On the interpretation of Fraunhofer line Doppler shifts at supergranule boundaries

We have used the SPO tower telescope and echelle spectrograph to study differences in the profiles of three Fei lines, between magnetic network and cells. Ca K slit-jaw pictures were used to identify the network and cell areas, and mean network and cell profiles were computed from digitized spectra for the g = 0 lines 4065, 5434, and the g = 1.5 line 5233. The profile bisectors show that the wings of all three lines are red-shifted in the network by between 75–200 m s^–1 relative to the cell profiles. But the redshift decreases in the line core and becomes less than the standard error of 20 m s^–1 near the line core minimum. This disappearance of the redshift at the cores of all 3 lines formed over the height range 250–500 km above _0.5 = 1, argues against a steady downflow at supergranule boundaries. We show that such red-shifted wings and a relatively unshifted core can result if granular convection is suppressed near the network flux tubes, without implying any downflow in the vicinity of these flux tubes. Our results also indicate that searches for large-scale convective velocity patterns should measure shifts of the line core, rather than the line wings which appear to be very sensitive to inhomogeneities in granule structure.Visiting Astronomers, Sacramento Peak Observatory.     

Distribution of absolute energy of bright Be stars in pleiades

We present newly measured energy distributions from 3200–7500 Å of five late-type Be stars in Pleiades cluster for search of peculiarities of Be stars continuum energy distributions. Empirical effective temperatures of Be stars have been derived by comparing observed and computed fluxes in the visible region. The variation of the flux in the Balmer continuum region of Pleione (28 Tau) has been discussed.     

Solar noise storms coordinated observations: May 16–24, 1981

We present the main results obtained from the coordinated observations of solar radio noise storms organized by C.E.S.R.A. in May 1981. They concern the structure and polarization of radio sources, and the relation with the photospheric magnetic field. A model of coronal magnetic field, accounting for the observations, is briefly discussed.     

The shape and structure of Mimas

The Voyager images have shown that Mimas and Enceladus have regular shapes, with topography of the order of 1% of the diameter. Therefore, we can compare the global shapes of these satellites with the corresponding figures of gravitational equilibrium. In the case of Mimas, this comparison rules out a homogeneous interior, but implies the existence of a denser, presumably rocky core within this small icy satellite.     

Limb-darkening and solar cycle variation of sunspot intensities

New observations of the umbral limb-darkening are presented. We find a real and significant decrease in the umbra/photosphere intensity ratio towards the limb. This result contrasts the findings of previous authors and we believe this to be the first time such a decrease is reported. Our conclusion is based on broad band pinhole photometer intensity observations of 22 large sunspots covering the spectral region 0.387–2.35 m. The data are selected from measurements on approximately 600 days during the last 15.5 yr. The application of the limb-darkening data to the study of the temperature stratification in the umbra is briefly discussed. The observations confirm the suggestion that the umbra/photosphere intensity ratio seems to be a linear function of the phase in the solar cycle.     

Dynamic evolution of recurrent mass ejections observed in Hα and Civ lines

During a coordinated SMY program, the consecutive formation of two new active centers merging together within AR 2646 was observed from 28 August, to 5 September, 1980. The two preceding spots compressed an inverse polarity spot on 1 September 1980, causing recurrent ejecta of matter with time intervals around 10 min. The observations of the MSDP spectrograph operating in H at the Meudon Solar tower and of the UVSP spectrometer on SMM in the Civ 1548 Å line show that cold and hot material had the same projection, although the upward Civ velocity structure was more extended than the H one. We present evidence that observed contrasts of the H absorbing structure can be interpreted in terms of a dynamic cloud model overlying the chromosphere. H matter follows a magnetic channel with upward velocity around 20–30 km s^–1 in the first phase of the event and with downward velocity ( - 40 km s^–1) in the second phase. The stored energy is not sufficient to trigger a flare, nor even to propulse matter along the full length of an arch, because of the periodic reorganisation of the magnetic field.     

