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Time series of simultaneous high resolution filtergram observations in white light and in CaK2 have been employed to study the dynamical interdependence of the ‘low’ and the ‘high’ layers of the solar atmosphere, the 3-D propagation of perturbations in the stratification, and the excitation of p-mode and other oscillations. Impulsive and oscillatory perturbations have been isolated in the wavenumber and frequency regime, and their mutual interaction was also studied.Several of our findings challenge interpretation and deserve further study. •The occurrence of a granule can be clearly recognized in the upper chromosphere.•A granule induces low brightness and low oscillation amplitudes at the CaK2 level, whereas the opposite happens at the intergranular border.•It is not always evident that the ‘source’ of the perturbation is located at the lower, i.e. the photospheric layer.•It is far from being clear which components of the various perturbations contribute to a net outward mechanical energy flux.

We investigate the influence of the solar atmospheric temperature stratification on the amplitude of waves at different heights and its dependence on frequency and wave number. Special interest is taken in the influence of atmospheric layers on the appearence of the recently observed p-mode crossing features and their location in the Fourier domain. We consider four stratification models. One of them is the standard model with convection-zone, VAL-atmosphere and corona. The others are modifications of this model in order to discuss the influence of specific layers of the atmosphere. The changes in the temperature structure significantly influence the velocity amplitude at certain frequency-wave number combinations at certain heights.

In continuation of a series of studies devoted to the dynamics of the solar photosphere and chromosphere we have attempted to further extend the range of heights in the atmosphere towards the transition region by including observations of the He I 10830 line. We have recorded simultaneous time series of He I 10830 and Mg I 8807 spectra in the quiet solar atmosphere using the echelle spectrograph at the German Vacuum Tower Telescope in Izaña, Tenerife. The velocity signal derived from the Doppler shifts of He 10830 clearly reveals oscillatory motions. The intensity of He 10830, on the other hand, is hardly affected by the oscillations. In the cell interior the 3-min oscillations prevail. Longer periods are found ain the cell boundaries of the chromospheric network where He absorption is enhanced. The V–V phase difference spectrum between the oscillations of He 10830 and those of Mg 8807 confirms previous observations of a non-propagating component that dominates the acoustic wave spectrum in the chromosphere.

Observations of a fairly regular sunspot penumbra near disk center have been carried out using a Stokes V polarimeter at the German Vacuum-Tower-Telescope in Izaña, Tenerife. We obtained two-dimensional spectral data by scanning the limb oriented sector of the penumbra in steps of 1” with the slit parallel to the solar limb. From Stokes V and Stokes I spectra of four magnetic sensitive lines (Fe I 5247.1, Cr I 5247.6, Fe I 5250.2, and Fe I 5250.7) obtained with 1024 × 1024 pixel CCDs we have determined Doppler shifts and several magnetic parameters. The results of a correlation analysis point out a clear relation between continuum brightness and magnetic field inclination in the sense of steeper field lines in the bright penumbral filaments. There is also a doubtless connection between intensity and Doppler shift. We did find indications for a correlation between field strength and brightness which is not uniform across the penumbra, though.

We study the oscillatory behaviour of small-scale magnetic flux-tube concentrations and their immediate surroundings by analysing high spatial resolution time series of spectra of four Zeeman sensitive lines (Fe I 5247.1, Cr I 5247.6, Fe I 5250.2, Fe I 5250.7) taken simultaneously in left-hand and right-hand circularly polarized light with the Echelle spectrograph at the Vacuum Tower Telescope in Izaña, Tenerife. The velocity field inside the magnetic elements is dominated by the 5-min oscillations which also show up as periodic variations in the relative amplitude asymmetry of the Stokes V profiles. In other parameters as for instance the Stokes V peak separation we cannot detect an oscillatory component. Neither the magnetic line ratio nor the thermal line ratio is affected by the 5-min oscillations, although the latter reveals remarkable spatiotemporal variations.

As potential contributors to the heating of the quiet chromosphere short period acoustic waves are of considerable astrophysical interest. Yet, in spite of numerous observational studies of high-frequency chromospheric velocity and brightness fluctuations their physical properties are not well known. We introduce a novel analytic aspect of the high-frequency component of atmospheric oscillations into the discussion.

