Further analysis of singular vector and ENSO predictability in the Lamont model—Part I: singular vector and the control factors

In this study, singular vector analysis was performed for the period from 1856 to 2003 using the latest Zebiak–Cane model version LDEO5. The singular vector, representing the optimal growth pattern of initial perturbations/errors, was obtained by perturbing the constructed tangent linear model of the Zebiak–Cane model. Variations in the singular vector and singular value, as a function of initial time, season, ENSO states, and optimal period, were investigated. Emphasis was placed on exploring relative roles of linear and nonlinear processes in the optimal perturbation growth of ENSO, and deriving statistically robust conclusions using long-term singular vector analysis. It was found that the first singular vector is dominated by a west–east dipole spanning most of the equatorial Pacific, with one center located in the east and the other in the central Pacific. Singular vectors are less sensitive to initial conditions, i.e., independence of seasons and decades; while singular values exhibit a strong sensitivity to initial conditions. The dynamical diagnosis shows that the total linear and nonlinear heating terms play opposite roles in controlling the optimal perturbation growth, and that the linear optimal perturbation is more than twice as large as the nonlinear one. The total linear heating causes a warming effect and controls two positive perturbation growth regions: one in the central Pacific and the other in the eastern Pacific; whereas the total linearized nonlinear advection brings a cooling effect controlling the negative perturbation growth in the central Pacific.     

The lithospheric mantle beneath the Kerguelen Islands (Indian Ocean): petrological and petrophysical characteristics of mantle mafic rock types and correlation with seismic profiles

Deep-seated meta-igneous xenoliths brought to the surface by alkali basaltic magmas from the Kerguelen Islands reveal that basaltic magmas have intruded the upper mantle throughout their geological evolution. These xenoliths record volcanic activity associated with their early South East Indian Ridge location and subsequent translation to an intraplate setting over the Kerguelen Plume. The meta-igneous xenoliths sample two distinctive geochemical episodes: one is tholeiitic transitional and one is alkali basaltic. Geothermobarometry calculations provide a spatial context for the rock type sequence sampled and for interpreting petrophysical data. The garnet granulites equilibrated over a pressure range of 1.15 to 1.35 GPa and the garnet pyroxenite at 1.8 GPa. Ultrasonic measurements of compressional wave speed V_P have been carried out at pressures up to 1 GPa, and densities measured for representative samples of meta-igneous xenoliths and for a harzburgite that represents the peridotitic mantle. V_P and density have also been calculated using modal proportions of minerals and appropriate elastic properties for the constituent minerals. Calculated and measured V_P agree well for rock types with microstructures not complicated by kelyphitic breakdown of garnet and/or pervasive grain-boundary cracking. Pyroxene granulites have measured and calculated V_P within the range 7.37-7.52 km/s; calculated velocities for the garnet granulites and pyroxenites range from 7.69 to 7.99 km/s, whereas measured and calculated V_P for a mantle harzburgite are 8.45 and 8.29 km/s respectively. The seismic structure observed beneath the Kerguelen Islands can be explained by (1) a mixture of underplated pyroxene granulites and ultramafic rocks responsible for the 2-3 km low velocity transitional zone below the oceanic layer 3, (2) varying proportions of granulites and pyroxenites in different regions within the upper mantle producing the lateral heterogeneities, and (3) intercalation of the granulites and pyroxenites throughout the entire upper mantle column, along with elevated temperatures, accounting for the relatively low mantle velocities (7.70-7.95 km/s).     

A Retrospective Analysis of Ozone Formation in the Lower Fraser Valley,British Columbia,Canada. Part II: Influence of Emissions Reductions on Ozone Formation

