Search

The study presents the results of the correlation analysis for the average seasonal values of intensity of solar UV radiation (297–330 nm), as well as for the energy of the lines of solar spectral irradiance with total solar irradiance and total magnetic field of the Sun for the period of 2008–2018 (the 24th cycle of solar activity). The analysis is carried out using the spectral observations of solar UV radiation at Novolazarevskaya station (Antarctica), the SORCE spacecraft and WSO (Wilcox Solar Observatory) data. The dependence of the UVB-UVA radiation of 280–315 nm (UV-B) and 315–400 nm (UV-A) on changes in the total magnetic field of the Sun is revealed.

Solar activity changes with about 11-year periodicity, two 11-year cycles form a complete 22-year magnetic cycle of the Sun. Solar cycle 25 has recently begun, and it is important to know in advance what and when it will be at its maximum. The paper predicts the maximal sunspot (Wolf) number in solar cycle 25 separately in the northern and southern hemispheres. The absolute value of the polar magnetic field near the cycle minimum was used as a precursor of the cycle maximum. The values of solar polar magnetic field measured at the Wilcox Solar Observatory of Stanford University since 1976 and sunspot numbers in the N- and S-hemispheres in 1975–2020 (in solar cycles 21–24) are analyzed. For the time interval 1992–2020, sunspot numbers in the N- and S-hemispheres were used according to SILSO ( http://sidc.oma.be/SISLO , Version 2.0), and for the time interval 1975–1992, sunspot numbers were taken from the paper (Temmer et al., 2006, Astron. Astrophys. 2006, 447, 735) and reduced to the modern SILSO scale. Sunspot numbers in minima and maxima as well as corresponding times in solar cycles 21–24 in the N- and S-hemispheres were found. The correlation coefficient at different time lags between the smoothed monthly sunspot number and the modulus of the Sun’s polar magnetic field in the northern and southern hemispheres has been calculated. It was found that maximal correlation coefficients between these parameters are 0.587 at a time lag of 4.76 years in the N-hemisphere and 0.680 at a time lag of 5.45 years in the S-hemisphere. A qualitative forecast of maximal sunspot numbers in solar cycle 25 in the N- and S-hemisphere was obtained when the graphs of the polar fields were shifted forward in time relative to the sunspot numbers graphs by 4.76 and 5.45 years, respectively. This indicates that solar cycle 25 will be slightly stronger than the previous cycle. Using the absolute values of the mean polar magnetic fields during the 2 years interval just before the cycle minimum in the N- and S-hemispheres as precursors we found that predicted maximal sunspot numbers in the N- and S-hemisphere are 66 ± 17 and 83 ± 21, respectively. This quantitatively confirms that solar cycle 25 will be slightly (4–10%) more active than the previous one.

Based on the previously proposed steady-state 3D model of a solar facular knot, we have developed its modified version in which the solitary nature of the facular object is reflected: its magnetic field is sharply bounded in the radial direction. The facula temperature profile calculated for the steady state of such a magnetic structure is compared with the high-resolution filtergram taken in the photospheric TiO 7057 A line at Big Bear Solar Observatory on June 19, 2017, at the New Solar Telescope (with a 1.6-m aperture). The image shows two closely spaced very dark micropores with a diameter $${\sim}300$$ km each. The micropores are surrounded by a fan of thin, light, radially elongated fibrils resembling a sunspot penumbra. The theoretically calculated $$T$$ profile of the facular knot completely reproduces these morphological features of the object being modeled.

The radio astronomy group in the Indian Institute of Astrophysics (IIA) has been carrying out routine observations of radio emission from the solar corona at low frequencies (${\approx}$40-440MHz) at the Gauribidanur observatory, about 100km north of Bangalore. Since IIA has been performing regular observations of the solar photosphere and chromosphere using different optical telescopes in its Kodaikanal Solar Observatory (KSO) also, the possibilities of obtaining two-dimensional radio images of the solar chromosphere using low-cost instrumentation to supplement the optical observations are being explored. As a part of the exercise, recently the group had developed prototype instrumentation for interferometric observations of radio emission from the solar chromosphere at high frequencies (${\approx}$11.2GHz) using two commercial dish TV antennas. The hardware set-up and initial observations are presented., Published in Solar Physics, 11 pages, 6 figures

The longitudinal asymmetry of the photospheric magnetic field distribution is studied based on data from the Kitt Peak National Solar Observatory (synoptic maps for 1976–2016). Vector summation is used to weaken the effect of a stochastic component uniformly distributed along the longitude and to emphasize the stable nonaxisymmetric field component. Distributions of magnetic fields with different strength are considered: strong (B > 50 G), weak (B B > 5 G). It is shown that the longitudinal asymmetry in all the groups of fields varies in phase with the 11-year solar cycle. The asymmetry of the strong and medium fields varies in phase with the magnetic fluxes of these fields, whereas that of weak fields is in antiphase with the flux of the weak fields. The longitudinal distributions of the strong and medium magnetic fields resemble each other in shape: the distribution maximum is located at a longitude of ~180° during the ascent–maximum period of the solar cycle and at a longitude of ~0°/360° during the decrease–minimum period. Weak fields show the opposite picture: their distribution maximum is always located at the longitude of the strong and medium field minimum.

We present the results of the multi- wavelength study of the two-ribbon solar flare on July 19, 2000 in the active region NOAA 9087. The evo- lution and morphological properties of the flare pro- ductive active region have been analyzed. The active region was growing rapidly and showed a complex mul- tipolar magnetic field configuration. It was large, pro- ducing many events, including the flare under consid- eration. The 3N/M6.4 two-ribbon flare was a promi- nent, long duration event in the active region evolution. According to Solar Geophysical Data (SGD) the flare lasted 2.5 hours. The flare energy release took place in many sites of the active region. We used combination of data from space and ground based observatories for study. The hard X-ray (HXR) and soft X-ray (SXR) data were obtained at the Yohkoh Telescopes (HXT and SXT) and Geostationary Operational Environmental Satellite (GOES). The full- disk magnetograms and EUV-images were provided by the Solar and Heliospheric Observatory (SOHO) Michelson Doppler Imager (MDI) and Extreme ultra- violet Imaging Telescope (EIT). We used the H α filter- grams from the Meudon spectroheliograph and white light images of Big Bear Solar Observatory (BBSO). All the data show continuously evolving SXR, EUV and H α features during the flare. The HXR and the type III radio bursts were observed at the flare onset. The first H α flare kernels and the surge, connected with the filament eruption, were initiated near a large positive-polarity sunspot. The main bright kernels of the flare occurred at the centre of the active region near magnetic neutral line, after that the flare ribbons appeared along it. It was found that HXR coronal source was located along a magnetic polarity inversion line of the active region. EUV loop structures indicate the observational evidence of a magnetic reconnection during the main phase of the flare.

