Subjects -> ASTRONOMY (Total: 94 journals)
Showing 1 - 46 of 46 Journals sorted alphabetically
Advances in Astronomy     Open Access   (Followers: 49)
Annual Review of Astronomy and Astrophysics     Full-text available via subscription   (Followers: 50)
Annual Review of Earth and Planetary Sciences     Full-text available via subscription   (Followers: 67)
Artificial Satellites     Open Access   (Followers: 21)
Astrobiology     Hybrid Journal   (Followers: 11)
Astronomical & Astrophysical Transactions: The Journal of the Eurasian Astronomical Society     Hybrid Journal   (Followers: 7)
Astronomical Review     Open Access   (Followers: 5)
Astronomische Nachrichten     Hybrid Journal   (Followers: 4)
Astronomy & Geophysics     Hybrid Journal   (Followers: 49)
Astronomy and Astrophysics     Full-text available via subscription   (Followers: 67)
Astronomy and Computing     Hybrid Journal   (Followers: 6)
Astronomy Letters     Hybrid Journal   (Followers: 22)
Astronomy Reports     Hybrid Journal   (Followers: 22)
Astronomy Studies Development     Open Access   (Followers: 15)
Astroparticle Physics     Hybrid Journal   (Followers: 10)
Astrophysical Bulletin     Hybrid Journal   (Followers: 4)
Astrophysics     Hybrid Journal   (Followers: 35)
Astrophysics and Space Science     Hybrid Journal   (Followers: 49)
Astrophysics and Space Sciences Transactions (ASTRA)     Open Access   (Followers: 60)
Astropolitics: The International Journal of Space Politics & Policy     Hybrid Journal   (Followers: 13)
Celestial Mechanics and Dynamical Astronomy     Hybrid Journal   (Followers: 15)
Chinese Astronomy and Astrophysics     Full-text available via subscription   (Followers: 25)
Colloid Journal     Hybrid Journal   (Followers: 2)
Comptes Rendus : Physique     Open Access   (Followers: 2)
Computational Astrophysics and Cosmology     Open Access   (Followers: 6)
Earth and Planetary Science Letters     Hybrid Journal   (Followers: 143)
Earth, Moon, and Planets     Hybrid Journal   (Followers: 47)
Earth, Planets and Space     Open Access   (Followers: 77)
EAS Publications Series     Full-text available via subscription   (Followers: 8)
EPL Europhysics Letters     Partially Free   (Followers: 8)
Experimental Astronomy     Hybrid Journal   (Followers: 38)
Expert Opinion on Astronomy and Astrophysics     Open Access   (Followers: 8)
Extreme Life, Biospeology & Astrobiology - International Journal of the Bioflux Society     Full-text available via subscription   (Followers: 4)
Few-Body Systems     Hybrid Journal   (Followers: 1)
Foundations of Physics     Hybrid Journal   (Followers: 40)
Frontiers in Astronomy and Space Sciences     Open Access   (Followers: 15)
Galaxies     Open Access   (Followers: 6)
Globe, The     Full-text available via subscription   (Followers: 3)
Gravitation and Cosmology     Hybrid Journal   (Followers: 6)
Icarus     Hybrid Journal   (Followers: 71)
International Journal of Advanced Astronomy     Open Access   (Followers: 21)
International Journal of Astrobiology     Hybrid Journal   (Followers: 4)
International Journal of Astronomy     Open Access   (Followers: 22)
International Journal of Astronomy and Astrophysics     Open Access   (Followers: 36)
International Journal of Satellite Communications Policy and Management     Hybrid Journal   (Followers: 15)
