Determining the motion of the Solar system relative to the cosmic microwave background using Type Ia supernovae     

Christopher Gordon  Kate Land  An&#;e Slosar 《Monthly notices of the Royal Astronomical Society》2008,387(1):371-376

We estimate the Solar system motion relative to the cosmic microwave background using Type Ia supernovae (SNe) measurements. We take into account the correlations in the error bars of the SNe measurements arising from correlated peculiar velocities. Without accounting for correlations in the peculiar velocities, the SNe data we use appear to detect the peculiar velocity of the Solar system at about the 3.5σ level. However, when the correlations are correctly accounted for, the SNe data only detect the Solar system peculiar velocity at about the 2.5σ level. We forecast that the Solar system peculiar velocity will be detected at the 9σ level by GAIA and the 11σ level by the Large Synoptic Survey Telescope. For these surveys, we find the correlations are much less important as most of the signal comes from higher redshifts where the number density of SNe is insufficient for the correlations to be important.  相似文献   

Real-Time Assessment of the 16 September 2015 Chile Tsunami and Implications for Near-Field Forecast     

Liujuan Tang  Vasily V. Titov  Christopher Moore  Yong Wei 《Pure and Applied Geophysics》2016,173(2):369-387

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Tsunami Simulation Using Sources Inferred from Various Measurement Data: Implications for the Model Forecast     

Edison Gica  Vasily V. Titov  Christopher Moore  Yong Wei 《Pure and Applied Geophysics》2015,172(3-4):773-789

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A simple two‐parameter model for scaling hillslope surface runoff          下载免费PDF全文

Gary J. Sheridan  Philip J. Noske  Patrick N.J. Lane  Owen D. Jones  Christopher B. Sherwin 《地球表面变化过程与地形》2014,39(8):1049-1061

The objective of this research was to develop and parameterise a physically justified yet low‐parameter model to quantify observed changes in surface runoff ratios with hillslope length. The approach starts with the assumption that a unit of rainfall‐excess runoff generated at a point is a fraction β of precipitation P (m) which travels some variable distance down a slope before reinfiltrating, depending on the local rainfall, climate, soils, etc. If this random distance travelled Y is represented by a distribution, then a survival function will describe the probability of this unit of runoff travelling further than some distance x (m). The total amount of per unit width runoff Q (m²) flowing across the lower boundary of a slope of length λ (m) may be considered the sum of all the proportions of the units of rainfall excess runoff integrated from the lower boundary x = 0 to the upper boundary x = λ of the slope. Using these assumptions we derive a model Q(λ) = βPμλ/(μ + λ), (μ > 0, 0 ≤ β ≤ 1, λ ≥ 0) that describes the change in surface runoff with slope length, where μ (m) is the mean of the random variable Y. Dividing both sides of this equation by Pλ yields a simple two‐parameter equation for the dimensionless hillslope runoff ratio Q_h(λ) = βμ/(μ + λ). The model was parameterised with new rainfall and runoff data collected from three replicates of bounded 2 m wide plots of four different lengths (0.5, 1.0, 2.0 and 4.0 m) for 2 years from a forested SE Australian site, and with 32 slope length–runoff data sets from 12 other published studies undertaken between 1934 and 2010. Using the parameterised model resulted in a Nash and Sutcliffe statistic between observed and predicted runoff ratio (for all data sets combined) of 0.93, compared with –2.1 when the runoff ratio was fixed at the value measured from the shortest plot. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Robust classification for the joint velocity‐intermittency structure of turbulent flow over fixed and mobile bedforms          下载免费PDF全文

Christopher J. Keylock  Arvind Singh  Jeremy G. Venditti  Efi Foufoula‐Georgiou 《地球表面变化过程与地形》2014,39(13):1717-1728

Two datasets of turbulence velocities collected over different bedform types under contrasting experimental conditions show similarity in terms of velocity‐intermittency characteristics and suggest a universality to the velocity‐intermittency structure for flow over bedforms. One dataset was obtained by sampling flow over static bedforms in different locations, and the other was based on a static position but mobile bedforms. A flow classification based on the velocity‐intermittency behaviour is shown to reveal some differences from that based on an analysis of Reynolds stresses, boundary layer correlation and turbulent kinetic energy. This may be attributed to the intermittency variable, which captures the local effect of individual turbulent flow structures. Locations in the wake region or the outer layer of the flow are both shown to have a velocity‐intermittency behaviour that departs from that for idealized wakes or outer layer flow because of the superposition of localized flow structures generated by bedforms. The combined effect of this yields a velocity‐intermittency structure unique to bedform flow. The use of a time series of a single velocity component highlights the potential power of our approach for field, numerical and laboratory studies. The further validation of the velocity‐intermittency method for non‐idealized flows undertaken here suggests that this technique can be used for flow classification purposes in geomorphology, hydraulics, meteorology and environmental fluid mechanics. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

The full set of gas giant structures: I: On the origin of planetary masses and the planetary initial mass function     

Christopher H. Broeg 《Icarus》2009,204(1):15-31

Context

Current planet search programs are detecting extrasolar planets at a rate of 60 planets per year. These planets show more diverse properties than was expected.

