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Blobs in recurring extreme-ultraviolet jets
摘要： Context. Coronal jets are one type of ubiquitous small-scale activity that is caused by magnetic reconnection in the solar corona. They are often associated with cool surges in the chromosphere. Aims. In this paper, we report our discovery of blobs in the recurrent and homologous jets that occurred at the western edge of the NOAA active region 11259 on 2011 July 22. Methods. The jets were observed in the seven extreme-ultraviolet (EUV) ?lters of the Atmospheric Imaging Assembly instrument aboard the Solar Dynamics Observatory. Using the base-di?erence images of the six ?lters (94, 131, 171, 211, 193, and 335 ?), we carried out the di?erential emission measure (DEM) analyses to explore the thermodynamic evolutions of the jets. The jets were accompanied by cool surges observed in the Hα line center of the ground-based telescope in the Big Bear Solar Observatory. Results. The jets that had lifetimes of 20?30 min recurred at the same place for three times with an interval of 40?45 min. Interestingly, each of the jets intermittently experienced several upward eruptions at the speed of 120?450 km s?1. After reaching the maximum heights, they returned back to the solar surface, showing near-parabolic trajectories. The falling phases were more evident in the low-T ?lters than in the high-T ?lters, indicating that the jets experienced cooling after the onset of eruptions. We identi?ed bright and compact blobs in the jets during their rising phases. The simultaneous presence of blobs in all the EUV ?lters were consistent with the broad ranges of the DEM pro?les of the blobs (5.5 ≤ log T ≤ 7.5), indicating their multi-thermal nature. The median temperatures of the blobs were ～2.3 MK. The blobs that were ～3 Mm in diameter had lifetimes of 24?60 s. Conclusions. To our knowledge, this is the ?rst report of blobs in coronal jets. We propose that these blobs are plasmoids created by the magnetic reconnection as a result of tearing-mode instability and are ejected out along the jets.
关键词： Sun: chromosphere,Sun: corona,Sun: activity
更新于2025-09-23 15:23:52
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CONFINED FLARES IN SOLAR ACTIVE REGION 12192 FROM 2014 OCTOBER 18 TO 29
摘要： Using the observations from the Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory, we investigate 6 X-class and 29 M-class ?ares occurring in solar active region (AR) 12192 from October 18 to 29. Among them, 30 (including 6 X- and 24 M-class) ?ares originated from the AR core, and the other 5 M-?ares appeared at the AR periphery. Four of the X-?ares exhibited similar ?aring structures, indicating they were homologous ?ares with an analogous triggering mechanism. The possible scenario is that photospheric motions of emerged magnetic ?uxes lead to shearing of the associated coronal magnetic ?eld, which then yields a tether-cutting favorable con?guration. Among the ?ve periphery M-?ares, four were associated with jet activities. The HMI vertical magnetic ?eld data show that the photospheric ?uxes of opposite magnetic polarities emerged, converged, and canceled with each other at the footpoints of the jets before the ?ares. Only one M-?are from the AR periphery was followed by a coronal mass ejection (CME). From October 20 to 26, the mean decay index of the horizontal background ?eld within the height range of 40–105 Mm is below the typical threshold for torus instability onset. This suggests that a strong con?nement from the overlying magnetic ?eld might be responsible for the poor CME production of AR 12192.