International Letters of Chemistry, Physics and Astronomy     Open Access   (Followers: 8)
ISRN Astronomy and Astrophysics     Open Access   (Followers: 14)
Journal for the History of Astronomy     Full-text available via subscription   (Followers: 20)
Journal of Astrobiology & Outreach     Open Access   (Followers: 5)
Journal of Astronomical Instrumentation     Open Access   (Followers: 3)
Journal of Astrophysics     Open Access   (Followers: 33)
Journal of Astrophysics and Astronomy     Open Access   (Followers: 58)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 133)
Journal of Geophysical Research : Planets     Full-text available via subscription   (Followers: 116)
Journal of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 136)
Journal of High Energy Astrophysics     Full-text available via subscription   (Followers: 25)
Kinematics and Physics of Celestial Bodies     Hybrid Journal   (Followers: 11)
KronoScope     Hybrid Journal   (Followers: 1)
Macalester Journal of Physics and Astronomy     Open Access   (Followers: 5)
Monthly Notices of the Royal Astronomical Society     Hybrid Journal   (Followers: 13)
Monthly Notices of the Royal Astronomical Society : Letters     Hybrid Journal   (Followers: 2)
Nature Astronomy     Hybrid Journal   (Followers: 14)
New Astronomy     Hybrid Journal   (Followers: 26)
New Astronomy Reviews     Full-text available via subscription   (Followers: 19)
Nonlinear Dynamics     Hybrid Journal   (Followers: 19)
NRIAG Journal of Astronomy and Geophysics     Open Access   (Followers: 4)
Physics of the Dark Universe     Open Access   (Followers: 4)
Planetary and Space Science     Hybrid Journal   (Followers: 106)
Planetary Science     Open Access   (Followers: 52)
Proceedings of the International Astronomical Union     Full-text available via subscription   (Followers: 2)
Publications of the Astronomical Society of Australia     Hybrid Journal   (Followers: 3)
Publications of the Astronomical Society of Japan     Hybrid Journal   (Followers: 4)
Research & Reviews : Journal of Space Science & Technology     Full-text available via subscription   (Followers: 20)
Research in Astronomy and Astrophysics     Full-text available via subscription   (Followers: 38)
Revista Mexicana de Astronomía y Astrofísica     Open Access   (Followers: 3)
Science China : Physics, Mechanics & Astronomy     Full-text available via subscription   (Followers: 4)
Science China Physics, Mechanics & Astronomy     Hybrid Journal   (Followers: 4)
Solar Physics     Hybrid Journal   (Followers: 29)
Solar System Research     Hybrid Journal   (Followers: 15)
Space Science International     Open Access   (Followers: 118)
Space Science Reviews     Hybrid Journal   (Followers: 92)
Space Weather     Full-text available via subscription   (Followers: 27)
Transport and Aerospace Engineering     Open Access   (Followers: 13)
Universe     Open Access   (Followers: 6)
Similar Journals
Journal Cover
Solar Physics
Journal Prestige (SJR): 1.517
Citation Impact (citeScore): 3
Number of Followers: 29  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1573-093X - ISSN (Online) 0038-0938
Published by Springer-Verlag Homepage  [2469 journals]
  • Correction to: Wavelet Analysis of Forbush Decreases at High-Latitude
           Stations During Geomagnetic Disturbances