Results of studies of motions in a filament during its slow ascent and eruption based on spectral observations obtained at the Sayan Solar Observatory are presented. SDO/HMI data on the longitudinal magnetic field and SDO/AIA images in the EUV are also considered. Short-period (∼5 min) vertical oscillations of the filament as a whole were detected during its ascent. An acceleration of the rise of the filament was accompanied by the rupture of an orthogonal loop above the filament, which was observed in 193 A EUV images obtained with SDO/AIA over a long time preceding the event. Two hours before the partial eruption of the filament, SDO/HMI data indicate an increase in the magnetic flux by 2 × 1019 Mx at the footpoints of the loop. The emission from the loop rupture piont propagated toward the east and west along a neutral line, and brightenings were observed at the boundaries of the filament channel. Emission loops were visible in all SDO/AIA channels, testifying to strong heating of the filament plasma. During the rapid phase of the eruption, the filament moved with an acceleration ∼21 m/s2. Hα images show the filament splitting into fragments parallel to its axis during the eruption. The results of these studies of the eruption of the filament are in agreement with other results in the literature, and are supplemented by new observational facts. Vertical oscillations (∼5 min) of the filament as a whole are observed before the ascent phase. During the ascent phase, an interaction of the filament with a higher-lying coronal loop is observed.

We present the results of optical spectroscopy for 39 quasar candidates at photometric redshifts zphot ≳ 3 from the catalog by Khorunzhev et al. (2016) (K16). This is a catalog of quasar candidates and known type 1 quasars selected among the X-ray sources of the 3XMM-DR4 catalog of the XMM-Newton serendipitous survey. We have performed spectroscopy for new candidates at the 1.6-m AZT-33IK telescope of the Sayan Solar Observatory and the 6-m BTA telescope of the Special Astrophysical Observatory. Predominantly X-ray bright quasar candidates that could be used to construct the X-ray luminosity function at luminosities LX,2–10 > 1045 erg s−1 have been selected. The purity of the candidates from K16 with a high X-ray flux has turned out to be lower than the purity of the quasi-random sample investigated by us previously. We have estimated the observing efficiency of quasar candidates as a function of their photometric redshift.

The rotational profile of the Sun is considered to be one of the key inputs in a solar dynamo model. Hence, precise and long-term measurements of this quantity is important for our understanding of solar magnetism and its variability. In this study, we use the newly digitized, white light sunspot data (1923 -- 2011) from Kodaikanal Solar Observatory (KoSO) to derive the solar rotation profile. An automated correlation based sunspot tracking algorithm is implemented to measure the rotation parameters, $A$, the equatorial rotation rate and $B$, the latitudinal gradient. Our measurements of $A=14.381\pm0.004$ and $B=-2.72\pm0.04$ compare well with previous studies. In our analysis, we find that the bigger sunspots (with area $>$400~$��$Hem) rotate slower than the smaller ones. At the same time, we do not find any variation in the rotation rates between activity extremes, i.e solar maxima and minima. Lastly, we employ our tracking algorithm on the Michelson Doppler Imager (MDI) data and compare the MDI results with our KoSO values., 16 pages, 7 figures, accepted for publication in Solar Physics

Total solar eclipses (TSEs) provide a unique opportunity to quantify the properties of the K-corona (electrons), F-corona (dust) and E-corona (ions) continuously from the solar surface out to a few solar radii. We apply a novel inversion method to separate emission from the K- and F-corona continua using unpolarized total brightness (tB) observations from five 0.5 nm bandpasses acquired during the 2019 July 2 TSE between 529.5 nm and 788.4 nm. The wavelength dependence relative to the photosphere (i.e., color) of the F-corona itself is used to infer the tB of the K- and F-corona for each line-of-sight. We compare our K-corona emission results with the Mauna Loa Solar Observatory (MLSO) K-Cor polarized brightness (pB) observations from the day of the eclipse, and the forward modeled K-corona intensity from the Predictive Science Inc. (PSI) Magnetohydrodynamic (MHD) model prediction. Our results are generally consistent with previous work and match both the MLSO data and PSI-MHD predictions quite well, supporting the validity of our approach and of the PSI-MHD model. However, we find that the tB of the F-corona is higher than expected in the low corona, perhaps indicating that the F-corona is slightly polarized -- challenging the common assumption that the F-corona is entirely unpolarized., Comment: 25 pages, 9 figures, accepted for publication in ApJ

Flat-field reflects the non-uniformity of the photometric response at the focal plane of an instrument, which uses digital image sensors, such as Charge Coupled Device (CCD) and Complementary Metal-Oxide-Semiconductor (CMOS). This non-uniformity must be corrected before being used for scientific research. In this paper, we assess various candidate methods via simulation using available data so as to figure the in-flight flat-field calibration methodology for the Lyman-alpha Solar Telescope (LST). LST is one of the payloads for the Advanced Space-based Solar Observatory (ASO-S) mission and consists of three instruments: a White-light Solar Telescope (WST), a Solar Disk Imager (SDI) and a dual-waveband Solar Corona Imager (SCI). In our simulations, data from the Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) mission are used. Our results show that the normal KLL method is appropriate for in-flight flat-field calibration of WST and implementing a transmissive diffuser is applicable for SCI. For the in-flight flat-field calibration of SDI, we recommend the KLL method with off-pointing images with defocused resolution of around 18″, and use the local correlation tracking (LCT) algorithm instead of limb-fitting to determine the relative displacements between different images.

Solar prominences are structures of importance because of their role in polar field reversal. We study the long-term variation of the time latitude distribution of solar prominences in this article. To accomplish this, we primarily used the digitised disc-blocked Ca II K spectroheliograms as recorded from Kodaikanal Solar Observatory for the period of 1906 -- 2002. For improving the data statistics we included full disc H_alpha images from Meudon and Kanzelhohe Observatory which are available after 1980. We developed an automated technique to identify the latitudinal locations of prominences in daily images from all three datasets. Derived time-latitude distribution clearly depicted pole-ward migration of prominence structures for 10 cycles (15-24). Unlike previous studies, we separated the rate of pole-ward migration during on-set and near pole, using piece-wise linear fits. In most cases, we found acceleration in pole-ward migration with the change occurring near +/- 70 degree latitudes. The derived migration rates for such large number of solar cycles can provide important inputs towards understanding polar field build-up process., 21 pages, 8 figures, 3 tables, published in Earth and Space Science, January, 2020

Following the success of the first mission, the High-Resolution Coronal Imager (Hi-C) was launched for a third time (Hi-C 2.1) on 29th May 2018 from the White Sands Missile Range, NM, USA. On this occasion, 329 seconds of 17.2 nm data of target active region AR 12712 was captured with a cadence of ~4s, and a plate scale of 0.129''/pixel. Using data captured by Hi-C 2.1 and co-aligned observations from SDO/AIA 17.1 nm we investigate the widths of 49 coronal strands. We search for evidence of substructure within the strands that is not detected by AIA, and further consider whether these strands are fully resolved by Hi-C 2.1. With the aid of Multi-Scale Gaussian Normalization (MGN), strands from a region of low-emission that can only be visualized against the contrast of the darker, underlying moss are studied. A comparison is made between these low-emission strands with those from regions of higher emission within the target active region. It is found that Hi-C 2.1 can resolve individual strands as small as ~202km, though more typical strands widths seen are ~513km. For coronal strands within the region of low-emission, the most likely width is significantly narrower than the high-emission strands at ~388km. This places the low-emission coronal strands beneath the resolving capabilities of SDO/AIA, highlighting the need of a permanent solar observatory with the resolving power of Hi-C., 19 pages, 10 images, 3 tables

