Tidal power from wedge-shaped estuaries — an analytical model with friction, applied to the Bristol Channel

Summary. The analytical wedge-shaped model of tidal propagation with friction described in an earlier paper which has complex Bessel function solutions, has been applied to the Bristol Channel with the introduction of a power-generating barrier. An analytical solution is possible for a linear flow condition at the barrier, assuming time variation at a single dominant tidal frequency, which requires symmetrical lunar operation of the barrage. Having obtained an analytical expression for the available power, the flow condition at the barrier is optimized to maximize the available power. If a phase lag is introduced between the water head and the flow at the barrier, significant increases in power are attainable. Variation of the upper end boundary condition indicates that closing off the upper Severn Estuary to tidal propagation would enable more power to be extracted at the barrage. Modification of the mouth boundary condition to take into account the response of the external sea to variations of flow across the mouth indicates a small reduction in available power. The model is intended as a simple indicator of the overall dynamics, rather than a prediction of the detailed response to the introduction of a barrier.     

The North-West European Shelf seas: The sea bed and the sea in motion. II. Physical and chemical oceanography,and physical resources: Edited by F. T. Banner,M. B. Collins and K. S. MassieElsevier Scientific Publishing Co., Amsterdam, 1980, xii+338 pp., £46·73

Total, chemical and biological oxygen demand of intertidal sediment cores from 12 stations in a mangrove swamp in southern Africa were measured under mean temperature and salinity conditions. In addition to measuring oxygen removed from water overlying cores, the uptake of oxygen from air overlying sealed cores was also determined. Total oxygen consumption ranged from 2·9 to 37·0 ml O₂ m^?2 h^?1 in water and from 22·1 to 81·6 ml O₂ m^?2 h^?1 in air. Chemical oxygen demand usually equalled or exceeded the total, underlining problems in the measurement of this parameter. Since oxygen is not present below a few millimeters in the sediment, it is concluded that oxygen diffusing from the overlying water or air is rapidly utilized at the surface and its uptake rate does not give any measure of metabolic activity deeper down. The oxygen content of the overlying water present during high tide may drop to relatively low levels due to this demand.     

INFORMATION THEORY AND SEQUENCES OF LAND USE: AN APPLICATION

This paper addresses the question of how far into the past previous land-use patterns provide significant information concerning present or future patterns. The provision of information is viewed as a reduction in uncertainty. An information-theoretic approach that permits both statistical and graphical analysis is suggested. Application of this method to the analysis of land-use change in three townships on the fringe of Akron, Ohio suggests that, to a varying degree, the processes of change are first-order Markov processes.     

Stochastic-growth theory of Langmuir growth-rate fluctuations in type III solar radio sources

Fluctuations in type III beams are produced by quasilinear interactions with clumpy Langmuir waves in type III radio sources. The properties of these fluctuations are estimated and shown to yield Langmuir growth rates and growth-rate fluctuations consistent with those required by the recent stochastic-growth theory of type III radio bursts, with observations, and with existing theoretical constraints. This strengthens the basis of stochastic-growth theory and provides an essential consistency test for this model.     

Solar cycle changes to planetary wave propagation and their influence on the middle atmosphere circulation

Recent observations suggest that there may be a causal relationship between solar activity and the strength of the winter Northern Hemisphere circulation in the stratosphere. A three-dimensional model of the atmosphere between 10–140 km was developed to assess the influence of solar minimum and solar maximum conditions on the propagation of planetary waves and the subsequent changes to the circulation of the stratosphere. Ultraviolet heating in the middle atmosphere was kept constant in order to emphasise the importance of non-linear dynamical coupling. A realistic thermo-sphere was achieved by relaxing the upper layers to the MSIS-90 empirical temperature model. In the summer hemisphere, strong radiative damping prevents significant dynamical coupling from taking place. Within the dynamically controlled winter hemisphere, small perturbations are reinforced over long periods of time, resulting in systematic changes to the stratospheric circulation. The winter vortex was significantly weakened during solar maximum and western phase of the quasi-biennial oscillation, in accordance with reported 30 mb geopotential height and total ozone measurements.     

Interferometric evidence for the observation of ground backscatter originating behind the CUTLASS coherent HF radars

Interferometric techniques allow the Super-DARN coherent HF radars to determine the elevation angles of returned backscatter, giving information on the altitude of the scatter volume, in the case of ionospheric backscatter, or the reflection altitude, in the case of ground backscatter. Assumptions have to be made in the determination of elevation angles, including the direction of arrival, or azimuth, of the returned signals, usually taken to be the forward look-direction (north) of the radars, specified by the phasing of the antenna arrays. It is shown that this assumption is not always valid in the case of ground backscatter, and that significant returns can be detected from the backward look-direction of the radars. The response of the interferometer to backscatter from behind the radar is modelled and compared with observations. It is found that ground backscatter from a field-of-view that is the mirror image of the forward-looking field-of-view is a common feature of the observations, and this interpretation successfully explains several anomalies in the received backscatter.