Some aspects of internal wave motions

Summary Internal waves are considered on the hypotheses of small disturbances and the Boussinesq approximation. Consideration is given to the lowest internal mode propagating along athin thermocline, and an approximate calculation is made of the dispersion relation, including an explicit representation of the dominant correction for thermocline thickness. Then, the Stokes drift velocity is calculated (a) approximately for this mode in the thin-thermocline model, and (b) numerically for the first two internal modes associated with a single thick thermocline. Finally, a calculation is made of the mass transport velocity field induced by the interaction between pairs of waves (surface or internal), having thesame frequency but arbitrary directions of propagation.     

Double boundary layers in standing surface waves

Summary The double boundary-layer theory ofStuart (1963, 1966) andRiley (1965, 1967) is employed to investigate the mass transport velocity due to two-dimensional standing waves in a homogeneous fluid. The double boundary-layer structure occurs only at the bottom, and the existence of jet-like motions is predicted, due to the nature of the mean flows in the bottom boundary layers. A vector equation governing mean motions in the secondary layer is derived for threedimensional wave motions.     

Forecasting the Conditional Probabilities of Natural Disasters in Canada as a Guide for Disaster Preparedness

A variety of natural disasters occur in Canada. Yet apart from simple ``return period' calculations, no apparent research seems to have made systematic use of the OCIPEP database on all natural disasters in Canada over the period of 1900 to 2000. This paper (a) describes the main characteristics of natural disasters in Canada, and (b) presents a methodology that is a first attempt to use the database to forecast conditional probabilities of each type of natural disaster. The forecast probabilities can then be used to work out the expected social costs of each type of natural disaster. The expected costs in turn suggest what kind of policy priorities are indicated for disaster preparedness. The key results of this methodology are that Hydrometeorological Disasters are increasing over time and of these, the ranking in order of priority for preparedness should be droughts, heat waves, floods and ice storms.     

Damping characteristics of gravity waves obliquely incident on a monomolecular film: Part II

Calculations of viscous damping chracteristics of gravity waves, propagating obliquely across finite monomolecular films, are represented graphically to demonstrate the influence of angle of incidence, film edges, and surfactant properties. It is found that regions of negative damping may occur, particularly towards the rear of extensible slicks. For wide slicks, both the amplitude and the domain of significant edge effects on the local damping coefficient decrease with angle of incidence. Multiple-slick systems can damp waves more effectively—with appropriate choice of surface-active material—than an equivalent single slick.     

Estimating baselines for climate change for less developed countries: the case of the Sahel

Abstract

The UN Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol provide mechanisms for assisting less developed countries that are adversely affected by climate change. Such assistance would need a baseline, which ideally would set a precise date for specific impacts of climate change. This article presents the results of statistical tests that we carried out and, for the African region of the Sahel, finds that for precipitation (affecting food supply), impacts due to climate change can be ‘dated’ to the year 1967, when precipitation fell drastically, affecting the local food supply. Such a statistically robust benchmark would be useful to the Subsidiary Body for Scientific and Technological Advice (SBSTA) of the UNFCCC. The method illustrates how other baselines may be established for the important work of the SBSTA.     

State-to-state rotational transition rates of the HCO+ ion by collisions with helium

The rates of rotational transitions for HCO⁺, the most abundant ion in interstellar space, induced by collision with helium are obtained for temperatures ranging from 10 to 80 K. The calculations are based on a new potential energy surface for the He–HCO⁺ interaction and on a scattering matrix whose accuracy was checked by pressure broadening and shift measurements. The rates     decrease for increasing values of j and  Δ j   , with a temperature trend depending on the energy involved in the transitions: if it is small, the rates are almost constant, while an increase with T is found for other cases. Comparison with previous and less accurate results shows an agreement within 50 per cent. Comparison between state-to-state and pressure broadening cross-sections allows us to discuss importance and influence of elastic and inelastic collisions.     

On the second approximation to mass transport in the bottom boundary layer

The second approximation is obtained for the mass transport velocity within the oscillatory bottom boundary layer beneath sinusoidal progressive and standing waves of finite amplitude. This approximation includes a simple new term, which essentially ensures continuity of the vertical gradient of mass transport at the edge of the layer and is of third-order in the perturbation (or wave-slope) parameter. For long progressive waves in conditions of zero net mass flow, the term represents a moderate reduction in mass transport at the edge of the layer, compared with the first approximation of Longuet-Higgins. For standing waves of arbitrary length, the mass transport is reduced (increased) far from (near) the bottom, except near nodal locations where an increase (a reduction) is predicted. The proposed correction to the first approximation yields clearly improved results when compared with appropriate experimental evidence. Deficiencies in the higher-order theories of Sleath and Isaacson for propagating waves are disclosed.