Simultaneous H and K Ca ii,h and k Mg ii,Lα and Lβ H i profiles of the April 15, 1978 solar flare observed with the OSO-8/L.P.S.P. experiment

Solar flare observations have been performed with the multichannel L.P.S.P. experiment on board OSO-8 NASA Satellite. Simultaneous H and K Caii, h and k Mgii, L and L Hi profiles have been recorded on the plage just before the flare, during the flare onset and relaxation phases. The different behaviour of line profiles and intensities during the flare is evidenced and indicates a downward propagation with relaxation times increasing from the upper part to the lower part of the chromosphere related to line formation processes. Using the H observed profile, an upper limit of 8 × 10¹³ cm^-3 is derived for the electron density.     

A remarkable configuration of sector boundaries

A study of all the observed and well-defined sector boundaries from January 1957 to February 1975, published by Svalgaard (1974, 1975a, b), indicated that sector boundary key-dates, transformed into Bartels' days, have a significant preference to occur on certain days of the solar rotation. The eclectic distribution of these sector boundaries give some Bartels' days that are empty of cases, while on other days there is a significant excess over the average. Using this effect, we can predict, in high levels of significance, the possible occurrence of a (+,–) or (–,+) boundary within particular days of the solar rotation.     

Preirradiation history of Djermaia (H) chondritic breccia

Djermaia is a unique case among gas-rich chondrites. Twelve light xenoliths studied so far in the two available stones show unequivocal evidences of large preirradiation effects, which stand out most clearly when both cosmic-ray track and spallogenic rare-gas data are considered and compared to data from chondrites with a simple radiation history. Each of the two stones studied displays a specific xenolith population with distinct morphological and preirradiation characteristics. The first population consists of rounded and more- or less-shocked xenoliths which show evidences of short solar-flare irradiation (<1 my) and a longer residence under heavier shielding (～50 g/cm²). The second population shows neither clear indication of surface erosion nor evidence of solar-flare effects, and its preirradiation occured in deep-seated locations (～150 g/cm²).The size distribution of xenoliths is also different for the two populations, indicative of more active reworking processes in the top ～20 cm of the Djermaia regolith than at a depth of ～50 cm. The amount of ²¹Ne_sp accumulated during the preirradiation stage is substantial (25–60% of total ²¹Ne_sp), corresponding to a formal preexposure time of ～15 my for both stones, assuming static irradiation conditions. These results give an insight into the dynamics of the upper levels of the H-asteroid regolith, which appears to be in good agreement with the model of Housen, Wilkening, Chapman, and Greenberg (Icarus, 1979, 39, 317–351).     

Baroclinic instabilities in Jupiter's zonal flow

The baroclinic stability of Jupiter's zonal flow is investigated using a model consisting of two continuously stratified fluid layers. The upper layer, containing a zonal shear flow and representing the Jovian cloudy regions above p ～ 5 bars, is the same as Eady's (1949) model for the Earth. The lower layer has a relatively large but finite depth with a quiescent basic state, representing the deep Jovian fluid bulk below p ～ 5 bars. Due to the presence of the lower layer, the linearized non-dimensional growth rates are drastically reduced from the O(1) growth rates of the original Early model. Only very long wavelengths relative to the upper fluid's radius of deformation L₁ are unstable. Eddy transports of heat are also reduced relative to estimates based on scaling arguments alone. Since the hydrostatic approximation for the lower-layer perturbation breaks down at great depths, a second model is presented in which energy propagates downward in an infinitely deep lower fluid obeying the full linearized fluid equations. In this model, the growth rates are again very small, but now all wavelengths are unstable with maximum growth rates occurring for wavelengths O(1) relative to L₁. These results illustrate the importance for the upper-layer meteorology of the interface boundary condition with the lower fluid, which is radically different from the rigid lower boundary of the Earth's troposphere.