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Book ; Online: Similarities of magnetoconvection in the umbra and in the penumbra of sunspots

Löptien, B. / Lagg, A. / van Noort, M. / Solanki, S. K.

2021

Abstract: Context. It is unclear why there is a rather sharp boundary in sunspots between the umbra and the penumbra. Both regions exhibit magnetoconvection, manifesting in penumbral filaments in the penumbra and in umbral dots in the umbra. Aims. Here we compare ... ...

Abstract	Context. It is unclear why there is a rather sharp boundary in sunspots between the umbra and the penumbra. Both regions exhibit magnetoconvection, manifesting in penumbral filaments in the penumbra and in umbral dots in the umbra. Aims. Here we compare the physical properties of umbral dots and penumbral filaments. Our goal is to understand how the properties of these convective features change across the boundary between the umbra and the penumbra and how this is related to the rapid increase in brightness at the umbra-penumbra boundary. Methods. We derived ensemble averages of the physical properties of different types of convective features based on observations of two sunspots with Hinode. Results. There are strong similarities between the convective features in the outer parts of the umbra and the ones in the penumbra, with most physical parameters being smooth and continuous functions of the length of the features. Conclusions. Our results indicate that the transition in brightness from the umbra to the penumbra is solely caused by an increased effectiveness of magnetoconvection within individual convective cells. There is no significant difference in the number density of convective elements between the outer umbra and the inner penumbra. Penumbral filaments exhibit a larger area and a higher brightness compared to umbral dots. It is still unclear, how exactly the underlying magnetic field causes the increase in size and brightness of convective features in the penumbra. Comment: 8 pages, 5 figures. Accepted for publication in Astronomy & Astrophysics
Keywords	Astrophysics - Solar and Stellar Astrophysics
Subject code	612
Publishing date	2021-10-04
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book: Phase B/B+ für das Ballonteleskop SUNRISE

Solanki, S. K

Schlussbericht ; Laufzeit: 1. Juli 2002 bis 15. Dezember 2003

2004

Title variant	Final Report of the SUNRISE Telescope Phase B Study
Institution	Max-Planck-Institut für Aeronomie
Author's details	Max-Planck-Institut für Aeronomie. Projektleiter: S. K. Solanki
Language	German
Size	[7] Bl
Publishing place	Katlenburg-Lindau
Document type	Book
Note	Förderkennzeichen BMBF 50OU0201. - Engl. Zsfassung u.d.T.: Final Report of the SUNRISE Telescope Phase B Study
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Article ; Online: Ultra-high-resolution observations of persistent null-point reconnection in the solar corona.

Cheng, X / Priest, E R / Li, H T / Chen, J / Aulanier, G / Chitta, L P / Wang, Y L / Peter, H / Zhu, X S / Xing, C / Ding, M D / Solanki, S K / Berghmans, D / Teriaca, L / Aznar Cuadrado, R / Zhukov, A N / Guo, Y / Long, D / Harra, L /

Smith, P J / Rodriguez, L / Verbeeck, C / Barczynski, K / Parenti, S

Nature communications

2023 Volume 14, Issue 1, Page(s) 2107

Abstract: Magnetic reconnection is a key mechanism involved in solar eruptions and is also a prime possibility to heat the low corona to millions of degrees. Here, we present ultra-high-resolution extreme ultraviolet observations of persistent null-point ... ...

Abstract	Magnetic reconnection is a key mechanism involved in solar eruptions and is also a prime possibility to heat the low corona to millions of degrees. Here, we present ultra-high-resolution extreme ultraviolet observations of persistent null-point reconnection in the corona at a scale of about 390 km over one hour observations of the Extreme-Ultraviolet Imager on board Solar Orbiter spacecraft. The observations show formation of a null-point configuration above a minor positive polarity embedded within a region of dominant negative polarity near a sunspot. The gentle phase of the persistent null-point reconnection is evidenced by sustained point-like high-temperature plasma (about 10 MK) near the null-point and constant outflow blobs not only along the outer spine but also along the fan surface. The blobs appear at a higher frequency than previously observed with an average velocity of about 80 km s
Language	English
Publishing date	2023-04-13
Publishing country	England
Document type	Journal Article
ZDB-ID	2553671-0
ISSN	2041-1723 ; 2041-1723
ISSN (online)	2041-1723
ISSN	2041-1723
DOI	10.1038/s41467-023-37888-w
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Author Correction: Ultra-high-resolution observations of persistent null-point reconnection in the solar corona.