It is not yet fully understood how magnetohydrodynamic waves in the interior and atmosphere of the Sun are excited. Traditionally, turbulent convection in the interior is considered to be the source of wave excitation in the quiet Sun. Over the last few decades, acoustic events observed in the intergranular lanes in the photosphere have emerged as a strong candidate for a wave excitation source. Here we report our observations of wave excitation by a new type of event: rapidly changing granules. Our observations were carried out with the Fast Imaging Solar Spectrograph in the H$\alpha$ and Ca II 8542 $\unicode{xC5}$ lines and the TiO 7057 $\unicode{xC5}$ broadband filter imager of the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory. We identify granules in the internetwork region that undergo rapid dynamic changes such as collapse (event 1), fragmentation (event 2), or submergence (event 3). In the photospheric images, these granules become significantly darker than neighboring granules. Following the granules' rapid changes, transient oscillations are detected in the photospheric and chromospheric layers. In the case of event 1, the dominant period of the oscillations is close to 4.2 min in the photosphere and 3.8 min in the chromosphere. Moreover, in the Ca II$-$0.5 $\unicode{xC5}$ raster image, we observe repetitive brightenings in the location of the rapidly changing granules that are considered the manifestation of shock waves. Based on our results, we suggest that dynamic changes of granules can generate upward-propagating acoustic waves in the quiet Sun that ultimately develop into shocks., Comment: 11 pages, 13 figures, Accepted for publication in A&A

For the first time, a multiwavelength investigation of the oscillation dynamics in a solar facula from its birth to decay was carried out. We performed spectral observations of active region NOAA 12744 at the Horizontal Solar Telescope of the Sayan Solar Observatory in the H $\alpha $ , He i 10830 A, and Si i 10827 A lines. We used Solar Dynamics Observatory (SDO) line-of-sight magnetic field data and the 1600 A, 304 A, and 171 A UV channels. At the early stages of the facula evolution, we observed low-frequency (1 – 2 mHz) oscillations concentrated in its central part. In the lower solar atmosphere, this was registered in the intensity, line-of-sight velocity, and magnetic field signals. These frequencies were also observed in the transition region and corona (304 A and 171 A channels). At the maximum development phase of the facula evolution, the low frequency oscillations closely reproduced the coronal loop structures forming above the active region. At the decay phase, the spatial distributions of the observed frequencies resembled those found in and above the undisturbed chromospheric network. Our results indicate a direct relation of the low frequency oscillations observed in the lower solar atmosphere with the oscillations in the coronal loops, which happens probably through the loop footpoints.

In this study we present the old and new observational data concerning the problem of extreme magnetic fields (  5 kG) in the Sun's atmosphere. We emphasize that the upper limit of the intensity of the magnetic field in the solar atmosphere is unknown to date. Severny (1957) heuristically suggested that the magnetic fields in the sunspots could reach 50 kG. As for the observational data, at least three arguments in favor of the magnetic fields of the order of 104 G can be specified: (1) the dependence of the measured magnetic field on the factor geff2 of magnetosensitive lines (Gopasyuk et al., 1973; Lozitsky, 1980), (2) local extremums in splitting of bisectors in the profiles I ± V for lines with different Lande factors (Lozitsky, 1980; 2015) and (3) the reliable splitting of emission peaks in Fe I lines with very low Lande factors, about 0.01, in the spectra of powerful solar flares (Lozitsky, 1993; 1998). Theoretically, superstrong fields should have gigantic magnetic pressure and can exist only with a specific topology of field lines, apparently of a force-free type (Soloviev and Lozitsky, 1986). To further develop this problem, we are analyzing new observational data obtained with the NIRIS spectropolarimeter of the largest GST solar telescope of the Big Bear Solar Observatory (BBSO). Our observations relate to the active region NOAA 12673, which was the most flare-productive in the 24th cycle. Stokes-metric measurements are made in the FeI 15648.5 Е line with a signal-to-noise ratio of about 10-4. In this active region, superstrong magnetic field of 5.57 kG was discovered recently by Wang et al. (2018). An additional study of about 70 different places in this active region suggested that there were two types of places that can be conventionally called "typical" and "peculiar". In "typical" areas, the magnitude of the magnetic field in general is the greater, the less the intensity in the spectral continuum, and the maximum field here does not exceed 4 kG. All "peculiar" places correspond to positions with the highest intensity in the spectral continuum, and the magnetic field strength is here in the range of 3.0-5.7 kG. Notice, such strong magnetic fields were firstly discovered outside the sunspot umbra. The orientation of the magnetic field vector in "peculiar" places is close to the transversal, which is also atypical for "typical" regions and can reflect strong twisting of field lines.

We present evidences that anomalies in abundance of the chemical minor elements with the low first ionization potential (FIP) in the low corona of the late-type stars can be related with topology of the large-scale magnetic field. The solar observations show the increased abundances of the low FIP elements in compare to the abundances of the high FIP elements above the active regions and in the closed magnetic configurations of the low corona. Observational data of Ulysses and the Stanford Solar Observatory show high correlations between FIP effect of the solar wind, amount of the unsigned open magnetic flux, and the ratio between strength of the large-scale toroidal and poloidal magnetic field on the surface. The solar-type stars show the increase abundance of the low FIP elements relative to elements with the high FIP with the decrease of the large-scale poloidal magnetic field (and increase the toroidal component of the magnetic field). The branch of the fully convective stars demonstrates inversion of the FIP-effect. This inversion can be result from strong coronal activity, which is followed to the strong poloidal magnetic on these stars., Comment: 24 pages, 5 figures, accepted for publication on March 21, 2018 in Journal of Atmospheric and Solar-Terrestrial Physics (JASTP)

Low-degree solar p-mode observations from the long-lived Birmingham Solar Oscillations Network (BiSON) stretch back further than any other single helioseismic data set. Results from BiSON have suggested that the response of the mode frequency to solar activity levels may be different in different cycles. In order to check whether such changes can also be seen at higher degrees, we compare the response of medium-degree solar p-modes to activity levels across three solar cycles using data from Big Bear Solar Observatory (BBSO), Global Oscillation Network Group (GONG), Michelson Doppler Imager (MDI) and Helioseismic and Magnetic Imager (HMI), by examining the shifts in the mode frequencies and their sensitivity to solar activity levels. We compare these shifts and sensitivities with those from radial modes from BiSON. We find that the medium-degree data show small but significant systematic differences between the cycles, with solar cycle 24 showing a frequency shift about 10 per cent larger than cycle 23 for the same change in activity as determined by the 10.7 cm radio flux. This may support the idea that there have been changes in the magnetic properties of the shallow subsurface layers of the Sun that have the strongest influence on the frequency shifts., 6 pages, 3 figures, accepted by MNRAS 3rd July 2018

Evidence that the distribution of the abundances of admixtures with low first-ionization potentials (FIP 10 eV) in active regions and closed magnetic configurations in the lower corona. Observations with the ULYSSES spacecraft and at the Stanford Solar Observatory have revealed strong correlations between the manifestation of the FIP effect in the solar wind, the strength of the open magnetic flux (without regard to sign), and the ratio of the large-scale toroidal and poloidal magnetic fields at the solar surface. Analyses of observations of the Sun as a star show that the enhancement of the abundances of admixtures with low FIPs in the corona compared to their abundances in the photosphere (the FIP effect) is closely related to the solar-activity cycle and also with variations in the topology of the large-scale magnetic field. A possible mechanism for the relationship between the FIP effect and the spectral type of a star is discussed in the framework of solar–stellar analogies.