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      PubDate: 2022-05-20
       
  • Predicting the Maximum Amplitude of Solar Cycle 25 Using the Early Value
           of the Rising Phase

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      Abstract: Abstract The rising rate [ \(\beta _{\mathrm{a}}\) ] of a solar cycle is a good indicator for the subsequent maximum amplitude [ \(S_{\mathrm{m}}\) ] of sunspot numbers. We compared the correlation between \(S_{\mathrm{m}}\) and \(\beta _{\mathrm{a}}\) and that between \(S_{\mathrm{m}}\) and the early value of the smoothed monthly mean sunspot number [ \(S_{\mathrm{N}}\) ] \(\Delta m\) months after the solar minimum. Our main conclusions are as follows: i) The correlation coefficient [ \(r\) ] between \(S_{\mathrm{m}}\) and \(S_{\mathrm{N}}\) is slightly higher than that between \(S_{\mathrm{m}}\) and \(\beta _{\mathrm{a}}\) , and both increase with \(\Delta m\) as the cycle progresses; ii) In the first year of the cycle, the correlation is weak [ \(r\sim \) 0.56]. At the inflection point [ \(\Delta m=21\) ], the correlation is stronger [ \(r = 0.83\) ]. After the inflection point, \(r\) increases slowly with \(\Delta m\) . Three years after the solar minimum, \(r\geqslant 0.90\) . Around the average rise time [52 months], \(r=0.95\) ; iii) The correlation between \(S_{\mathrm{m}}\) and \(S_{\mathrm{N}}\) (or \(\beta _{\mathrm{a}}\) ) in even-numbered cycles is stronger than that in odd-numbered ones, and the latter is slightly weaker than that for all the cycles; iv) The mean relative error [ \(\eta \) ] of \(S_{\mathrm{m}}\) decreases and the MSE (Mean Square Error) skill score [ \(S_{\mathrm{c}}\) ] increases with \(\Delta m\) . One, two, three, and four years after the solar minimum: \(\eta \leqslant 19\%\) , \(14\%\) , \(10\%\) , and ...
      PubDate: 2022-05-20
       
  • Invited Review: Short-term Variability with the Observations from the
           Helioseismic and Magnetic Imager (HMI) Onboard the Solar Dynamics
           Observatory (SDO): Insights into Flare Magnetism

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      Abstract: Abstract Continuous vector magnetic-field measurements by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) allow us to study magnetic-field properties of many flares. Here, we review new observational aspects of flare magnetism described using SDO data, including statistical properties of magnetic-reconnection fluxes and their rates, magnetic fluxes of flare dimmings, and magnetic-field changes during flares. We summarize how these results, along with statistical studies of coronal mass ejections (CMEs), have improved our understanding of flares and the flare/CME feedback relationship. Finally, we highlight future directions to improve the current state of understanding of solar-flare magnetism using observations.
      PubDate: 2022-05-19
       
  • A Sunspot Catalog by Rafael Carrasco at the Madrid Astronomical
           Observatory for the Period 1931 – 1933

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      Abstract: Abstract A sunspot catalog was published by the Madrid Astronomical Observatory from sunspot observations made by Rafael Carrasco and his assistants for the period November 1931 – December 1933. We have digitized this catalog and carried out a quality control to detect inconsistencies. We present a machine-readable version of this sunspot catalog together with an erratum list. Moreover, we compared the Madrid sunspot number and area with other reference series. We found that sunspots in the northern hemisphere were predominant during this period, confirming previous studies. We have also analyzed the group morphological typologies registered in the catalog and show a butterfly diagram drawn with this new information. A comparison with the sunspot catalog by the Royal Greenwich Observatory shows that almost all the groups included in the Carrasco’s catalog are also present in the aforementioned catalog.
      PubDate: 2022-05-18
       
  • Kinematic Study of Radio-Loud CMEs Associated with Solar Flares and DH
           Type-II Radio Emissions During Solar Cycles 23 and 24

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      Abstract: Abstract We have statistically analyzed 379 radio-loud (RL) CMEs and their associated flares during the period 1996 – 2019 covering both Solar Cycles (SC) 23 and 24. We classified them into two populations based on the observation period: \(i\) ) 235 events that belong to SC 23 (August 1996 – December 2008) and \(\mathit{ii}\) ) 144 events that belong to SC 24 (January 2009 – December 2019). For both cycles, the mean sky-plane speed, projection corrected speed (space speed), and initial acceleration of RL CMEs are found to be similar. Moreover, the average residual acceleration of RL CMEs in SC 24 (−17.39 ±43.51 m s−2) is twice lower than that of the RL CMEs in SC 23 (−8.29 ±36.23 m s−2), which means that the deceleration of RL CMEs in SC 24 is twice as fast as in SC 23. RL CMEs reach their peak speed at higher altitudes in SC 23 (1443 ±504 km s−1; 13.82 ±7.40 R⊙) than SC 24 (1920 ±649 km s−1; 12.51 ±7.41 R⊙). We also observed that the mean apparent widths of RL CMEs in SC 23 are less than in SC 24, which is statistically significant. SC 23 has a lower average CME nose height (3.85 R⊙) at the start time of DH type-II bursts than that of SC 24 (3.46 R⊙). The starting frequencies of DH type-II bursts associated with RL CMEs for SC 24 are significantly larger (formed at lower heights) than those of SC 23. We found that there is a good correlation between the drift rates and the midfrequencies of DH type-II radio bursts for both of these solar cycles (R \(^{2} =\) 0.80, \(\varepsilon \) = 1.53). Most of the RL CMEs kinematics and their associated solar-flare properties are found to be similar for SC 23 and SC 24. The annual variations for the general population of CMEs are well consistent with the mean sunspot number but small variations in halo and RL CMEs are observed. We concluded that the reduced total pressure in the heliosphere for SC 24 enables RL CMEs to expand wider and decelerate faster, resulting in DH type-II radio emissions at lower heights than for SC 23.
      PubDate: 2022-05-16
       