Aims

We try to get an overview of possible gas giant (proto-) planets for a full range of orbital periods and stellar masses. This allows the prediction of the full range of possible planetary properties which might be discovered in the near future.

Methods

We calculate the purely hydrostatic structure of the envelopes of proto-planets that are embedded in protoplanetary disks for all conceivable locations: combinations of different planetesimal accretion rates, host star masses, and orbital separations. At each location all hydrostatic equilibrium solutions to the planetary structure equations are determined by variation of core mass and pressure over many orders of magnitude. For each location we analyze the distribution of planetary masses.

Results

We get a wide spectrum of core-envelope structures. However, practically all calculated proto-planets are in the planetary mass range. Furthermore, the planet masses show a characteristic bimodal, sometimes trimodal, distribution. For the first time, we identify three physical processes that are responsible for the three characteristic planet masses: self-gravity in the Hill sphere, compact objects, and a region of very low adiabatic pressure gradient in the hydrogen equation of state. Using these processes, we can explain the dependence of the characteristic masses on the planet’s location: orbital period, host star mass, and planetesimal accretion rate (luminosity). The characteristic mass caused by the self-gravity effect at close proximity to the host star is typically one Neptune mass, thus producing the so-called hot Neptunes.

Conclusions

Our results suggest that hot Jupiters with orbital period less than 64 days (the exact location of the boundary depends on stellar type and accretion rate) have quite distinct properties which we expect to be reflected in a different mass distribution of these planets when compared to the “normal” planetary population. We use our theoretical survey to produce an upper mass limit for embedded planets: the maximum embedded equilibrium mass (MEEM). This naturally explains the lack of high mass planets between 3 and 64 days orbital period.  相似文献   

The absence of endogenic methane on Titan and its implications for the origin of atmospheric nitrogen     

Christopher R. Glein  Steven J. Desch 《Icarus》2009,204(2):637-644

We calculate the D/H ratio of CH₄ from serpentinization on Titan to determine whether Titan’s atmospheric CH₄ was originally produced inside the giant satellite. This is done by performing equilibrium isotopic fractionation calculations in the CH₄-H₂O-H₂ system, with the assumption that the bulk D/H ratio of the system is equivalent to that of the H₂O in the plume of Enceladus. These calculations show that the D/H ratio of hydrothermally produced CH₄ would be markedly higher than that of atmospheric CH₄ on Titan. The implication is that Titan’s CH₄ is a primordial chemical species that was accreted by the moon during its formation. There are two evolutionary scenarios that are consistent with the apparent absence of endogenic CH₄ in Titan’s atmosphere. The first is that hydrothermal systems capable of making CH₄ never existed on Titan because Titan’s interior has always been too cold. The second is that hydrothermal systems on Titan were sufficiently oxidized so that C existed in them predominately in the form of CO₂. The latter scenario naturally predicts the formation of endogenic N₂, providing a new hypothesis for the origin of Titan’s atmospheric N₂: the hydrothermal oxidation of ¹⁵N-enriched NH₃. A primordial origin for CH₄ and an endogenic origin for N₂ are self-consistent, but both hypotheses need to be tested further by acquiring isotopic data, especially the D/H ratio of CH₄ in comets, and the ¹⁵N/¹⁴N ratio of NH₃ in comets and that of N₂ in one of Enceladus’ plumes.  相似文献   

Two Years of the STEREO Heliospheric Imagers     

Richard A. Harrison  Jackie A. Davies  Alexis P. Rouillard  Christopher J. Davis  Christopher J. Eyles  Danielle Bewsher  Steve R. Crothers  Russell A. Howard  Neil R. Sheeley  Angelos Vourlidas  David F. Webb  Daniel S. Brown  Gareth D. Dorrian 《Solar physics》2009,256(1-2):219-237

