Titles of theses     

Leslie Hewes 《The Professional geographer》2013,65(4):14-20

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Vortical and wave modes in 3D rotating stratified flows: random large-scale forcing     

Jai Sukhatme  Leslie M. Smith 《地球物理与天体物理流体动力学》2013,107(5):437-455

Utilizing an eigenfunction decomposition, we study the growth and spectra of energy in the vortical (geostrophic) and wave (ageostrophic) modes of a three-dimensional (3D) rotating stratified fluid as a function of ε = f/N, where f is the Coriolis parameter and N is the Brunt–Vaisala frequency. Throughout, we employ a random large-scale forcing in a unit aspect ratio domain and set these parameters such that the Froude and Rossby numbers are roughly comparable and much less than unity. Working in regimes characterized by moderate Burger numbers, i.e. Bu = 1/ε² < 1 or Bu ≥ 1, our results indicate profound change in the character of vortical and wave mode interactions with respect to Bu = 1. Indeed, previous analytical work concerning the qualitatively different nature of these interactions has been in limiting conditions of rotation or stratification domination (i.e. when Bu ? 1 or Bu ? 1, respectively). As with the reference state of ε = 1, for ε < 1 the wave mode energy saturates quite quickly and the ensuing forward cascade continues to act as an efficient means of dissipating ageostrophic energy. Further, these saturated spectra steepen as ε decreases: we see a shift from k ^?1 to k ^?5/3 scaling for k _f < k < k _d (where k _f and k _d are the forcing and dissipation scales, respectively). On the other hand, when ε > 1 the wave mode energy never saturates and comes to dominate the total energy in the system. In fact, in a sense the wave modes behave in an asymmetric manner about ε = 1. With regard to the vortical modes, for ε ≤ 1, the signatures of 3D quasigeostrophy are clearly evident. Specifically, we see a k ^?3 scaling for k _f < k < k _d and, in accord with an inverse transfer of energy, the vortical mode energy never saturates but rather increases for all k < k _f . In contrast, for ε > 1 and increasing, the vortical modes contain a progressively smaller fraction of the total energy indicating that the 3D quasigeostrophic subsystem, though always present, plays an energetically smaller role in the overall dynamics. Combining the vortical and wave modes, the total energy for k > k _f and ε ≤ 1 shows a transition as k increases wherein the vortical modes contain a large portion of the energy at large scales, while the wave modes dominate at smaller scales. There is no such transition when ε > 1 and the wave modes dominate the total energy for all k > k _f .  相似文献   

AUTOMATED ISOCHRONES AND THE LOCATIONS OF EMERGENCY MEDICAL SERVICES IN CITIES     

Leslie D. Mayhew 《The Professional geographer》1981,33(4):423-428

A method is described for the automatic calculation and graphical reproduction of isochrones around emergency medical centers in large cities. The isochrones are set for different time standards and for varying traffic conditions. The technique is based on the concept of a velocity field. It permits a rapid evaluation of coverage standards under different operating conditions.  相似文献   

Scattering of horizontally-polarized shear waves by surface irregularities     

Leslie B. Sills 《Geophysical Journal International》1978,54(2):319-348

Summary. The problem of the scattering of harmonic SH waves by an arbitrary surface irregularity in an otherwise semi-infinite elastic, homogeneous, isotropic two-dimensional half-space is examined in this study in order to ascertain the effect of topography on this type of seismic ground motion and to develop a useful scheme which can realistically handle arbitrary two-dimensional topography. Three geometric models are considered: a semicircular hill which is of academic interest; a mountain with a Gaussian shape which utilizes realistic dimensions and the combination of a ridge and a depression that models a region in Sylmar, California.
A singular Fredholm integral equation of the second kind for the displacement at the free surface is developed and solved numerically. In the case of the semicircular hill, horizontal ground motion can be more than twice that occurring in the case of smooth topography. The mountain simulated by a Gaussian profile experiences at its crest amplifications for certain angles of incidence and de-amplifications for other angles of incidence, as well as displacements whose amplitudes vary slowly with frequency on the side of the mountain which is in the same direction as the incident waves. The ridge-depression combination which is approximated by a sixth-order polynomial actually experienced shattered earth at its ridge crest during the San Fernando, California earthquake of 1971. This amplification is also exhibited by the results of the analysis which, predicts amplifications of over 75 per cent at the top of the ridge for waves arriving on the same side as the ridge.  相似文献   