  • Formation and Immediate Deformation of a Small Filament Through
           Intermittent Magnetic Interactions

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      Abstract: Abstract It is generally believed that filament formation involves a process of the accumulation of magnetic energy. However, in this article, we discuss the idea that filaments will not erupt and will only deform when the stored magnetic energy is released gradually. Combining high-quality observations from Solar Dynamics Observatory and other instruments, we present the formation and immediate deformation of a small filament (F1) in the active region (AR) 12760 on 28 – 30 April 2020. Before the filament formation, three successive dipoles quickly emerged with separation motions in the center of AR 12760. Due to the magnetic interaction between magnetic dipoles and pre-existing positive polarities, coronal brightenings consequently appeared in the overlying atmosphere. Subsequently, because of the continuous cancellation of magnetic flux that happened around the adjacent ends of F1 and another nearby filament (F2), the magnetic reconnections occurred intermittently between F1 and F2. Finally, F1 lessened in shear, and F2 became shorter. All the results show that the formation of F1 was closely associated with intermittent interactions between the sequence of emerging dipoles and pre-existing magnetic polarities, and the immediate deformation of F1 was intimately related to intermittent interactions between F1 and F2. We also suggest that the intermittent magnetic interactions driven by the continuous magnetic activities (magnetic-flux emergence, cancellation, and convergence) play an important role in the formation and deformation of filaments.
      PubDate: 2022-05-12
       
  • SOLar-STellar Irradiance Comparison Experiment II (SOLSTICE II):
           End-of-Mission Validation of the SOLSTICE Technique

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      Abstract: Abstract The SOLar-STellar Irradiance Comparison Experiment (SOLSTICE: McClintock, Rottman, and Woods, Solar Phys. 230, 225, 2005) onboard the SOlar Radiation and Climate Experiment (SORCE: Rottman, Solar Phys. 230, 7, 2005) observed ultraviolet solar spectral irradiance (SSI) from 2003 – 2020. This article gives an overview of the end-of-mission algorithms and calibration of SOLSTICE. Many of the algorithms were updated after the early mission, either due to an improved understanding of the instrument and the space environment, or due to operational constraints as the spacecraft systems aged. We validate the final official data version (V18) with comparisons to other observations and models. The SOLSTICE observations of the solar-cycle variability in the ultraviolet are compared to model estimates.
      PubDate: 2022-05-12
       
  • Narrowband Spikes Observed During the 13 June 2012 Flare in the
           800 – 2000 MHz Range

