Book review     

G. W. Ramsay 《新西兰海洋与淡水研究杂志》2013,47(3):569-571

Marion and Prince Edward Islands. Report on the South African Biological and Geological Expedition 1965–1966. Edited by E. M. van Zinderen Bakker, J. M. Winterbottom and R. A. Dyer. Balkema, Cape Town. $25.33.  相似文献   

Cluster analysis of tropical cyclone tracks in the Southern Hemisphere   总被引：1，自引：0，他引：1  

Hamish A. Ramsay  Suzana J. Camargo  Daehyun Kim 《Climate Dynamics》2012,39(3-4):897-917

A probabilistic clustering method is used to describe various aspects of tropical cyclone (TC) tracks in the Southern Hemisphere, for the period 1969–2008. A total of 7 clusters are examined: three in the South Indian Ocean, three in the Australian Region, and one in the South Pacific Ocean. Large-scale environmental variables related to TC genesis in each cluster are explored, including sea surface temperature, low-level relative vorticity, deep-layer vertical wind shear, outgoing longwave radiation, El Niño-Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO). Composite maps, constructed 2 days prior to genesis, show some of these to be significant precursors to TC formation—most prominently, westerly wind anomalies equatorward of the main development regions. Clusters are also evaluated with respect to their genesis location, seasonality, mean peak intensity, track duration, landfall location, and intensity at landfall. ENSO is found to play a significant role in modulating annual frequency and mean genesis location in three of the seven clusters (two in the South Indian Ocean and one in the Pacific). The ENSO-modulating effect on genesis frequency is caused primarily by changes in low-level zonal flow between the equator and 10°S, and associated relative vorticity changes in the main development regions. ENSO also has a significant effect on mean genesis location in three clusters, with TCs forming further equatorward (poleward) during El Niño (La Niña) in addition to large shifts in mean longitude. The MJO has a strong influence on TC genesis in all clusters, though the amount modulation is found to be sensitive to the definition of the MJO.  相似文献   

A Surface Model for Aeolian Dune Topography     

Travis Swanson  David Mohrig  Gary Kocurek  Man Liang 《Mathematical Geosciences》2017,49(5):635-655

A surface model for aeolian bedform topography is adapted from a surface model of subaqueous bedform topography. The aeolian bedform surface model is developed using a uniform grid with a cell-centered finite volume approximation of the sediment continuity equation. The resulting modeling framework approximates the dynamic motions of aeolian bedform topography driven by bedform field boundary conditions. The numerical model is applied to simulate bedforms growing from unimodal and bimodal transport regimes from both a fixed elevation (sediment source area) and within a domain with fully periodic boundary conditions. The rates at which modeled aeolian bedforms grow and morphologically mature are sensitive to the chosen boundary conditions. Video files of model simulations and source code for the presented aeolian bedform surface modeling framework are available in supplemental materials. The aeolian bedform surface model code is malleable and readily modified for exploratory study of dynamic bedform topography that inherits morphological traits from aeolian bedform field boundary conditions.  相似文献   

Iron concretions within a highly altered unit of the Berlins Porphyry,New Zealand: an abiotic or biotic story?     

Cox  Toni L.  Oze  Christopher  Horton  Travis W. 《Mineralogy and Petrology》2017,111(2):173-181

Mineralogy and Petrology - The Berlins Porphyry located on the South Island of New Zealand provides an opportunity to examine iron concretions formed in a subterranean system. Specifically, an...  相似文献   

Effects of gravity on the structure of post-shock accretion flows in magnetic cataclysmic variables     

Mark Cropper  Kinwah Wu  Gavin Ramsay  Aysegul Kocabiyik 《Monthly notices of the Royal Astronomical Society》1999,306(3):684-690

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Snow disappearance timing is dominated by forest effects on snow accumulation in warm winter climates of the Pacific Northwest,United States          下载免费PDF全文

Susan E. Dickerson‐Lange  Rolf F. Gersonde  Jason A. Hubbart  Timothy E. Link  Anne W. Nolin  Gwyneth H. Perry  Travis R. Roth  Nicholas E. Wayand  Jessica D. Lundquist 《水文研究》2017,31(10):1846-1862

Forests modify snow processes and affect snow water storage as well as snow disappearance timing. However, forest influences on snow accumulation and ablation vary with climate and topography and are therefore subject to temporal and spatial variability. We utilize multiple years of snow observations from across the Pacific Northwest, United States, to assess forest–snow interactions in the relatively warm winter conditions characteristic of maritime and transitional maritime–continental climates. We (a) quantify the difference in snow magnitude and disappearance timing between forests and open areas and (b) assess how forest modifications of snow accumulation and ablation combine to determine whether snow disappears later in the forest or in the open. We find that snow disappearance timing at 12 (out of 14) sites ranges from synchronous in the forest and open to snow persisting up to 13 weeks longer in the open relative to a forested area. By analyzing accumulation and ablation rates up to the day when snow first disappears from the forest, we find that the difference between accumulation rates in the open and forest is larger than the difference between ablation rates. Thus, canopy snow interception and subsequent loss, rather than ablation, set up longer snow duration in the open. However, at two relatively windy sites (hourly average wind speeds up to 8 and 17 m/s), differential snow disappearance timing is reversed: Snow persists 2–5 weeks longer in the forest. At the windiest sites, accumulation rates in the forest and open are similar. Ablation rates are higher in the open, but the difference between ablation rates in the forest and open at these sites is approximately equivalent to the difference at less windy sites. Thus, longer snow retention in the forest at the windiest sites is controlled by depositional differences rather than by reduced ablation rates. These findings suggest that improved quantification of forest effects on snow accumulation processes is needed to accurately predict the effect of forest management or natural disturbance on snow water resources.  相似文献   