关键词： Sun: coronal mass ejections (CMEs),Sun: ?ares,Sun: activity,Sun: UV radiation
更新于2025-09-23 15:22:29
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Solar total and spectral irradiance reconstruction over the last 9000 years
摘要： Context. Changes in solar irradiance and in its spectral distribution are among the main natural drivers of the climate on Earth. However, irradiance measurements are only available for less than four decades, while assessment of solar influence on Earth requires much longer records. Aims. The aim of this work is to provide the most up-to-date physics-based reconstruction of the solar total and spectral irradiance (TSI/SSI) over the last nine millennia. Methods. The concentrations of the cosmogenic isotopes 14C and 10Be in natural archives have been converted to decadally averaged sunspot numbers through a chain of physics-based models. TSI and SSI are reconstructed with an updated SATIRE model. Reconstructions are carried out for each isotope record separately, as well as for their composite. Results. We present the first ever SSI reconstruction over the last 9000 years from the individual 14C and 10Be records as well as from their newest composite. The reconstruction employs physics-based models to describe the involved processes at each step of the procedure. Conclusions. Irradiance reconstructions based on two different cosmogenic isotope records, those of 14C and 10Be, agree well with each other in their long-term trends despite their different geochemical paths in the atmosphere of Earth. Over the last 9000 years, the reconstructed secular variability in TSI is of the order of 0.11%, or 1.5 W m?2. After the Maunder minimum, the reconstruction from the cosmogenic isotopes is consistent with that from the direct sunspot number observation. Furthermore, over the nineteenth century, the agreement of irradiance reconstructions using isotope records with the reconstruction from the sunspot number by Chatzistergos et al. (2017, A&A, 602, A69) is better than that with the reconstruction from the WDC-SILSO series (Clette et al. 2014, Space Sci. Rev., 186, 35), with a lower χ2-value.
关键词： solar-terrestrial relations,Sun: faculae, plages,Sun: activity,Sun: magnetic fields
更新于2025-09-23 15:22:29
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Solar Irradiance Variability, Influenced by r Modes
摘要： A spectrum of the four-decade solar irradiance record has a prominent cluster of power for periodicities near 1 yr. Correlating irradiance with a bandpass filter showed that periodicity values were not constant, but varied sinusoidally with each cycle lasting 14 ± 1 yr. The large modulation amplitude makes solar frequencies ≈1 yr?1 hard to detect at the solar surface. After removing the modulation, a Lomb–Scargle spectrum exposed two true periodicities: 1.006 and 0.920 yr. They are interpreted as the synodic rotation periods of r modes of lowest angular degree (? = 1). The first propagates in the stable interior and the second in the convective envelope perturbed by its several flow fields. The rotational beat period of the two modes is about 10.9 yr. This is close to the average length of a solar cycle and possibly controls this average. The 1.006 yr periodicity dominates most of the filtered irradiance record but an abrupt change to about 0.8 yr occurs in mid-2010. Also found was evidence for higher-degree r modes (? = 2 to 8) and a curious sawtooth modulation with a recurrence period of 2.6 yr.
关键词： Sun: interior,Sun: activity,Sun: oscillations
更新于2025-09-23 15:22:29
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Analysis of full disc Ca II K spectroheliograms
摘要： Context. Historical Ca II K spectroheliograms (SHG) are unique in representing long-term variations of the solar chromospheric magnetic field. They usually suffer from numerous problems and lack photometric calibration. Thus accurate processing of these data is required to get meaningful results from their analysis. Aims. In this paper we aim at developing an automatic processing and photometric calibration method that provides precise and consistent results when applied to historical SHG. Methods. The proposed method is based on the assumption that the centre-to-limb variation of the intensity in quiet Sun regions does not vary with time. We tested the accuracy of the proposed method on various sets of synthetic images that mimic problems encountered in historical observations. We also tested our approach on a large sample of images randomly extracted from seven different SHG archives. Results. The tests carried out on the synthetic data show that the maximum relative errors of the method are generally <6.5%, while the average error is <1%, even if rather poor quality observations are considered. In the absence of strong artefacts the method returns images that differ from the ideal ones by <2% in any pixel. The method gives consistent values for both plage and network areas. We also show that our method returns consistent results for images from different SHG archives. Conclusions. Our tests show that the proposed method is more accurate than other methods presented in the literature. Our method can also be applied to process images from photographic archives of solar observations at other wavelengths than Ca II K.
