Recent development in oceanographical observational instruments enables us to come into touch with oceanographical microstructure processes directly. Observational evidence tells us that double diffusive convection plays an important role in such processes like mixing, transport of various properties, both vertically and laterally. In this article, we put emphasis on such processes, and try to review double diffusive convection in oceanography briefly. In § 1 the importance of the study of double diffusive convection in oceanography is presented. In § 2 the occurrence, vertical mass transport and stability of double diffusive convection are discussed. In § 3 the behavior of lateral intrusion driven by double diffusive convection is discussed. In § 4 we try to interpret the role of double diffusive convection in vertical mixing processes. In the final section, we consider future possibility of the study of double diffusive convection.

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A numerical method employing a finite-element method is adopted for an investigation of peristaltic pumping in which all the wave amplitude, the wall-wave slope, and the Reynolds number are large. The fluid mechanics of peristaltic mixing and transport are studied in detail by analyzing the reflux and the trapping phenomena. The results show that the inertia effect of the fluid and the effect of large wall slope enhance the backward flow from the narrowest region of the channel. The appearance of the reflux depends upon the Reynolds number as well as the wavenumber (mean channel width/wavelength).

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The effective length for spatial resolution of a hot-wire sensor has been shown by the author's previous paper, to be around 2/3 of its geometrical length provided that the nondimensionalized length is of order 3 or less. The result is, however, limited to velocity fluctuations centered at the center of the wire. In this paper, analysis is extended to randomly located fluctuations. With the assumption that fluctuations are spatially sinusoidal, the power spectral output of a hot-wire sensor is shown to decrease with the wire-length to wave-length ratio, with rates the smaller for the shorter (in nondimensionalized value) wire. In this sense, the effective length of a sensor wire with the nondimensional length less than 3 is found again to be about 2/3 of its geometrical length.

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