Solar Physics最新文献

The magnetic field changes the radiative output of the Sun and is the main source for all the solar surface features. To study the role of the underlying photospheric magnetic field in relation to emission features observed in the solar corona, we have used the full-disk soft X-ray images from Hinode/X-Ray Telescope (Hinode/XRT) and the magnetograms obtained from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) for a period of about 13 years (May 2010 – June 2023), which covers Solar Cycle 24 and the ascending phase of Solar Cycle 25. A sophisticated and established algorithm developed in Python is applied to the X-ray observations from Hinode/XRT to segment the different coronal features by creating segmentation maps of the active regions (ARs), coronal holes (CHs), background regions (BGs), and X-ray bright points (XBPs). Further, these maps have been applied to the full-disk (FD) line-of-sight (LOS) magnetograms from HMI to isolate the X-ray coronal features and photospheric magnetic counterparts, respectively. We computed full-disk and featurewise averages of X-ray intensity and LOS magnetic field (MF) over ARs, CHs, BGs, XBPs, and FD regions. Variations in the quantities resulting from the segmentation, namely the mean intensity, temperature from the filter ratio method, and the unsigned magnetic field of ARs, CHs, BGs, XBPs, and FD regions, are intercompared and compared with the sunspot number (SSN). We find that the X-ray intensity and temperature over ARs, CHs, BGs, XBPs, and FD regions are well correlated with the underlying magnetic field. We discuss the intensity, temperature, and magnetic field variations of the full-disk corona and of all the features. The time series plots of the unsigned magnetic field of the full disk and all the features show magnetic field fluctuations synchronized with the solar cycle (sunspot number). Although the magnetic field of all features varies, the mean, spatially smoothed magnitude of the magnetic field values estimated for the whole observed period of the full disk is around 8.9 ± 2.60 G, active regions (ARs) are around 34.4 ± 18.42 G, whereas BGs, CHs, and XBPs are 7.7 ± 1.72 G, 6.6 ± 1.04 G, and 15.62 ± 8.76 G, respectively. In addition, we find that the mean magnetic field contribution of the background regions (BGs) is around 85(%), whereas ARs, CHs, and XBPs are 11(%), 2(%), and 2(%), respectively, to the average magnetic field of the full disk. The magnetic field time series of all the features suggest that the features show a high variability in their magnetic field and the fluctuations in magnetic field are correlated to fluctuations in intensity and temperature, suggesting that the magnetic field is important in producing different emission features, which are associated with different intensity and temperature values. The magnetic field is responsible for the he

The Tautenburg Solar Laboratory is a new solar observation facility to develop full-disc instrumentation for a new synoptic solar network. In the first phase, a ful-disc spectropolarimeter based on a single tunable etalon placed at the telescope aperture is developed. The development includes a container-based light feed system and optical laboratory, the instrumentation as well as calibration and data reduction pipelines. The ultimate scientific goal is the quasisimultaneous observation of spectral lines for synoptic studies and helioseismic investigations of the Sun.

In 1876, Alfred Wolfer started observing the Sun and recording the properties of sunspots alongside Rudolf Wolf. Their observations became the basis for the construction of the sunspot-number series. After Wolf’s death in 1893, Wolfer became the primary observer for the sunspot-number series. Even though the observations of Wolf and Wolfer had an overlap of almost 17 years (1876–1893), this shift of primary observer from Wolf to Wolfer seems to have led to inconsistencies in the sunspot-number series, primarily due to inhomogeneities in Wolf’s observations. To address this issue we digitise Mittheilungen (Wolf’s journals) and analyse their tabulated datasets. These journals include the raw sunspot data from various observers that the Zürich Observatory used to compile the sunspot number series (SNV1). These datasets have been used as source data for the construction of the first version of the sunspot number (SNV1) series, but they were not digitally accessible for a recalibration of the sunspot-number series until recently. We have also acquired external datasets from recent archival investigations for contemporaneous sunspot observations. In this study, we use the Mittheilungen dataset to produce a new recalibration of the sunspot-number series covering 1816–1944, using four major observers (Tevel, Schwabe, Weber and Wolfer) as backbones. The availability of the raw data allows us to identify issues in the determination of the scaling factors or (k)-factors, between the records of different observers, but also the use of modern techniques for cross-calibrations. Our reconstruction for the years 1816–1944 is carried out with a novel method inspired by Chatzistergos et al. (Astron. Astrophys. 602, A69, 2017) allowing us to eliminate inconsistencies that resulted from the application of erroneous (k)-factors.

