Abstract. The structure and dynamics of the photosphere are investigated, with time series of broadband and monochromatic images of quiet granulation, at the solar disk center. Images were acquired with the IPM observing mode at the THEMIS telescope. Velocity and line center intensity fields, derived from the observation of three different photospheric lines, are used to study velocity and intensity patterns at different heights in the photosphere. Automatic segmentation procedures are applied to velocity and intensity frames to extract solar features, and to investigate the dependence of their properties at different scales and heights. We find a dependence of the statistical properties of upflow and downflow regions on the atmospheric height. Larger granules, passing through a great part of the photosphere, are used to investigate the damping of convective motions in stably stratified layers. The results suggest the occurrence of an intense braking in the deep photosphere (first ∼120 km). Furthermore, we investigate the temporal and spatial evolution of velocity fields, deriving typical time scales of dynamical processes relative to different solar features. In particular, for two selected isolated exploders, we reveal a velocity deceleration in the central region since the early phase of their fragmentation.
We reduce and analyze, in a uniform way, all of the data obtained by the Solar Disk Sextant (SDS) experiment, concerning high-precision measurements of the solar radius and oblateness, in the bandwidth 590 -670 nm, made onboard stratospheric balloons during a series of flights carried out in 1992, 1994, 1995, and 1996. The measured radius value appears anti-correlated with the level of solar activity, ranging from about 959.5 to 959.7 arcsec. Its variation from year to year is outside the error range, which is mostly due to a systematic diurnal behavior, particularly evident in the 1996 flight. The oblateness shows an analogous temporal behavior, ranging from about (4.3 to 10.3) × 10 −6 .
Abstract. Since 1981, several attempts to build series of semiempirical models designed to represent, in addition to the quiet Sun, the various types of magnetic regions across the solar disk (network, faculae and sunspots), have followed one another. Here we test the capability of those calculated by Fontenla et al. (1999) to reproduce different experimental data, comparing the computed spectra with the observations made by the PSPT of the Rome Observatory. In particular, we study the average center-limb variation of the network and facular contrast. In this way, we are able to single out the models best reproducing the different photospheric structures operationally identified by the PSPT observations and data analysis. We show also that it would be possible, with slight modifications of the models, to further improve the agreement with the experimental data.
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