic energy density. The thick black curves show the critical latitudes. The rightmost column shows the eigenfunctions of the 1D model at the surface. The retrograde propagation of these modes in the Carrington frame is illustrated as an online movie.

Copyright: Gizon, Laurent, Cameron, Robert H., Bekki, Yuto, Birch, Aaron C., Bogart, Richard S., Brun, Allan Sacha, Damiani, Cilia, Fournier, Damien, Hyest, Laura, Jain, Kiran, Lekshmi, B., Liang, Zhi-Chao, Proxauf, Bastian 2021, A&A, 652, L6 (doi: 10.1051/0004-6361/202141462)


Magnetic fields and the supply of low-frequency acoustic wave energy to the solar chromosphere

Maps of magnetic inclination angle (bottom panels), phase travel time (middle panels), and logarithm of energy flux (top panels) for a sunspot (left), plage region (middle), and quiet-network area (right). The phase travel time and energy flux are for acoustic waves of frequency 3 mHz propagating from 170 km (SDO/HMI line-core intensity) to 360 km (SDO/AIA 170 nm intensity).
It is found that the relatively less inclined magnetic field elements in the quiet Sun channel a significant amount of waves of frequency lower than the theoretical minimum acoustic cutoff frequency due to magnetic inclination. Indications that these waves steepen and start to dissipate within the height ranges probed were also derived. The flux of acoustic energy, in the 2-5 mHz frequency range, between the upper photosphere and lower chromosphere found to be in the range of 2.25-2.6 kW m-2, which is about twice the previous estimates.

Copyright: Rajaguru, S. P., Sangeetha, C. R., Tripathi, Durgesh 2019, ApJ, 871, 155 (doi: 10.3847/1538-4357/aaf883)


Magnetoacoustic wave energy dissipation in the atmosphere of solar pores

(a) Five small pores as observed by the Dunn Solar Telescope (DST), Sacramento Peak, New Mexico. Panel (a) illustrates the pores in a DST/ROSA 4170 Å continuum image. The position of the FIRS (Facility Infrared Spectropolarimeter) slit is depicted by a dashed yellow line, with each of the five solar pores captured labelled by a number 1–5.
(b) Energy flux (due to propagating magnetoacoustic sausage mode waves) displayed as a function of both distance across the slit and atmospheric height. Pore boundaries are highlighted by the vertical white dashed lines. The solid green line displays the inclination angles of the magnetic field along the slit. High energy fluxes towards the edges of pore structures (i.e. pores 2, 3 and 4) may be the result of surface mode waves, while more uniform energy structuring (i.e. pores 1 and 5) may be related to the presence of body mode waves. Energy flux values seen in non-pore regions are likely a result of convective overshoots and not specifically propagating magnetoacoustic wave phenomena.

Copyright: Gilchrist-Millar, Caitlin A., Jess, David B., Grant, Samuel D. T., Keys, Peter H., Beck, Christian, Jafarzadeh, Shahin, Riedl, Julia M., Van Doorsselaere, Tom, Ruiz Cobo, Basilio 2021, Phil. Trans. R. Soc. A 379: 20200172 (doi: 10.1098/rsta.2020.0172)


Transverse motions in sunspot super-penumbral fibrils

(a) The sunspot as observed in Ca II 8542 Å. The upper left image shows the chromospheric emission at the nominal line centre wavelength. Super-penumbral fibrils are seen to extend near-radially from the chromospheric umbra in the upper half, while those in the lower half are more curvilinear. The upper right-hand image shows the photospheric section of the sunspot as observed in the wings of the Ca II line (−0.942 Å). The lower two panels show the temporally averaged line width (left) and Doppler velocity (right) data products. The width and Doppler components of the fibrils can be seen in both data product images.
(b) An isolated set of fibrils in the CaII sunspot super-penumbra. The figure shows the outline of the fibril’s central axis along with the cross-cuts normal to the guide-line. For clarity, a small number of guide points and a large separation distance is chosen.
(c) Wave properties as a function of distance from the umbral centre. The figure displays the mean values for velocity and period, with the error bars denoting the standard errors on the mean.