A search for electron cyclotron maser emission from compact binaries     

Gavin Ramsay  Catherine Brocksopp  Kinwah Wu  Bruce Slee  Curtis J. Saxton 《Monthly notices of the Royal Astronomical Society》2007,382(1):461-465

Unipolar induction (UI) is a fundamental physical process, which occurs when a conducting body transverses a magnetic field. It has been suggested that UI is operating in RX J0806+15 and RX J1914+24, which are believed to be ultracompact binaries with orbital periods of 5.4 and 9.6 min, respectively. The UI model predicts that those two sources may be electron cyclotron maser sources at radio wavelengths. Other systems in which UI has been predicted to occur are short period extrasolar terrestrial planets with conducting cores. If UI is present, circularly polarized radio emission is predicted to be emitted. We have searched for this predicted radio emission from short period binaries using the Very Large Array (VLA) and Australian Telescope Compact Array (ATCA). In one epoch, we find evidence for a radio source, coincident in position with the optical position of RX J0806+15. Although we cannot completely exclude that this is a chance alignment between the position of RX J0806+15 and an artefact in the data reduction process, the fact that it was detected at a significance level of 5.8σ and found to be transient suggests that it is more likely that RX J0806+15 is a transient radio source. We find an upper limit on the degree of circular polarization to be ∼50 per cent. The inferred brightness temperature exceeds 10¹⁸ K, which is too high for any known incoherent process, but is consistent with maser emission and UI being the driving mechanism. We did not detect radio emission from ES Cet, RX J1914+24 or Gliese 876.  相似文献   

RX J0744−52: a probable new intermediate polar     

Gavin Ramsay  David A. H. Buckley  & Mark Cropper 《Monthly notices of the Royal Astronomical Society》1998,294(1):187-192

We present optical and X-ray data of the cataclysmic variable RX 0744−52 discovered using ROSAT by Motch et al. High-resolution spectroscopy centred on the Hα line indicates a probable orbital period of 3.60 h. From its distance (obtained using polarimetry), its X-ray luminosity, its X-ray colour and its X-ray/UV+optical ratio, we suggest that RX 0744−52 is a new intermediate polar. The absence of a significant coherent modulation in the X-ray light curve suggests either that RX 0744−52 has a low inclination or that the rotational and magnetic axes must be closely aligned. This is consistent with its small radial velocity amplitude.  相似文献   

A comparison of white dwarf mass estimators using the intermediate polar XY Ari     

Gavin Ramsay  Mark Cropper  Coel Hellier  & Kinwah Wu 《Monthly notices of the Royal Astronomical Society》1998,297(4):1269-1273

We determine the mass of the white dwarf in the eclipsing intermediate polar XY Ari following the method given in Cropper, Ramsay &38; Wu using a multitemperature bremsstrahlung model. By fitting X-ray spectra from Ginga RXTE and ASCA we find that the mean of the best fits to the data taken using different detectors is M _wd = 1.28 ± 0.04 M⊙. This figure is too high to be consistent with the mass of the white dwarf found by Hellier from X-ray eclipse timings. There are also small systematic differences between the masses derived using different X-ray satellites.  相似文献   

Climate change impacts on extreme floods I: combining imperfect deterministic simulations and non-stationary frequency analysis     

Ousmane Seidou  Andrea Ramsay  Ioan Nistor 《Natural Hazards》2012,61(2):647-659

Flood quantiles are routinely used in hydrologic engineering to design hydraulic structures, optimize erosion control structure and map the extent of floodplains. As an increasing number of papers are pointing out cycles and trends in hydrologic time series, the use of stationary flood distributions leads to the overestimation or underestimation of the hydrologic risk at a given time. Several authors tried to address this problem by using probability distributions with time-varying parameters. The parameters of these distributions were assumed to follow a linear or quadratic trend in time, which may be valid for the short term but may lead to unrealistic long-term projections. On the other hand, deterministic rainfall-runoff models are able to successfully reproduce trends and cycles in stream flow data but can perform poorly in reproducing daily flows and flood peaks. Rainfall-runoff models typically have a better performance when simulation results are aggregated at a larger time scale (e.g. at a monthly time scale vs. at a daily time scale). The strengths of these two approaches are combined in this paper where the annual maximum of the time-averaged outputs of a hydrologic model are used to modulate the parameters of a non-stationary GEV model of the daily maximum flow. The method was applied to the Kemptville Creek located in Ontario, Canada, using the SWAT (Soil and Water Assessment Tool) model as rainfall-runoff model. The parameters of the non-stationary GEV model are then estimated using Monte Carlo Markov Chain, and the optimal span of the time windows over which the SWAT outputs were averaged was selected using Bayes factors. Results show that using the non-stationary GEV distribution with a location parameter linked to the maximum 9-day average flow provides a much better estimation of flood quantiles than applying a stationary frequency analysis to the simulated peak flows.  相似文献