Aims. The purpose of this paper is to characterize the statistical properties of solar granulation in the photosphere and low chromosphere up to 650 km. Methods.We use velocity and intensity variations obtained at different atmospheric heights from observations in Ba ii 4554 Å. The observations were done during good seeing conditions at the VTT at the Observatorio del Teide on Tenerife. The line core forms rather high in the atmosphere and allows granulation properties to be studied at heights that have been not accessed before in similar studies. In addition, we analyze the synthetic profiles of the Ba ii 4554 Å line by the same method computed taking NLTE effects into account in the 3D hydrodynamical model atmosphere. Results. We suggest a 16-column model of solar granulation depending on the direction of motion and on the intensity contrast measured in the continuum and in the uppermost layer. We calculate the heights of intensity contrast sign reversal and velocity sign reversal. We show that both parameters depend strongly on the granulation velocity and intensity at the bottom photosphere. The larger the two parameters, the higher the reversal takes place in the atmosphere. On average, this happens at about 200-300 km. We suggest that this number also depends on the line depth of the spectral line used in observations. Despite the intensity and velocity reversal, about 40% of the column structure of granulation is preserved up to heights around 650 km.
Aims. We study the properties of solar granulation in a facular region from the photosphere up to the lower chromosphere. Our aim is to investigate the dependence of granular structure on magnetic field strength. Methods. We used observations obtained at the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife) using two different instruments: the Triple Etalon SOlar Spectrometer (TESOS) to measure velocity and intensity variations along the photosphere in the Ba ii 4554 Å line; and, simultaneously, the Tenerife Infrared Polarimeter (TIP-II) to the measure Stokes parameters and the magnetic field strength at the lower photosphere in the Fe i 1.56 μm lines. Results. We find that the convective velocities of granules in the facular area decrease with magnetic field while the convective velocities of intergranular lanes increase with the field strength. Similar to the quiet areas, there is a contrast and velocity sign reversal taking place in the middle photosphere. The reversal heights depend on the magnetic field strength and are, on average, about 100 km higher than in the quiet regions. The correlation between convective velocity and intensity decreases with magnetic field at the bottom photosphere, but increases in the upper photosphere. The contrast of intergranular lanes observed close to the disk center is almost independent of the magnetic field strength. Conclusions. The strong magnetic field of the facular area seems to stabilize the convection and to promote more effective energy transfer in the upper layers of the solar atmosphere, since the convective elements reach greater heights.
Aims. We study the properties of waves in a facular region of moderate strength in the photosphere and chromosphere. Our aim is to statistically analyse the wave periods, power, and phase relations as a function of the magnetic field strength and inclination. Methods. Our work is based on observations obtained at the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife) using two different instruments: the Triple Etalon SOlar Spectrometer (TESOS) in the Ba ii 4554 Å line to measure velocity and intensity variations through the photosphere and, simultaneously, the Tenerife Infrared Polarimeter (TIP-II), in the Fe i 1.56 μm lines to measure the Stokes parameters and magnetic field strength in the lower photosphere. Additionally, we use the simultaneous broadband filtergrams in the Ca ii H line to obtain information about intensity oscillations in the chromosphere.Results. We find several clear trends in the oscillation behaviour: (i) the period of oscillation increases by 15-20% with the magnetic field increasing from 500 to 1500 G. (ii) The temperature-velocity phase shifts show a strikingly different distribution in the facular region compared to the quiet region, a significant number of cases in the range from −180• to 180• is detected in the facula. (iii) The most powerful chromospheric Ca ii H intensity oscillations are observed at locations with strong magnetic fields (1.3-1.5 kG) inclined by 10-12 degrees, as a result of upward propagating waves with rather low phase speeds, and temperature-velocity phase shifts between 0• and 90• . (iv) The power of the photospheric velocity oscillations from the Ba ii line increases linearly with decreasing magnetic field inclination, reaching its maximum at strong field locations.
Abstract. We discuss the links between the photospheric 5-min oscillations and the granulation pattern using a 30-min time series of CCD spectrograms of solar granulation recorded with high spatial (0 5) and temporal (9.3 s) resolution. The observed images contain the Fe i 5324Å spectral line with good height coverage from the low photosphere up to the temperature minimum region. Amplitudes, phases and periods of the 5-min oscillations are found to be different above granules and intergranular lanes. Strong oscillations occur well separated temporally and spatially. Many features of this different behaviour can be described in the frame of a relatively simple model of wave propagation in the solar atmosphere. To that aim, we have introduced oscillations into a 3D snapshot of a theoretical time dependent solar model atmosphere. NLTE synthesis of the time series of the Fe i 5324Å line profiles was performed taking into account granular and oscillatory components of the velocity field. Both, observations and theoretical modeling, lead to similar results: (i) oscillations above granules and intergranular lanes occur with different periods; (ii) the most energetic intensity oscillations occur above intergranular lanes; the most energetic velocity oscillations occur above granules and lanes with maximum contrast, i.e. above the regions with maximum convective velocities; (iii) velocity oscillations at the lower layers of the atmosphere lead oscillations at the upper layers in intergranular lanes. In granules the phase shift is nearly zero. We conclude that differences in oscillations above granules and lanes are caused mainly by variations of the physical conditions in these structures.
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