Author name code: vonuexkuell ADS astronomy entries on 2022-09-14 author:"von Uexkull, Marina" OR author:"Uexkull, Marina von" ------------------------------------------------------------------------ Title: Simultaneous Observations of Chromospheric and Transition Region Oscillations in HI Lyman Transitions and in Optical Lines Authors: Curdt, W.; Heinzel, P.; Schmidt, W.; Tarbell, T.; von Uexküll, M.; Wilken, V. Bibcode: 1999ESASP.448..177C Altcode: 1999mfsp.conf..177C; 1999ESPM....9..177C No abstract at ADS Title: Chromospheric Oscillations Observed by SOHO/SUMER and VTT/GCT on Tenerife Authors: Curdt, W.; Heinzel, P.; Schmidt, W.; von Uexküll, M.; Wilken, V. Bibcode: 1999AGAb...15R..11C Altcode: 1999AGM....15..A12C Previous studies have revealed various oscillations in higher Lyman lines of hydrogen, as observed with SUMER on SOHO (Curdt & Heinzel 1998). The assumption that these periodic phenomena might be related to similar effects observed in optical lines like Ca II K led to the idea of simultaneous observations with the SOHO/SUMER instrument and the VTT/GCT telescopes on Tenerife. First results are presented here for the Lyman series and Lyman continuum. Power spectra in network and internetwork regions have been derived and a preliminary interpretation based on the wave propagation concept is given. In SUMER spectra we found a well-pronounced asymmetry of all Lyman lines, which is related to atmospheric dynamics. The time variation of co-spatial UV and optical data is presented and basic characteristics are discussed. Title: Chromospheric Oscillations Authors: Schmidt, W.; von Uexküll, M. Bibcode: 1999AGM....15..A14S Altcode: Sequences of high-resolution filtergrams taken at Ca K2v show regions in the interior of the Ca network with oscillations at 11 mHz. These regions do also have strong 3min oscillations. Periodic signals around 2.2 mHz are concentrated in small scale structures located at the cell boundaries. The observations have been carried at at the Vacuum-Tower Telescope on Tenerife in May 1999, along with a coordinated SOHO-SUMER campaign. Title: Diagnostics and Dynamics of the Solar Chromosphere Authors: Kneer, F.; von Uexküll, M. Bibcode: 1999ASSL..239...99K Altcode: 1999msa..proc...99K Research of the chromosphere of the Sun is exciting, as it has been over more than a century. The present contribution can only give glimpses into the wealth of chromospheric structures and dynamics. Likewise, in view of the limited space, it is not possible to present in due balance the published work on the solar chromosphere. The reader is referred to the monographs by Bray and Loughhead (1974, with a historical account and many references to early work) and by Athay (1976) for the state of knowledge two decades ago. Among the conferences dealing meanwhile with the chromosphere we mention the proceedings edited by Bonnet and Delache (1976) and by Ulmschneider et al. (1991). Withbroe and Noyes (1977) treated the mass and energy flow in the chromosphere and corona; a throughout account of the Ca II K2v cell grains is given by Rutten and Uitenbroek (1991); the review by Narain and Ulmschneider (1996) deals with chromospheric and coronal heating mechanisms. Last but not least, the book ``Le Soleil'' by Secchi (1877) is historically precious and full of still viable ideas. Title: TESOS, a double Fabry-Perot instrument for solar spectroscopy Authors: Kentischer, T. J.; Schmidt, W.; Sigwarth, M.; Uexkuell, M. V. Bibcode: 1998A&A...340..569K Altcode: A double Fabry-Perot spectrometer in a telecentric configuration (TESOS: Telecentric Etalon SOlar Spectrometer) has been developed and installed in the Vacuum Tower Telescope at the Observatorio del Teide, Tenerife. The control system allows to switch from one wavelength band to another within 2 seconds. The telecentric configuration provides a constant wavelength passband across the field of view. Servo-stabilized etalons and a stable thermal environment provide a wavelength stability of <0.3 picometer per hour. We present initial results obtained with this instrument. Title: Oscillations of the Sun's chromosphere. VIII. Horizontal motions of CA II K bright points Authors: Wellstein, S.; Kneer, F.; von Uexkuell, M. Bibcode: 1998A&A...335..323W Altcode: We present a re-analysis of a time series of solar disc centre Ca ii K2v filtergrams taken with the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. We concentrate on the measurements of proper motions of K grains in the internetwork regions and of bright points in the chromospheric network. For the K grains we find horizontal velocities of 2-15 