The changing magnetic fields of the Sun are generated and maintained by a solar dynamo, the exact nature of which remains an unsolved fundamental problem in solar physics. Our objective in this paper is to investigate the role and impact of converging flows toward Bipolar Magnetic Regions (BMR inflows) on the Sun’s global solar dynamo. These flows are large-scale physical phenomena that have been observed and so should be included in any comprehensive solar dynamo model. We have augmented the Surface flux Transport And Babcock–LEighton (STABLE) dynamo model to study the nonlinear feedback effect of BMR inflows with magnitudes varying with surface magnetic fields. This fully-3D realistic dynamo model produces the sunspot butterfly diagram and allows a study of the relative roles of dynamo saturation mechanisms such as tilt-angle quenching and BMR inflows. The results of our STABLE simulations show that magnetic field-dependent BMR inflows significantly affect the evolution of the BMRs themselves and result in a reduced buildup of the global poloidal field due to local flux cancellation within the BMRs, to an extent that is sufficient to saturate the dynamo. As a consequence, for the first time, we have achieved fully 3D solar dynamo solutions, in which BMR inflows alone regulate the amplitudes and periods of the magnetic cycles.

Coronal mass ejections (CMEs) play a key role in determining space-weather conditions. Therefore, it is important to understand their evolution throughout the heliosphere. In this work, we carefully analyze the evolution of two kinematically different CMEs that erupted on 16 June 2010 and 14 June 2011, in a range of heliospheric distances of approximately 4 – 18 solar radii. From nearly simultaneous coronagraph images from the Solar-Terrestrial Relations Observatory and Solar and Heliospheric Observatory, we estimate the three-dimensional speed and acceleration–time profiles. We use these profiles to calculate the dynamic and thermodynamic parameters of the CMEs, such as the contribution of the forces and the polytropic index by means of the Flux Rope Internal State (FRIS) model, which assumes a self-similar evolution. We further test the validity of this assumption by comparing with observed quantities near the Sun and at 1 AU. We find that the kinematic properties of the two events differ in their evolution, which has an impact on the relative importance of the internal forces and on the thermodynamic quantities. In addition, our analysis reveals that the assumption of self-similar evolution is valid for the behavior in the middle corona for both events. At larger distances, however, this only holds for the 16 June 2010 event, which is significantly slower than the other.

The orbit of the Solar Orbiter mission carries it and the Polarimetric and Helioseismic Imager (PHI), which is onboard, away from the Sun–Earth line, opening up the first ever possibility of doing stereoscopy of solar photospheric structures. We present a method for a stereoscopic analysis of the height variations in the solar photosphere. This method enables the estimation of relevant quantities, such as the Wilson depression of sunspots and pores. We demonstrate the feasibility of the method using simulated Stokes-(I) continuum observations of an MHD simulation of the solar-surface layers. Our method estimates the large-scale variations in the solar surface by shifting and correlating two virtual images, mapped from the same surface feature observed from two different vantage points. The resulting vector is then introduced as an initial height estimate in the least-squares Broyden–Fletcher–Goldfarb–Shanno (BFGS) optimization algorithm to reproduce smaller scale structures. The height estimates from the simulated images reproduce well the overall height variations of the MHD simulation. We studied which viewing angles give the best results and found the optimal separation of the view points to be between (10^{circ }) and (40^{circ }); but neither viewing direction should be inclined by more than (30^{circ }) from the vertical to the solar surface. The method yields reliable results if the data have a signal-to-noise ratio of 50 or higher. The influence of the spatial resolution of the observed images is considered and discussed.