Copyright: Morton, R. J., Mooroogen, K., Henriques, V. M. J. 2021, Phil. Trans. R. Soc. A 379: 20200183 (doi: 10.1098/rsta.2020.0183)


Torsional oscillations within a magnetic pore in the solar photosphere

Alfvén waves have proven to be important in a range of physical systems due to their ability to transport non-thermal energy over long distances in a magnetized plasma. This property is of specific interest in solar physics, where the extreme heating of the atmosphere of the Sun remains unexplained. In an inhomogeneous plasma such as a flux tube in the solar atmosphere, they manifest as incompressible torsional perturbations. However, despite evidence in the upper atmosphere, they have not been directly observed in the photosphere. Here, we report the detection of antiphase incompressible torsional oscillations observed in a magnetic pore in the photosphere by the Interferometric Bidimensional Spectropolarimeter (IBIS) at the Dunn Solar Telescope (DST). State-of-the-art numerical simulations suggest that a kink mode is a possible excitation mechanism of these waves.
Panel b: Measured angular rotation oscillations of the two lobes of the magnetic pore, as obtained from a cross-correlation tracking analysis at the edges of the flux tube.
Panel d: Schematic depicting the m = 1 antisymmetric torsional Alfvén oscillations in the magnetic structure.

Copyright: Marco Stangalini, Robertus Erdélyi, Callum Boocock, David Tsiklauri, Christopher J. Nelson, Dario Del Moro, Francesco Berrilli, and Marianna B. Korsós 2021, Nature Astronomy, advance online publications (doi: 10.1038/s41550-021-01354-8)


Wave phenomena in sunspots

Wave dynamics in a sunspot, observed with the ground-based Dunn Solar Telescope (DST) in New Mexico, has been illustrated. The simultaneous scanning of multiple spectral lines in the visible to near-infrared range has allowed a fine sampling of the photosphere and chromosphere above the sunspot. Sunspot waves are detected throughout all atmospheric layers, from the lower photosphere to the upper transition region and corona. Umbral flashes and running penumbral waves are most prominent in the sunspot chromosphere. All oscillations in spectral intensity and Doppler velocity occur unceasingly at periods of a few minutes for the observational timespan. The most likely driving mechanism is the absorption of p-modes by the sunspot in the upper convection zone and lower photosphere. Magnetoacoustic waves are also driven by perturbations of the magnetic field lines.

Copyright: Johannes Löhner-Böttcher 2015, PhD thesis


The Effects of Transients on Photospheric and Chromospheric Power Distributions

Left: Images of a quiet region as seen in different layers of the solar atmosphere along with the corresponding magnetogram from photosphere at the bottom. Bottom to top: line-of-sight (LOS) magnetogram obtained by using Fe 6302 Å Stokes V profiles, visible continuum, and narrow-band filter images taken at different positions across the Hα line profile as indicated (Hα + 0.906 Å, Hα + 0.543 Å, Hα + 0.362 Å and Hα core). The long tick marks on the magnetogram represent 10 Mm intervals.
Right: Distribution of dominant periods (of intensity oscillations) in different layers along with the corresponding magnetogram at the bottom. The green, red, and yellow colors roughly represent periods around 3, 5, and 7 minutes, respectively.

Copyright: Tanmoy Samanta, Vasco M. J. Henriques, Dipankar Banerjee, Sayamanthula Krishna Prasad, Mihalis Mathioudakis, David B. Jess, and Vaibhav Pant 2016, The Astrophysical Journal, 828, 23


An overall view of temperature oscillations in the solar chromosphere with ALMA

Global oscillations in one of the most magnetically quiescent datasets studied in this research article.
Top left: A brightness-temperature map from the ALMA’s Band-3 observations from 12 April 2018. The blue ellipse on the bottom-left corner of the panel represents the beam size of the observations. Top right: Spatially averaged brightness-temperature power spectra from fast Fourier (dash-dotted black line) and Lomb– Scargle (solid red line) transforms. The purple and yellow stripes have been depicted to mark period ranges corresponding to the 3 and 5 min windows (each with a width of 1 min), respectively. The chromospheric characteristic frequencies of the global p-mode oscillations (i.e., around 3-5~mHz) is evident. Bottom left: Line-of-sight photospheric magnetic fields (Blos) from SDO/HMI with a factor of two larger FOV than that of ALMA. The range of Blos values has been indicated in the upper left corner. The ALMA’s FOV is marked with the dashed square. Bottom right: Top view of field extrapolation of the surface magnetic field (from SDO/HMI) at the chromosphere heights (for the ALMA’s FOV). The colours represent inclination, from vertical (blue) to horizontal (red).

