La Palma observations of umbral flashes

Voort, L. H. M. Rouppe van der; Rutten, R. J.; Sütterlin, P.; Sloover, P.J.; Krijger, J. M.

doi:10.1051/0004-6361:20030237

Cited by 112 publications

(18 citation statements)

References 57 publications

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“…The identification of umbral flashes was carried out by applying a running mean subtraction method, similar to that employed by Rouppe van der Voort et al (2003) and Madsen et al (2015), to the wavelength-integrated time series defined above. Using a running mean allows long-duration time series to be more accurately normalized through the removal of brightenings that exist for longer time intervals than the UFs.…”

Section: Flash Identificationmentioning

confidence: 99%

“…There are a few studies that have started to provide insight into chromospheric magnetic field perturbations, through the analysis of nonlinear shock fronts resulting from the steepening of magnetoacoustic waves in sunspot umbrae (Rouppe van der Voort et al 2003;Centeno et al 2006;de la Cruz Rodríguez et al 2013;Henriques et al 2017). These shock fronts, commonly known as "umbral flashes" (UFs; Beckers & Tallant 1969), are ideal candidates to study subsequent chromospheric magnetic field fluctuations, since they are energetic, highly nonlinear, and display well defined properties, allowing their effects on the localized umbral magnetic field to be investigated.…”

Section: Introductionmentioning

confidence: 99%

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The Magnetic Response of the Solar Atmosphere to Umbral Flashes

Houston

Jess

Ramos

et al. 2018

ApJ

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Chromospheric observations of sunspot umbrae offer an exceptional view of magneto-acoustic shock phenomena and the impact they have on the surrounding magnetically-dominated plasma. We employ simultaneous slit-based spectro-polarimetry and spectral imaging observations of the chromospheric He I 10830 Å and Ca II 8542 Å lines to examine fluctuations in the umbral magnetic field caused by the steepening of magneto-acoustic waves into umbral flashes. Following the application of modern inversion routines, we find evidence to support the scenario that umbral shock events cause expansion of the embedded magnetic field lines due to the increased adiabatic pressure. The large number statistics employed allow us to calculate the adiabatic index, γ = 1.12 ± 0.01, for chromospheric umbral locations. Examination of the vector magnetic field fluctuations perpendicular to the solar normal revealed changes up to ∼200 G at the locations of umbral flashes. Such transversal magnetic field fluctuations have not been described before. Through comparisons with non-linear force-free field extrapolations, we find that the perturbations of the transverse field components are orientated in the same direction as the quiescent field geometries. This implies that magnetic field enhancements produced by umbral flashes are directed along the motion path of the developing shock, hence producing relatively small changes, up to a maximum of ∼8 degrees, in the inclination and/or azimuthal directions of the magnetic field. Importantly, this work highlights that umbral flashes are able to modify the full vector magnetic field, with the detection of the weaker transverse magnetic field components made possible by high-resolution data combined with modern inversion routines.

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Section: Flash Identificationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Magnetic Response of the Solar Atmosphere to Umbral Flashes

Houston

Jess

Ramos

et al. 2018

ApJ

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“…In the chromosphere, strong three-minute oscillations dominate in the umbra; these oscillations at first were considered as standing acoustic waves (Lites, 1988;Georgakilas, Christopoulou, and Koutchmy, 2000). Later, these waves were shown to be moving upward (Rouppe van der Voort et al, 2003); also they were shown not to be a simple continuation of the running penumbral waves (RPW) in the horizontal direction (Kobanov, Kolobov, and Makarchik, 2006). New observations with ever-increasing spatial and temporal resolution capabilities reveal many new facts about the sunspot's fine structure (Jess et al, 2015;Khomenko and Collados, 2015;Yuan et al, 2014;Sych and Nakariakov, 2014;Sych, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…Naturally, the question was raised on the origin of RPWs: two concepts were proposed. The first one is that RPWs are real waves propagating horizontally across the penumbra (Alissandrakis, Georgakilas, and Dialetis, 1992;Tsiropoula, Alissandrakis, and Mein, 2000;Tziotziou et al, 2004Tziotziou et al, , 2006; and the second concept implies them to be an apparent effect-a result of waves rising to the surface along inclined magnetic tubes, thus appearing first at the inner penumbra and then farther from the sunspot centre (Rouppe van der Voort et al, 2003;Bogdan and Judge, 2006;Kobanov, Kolobov, and Makarchik, 2006;Bloomfield, Lagg, and Solanki, 2007;Kobanov, Kolobov, and Chupin, 2008;Cho et al, 2015). The same effect is also deemed to be responsible for umbral flashes; and indeed, recently, researchers tend to consider umbral flashes and RPWs as manifestations of one phenomenon (Madsen, Tian, and DeLuca, 2015).…”