A mechanistic exploration of how ozone formation in the Lower Fraser Valley (LFV) has changed over a 20-year (1985–2005) retrospective period was performed using numerical models, observations, and emissions data from four key episodes selected from the 20-year period. The motivation for this study was the observed differences in trends in summertime episodic ozone concentrations recorded at various monitoring stations within the valley; stations in the western part of the valley have generally shown a noticeable reduction in episodic ozone concentrations whereas stations in the eastern part of the valley have shown little or no improvement in their maximum 8-hour averaged ozone concentrations. Concurrent with these air quality changes, there has been a well-documented reduction in ozone precursor emissions along with an observed shift in the population patterns within the valley over the 20-year period. Ozone formation for four episodes, encompassing the different meteorological regimes that occur during LFV ozone events and spanning the retrospective period, were investigated using the Weather Research and Forecasting (WRF)-Sparse Matrix Operator Kernel Emission (SMOKE)-Community Multiscale Air Quality (CMAQ) modelling system. For each episode, two simulations, intended to isolate the effects of emission changes from meteorological changes, were performed: one with emissions set at the 1985 level and the other with emissions set at the 2005 level. Based on analysis of the model output, observational data, and precursor emission inventories, we find that the Port Moody station in the western LFV remains a volatile organic compound (VOC)-sensitive location; the central part of the LFV around the town of Chilliwack has generally changed from being VOC-limited to being NO_x-limited; the easternmost part of the valley around the town of Hope has been and remains NO_x-limited. Furthermore, based on the observational data and numerical model output, ozone production efficiency as a function of NO has increased noticeably at Chilliwack and likely in the other eastern parts of the valley. This efficiency increase has likely offset some of the benefits resulting from local NO_x emission reductions.

RÉSUMÉ?[Traduit par la rédaction] Nous avons effectué une exploration mécaniste de la façon dont la formation de l'ozone dans la vallée du bas Fraser (VBF) a changé au cours d'une période rétrospective de 20 ans (1985–2005) en nous servant de modèles numériques, d'observations et de données sur les émissions pour quatre épisodes clés choisis dans la période de 20 ans. Ce sont les différences observées entre les tendances dans les concentrations épisodiques d'ozone enregistrées à certaines stations de surveillance dans la vallée qui ont motivé cette étude : les stations dans la partie ouest de la vallée ont généralement affiché une réduction notable des concentrations épisodiques d'ozone alors que les stations dans la partie est de la vallée n'ont montré que peu ou pas d'amélioration dans les valeurs maximales des concentrations moyennes d'ozone sur 8 heures. Concurremment avec ces changements dans la qualité de l'air, il s'est produit une réduction bien documentée dans les émissions de précurseurs de l'ozone en même temps qu'un déplacement observé dans les configurations de population dans la vallée au cours de la période de 20 ans. Nous avons étudié la formation d'ozone au cours de quatre épisodes, englobant les différents régimes météorologiques survenus lors des événements d'ozone dans la VBF et couvrant la période rétrospective, à l'aide du système de modélisation SMOKE (Sparse Matrix Operator Kernel Emissions) – CMAQ (Community Multiscale Air Quality) du WRF (Weather Research and Forecasting). Pour chaque épisode, nous avons effectué deux simulations visant à isoler l'effet des changements dans les émissions de l'effet des changements météorologiques, l'une avec les émissions réglées au niveau de 1985 et l'autre avec les émissions réglées au niveau de 2005. En nous basant sur l'analyse de la sortie du modèle, les données d'observation et les inventaires des émissions de précurseurs, nous trouvons que la stations de Port Moody dans l'ouest de la VBF demeure un endroit sensible aux composés organiques volatiles (COV); la partie centrale de la VBF, autour de la ville de Chilliwack, a généralement changé de « limitée par les COV » à « limitée par les NO_x »; la partie la plus à l'est de la vallée, autour de la ville de Hope, était et est restée « limitée par les NO_x ». De plus, d'après les données d'observation et la sortie du modèle numérique, l'efficacité de la production d'ozone en fonction de NO a notablement augmenté à Chilliwack et vraisemblablement dans les autres parties de l'est de la vallée. Cette augmentation d'efficacité a probablement annulé certains gains provenant des réductions dans les émissions locales de NO_x.     

Geography’s changing lexicon: measuring disciplinary change in Anglophone human geography through journal content analysis

Much writing on changing trends in geographical practices is based on subjective interpretations of the discipline’s scholarly output. This paper introduces a data source which provides quantitative information on the discipline’s lexicon through full-text searching of the contents of five of the discipline’s major Anglophone journals. Analysis of the large data set identifies two main trends in geography’s language and practices during the period 1950-1998: one group of terms associated with quantitative work became prominent in the 1970s but declined in relative importance thereafter - though by no means disappearing from the lexicon; the other, comprising a range of terms generally associated with cultural and social geography, increased in prominence from the 1980s on.