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Bernasconi, P. N.; Rust, David M.; Georgoulis, Manolis K.; Labonte, B. J.

doi:10.1023/a:1020943816174

Cited by 77 publications

(73 citation statements)

References 22 publications

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“…Then, the dispersed flux elements partially evacuate and merge (Kitiashvili et al 2010) to form pores and sunspots. The coalescence of the emerged flux elements in the simulations agrees with observations of Bernasconi et al (2002) and Schlichenmaier et al (2010a), for example. The tetheredballoon model of Spruit (1981) predicts that the coalescence of small flux patches (Pariat et al 2004;Rezaei et al 2012a) is a surface phenomenon since these flux elements are deeply anchored.…”

Section: Introductionsupporting

confidence: 84%

Properties of sunspot umbrae observed in cycle 24

Kiess

Rezaei

Schmidt

2014

A&A

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Aims. There is an ongoing debate whether the solar activity cycle is overlaid with a long-term decline that may lead to another grand minimum in the near future. We used the size, intensity, and magnetic field strength of sunspot umbrae to compare the present cycle 24 with the previous one. Methods. We used data of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory and selected all sunspots between May 2010 and October 2012, using one image per day. We created two subsets of this dataset with a manual tracking algorithm, both without duplication. One contains each sunspot (910 umbrae within 488 spots) and was used to analyze the distribution of umbral areas, selected with an automated thresholding method. The other subset contains 205 fully evolved sunspots. We estimated their magnetic field and the total magnetic flux and discuss the relations between umbral size, minimum continuum intensity, maximum field strength, and total magnetic flux. Results. We find non-linear relations between umbral minimum intensity and size and between maximum magnetic field strength and size. The field strength scales linearly with the intensity and the umbral size scales roughly linearly with the total magnetic flux, while the size and field strength level off with stronger flux. When separated into hemispheres and averaged temporally, the southern umbrae show a temporal increase in size and the northern umbrae remain constant. We detected no temporal variation in the umbral mean intensity. The probability density function of the umbral area in the ascending phase of the current solar cycle is similar to that of the last solar cycle. Conclusions. From our investigation of umbral area, magnetic field, magnetic flux, and umbral intensity of the sunspots of the rising phase of cycle 24, we do not find a significant difference to the previous cycle, and hence no indication for a long-term decline of solar activity.

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Section: Introductionsupporting

confidence: 84%

Properties of sunspot umbrae observed in cycle 24

Kiess

Rezaei

Schmidt

2014

A&A

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“…In emergence sites a wave-like structure has been observed, indicating that flux tubes emerge at several places, in a sea-serpent fashion, creating a mixed-polarity field where a substantial amount of flux may be cancelled (Bernasconi et al 2002). A similar feature has been recently observed in sunspot penumbrae by Sainz-Dalda and Bellot-Rubio (2008).…”

Section: Sunspots and Ephemeral Regionssupporting

confidence: 62%

“…A solar influence on the Earth upper atmosphere was suggested by Lord Carrington in the nineteen century, but for clear evidence of a continuous outflow of fast particles from the Sun, we must go to the fifties of last centuries, when Biermann, studying the shape of the cometary ion tails, deduced a particle flow from the Sun, with an average speed of around 475 km/sec (Biermann 1951(Biermann , 1953.…”

Section: Historical Backgroundmentioning

confidence: 99%

Solar Weather Event Modelling and Prediction

et al. 2009

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Key drivers of solar weather and mid-term solar weather are reviewed by considering a selection of relevant physics-and statistics-based scientific models as well as a selection of related prediction models, in order to provide an updated operational scenario for space weather applications. The characteristics and outcomes of the considered scientific and prediction models indicate that they only partially cope with the complex nature of solar activity for the lack of a detailed knowledge of the underlying physics. This is indicated by the fact that, on one hand, scientific models based on chaos theory and non-linear dynamics reproduce better the observed features, and, on the other hand, that prediction models based on statistics and artificial neural networks perform better. To date, the solar weather prediction success at most time and spatial scales is far from being satisfactory, but the forthcoming ground-and space-based high-resolution observations can add fundamental tiles to the modelling and predicting frameworks as well as the application of advanced mathematical approaches in the analysis of diachronic solar observations, that are a must to provide comprehensive and homogeneous data sets.

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“…Paper I showed that at high resolution upright flame morphology in limbward viewing is a distinctive EB characteristic. It was used in Paper II to establish EB brightness criteria, but these may fail close to disk center (Paper III) where differentiation with the MCs that produce EBs (as in the serpentine U-loop pull-up scenario of EB formation of e.g., Bernasconi et al 2002;Pariat et al 2004;Isobe et al 2007;Archontis & Hood 2009;Pariat et al 2009) is less easy, as already pointed out by Ellerman (1917) and later by Bruzek & Durrant (1977).…”

Section: Terminologymentioning

confidence: 99%

Hαfeatures with hot onsets

Rutten

2016

A&A

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Ellerman bombs are transient brightenings of the wings of the Balmer lines that uniquely mark reconnection in the solar photosphere.They are also bright in strong Ca ii and ultraviolet lines and in ultraviolet continua, but they are not visible in the optical continuum and the Na i D and Mg i b lines. These discordant visibilities invalidate all published Ellerman bomb modeling. I argue that the assumption of Saha-Boltzmann lower-level populations is informative to estimate bomb-onset opacities for these diverse diagnostics, even and especially for Hα, and employ such estimates to gauge the visibilities of Ellerman bomb onsets in all of them. They constrain Ellerman bomb formation to temperatures 10 000−20 000 K and hydrogen densities around 10 15 cm −3 . Similar arguments likely hold for Hα visibility in other transient phenomena with hot and dense onsets.

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Cited by 77 publications

References 22 publications

Properties of sunspot umbrae observed in cycle 24

Properties of sunspot umbrae observed in cycle 24

Solar Weather Event Modelling and Prediction

Hαfeatures with hot onsets

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