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      Abstract: Abstract Narrowband (∼5 MHz) and short-lived (∼0.01 s) spikes with three different distributions in the 800 – 2000 MHz radio spectrum of the 13 June 2012 flare are detected and analyzed. We designate them as SB (spikes distributed in a broad band or bands), SZ (spikes distributed in zebra-like bands) and SBN (spikes distributed in broad and narrow bands). On analyzing AIA/SDO images of the active region NOAA 11504, a rough correspondence between groups of the spikes observed at 1000 MHz and peaks in the time profiles of AIA channels taken from the flare subarea close to the leading sunspot is found. Among the types of spikes the SZ type is the most interesting because it resembles zebras. Therefore, using autocorrelation and crosscorrelation methods we compare SZ and SBN spikes with the typical zebra observed in the same frequency range. While the ratio of SZ band frequencies with their frequency separation (220 MHz) is about 4, 5, and 6, in the zebra the frequency stripe separation is about 24 MHz and the ratio is around 50. Moreover, the bandwidth of SZ bands, which consists of clouds of narrowband spikes, is much broader than that of zebra stripes. This comparison indicates that SZ spikes are generated in a different way from the zebra, but in a similar way to SBN spikes. We successfully fit the SZ band frequencies by the Bernstein modes. Based on this fitting we interpret SZ and SBN spikes as those generated in the model of Bernstein modes. Thus, the magnetic field and plasma density in the SZ spike source are estimated to be about 79 G and 8.4 × 109 cm−3, respectively.
      PubDate: 2022-05-09
       
  • Relationships Between the Spectra of Near-Earth Proton Enhancements, Hard
           X-Ray Bursts, and CME Speeds

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      Abstract: Abstract Some studies propose the transfer of flare-accelerated protons in an erupting flux rope until its reconnection with an open structure releases the trapped protons. Coulomb collisions in the dense flux-rope body deplete the low-energy part of the proton spectrum. On the other hand, shock acceleration progressively replenishes this part of the spectrum. These processes form a double power-law proton spectrum that is usually observed at the Earth’s orbit. We analyze the correlations between the slopes of near-Earth proton spectra below and above the break energy, on the one hand, and photon indices of the corresponding hard X-ray (HXR) bursts and speeds of associated coronal mass ejections (CMEs), on the other hand. We use catalogs of proton events in 1991 – 2006, HXR spectra obtained by Yohkoh and the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI), and CME catalogs. Significant correlations have been found between the proton spectral slopes i) above the break energy and HXR spectral indices (0.86), and ii) below the break energy and CME speeds (−0.75). The results indicate a statistical predominance of flare acceleration at higher proton energies and shock acceleration at their lower energies. The highest-energy proton spectra reconstructed in ground-level events exhibit the second break with the steepest slope above it. Neither this slope nor the second-break energy correlates with any other parameter. This peculiarity requires understanding.
      PubDate: 2022-05-06
       
  • Spatial and Temporal Variations of 2 – 10 MeV nuc−1 He/H in
           Gradual Solar Energetic Particle Events

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      Abstract: Abstract In a previous work (Kahler and Brown, 2021; henceforth KB21) we found that 4 – 53 MeV nuc−1 He/H ratios measured at peak intensities of 43 gradual solar energetic-particle (SEP) events were significantly correlated with solar-wind (SW) He/H ratios and with SEP event peak intensities. Here, we extend that work by examining He/H ratios from onsets through peaks of 12 large 1.8 – 10.0 MeV nuc−1 SEP events observed with the Low Energy Telescope (LET) on both STEREO A and B (STA/B) spacecraft when their longitudinal separation angle was < 90∘ in 2013 – 2014. We discuss the challenges of choosing matching five 1-hour periods of STA/B SEP profiles to characterize He/H in the LET energy ranges 1.8 – 3.6, 4.0 – 6.0, and 6.0 – 10.0 MeV nuc−1. The roles of rigidity-dependent transport or of anomalous He production in large variations of He/H are assessed with 6.0 – 10.0 MeV nuc−1 O/He. The STA/B SW data do not include He/H, but we confirm the KB21 results that SEP He/H extends over a range of 0.001 to 0.1, decreasing with increasing energy, and increasing with event peak H intensities. Differences of STA/B log He/H are not correlated with STA/B angular separations. The six cases of SEP events occurring within interplanetary coronal mass ejections (ICMEs) show somewhat higher H peak intensities and He/H than those outside ICMEs. We interpret the low He/H events as predominately SEP3 and high He/H as SEP4 events in the Reames (2020) SEP event-classification system.
      PubDate: 2022-05-04
       
