The Shape of the Solar Limb: Models and Observations     

G. Thuillier  J. Claudel  D. Djafer  M. Haberreiter  N. Mein  S. M. L. Melo  W. Schmutz  A. Shapiro  C. I. Short  S. Sofia 《Solar physics》2011,268(1):125-149

In this paper we compare observed, empirical, and modelled solar limb profiles and discuss their potential use to derive physical properties of the solar atmosphere. The PHOENIX, SolMod3D, and COSI radiative transfer codes as well as VAL-C models are used to calculate the solar limb shape under different assumptions. The main properties of each model are shown. The predicted limb shape as a function of wavelength for different features on the solar disk, such as quiet Sun, sunspots, and faculae, is investigated. These models provide overall consistent limb shapes with some discrepancies that are discussed here in terms of differences in solar atmosphere models, opacities, and the algorithms used to derive the solar limb profile. Our analysis confirms that the most common property of all models is limb shapes that are much steeper than what is observed, or predicted by the available empirical models. Furthermore, we have investigated the role of the Fraunhofer lines within the spectral domain used for the solar limb measurements. Our results show that the presence of the Fraunhofer lines significantly displaces the limb inflection point from its position estimated assuming only the photospheric continuum. The PICARD satellite, launched on 15 June 2010, will provide measurements of the limb shape at several wavelengths. This work shows that the precision of these measurements allows for discrimination among the available models.  相似文献   

Population Change in U.S. Cities: Estimating and Explaining the Extent of Decline and Level of Resurgence   总被引：1，自引：0，他引：1  

John Rennie Short  Michael Mussman 《The Professional geographer》2013,65(1):112-123

The revalorization of the U.S. metropolis and restructuring of the U.S. economy are leading to increasingly complex patterns of population growth and decline. In this article we provide an empirical context for understanding the embodied nature of these changes by analyzing the long-term, demographic changes for the 100 largest cities. In terms of population change we identify four model urban types: steady decline, continuous increase, growth interrupted, and slowly resurgent. We consider, in detail, cities where population decline has halted and others where there are indications of population resurgence. The article focuses on these resurgent cities, provides some causal explanations, discusses the role of gentrification, and explores policy implications.  相似文献   

Temporal variation of intertidal seagrass in southern China (2008–2014)     

Guanglong Qiu  Frederick T. Short  Hangqing Fan  Guohua Liu 《Ocean Science Journal》2017,52(3):397-410

Understanding the temporal dynamics of seagrasses and the major influences on seagrass growth is critical for seagrass habitat conservation and administration. However, little work has been done regarding these issues in southern China. To examine inter-annual and seasonal variations of the intertidal Halophila ovalis community in southern China, we conducted quarterly sampling using the SeagrassNet methodology and assessed environmental conditions as well as direct anthropogenic impacts on the seagrass meadow from July 2008 to October 2014. Our study demonstrated strong inter-annual and seasonal dynamics of the intertidal seagrass meadow in the study area. Generally, the community performed best (highest seagrass cover, leaf area, shoot density, total biomass) in summer and worst in spring among the 4 seasons. The temporal variations in the seagrass community attributes (e.g. above-ground biomass) were significantly affected by precipitation, atmospheric visibility, and salinity, while leaf width was significantly negatively correlated with temperature, atmospheric visibility and salinity. Temperature was a major factor influencing the seagrass community (both macroalgae and seagrass), with temperature data showing an inverse relationship between seagrass and macroalgae. The above-ground: below-ground biomass ratio and leaf width of H. ovalis were the most sensitive plant parameters monitored when assessing environmental interactions. Human physical disturbances did not have a significant effect on seagrass dynamics in the study area. We concluded that long-term monitoring (like SeagrassNet) is valuable in understanding the relationship between environmental variables and seagrasses.  相似文献   

