Tidal wave diffraction by channels and bays     

John W. Miles 《地球物理与天体物理流体动力学》2013,107(1):155-171

Abstract

A Kelvin wave in a semi-infinite ocean with a narrow (compared with the wavelength) continental shelf is diffracted by a narrow gap that feeds any of a second semi-infinite ocean, a semi-infinite channel, a closed channel of finite length, a small bay, or a channel terminated by a bay. An equivalent electrical circuit is constructed, in which the incident-wave displacement in the gap appears as the input voltage and the flow into the gap appears as the input current. Approximations to the elements of this circuit are constructed from a quadratic functional that is derived from the integral equation implied by the boundary-value problem. The phase shift in the diffracted Kelvin wave is calculated, and numerical results are given for representative configurations. The general results are applicable to other tidal waves in the semi-infinite ocean, e.g., a Poincaré wave. A model of San Francisco Bay, opening into the ocean through a short, narrow channel (the Golden Gate) and fed by rivers through a long channel (Carquinez Straits), is constructed. It yields a resonant period of 4.6h and a time delay of 3.6 sec for a semi-diurnal (12.4h) Kelvin wave.  相似文献   

On liquid phases in cometary nuclei     

Richard Miles  George A. Faillace 《Icarus》2012,219(2):567-595

In this paper we review the relevant literature and investigate conditions likely to lead to melting of H₂O ice, methanol (CH₃OH) ice, ethane (C₂H₆) ice and other volatile ices in cometary nuclei. On the basis of a heat balance model which takes account of volatiles loss, we predict the formation of occasional aqueous and hydrocarbon liquid phases in subsurface regions at heliocentric distances, r_h of 1–3 AU, and 5–12 AU, respectively. Low triple-point temperatures and low vapour pressures of C₂H₆, C₃H₈, and some higher-order alkanes and alkenes, favour liquid phase formation in cometary bodies at high r_h. Microporosity and the formation of a stabilization crust occluding the escape of volatiles facilitate liquid-phase formation. Characteristics of the near-surface which favour subsurface melting include; low effective surface emissivity (at low r_h), high amorphous carbon content, average pore sizes of ～10 μm or less, presence of solutes (e.g. CH₃OH), mixtures of C₂–C₆ hydrocarbons (for melting at high r_h), diurnal thermal cycling, and slow rotation rate. Applying the principles of soil mechanics, capillary forces are shown to initiate pre-melting phenomena and subsequent melting, which is expected to impart considerable strength of ～10⁴ Pa in partially saturated layers, reducing porosity and permeability, enhancing thermal conductivity and heat transfer. Diurnal thermal cycling is expected to have a marked effect on the composition and distribution of H₂O ice in the near-surface leading to frost heave-type phenomena even where little if any true melting occurs. Where melting does take place, capillary suction in the wetted zone has the potential to enhance heat transfer via capillary wetting in a low-gravity environment, and to modify surface topography creating relatively smooth flat-bottomed features, which have a tendency to be located within small depressions. An important aspect of the “wetted layer” model is the prediction that diurnal melt–freeze cycles alter the mixing ratio vs. depth of solutes present, or of other miscible components, largely through a process of fractional crystallization, but also potentially involving frost heave. Wetted layers are potentially durable and can involve significant mass transport of volatile materials in the near-surface, increasing in extent over many rotations of the nucleus prior to and just after perihelion passage, and causing stratification and trapping of the lowest-melting mixtures at depths of several metres. A possible mechanism for cometary outbursts is proposed involving a heat pulse reaching the liquid phase in the deepest wetted zone, leading to supersaturation and triggering the sudden release under pressure of dissolved gases, in particular CO₂, CO, CH₄ or N₂, contained beneath a consolidated near-surface layer. This study indicates that liquid water can persist for long periods of time in the near-surface of some intermediate-sized bodies (10²–10³ km radius) within protoplanetary discs.  相似文献   

Wavelength Dependence of the Helioseismic and Magnetic Imager (HMI) Instrument onboard the Solar Dynamics Observatory (SDO)     

Sébastien Couvidat  Jesper Schou  Richard A. Shine  Rock I. Bush  John W. Miles  Philip H. Scherrer  Richard L. Rairden 《Solar physics》2012,275(1-2):285-325