  • Oscillation Dynamics in Short-Lived Facular Regions During Their Lifetime

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      Abstract: Abstract We performed a multi-wave study of the oscillation dynamics in short-lived facular regions during their lifetime. We studied oscillations in five regions, three of which belonged to the beginning of the current solar-activity cycle and two of them existed at the end of the previous cycle. We found that in the facular regions of the current cycle, low-frequency (1 – 2 mHz) oscillations dominated in the early stages of the facular formation, while in the regions of the previous cycle, five-minute oscillations dominated at this stage. At the maximal development phase of all the facular regions, the locations of the observed low frequencies are closely related to those of the coronal loops. These results support the idea that the sources of the low-frequency oscillations in the loops lie at the loops’ foot points.
      PubDate: 2022-05-04
       
  • Spectroscopy of Electric-Field Oscillations in the Solar Wind During the
           Passage of a Type III Radio Burst Using Observations Compared with
           Self-Similar Theory

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      Abstract: Abstract We present a spectrum of electric-field oscillations observed in situ in the solar wind by the WAVES experiment on the Wind spacecraft during the passage of a type III solar radio burst. 19 frequencies of this spectrum are compared with recent predictions of a self-similar nonlinear theory of two-dimensional electron oscillations (Osherovich and Fainberg, 2018).
      PubDate: 2022-05-02
       
  • A Diligent Analysis of the Flash and Coronal Spectrum of the Total Solar
           Eclipse of 20 March 2015

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      Abstract: Abstract During totality of the solar eclipse of 20 March 2015, at Svalbard, Norway, the emission spectra of the solar chromosphere and corona were captured with a slitless spectrograph. A very lucky coincidence of a large number of sunspots and Active Regions (ARs) around the solar limb allowed us to observe a number of different spectroscopic effects. This eclipse took place about one year after the second solar maximum of the double-peaked Solar Cycle 24, which produced less activity than the previous stronger solar maxima. The spectra taken during the eclipse show strong and high activity of the green coronal line Fe xiv (5303 Å) and the lower intensity of the red coronal line Fe x (6374 Å). After subtraction of the emitted continuum of K+(F) corona, the detection and identification of several extremely weak emission lines, including the two forbidden emission lines of Ca xv (5694 Å and 5446 Å) and also Ni xiii (5116 Å) and Ni xv (6702 Å), was possible. The large number of ARs also led to the observation of a continuum brightening in ARs and a continuum darkening in surrounding areas.
      PubDate: 2022-04-21
       
  • Exploring the Circular Polarisation of Low–Frequency Solar Radio
           Bursts with LOFAR

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      Abstract: Abstract The Sun is an active star that often produces numerous bursts of electromagnetic radiation at radio wavelengths. Low frequency radio bursts have recently been brought back to light with the advancement of novel radio interferometers. However, their polarisation properties have not yet been explored in detail, especially with the Low Frequency Array (LOFAR), due to difficulties in calibrating the data and accounting for instrumental leakage. Here, using a unique method to correct the polarisation observations, we explore the circular polarisation of different sub-types of solar type III radio bursts and a type I noise storm observed with LOFAR, which occurred during March–April 2019. We analysed six individual radio bursts from two different dates. We present the first Stokes V low frequency images of the Sun with LOFAR in tied-array mode observations. We find that the degree of circular polarisation for each of the selected bursts increases with frequency for fundamental emission, while this trend is either not clear or absent for harmonic emission. The type III bursts studied, that are part of a long–lasting type III storm, can have different senses of circular polarisation, occur at different locations and have different propagation directions. This indicates that the type III bursts forming a classical type III storm do not necessarily have a common origin, but instead they indicate the existence of multiple, possibly unrelated acceleration processes originating from solar minimum active regions.
      PubDate: 2022-04-20
       