km s(-1) , values much lower than those deduced by Steffens et al. (1996) from a smaller sample, analyzed differently. In accord with our earlier conclusion from k-omega diagrams (Kneer & von Uexkuell 1993) and with numerical simulations by Carlsson & Stein (1997) high-frequency (pseudo-) p-modes can viably explain the K grains. Yet, the rareness of the K grains may indicate a connection to magnetic fields. The proper motions of the network bright points are non-periodic, very impulsive, with velocities of 7-10 km s(-1) . Estimating the energy flux if these motions are magnetic kink waves (cf. Choudhuri et al. 1993, Muller et al. 1994), we find it sufficient to heat the solar corona, but too small to cover the radiative losses of the chromospheric network. Title: Arch Filament Systems Associated with X-Ray Loops Authors: Malherbe, J. M.; Schmieder, B.; Mein, P.; Mein, N.; Van Drielgesztelyi, L.; Von Uexküll, M. Bibcode: 1998SoPh..180..265M Altcode: Using multi-wavelength observations obtained with the Tenerife telescopes (VTT and GCT) and with the Yohkoh satellite, we observed new emerging flux with an associated arch filament system (AFS) in the chromosphere and bright X-ray loops in the corona. We observed the change of connectivity of the X-ray loop footpoints which may be at the origin of the occurrence of a subflare. Densities, gas and magnetic pressures of cold AFS and hot loops were derived and discussed. The extrapolation of the photospheric magnetic field observed with the GCT in a linear force-free field assumption (constant α) shows that this region, in spite of having roughly a global potential configuration, consists of two systems of arch filaments. We found these two systems best fitted with two sheared magnetic topologies of opposite α values of ± 0.1 Mm-1 Title: Flare Multi-Line 2D-SPECTROSCOPY Authors: Mein, P.; Mein, N.; Malherbe, J. -M.; Heinzel, P.; Kneer, F.; von Uexkull, M.; Staiger, J. Bibcode: 1997SoPh..172..161M Altcode: 1997ESPM....8..161M A small flare was observed at the Teide Observatory on October 5, 1994. Simultaneous data were obtained at the German Vacuum Tower Telescope (VTT) with the MSDP spectrograph providing high-resolution imaging spectroscopy in two chromospheric lines, and the Gregory Coudé Telescope (GCT) providing information about the magnetic field. Basic flare characteristics are: Title: First Observations SUMER - VTT, SI IV - CA II K Authors: Balthasar, H.; von Uexkull, M.; Innes, D.; Gigas, D.; Wilhelm, K. Bibcode: 1997ASPC..118..315B Altcode: 1997fasp.conf..315B We tried to do a comparison of Ca II K (393.3 nm) filtergrams obtained at the Vacuum Tower Telescope on Tenerife with spectra in the line Si IV 139.4 nm obtained simultaneously with the SUMER telescope on the SOHO-spacecraft. Some bright features can be well identified in both observations. We compare temporal changes of the brightness for these common features. Title: Oscillations of the Sun's chromosphere. VII. K grains revisited. Authors: von Uexkuell, M.; Kneer, F. Bibcode: 1995A&A...294..252V Altcode: We analyse time sequences of high spatial resolution filtergrams obtained simultaneously in Mg b_2_ and Ca K_2v_ from quiet Sun disc centre with the Vacuum Tower Telescope at Observatorio del Teide, Tenerife. Special attention is paid to the temporal evolution of the bright points, or K grains, in the interior of the chromospheric network. These represent the intensity maxima of brightness oscillations in K_2v_ with large amplitude. The oscillations last 1 to 5 periods of 150-240s duration and are strongly non-sinusoidal. They do not appear to be excited by pulses from below and then to decay. They rather exhibit the beat phenomenon of a horizontally extended wave field. The high amplitude oscillations occur only rarely, during 5-10% of the time, if we pose the limit that high amplitude means that the maximum intensity is a factor 1.5 larger than the average intensity. The power spectrum does not show any signature of a chromospheric "3 min" mode nor of a mode at the acoustic cutoff frequency (period 3.5min), nor do we find a power ridge at constant frequency. Instead, as in our earlier finding, the chromospheric oscillations are ordered in modes in continuation of the 5min modes. Modeling will thus need to adopt that the waves propagate in a three-dimensional medium with, at least partially, reflecting boundaries. The bright points of the chromospheric network behave very differently, more chaotic, like noise. They show most power at low frequencies which we interpret as the consequence of the stochastic intensity fluctuations. Title: Wellen in der Sonnenchromosphäre. Authors: Kneer, F.; von Uexküll, M. Bibcode: 1994S&W....33..871K Altcode: No abstract at ADS Title: Oscillations of the Sun's chromosphere. VI. K grains, resonances, and gravity waves. Authors: Kneer, F.; von Uexkuell, M. Bibcode: 1993A&A...274..584K Altcode: We present observations of simultaneous filtergram time sequences in Mg b2, Ca K and Hα obtained from quiet Sun disc centre with the Vacuum Tower Telescope at Observatorio del Teide, Tenerife. Fourier analyses are performed to obtain power, coherence and phase spectra in the k-ω plane. There, the dominant features are the wellknown ridges of the 5 min resonant modes. Yet in the chromosphere the ridges extend to high wavenumbers (wavelengths ≍ 1.3 Mm) and to high frequencies (periods ≍ 105 s). Neither the famous chromospheric "3 min" oscillations nor an oscillation at the acoustic cutoff frequency (period 210 s) appear exceptionally pronounced. The signature of gravity waves is indicated from phase relations.

We distinguish between the behaviour in the interior of the chromospheric network and on the boundary. The network boundary behaves less oscillatory than the interior. In snapshots of chromospheric intensities the K grains (Beckers 1964), or, synonymously the bright cell points, appear in the cell interior. They represent the phases of high temperature of a wave field with partly resonant and coherent properties. (We take intensity fluctuations as proxies for temperature fluctuations.) The waves are only partly upward propagating p-modes with a multitude of eigenvalues in frequency and wavenumber, like the subphotospheric p-modes. We suggest that an excitation mechanism acts within the chromosphere itself to drive the waves. This could explain the phase relations between intensity and velocity oscillations. Title: On the structure of spectral line gap regions Authors: Kneer, F.; von Uexkuell, M. Bibcode: 1991A&A...247..556K Altcode: The analysis of a photographic spectrogram of the plage region near the disk center of the sun is undertaken to study small-scale magnetic features with special attention given to the structure of fluxtubes, and a related model is developed. Line-gap regions are identified in the Fe-I line which are characterized by redshifts and fluctuation velocity as well as an asymmetric profile indicative of a direct relationship between increasing downflow and increasing depth. The observations are compared to calculated line profiles in which a magnetic tube under certain conditions is present. The pressure and density are calculated for the tube under the assumption of hydrostatic equilibrium, and the observed intensity profiles can be reproduced when the correct parameters are used. The calculations demonstrate that a strong kilogauss magnetic field can be introduced to explain the line gap in the Fe-II 6149-A line. Title: Oscillations of the sun's chromosphere. V - Importance of network dynamics for chromospheric heating Authors: von Uexkuell, M.; Kneer, F.; Malherbe, J. M.; Mein, P. Bibcode: 1989A&A...208..290V Altcode: A 64-min time sequence of disk center H-alpha spectrograms taken with the MSDP spectrograph at the Observatoire du Pic du Midi is analyzed. This type of spectrograph allows spectroscopy of a two-dimensional field of view. From the H-alpha line profiles at each pixel, line-shift and minimum intensity fluctuation are determined as functions of spatial and temporal coordinates. A frequency analysis with standard Fourier techniques is performed. It is confirmed that in the interior of the chromospheric network cells the oscillatory behavior dominates, whereas at the boundaries one generally finds random motions on scales of 2-10 arcsec. The random behavior of the H-alpha structures outlines the permanent rearrangement of the magnetic field lines pushed around by the subphotospheric granular flow. Title: Two-dimensional spectroscopy of the Sun in Hα. Authors: von Uexküll, M.; Kneer, F.; Mein, P. Bibcode: 1988AGAb....1...11V Altcode: No abstract at ADS Title: Oscillations of the sun's chromosphere. IV - Temporal evolution of H-alpha profile Authors: Kneer, F.; von Uexkuell, M. Bibcode: 1986A&A...155..178K Altcode: H-alpha observations of the quiet solar chromosphere at disk center are presented, including a 9 min time sequence of photographic filtergrams in line center and + or - 0.5 A and a 54 min sequence of photographic spectrograms. The very different dynamical behavior of the interior and boundary of the network cells is emphasized. The dominant processes in the interior are waves in the 5 min period range and