Smith, P J / Rodriguez, L / Verbeeck, C / Barczynski, K / Parenti, S

Nature communications

2023 Volume 14, Issue 1, Page(s) 2372

Language	English
Publishing date	2023-04-25
Publishing country	England
Document type	Published Erratum
ZDB-ID	2553671-0
ISSN	2041-1723 ; 2041-1723
ISSN (online)	2041-1723
ISSN	2041-1723
DOI	10.1038/s41467-023-38149-6
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Book ; Online: Solar cyclic activity over the last millennium reconstructed from annual 14C data

Usoskin, I. G. / Solanki, S. K. / Krivova, N. / Hofer, B. / Kovaltsov, G. A. / Wacker, L. / Brehm, N. / Kromer, B.

2021

Abstract: The 11-year solar cycle is the dominant pattern of solar activity reflecting the oscillatory dynamo mechanism in the Sun. Solar cycles were directly observed since 1700, while indirect proxies suggest their existence over a much longer period of time but ...

Abstract	The 11-year solar cycle is the dominant pattern of solar activity reflecting the oscillatory dynamo mechanism in the Sun. Solar cycles were directly observed since 1700, while indirect proxies suggest their existence over a much longer period of time but generally without resolving individual cycles and their continuity. Here we reconstruct individual cycles for the last millennium using recent 14C data and state-of-the-art models. Starting with the 14C production rate determined from the so far most precise measurements of radiocarbon content in tree rings, solar activity is reconstructed in three physics-based steps: (1) Correction of the 14C production rate for the changing geomagnetic field; (2) Computation of the open solar magnetic flux; and (3) Conversion into sunspot numbers outside of grand minima. Solar activity is reconstructed for the period 971-1900 (85 individual cycles). This more than doubles the number of solar cycles known from direct solar observations. We found that lengths and strengths of well-defined cycles outside grand minima are consistent with those obtained from the direct sunspot observations after 1750. The validity of the Waldmeier rule is confirmed at a highly significant level. Solar activity is found to be in a deep grand minimum when the activity is mostly below the sunspot formation threshold, during about 250 years. Therefore, although considerable cyclic variability in 14C is seen even during grand minima, individual solar cycles can hardly be reliably resolved therein. Three potential solar particle events, ca. 994, 1052 and 1279 AD, are shown. A new about 1000-year long solar activity reconstruction, in the form of annual (pseudo) sunspot numbers with full assessment of uncertainties, is presented based on new high-precision 14C measurements and state-of-the-art models, more than doubling the number of individually resolved solar cycles. Comment: Accepted for publication in Astronomy and Astrophysics
Keywords	Astrophysics - Solar and Stellar Astrophysics
Subject code	621
Publishing date	2021-03-28
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Convective motions and net circular polarization in sunspot penumbrae

Borrero, J. M. / Solanki, S. K.

2009

Abstract: We have employed a penumbral model, that includes the Evershed flow and convective motions inside penumbral filaments, to reproduce the azimuthal variation of the net circular polarization (NCP) in sunspot penumbrae at different heliocentric angles for ... ...

Abstract	We have employed a penumbral model, that includes the Evershed flow and convective motions inside penumbral filaments, to reproduce the azimuthal variation of the net circular polarization (NCP) in sunspot penumbrae at different heliocentric angles for two different spectral lines. The theoretical net circular polarization fits the observations as satisfactorily as penumbral models based on flux-tubes. The reason for this is that the effect of convective motions on the NCP is very small compared to the effect of the Evershed flow. In addition, the NCP generated by convective upflows cancels out the NCP generated by the downflows. We have also found that, in order to fit the observed NCP, the strength of the magnetic field inside penumbral filaments must be very close to 1000 G. In particular, field-free or weak-field filaments fail to reproduce both the correct sign of the net circular polarization, as well as its dependence on the azimuthal and heliocentric angles. Comment: Accepted for publication in the Astrophysical Journal. 10 pages, 7 figures (3 in color). Uses emulatedapj
Keywords	Astrophysics - Solar and Stellar Astrophysics
Subject code	612
Publishing date	2009-11-13
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: The Laschamp geomagnetic excursion featured in nitrate record from EPICA-Dome C ice core.