关键词： Sun: activity,Sun: chromosphere,Sun: faculae, plages,techniques: image processing
更新于2025-09-23 15:21:01
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Using the Sun to estimate Earth-like planet detection capabilities
摘要： Context. Stellar variability, at a variety of timescales, can strongly affect the ability to detect exoplanets, in particular when using radial velocity (RV) techniques. Accurately characterized solar variations are precious in this context to study the impact of stellar variations on planet detectability. Here we focus on the impact of small timescale variability. Aims. The objective of this paper is to model realistic RV time series due to granulation and supergranulation and to study in greater detail the impact of granulation and supergranulation on RV times series in the solar case. Methods. We have simulated a collection of granules and supergranules evolving in time to reproduce solar photometric and RV time series. Synthetic time series are built over the full hemisphere over one solar cycle. Results. We obtain intensity and RV rms due to solar granulation of respectively 0.8 m/s and 67 ppm, with a strong variability at timescales up to more than 1 h. The rms RV due to supergranulation is between 0.28 and 1.12 m/s. Conclusions. To minimize the effect of granulation, the best strategy is to split the observing time during the night into several periods instead of observing over a consecutive duration. However, the best strategy depends on the precise nature of the signal. The granulation RV remains large after even an hour of smoothing (about 0.4 m/s) while the supergranulation signal cannot be significantly reduced on such timescales: a reduction of a factor 2 in rms RV can for example be obtained over 7 nights (with 26 min/night). The activity RV variability dominates at larger timescales. Detection limits can easily be as high as 1 MEarth or above for periods of tens or hundreds of days. The impact on detection limits is therefore important and may prevent the detection of 1 MEarth planets for long orbital periods, while the impact is much smaller at small orbital periods. These results do not take the presence of pulsations into account.
关键词： Sun: granulation,Sun: activity,stars: solar-type,planetary systems,techniques: radial velocities,stars: activity
更新于2025-09-23 15:19:57
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Solar jet-like features rooted in flare ribbons
摘要： Employing the high spatio-temporal Interface Region Imaging Spectrograph 1330 ?A observations, we investigated the jet-like features that occurred during the X8.2 class ?are in NOAA active region (AR) 12673 on 2017 September 10. These jet-like features were rooted in the ?are ribbons. We examined 15 features, and the mean values of the lifetimes, projected widths, lengths, and velocities of these features were 87 s, 890 km, 2.7 Mm, and 70 km s?1, respectively. We also observed many jet-like features which happened during the X1.0 class ?are on 2014 October 25. We studied the spectra at the base of a jet-like feature during its development. The Fe XXI 1354.08 ?A line in the corona displays blueshift, while the Si IV 1402.77 ?A line in the transition region exhibits redshift, which indicates the chromospheric evaporation. This is the ?rst time that the jet-like features are reported to be rooted in the ?are ribbons, and we suggest that these jet-like features were driven by the mechanism of chromospheric evaporation.
关键词： Sun: atmosphere,Sun: ?ares,Sun: evolution,Sun: activity
更新于2025-09-19 17:15:36
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Flux rope proxies during 2013 detected by the Solar Dynamics Observatory
摘要： Context. The relationship between ?ux ropes and coronal mass ejections (CMEs) is of great importance for understanding the CME initiation, but we do not know how many ?ux ropes in the atmosphere can be detected. Aims. We aim to determine the number of ?ux rope proxies and understand the distribution of the proxies over the visible solar disk. Methods. By employing the observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory, we counted the number of the ?ux rope proxies from 2013 January to 2013 December. Results. We detected 1354 (3.7 every day) rope proxies during this period and classi?ed them into three types according to their temperature properties and particular (sigmoid) structures. The ?rst type is that the rope proxies are detected in both lower and higher temperature lines. The second is that the rope proxies can only be detected in higher temperature lines, and the third is that the proxies display sigmoid structures in extreme ultraviolet channels. Six hundred and ?fty-eight proxies of the 1354 that belong to the ?rst type are tracked by active or eruptive material of ?laments or prominences. Four hundred and eighty-seven proxies appear to be rising from the lower atmosphere or brightening in the corona, and belong to the second type. The remaining 209 display sigmoid structures, and they are attributed to the third type. We detected 497 rope proxies, which is 37% of the total, in the northern hemisphere. Conclusions. Our ?ndings imply a signi?cantly asymmetric distribution of the rope proxies over the visible solar disk.
