OLR (1988) 35 (6) A. Physical Oceanography 527

88:3305 Sleath, J.F.A., 1988. Transition in oscillatory flow

over rough beds. J. WatWay Port coast. Ocean Engng, Am. Soc. cir. Engrs, 114(1):18-33. Engng Dept., Univ. of Cambridge, Cambridge CB2 IPZ, UK.

88:3306 Weaver, A.J. and W.W. Hsieh, 1987. The influence

of buoyancy flax from estuaries on continental sheff circulation. J. phys. Oceanogr., 17(11):2127- 2140.

Most studies of shelf circulation involve coastally- trapped wave models which treat the shore as a uniform boundary. In reality the shoreline is inter- rupted by estuaries with an outflow of less dense water (or in some areas, because of intense evapo- ration, denser water). In addition, the estuarine locale may be marked by a topographic interruption in the form of a submarine canyon. Two previous approaches to estuarine outflow are combined and extended in the present study to address the aforementioned problems. The resulting 3-D model also enables the study of transient motions such as rain- or meltwater flood conditions, which are treated as a Rossby adjustment problem. Dept. of Oceanogr., Univ. of British Columbia, Vancouver, BC V6T IWS, Canada. (fcs)

88:3307 Weir, D.J. and J. McManus, 1987. The role of wind

in generating turbidity maxima in the Tay Estuary [Scotland]. Continent. Shelf Res., 7(11- 12): 1315-1318. Dept. of Geol., The Univ., Dun- dee DD1 4HN, Scotland, UK.

A300. Fluid mechanics

88:3308 Gavoret, Jean, 1987. Frontal instability modes in the

atmosphere and in the oceans. C. r. Acad. Sci., Paris, (S~r. II)305(15):1235-1238. (In French, English abstract.)

The lateral stability of a frontal surface separating two media with different densities is studied for flows within the fl-plane approximation. Considered are geostrophic zonal currents on both sides of a linear west-east frontal trace. The dispersion relation for the 2-D instability modes is derived, and its implications on observed phenomena in the atmos- phere and oceans are discussed. Inst. de Phys. du Globe de Paris, 4, place Jussieu, 75252 Paris Cedex 05, France.

88:3309 Holloway, Greg, 1987. Systematic forcing of large-

scale geophysical flows by eddy-topography in- teraction. J. Fluid Mech., 184:463-476.

The interaction of eddies with variations in topog- raphy, together with a tendency for large-scale wave propagation, generates a systematic stress which acts upon large-scale mean flows. This stress resists the midlatitude tropospheric westerlies, resists the oce- anic Antarctic Circumpolar Current, and may be a dominant mechanism in driving coastal undercur- rents. Associated secondary circulation provides a systematic upwelling in coastal oceans, pumping deeper water onto continental shelf areas. The derivation rests in turbulence closure theory and is supported by numerical experiments. Inst. of Ocean Sci., Sidney, BC V8L 4B2, Canada.

88:3310 Pratt, L.J. and Laurence Armi, 1987. Hydraulic

control of flows with nonuniform potential vor- ticity. J. phys. Oceanogr., 17(11):2016-2029.

The channel cross section is rectangular and poten- tial vorticity is assumed to be prescribed in terms of streamfunction. The problem can be expressed in two forms, the first an algebraic relation between channel geometry and a single dependent flow variable, the second a pair of quasi-linear differential equations relating the geometry to two dependent flow variables. From these forms a general 'branch condition' is derived indicating a merger of different solutions having the same flow rate and energy. This condition implies that the flow is critical with respect to a certain long wave. An example is given in which potential vorticity is a linear function of stream- function and the rotation rate is zero. When the potential vorticity gradient points downstream, allowing propagation of potential vorticity waves against the flow, multiple pairs of steady states are possible, each having a unique modal structure. Critical control of higher-mode solutions is primarily over vorticity, rather than depth. Flow reversals arise in some situations, possibly invalidating the pre- scription of potential vorticity. WHOI, Woods Hole, MA 02543, USA.

88:3311 Shepherd, T.G., 1987. Non-ergodicity of inviscid

two-dimensional flow on a beta-plane and on the surface of a rotating sphere. J. Fluid Mech., 184:289-302. Dept. of Appl. Math. and Theo- retical Phys., Univ. of Cambridge, Silver St., Cambridge, CB3 9EW, UK.