New 1982 — 1990 photometry of λ Andromedae and its 11-year cycle

We present photoelectric photometry of λ And never before published, obtained between February 1982 and December 1990 at 29 different observatories. Then we combine it with all other photometry available to us (previously published, contained in the I.A.U. Commission 27 Archives, and obtained with the Vanderbilt 16-inch automatic telescope but not yet published), to yield a 14.8-year data base. Analysis reveals a long-term cycle in mean brightness, with a full range of 0^m.15 and a period of 11.4 ± 0.4 years. Because most of our new photometry was concentrated in the 1983-84 observing season, we analyze that one well-defined light curve with a two-spot model. Spot A keeps a 0^m.04 amplitude throughout four rotation cycles whereas the amplitude of spot B diminishes from 0^m.09 down almost to 0^m.03. The spot rotation periods were 55^d.9 ± 0^d.6 and 520^d.8 ± 1^d.0, respectively.     

Progress in coronal physics

This paper reviews research highlights of the past five years. Considerable progress has been made in observing and interpreting coronal mass ejections. The stability of coronal loops is much better understood and new observations of the onset of wind streams in coronal holes have been made. Observations from the Solar Maximum Mission should helpt to clarify the physics of the active corona.The mechanisms that heat the corona and accelerate the high-speed wind streams remain to be identified, however.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Bending waves and the structure of Saturn's rings

The surface mass density profiles at four locations within Saturn's rings are calculated using Voyager spacecraft images of spiral bending waves. Bending waves are vertical corrugations in Saturn's rings which are excited at vertical resonances of a moon, e.g., Mimas, whose orbit is inclined with respect to the mean plane of the rings. Bending waves propagate toward Saturn by virtue of the rings' self-gravity; their wavelength depends on the local surface mass density of the rings. Observations of bending waves can thus be used to determine the surface density in regions of Saturn's rings near vertical resonances. The average surface density of the outer B ring near Mimas' 4:2 inner vertical resonance is 54 ± 10 g cm^?2. Surface density in this region probably varies by ～ 30% over radial length scales of tens of kilometers; and irregular radial structure is present on similar length scales in this region. Surface densities ranging from 24 g cm^?2 to 45 g cm^?2 are found in the A ring. Small scale variations in surface density are not seen in the A ring, consistent with its more uniform optical appearance.     

Cloud computing and virtualization within the regional climate model and evaluation system

The Regional Climate Model Evaluation System (RCMES) facilitates the rapid, flexible inclusion of NASA observations into climate model evaluations. RCMES provides two fundamental components. A database (RCMED) is a scalable point-oriented cloud database used to elastically store remote sensing observations and to make them available using a space time query interface. The analysis toolkit (RCMET) is a Python-based toolkit that can be delivered as a cloud virtual machine, or as an installer package deployed using Python Buildout to users in order to allow for temporal and spatial regridding, metrics calculation (RMSE, bias, PDFs, etc.) and end-user visualization. RCMET is available to users in an “offline”, lone scientist mode based on a virtual machine dynamically constructed with model outputs and observations to evaluate; or on an institution’s computational cluster seated close to the observations and model outputs. We have leveraged RCMES within the content of the Coordinated Regional Downscaling Experiment (CORDEX) project, working with the University of Cape Town and other institutions to compare the model output to NASA remote sensing data; in addition we are also working with the North American Regional Climate Change Assessment Program (NARCCAP). In this paper we explain the contribution of cloud computing to RCMES’s specifically describing studies of various cloud databases we evaluated for RCMED, and virtualization toolkits for RCMET, and their potential strengths in delivering user-created dynamic regional climate model evaluation virtual machines for our users.     