The Helioseismic and Magnetic Imager (HMI) instrument will produce Doppler-velocity and vector-magnetic-field maps of the solar surface, whose accuracy is dependent on a thorough knowledge of the transmission profiles of the components of the HMI optical-filter system. Here we present a series of wavelength-dependence calibration tests, performed on the instrument from 2005 onwards, to obtain these profiles. We obtained the transmittances as a function of wavelength for the tunable and non-tunable filter elements, as well as the variation of these transmittances with temperature and the angle of incidence of rays of light. We also established the presence of fringe patterns produced by interferences inside the blocking filter and the front window, as well as a change in transmitted intensity with the tuning position. This thorough characterization of the HMI-filter system confirmed the very high quality of the instrument, and showed that its properties are well within the required specifications to produce superior data with high spatial and temporal resolution.  相似文献   

Modeling of multi-interface, diverging, hydrodynamic experiments for the National Ignition Facility     

M. J. Grosskopf  R. P. Drake  C. C. Kuranz  A. R. Miles  J. F. Hansen  T. Plewa  N. Hearn  D. Arnett  J. C. Wheeler 《Astrophysics and Space Science》2009,322(1-4):57-63

The National Ignition Facility (NIF) will soon provide experiments with far more than ten times the energy than has been previously available on laser facilities. In the context of supernova-relevant hydrodynamics, this will enable experiments in which hydrodynamic instabilities develop from multiple, coupled interfaces in a diverging explosion. This paper discusses the design of such blast-wave-driven explosions in which the relative masses of the layers are scaled to those within the star. It reports scaling simulations with CALE to model the global dynamics of such an experiment. CALE is a hybrid, Arbitrary Lagrangian-Eulerian code. The simulations probed the instability growth and multi-interface interactions in mass-scaled systems using different materials. The simulations assist in the target design process and in developing an experiment that can be diagnosed.  相似文献   

Intra-seasonal and inter-annual variations in phytoplankton biomass,primary production and bacterial production at North West Cape,Western Australia: Links to the 1997–1998 El Niño event     

Miles Furnas 《Continental Shelf Research》2007

Phytoplankton biomass, community and size structure, primary production and bacterial production were measured at shelf and continental slope sites near North West Cape, Western Australia (20.5°S–22.5°S) over two summers (October–February 1997–1998 and 1998–1999), and in April 2002. The North West Cape region is characterized by upwelling-favorable, southwesterly winds throughout the summer. Surface outcropping of upwelled water is suppressed by the geostrophic pressure gradients and warm low-density surface waters of the southward flowing Leeuwin Current. Strong El Niño (ENSO) conditions (SOI <0) prevailed through the summer of 1997–1998 which resulted in lower sea levels along the northwestern Australian coast and a weaker Leeuwin Current. La Niña conditions prevailed during the 1998–1999 summer and in April 2002. During the summer of 1997–1998, the North West Cape region was characterized by a shallower thermocline (nutricline), resulting in larger euphotic zone stocks of inorganic nitrogen and silicate over the continental slope. There was evidence for episodic intrusions of upper thermocline waters and the sub-surface chlorophyll maximum onto the outer continental shelf in 1997–1998, but not in 1998–1999. Pronounced differences in phytoplankton biomass, community size structure and productivity were observed between the summers of 1997–1998 and 1998–1999 despite general similarities in irradiance, temperature and wind stress. Phytoplankton primary production and bacterial production were 2- to 4-fold higher during the summer of 1997–1998 than in 1998–1999, while total phytoplankton standing crop increased by<2-fold. Larger phytoplankton (chiefly diatoms in the >10 μm size fraction) made significant contributions to phytoplankton standing crop and primary production during the summer of 1997–1998, but not 1998–1999. Although there were no surface signs of upwelling, primary production rates near North West Cape episodically reached levels (3–8 g C m⁻² day⁻¹) characteristic of eastern boundary Ekman upwelling zones elsewhere in the world. Bacterial production (0.006–1.2 g C m⁻² day⁻¹) ranged between 0.6 and 145 percent (median=19 percent) of concurrent primary production. The observed differences between years and within individual summers suggest that variations in the Leeuwin Current driven by seasonal or ENSO-related changes in the Indonesian throughflow region may have episodic, but significant influences on pelagic productivity along the western margin of Australia.  相似文献   

Water quality guidelines for the Great Barrier Reef World Heritage Area: a basis for development and preliminary values     