Traversi, R / Becagli, S / Poluianov, S / Severi, M / Solanki, S K / Usoskin, I G / Udisti, R

Scientific reports

2016 Volume 6, Page(s) 20235

Abstract: Here we present the first direct comparison of cosmogenic (10)Be and chemical species in the period of 38-45.5 kyr BP spanning the Laschamp geomagnetic excursion from the EPICA-Dome C ice core. A principal component analysis (PCA) allowed to group ... ...

Abstract	Here we present the first direct comparison of cosmogenic (10)Be and chemical species in the period of 38-45.5 kyr BP spanning the Laschamp geomagnetic excursion from the EPICA-Dome C ice core. A principal component analysis (PCA) allowed to group different components as a function of the main sources, transport and deposition processes affecting the atmospheric aerosol at Dome C. Moreover, a wavelet analysis highlighted the high coherence and in-phase relationship between (10)Be and nitrate at this time. The evident preferential association of (10)Be with nitrate rather than with other chemical species was ascribed to the presence of a distinct source, here labelled as "cosmogenic". Both the PCA and wavelet analyses ruled out a significant role of calcium in driving the (10)Be and nitrate relationship, which is particularly relevant for a plateau site such as Dome C, especially in the glacial period during which the Laschamp excursion took place. The evidence that the nitrate record from the EDC ice core is able to capture the Laschamp event hints toward the possibility of using this marker for studying galactic cosmic ray flux variations and thus also major geomagnetic field excursions at pluri-centennial-millennial time scales, thus opening up new perspectives in paleoclimatic studies.
Language	English
Publishing date	2016-01-28
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/srep20235
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Book ; Online: EUV jets, type III radio bursts and sunspot waves investigated using SDO/AIA observations

Innes, D. E. / Cameron, R. H. / Solanki, S. K.

2011

Abstract: Images from the Solar Dynamics Observatory (SDO) at 211A are used to identify the solar source of the type III radio bursts seen in WIND/WAVES dynamic spectra. We analyse a 2.5 hour period during which six strong bursts are seen. The radio bursts ... ...

Abstract	Images from the Solar Dynamics Observatory (SDO) at 211A are used to identify the solar source of the type III radio bursts seen in WIND/WAVES dynamic spectra. We analyse a 2.5 hour period during which six strong bursts are seen. The radio bursts correlate very well with the EUV jets coming from the western side of a sunspot in AR11092. The EUV jet emission also correlates well with brightening at what looks like their footpoint at the edge of the umbra. For 10-15 min after strong EUV jets are ejected, the footpoint brightens at roughly 3 min intervals. In both the EUV images and the extracted light curves, it looks as though the brightening is related to the 3-min sunspot oscillations, although the correlation coefficient is rather low. The only open field near the jets is rooted in the sunspot. We conclude that active region EUV/X-ray jets and interplanetary electron streams originate on the edge of the sunspot umbra. They form along a current sheet between the sunspot open field and closed field connecting to underlying satellite flux. Sunspot running penumbral waves cause roughly 3-min jet footpoint brightening. The relationship between the waves and jets is less clear. Comment: 4 pages, 7 figures, Accepted by A&A Letters. For associated gif movie, see http://www.mps.mpg.de/data/outgoing/innes/jets/losb_304_211_rd.gif
Keywords	Astrophysics - Solar and Stellar Astrophysics
Subject code	520 ; 551
Publishing date	2011-06-17
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: First Perihelion of EUI on the Solar Orbiter mission

