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   

Engineering geomorphological interpretation of the Mitchell Creek Landslide,British Columbia,Canada     

Anne Clayton  Doug Stead  Derek Kinakin  Andrea Wolter 《Landslides》2017,14(5):1655-1675

The recent assessment of the Mitchell Creek Landslide (MCL) in northern British Columbia is a good case history of engineering geomorphological analysis of a large landslide. It was completed using historic aerial photographs, with approximately 20-year time intervals dating back to the mid-twentieth century and field investigations completed between 2008 and 2014. The large bedrock slide initiated between 1956 and 1972 and continues to experience ongoing annual movements. Significant glacial downwasting and retreat has been observed in the photographic record, and it is hypothesized that alpine glaciation has contributed to development of the MCL. This paper documents four aspects of the engineering geomorphological assessment completed at the MCL: (i) topographic evolution, (ii) slope morphology, (iii) deformation features, and (iv) displacement behavior. Four distinct geomorphic zones have been defined at the MCL based on these analyses, controlled by different failure mechanisms. The extents of these zones have changed little over the documented history of the landslide, and rates of movement estimated from aerial photography have been consistent over the last 60 years. Retreat of the Mitchell Valley Glacier appears to have played an important role in landslide initiation, as the ice mass receded the kinematic freedom of the slope increased. This study of the initiation and development of the MCL demonstrates the capabilities of a multi-faceted approach to engineering geomorphology. The combination of historical aerial photographs with digital photogrammetric modeling and point cloud analysis techniques, and geomorphological mapping, allows for development of a robust understanding of landslide behavior.  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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Summary findings of the fourth international radiocarbon intercomparison (FIRI)(1998–2001)     

Elisabetta Boaretto  Charlotte Bryant  Israel Carmi  Gordon Cook  Steinar Gulliksen  Doug Harkness  Jan Heinemeier  John McClure  Edward McGee  Philip Naysmith  Goran Possnert  Marian Scott  Hans van der Plicht  Mark van Strydonck 《第四纪科学杂志》2002,17(7):633-637

Interlaboratory comparisons have been widely used in applied radiocarbon science. These are an important part of ongoing quality assurance (QA) programmes, which are vital to the appropriate interpretation of the evidence provided by the ¹⁴C record in Quaternary applications (including climate change and environmental reconstruction). International comparisons of laboratory performance are an essential component of the quality assurance process in radiocarbon dating. If the user community is to have confidence in radiocarbon results, it needs to be assured that laboratories world wide are producing measurements that are reliable and in accordance with ‘good practice’. The findings from the most recent (completed in 2001) and extensive (more than 90 participating laboratories) radiocarbon intercomparison (FIRI) are reported here. This study was designed (i) to assess comparability, or otherwise, of the results from different laboratories and (ii) to quantify the extent and possible causes of any interlaboratory variation. The results demonstrate that there are no significant differences amongst the main measurement techniques (gas proportional counting, liquid scintillation counting and accelerator mass spectrometry (AMS)) but there is evidence of small laboratory offsets relative to known age samples for some laboratories. There is also evidence in some cases of underestimation of measurement precision. Approximately 10% of all results were classified as extreme (outliers) and these results were generated by 14% of the laboratories. Overall, the evidence supports the fact that radiocarbon laboratories are generally accurate and precise but that, notwithstanding internal QA procedures, some problems still occur, which can best be detected by participation in independent intercomparisons such as FIRI, where the results allow individual laboratories to assess their performance and to take remedial measures where necessary. The results from FIRI are significant in that they show a broad measure of agreement between measurements made in different laboratories on a wide range of materials and they also demonstrate no statistically significant difference between measurements made by radiometric or AMS techniques. Copyright © 2002 John Wiley & Sons, Ltd.  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   

Singapore: A Developmental City State by Martin Perry, Lily Kong and Brenda Yeoh.     

Doug Johnston 《New Zealand geographer》1998,54(2):55-55

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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   

On the origin and the tectonic implications of magnetic overprinting of the Old Red Sandstone, Shetland     

T. H. Torsvik  B. A. Sturt  D. M. Ramsay 《Geophysical Journal International》1989,99(3):749-759

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Marine geology of the Sodwana Bay shelf, southeast Africa     

P.J Ramsay 《Marine Geology》1994,120(3-4):225-247

The geostrophic current-controlled northern Zululand shelf displays a unique assemblage of interesting physical, sedimentological and biological phenomena. The shelf in this area is extremely narrow (3 km) and is characterised by submarine canyons, coral reefs, and steep gradients on the continental slope. Three submarine canyons occur in the study area and are classified as mature- or youthful-phase canyons depending on the degree to which they breach the shelf. These canyons originated as mass-wasting features which were exploited by palaeo-drainage during sea-level regressions. Shelf lithology is dominated by a series of coast-parallel patch coral reefs which have colonised beachrock and aeolianite sequences that extend semi-continuously from −5 to −95 m, and delineate late Pleistocene palaeocoastline events. The unconsolidated sediment on the shelf is either shelf sand (mainly terrigenous quartz grains) or bioclastic sediment. Large-scale subaqueous dunes commonly form in the unconsolidated sediment on the outer-shelf due to the Agulhas Current flow. These dunes occur as two distinct fields at depths of −35 to −70 m; the major sediment transport direction is towards the south, but occasional bedload parting zones exist where the bedform migration direction changes from south to north.  相似文献