The Solar Oscillations Investigation - Michelson Doppler Imager

The Solar Oscillations Investigation (SOI) uses the Michelson Doppler Imager (MDI) instrument to probe the interior of the Sun by measuring the photospheric manifestations of solar oscillations. Characteristics of the modes reveal the static and dynamic properties of the convection zone and core. Knowledge of these properties will improve our understanding of the solar cycle and of stellar evolution. Other photospheric observations will contribute to our knowledge of the solar magnetic field and surface motions. The investigation consists of coordinated efforts by several teams pursuing specific scientific objectives.The instrument images the Sun on a 1024² CCD camera through a series of increasingly narrow spectral filters. The final elements, a pair of tunable Michelson interferometers, enable MDI to record filtergrams with a FWHM bandwidth of 94 m. Normally 20 images centered at 5 wavelengths near the Ni I 6768 spectral line are recorded each minute. MDI calculates velocity and continuum intensity from the filtergrams with a resolution of 4 over the whole disk. An extensive calibration program has verified the end-to-end performance of the instrument.To provide continuous observations of the longest-lived modes that reveal the internal structure of the Sun, a carefully-selected set of spatial averages are computed and downlinked at all times. About half the time MDI will also be able to downlink complete velocity and intensity images each minute. This high rate telemetry (HRT) coverage is available for at least a continuous 60-day interval each year and for 8 hours each day during the rest of the year. During the 8-hour HRT intervals, 10 of the exposures each minute can be programmed for other observations, such as measurements in MDI's higher resolution (1.25) field centered about 160 north of the equator; meanwhile, the continuous structure program proceeds during the other half minute. Several times each day, polarizers will be inserted to measure the line-of-sight magnetic field.MDI operations will be scheduled well in advance and will vary only during the daily 8-hour campaigns. Quick-look and summary data, including magnetograms, will be processed immediately. Most high-rate data will be delivered only by mail to the SOI Science Support Center (SSSC) at Stanford, where a processing pipeline will produce 3 Terabytes of calibrated data products each year. These data products will be analyzed using the SSSC and the distributed resources of the co-investigators. The data will be available for collaborative investigations.The MDI Engineering Team leaders include: D. Akin, B. Carvalho, R. Chevalier, D. Duncan, C. Edwards, N. Katz, M. Levay, R. Lindgren, D. Mathur, S. Morrison, T. Pope, R. Rehse, and D. Torgerson.     

Modelling, design and diagnostics for a photoionised plasma experiment

Photoionised plasmas are common in astrophysical environments and new high resolution spectra from such sources have been recorded in recent years by the Chandra and XMM-Newton satellites. These provide a wealth of spectroscopic information and have motivated recent efforts aimed at obtaining a detailed understanding of the atomic-kinetic and radiative characteristics of photoionised plasmas. The Z-pinch facility at the Sandia National Laboratories is the most powerful terrestrial source of X-rays and provides an opportunity to produce photoionised plasmas in a well characterised radiation environment. We present modelling work and experimental design considerations for a forthcoming experiment at Sandia in which X-rays from a collapsing Z-pinch will be used to photoionise low density neon contained in a gas cell. View factor calculations were used to evaluate the radiation environment at the gas cell; the hydrodynamic characteristics of the gas cell were examined using the Helios-CR code, in particular looking at the heating, temperature and ionisation of the neon and the absorption of radiation. Emission and absorption spectra were also computed, giving estimates of spectra likely to be observed experimentally.     

Precipitation extremes and the impacts of climate change on stormwater infrastructure in Washington State

The design of stormwater infrastructure is based on an underlying assumption that the probability distribution of precipitation extremes is statistically stationary. This assumption is called into question by climate change, resulting in uncertainty about the future performance of systems constructed under this paradigm. We therefore examined both historical precipitation records and simulations of future rainfall to evaluate past and prospective changes in the probability distributions of precipitation extremes across Washington State. Our historical analyses were based on hourly precipitation records for the time period 1949–2007 from weather stations in and near the state’s three major metropolitan areas: the Puget Sound region, Vancouver (WA), and Spokane. Changes in future precipitation were evaluated using two runs of the Weather Research and Forecast (WRF) regional climate model (RCM) for the time periods 1970–2000 and 2020–2050, dynamically downscaled from the ECHAM5 and CCSM3 global climate models. Bias-corrected and statistically downscaled hourly precipitation sequences were then used as input to the HSPF hydrologic model to simulate streamflow in two urban watersheds in central Puget Sound. Few statistically significant changes were observed in the historical records, with the possible exception of the Puget Sound region. Although RCM simulations generally predict increases in extreme rainfall magnitudes, the range of these projections is too large at present to provide a basis for engineering design, and can only be narrowed through consideration of a larger sample of simulated climate data. Nonetheless, the evidence suggests that drainage infrastructure designed using mid-20th century rainfall records may be subject to a future rainfall regime that differs from current design standards.     