  • Two New Methods for Counting and Tracking the Evolution of Polar Faculae

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      Abstract: Abstract Polar faculae are the footpoints of magnetic-field lines near the Sun’s poles that are seen as bright regions along the edges of granules. The time variation in the number of polar faculae has been shown to correlate with the strength of the polar magnetic field and to be a predictor of the subsequent solar cycle. Due to the small size and transient nature of these features, combined with different techniques and observational factors, previous counts of polar faculae differ in magnitude. Further, there were no scalable techniques to measure the statistical properties of the faculae, such as the variation of the facular lifetime with time or solar activity. Using data from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO), we present two new methods for tracking faculae and measuring their properties. In the first, we calculate the pixel-by-pixel standard deviation of the HMI continuum intensity images over one day, visualizing the faculae as streaks. The lifetime of the facula is found by dividing the angular length of the streaks by the latitude-dependent rotation rate. We apply this method to the more visible pole each day for a week every six months, from September 2010 to March 2021. Combining all of the measured facular lifetimes provides a statistical distribution with a mean of 6.0 hours, a FWHM of 5.4 hours, and a skew towards longer lifetimes, with some faculae lasting up to 1 day. In the second method, we overlay images of the progressive standard deviation with the HMI magnetogram to show the close relationship between the facular candidates and the magnetic field. The results of this method allow us to distinguish between motion due to the Sun’s rotation and “proper motion” due to faculae moving across the Sun’s surface, confirming that faculae participate in convective motions at the poles. Counts of polar faculae using both methods agree with previous counts in their variation with the solar cycle and the polar magnetic field. These methods can be extended to automate the identification and measurement of other properties of polar faculae, which would allow for daily measurements of all faculae since SDO began operation in 2010.
      PubDate: 2022-04-20
       
  • Mitigation of Radio Frequency Interference in the Solar Radio Spectrum
           Based on Deep Learning

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      Abstract: Abstract Radio frequency interference (RFI) may contaminate the signal received by solar radio telescopes. The existence of RFI in the solar radio spectrum affects the accuracy and efficiency of the extraction of burst parameters, which is related to the quality of scientific results and even the authenticity of conclusions. Therefore, it is necessary to carry out research on RFI recognition algorithms for solar radio data. This article aims to compare the recognition performance of six different deep-learning networks (FCN, Deconvnet, Segnet, Unet, Dual-Resunet, and DSC Based Dual-Resunet) on the RFI in solar radio spectra observed by the Chinese Solar Broadband Radio Spectrometer (SBRS). The accuracy and convergence speed in the training process, as well as various performance metrics in the test, indicate that the proposed DSC Based Dual-Resunet is the most suitable neural-network for this task and can achieve both performance and light weight. The RFI recognition accuracy of the DSC Based Dual-Resunet is close to Unet when there is no burst in the spectrum, but in the case of a burst DSC Based Dual-Resunet is obviously better than Unet in terms of RFI recognition. Moreover the model size and number of parameters are approximately 12.5% of those of Unet, and the amount of computation is 38% of that of Unet, which greatly improves the computation efficiency and is of great significance for the realization of the network on mobile hardware. It is promising for the large-scale application of RFI recognition for solar radio telescopes.
      PubDate: 2022-04-20
       
  • On Modeling ICME Cross-Sections as Static MHD Columns

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      Abstract: Abstract Solar coronal mass ejections are well-known to expand as they propagate through the heliosphere. Despite this, their cross-sections are usually modeled as static plasma columns within the magnetohydrodynamics (MHD) framework. We test the validity of this approach using in-situ plasma data from 151 magnetic clouds (MCs) observed by the WIND spacecraft and 45 observed by the Helios spacecraft. We find that the most probable cross-section expansion speeds for the WIND events are only \(\approx 0.06\) times the Alfvén speed inside the MCs, while the most probable cross-section expansion speeds for the Helios events is \(\approx 0.03\) . MC cross-sections can thus be considered to be nearly static over an Alfvén crossing timescale. Using estimates of electrical conductivity arising from Coulomb collisions, we find that the Lundquist number inside MCs is high ( \(\approx 10^{13}\) ), suggesting that the MHD description is well justified. The Joule heating rates using our conductivity estimates are several orders of magnitude lower than the requirement for plasma heating inside MCs near the Earth. While the (low) heating rates we compute are consistent with the MHD description, the discrepancy with the heating requirement points to possible departures from MHD and the need for a better understanding of plasma heating in MCs.
      PubDate: 2022-04-13
       