Copyright: S. Jafarzadeh, S. Wedemeyer, B. Fleck, M. Stangalini, D. B. Jess, R. J. Morton, M. Szydlarski, V. M. J. Henriques, X. Zhu, T. Wiegelmann, J. C. Guevara Gómez, S. D. T. Grant, B. Chen9, K. Reardon and S. M. White 2021, Phil. Trans. R. Soc. A 379: 20200174


Evolution of Complex 3D Motions in Spicules

Three dimensional visualization of coupled MHD wave modes are illustrated in a spicule, obtained from high-resolution observations with the Swedish 1-m Solar Telescope. The four columns illustrate the 3D structure at different time steps indicated on the top. Top row: coupled transverse and width with intensity. Bottom row: transverse and azimuthal shear components. The azimuthal shear/torsion component magnitude exhibits field-aligned upward and downward motions, possibly due to perturbed Lorentz forces.

Copyright: Rahul Sharma, Gary Verth, and Robertus Erdélyi 2018, The Astrophysical Journal, 853, 61


The Sun at millimeter wavelengths -- II. Small-scale dynamic events in ALMA Band 3

Detailed study of an event. a-e) The top panels show a close up of the surroundings at different time steps, t1 to t5 from left to right, through the shock wave event. The time of the Tb peak is marked by t3 = 14:46:38. t1 and t2 mark 70 s and 26 s prior the peak and t4 and t5 mark 26 s and 70 s after the peak. The center location is marked by a blue cross. The contour lines marks the half maximum of the maximum ∆Tb peak. f-g) Space-time diagrams for a vertical and horizontal slit across the FOV at the center location, which is marked with blue dots for the time steps t1 to t5 . Velocity slopes for 10 and 20 km s −1 are indicated by blue dotted and white dashed lines, respectively. The color code is the same in all panels. h) The time evolution of the brightness temperature of the center location, where the time steps t1 to t5 are indicated by blue dotted vertical lines. Both the original data (black) and the averaged data (green) are shown. The horizontal and vertical black dashed lines mark the event lifetime and brightness temperature excess.

Copyright: Henrik Eklund, Sven Wedemeyer, Mikolaj Szydlarski, Shahin Jafarzadeh, and Juan Camilo Guevara Gómez 2020, Astronomy & Astrophysics, in press


Numerical Simulations of Quiet Sun Oscillations

A comparison between oscillations in a quiet Sun background model from the three-dimensional Semi-spectral Linear MHD (SLiM) code, and observations with SOHO/MDI.

"The azimuthally averaged power spectrum (on a log scale where black is high and white low) of 8 hours of vertical velocity data from the SLiM simulation (top) and 24 hours of SOHO/MDI full-disk, line-of-sight Doppler observations (bottom). The eigenfrequencies of Model S (Christensen-Dalsgaard et al. 1996) are overplotted as dashed lines. Modes with a horizontal phase speed ω/k greater than c(zb)/(1+ zb/R) (solid line in top panel) encounter the bottom sponge layer before reaching their lower turning point."

Copyright: Hannah Schunker, Robert Cameron, and Laurent Gizon 2009, ASP Conference Series, Vol. 416, 49


Collisional ionisation, recombination and ionisation potential in two-fluid slow-mode shocks: analytical and numerical results

Close-up of the slow mode shock for the IRIP (Collisional ionisation, recombination and ionisation potential) model showing vx velocity (top left), temperature (top right) and density (lower left) for plasma (blue) and neutral (red) species. The lower right panel shows the ionisation (orange) and recombination (green) rates.

Copyright: Ben Snow & Andrew Hillier, Astronomy & Astrophysics, in press


The dynamics of 3-minute wavefronts and their relation to sunspot magnetic fields

The frequency distribution of oscillation power corresponding to the instantaneous wavefront visible at 00:14:33 UT (panel a). The contours show a broadband ∼3-minute wavefront superimposed on the narrowband power distributions corresponding to periods in the range of 1.8 – 3.8 minutes. The corresponding power spectra for the selected points on the wavefront ridge, as a function of period. The coloured lines reflect the locations marked by the coloured dots in the upper-left panel. The first area is associated with a pulsating source.

