No abstract available

[en] A procedure is described that should allow photographic recording of the complex amplitude of photospheric oscillations as a function of the position on the solar disk. Underlying acoustic sources might be visualized by observing such an hologram under coherent illumination

[en] A sunspot photograph having resolution approaching 0''.2 is presented. It reveals that the photospheric penumbra has the following characteristics

[en] Measurements of the proper motions of young bipolar sunspot groups show that these groups rotate faster than the surrounding photosphere. The results of time series analysis carried out on the irradiance records of the SMM/ACRIM radiometer and on the projected areas of the young, active sunspot groups showed a period near to 24 days in 1980, the year of the solar maximum. The main period in the projected areas of the old sunspot groups was 28 days, which corresponded to the mean photospheric rotation. The faster proper motion of the young sunspot groups as well as the 24 days periodicity of the young active spot areas might indicate that the young sunspots are connected to the deeper regions of the Sun which rotate faster than the photosphere. Thus, the sunspot groups in the early stage of their life would be an indicator of rotation of the deeper layers of the Sun. (author). 4 figs., 2 tabs., 20 refs

[en] We observe that intergranular jets, originating in the intergranular space surrounding individual granules, tend to be associated with granular fragmentation, in particular, with the formation and evolution of a bright granular lane (BGL) within individual granules. The BGLs have recently been identified as vortex tubes by Steiner et al. We further discover the development of a well-defined bright grain located between the BGL and the dark intergranular lane to which it is connected. Signatures of a BGL may reach the lower chromosphere and can be detected in off-band Hα images. Simulations also indicate that vortex tubes are frequently associated with small-scale magnetic fields. We speculate that the intergranular jets detected in the New Solar Telescope (NST) data may result from the interaction between the turbulent small-scale fields associated with the vortex tube and the larger-scale fields existing in the intergranular lanes. The intergranular jets are much smaller and weaker than all previously known jet-like events. At the same time, they appear much more numerous than the larger events, leading us to the speculation that the total energy release and mass transport by these tiny events may not be negligible in the energy and mass-flux balance near the temperature minimum atop the photosphere. The study is based on the photospheric TiO broadband (1.0 nm) filter data acquired with the 1.6 m NST operating at the Big Bear Solar Observatory. The data set also includes NST off-band Hα images collected through a Zeiss Lyot filter with a passband of 0.025 nm.

[en] The results of determinations of the azimuthal and meridional velocities by time–distance helioseismology from Helioseismic and Magnetic Imager on board Solar Dynamics Observatory from 2010 May to 2020 September at latitudes and Stonyhurst longitudes from − 60° to + 60° and depths to about 19 Mm below the photosphere are used to analyze spatiotemporal variations of the solar differential rotation and meridional circulation. The pattern of torsional oscillations, or latitudinal belts of alternating “fast” and “slow” zonal flows migrating from high latitudes toward the equator, is found to extend in the time–latitude diagrams over the whole time interval. The oscillation period is comparable with a doubled solar-activity-cycle and can be described as an extended solar cycle. The zonal-velocity variations are related to the solar-activity level, the local-velocity increases corresponding to the sunspot-number increases and being localized at latitudes where the strongest magnetic fields are recorded. The dramatic growth of the zonal velocities in 2018 appears to be a precursor of the beginning of Solar Cycle 25. The strong symmetrization of the zonal-velocity field by 2020 can be considered another precursor. The general pattern of poleward meridional flows is modulated by latitudinal variations similar to the extended-solar-cycle behavior of the zonal flows. During the activity maximum, these variations are superposed with a higher harmonic corresponding to meridional flows converging to the spot-formation latitudes. Our results indicate that variations of both the zonal and meridional flows exhibit the extended-solar-cycle behavior, which is an intrinsic feature of the solar dynamo.

[en] For the period 1966-1978, a negative correlation has been found between the mean center-to-center distance of the granules and solar activity as expressed by the Wolff number or by the radio-flux at 2800 MHz. This behaviour results from a global shrinking of the histogram towards small distances when the activity increases

[en] An improved semi-empirical model of photospheric faculae is presented in tabular form. The limitations of the model as well as other possible improvements are discussed

[en] The investigation of the rotation of sunspots based on the daily drawings of the Sun, made at the Mt. Wilson Observatory in the years 1917-1924 showed that of the 146 sunspots which rotated, 60 % rotated in the ENW direction, in the N, as well as the S hemisphere. The observed rotational motion, corresponding to the direction in both hemispheres, counteracts the effect of differential rotation, as well as the action of the Coriolis force. It is probably due to the dynamics of the development of the group magnetic field. (author)

[en] We studied flux emergence events of sub-granular scale in a solar active region. The New Solar Telescope (NST) of the Big Bear Solar Observatory made it possible to clearly observe the photospheric signature of flux emergence with very high spatial (0.''11 at 7057 A) and temporal (15 s) resolution. From TiO observations with the pixel scale of 0.''0375, we found several elongated granule-like features (GLFs) stretching from the penumbral filaments of a sunspot at a relatively high speed of over 4 km s^-1. After a slender arched darkening appeared at the tip of a penumbral filament, a bright point (BP) developed and quickly moved away from the filament, forming and stretching a GLF. The size of a GLF was approximately 0.''5 wide and 3'' long. The moving BP encountered nearby structures after several minutes of stretching, and the well-defined elongated shape of the GLF faded away. Magnetograms from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager and NST/InfraRed Imaging Magnetograph revealed that those GLFs are photospheric indicators of small-scale flux emergence, and their disappearance is related to magnetic cancellation. From two well-observed events, we describe detailed development of the sub-structures of GLFs and different cancellation processes that each of the two GLFs underwent.