A simple algorithm has been developed to detect the onset of coronal mass ejections (CMEs), together with speed estimates, in near-real-time using linearly polarized white-light solar coronal images from the Mauna Loa Solar Observatory K-Cor telescope. Ground observations in the low corona can warn of CMEs well before they appear in space coronagraphs. The algorithm used is a variation on the Solar Eruptive Event Detection System (SEEDS) developed at George Mason University. It was tested against K-Cor data taken between 29 April 2014 and 20 February 2017, on days identified as containing CMEs. This resulted in testing of 139 days' worth of data containing 171 CMEs. The detection rate varied from close to 80% when solar activity was high, down to as low as 20–30% when activity was low. The difference in effectiveness with solar cycle is attributed to the relative prevalence of strong CMEs between active and quiet periods. There were also twelve false detections, leading to an average false detection rate of 8.6%. The K-Cor data were also compared with major Solar Energetic Particle (SEP) storms during this time period. There were three SEP events detected either at Earth or at one of the two STEREO spacecraft when K-Cor was observing during the relevant time period. The algorithm successfully generated alerts for two of these events, with lead times of 1–3 hours before the SEP onset at 1 AU. The third event was not detected by the automatic algorithm because of the unusually broad width in position angle.

We present the results of optical spectroscopy for 19 quasar candidates at photometric redshifts $\zphot \gtrsim 3$, \Nobs \ of which enter into the Khorunzhev et al.~(2016) catalog (K16). This is a catalog of quasar candidates and known type 1 quasars selected among the X-ray sources of the \textit{3XMM-DR4}catalog of the XMM-Newton serendipitous survey. We have performed spectroscopy for a quasi-random sample of new candidates at the 1.6-m \Azt \ telescope of the Sayan Solar Observatory and the 6-m BTA telescope of the Special Astrophysical Observatory. The spectra at \Azt \ were taken with the new low- and medium-resolution ADAM spectrograph that was produced and installed on the telescope in 2015. Fourteen of the \Nobs \ candidates actually have turned out to be quasars; 10 of them are at spectroscopic redshifts z > 3. The high purity of the sample of new candidates suggests that the purity of the entire K16 catalog of quasars is probably 70--80\%. One of the most distant ($\zspec=5.08$) optically bright ($i^\prime\lesssim 21$) quasars ever detected in X-ray surveys has been discovered., Comment: russian text in Pisma v astronomicheskii Zhurnal (2017) 43: 159

Observation of the main sunspot of AR11692 were carried out with the 1m New Vacuum Solar Telescope (NVST) located on the Fuxian Solar Observatory (FSO) with the Hα on 2013 march 13. The high cadence Hα intensity images show that running waves formed periodically within umbra, and propagate outwards with the shape of partial arcs. The running waves run across the umbra-penumbra boundary and disappear at the outer edge of the penumbra eventually. Confusingly, the period of the running waves within umbra is half of that within penumbra, i.e., the former is a typical 3-min oscillation with a period of 156s and the latter is typical 5-min oscillation with a period of 312s. To investigate the nature of the umbral and penumbral oscillations, we selected 300 sample points from the umbra and 150 sample points from the penumbra, respectively, of the sunspot to analyze the distributions of the extreme values related to the intensity profiles of the sample points. It is found that there are significant difference between the distributions of the extreme values related to umbral and penumbral oscillation intensity profiles. When a possible steady solar radiation, which was replaced by the average of troughs of the umbral oscillation intensity profile, was filtered from the umbral oscillation intensity, the distribution of the trough values is a normal distribution symmetrical about zero, the distribution of the crest values is a skewed distribution. When another possible steady solar radiation, which was replaced by the average of the penumbral oscillation intensity profile, was filtered from the penumbral oscillation intensity, while the distribution of the crest values and trough values were a pair of skewed distribution symmetrical about zero. According to the statistical characteristic of umbral and penumbral oscillations, an interpretation seemingly no having physical meaning was used to explain the statistical results. The possible interpretation for the phenomenon is that the pair of oscillations with different period in the intensity are produced by a same wave with a basis oscillation period of 312s. The basis wave can be expressed as Z ( x , y , t ) = A ( x , y ) c o s ( ω t + θ ) , where ω = ( 2 π ) / 312 is the angular frequency of the wave. In the umbra, the intensity due to the wave is proportional to the square of the displacement of the wave, I U = a 2 Z 2 = a 2 2 A 2 ( x , y ) [ 1 + c o s ( 2 ω t + 2 θ ) ] , while the intensity in the penumbra due to the wave is proportional to the basis wave, I P = a 1 Z = A ( x , y ) c o s ( ω t + θ ) . Correspondingly, the period of the intensity within umbra is T U = 156 s , while the period of the intensity within penumbra is T P = 312 s .

In this paper, we present a study of an M2.2 class solar flare of 26 November 2000 from NOAA AR 9236. The flare was well observed by various ground based observatories (ARIES, Learmonths Solar Observatory) and space borne instruments (SOHO, HXRS, GOES) in time interval between 02:30 UT to 04:00 UT. The flare started with long arc-shape outer flare ribbon. Afterwards the main flare starts with two main ribbons. Initially the outer ribbons start to expand with an average speed ($\sim$ 20 km s$^{-1}$) and later it shows contraction. The flare was associated with partial halo coronal mass ejection (CMEs) which has average speed of 495 km s$^{-1}$. The SOHO/MDI observations show that the active region was in quadrupolar magnetic configuration. The flux cancellation was observed before the flare onset close to flare site. Our analysis indicate the flare was initiated by the magnetic breakout mechanism., 15 pages, 5 figures

Using the H$\alpha$ data from the New Vacuum Solar Telescope (NVST) at the Fuxian Solar Observatory together with multi-wavelength images and magnetograms obtained by Solar Dynamics Observatory (SDO), we study the detailed process of three homologous confined flares in active-region (AR) NOAA 11861 on 2013 October 12. All of the three flares occurred at same location, with similar morphologies and comparable class. Through analyzing the evolution of magnetic field and flow field, we found an emergence of magnetic flux and a strong shearing motion between two opposite polarities near the following sunspot. The magnetic flux and the average transverse field strength exhibited a decrease before each eruption and reached the lowest point at the onset of each eruption. By calculating the shearing and the emergence energy in the photosphere, we found that the integral of energy injected from the photosphere, for a few hours, could provide enough energy for the flares. The reconnection between different loops was observed in H$\alpha$ images during the occurrence of each flare. These results suggest that the emerging magnetic flux and the shearing motion in the photosphere can inject the energy to the sheared magnetic loops and the energy finally was released via magnetic reconnection to power the solar flares., Comment: 12 pages, 7 figures, accepted for publication in ApJ