Copyright: Sych, Robert, Jess, David B., Su, Jiangtao 2020, Phil. Trans. R. Soc. A, in press


High-frequency oscillations in small chromospheric bright features observed with ALMA

Fluctuations in brightness temperature (black) and size (red) of three small bright features. The horizontal black, dotted line in the top panel marks the size of the major axis of the synthetic elliptical median beam (i.e., the spatial-resolution element). An anti-correlation between oscillations of the two quantities is evident.

Copyright: Guevara Gómez, J. C., Jafarzadeh, S., Wedemeyer, S., Szydlarski, M., Stangalini, M., Fleck, B., Keys, P. 2020, Phil. Trans. R. Soc. A, in press


Acoustic-gravity wave propagation characteristics in 3D radiation hydrodynamic simulations of the solar atmosphere

Frequency-height phase diagrams (cuts at constant wave numbers at approximately 2 (top) and 4 Mm-1 (bottom) through the stacks of the layer-by-layer 2D k-ω phase difference diagrams) for the MANCHA3D model (left) and comparison to a MURaM (middle) and Bifrost (right) model. This works reveals considerable differences between the various models.

Copyright: Fleck, B., Carlsson, M., Khomenko, E., Rempel, M., Steiner, O., Vigeesh, G. 2020, Phil. Trans. R. Soc. A, in press


Oscillations on Width and Intensity of Slender Ca ii H Fibrils from Sunrise/SuFI

Example of intensity maxima and width detections along cuts perpendicular to the axis of an SCF. Plotted are vertically stacked images of a fibril recorded in Ca ii H observed at different times. Individual images, recorded every 7 s, are separated by horizontal black lines. The red dots within a given image represent the locations of the fibril's maximum intensity along a series of cuts roughly perpendicular to the backbone of the fibril, while the vertical black lines indicate the width of the fibril at the same locations. The color represents intensity, normalized to the mean value of the quiet region in the SUFI frame. An anti-correlation between width and intensity oscillations suggests the presence of fast sausage mode.

Copyright: Gafeira, R., Jafarzadeh, S., Solanki, S. K., Lagg, A., van Noort, M., Barthol, P., Blanco Rodríguez, J.,del Toro Iniesta, J. C., Gandorfer, A., Gizon, L., Hirzberger, J., Knölker, M., Orozco Suárez, D., Riethmüller, T. L.,Schmidt, W. 2017, The Astrophysical Journal Supplement Series, 229, 7 (doi: 10.3847/1538-4365/229/1/7)


Vortices evolution in the solar atmosphere

Co-spatial images revealing the structure of a sunspot observed at 13:00 UT on 24 August 2014. The lower image shows the magnitude of the photospheric magnetic field from HMI/SDO, revealing high umbral field strengths (colour bar relates to the field strengths in gauss). The image above is taken from the blue wing of the Ca II 8542 Å spectral line from DST, displaying the photospheric representation of the sunspot. Above this is the photospheric plasma temperature of the region derived from CAISAR at log(τ 500nm) ~ −2 (or ~ 250 km above the photosphere), showing the clear temperature distinction between the umbra, penumbra and surrounding quiet Sun (colour bar in units of kelvin). The upper image shows the chromospheric core of the Ca II 8542 Å spectral line from DST, highlighting the strong intensity gradient between the umbra and penumbra at these heights. In each of these images, the red contours represent the inner and outer boundaries of the plasma-β = 1 region at the height where shocks first begin to manifest (~ 250 km), where magneto-acoustic and Alfvén waves can readily convert.

Copyright: José R. Canivete Cuissa and Oskar Steiner 2020, Astronomy & Astrophysics, 639, A118 (doi: 10.1051/0004-6361/202038060)


Unveiling the magnetic nature of chromospheric vortices

Perturbations in intensity (left), LOS Doppler velocity (middle), and Circular Polarisation (right) as a function of angle and time in a polar grid centered one of the events and averaged over radius. The line highlights the phase propagation of the wave patterns with their corresponding periodicity.