with shorter periods. The energy flux in these waves is estimated to be too small to account for the radiative losses from standard chromospheric models. In the cell boundaries, the material flows down, on time average, near the centers of rosettes. The short time fluctuations are mainly stochastic while the oscillations are reduced. This suggests that the energy balance in the cell boundaries is determined by MHD turbulence. Title: Oscillations of the sun's chromosphere. III - Simultaneous H-alpha observations from two sites Authors: von Uexkuell, M.; Kneer, F.; Mattig, W.; Nesis, A.; Schmidt, W. Bibcode: 1985A&A...146..192V Altcode: The authors analyze time sequences of Hα filtergrams taken simultaneously from two distant observatories, Capri and Izaña. By means of a coherence analysis the authors discriminate between instrumental effects including seeing and truly solar intensity fluctuations. Waves with periods as short as 60 s are present in the solar chromosphere; the lower limit is set by the time resolution of the observations. Title: Oscillations of the sun's chromosphere. II - H-alpha line centre and wing filtergram time sequences Authors: Kneer, F.; von Uexkuell, M. Bibcode: 1985A&A...144..443K Altcode: In order to investigate the dynamics of the solar chromosphere we perform a Fourier analysis of time sequences (total duration 128 min) of Hα photographic filtergrams taken simultaneously at disc centre in line centre and ±0.5 Å from the line centre. The results are: (i) At low frequencies (periods >450 s) the brightness fluctuations are caused by the temporal evolution of Hα structures at the boundaries of the chromospheric network. We observe that much of the coarse chromospheric structure survives the 128 min time span. We derive lifetimes of 2-8 min for the small-scale structure and 5-20 min for the larger structures. (ii) The modal structure of the 5 min oscillation is clearly visible in the power spectra of the three filtergram. The fundamental (f) mode can be followed to high horizontal wavenumbers kh ≍3.7 Mm-1 and follows the expected relationship ω2f = gkh, where g is the surface gravity. (iii) A chromospheric resonant mode cannot be found in the k - ω plane. (iv) The higher resonant p modes reach into the acoustic wave domain (periods T ≍ 150 s) and thus require the transition zone as the upper reflecting layer. (v) We find no evidence for internal gravity waves. (vi) From a coherence and phase analysis we conclude that the brightness fluctuations of the chromospheric structure seen in -0.5 Å lead those in +0.5 Å by 2 min at kh =2 Mm -1 and by 4 min at kh =0.5 Mm-1. (vii) From the same coherence and phase analysis we can identify acoustic waves in the solar atmosphere with periods as short as 80 s. They possess as much power as the 5 min oscillations and are seen better outside the chromospheric network than within the network. (viii) The phase difference between intensity in Hα line centre and velocity, constructed from the two Hα wing filtergrams, decreases from about 90° at low frequencies and high wavenumbers to 0° at high frequencies and low wavenumbers. Tentatively we interpret this as a change from mainly standing waves for the low order p modes to mainly upward propagating waves in the acoustic wave domain. Acoustic waves are thus candidates for the heating process of the inter-network regions. Title: Waves in the chromosphere observed in Hα. Authors: Kneer, F.; von Uexküll, M. Bibcode: 1985cdm..proc..282K Altcode: The authors analyze Hα filtergram time sequences and emphasize the further development and use of filter spectroscopy for studies on the dynamics of the solar atmosphere. Title: Chromospheric umbral oscillations. Authors: Mattig, W.; von Uexküll, M.; Kneer, F. Bibcode: 1984ESASP.220...59M Altcode: 1984ESPM....4...59M No abstract at ADS Title: The chromosphere above sunspot umbrae. IV. Frequency analysis of umbral oscillations. Authors: von Uexküll, M.; Kneer, F.; Mattig, W. Bibcode: 1983A&A...123..263V Altcode: The authors analyse time sequences of photographic spectrograms in Ca II H, K, 8498 Å, and 8542 Å, in Sodium D1 and D2, in Ni I 5893 Å and Hα, obtained from two sunspots. The frequency analysis of line intensities and shifts for the umbral chromospheric oscillations in the period range 110 s-200 s is discussed. Title: The chromosphere above sunspot umbrae. IV - Frequency analysis of umbral oscillations Authors: Uexkuell, M. V.; Kneer, F.; Mattig, W. Bibcode: 1983A&A...123..263U Altcode: An analysis is made of time sequences of photographic spectrograms in Ca II H, K, 8498 A, and 8542 A, in sodium