Imaging of the heliosphere is a burgeoning area of research. As a result, it is awash with new results, using novel applications, and is demonstrating great potential for future research in a wide range of topical areas. The STEREO (Solar TErrestrial RElations Observatory) Heliospheric Imager (HI) instruments are at the heart of this new development, building on the pioneering observations of the SMEI (Solar Mass Ejection Imager) instrument aboard the Coriolis spacecraft. Other earlier heliospheric imaging systems have included ground-based interplanetary scintillation (IPS) facilities and the photometers on the Helios spacecraft. With the HI instruments, we now have routine wide-angle imaging of the inner heliosphere, from vantage points outside the Sun-Earth line. HI has been used to investigate the development of coronal mass ejections (CMEs) as they pass through the heliosphere to 1 AU and beyond. Synoptic mapping has also allowed us to see graphic illustrations of the nature of mass outflow as a function of distance from the Sun – in particular, stressing the complexity of the near-Sun solar wind. The instruments have also been used to image co-rotating interaction regions (CIRs), to study the interaction of comets with the solar wind and CMEs, and to witness the impact of CMEs and CIRs on planets. The very nature of this area of research – which brings together aspects of solar physics, space-environment physics, and solar-terrestrial physics – means that the research papers are spread among a wide range of journals from different disciplines. Thus, in this special issue, it is timely and appropriate to provide a review of the results of the first two years of the HI investigations.  相似文献   

Pre-CME Onset Fuses – Do the STEREO Heliospheric Imagers Hold the Clues to the CME Onset Process?     

Richard A. Harrison  Christopher J. Davis  Jackie A. Davies 《Solar physics》2009,259(1-2):277-296

Understanding the onset of coronal mass ejections (CMEs) is surely one of the holy grails of solar physics today. Inspection of data from the Heliospheric Imagers (HI), which are part of the SECCHI instrument suite aboard the two NASA STEREO spacecraft, appears to have revealed pre-eruption signatures which may provide valuable evidence for identifying the CME onset mechanism. Specifically, an examination of the HI images has revealed narrow rays comprised of a series of outward-propagating plasma blobs apparently forming near the edge of the streamer belt prior to many CME eruptions. In this pilot study, we inspect a limited dataset to explore the significance of this phenomenon, which we have termed a pre-CME ‘fuse’. Although, the enhanced expulsion of blobs may be consistent with an increase in the release of outward-propagating blobs from the streamers themselves, it could also be interpreted as evidence for interchange reconnection in the period leading to a CME onset. Indeed, it is argued that the latter could even have implications for the end-of-life of CMEs. Thus, the presence of these pre-CME fuses provides evidence that the CME onset mechanism is either related to streamer reconnection processes or the reconnection between closed field lines in the streamer belt and adjacent, open field lines. We investigate the nature of these fuses, including their timing and location with respect to CME launch sites, as well as their speed and topology.  相似文献   

Vulnerability to epidemic malaria in the highlands of Lake Victoria basin: the role of climate change/variability, hydrology and socio-economic factors     

Shem O. Wandiga  Maggie Opondo  Daniel Olago  Andrew Githeko  Faith Githui  Michael Marshall  Tim Downs  Alfred Opere  Christopher Oludhe  Gilbert O. Ouma  Pius Z. Yanda  Richard Kangalawe  Robert Kabumbuli  James Kathuri  Eugene Apindi  Lydia Olaka  Laban Ogallo  Paul Mugambi  Rehema Sigalla  Robinah Nanyunja  Timothy Baguma  Pius Achola 《Climatic change》2010,99(3-4):473-497

Endemic malaria in most of the hot and humid African climates is the leading cause of morbidity and mortality. In the last twenty or so years the incidence of malaria has been aggravated by the resurgence of highland malaria epidemics which hitherto had been rare. A close association between malaria epidemics and climate variability has been reported but not universally accepted. Similarly, the relationship between climate variability, intensity of disease mortality and morbidity coupled with socio-economic factors has been mooted. Analyses of past climate (temperature and precipitation), hydrological and health data (1961–2001), and socio-economics status of communities from the East African highlands confirm the link between climate variability and the incidence and severity of malaria epidemics. The communities in the highlands that have had less exposure to malaria are more vulnerable than their counterparts in the lowlands due to lack of clinical immunity. However, the vulnerability of human health to climate variability is influenced by the coping and adaptive capacities of an individual or community. Surveys conducted among three communities in the East African highlands reveal that the interplay of poverty and other socio-economic variables have intensified the vulnerability of these communities to the impacts of malaria.  相似文献