Section: Introductionmentioning

confidence: 99%

Peculiarity of the Oscillation Stratification in Sunspot Penumbrae

2016

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Spatial distributions of the dominant oscillation frequency obtained for four sunspots show a feature shared by all the analysed levels of the solar atmosphere in these sunspots. This feature located in the inner penumbrae indicates that this region has favourable conditions for 2.5-4 mHz oscillation propagation. This agrees with the fact that the spectral composition of the oscillations at three atmospheric heights (Fe i 6173 Å, 1700 Å, and He ii 304 Å) in this region are similar. There have been previous evidence of particular similarities along height of photospheric magnetic field strength, line-of-sight velocity, and temperature profile in the inner penumbra, where the internal boundary of the Evershed flow is located. The finding of the same dominant oscillation frequency at a range of altitudes from the chromosphere up to the transition region extends the height range, suggesting similarities in physical conditions.

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“…This was first motivated by Alissandrakis et al (1992) and Tsiropoula et al (1996Tsiropoula et al ( , 2000 who suggested that umbral oscillations trigger RWs which then propagate across the sunspot into the penumbra. The other theory suggests that the apparent radial propagation of RWs is a signature of upward-propagating magnetoacoustic modes traveling along inclined field lines (Christopoulou et al , 2001Rouppe van der Voort et al 2003;Bloomfield et al 2007;Jess et al 2013). Work over the past decade has focused on multi-altitude observations of RWs and UFs.…”

Section: Introductionmentioning

confidence: 99%

Observations of Umbral Flashes and Running Sunspot Waves With the Interface Region Imaging Spectrograph

Madsen

Tian

DeLuca

2015

ApJ

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We present simultaneous, high-resolution, multi-temperature observations of running waves and umbral flashes in a sunspot with the Interface Region Imaging Spectrograph. We analyze intensity variations in slit-jaw images to investigate the relationship between running waves in the 1400 Å (Si iv/transition region) passband and umbral flashes in the 2796 Å (Mg ii/chromosphere) passband. Using global wavelet analysis, we find that the dominant wave periods increase from approximately 150 s near the sunspot center to about 300 s in the penumbra in both passbands. This coincides extremely well with the radially increasing inclination of magnetic field lines observed with Solar Dynamics Observatory/Helioseismic and Magnetic Imager, suggesting that the waves are propagating vertically along the inclined field lines. Furthermore, apparent horizontal velocities for running waves decrease from about 12 km s −1 in the umbra to about 4 km s −1 in the penumbra which is predicted by the same inclined field geometry. Finally, we find that umbral flashes lead running waves in both the spatial and temporal domains. The former result is attributable to the inclined field geometry; however, the geometry does not predict the radially increasing time lag which is likely due to the opacity difference between the emission lines that dominate the two passbands. These results suggest that running waves and umbral flashes both originate from photospheric p-mode oscillations and are manifestations of upward-propagating slow magnetoacoustic modes at different altitudes and temperatures. The apparent trans-sunspot propagation of running waves is not real but rather an image of these upward-propagating modes traveling along field lines of radially increasing inclination.

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La Palma observations of umbral flashes

Cited by 112 publications

References 57 publications

The Magnetic Response of the Solar Atmosphere to Umbral Flashes

The Magnetic Response of the Solar Atmosphere to Umbral Flashes

Peculiarity of the Oscillation Stratification in Sunspot Penumbrae

Observations of Umbral Flashes and Running Sunspot Waves With the Interface Region Imaging Spectrograph

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