D1 and D2, and in Ni I 5893 A and H-alpha obtained from two sunspots with the Vacuum Tower Telescope at Sacramento Peak Observatory. The two sunspot chromospheres are found to behave similarly with regard to their phase relationships but somewhat differently with regard to the oscillation resonant frequencies. In one and the same umbra, oscillation modes having different frequencies may be excited. The vertical velocity of propagation of the phase in umbral chromospheres, which is 10-25 km/s, decreases with increasing frequency and is much lower than the Alfven speed. The umbral chromospheric oscillations are thus slow mode waves. The downward motion enhances the intensity by some 65 deg (H-alpha) to 85 deg (D1), indicating dissipation of mechanical energy. It is also found that the mechanical energy flux of the umbral chromospheric oscillations is not sufficient to account for the chromospheric radiative losses. Title: Brightness oscillations of the sun's chromosphere in K and H-alpha Authors: Kneer, F.; von Uexkuell, M. Bibcode: 1983A&A...119..124K Altcode: The authors have performed a power analysis of time sequences of photographic K and Hα filtergrams from disc center of the sun. The results are: In the k-ω-diagram from the Ca II K filtergrams, the modal structure of the 5-min-oscillation is clearly seen. The 5-min modes are difficult to detect in the k-ω-diagrams from the Hα sequences. In both lines, K and Hα, the authors observe ridges in the k-ω-diagrams running parallel to the kh-axis. Their periods correspond to the chromospheric 3-min-oscillation. But power appears also, in discrete ridges, at shorter periods P = 60 s...150 s, where the lower limit is given by the Nyquist frequency of the observations. After subtraction of the time averaged intensity at each position in the filtergrams, the rms fluctuations are 3.5% in K and 4.0% in Hα. Title: New features of the oscillation spectrum of the sun Authors: Kneer, F.; von Uexkuell, M.; Newkirk, G., Jr. Bibcode: 1982A&A...113..129K Altcode: The results of a Fourier analysis of observations of brightness fluctuations in a sequence of CN 3883 Angstrom filtergrams are presented. From the 75 min time interval and field of view of 170 x 220 sq arcsec, a 40 sec sampling interval was examined, maintaining a spatial resolution as high as 1600 km. The data is filtered for a high wavenumber power spectrum, and an average power coefficient is calculated by examining power spectra for each of the sub-arrays. It is concluded that the 5 min velocity oscillation modal structure is easily detected in brightness fluctuations in the CN band, the surface gravity mode is the strongest single feature aside from the zero frequency ridge caused by convection, and the trapped chromospheric mode may be represented by a constant frequency ridge. Improved broad band filtergrams may be used to analyze little explored regions of the oscillation spectrum and to interpret intensity fluctuations as temperature fluctuations. Title: Zur Struktur der Chromosphäre über Sonnenflecken Authors: Kneer, F.; Mattig, W.; von Uexküll, M. Bibcode: 1982MitAG..55...65K Altcode: No abstract at ADS Title: Chromosphärische Helligkeits-oszillationen Authors: Kneer, F.; Newkirk, G.; von Uexküll, M. Bibcode: 1982MitAG..55...70K Altcode: No abstract at ADS Title: The Chromosphere above Sunspot Umbrae - Part Three - Spatial and Temporal Variations of Chromospheric Lines Authors: Kneer, F.; Mattig, W.; Uexkull, M. V. Bibcode: 1981phss.conf..318K Altcode: No abstract at ADS Title: Observations of Chromospheric Lines from OSO-8 Authors: Grossmann-Doerth, U.; Kneer, F.; Uexkuell, M.; Artzner, G. E.; Vial, J. C. Bibcode: 1980SoPh...66....3G Altcode: The line profiles of Lα, Ca II K and Mg IIk were measured with the spectrometer of the `Laboratoire de Physique Stellaire et Planétaire' on board of OSO-8. The results of these measurements are presented. Title: Spectral investigation of the chromosphere. VI: Observations of Halpha close to the limb. Authors: Grossmann-Doerth, U.; von Uexkuell, M. Bibcode: 1977SoPh...55..321G Altcode: Several hundred Hα spectrograms from areas close to the solar limb were taken with the 35 cm Coudé refractor at Anacapri. The 41 spectra with the greatest spatial resolution were selected and analysed. At the supergranular boundaries a considerable fraction of the line profiles were found to correspond to Beckers' Cloud Model (BCM). Moreover, the BCM parameters of the dark mottles at the limb appear to be approximately equal to those from the center of the disk. On the other hand, we also obtained evidence in disagreement