In continuation of a series of studies devoted to the dynamics of the solar photosphere and chromosphere we have attempted to further extend the range of heights in the atmosphere towards the transition region by including observations of the He I 10830 line. We have recorded simultaneous time series of He I 10830 and Mg I 8807 spectra in the quiet solar atmosphere using the echelle spectrograph at the German Vacuum Tower Telescope in Izana, Tenerife. The velocity signal derived from the Doppler shifts of He 10830 clearly reveals oscillatory motions. The intensity of He 10830, on the other hand, is hardly affected by the oscillations. In the cell interior the 3-min oscillations prevail. Longer periods are found ain the cell boundaries of the chromospheric network where He absorption is enhanced. The V-V phase difference spectrum between the oscillations of He 10830 and those of Mg 8807 confirms previous observations of a non-propagating component that dominates the acoustic wave spectrum in the chromosphere.

Recent observational studies of the spatial and temporal relations between impulsive and periodic perturbations (Deubner and Kleineisel, 1997; Espagnet et al., 1996; see also Goode et al., these proceedings) suggest that oscillations in the solar atmosphere are excited locally and stochastically by turbulent convection. Proper characterization of the dynamical processes involved requires careful analysis of the observations in the spatial as well as in the temporal domain. Wavelet transforms (Combes et al., 1984) allow the characterization of waveforms together with the temporal delays that occur between the observed fluctuations. We have employed Morlet wavelets (Daubechies, 1992) in the present analysis. In addition to the phase relation between convective eddies and the atmospheric waves we study in particular the 2-D spatial evolution of the perturbations, to better distinguish different modes of oscillation. The observational material used is the same as in Deubner and Kleineisel (1997).

Short period oscillations (with periods less than 150 s) are shown to be non-uniformly distributed on the solar surface, and in time. Rather, they appear concentrated in short bursts which preferentially occur in regions with strong instantaneous downflow motion throughout the observed extent of the solar atmosphere.

The value of p-modes of high degree l as a diagnostic for the structure and dynamics of the solar envelope is reviewed.

The amount of energy carried in the solar atmosphere by short period acoustic waves is particularly uncertain in the range of frequencies (ν ≥ 10mHz) which is potentially relevant for acoustic heating.

Photoelectric polarisation measurements in a stable sunspot (type H) with a particularly dark umbra carried out with the Capri magnetograph have been evaluated in terms of Unno's (1956) theory to give the value and direction of the magnetic field vector. A linear increase of the inclination angle with distance from the spot centre up tor ≈ 1.2Rs results, as originally found by Hale and Nicholson (1938) with a different procedure. The field strength decreases from the maximum value (about 3300Γ) to about 15% at the penumbral border, still continuously decreasing outside the spot. The projected field direction deviates considerably from the radial symmetry in several parts of the spot region, but it is in good agreement with that of the overlaying chromospheric structures.

With the Capri magnetograph of the Fraunhofer Institute simultaneous measurements of sightline velocities and longitudinal magnetic fields have been carried out, in order to investigate the dependence of the 300-sec oscillation of sightline velocities on the magnetic-field strengths, and the oscillatory behavior of the latter, if there is any.

The value of p-modes of high degree l as a diagnostic for the structure and dynamics of the solar envelope is reviewed.

A time series of simultaneously measured velocity (V) and intensity (I) fluctuations of different spectral lines formed in the photosphere and low chromosphere is analysed. In order to separate the different patterns of motions (granulation, mesogranulation, gravity waves, acoustic waves) V-V and V-I phase difference spectra have been computed not only with respect to frequency v but also to the horizontal wavenumber kx. The V-V phase difference spectra of the Na Di line and two photospheric Fe I lines (5929.7A, 5930.2A) clearly show the existence of gravity waves in the solar atmosphere. The V-I phase spectra also exhibit the behaviour of gravity waves at high wavenumbers (kx≥1.7 Mm-1). At low wavenumbers one finds positive V-I phase differences. This we take as an indication for convective motions with a typical spatial scale of more than 5" (mesogranulation)

The question of the isotropy of the p-modes with respect to orientation on th solar disk was recently addressed by Kuhn (1984). He found significantly greater power at low wavenumbers (1≲30) in his measurements with the slit oriented in E-W direction as compared to the N-S orientation.