Berghmans, D. / Antolin, P. / Auchère, F. / Cuadrado, R. Aznar / Barczynski, K. / Chitta, L. P. / Gissot, S. / Harra, L. / Huang, Z. / Janvier, M. / Kraaikamp, E. / Long, D. M. / Mandal, S. / Mierla, M. / Parenti, S. / Peter, H. / Rodriguez, L. / Schühle, U. / Smith, P. J. /

Solanki, S. K. / Stegen, K. / Teriaca, L. / Verbeeck, C. / West, M. J. / Zhukov, A. N. / Appourchaux, T. / Aulanier, G. / Buchlin, E. / Delmotte, F. / Gilles, J. M. / Haberreiter, M. / Halain, J. -P. / Heerlein, K. / Hochedez, J. -F. / Gyo, M. / Poedts, S. / Rochus, P.

2023

Abstract: Context. The Extreme Ultraviolet Imager (EUI), onboard Solar Orbiter consists of three telescopes: the two High Resolution Imagers in EUV (HRIEUV) and in Lyman-{\alpha} (HRILya), and the Full Sun Imager (FSI). Solar Orbiter/EUI started its Nominal ... ...

Abstract	Context. The Extreme Ultraviolet Imager (EUI), onboard Solar Orbiter consists of three telescopes: the two High Resolution Imagers in EUV (HRIEUV) and in Lyman-{\alpha} (HRILya), and the Full Sun Imager (FSI). Solar Orbiter/EUI started its Nominal Mission Phase on 2021 November 27. Aims. EUI images from the largest scales in the extended corona off limb, down to the smallest features at the base of the corona and chromosphere. EUI is therefore a key instrument for the connection science that is at the heart of the Solar Orbiter mission science goals. Methods. The highest resolution on the Sun is achieved when Solar Orbiter passes through the perihelion part of its orbit. On 2022 March 26, Solar Orbiter reached for the first time a distance to the Sun close to 0.3 au. No other coronal EUV imager has been this close to the Sun. Results. We review the EUI data sets obtained during the period 2022 March-April, when Solar Orbiter quickly moved from alignment with the Earth (2022 March 6), to perihelion (2022 March 26), to quadrature with the Earth (2022 March 29). We highlight the first observational results in these unique data sets and we report on the in-flight instrument performance. Conclusions. EUI has obtained the highest resolution images ever of the solar corona in the quiet Sun and polar coronal holes. Several active regions were imaged at unprecedented cadences and sequence durations. We identify in this paper a broad range of features that require deeper studies. Both FSI and HRIEUV operate at design specifications but HRILya suffered from performance issues near perihelion. We conclude emphasising the EUI open data policy and encouraging further detailed analysis of the events highlighted in this paper.
Keywords	Astrophysics - Solar and Stellar Astrophysics ; Physics - Space Physics
Subject code	621
Publishing date	2023-01-13
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Reconstructed and measured total solar irradiance

Wenzler, T. / Solanki, S. K. / Krivova, N. A.

Is there a secular trend between 1978 and 2003?

2009

Abstract: Total solar irradiance reconstructed between 1978 and 2003 using solar surface magnetic field distributions is compared with three composites of total solar irradiance measurements. A good correspondence is found with the total solar irradiance composite ...

Abstract	Total solar irradiance reconstructed between 1978 and 2003 using solar surface magnetic field distributions is compared with three composites of total solar irradiance measurements. A good correspondence is found with the total solar irradiance composite from PMOD/WRC, with no bias between the three cycles. The agreement with the other composites (the ACRIM composite, mainly based on the Active Cavity Radiometer Irradiance Monitors I, II & III, and the IRMB composite from the Institut Royal Meteorologique Belgique) is significantly poorer. In particular, a secular increase in the irradiance exhibited by these composites is not present in the reconstructions. Hence any secular trend in total solar irradiance between 1978 and 2003 is not due to magnetic fields at the solar surface.
Keywords	Astrophysics - Solar and Stellar Astrophysics ; Astrophysics - Instrumentation and Methods for Astrophysics
Subject code	621
Publishing date	2009-09-16
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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