Studies of granular velocities

Vertical small scale velocities deduced from highly resolved spectra in the center of the solar disk, obtained with a RCA image intensifier tube, are discussed. As a main result we find that the velocities of small elements (< 2) are remarkably larger in active regions around sunspots than in the quiet Sun. In both cases the velocities decrease with height in the solar atmosphere (Figure 2).Mitteilungen aus dem Fraunhofer-Institut Nr. 145.     

Differential rotation and giant cell circulation of solar Ca+-network

We report new results obtained from high precision computer controlled tracings of ca. 400 bright Ca⁺-mottles made during summer 1975 in continuation of our 1974 program (Schröter and Wöhl, 1975). In particular, we looked in 1975 for the existence of a giant circulation pattern in the equatorial zone. We find for the differential rotation: = 13.93 – 2.90 sin² B (deg/day, sidereal) when combining the new measurements with those obtained in 1974. Observations from 26th April until June 19th give strong evidence that at that time four giant circulation cells, crossing the solar equator, (i.e. a nonaxisymmetric velocity field pattern with respect to the solar equator) did exist. This yields two more rapid and two slower rotating sectors with v = ±80 m s^–1. These giant cells transport angular momentum towards the equator.     

Desorption of molecules from interstellar grains and the heating of dust clouds

Temperature fluctuations induced in very small (r10^–3 ) interstellar grains by the absorption of photons from the ultra-violet radiation field or by energy released on molecule formation are shown to lead to significant gas heating due to thermal desorption of condensed atoms or molecules. For clouds with N(H)=1–10×10²⁰ cm^–2, heating rates due to this process are comparable to direct heating by cosmic rays or grain photoelectrons.     

Effects of diverging coronal fields on the solar wind expansion

The expansion of the solar wind in divergent flux tubes is calculated by taking into account a magnetic acceleration of the particles, analogous to the magnetic mirror effect.The resulting force term included in the magnetohydrodynamical equations describes a conversion of thermal into kinetic energy. This causes an additional acceleration of the solar wind plasma which has never been taken into account before. The force is directed opposite to the magnetic field gradient. Consequently, in this case the solar wind velocity increases faster to its asymptotic value than it does for corresponding nonmagnetic solutions. Therefore inside and close to the solar corona markedly higher velocities are found. Compared to strictly hydrodynamical models, the critical point is shifted towards the Sun, and the radial decrease of the ratio of thermal to kinetic energy is faster.The necessary prerequisites for these calculations are (a) that the gyroperoid _g of the plasma particles is much shorter than the Coulomb collision time _c , and (b) that the collision time _c is shorter than the characteristic time _d in which an appreciable amount of thermal anisotropy is built up. Thus it is (a) insured that the particles have established magnetic moments and follow the guiding center approximation, and (b) an almost isotropic velocity distribution function is maintained which, in this first approximation of a purely radial expansion, justifies the use of isotropic pressures and temperatures.Both (a) and (b) are shown to be fulfilled in a region around the Sun out to about 20R , and thermal anisotropies developing outside of this region could explain the observed magnetically aligned anisotropies at 1 AU.     

Adiabatic plasma convection in a dipole field: Variation of plasma bulk parameters with L

We here investigate the motion of particles in a dipole magnetic field under the assumption of conservation of the first two adiabatic invariants. The results are then combined with Liouville's theorem to obtain the variation of the distribution function, and hence the plasma bulk parameters with L-shell. A comparison of the numerical results with recently published analytical approximations is made. Finally, the results are used to describe the structure of the ring current plasma in the outer radiatoin zone, the effects of the Alfvén layers being quantitatively evaluated for a simple electric field model.     

The spectral reflectivity of select areas on Europa

The July 12, 1973, occultation of Europa by Io was observed in 30 wavelength channels in the spectral region λλ3200-11, 000 Å with the 200-inch Hale telescope and a multichannel spectrometer. The data are presented in absolute units above the Earth's atmosphere. The data are analyzed to obtain the spectral reflectivity of seven localized areas on the disk of Europa centered on 324°W longitude. The equatorial material is confirmed to be darker than the eastward-skewed bright north polar cap and a hint is evident that the darker material as well may be somewhat redder than the cap material.     

Pioneer 10 ultraviolet photometer observations of the Jovian hydrogen torus: The angular distribution

The Pioneer 10 ultraviolet photometer observations of the Jovian hydrogen torus are analyzed to obtain the angular distribution. The cloud is asymmetric about Io, where the atoms presumably originate, with the greater density occurring in the trailing portion. A simple model which assumes Jeans escape from the atmosphere of Io is developed and compared to the observations. The results suggest that the exospheric temperature is high (～3000 K) and that the ionization lifetime of the cloud atoms is ～1 × 10⁵ sec.     

Evidence for downflow following a coronal transient?

On 11 September 1973 a peculiar prominence was observed. The prominence displayed strong ( 50km s^–1) systematic motions toward and away from the observer. The unusual spectrographic appearance of the prominence might have been due to downflowing material lifted into the corona during an earlier coronal transient.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.