Geochronology and petrochemistry of Easter and Sala y Gomez Islands: implications for the origin of the Sala y Gomez Ridge

Easter and Sala y Gomez Islands lie along the Sala y Gomez Ridge, a broad zone of high topography and scattered seamounts extending east-southeast from the East Pacific Rise. K-Ar ages and major element abundances of volcanic rocks from these islands are used to test the fixed melting spot hypothesis for the origin of this feature. Poike volcano, the oldest center on Easter Island, was constructed in two episodes, occurring at 2.5 and 0.9 m.y. ago. Eruptive activity on Sala y Gomez was nearly contemporaneous with the earliest volcanism on Easter Island. No migration of volcanism with time is apparent along the Sala y Gomez Ridge. Basaltic rocks from Easter Island have tholeiitic affinities, while those dredged from the base of Sala y Gomez belong to an alkali olivine basalt series. Differences in basalt chemistry suggest that the volcanic rocks from the two islands formed from magmas that equilibrated at different pressures, and a model is presented which relates the character of the erupted liquids to magma segregation at the base of a progressively thickening lithosphere. The islands and seamounts comprising the Sala y Gomez Ridge do not fall on a small circle about the Nazca-mantle pole of absolute motion. Available evidence, therefore, does not support a fixed melting spot origin for Easter Island, Sala y Gomez, and the Sala y Gomez Ridge. Rather, it appears that the Sala y Gomez Ridge formed along a leaky fracture zone, and in response to a major re-orientation of spreading centers in this area.     

From subduction to transform motion: a seabeam survey of the Hellenic trench system

Preliminary results of a multi-narrow beam survey of the Hellenic trench system, in the Eastern Mediterranean, are presented. The southwestern Ionian branch is divided in small basins, partly filled with Pleistocene sediments. The morphology suggests that the basins are deformed by a compressional stress acting roughly perpendicularly to the trench along N50°E. This direction is the direction of the regional slip vector of the shallow thrust-type earthquakes. The structure of the southeastern Pliny-Strabo branch is quite different. Narrow en-e´chelon slots, oriented N40°E, have been mapped within the main troughs oriented N60°E. The regional earthquake slip vector is also oriented along N40°E. We conclude that the Hellenic trench system is an active subduction system, dominated by thrust along the Ionian branch and by transform motion along the Pliny-Strabo branch.     

Evaluating new fault-controlled hydrothermal dolomitization models: Insights from the Cambrian Dolomite,Western Canadian Sedimentary Basin

Fault-controlled hydrothermal dolomitization in tectonically complex basins can occur at any depth and from different fluid compositions, including ‘deep-seated’, ‘crustal’ or ‘basinal’ brines. Nevertheless, many studies have failed to identify the actual source of these fluids, resulting in a gap in our knowledge on the likely source of magnesium of hydrothermal dolomitization. With development of new concepts in hydrothermal dolomitization, the study aims in particular to test the hypothesis that dolomitizing fluids were sourced from either seawater, ultramafic carbonation or a mixture between the two by utilizing the Cambrian Mount Whyte Formation as an example. Here, the large-scale dolostone bodies are fabric-destructive with a range of crystal fabrics, including euhedral replacement (RD1) and anhedral replacement (RD2). Since dolomite is cross-cut by low amplitude stylolites, dolomitization is interpreted to have occurred shortly after deposition, at a very shallow depth (<1 km). At this time, there would have been sufficient porosity in the mudstones for extensive dolomitization to occur, and the necessary high heat flows and faulting associated with Cambrian rifting to transfer hot brines into the near surface. While the δ¹⁸O_water and ⁸⁷Sr/⁸⁶Sr ratios values of RD1 are comparable with Cambrian seawater, RD2 shows higher values in both parameters. Therefore, although aspects of the fluid geochemistry are consistent with dolomitization from seawater, very high fluid temperature and salinity could be suggestive of mixing with another, hydrothermal fluid. The very hot temperature, positive Eu anomaly, enriched metal concentrations, and cogenetic relation with quartz could indicate that hot brines were at least partially sourced from ultramafic rocks, potentially as a result of interaction between the underlying Proterozoic serpentinites and CO₂-rich fluids. This study highlights that large-scale hydrothermal dolostone bodies can form at shallow burial depths via mixing during fluid pulses, providing a potential explanation for the mass balance problem often associated with their genesis.     

Dimensions of drought: South African case studies

The recent drought in southern Africa has underscored the need for detailed analysis of the phenomenon. While geographers have researched the causes and impacts of drought in many African contexts, South Africa and in particular its Bantustans have not received sufficient similar attention. This paper outlines firstly the dimensions of drought in South Africa, including the biophysical and socio-economic factors. Issues such as land-use management, drought planning and relief are interrogated in the South African context. The final section of the paper highlights these debates with specific reference to case studies of past and present drought initiatives in South Africa.