Copyright: Murabito, M., Shetye, J., Stangalini, M., Verwichte, E., Arber, T., Ermolli, I., Giorgi, F., Goffrey, T. 2020, Astronomy & Astrophysics, 639, A59 (doi: 10.1051/0004-6361/202038360)


Magnetohydrodynamic Nonlinearities in Sunspot Atmospheres: Chromospheric Detections of Intermediate Shocks

Left: shock LOS Doppler velocities plotted as a function of their quiescent (i.e., pre-shock) Doppler velocities for the same pixel location. The background blue–red color scheme helps visualize the Doppler velocities corresponding to each quadrant of the plot, with progressively more blue and red colors representing larger up- and downflowing material, respectively. Right: shock temperature changes displayed as a function of the pre-shock background temperature. The background blue–red color scheme provides a visual representation of temperature, with more red colors corresponding to both hotter quiescent and shock-induced temperatures. In both panels the colored data points correspond to the optical depths at which the plasma parameters are extracted, as defined in the legends located in the upper left corner of each panel.

Copyright: Houston, S. J., Jess, D. B., Keppens, R., Stangalini, M., Keys, P. H., Grant, S. D. T., Jafarzadeh, S., McFetridge, L. M., Murabito, M., Ermolli, I., Giorgi, F. 2020, The Astrophysical Journal, 892, 49 (doi: 10.3847/1538-4357/ab7a90)


Third meeting of the WaLSA Team / Theo Murphy international scientific meeting
Chicheley Hall of The Royal Society, UK; 10-11 February 2020


Long-period magnetic field oscillations and motions in isolated sunspots

Penumbral distribution of the wavelet power of a sunspot, NOAA AR12218, and its comparison to the spatial distribution of the magnetic field and coronal emission. The upper left panel represents the spatial distribution of events, where the penumbra is divided into four 90 degrees sectors (north, east, south, and west). The upper and lower right panels show the HMI line-of-sight magnetogram (saturated between -200 and 200 gauss) and the corresponding coronal image in the AIA 171 Å filter (with the area denoted with a white square zoomed in the lower left corner of the image). Both display an extended field of view at the time the sunspot was crossing the central meridian. Finally, the lower left panel represents a histogram of the integrated azimuthal distribution of magnetic fluxes and wavelet power. The black and red lines show the magnetic flux around the target sunspot of the same and opposite polarity, respectively, and the blue line corresponds to the wavelet power of the studied sunspot.

Copyright: A. B. Griñón-Marín, A. Pastor Yabar, H. Socas-Navarro, & Rebecca Centeno 2020, Astronomy & Astrophysics, 635, A64 (doi: 10.1051/0004-6361/201936589)


A chromospheric resonance cavity in a sunspot mapped with seismology

Three-dimensional visualization of the geometric extent of the chromosphere above active region NoAA 12565. The geometric extent of the chromosphere, visualized here as the pink isocontours extending upwards from the photospheric (ROSA 4170 Å continuum) umbra and through the chromospheric (IBIS 8542 Å line core). It can be seen that the depth of the resonance cavity is suppressed in the immediate vicinity of the trans-umbral filamentary structure, providing geometric heights of approximately 1,300 km, which is consistent with the depth measured at the outermost edges of the umbra. The cores of the umbrae display the largest resonance cavity depths, often with geometric heights on the order of 2,300 km. An image of the Earth is added to provide a sense of scale. Note that the pink resonance cavity depth contours are not to scale. Credit: Earth image, NOAA.

Copyright: David B. Jess, Ben Snow, Scott J. Houston, Gert J. J. Botha, Bernhard Fleck, S. Krishna Prasad, Andrés Asensio Ramos, Richard J. Morton, Peter H. Keys, Shahin Jafarzadeh, Marco Stangalini, Samuel D. T. Grant & Damian J. Christian 2020, Nature Astronomy, 4, 220 (doi: 10.1038/s41550-019-0945-2)


The Magnetic Response of the Solar Atmosphere to Umbral Flashes

Top left: ROSA 4170 Å continuum image of active region NOAA 12565. Middle left: IBIS blue-wing snapshot acquired at 8540.82 Å (line core −1.3 Å). Bottom left: IBIS Ca II 8542 Å line-core image, where the green contour represents the location of the outer umbral boundary. In each panel, the solid red line represents the orientation and position of the FIRS spectral slit. Right panel: velocity–time image showing the spectral and temporal evolution of the He I 10830 Å Stokes I line profile, where the black-to-white color scale represents the inverse spectral intensities to aid visual clarity. The vertical dashed red line represents the rest position of the He I 10830 Å line core.

