Ultraviolet spectroscopic observations of coronal streamers in the SOHO era

Measurements made with the Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory can be used to determine physical parameters in the solar corona such as hydrogen and ion kinetic temperatures, electron densities, and absolute elemental abundances. Hydrogen and ion outflow velocities can be determined by combining the UV spectroscopic measurements with white light polarized brightness measurements. These combined measurements can be used to reveal physical characteristics of coronal streamers. To date we have studied plasma properties, such as the variation of plasma outflows in quiescent streamers, primarily in classic helmet streamers at solar minimum. Out-flows have not been observed in the centers of coronal streamers suggesting that these are closed magnetic field regions. We propose to study all of the coronal streamers in the UVCS synoptic dataset in order to investigate different types of streamers and their long-term evolution.     

Shock‐induced formation of wüstite and fayalite in a magnetite‐quartz target rock

Projectile–target interactions as a result of a large bolide impact are important issues, as abundant extraterrestrial material has been delivered to the Earth throughout its history. Here, we report results of shock‐recovery experiments with a magnetite‐quartz target rock positioned in an ARMCO iron container. Petrography, synchrotron‐assisted X‐ray powder diffraction, and micro‐chemical analysis confirm the appearance of wüstite, fayalite, and iron in targets subjected to 30 GPa. The newly formed mineral phases occur along shock veins and melt pockets within the magnetite‐quartz aggregates, as well as along intergranular fractures. We suggest that iron melt formed locally at the contact between ARMCO container and target, and intruded the sample causing melt corrosion at the rims of intensely fractured magnetite and quartz. The strongly reducing iron melt, in the form of μm‐sized droplets, caused mainly a diffusion rim of wüstite with minor melt corrosion around magnetite. In contact with quartz, iron reacted to form an iron‐enriched silicate melt, from which fayalite crystallized rapidly as dendritic grains. The temperatures required for these transformations are estimated between 1200 and 1600 °C, indicating extreme local temperature spikes during the 30 GPa shock pressure experiments.     

Transport and distribution of bacteria and diatoms in the aqueous surface microlayer of a salt marsh

The effects of tide and wind upon the distribution and transport of bacteria and diatoms in the aqueous surface microlayers of a Massachusetts and San Francisco Bay salt marsh were examined. The compression of the surface films by both tide and wind resulted in significant enrichments of bacterioneuston. At the San Francisco Bay site, significant numbers of diatoms were transported within the microlayer over a tidal cycle.     

A moated knoll in the Canary Passage

Summary A 100-fathoms high one-mile-wide elongate knoll approximately ten nautical miles long lies in 650 fms (1200 m) depth in the Canary Passage. The long axis is parallel to the axis of the passage. The knoll is flanked by a moat 5 to 20 fms deep which in turn is surrounded by a gentle arch or ridge of similar height. Although similar moats have been interpreted as a result of downward isostatic adjustments of islands and seamounts, this moat is considered the product of bottom scour by ocean currents.

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Über eine von einem Graben umgebene Kuppe in der Canary Passage

Zusammenfassung Eine 100 fathoms hohe, 1 Seemeile breite längliche Kuppe, ungefähr 10 Seemeilen lang, liegt in 650 fathoms (1200 m) Tiefe in der Canary Passage. Ihre Längsachse verläuft parallel zur Axe der Passage. Die Kuppe ist von einem 5 bis 20 fathoms tiefen Graben umgeben, welcher seinerseits von einer sanften Erhebung oder Wall gleichbleibender Höhe gesäumt wird. Obgleich ähnliche Gräben als Ergebnis abwärts gerichteten isostatischen Ausgleichs von Inseln undseamounts gedeutet werden, hält man diesen Graben für eine Folgeerscheinung der Erosion durch Meeresströmungen.

