[en] Fine prominence features have been predicted to explain the presence of faint luminous chromospheric emissions in the solar corona. This paper describes very fine structures of the order of 200 km in diameter seen at Hα and extending from the center of a sunspot into the corona

[en] In connection with the problem of solar flares as well as for the solution of the problems of solar activity region dynamic as a whole the stability of rope magnetic structures in the Sun is considered. It is shown that the twisted magnetic rope has two equilibrium states: a) radius of the curvature R= infinity, the twisting degree is arbitrary; b) kappa=2, R not equal to infinity. The instability condition for the first state is well known: kappa>2. The second state is stable against the stretching of the rope if external pressure is conserved. But it could be unstable when the stretching is followed by the transversal expansion due to inhomogeneity of the external medium. The instability occurs when the cross section radius grows faster than the length of the rope. The rope emerging on the surface of the Sun has been analyzed on the basis of the results obtained

[en] We study the propagation of a train of acoustic shocks guided by diverging magnetic fields through a static model of the solar chromospheric network and transition region. Our results show that for initial flux densities of the order 10⁶ ergs cm^-2s^-1 in the lower chromosphere, the local efficiency of acoustic transmission into the corona can be much higher than calculated for a plane parallel atmosphere. Thus acoustic energy will tend to be deposited at higher chromospheric levels in diverging magnetic fields, and magnetic guiding may well influence the temperature profile of the network and plages. But the total flux that can be transmitted into the corona along such diverging fields is severely limited, since the magnetic elements occupy a small fractional area of the photosphere, and the transmission efficiency is a rapidly decreasing function of initial acoustic flux density. We conclude that diverging magnetic fields and a varying ratio of specific heats are not likely to allow high frequency shocks to dissipate high enough in a static atmosphere, to contribute significantly to the coronal energy balance. This result strengthens the view that acoustic waves do not heat the solar corona. However, the conclusion may be sensitive to the influence of observed mass motions, such as spicules. (orig.)

[en] The relation of active region SD 55/1975, investigated during a cooperative observational programme, to the background magnetic field development is demonstrated. The studied active region represents only a small part of a more general evolutionary process of the magnetic field: it appears during the early stages of a new ''impulse of activity'' in the main active magnetic longitude as a substantial component of a complex activity. All its morphological changes in the photosphere as well as in the chromosphere are clearly related to the subsequent formations of new secondary magnetic fluxes and to the strong renewal of activity at the end of the observation interval. A difference seems to exist between the rotational velocity of the photospheric magnetic fields and the low-intensity green corona related to them, and the velocity of coronal maxima. (author)

[en] The intermediate band uvbyβ photometric system is used to observe solar active (plage) regions and quiescent regions in an effort to determine the effect of chromospheric activity on photometric metallicity measurements. We find that the active regions appear metal deficient with respect to the quiet Sun by approximately 35%

[en] We investigate energy transport by pressure waves, derived from observations of chromospheric line profiles. (orig./WL)

[en] A three-component model of the solar chromosphere, developed from ground based observations of the Ca II K chromospheric emission, is used to calculate the variability of the Lyman alpha flux between 1969 and 1980. The Lyman alpha flux at solar minimum is required in the model and is taken as 2.32 x 10¹¹ photons/cm²/s. This value occurred during 1975 as well as in 1976 near the commencement of solar cycle 21. The model predicts that the Lyman alpha flux increases to as much as 5 x 10¹¹ photons/cm²/s at the maximum of the solar cycle. The ratio of the average fluxes for December 1979 (cycle maximum) and July 1976 (cycle minimum) is 1.9. During solar maximum the 27-day solar rotation is shown to cause the Lyman alpha flux to vary by as much as 40% or as little as 5%. The model also shows that the Lyman alpha flux varies over intermediate time periods of 2 to 3 years, as well as over the 11-year sunspot cycle. We conclude that, unlike the sunspot number and the 10.7-cm radio flux, the Lyman alpha flux had a variability that was approximately the same during each of the past three cycles. Lyman alpha fluxes calculated by the model are consistent with measurements of the Lyman alpha flux made by 11 of a total of 14 rocket experiments conducted during the period 1969--1980. The model explains satisfactorily the absolute magnitude, long-term trends, and the cycle variability seen in the Lyman alpha irradiances by the OSO 5 satellite experiment. The 27-day variability observed by the AE-E satellite experiment is well reproduced. However, the magntidue of the AE-E 1 Lyman alpha irradiances are higher than the model calculations by between 40% and 80%. We suggest that the assumed calibration of the AE-E irradiances is in error

[en] Discusses the question of how some reasonably common types of stars, such as the carbon stars and the S stars, manage to show off at their surfaces, for us to observe, a fair sampling of the products of the nuclear burning going on deep in their cores. (Auth.)

[en] General considerations concerning the scaling properties of magnetic-field--related colonal heating mechanisms are used to build a two-parameter model for the heating of closed coronal regions. The model perdicts the way in which coronal temperature and electron density are related to photospheric magnetic field strength and the size of the region, using the additional constraint provided by the scaling law of rosner, tucker, and Viaiana. The model successfully duplicates the observed scaling of total thermal energy content with total longitudinal flux; it also predict a relation between the coronal energy density (or pressure) and the longitudinal field strength modified by the region scale size. The observational data yield a similar relation, pproportional< B>/sup 1.6/. A parameter of the theory, which is evaluated by fitting to the data, is the product αupsilon/sub phi/, where α is the ratio of azimuthal to longitudinal magnetic field and upsilon/sub phi/ is the effective twisting velocity of the loop footpoints, which supplies the energy for coronal heating

[en] We report observations of disk-center solar continuum brightness fluctuations. These observations show features that may be interpreted as internal gravity waves trapped in the solar photosphere and chromosphere. We discuss the reasons for this interpretation, and some of its implications