Copyright: S. J. Houston, D. B. Jess, A. Asensio Ramos, S. D. T. Grant, C. Beck, A. A. Norton, and S. Krishna Prasad 2018, The Astrophysical Journal, 860, 28 (doi: 10.3847/1538-4357/aab366)


Two-fluid simulations of waves in the solar chromosphere

Simulations of acoustic wave propagation in a homogeneous plasma. Numerically (red dashed line) and analytically (green solid line) calculated time evolution of the velocity of neutrals and charges as a function of time. Below the panels showing the velocity of neutrals, the difference (Δ) between the numerical solution and the analytical solution for unz is given. Time is measured in units of the wave period, 2π/ωR. Panels from left to right and from top to bottom: simulations for different values of the wavenumber k.

Copyright: B. Popescu Braileanu, V. S. Lukin, E. Khomenko and Á. de Vicente 2019, Astronomy & Astrophysics, 627, A25 (doi: 10.1051/0004-6361/201834154)


Spiral-shaped wavefronts in a sunspot umbra

Temporal evolution of the Doppler velocity, inferred from the GFPI Fe I 5435 Å restored images (from observations with GREGOR; a 1.5 m solar telescope), during the appearance of a two-armed spiral wavefront, filtered in frequency bands. From left to right columns: 2–8 mHz, 2–3.5 mHz, 3.5–4.7 mHz, 4.7–8 mHz. T The black lines mark the umbral and penumbral boundaries. The green circles highlight the location of the spiral wavefronts.

Copyright: Tobías Felipe, C. Kuckein, Elena Khomenko, and I. Thaler 2019, Astronomy & Astrophysics, 621, A43 (doi: 10.1051/0004-6361/201834367)


Second meeting of the WaLSA Team
Oslo, Norway; 12-16 August 2019


Semi-empirical model atmospheres for the chromosphere of the sunspot penumbra and umbral flashes

Columns showing the observed (black dots; from the Swedish 1- Solar Telescope, SST) and synthetic (red) full Stokes spectra in units of normalized HSRA (Gingerich et al. 1971) continuum intensity at disk center at a wavelength in the middle of the spectral range, and their atmospheric parameters such as temperature, LOS magnetic field, velocity, and microturbulent velocity for three different models: hot penumbra (asterisk), cool penumbra ('cross') and umbral flash ('plus sign'), respectively. The continuous line overplotted on the dashed line for the LOS magnetic field, shows the variation of the magnetic field in the region log(tau) = [-6,-2] where the Ca 8542 spectra is most sensitive.

Copyright: S. Bose, Vasco M.J. Henriques, L. Rouppe van der Voort, and T.M.D. Pereira 2019, Astronomy & Astrophysics, 627, A46 (doi: 10.1051/0004-6361/201935289)


Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI

Left: A dense forest of slender bright fibrils near a small solar active region seen in high-quality narrowband Ca ii H images from the SuFI instrument onboard the Sunrise balloon-borne solar observatory.
Right: Phase speeds in an example slender Ca ii H fibril (SCF) with an indication of wave propagation. The curves in panels (a)–(e) represent displacement of the SCF along a series of cuts across the fibril shown in the upper panel, from left to right, respectively. The red triple-dot–dashed lines are the centroids of a Gaussian fit to the oscillations smoothed by convolving with a boxcar filter of 0.05 arcsec width. The green lines indicate waves propagation in the SCF in a direction corresponding to from right to left in the top panel.

Copyright: Shahin Jafarzadeh, Sami K. Solanki, Ricardo Gafeira, Michiel van Noort, et al. 2017, The Astrophysical Journal Supplement Series, 229, 1, 9 (doi: 10.3847/1538-4365/229/1/9)


Observations of ubiquitous compressive waves in the Sun’s chromosphere

(a) Typical ROSA Hα example of a pair of relatively large dark flux tubes at t=1,536 s measured from the beginning of the data series. (b) Time-distance plot revealing the dynamic motion. The position of the cross-cut is shown in (a), with the given distance starting at the top of the cross-cut. Times are given in seconds from the start of the data set. The results from a Gaussian fitting are over-plotted and show the nonlinear fast MHD kink wave (red line shows the central axis of the structure) and the fast MHD sausage mode (yellow bars show the measured width of structure). The transverse motion has a period of 232±8 s and we detect multi-directional propagating transversal wave trains in the MFT travelling with speeds of 71±22 km/s upwards and 87±26 km/s downwards. The typical velocity amplitudes are 5 km/s. The fast MHD sausage mode has a period of 197±8 s, a phase speed of 67±15 km/s and apparent velocity amplitudes of 1–2 km/s. (c) Comparison of MFTs intensity (blue) and width (red) perturbations from the Gaussian fitting. The data points have been fitted with a smoothed 3-point box-car function. The observed out-of-phase behaviour is typical of fast MHD sausage waves. The error bars plotted are the one-sigma errors on each data point calculated from the Gaussian fitting.