Statistical relations between the geomagnetic Dst index, cosmic ray variations, and solar wind characteristics are compared for Forbush decreases associated with: (i) coronal mass ejections from active regions (AR-CMEs) accompanied by solar flares, (ii) filament eruptions outside active regions, (iii) corotating interaction regions (CIRs) caused by high-speed streams from coronal holes, (iv) mixed events induced by two or more solar sources. Relationships of geomagnetic indices and parameters of cosmic rays and the solar wind are also compared between sporadic events with or without magnetic clouds (MCs) and between Solar Cycles (SCs) 23 and 24. The results reveal that interplanetary disturbances originated by AR-CMEs associated with an MC are most geoeffective and cause powerful geomagnetic storms, while CIRs create only moderate and weak storms. Sporadic and recurrent events differ in values of the Dst index and southward component of the magnetic field, as well as in the relationship between them. For sporadic events, geomagnetic activity is more affected by the presence or absence of an MC than by the type of solar source. Interplanetary disturbances associated with AR-CMEs are more effective in SC 23 while those associated with other types of solar sources have approximately the same geoeffectiveness in both SCs.

Abstract

We have developed a comprehensive catalog of the variable differential rotation measured near the solar photosphere. This catalog includes measurements of these flows obtained using several techniques: direct Doppler, granule tracking, magnetic pattern tracking, global helioseismology, as well as both time-distance and ring-diagram methods of local helioseismology. We highlight historical differential rotation measurements to provide context, and thereafter provide a detailed comparison of the MDI-HMI-GONG-Mt. Wilson overlap period (April 2010 – Jan 2011) and investigate the differences between velocities obtained from different techniques and attempt to explain discrepancies. A comparison of the rotation rate obtained by magnetic pattern tracking with the rotation rates obtained using local and global helioseismic techniques shows that magnetic pattern tracking measurements correspond to helioseismic flows located at a depth of 25 to 28 Mm. In addition, we show the torsional oscillation from Sunspot Cycles 23 and 24 and discuss properties that are consistent across measurement techniques. We find that acceleration derived from torsional oscillation is a better indicator of long-term trends in torsional oscillation compared to the residual velocity magnitude. Finally, this analysis will pave the way toward understanding systematic effects associated with various flow measurement techniques and enable more accurate determination of the global patterns of flows and their regular and irregular variations.

The solar soft X-ray observations from the GOES satellites now span two full Hale cycles and provide one of the best quantitative records of solar activity, with nearly continuous flare records since 1975. We present a uniform new reduction of the entire time series for 1975 to 2022 at NOAA class C1 level or above, to characterize the occurrence distribution function (ODF) of the flares observed in the 1 – 8 Å spectral band. The analysis includes estimates of the peak fluxes of the 12 flares that saturated in the 1 – 8 Å time series. In contrast to the standard NOAA classifications, these new estimates use the full time resolution of the sampling and have a preflare background level subtracted for all events. Our new estimates include NOAA’s latest calibrations for the GOES-1 through GOES-15 data covering 1975 – 2016. For each of the 12 saturated events we have made new estimates of peak fluxes based on fits to the rise and fall of the flare time profile, and have validated our extrapolation schemes by comparing with artificially truncated but unsaturated X10-class events. In this new estimation, SOL2003-11-04 (the most energetic unambiguously observed event) has a peak flux of (4.32 times 10^{-3}text{ W}/text{m}^{2}). This corresponds to X43 on the new scale, or X30 on the old scale. We provide a list in the Appendix for peak fluxes of all 37 events above (10^{-3}text{ W}/text{m}^{2}), the GOES X10 level, including the 12 saturated events. The full list now gives us a first complete sample from which we obtain an occurrence distribution function (ODF) for peak energy flux (S), often represented as a power-law (dF/dE propto E^{-alpha }), for which we find (alpha = 1.973 pm 0.014) in the range M1 to X3. The power-law description fails at the high end, requiring a downward break in the ODF above the X10 level. We give a tapered power-law description of the resulting CCDF (complementary cumulative distribution function) and extrapolate it into the domain of “superflares,” i.e., flares with bolometric energies (>10^{33}text{ erg}). Extrapolation of this fit provides estimates of 100-yr and 1000-yr GOES peak fluxes that agree reasonably well with other such estimates using different data sets and methodology, although there is some tension between our 10,000-yr (the Holocene time-scale) estimate and the GOES class obtained for the out-sized 774 AD solar proton event as inferred from cosmogenic nuclide records.