Progress in our understanding of the solar corona requires that the results of advanced magnetohydrodynamic models driven by measured magnetic fields, and particularly the underlying heating models, be thoroughly compared with coronal observations. The comparison has so far mainly concerned the global morphology of the corona, synthetic images calculated from the models being compared with observed images. We go one step further by performing detailed quantitative comparisons between the calculated polarized radiance $pB$ using the three-dimensional electron density produced by MHD models and well calibrated polarized images obtained by the Large Angle Spectrometric Coronagraph LASCO-C2 coronagraph complemented by ground-based images when available from the Mauna Loa Solar Observatory Mark IV and K-Cor instruments to extend the comparison to the inner coronal region 1.0 – 2.5 $\mbox{R}_{\odot }$, which is inaccessible to C2. We take advantage of the high-resolution and high-quality MHD predictions performed for several solar eclipses (1 August 2008, 11 July 2010, 13 November 2012, and 21 August 2017) and for the first perihelion passage of the Parker Solar Probe (5 November 2018) using two different three-dimensional MHD models relying on either a thermodynamic or a wave-turbulence-driven methodologies to heat the corona. Both models are generally able to match the observed structure and photometry of the corona albeit with various degrees of fidelity for which there is no obvious explanation. However, two limitations emerge, the complexity of coronae of the maximum type and the time lapse between the completion of the magnetograph measurements and the prediction.

The extended minimum of Solar Cycle 23, the extremely quiet solar-wind conditions prevailing, and the mini-maximum of Solar Cycle 24 drew global attention and many authors have since attempted to predict the amplitude of the upcoming Solar Cycle 25, which is predicted to be the third successive weak cycle; it is a unique opportunity to probe the Sun during such quiet periods. Earlier work has established a steady decline, over two decades, in solar photospheric fields at latitudes above $45^{\circ}$ and a similar decline in solar-wind micro-turbulence levels as measured by interplanetary scintillation (IPS) observations. However, the relation between the photospheric magnetic fields and those in the low corona/solar-wind are not straightforward. Therefore, in the present article, we have used potential-field source-surface (PFSS) extrapolations to deduce global magnetic-fields using synoptic magnetograms observed with National Solar Observatory (NSO), Kitt Peak, USA (NSO/KP) and Solar Optical Long-term Investigation of the Sun (NSO/SOLIS) instruments during 1975-2018. Furthermore, we have measured the normalized scintillation index [m] using the IPS observations carried out at the Institute of Space Earth Environment Research (ISEE), Japan during 1983-2017. From these observations, we have found that, since the mid-1990s, the magnetic-field over different latitudes at 2.5 $\rm R_{\odot}$ and 10 $\rm R_{\odot}$(extrapolated using PFSS method) has decreased by $\approx 11.3-22.2 \%$. In phase with the declining magnetic-fields, the quantity m also declined by $\approx 23.6 \%$. These observations emphasize the inter-relationship between the global magnetic-field and various turbulence parameters in the solar corona and solar wind., Comment: Accepted for publication in Solar Physics, 16 pages, 5 Figures, 1 Table

The Sun's polar magnetic fields change their polarity near the maximum of sunspot activity. We analyzed the polarity reversal epochs in Solar Cycles 21 to 24. There was a triple reversal in the N-hemisphere in Solar Cycle 24 and single reversals in the rest of cases. Epochs of the polarity reversal from measurements of the Wilcox Solar Observatory (WSO) are compared with ones when the reversals were completed in the N- and S-hemispheres. The reversal times were compared with hemispherical sunspot activity and with the Heliospheric Current Sheet (HCS) tilts, too. It was found that reversals occurred at the epoch of the sunspot activity maximum in Cycles 21 and 23, and after the corresponding maxima in Cycles 22 and 24, and one-two years after maximal HCS tilts calculated in WSO. Reversals in Solar Cycles 21, 22, 23, and 24 were completed first in the N-hemisphere and then in the S-hemisphere after 0.6, 1.1, 0.7, and 0.9 years, respectively. The polarity inversion in the near-polar latitude range \pm(55-90)^\circ occurred from 0.5 to 2.0 years earlier that the times when the reversals were completed in corresponding hemisphere. Using the maximal smoothed WSO polar field as precursor we estimated that amplitude of Solar Cycle 25 will reach 116 \pm 12 in values of smoothed monthly sunspot numbers and will be comparable with the current cycle amplitude equaled to 116.4., 12 pages with 6 figures and 1 table

Magnetic flux ropes (MFRs) are important physical features closely related to solar eruptive activities with potential space weather consequences. Studying MFRs in the low solar atmosphere can shed light on their origin and subsequent magnetic structural evolution. In recent years, observations of solar photosphere and chromosphere reached a spatial resolution of 0.1 to 0.2 arcsec with the operation of meter class ground-based telescopes, such as the 1.6m Goode Solar Telescope at Big Bear Solar Observatory and the 1m New Vacuum Solar Telescope at Yunnan Observatory. The obtained chromospheric Halpha filtergrams with the highest resolution thus far have revealed detailed properties of MFRs before and during eruptions, and the observed pre-eruption structures of MFRs are well consistent with those demonstrated by nonlinear force-free field extrapolations. There are also evidences that MFRs may exist in the photosphere. The magnetic channel structure, with multiple polarity inversions and only discernible in high-resolution magnetograph observations, may be a signature of photospheric MFRs. These MFRs are likely formed below the surface due to motions in the convection zone and appear in the photosphere through flux emergence. Triggering of some solar eruptions is associated with an enhancing twist in the low-atmospheric MFRs.

Over the solar-activity cycle, there are extended periods where significant discrepancies occur between the spacecraft-observed total (unsigned) open magnetic flux and that determined from coronal models. In this article, the total open heliospheric magnetic flux is computed using two different methods and then compared with results obtained from in-situ interplanetary magnetic-field observations. The first method uses two different types of photospheric magnetic-field maps as input to the Wang Sheeley Arge (WSA) model: i) traditional Carrington or diachronic maps, and ii) Air Force Data Assimilative Photospheric Flux Transport model synchronic maps. The second method uses observationally derived helium and extreme-ultraviolet coronal-hole maps overlaid on the same magnetic-field maps in order to compute total open magnetic flux. The diachronic and synchronic maps are both constructed using magnetograms from the same source, namely the National Solar Observatory Kitt Peak Vacuum Telescope and Vector Spectromagnetograph. The results of this work show that the total open flux obtained from observationally derived coronal holes agrees remarkably well with that derived from WSA, especially near solar minimum. This suggests that, on average, coronal models capture well the observed large-scale coronal-hole structure over most of the solar cycle. Both methods show considerable deviations from total open flux deduced from spacecraft data, especially near solar maximum, pointing to something other than poorly determined coronal-hole area specification as the source of these discrepancies., 20 pages, 6 figures