Moss A  Brodie J  Furnas M 《Marine pollution bulletin》2005,51(1-4):76-88

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZECC Guidelines) provide default national guideline values for a wide range of indicators of relevance to the protection of the ecological condition of natural waters. However, the ANZECC Guidelines also place a strong emphasis on the need to develop more locally relevant guidelines. Using a structured framework, this paper explores indicators and regional data sets that can be used to develop more locally relevant guidelines for the Great Barrier Reef World Heritage Area (GBRWHA). The paper focuses on the water quality impacts of adjacent catchments on the GBRWHA with the key stressors addressed being nutrients, sediments and agricultural chemicals. Indicators relevant to these stressors are discussed including both physico-chemical pressure indicators and biological condition indicators. Where adequate data sets are available, guideline values are proposed. Generally, data were much more readily available for physico-chemical pressure indicators than for biological condition indicators. Specifically, guideline values are proposed for the major nutrients nitrogen (N) and phosphorus (P) and for chlorophyll-a. More limited guidelines are proposed for sediment related indicators. For most agricultural chemicals, the ANZECC Guidelines are likely to remain the default of choice for some time but it is noted that there is data in the literature that could be used to develop more locally relevant guidelines.  相似文献   

Missing women: Reflections on the experiences of Swazi migrant women on the Rand, 1920–1970     

Miranda Miles 《GeoJournal》1993,30(1):85-91

The migration of Swazi women to the Witwatersrand in the period 1920–1970 marked an era of change in the lives of many Swazi women. Under the constraints of rural impoverishment, many women were forced onto the Swazi labour market, one which had little room for women. By the 1930s the exodus of Swazi women to the Rand had gathered so much momentum, that women quickly became objects of national concern to the British colonial government, Swazi traditional authorities and South African authorities. Their experiences as migrant workers in South Africa have largely gone unnoticed. As African women, they suffered the triple oppression of class, race and gender, and as foreign women were subject to a battery of laws designed to keep foreign Africans out of South Africa. The personal experiences of Swazi women as migrants and workers in South Africa are examined here, using life-history or personal narrative techniques which have considerable potential as a way of recovering hidden histories and reinstating the marginalised as makers of their own past.  相似文献   

The ocean–continent boundary off the western continental margin of Iberia—II. Crustal structure in the Tagus Abyssal Plain     

L. M. Pinheiro  R. B. Whitmarsh  P. R. Miles 《Geophysical Journal International》1992,109(1):106-124

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Large-scale transport of a CO-enhanced air mass from Europe to the Middle East     

V. S. Connors  T. Miles  H. G. Reichle Jr. 《Journal of Atmospheric Chemistry》1989,9(4):479-496

On 14 November 1981, the shuttle-borne Measurement of Air Pollution from Satellites (MAPS) experiment observed a carbon monoxide (CO) enhanced air mass in the middle troposphere over the Middle East. The primary source of this polluted air was estimated by constructing adiabatic isentropic trajectories backwards from the MAPS measurement location over a 36 h period. The isentropic diagnostics indicate that CO-enhanced air was transported southeastward over the Mediterranean from an organized synoptic-scale weather regime, albeit of moderate intensity, influencing central Europe on 12 November. Examination of the evolving synoptic scale vertical velocity and precipitation patterns during this period, in conjunction with METEOSAT visible, infrared, and water vapor imagery, suggests that the presence of this disturbed weather system over Europe may have created upward transport of CO-enhanced air between the boundary-layer and midtropospheric levels, and subsequent entrainment in the large-scale northwesterly jet stream flow over Europe and the Mediterranean.  相似文献   

An analogue model for studying magnetic variations induced by ocean waves     

T. Miles  H.W. Dosso  T.P. Ng 《Physics of the Earth and Planetary Interiors》1977,14(2):137-142

The scale factors to permit a laboratory analogue model study of the problem of magnetic fields induced by ocean waves in the earth's field are derived. An analogue model employing surface fluid waves in mercury to simulate ocean waves is described. In the analogue model, magnetic field measurements were made 1 cm above a 2 cm deep model mercury ocean for a wave period of 0.21 s. This model simulates measurements 38 m above the surface of a shallow ocean 78 m deep for a wave period of 13 s. The validity of the analogue modelling technique is established by the good agreement obtained in comparing the analogue model measurements of the induced magnetic fields with fields using Podney's expression for an ocean of finite depth.  相似文献