with the general applicability of the BCM to all features of the chromospheric fine structure. Title: Spectral Investigation of the Chromosphere. V: Observation and Analysis of Hβ Authors: Grossmann-Doerth, U.; Uexkuell, M. V. Bibcode: 1975SoPh...42..303G Altcode: The results of the analysis of 16 Hβ spectra taken with high spatial resolution are presented. The properties of the line profile in the boundary regions of supergranular cells (SGB) are described by the statistical distribution functions and correlation coefficients of four parameters which determine the shape of a suitable fitting curve. Although some of the line profile properties of both Hβ and Hα in the SGB can be interpreted in terms of a model which was recently proposed by Durrant (1975) the agreement between that theory and our observations is not entirely satisfactory. Title: Properties of the solar Ca ii K-Line at high spatial resolution Authors: Grossmann-Doerth, U.; Kneer, F.; Uexküll, M. v. Bibcode: 1974SoPh...37...85G Altcode: The analysis of three Ca II K-spectra with spatial resolution of ∼1″ is described and its results presented. The comparison of the observed single peak line profiles with model computation leads to some conclusions regarding the non-uniform large-scale velocity fields in the chromosphere. Title: Spectroscopic Investigation of the Chromosphere. III: Hα Line Profile from the Interior Supergranular Cells Authors: Grossmann-Doerth, Ulrich; Von Uexküll, Marina Bibcode: 1973SoPh...30...71G Altcode: The line profile of H⇓ as emanating from the interior of supergranular cells was measured at sin θ = 0, 0.6, 0.8 and 0.9. The measurements are described and the results presented. Title: Spectral Investigation of the Chromosphere. II. The Nature of the Mottles and a Model of the Overall Structure Authors: Grossmann-Doerth, Ulrich; Von Uexküll, Marina Bibcode: 1973SoPh...28..319G Altcode: Highly resolved Hα spectra and filtergrams obtained at the Fraunhofer Observatory on Capri were analysed by a method whose principles have been described before. As a result the tentative conclusion of our previous work has been confirmed: The mottles of the chromospheric fine structure are clouds superimposed on the low chromosphere. Furthermore, it is proposed that the latter is identical with the interior of the supergranular cells whose spatial averages lend themselves to an interpretation in terms of a spherically symmetric model. On the other hand, we present evidence that the boundary regions which are formed by the mottles of the fine structure pattern and which constitute the upper chromosphere are not adequately described by spatial averages. Instead, the properties of the individual structural elements should be taken into account by an appropriate theory, if only in a statistical fashion. Some of these properties, viz. source function, optical thickness, Doppler width and velocity, were measured for a large number of elements. On the basis of indirect evidence we suggest that the spicules seen on limb photographs of chromospheric lines are identical with the elements of the supergranule boundary structure. Title: Die Struktur der solaren Chromosphäre Authors: Grossmann-Doerth, U.; von Uexküll, M. Bibcode: 1973MitAG..32..187G Altcode: No abstract at ADS Title: Spectral Investigation of Chromospheric Fine Structure Authors: Grossmann-Doerth, Ulrich; Von Uexküll, Marina Bibcode: 1971SoPh...20...31G Altcode: Hα spectra and effectively simultaneous filtergrams were taken at the Fraunhofer Observatory on Capri with the 35 cm domeless Coudé. The spatial resolution of the 19 best spectra selected for analysis was estimated to be 1-2 arc sec. The comparison of several hundred Hα line profiles emitted by typical chromospheric structure elements with theoretical prediction yielded strong evidence to suggest that the chromosphere consists of two parts: A lower, rather uniform layer at rest superposed by `clouds' (condensations of great spatial variability) which constitute the well-known structure pattern of Hα filtergrams. For most image points the line-of-sight velocity, optical thickness, source function and Doppler broadening of these clouds could be determined. While the values of the latter three quantities were found to be similar to what Beckers (1968) has found for limb spicules the velocity of the bright and of the dark mottles is considerably smaller than to be expected if these features were the spicules as seen on the disk. However, our results do not rule out the possibility that the spicules rise at the centers of rosettes where they are difficult to detect.