Subtidal Eelgrass Declines in the Great Bay Estuary,New Hampshire and Maine,USA     

Nora T. Beem  Frederick T. Short 《Estuaries and Coasts》2009,32(1):202-205

Long-term monitoring of eelgrass (Zostera marina L.) beds in the central subtidal portion of the Great Bay Estuary showed declines at both transplanted sites and reference beds. Eelgrass beds transplanted as mitigation for habitat loss from port development reached comparable functions (e.g., primary production, canopy structure) to natural reference sites by the late 1990s, within 6 years of transplanting. Data from 2001 to the present show significant declines in eelgrass parameters (biomass, shoot density, canopy height, leaf area) at all sites, suggesting that these declines are the result of an estuary-wide factor.  相似文献   

Long term monitoring for oil in the Exxon Valdez spill region   总被引：2，自引：1，他引：1  

Payne JR  Driskell WB  Short JW  Larsen ML 《Marine pollution bulletin》2008,56(12):2067-2081

In the aftermath of the 1989 Exxon Valdez oil spill, a Long Term Environmental Monitoring Program (LTEMP) has been regularly sampling mussels (and some sediments) for polycyclic aromatic and saturated hydrocarbons (PAH and SHC) at sites in Port Valdez, Prince William Sound, and the nearby Gulf of Alaska region. After 1999, a decreasing trend appears in total PAH (TPAH) in tissues at all sites with current values below 100 ng/g dry weight (many below 50 ng/g). Currently, most samples reflect a predominantly dissolved-phase signal. This new low in TPAH likely represents ambient background levels. Synchrony in TPAH time-series and similarities in the hydrocarbon signatures portray regional-scale dynamics. The five inner Prince William Sound sites show similar composition and fluctuations that are different from the three Gulf of Alaska sites. The two Port Valdez sites represent a unique third region primarily influenced by the treated ballast water discharge from the Alyeska Marine Terminal. Prince William Sound has reverted to a stable environment of extremely low level contamination in which local perturbations are easily detected.  相似文献   

Photosynthetic responses of subtidal seagrasses to a daily light cycle in Torres Strait: A comparative study     

Stuart J. Campbell  Simon P. Kerville  Robert G. Coles  Fred Short 《Continental Shelf Research》2008

In this study, we examined the photosynthetic responses of five common seagrass species from a typical mixed meadow in Torres Strait at a depth of 5–7 m using pulse amplitude modulated (PAM) fluorometry. The photosynthetic response of each species was measured every 2 h throughout a single daily light cycle from dawn (6 am) to dusk (6 pm). PAM fluorometry was used to generate rapid light curves from which measures of electron transport rate (ETR_max), photosynthetic efficiency (α), saturating irradiance (E_k) and light-adapted quantum yield (ΔF/F′_m) were derived for each species. The amount of light absorbed by leaves (absorption factor) was also determined for each species. Similar diurnal patterns were recorded among species with 3–4 fold increases in maximal electron rate from dawn to midday and a maintenance of ETR_max in the afternoon that would allow an optimal use of low light by all species. Differences in photosynthetic responses to changes in the daily light regime were also evident with Syringodium isoetifolium showing the highest photosynthetic rates and saturating irradiances suggesting a competitive advantage over other species under conditions of high light. In contrast Halophila ovalis, Halophila decipiens and Halophila spinulosa were characterised by comparatively low photosynthetic rates and minimum light requirements (i.e. low E_k) typical of shade adaptation. The structural makeup of each species may explain the observed differences with large, structurally complex species such as Syringodium isoetifolium and Cymodocea serrulata showing high photosynthetic effciciencies (α) and therefore high-light-adapted traits (e.g. high ETR_max and E_k) compared with the smaller Halophila species positioned lower in the canopy. For the smaller Halophila species these shade-adapted traits are features that optimise their survival during low-light conditions. Knowledge of these characteristics and responses improves our understanding of the underlying causes of changes in seagrass biomass, growth and survival that occur when modifications in light quantity and quality arise from anthropogenic and climatic disturbances that commonly occur in Torres Strait.  相似文献   