关键词： prominences,Sun: magnetic ?elds,Sun: activity,Sun: ?laments
更新于2025-09-19 17:15:36
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Horizontal flow fields observed in Hinode G-band images
摘要： Context. Solar pores are penumbra-lacking magnetic features, that mark two important transitions in the spectrum of magnetohydrodynamic processes: (1) the magnetic field becomes sufficiently strong to suppress the convective energy transport and (2) at some critical point some pores develop a penumbra and become sunspots. Aims. The purpose of this statistical study is to comprehensively describe solar pores in terms of their size, perimeter, shape, photometric properties, and horizontal proper motions. The seeing-free and uniform data of the Japanese Hinode mission provide an opportunity to compare flow fields in the vicinity of pores in different environments and at various stages of their evolution. Methods. The extensive database of high-resolution G-band images observed with the Hinode Solar Optical Telescope (SOT) is a unique resource to derive statistical properties of pores using advanced digital image processing techniques. The study is based on two data sets: (1) photometric and morphological properties inferred from single G-band images cover almost seven years from 2006 October 25 to 2013 August 31; and (2) horizontal flow fields derived from 356 one-hour sequences of G-band images using local correlation tracking (LCT) for a shorter period of time from 2006 November 3 to 2008 January 6 comprising 13 active regions. Results. A total of 7643/2863 (single/time-averaged) pores builds the foundation of the statistical analysis. Pores are preferentially observed at low latitudes in the southern hemisphere during the deep minimum of solar cycle No. 23. This imbalance reverses during the rise of cycle No. 24, when the pores migrate from high to low latitudes. Pores are rarely encountered in quiet-Sun G-band images, and only about 10% of pores exist in isolation. In general, pores do not exhibit a circular shape. Typical aspect ratios of the semi-major and -minor axes are 3:2 when ellipses are fitted to pores. Smaller pores (more than two-thirds are smaller than 5 Mm2) tend to be more circular, and their boundaries are less corrugated. Both the area and perimeter length of pores obey log-normal frequency distributions. The frequency distribution of the intensity can be reproduced by two Gaussians representing dark and bright components. Bright features resembling umbral dots and even light bridges cover about 20% of the pores’ area. Averaged radial profiles show a peak in the intensity at normalized radius RN = r/Rpore = 2.1, followed by maxima of the divergence at RN = 2.3 and the radial component of the horizontal velocity at RN = 4.6. The divergence is negative within pores strongly suggesting converging flows towards the center of pores, whereas exterior flows are directed towards neighboring supergranular boundaries. The photometric radius of pores, where the intensity reaches quiet-Sun levels at RN = 1.4, corresponds to the position where the divergence is zero at RN = 1.6. Conclusions. Morphological and photometric properties as well as horizontal flow fields have been obtained for a statistically meaningful sample of pores. This provides critical boundary conditions for MHD simulations of magnetic flux concentrations, which eventually evolve into sunspots or just simply erode and fade away. Numerical models of pores (and sunspots) have to fit within these confines, and more importantly ensembles of pores have to agree with the frequency distributions of observed parameters.
关键词： methods: statistical,sunspots,Sun: activity,methods: data analysis,Sun: photosphere,techniques: image processing
更新于2025-09-19 17:15:36
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Solar Ultraviolet Bursts
摘要： The term “ultraviolet (UV) burst” is introduced to describe small, intense, transient brightenings in ultraviolet images of solar active regions. We inventorize their properties and provide a de?nition based on image sequences in transition-region lines. Coronal signatures are rare, and most bursts are associated with small-scale, canceling opposite-polarity ?elds in the photosphere that occur in emerging ?ux regions, moving magnetic features in sunspot moats, and sunspot light bridges. We also compare UV bursts with similar transition-region phenomena found previously in solar ultraviolet spectrometry and with similar phenomena at optical wavelengths, in particular Ellerman bombs. Akin to the latter, UV bursts are probably small-scale magnetic reconnection events occurring in the low atmosphere, at photospheric and/or chromospheric heights. Their intense emission in lines with optically thin formation gives unique diagnostic opportunities for studying the physics of magnetic reconnection in the low solar atmosphere. This paper is a review report from an International Space Science Institute team that met in 2016–2017.
关键词： Sun: activity,Sun: atmosphere,Sun: UV radiation,Sun: transition region
更新于2025-09-10 09:29:36