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Sur un récif submergé entouré d'un fossé dans le «Canary Passage»

Résumé Dans le «Canary Passage» il se trouve un récif submergé oblong, haute de 100 fathoms, ayant 1 mille marin de large et d'environ 10 milles marins de long. Il est situé à 650 fathoms (1200 mètres) de profondeur. Son axe longitudinal est parallèle à l'axe du «Canary Passage». Un fossé ayant 5 à 20 fathoms de profondeur longe le récif. Ce fossé est de son tour entouré d'un bombement ou d'une dorsale faible d'égal hauteur. Bien qu'on ait regardé de pareils fossés comme étant le produit d'une adaptation d'isostasie des îles et desseamounts, on suppose que ce fossé est dû à l'érosion du fond causée par les courants océaniques.

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This study was supported in part by the Office of Naval Research under Contract Nonr-266(48) and in part by The Bell Telephone Laboratories.Lamont Geological Observatory Contribution No. 707.     

Clearing the Martian air: The troubled history of dust storms

This note is an attempt to resolve some misconceptions regarding the historical record of the Martian atmospheric phenomena referred to as “dust storms,” but often called yellow storms, yellow clouds, planetwide dust storms, global dust storms, great dust storms, etc. The known frequency of planet-encircling storms will be specifically addressed. Better knowledge of the sizes, frequencies, and locations of Martian dust storms is needed for atmospheric modeling and for future mission planning.     

Theory of radio occultation by Saturn's rings

The radio occultation technique is developed here as a new method for the study of the physical properties of planetary ring systems. Particular reference is made to geometrical and system characteristics of the Voyager dual-wavelength (13 and 3.6 cm) experiment at Saturn. The rings are studied based on the perturbations they introduce in the spectrum of coherent sinusoidal radio signals transmitted through the rings from a spacecraft in the vicinity of the planet to Earth. Two separate signal components are identified in a perturbed spectrum: a sinusoidal component that remains coherent with the incident signal but is reduced in intensity and possibly changed in phase, and a Doppler-broadened incoherent component whose spectral shape and strength are determined by the occultation geometry and the radial variation of the near-forward radar cross section of illuminated ringlets. Both components are derived in terms of the physical ring properties starting from a conventional radar formulation of the problem of single scattering on ensembles of discrete scatterers, which is then generalized to include near-forward multiple scattering. The latter is accomplished through special solutions of the equation of transfer for particles that are larger than the wavelength. When the occultation geometry is optimized, contributions of an individual ringlet to a perturbed spectrum can be identified with radial resolution on the order of a few kilometers for the coherent component and a few hundred kilometers for the incoherent one, thus permitting high-resolution reconstruction of the radial profile of the optical depth, as well as reconstruction of the radar cross section of resolved ringlets. Simultaneous estimates of the optical depth and radar cross section of a ringlet at 3.6 cm-gl allow separation of its aerial density and particle size, if the particles are of known material and form a narrow size distibution with radii greater than several tens of centimeters. This separation is also achieved for radii ?10 cm from differential effects on the coherent signal parameters at 3.6- and 13-cm wavelengths. For the more general case of a broad size distribution modeled by a power law, the absence of differential effects on the coherent signal binds the minimum size to be ?10 cm. In this case, the radius inferred from an estimate of the radar cross section represents an equivalent radius, which is strongly controlled by the maximum size of the distribution provided that the power index is in the range 3 to 4. On the other hand, detection of differential coherent signal extinction determines an upper bound on the maximum size and a lower bound on the power index, assuming water-ice particles. These bounds, together with an inferred equivalent size, constrain the size distribution at both its small and large ends.     

Marine Layer Stratus Study

The intent of this study is to develop a better understanding of the behavior of late spring through early fall marine layer stratus and fog at Vandenberg Air Force Base, which accounts for a majority of aviation forecasting difficulties. The main objective was to use Leipper (1995) study as a starting point to evaluate synoptic and mesoscale processes involved, and identify specific meteorological parameters that affected the behavior of marine layer stratus and fog. After identifying those parameters, the study evaluates how well the various weather models forecast them. The main conclusion of this study is that weak upper-air dynamic features work with boundary layer motions to influence marine layer behavior. It highlights the importance of correctly forecasting the surface temperature by showing how it ties directly to the wind field. That wind field, modified by the local terrain, establishes the low-level convergence and divergence pattern and the resulting marine layer cloud thicknesses and visibilities.