We compared the long-term variation (1992–2017) in solar polar brightening observed with the Nobeyama Radioheliograph, the polar solar-wind velocity with interplanetary scintillation observations at the Institute for Space-Earth Environmental Research, and the coronal-hole distribution computed by potential-field calculations of the solar corona using synoptic magnetogram data obtained at the National Solar Observatory/Kitt Peak. First, by comparing the solar-wind velocity [V] and the brightness temperature [Tb] in the polar region, we found good correlation coefficients (CCs) between V and Tb in the polar regions, CC = 0.91 (0.83) for the northern (southern) polar region, and we obtained the V–Tb relationship as V=12.6(Tb−10,667)^1/2+432. We also confirmed that the CC of V–Tb is higher than those of V–B and V–B/f, where B and f are the polar magnetic-field strength and magnetic-flux expansion rate, respectively. These results indicate that Tb is a more direct parameter than B or B/f for expressing solar-wind velocity. Next, we analyzed the long-term variation of the polar brightening and its relation to the area of the polar coronal hole [A]. As a result, we found that the polar brightening matches the probability distribution of the predicted coronal hole and that the CC between Tb and A is remarkably high, CC = 0.97. This result indicates that the polar brightening is strongly coupled to the size of the polar coronal hole. Therefore, the reasonable correlation of V – Tb is explained by V – A. In addition, by considering the anti-correlation between A and f found in a previous study, we suggest that the V – Tb relationship is another expression of the Wang–Sheeley relationship (V – 1/f) in the polar regions., ファイル公開：2020/03/01

Over past 51 years (1968–2018) the general magnetic field of the Sun was measured nearly each day by the Crimean Astrophysical Observatory, the Wilcox Solar Observatory and five others. It is shown that the annual variation of this field (longitudinal component), thought to be caused by the inclination of the Sun’s axis to ecliptic, is splitted into two components with periods 0.954(3) years and 1.034(4) years (with mean amplitudes $\approx 0.044$ G). But while the first one agrees well with the expected period 0.957(4) years (caused by the 11-year polar field reversals and coupled to the yearly projection effect), the second one is shifted relative to its theoretical value, 1.047(4) years, by $\Delta = 0.013(5)$ years (99% confidence). The beat period of the two observed components, 12.3(7) years, agrees well with the Jovian period 11.9 years, being close also to the length of the 11-year cycle. Since the modern astronomy rejects a planetary influence on the Sun, the origin of both the 1.034-year periodicity and the shift $\Delta $ remains to be mysterious.

Prior to the availability of digital cameras, the solar observational images are typically recorded on films, and the information such as date and time were stamped in the same frames on film. It is significant to extract the time stamp information on the film so that the researchers can efficiently use the image data. This paper introduces an intelligent method for extracting time stamp information, namely, the Convolutional Neural Network (CNN), which is an algorithm in deep learning of multilayer neural network structures and can identify time stamp character in the scanned solar images. We carry out the time stamp decoding for the digitized data from the National Solar Observatory from 1963 to 2003. The experimental results show that the method is accurate and quick for this application. We finish the time stamp information extraction for more than 7 million images with the accuracy of 98\%., 14 pages, 12 figures, 5 tables, accepted for publication in Advances in Astronomy

We use the synoptic maps of the photospheric magnetic field observed at Wilcox Solar Observatory, Mount Wilson Observatory, Kitt Peak, SOHO/MDI, SOLIS/VSM, and SDO/HMI to study the distribution of weak photospheric magnetic field values in 1974–2018. We fit the histogram distribution of weak field values for each synoptic map of the six data sets separately with a parameterized Gaussian function in order to calculate the possible shift (to be called here the weak-field asymmetry) of the maximum of the Gaussian distribution from zero. We estimate the statistical significance of the weak-field asymmetry for each rotation. We also calculate several versions of lower-resolution synoptic maps from the high-resolution maps and calculate their rotational weak-field asymmetries. We find that the weak-field asymmetries increase with decreasing map resolution. A very large fraction of weak-field asymmetries are statistically significant, with the fraction of significant weak-field asymmetries increasing with decreasing resolution. Significant weak-field asymmetries of high- and low-resolution maps mainly occur at the same times and have the same sign. Weak-field asymmetries for the different data sets and resolutions vary quite similarly in time, and their mutual correlations are very high, especially for low-resolution maps. These results give strong evidence for weak-field asymmetries reflecting a real feature of weak field values, which is best seen in medium- and low-resolution synoptic maps and is most likely related to the supergranulation scale of the photospheric field.

In the highly dynamic chromosphere, there exist many kinds of small-scale activities, such as spicules, surges, and Ellerman bombs. Here, we report the discovery of a new phenomenon in the chromosphere observed with the New Vacuum Solar Telescope at the Fuxian Solar Observatory. In the high tempo-spatial resolution H$\alpha$ images, some dark or bright structures are found to fly along the curved trajectory, looking like cannonballs. Their average size, mass, and velocity are about 1.5 $\times$ 10$^{9}$ km$^{3}$, 1.5 $\times$ 10$^{8}$ kg, and 56 km s$^{-1}$, respectively. In the simultaneous (extreme-)ultraviolet images obtained by the Solar Dynamics Observatory, these cannonballs appear as brighter features compared to the surrounding area, implying that there exists some kind of heating during this process. The photospheric magnetograms show the magnetic flux emergence and interaction with the pre-existing fields. These observations reveal that the cannonballs are chromospheric material blobs launched due to the magnetic reconnection between emerging magnetic flux and the pre-existing loops., Comment: Accepted for publication in ApJL

The umbral oscillations of velocity are commonly observed in the chromosphere of a sunspot. Their sources are considered to be either the external p-mode driving or the internal excitation by magnetoconvection. Even though the possibility of the p-mode driving has been often considered, the internal excitation has been rarely investigated. We report the identification of the oscillation patterns that may be closely related to the events of internal excitation from the observations of velocity oscillations in the temperature minimum region of two sunspots. The velocities were determined from the spectral data of the Fe I 5435 A line, a magnetically insensitive line, taken with the Fast Imaging Solar Spectrograph of the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory. As a result, we identified 4 oscillation patterns of 2.0 * 10^3 km coherent size that were clearly identified for about 7.9 minutes with oscillation amplitude of 9.3 * 10^-2 km/s. The power of the oscillations in these centers was concentrated in the 3 minute band. All the oscillation centers were located above the umbral dots undergoing noticeable morphological and dynamical changes that may be regarded as an observable signature of small-scale magnetoconvection inside the umbrae. Our results support the notion that magnetoconvection associated with umbral dots inside sunspots can drive the 3 minute umbral oscillations., Comment: Accepted for publication in the Astrophysical Journal

Solar radio spikes are narrowband, short duration radio bursts. They are excited by the energetic electrons accelerated during small scale magnetic reconnections. Spikes play an important role in diagnosing magnetic reconnections and studying electron accelerations. In this paper, the solar radio spikes observed by the Chashan Solar Observatory (CSO) spectrograph combined with observations from the Solar Dynamics Observatory (SDO) are used to study the properties of spikes with harmonics. The CSO data show that the central frequency ratio of the third to the second harmonic is $1.35 \pm 0.01$ and the third harmonic has a larger absolute and relative bandwidth, but a shorter duration than the second one. By studying the correlation between light curves of the solar radio spike and those of bright points at different Extreme UltraViolet (EUV) passbands, the best associated EUV bright point and passbands are determined. The spike source properties are discussed based on the extrapolated magnetic field around the associated EUV bright point.