AN AGRICULTURAL GEOGRAPHY OF GREAT BRITAIN. By D. W. Gilchrist Shirlaw     

Leslie Symons 《New Zealand geographer》1967,23(1):92-92

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Evaluation of the uncertainty of groundwater model predictions associated with conceptual errors: A per-datum approach to model calibration     

Petros Gaganis  Leslie Smith 《Advances in water resources》2006

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The active tropical cyclone season of 2005–2006 over Northwest Australia: Operational model performance and high resolution case studies     

B. W. Buckley  L. M. Leslie  M. Leplastrier  L. Qi 《Meteorology and Atmospheric Physics》2007,97(1-4):69-91

Summary There are three main aims of this study. First, the main features of the active 2005–2006 Australian region tropical cyclone (TC) season are summarized, with particular emphasis on the northwest Australian region. Second, an assessment is made of the skill of the available operational global and regional numerical weather prediction (NWP) models for three of the most significant TCs (TCs Clare, Glenda and Hubert), each of which made landfall on the northwest coast of Australia. Third, high-resolution numerical modelling simulations of these same three TCs are described in detail. The numerical weather prediction (NWP) model used here was developed at the University of Oklahoma, and in this study it utilises initial and boundary conditions obtained from archived analyses and forecasts provided by the Australian Bureau of Meteorology, as well as a 4D-Var data assimilation scheme to ingest all available satellite data. The high-resolution numerical model is multiply two-way nested, with the innermost domain having a resolution of 5 km. It was found that unlike the operational models, which were restricted by relatively low resolution and less data, the high resolution model was able to capture most of the major features of all three TC lifecycles including development from initial tropical depressions, intensification, and their tracks, landfall, and associated rainfall and wind fields.  相似文献   

Tornado outbreaks associated with landfalling hurricanes in the North Atlantic Basin: 1954–2004     

S. M. Verbout  D. M. Schultz  L. M. Leslie  H. E. Brooks  D. J. Karoly  K. L. Elmore 《Meteorology and Atmospheric Physics》2007,97(1-4):255-271

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Creative cities?   总被引：1，自引：0，他引：1  

Deborah Leslie 《Geoforum》2005,36(4):403-405

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A comparison of high-order explicit and non-oscillatory finite difference advection schemes for climate and weather models     

K.-A. Tan  R. P. Morison  L. M. Leslie 《Meteorology and Atmospheric Physics》2005,89(1-4):251-267

Summary The Euler equations govern the behavior of a fluid in motion. They have long been used as a test-bed for assessing the accuracy and efficiency of numerical schemes for solving them. This study focused on advection dominated flows so all other terms in the equations are omitted. The study examined only explicit schemes and does not address the many alternative approaches such as semi-Lagrangian and implicit formulations. The schemes examined here were applied to test cases of increasing complexity as it is well-known that a particular scheme may work very well on some test problems but fail on others. To avoid such problems, we began with the standard tests such as the advection of sine waves and various other one-dimensional shapes, then moved on to two-dimensional problems and finally tested cases that have many scales.Summarizing, the results from the range of test cases, it was found that the schemes that perform best are high-order upwind schemes, with diminishing returns above fifth- and sixth-order.Finally, the schemes were applied to cases where scalar advection requires that constraints such as positive-definiteness be satisfied. For these problems, the Flux Corrected Transport (FCT) and weighted essentially non-oscillatory (WENO) schemes were also applied. Similar conclusions were drawn, namely, that fifth- and sixth-order FCT and WENO schemes produced excellent simulations. However, these schemes were more computationally expensive than the standard high-order upwind and centred schemes.  相似文献