Coupled substitutions in the tourmaline group

Statistical analysis of 136 natural tourmaline compositions from the literature reveals the presence and extent of coupled substitutions involving several cations and structural sites. In schorls and dravites these are a dehydroxylation type substitution (1) (OH)^–+R²⁺ = R³⁺+O^2– and an alkali-defect type substitution (2) R⁺+R²⁺ = R³⁺+, Al³⁺ being the predominant R³⁺ action. Substitution (1) which represents solid solution towards a proton-deficient end-member, R⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃ Si₆O₁₈O₃(OH), accounts for three times as much of the observed compositional variability as does (2) which represents substitution toward a hypothetical alkali-free end-member, (R ₂ ²⁺ R³⁺) R ₆ ³⁺ (BO₃)₃Si₆O₁₈(OH)₄. The occurrence of both of these substituions produces intermediates between end-member schorl/ dravite, R⁺ R ₃ ²⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈(OH)₄, and a new series within the tourmaline group, R _1–x ⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈O_3–x (OH)_1+x.In addition to dehydroxylation type, 2(OH)^–+Li⁺ = R³⁺+20^2–, and possibly alkali-defect type, 2R⁺+Li⁺ = R³⁺+2, substitutions, a third type Li⁺+O^2– = (OH)^–+, occurs in the elbaites giving rise to Li-poor, proton-rich species. All three substitutions serve to reduce the Li-content of natural elbaite which, as a result, does not attain the composition of the ideal end-member, Na(Li_1.5Al_1.5)Al₆(BO₃)₃Si₆O₁₈(OH)₄. Substitution from elbaite and schorl/dravite toward R _1–x ⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈O_3–x(OH)_1+x is very extensive and may be complete.Substitution toward R _1–x ⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈O_3–x(OH)_1+x results in improved local charge balance. The mean deviation from oxygen charge saturation is at a maximum in end-member schorl, dravite and elbaite. Substitutions (1) and (2) progressively decrease but substitution (1) does so more effectively, which may explain its predominance in nature. However, alkali-defective end-members appear to be unstable regardless of . Substitution (3) in the elbaites cannot be discussed on the basis of charge balance considerations at present due to the lack of structural information on proton-rich species.     

Fe2+ -F avoidance in silicates

Fe²⁺-F avoidance, reported in the literature in micas and amphiboles, can be accounted for by crystal field theory. The crystal field splitting parameter, Δ_O, of Fe²⁺ octahedrally coordinated to F^? is significantly smaller than its value when (OH)^? is the coordinating anion. Thus, the presence of Fe²⁺ is not favored at sites where F^? substitutes for (OH)^? due to smaller crystal field stabilization energy.     

Rare earth elements in granitic rocks

The younger granites in Finland contain more REE than the older ones. In the youngest, postorogenic rapakivi granites, the total REE concentration is highest, the light REE are more enriched, and the negative Eu anomaly is more pronounced than in the older granites. The enrichment of the light REE, the anomalous behavior of the extreme elements (La, Ce, and Lu) in normalized graphs, and the depletion of Eu indicate the degree of differentiation the rock has undergone. These features are usually more pronounced in large, homogeneous granites than in metamorphic or volcanogenic rocks. Silicic vein rocks usually contain less REE than the granites proper; the distribution pattern in many is as in granites, but in some the heavy elements are more enriched. The positive Eu anomaly in Precambrian metamorphic rocks is tentatively attributed to metamorphic differentiation and to the secretion of silicic material from the host rock.     

Medical or health geography? Populations,peoples and places

While medical geography has grown eclectic to the point where a growing number of medical geographers prefer the terms health geographer, health geography, or the geography of health, schisms have nonetheless developed between Mayer et al. and those who have urged medical geographers to seek new epistemologies. Lost in this debate is the rapid and considerable growth of research by medical and health geographers. The author first reviews recent research on the mapping and modeling of diseases, then examines the literature on the access, delivery, and planning of health services. He then considers the debate over medical geography versus a geography of health. Opportunities are identified where medical, health, and population geographers can productively collaborate. Sharing many of the same theoretical and methodological strengths, weaknesses, and frustrations, medical, health, and population geographers need to work together toward creating inclusive geographies.