We present the formation and eruption of a sigmoidal filament driven by rotating network magnetic fields (RNFs) near the center of the solar disk, which was observed by the 1 m aperture New Vacuum Solar Telescope at the Fuxian Solar Observatory on 2018 July 12. Counterclockwise RNFs twist two small-scale filaments at their northeastern foot-point region, giving a rotation of nearly 200° within about 140 minutes. The motion of the RNF has a tendency to accelerate at first and then decelerate obviously, as the average rotation speed increased from 10 to 150° hr−1, and then slowed down to 50° hr−1. Coalescence then occurs between filaments F1 and F2. Meanwhile the fine structures in the southwestern region of the filament was involved in another interaction of coalescence. The subsequent EUV brightening due to plasma heating is observed in the two interaction regions. These interacting structures, including F1, F2 and the fine structures in the southwestern region, eventually evolve into a larger-scale sigmoidal filament twisted in the same direction as the RNFs gave. The twist of the sigmoidal filament has exceeded 4π and the filament finally erupted. The motion of the sigmoidal filament remains uniform until a nearby jet collides, causing the filament to erupt faster. These results provide evidence that RNF plays an important role in the formation and eruption of the sigmoidal filament. The phenomena also suggests that the kink instability is the trigger mechanism for the filament eruption.

Context. Weak magnetic field elements make a dominant contribution to the total magnetic field on the solar surface. Even so, little is known of their long-term occurrence. Aims. We study the long-term spatial–temporal evolution of the weak-field shift and skewness of the distribution of photospheric magnetic field values during solar cycles 21−24 in order to clarify the role and relation of the weak field values to the overall magnetic field evolution. Methods. We used Wilcox Solar Observatory (WSO) and the Synoptic Optical Long-term Investigations of the Sun Vector SpectroMagnetograph synoptic maps to calculate weak-field shifts for each latitude bin of each synoptic map, and thereby constructed a time–latitude butterfly diagram for shifts. We also calculated butterfly diagrams for skewness for all field values and for weak field values only. Results. The weak-field shifts and (full-field) skewness depict a similar spatial–temporal solar cycle evolution to that of the large-scale surface magnetic field. The field distribution has a systematic non-zero weak-field shift and a large skewness already at (and after) the emergence of the active region, even at the highest resolution. We find evidence for coalescence of opposite-polarity fields during the surge evolution. This is clearly more effective at the supergranulation scale. However, a similar dependence of magnetic field coalescence on spatial resolution was not found in the unipolar regions around the poles. Conclusions. Our results give evidence for the preference of even the weakest field elements toward the prevailing magnetic polarity since the emergence of an active region, and for a systematic coalescence of stronger magnetic fields of opposite polarities to produce weak fields during surge evolution and at the poles. We also find that the supergranulation process is reduced or turned off in the unipolar regions around the poles. These observations improve the understanding not only of the development of the weakest magnetic field elements, but also of the dynamics of magnetic fields at large, and even of processes below the solar surface.

Results of analysis of multi-scale and turbulent properties of observed photospheric granulation patterns in undisturbed solar photosphere are presented. Data were obtained with the New Solar Telescope at Big Bear Solar observatory. Different types of magnetic environment were explored: a coronal hole (CH) area, a quiet sun (QS) intranetwork area, a QS/network area, and an area with small pores. The property of multifractality was revealed for granulation patterns in all environments on scales below 600 km. The degree of multifractality tends to be stronger as the magnetic environment becomes weaker. Analysis of turbulent diffusion on scales less than 1000–2000 km revealed the regime of super-diffusivity for all data sets. Super-diffusion becomes stronger from the QS/network to the QS/intranetwork to the CH. Both multifractality and super-diffusivity on very small scales are associated with the fast turbulent dynamo action. The results show that the most favorable conditions for the fast turbulent dynamo are met outside the network, inside vast areas of weakest magnetic fields, which supports the idea of nonlocal, deep turbulent dynamo.

We report on the co-existence of longitudinal and transverse oscillations in an active filament. On March 15$^{th}$ 2013, a M1.1 class flare was observed in the active region AR 11692. A CME was found to be associated with the flare. {The CME generated a shock wave that triggered the oscillations in a nearby filament}, situated at the south-west of the active region as observed from National Solar Observatory (NSO)\textit{Global Oscillation Network Group}(GONG) H$\alpha$ images. In this work we report the longitudinal oscillations in the two ends of the filament, co-existing with the transverse oscillations. We propose a scenario in which {an} incoming shock wave hits the filament obliquely and triggers both longitudinal and transverse oscillations. Using the observed parameters, we estimate the lower limit of the magnetic field strength. We use simple pendulum model with gravity as the restoring force to estimate the radius of curvature. We also calculate the mass accretion rate which causes the filament motions to damp quite fast., Comment: Accepted for publication in Solar Physics

Photospheric magnetic fields are studied using synoptic maps from 1976 to 2003 produced at the National Solar Observatory, Kitt Peak (NSO/KP). Synoptic maps were averaged over the time interval of nearly three solar cycles (Solar Cycles 21-23). The change in the latitudinal distribution was considered for the following groups of magnetic field values: B = 0-5 G, B = 5-15 G, B = 15-50 G, and B>50 G. Magnetic fields in each of the above groups have common latitudinal distribution features, while for different field groups these features are significantly different. Each of the groups is closely related to a certain manifestation of solar activity. Strong magnetic fields are connected with two types of solar activity: active regions (magnetic fields B>15 G)that are related to sunspot zones, and polar faculae (magnetic fields 50 G > B > 15 G) that occupy latitudes around 65$^\circ$-75$^\circ$. Fields from 5 to 15 G occupy the polar regions and are connected with polar coronal holes (the global solar dipole). Fields of B, 11 pages, 8 figures

The Doppler motions in a filament and the underlying photosphere over the several days before its eruption are analyzed. A large filament in the northern hemisphere near the central meridian observed from August 31-September 2, 2014 erupted on September 2, 2014. The filament lost the bulk of its mass as a result of its eruption, and the process of its reconstruction had begun a day later. Observations of this filament in a spectral range encompassing the Hβ λ 486.1 nm (chromospheric) and Fe I λ 485.9 nm (photospheric) lines were carried out on the Horizontal Solar Telescope of the Sayan Solar Observatory on August 31-September 2, 2014. Analysis of the Doppler motions in and beneath the filament yielded the following results. Strong rotational motions were present in the filament over a prolonged period (the entire three days of observations). The coincidence of the steady-state motions of the photosphere and filament was disrupted at the moment of destabilization of the filament by the emergence of new magnetic flux. Short-period (about five-minute) photospheric oscillationswith a train-like character arose in filament from time to time several hours before the eruption. Large segments underwent nearly vertical oscillations in the initial phase of the ascent of the filament.

Interhelioprobe (IHP), an analogue to the ESA Solar Orbiter, is the prospective Russian space solar observatory intended for in-situ and remote sensing investigations of the Sun and the inner heliosphere from a heliocentric orbit with the perihelion of about 60 solar radii. One of several instruments on board will be the Bragg crystal spectrometer ChemiX which will measure X-ray spectra from solar corona structures. Analysis of the spectra will allow the determination of the elemental composition of plasma in hot coronal sources like flares and active regions. ChemiX is under development at the Wroclaw Solar Physics Division of the Polish Academy of Sciences Space Research Centre in collaboration with an international team (see the co-author list). This paper gives an overview of the ChemiX scientific goals and design preparatory to phase B of the instrument development.

