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The data of Reed (1983) are analysed to produce the following empirical equations for the amplitude p 0 (overall fluctuation) in Pascals of the air pressure wave associated with a volcanic eruption of volume V km3 or a nuclear explosion of strength M Mt: Here s is the distance from the source in km. $$\begin{gathered} \log _{10} p_0 = 4.44 + \log _{10} V - 0.84\log _{10} s \hfill \\ {\text{ }} = 3.44 + \log _{10} M - 0.84\log _{10} s. \hfill \\ \end{gathered} $$ Garrett's (1970) theory is examined on the generation of water level fluctuations by an air pressure wave crossing a water depth discontinuity such as a continental shelf. The total amplitude of the ocean wave is determined to be where c 2 1 = gh 1, c 2 2 = gh 2, g is acceleration of gravity, h 1 and h 2 are the water depths on the ocean and shore side of the depth discontinuity, c is the speed of propagation of the air pressure wave, and ? is the water density. $$B = \left[ {\frac{{c_2^2 }}{{c^2 - c_2^2 }} + \frac{{c^2 (c_1 - c_2 )}}{{(c - c_1 )(c^2 - c_2^2 )}}} \right]\frac{{p_0 }}{{g\varrho }}$$ It is calculated that a 10 km3 eruption at Mount St. Augustine would cause a 460 Pa air pressure wave and a discernible water level fluctuation at Vancouver Island of several cm amplitude. 相似文献
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The paper of Reid and Whitaker (1976) on the effects of a vegetation canopy on flow of water is re-examined. Their assumptions on the equality of various drag coefficients are replaced by more realistic calculations. A new method for calculating wind stress on water is presented for the case when the vegetation extends above the water surface.For the case of vanishingly small water depth, it is shown that the horizontal stress is approximately constant in the vertical. This results in a diagnostic relationship for the water current as a function of the wind stress and bottom roughness.A new expression for the vertically averaged frictional force per unit mass is derived on the assumption that the friction velocity varies linearly with height. The vertical rate of change of friction velocity depends on the mean water current, the wind stress, the bottom roughness, and the water depth. This work has a possible application in the mitigation of storm surges. 相似文献
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Summary The analytical solution of a linear barotropic model is derived, including details of the quasi-geostrophic initialization procedure. The prognostic equations are integrated using three different methods of treating the meteorological and gravitational modes separately. These are a semi-Eulerian, semi-implicit (EI) technique, a semi-Lagrangian, semi-implicit (LI) procedure, and a split-explicit (SE) method. The stability criteria and phase speeds are derived for each of the three techniques.The following theoretical conclusions are derived. Of course, in actual numerical integrations particularly those using more complex models, the results are not so unequivocal.The stability of the EI procedure is governed by the CFL criterion for the meteorological mode. Gravity waves have no effect on the timestep but move more slowly than the analytical waves. The LI method is unconditionally stable with respect to both meteorological and gravitational modes. There is thus no timestep restriction. However, the gravity waves have the same reduced phase speed as in the EI technique. The SE procedure has CFL timestep criteria for both the meteorological and gravitational calculations. However, its gravity wave phase speeds are relatively accurate. Moreover, it is the only one of the three methods that handles the nearly-compensating pressure gradient and Coriolis forces together. From the point of computational efficiency, the LI technique is probably the best. 相似文献
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Abstract Observations of the changes in mean annual and seasonal precipitation with time in British Columbia and western Alberta between the periods 1931–60 and 1951–80 indicate that more stations show an increase than a decrease. Changes tend to be positive on the coast, negative in south‐central British Columbia, positive on the west slopes of the Rockies, and negative to the east. This suggests an orographic influence and increased flow from the southwest at mountain‐top. The possibility that these changes in precipitation are associated with CO2 warming is considered. Both the surface air temperature and sea surface temperature were raised by 2°C for cyclogenesis events over the northeastern Pacific and the consequences were investigated with the aid of a limited‐area, 8‐level primitive equations model. The lows are deepened by as much as 6 mb and precipitation amounts are increased up to 8 mm owing to the increased mixing ratio and the feedback of latent heat energy. 相似文献
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Maurice Danard 《大气与海洋》2013,51(4):466-470
Abstract The importance of boundary‐layer convergence of mass and water vapour on the pressure tendency is studied. Mass convergence tends to fill the low while moisture convergence deepens it, owing to the subsequent release of latent heat. It is estimated that at dew points above about 18°C, the moisture convergence effect becomes dominant; that is, the C1SK mechanism is important at high dew points. 相似文献
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M. B. Danard M. C. Rasmussen T. S. Murty R. F. Henry Z. Kowalik S. Venkatesh 《Natural Hazards》1984,2(2):153-171
Storm surges in the Beaufort Sea present a severe problem for navigation as well as for offshore oil drilling activities. Influence of ice cover on storm surges in the Beaufort Sea is examined making use of a numerical model as well as a set of observations.The automated shallow-water model of Henry has been modified to incorporate ice cover and is adapted to the Beaufort Sea. The leading edge of the permanent ice is calculated from the loci of identifiable points. Generalized similarity theory is employed to compute wind stresses. Simulations are made using model-predicted ice concentrations and observed ice concentrations. Ice motion is relatively small in units of model grid distance (approximately 18 km) during surges. Spherical effects are important and should be included in future adaptations of the model. Comparison of the computed surges with observed surges for eight different events showed reasonable agreement. 相似文献
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Maurice Danard 《大气与海洋》2013,51(2):485-493
Abstract The effects of virtual temperature on parcel buoyancy are investigated and the following results obtained. For descent or unsaturated ascent, the buoyancy acceleration is enhanced if the mixing ratio increases with pressure. However, for saturated ascent, the buoyancy acceleration is inhibited unless the lapse rate of mixing ratio exceeds a value slightly greater than that along a moist adiabat. This criterion is evaluated for several mean soundings. For the case of Oklahoma supercells, the mixing ratio lapse rate is clearly large enough. However, for other cases it often is not. Horizontal gradients in water vapour and condensed water can have a significant influence on the thermal wind. 相似文献
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This paper describes a one-level variational adjustment process for producing mass-consistent surface winds in the Barrow Strait area, N.W.T. To achieve this result, the continuity equation is employed as a physical constraint. The variational technique adjusts mean winds (vertically averaged through the planetary boundary layer); therefore, a relationship is required between surface and mean winds. Use is made of existing velocity profiles, but interpolation may be used between surface and geostrophic winds. The model was found to be strongly dependent upon specification of boundary-layer height. Channeling effects are not readily seen until topography begins to protrude through the boundary layer. The model might thus be better suited to areas where shallow inversion layers are well defined. By application of the variational adjustment, errors in continuity are reduced by six orders of magnitude. Upon comparison of the variational technique with a diagnostic, one-level, primitive equation model, median errors between computed and observed surface winds were found to be comparable. 相似文献
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Maurice Danard 《Boundary-Layer Meteorology》1981,20(3):397-398
A method is presented for estimating the height of the constant flux layer. 相似文献