Statistical simulation of wave climate and extreme beach erosion     

D.P. Callaghan  P. Nielsen  A. Short  R. Ranasinghe 《Coastal Engineering》2008

Recent developments in extreme values modelling have been used to develop a framework for determining the coastal erosion hazard on sandy coastlines. This framework quantitatively reproduced the extreme beach erosion volumes obtained from field measurements at Narrabeen Beach, Australia. This encouraging finding was achieved using Kriebel and Dean's [Kriebel, D.L. and Dean, R.G., 1993. Convolution method for time-dependent beach profile response. Journal of Waterway, Port, Coastal and Ocean Engineering, 119(2): 204–226.] simple beach erosion and accretion model. The method includes allowances for joint probability between all basic erosion variates including; wave height, period and direction, event duration, tidal anomalies and event spacing. A new formulation for the dependency between wave height and period has been developed. It includes the physical wave steepness limitation. Event grouping, where significantly more erosion can occur from two closely spaced storms is handled by temporally simulating the synthetic wave climate and the resulting beach erosion and accretion.  相似文献   

Impact of river training walls on adjacent beaches, Ballina, New South Wales, Australia     

黄海军 《中国海洋湖沼学报》1999,17(1):41-48

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Pleistocene stratigraphy of the Boco Plain,western Tasmania     

P. C. Augustinus  S. A. Short  E. A. Colhoun 《Australian Journal of Earth Sciences》2013,60(6):581-591

The Late Devonian‐Early Carboniferous Mansfield Basin is the northernmost structural sub‐basin of the Mt Howitt Province of east‐central Victoria. It is comprised predominantly of continental clastic sedimentary rocks, and is superimposed upon deformed Cambrian to Early Devonian marine sequences of the Palaeozoic Lachlan Fold Belt. This paper documents evidence for synsedimentary deformation during the early history of the Mansfield Basin, via sedimentological, structural and stratigraphic investigations. Repeating episodes of folding, erosion and sedimentation are demonstrated along the preserved western margins of Mansfield Basin, where fold structures within the lower sequences are truncated by intrabasinal syntectonic unconformities. A convergent successor basin setting (an intermontane setting adjacent to, or between major fault zones) is suggested for initial phases of basin deposition, with synsedimentary reverse faulting being responsible for source uplift and subsequent basin deformation. Palaeocurrents within conglomerate units indicate derivation from the west and are consistent with episodic thrusting along basin margin faults providing elevated source regions. Periods of tectonic quiescence are represented by finer grained meandering fluvial facies (indicative of lower regional topographic gradients) which display drainage patterns that appear not to have been influenced by bounding faults to the west. An up‐sequence increase in the textural and compositional maturity of basin sandstones and conglomerates is proposed to be a result of the incorporation of basin fill into ongoing basin deformation, with unstable metapelitic rocks being progressively winnowed from clast populations. Rather than resulting from Carboniferous (Kanimblan) reactivation of extensional structures, as is generally assumed, the deformation observed within the lower units of the Mansfield Basin is suggested here to be essentially syndepositional and at least Late Devonian in age.  相似文献   

Chronic Nutrient Enrichment Increases the Density and Biomass of the Mudsnail, Nassarius obsoletus     

David Samuel Johnson  Meghan I. Short 《Estuaries and Coasts》2013,36(1):28-35

In summer 2009, the effects of 6 years of landscape-level experimental nutrient enrichment on the eastern mudsnail, Nassarius obsoletus (formerly Ilyanassa obsoleta), were examined. The experiment was conducted in five tidal creeks (two nutrient-enriched, three reference creeks) in the Plum Island Estuary, Massachusetts, USA. (42°44′ N, 70°52′ W). After 6 years of enrichment, N. obsoletus size structure differed between treatment creeks with adult snails on average 14 % larger in enriched creeks. N. obsoletus densities (in individuals per square meter) and biomass (in grams dry weight per square meter) were four times higher in nutrient-enriched versus reference creeks. Nutrient enrichment did not significantly affect the biomass of benthic microalgae (a N. obsoletus food resource), but snail density was significantly correlated with benthic microalgal biomass, suggesting bottom–up control of snails. N. obsoletus is abundant on the east and west coast of North America; thus, N. obsoletus density and biomass may be useful variables for monitoring eutrophication effects on North American estuaries.  相似文献