Showing papers by "Ensenada Center for Scientific Research and Higher Education published in 1987"

Seasonal and interannual thermohaline variability in the Guaymas Basin of the Gulf of California

Abstract: Temperature and salinity data for the years 1939–1983 are used to investigate seasonal and interannual scales of the hydrographic variability across the Guaymas Basin, which is located between 27° and 28°N in the Central Gulf of California. Winter conditions extend from December to April and summer conditions from June to October, with transition periods in May and November. Sea surface temperature increases from about 16°C in February–March to 31°C in August. No clear seasonal cycle in surface salinity was found. Typical values are above 35.1‰ even in winter, and up to 35.5‰ in November. Relatively cold and low salinity near-surface waters observed in June 1957 and in June 1982, suggest advection of California Current Water to the Guaymas Basin. Subtropical Subsurface Water may occur around the year, but is obscured by vertical mixing with Gulf Water mainly during winter, when vertical stratification is weaker. The Intermediate and Deep Pacific Water masses successively fill the Guaymas Basin to the bottom (2000 m), showing very stable T-S characteristics. Positive sea level anomalies at Guaymas increases during El Nin˜o years, and anomalous low salinity and high temperature at the surface indicate the presence in the Guaymas Basin of water from the south. Observed differences reached 0.4‰ in surface salinity and 3°–5°C in surface temperature. There is evidence that the observed low salinities could not be due to abundant precipitation. An additional effect is a deepening of the winter pycnocline down about 200 m, compared to the usual depth of

Nonlinear integral equations for electromagnetic inverse problems

Abstract: The scaling properties of Maxwell’s equations allow the existence of simple yet general nonlinear integral equations for electrical conductivity. These equations were developed in an attempt to reduce the generality of linearization to the exclusive scope of electromagnetic problems. The reduction is achieved when the principle of similitude for quasi‐static fields is imposed on linearized forms of the field equations. The combination leads to exact integral relations which represent a unifying framework for the general electromagnetic inverse problem. The equations are of the same form in both time and frequency domains and hold for all observations that scale as electric and magnetic fields do; direct current resistivity and magnetometric resistivity methods are considered as special cases. The kernel functions of the integral equations are closely related, through a normalization factor, to the Frechet kernels of the conventional equations obtained by linearization. Accordingly, the sensitivity functio...

On the stability of elliptical vortex solutions of the shallow-water equations

Abstract: The one-layer reduced gravity (or ‘shallow water’) equations in the f-plane have solutions such that the active layer is horizontally bounded by an ellipse that rotates steadily. In a frame where the height contours are stationary, fluid particles move along similar ellipses with the same revolution period. Both motions (translation along an elliptical path and precession of that orbit) are anticyclonic and their frequencies are not independent; a Rossby number (R0) based on the combination of both of them is bounded by unity. These solutions may be taken, with some optimism, as a model of ocean warm eddies; their stability is studied here for all values of R0 and of the ellipse eccentricity (these two parameters determine uniquely the properties of the solution).Sufficient stability conditions are derived from the integrals of motion; f-plane flows that satisfy them must be either axisymmetric or parallel. For the model vortex, the circular case simply corresponds to a solid-body rotation, and is found to be stable to finite-amplitude perturbations for all values of R0. This includes R0 > ½, which implies an anticyclonic absolute vorticity.The stability of the truly elliptical cases are studied in the normal modes sense. The height perturbation is an n-order polynomial of the horizontal coordinates; the cases for 0 ≤ n ≤ 6 are analysed, for all possible values of the Rossby number and of the eccentricity. All eddies are stable to perturbations with n ≤ 2. (A property of the shallow-water equations, probably related to the last result, is that a general finite-amplitude n-order field is an exact nonlinear solution for n ≤ 2.) Many vortices - noticeably the more eccentric ones - are unstable to perturbations with n ≥ 3; growth rates are O(R02f) where f is the Coriolis parameter.

Industrial Development Effects on the Ecology of a Pacific Mexican Estuary

Abstract: In November 1983, the construction of the first part of an assembling plant of jackets to support oil-drilling platforms began at Punta Banda estuary, a 16.40 km 2 coastal estuary located 150 km south of the USA-Mexico border. The area that is being built on (0.45 km 2 ) is located at the south-west corner of the estuary and is delimited by a dike. The second part of the construction, covering a further 0.40 km 2 , will extend to the south-east and will require some deflection of the main circulation channel.

Tides and currents in Fury and Hecla Strait

Abstract: Under-ice current measurements reveal a homogeneous flow of water along Fury and Hecla Strait; it had a westward direction during the passage, over Igloolik, of low pressure cells in the atmosphere and an eastward direction at other times. It is presumed that barometric pressure differences between the Gulf of Boothia and Foxe Basin control partly the direction of the flow. The diurnal and semidiurnal components of the tidal currents also have a simple structure across the section of measurements. The subtidal and tidal components of the current all have the same order of magnitude, namely some 15 cm/s. The vertical tide progresses eastward; the diurnal component diminshhes abruptly once it enters Foxe Basin while the semidiurnal component increases steadily, its mean amplitude rising from 48 to 68 cm between the two extremities of the channel. Convective and frictional effects are evident in the water level records, indicating marked non-linear effects in the tides and currents, an eastward decrease in the diurnal currents and an increase in the semidiurnal ones.