Surface Potential Gradient Research Articles

The Stability of Currents in the Atmosphere and the Ocean: Part I

The stability with respect to quasi-geostrophic disturbances of atmospheric and oceanic currents containing both horizontal and vertical shear is investigated for both a continuously stratified and a twolayer model. Certain necessary conditions for instability are derived. The potential vorticity gradient of the basic flow must be both positive and negative for instability to occur in the two-layer model. In the continuous model the condition for instability states that the potential vorticity gradient must either change sign or be balanced by surface terms incorporating the surface potential temperature gradient and topographical variations. For a large class of flows, the product of the zonal current and the potential vorticity gradient must be somewhere positive for instability to occur, and the maximum of this product bounds the growth rate. The square of the growth rate is bounded for an arbitrary flow field by the maximum value of the available mean kinetic and potential energy densities. The phase speed of unstable waves is within limits specified by the mean velocity field, the planetary vorticity gradient, and topographical variations across the stream. It is also shown that a wide class of flows in the two-layer model must be stable for sufficiently high zonal wave number.

Electrical Measurements and Their Interpretation In Underground Cable Corrosion Problems

Abstract Methods of making duct surveys, surface potential gradient surveys, measurements of cable to reference electrode potentials, sheath current measurements and earth resistivity measurements are described. Examples are given of various types of measurement and their interpretation. It is pointed out that a single measurement of the potential between a cable sheath and a reference electrode in contact with nearby earth may not reveal the existence of a corrosive condition. Emphasis is given to the difference in polarity between self-produced corrosion cells and those resulting from external influences such as stray current or contact with a more noble metal. The importance of employing a variety of measurements in any particular study is shown. References are given to techniques employed by other workers in making underground corrosion tests. 4.5.3

Earth Potential or Surface Potential Gradient Tests on Buried Cables

Abstract Earth potential or surface potential gradient tests, their types, uses and limitations are discussed. Topics covered include range of potentials, selection of areas for tests, installation of remedial measures on buried telephone cables, determination of buried structure location and meter circuits for measuring potential gradients. Data are given also on hot spot areas, changes in insulation resistance of the covering on a buried cable and interference effects on other buried structures and railroads from cathodic protection installations. 4.5.3

On the flow of electric current in semi-infinite stratified media

We suppose a semi-infinite medium to be built up of layers in each of which the electrical conductivity is finite. Direct current is introduced at a point electrode on the free surface and flows to a second electrode at a given distance away. It is obvious that the stream-lines and equipotentials accessible to measurements on the free surface will depend on the conductivities, depths and thicknesses of the strata. The problem dealt with in the present paper is to build up a theory of electrical conduction in stratified media which will enable the nature of the stratification to be deduced from measurements of surface potential gradients. From the mathematical point of view, it is sufficient to obtain a solution for a single electrode from which current flows symmetrically to infinity. When the surface potential has been obtained for this simplified problem, the potential distribution for flow between several electrodes is found by addition.