By use of the high-resolution spectral data and the broadband imaging obtained with the Goode Solar Telescope at the Big Bear Solar Observatory on 2013 June 6, the spectra of three typical photospheric bright points (PBPs) have been analyzed. Based on the H$\alpha$ and Ca II 8542 \AA line profiles, as well as the TiO continuum emission, for the first time, the non-LTE semi-empirical atmospheric models for the PBPs are computed. The attractive characteristic is the temperature enhancement in the lower photosphere. The temperature enhancement is about 200 -- 500 K at the same column mass density as in the atmospheric model of the quiet-Sun. The total excess radiative energy of a typical PBP is estimated to be 1$\times$10$^{27}$ - 2$\times$10$^{27}$ ergs, which can be regarded as the lower limit energy of the PBPs. The radiation flux in the visible continuum for the PBPs is about 5.5$\times$10$^{10}$ ergs cm$^{-2}$ s$^{-1}$. Our result also indicates that the temperature in the atmosphere above PBPs is close to that of a plage. It gives a clear evidence that PBPs may contribute significantly to the heating of the plage atmosphere. Using our semi-empirical atmospheric models, we estimate self-consistently the average magnetic flux density $B$ in the PBPs. It is shown that the maximum value is about one kilo-Gauss, and it decreases towards both higher and lower layers, reminding us of the structure of a flux tube between photospheric granules., Comment: 18 pages, 10 figures, 1 tables. Accepted to ApJ

We examine Big Bear Solar Observatory (BBSO) Goode Solar Telescope (GST) high-spatial resolution (0''.06), high-cadence (3.45 s), H-alpha-0.8 Angstrom images of central-disk solar spicules, using data of Samanta et al. (2019). We compare with coronal-jet chromospheric-component observations of Sterling et al. (2010a). Morphologically, bursts of spicules, referred to as "enhanced spicular activities" by Samanta et al. (2019), appear as scaled-down versions of the jet's chromospheric component. Both the jet and the enhanced spicular activities appear as chromospheric-material strands, undergoing twisting-type motions of ~20---50 km/s in the jet and ~20---30 km/s in the enhanced spicular activities. Presumably, the jet resulted from a minifilament-carrying magnetic eruption. For two enhanced spicular activities that we examine in detail, we find tentative candidates for corresponding erupting microfilaments, but not expected corresponding base brightenings. Nonetheless, the enhanced-spicular-activities' interacting mixed-polarity base fields, frequent-apparent-twisting motions, and morphological similarities to the coronal jet's chromospheric-temperature component, suggest that erupting microfilaments might drive the enhanced spicular activities but be hard to detect, perhaps due to H-alpha opacity. Degrading the BBSO/GST-image resolution with a 1''.0-FWHM smoothing function yields enhanced spicular activities resembling the "classical spicules" described by, e.g., Beckers (1968). Thus, a microfilament eruption might be the fundamental driver of many spicules, just as a minifilament eruption is the fundamental driver of many coronal jets. Similarly, a 0".5-FWHM smoothing renders some enhanced spicular activities to resemble previously-reported "twinned" spicules, while the full-resolution features might account for spicules sometimes appearing as 2D-sheet-like structures.

The Advanced Space-based Solar Observatory (ASO-S) mission aims to explore two most spectacular eruptions in the Sun: solar flares and coronal mass ejections (CMEs), and their magnetism. For the studies of CMEs, the payload Lyman-alpha Solar Telescope (LST) has been proposed. It includes a traditional white-light coronagraph and a Lyman-alpha coronagraph which opens a new window to CME observations. Polarization measurements taken by white-light coronagraphs are crucial to derive fundamental physical parameters of CMEs. To make such measurements, there are two options of Stokes polarimeter which have been used by existing white-light coronagraphs for space missions. One uses a single or triple linear polarizers, the other involves both a half-wave plate and a linear polarizer. We find that the former option subjects to less uncertainty in the derived Stokes vector propagated from detector noise. The latter option involves two plates which are prone to internal reflections and may have a reduced transmission factor. Therefore, the former option is adopted as our Stokes polarimeter scheme for LST. Based on the parameters of the intended linear polarizer(s) colorPol provided by CODIXX and the half-wave plate 2-APW-L2-012C by Altechna, it is further shown that the imperfect maximum transmittance of the polarizer significantly increases the variance amplification of Stokes vector by at least about 50% when compared with the ideal case. The relative errors of Stokes vector caused by the imperfection of colorPol polarizer and the uncertainty due to the polarizer assembling in the telescope are estimated to be about 5%. Among the considered parameters, we find that the dominant error comes from the uncertainty in the maximum transmittance of the polarizer., 16 pages, 5 figure, Research in Astronomy and Astrophysics, accepted

Aims: To investigate solar polar fields during cycle 24, using measurements of solar magnetic fields in the latitude range 55 - 90 degree and 78 - 90 degree, to report a prolonged and unusual hemispheric asymmetry in the polar field reversal pattern in solar cycle 24. Methods: This study was carried out using medium resolution line-of-sight synoptic magnetograms from the magnetic database of the National Solar Observatory at Kitt Peak (NSO/KP), USA for the period between February 1975 and October 2017, covering solar cycles 21-24 and high-resolution line-of-sight synoptic magnetograms from the Michaelson Doppler Imager instrument onboard the Solar Heliospheric Observatory. Synoptic magnetograms using radial measurements from the Heliospheric Magnetic Imager instrument onboard the Solar Dynamics Observatory, covering solar cycle 23 and 24, were also used. Results: We show that the Southern solar hemisphere unambiguously reversed polarity in mid-2013 while the reversal in the field in the Northern solar hemisphere started as early as June 2012, was followed by a sustained period of near-zero field strength lasting until the end of 2014, after which the field began to show a clear rise from its near-zero value. While this study compliments a similar study carried out using microwave brightness measurements (Gopalswamy et al. 2016) which claimed that the field reversal process in cycle 24 was completed by the end of 2015, our results show that the field reversal in cycle 24 was completed earlier i.e. in late 2014. Signatures of this unusual field reversal pattern were also clearly identifiable in the solar wind, using our observations of interplanetary scintillation at 327 MHz which supported our magnetic field observations and confirmed that the field reversal process was completed at the end of 2014., 11 pages, 7 figures, Under review in A&A

This paper presents the latest observations from the newly-built solar radio spectrograph at the \emph{Chashan Solar Observatory}. On July 18 2016, the spectrograph records a solar spike burst event, which has several episodes showing harmonic structures, with the second, third, and fourth harmonics. The lower harmonic radio spike emissions are observed later than the higher harmonic bands, and the temporal delay of the second (third) harmonic relative to the fourth harmonic is about 30\ --\ 40 (10) ms. Based on the electron cyclotron maser emission mechanism, we analyze possible causes of the temporal delay and further infer relevant coronal parameters, such as the magnetic field strength and the electron density at the radio source., Comment: 17 pages,6 figures

Polarity imbalance of the photospheric magnetic field was studied using synoptic maps of NSO Kitt Peak (1976-2016). Imbalance of positive and negative fluxes was considered for the fields with strength B>50 G in the sunspot zone (5 deg - 40 deg) and for the fields with strength B, 22 pages, 10 Postscript figures, uses solarphysics.cls, spr-sola-addons.sty