  • Sympathetic Quiet and Active Region Filament Eruptions

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      Abstract: Abstract We present the observations of three sympathetic filament eruptions occurring on 19 July 2015, namely F1, F2, and F3. The events were observed in UV and EUV by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory and in H \(\alpha \) by the Mauna Loa Solar Observatory (MLSO) of the Global Oscillation Network Group. As filament F1 starts to erupt, a part of it falls close to the locations of filaments F2 and F3. Our observations indicate that this drives the eruption of F2 and F3, which merge in the process, and trigger a coronal mass ejection and a long-duration GOES C2.1 class flare. We discuss the dynamics and kinematics of these three filament eruptions and related phenomena.
      PubDate: 2022-04-07
       
  • Solar-Cycle Variability Results from the Solar Radiation and Climate
           Experiment (SORCE) Mission

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      Abstract: Abstract The Solar Radiation and Climate Experiment (SORCE) was a NASA mission that operated from 2003 to 2020 to provide key climate-monitoring measurements of total solar irradiance (TSI) and solar spectral irradiance (SSI). This 17-year mission made TSI and SSI observations during the declining phase of Solar Cycle 23, during all of Solar Cycle 24, and at the very beginning of Solar Cycle 25. The SORCE solar-variability results include comparisons of the solar irradiance observed during Solar Cycles 23 and 24 and the solar-cycle minima levels in 2008 – 2009 and 2019 – 2020. The differences between these two minima are very small and are not significantly above the estimate of instrument stability over the 11-year period. There are differences in the SSI variability for Solar Cycles 23 and 24, notably for wavelengths longer than 250 nm. Consistency comparisons with SORCE variability on solar-rotation timescales and solar-irradiance model predictions suggest that the SORCE Solar Cycle 24 SSI results might be more accurate than the SORCE Solar Cycle 23 results. The SORCE solar-variability results have been useful for many Sun–climate studies and will continue to serve as a reference for comparisons with future missions studying solar variability.
      PubDate: 2022-04-06
       
  • Comparing the Sun Watcher Using Active Pixel System Detector and Image
           Processing Instrument to the Atmosphere Imaging Assembly Instrument
           Through Measurements of Polar Coronal Holes

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      Abstract: Abstract The PRoject for OnBoard Autonomy 2/Sun Watcher using Active pixel system detector and image Processing (PROBA2/SWAP) instrument images the full-disk extreme ultraviolet (EUV) Sun using a complementary metal-oxide semiconductor active-pixel sensor (CMOS-APS) detector with a filter centered on a 174 Å passband at a cadence of one to two minutes. In contrast, the Atmosphere Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) has a passband filter centered on 171 Å and uses a charge-coupled device (CCD) detector to make full-disk observations of the EUV corona. The images that these two telescope designs produce are visually quite similar in active regions, coronal loops, and the quiet corona. This work takes a deeper look at the stability of the most difficult coronal features to capture in an image: polar coronal holes. Polar coronal holes are the longest-lived features on the Sun and are critical to understand the global state of the solar corona, but because of an oblique viewing angle, obstruction due to the coronal plasma scale height and lack of ground-truth magnetic-field measurements make reliable segmentation of polar holes difficult. We use perimeter tracing to make consistent measurements of a polar-hole’s perimeter and area in both SWAP 174 Å and AIA 171 Å images. The generated time series of coronal-hole parameters rarely agree with each other. Direct comparison of polar-hole measurements generated by these two imagers allows us to simultaneously analyze the physical properties of polar coronal holes and to identify systematic differences between the two different instruments.
      PubDate: 2022-04-06
       
 
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