Photoelectric polarization measurements in a stable sunspot (type H) with a particularly dark umbra, where ‘umbral dots’ were virtually lacking, have been carried out with the Capri magnetograph (Deubner, 1969). The measurements were evaluated in terms of Unno’s theory to give the value and direction of the magnetic field vector. The parameters η0 = 5, β0 = 2.5 and ΔλD=40mA have been adopted for the Fe I 5250 line. Taking the configuration of the sunspot into account as well as simple conditions of steadiness of the distributions to be obtained, it is possible to derive the magnetic vector field from two-dimensional records of circular and linear polarization without ambiguities.

With the Capri magnetograph of the Fraunhofer Institute simultaneous measurements of sightline velocities and longitudinal magnetic fields have been carried out, in order to investigate the dependence of the 300-sec oscillation of sightline velocities on the magnetic-field strengths, and the oscillatory behavior of the latter, if there is any.

We discuss the properties of the solar background signal as observed in high-quality, l-ν power and phase difference spectra of the continuum (C), velocity (V), and line intensity (I) fluctuations of the Ni I 6768 A line. These spectra were generated from high-resolution images acquired by the Michelson Doppler Imager on board SOHO. We confirm that the background signal in the velocity power spectra can be reproduced by a composite model with two quasi-stationary components, describing large-scale and small-scale convective motions, and a periodic component. The line and continuum intensity power spectra require additional quasi-stationary and periodic components. The extra quasi-stationary component dominates the intensity and continuum background signals over the spectral region where the I-V phase difference spectra show essentially constant negative phase difference: i.e., below and in between the p-mode ridges (called the plateau-interridge regime by Deubner et al.). Since the I-V phase between the p-mode ridges is not random, the solar background beneath the p-modes must be considered as coherent. We thus speculate that the negative phase regime may be the manifestation of a correlated background. Such a background has been proposed to explain the opposite sense of the asymmetries of the p-mode line profiles in velocity and brightness oscillations.

Photoelectric polarization measurements in a stable sunspot (type H) with a particularly dark umbra, where ‘umbral dots’ were virtually lacking, have been carried out with the Capri magnetograph. The measurements were evaluated in terms of Unno's theory to give the value and direction of the magnetic field vector. The parameters η0 = 5, β0 = 2.5 and ΔλD = 40mÅ have been adopted for the Fe I 5250 line. Taking the configuration of the sunspot into account as well as simple conditions of steadiness of the distributions to be obtained, it is possible to derive the magnetic vector field from two-dimensional records of circular and linear polarization without ambiguities.

A new technique for measuring solar photospheric and subphotospheric rotation rates is described. The technique utilizes the standing-wave nature of the nonradial p-mode oscillations of the whole sun. Specifically, the technique is based upon the observed concentration of p-mode oscillatory power into well defined ridges in two-dimensional wavenumber-frequency power spectra. The frequencies of the ridges in the eastward- and westward-traveling portions of an individual spectrum are systematically shifted in opposite directions by a drift of the standing-wave pattern across the observing field of view. The magnitudes of these frequency shifts are related to the drift velocity and to the horizontal wavenumber in such a way that measurement of the observed frequency shifts in a spectrum yields the drift velocity for that observing run. By guiding on the solar limbs and observing the velocity field at disk center, the observed drift velocity obtained in this way is exactly the rotational velocity of the solar p-mode pattern, and of the solar gas itself.

The splitting of p-mode eigenfrequencies due to a depth-dependent solar rotation rate is considered. It is shown that to a first approximation this splitting can be treated as resulting from the translation of the wave pattern across the field of view with a velocity equal the actual velocity at a depth called the effective depth. The effective depths for a model solar envelope with l/H = 3 are presented as a function of position on the (kh, omega)-plane. The combination of omega near 0.025/s and kh near 0 yields the deepest probe of the solar envelope. For this same combination of kh and omega it is possible to resolve individual groups of eigenmodes in frequency but not in spatial wavenumber. Achievement of this resolution observationally may permit a determination of the lifetime of these particular modes.