Copyright: Richard J. Morton, Gary Verth, David B. Jess, David Kuridze, Michael S. Ruderman, Mihalis Mathioudakis, and Robertus Erdélyi 2012, Nature Communications, 3, 1315 (doi: 10.1038/ncomms2324)


Signatures of running penumbral waves in sunspot photospheres

Three-dimensional view of intensities and peak periods of intensity wave power of a sunspot at various wavelength positions. The intensities (left) show the sunspot at August 21st 2013 at 15:00:06 UTC (±3 s). The images along the z-axis belong to several line core and wing positions of Fe I 630.15 nm, Na I 589.6 nm, and Ca II 854.2 nm. The corresponding time-averaged (≈1h) distribution of peak periods TPEAK of the intensity wave power is shown on the right. The periods are scaled from 2.5 min (dark blue) to 8 min (dark red). The black contours indicate the location of the umbra (inner) and penumbra (outer) in continuum intensity (bottom panel). Whereas the length of the axis arrows represent distances around 1.5 Mm, the image positions along the z-axis are not to scale.

Copyright: J. Löhner-Böttcher and N. Bello González 2018, Astronomy & Astrophysics, 580, A53 (doi: 10.1051/0004-6361/201526230)


Photospheric observations of surface and body modes in solar magnetic pores

This stack image shows the basis of designation of a sausage surface mode in a pore. The bottom panel shows the LOS magnetogram from HMI indicating the magnetic field of the pore and the sharp boundary in terms of magnetic field at the pore's edge. Above this is the full FOV ROSA G-band image showing the photospheric appearance of the pore taken on 2011 December 10. The blue box indicates the expanded region shown in the top three panels. The expanded G-band image has blue contours indicating the pore boundary established for that particular frame. Above this is the time-averaged pore boundary map showing the variation in boundary location during this observation sequence, where the arrows indicate the sausage mode oscillations present. The top panel is a two-dimensional power plot of the power across the pore obtained with wavelet transforms of the data filtered at a frequency of ~4.6 mHz. The blue contour shows the time average pore boundary location. Peaks in power at this boundary indicate that a sausage mode is observed at this frequency.

Copyright: Keys, P. H., Morton, R. J., Jess, D. B., Verth, G., et al. 2018, The Astrophysical Journal, 857, 28 (doi: 10.3847/1538-4357/aab432)


Alfvén wave dissipation in the solar chromosphere

Co-spatial images revealing the structure of a sunspot observed at 13:00 UT on 24 August 2014. The lower image shows the magnitude of the photospheric magnetic field from HMI/SDO, revealing high umbral field strengths (colour bar relates to the field strengths in gauss). The image above is taken from the blue wing of the Ca II 8542 Å spectral line from DST, displaying the photospheric representation of the sunspot. Above this is the photospheric plasma temperature of the region derived from CAISAR at log(τ 500nm) ~ −2 (or ~ 250 km above the photosphere), showing the clear temperature distinction between the umbra, penumbra and surrounding quiet Sun (colour bar in units of kelvin). The upper image shows the chromospheric core of the Ca II 8542 Å spectral line from DST, highlighting the strong intensity gradient between the umbra and penumbra at these heights. In each of these images, the red contours represent the inner and outer boundaries of the plasma-β = 1 region at the height where shocks first begin to manifest (~ 250 km), where magneto-acoustic and Alfvén waves can readily convert.

Copyright: Grant, S. D. T., Jess, D. B., Zaqarashvili, T. V., et al. 2018, Nature Physics, 14, 480 (doi: 10.1038/s41567-018-0058-3)


Kickoff meeting of the WaLSA Team
Oslo, Norway; 7-11 January 2019