- Settore: Education
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Founded in 1876, Texas A&M University is a U.S. public and comprehensive university offering a wide variety of academic programs far beyond its original label of agricultural and mechanical trainings. It is one of the few institutions holding triple federal designations as a land-, sea- and ...
A current that flows eastward along the Algerian coast in the Mediterranean Sea. It flows as a narrow, easily distinguished current for around 300 km from about 0 to 4° E with a width of less than 30 km, average and maximum velocities of 0. 4 and 0. 8 m/s, respectively, and a tranport of about 0. 5 Sv. This is a continuation of the current associated with the Almeria-Oran Front that is itself a continuation of the flow of Atlantic Ocean water entering through the Gibraltar Strait.
Industry:Earth science
An isotope of argon that is useful as a tracer in ocean studies. It is a radioactive inert gas with a half life of 269 years and is produced in the atmosphere by cosmic ray interactino with Argon-40. It is well-mixed through the troposphere and its variation in concentration over the last 1000 years has been estimated to be no more than about 7%. This means that its distribution in the atmosphere and ocean is in steady state.
It enters the ocean by gas exchange with the equilibrium time between the surface mixed layer and the atmosphere being about a month. The equilibrium concentration in surface water is calculated from the solubility of argon, a well known function of temperature and salinity, and the also well known concetration of Ar-39 in the atmosphere. The surface concentration in regions of deep water formation, where the surface water may not equilibrate with the atmosphere due to rapid convection processes, can be determined from measurements. Measurement is at present an onerous process requiring 1500 liters of water, and the concentration measured is reported in % modern, i.e. the Ar-39:Ar:40 ratio of the sample divided by the Ar-39:Ar:40 ratio of the troposphere. The minimum detectable limit is about 5% modern (with an error of 3-5% modern) which corresponds to an age of 1100 years with a resolution of about 50 years.
Argon-39 is an ideal tracer for investigating mixing and circulation in the deep ocean and in the mid to lower thermocline. Its distribution is in steady state and the boundary conditions are well known, i.e. there is no flux across the ocean bottom and the surface water concentration is known everywhere. Its distribution in the ocean interior is affected only by circulation, mixing and radioactive decay process, and since the decay rate is know it serves as a clock for circulation and mixing processes.
Industry:Earth science
The inference of the state of the ocean from precise measurements of the properties of sound waves passing through it. This technique takes advantage of the facts that the properties of sound in the ocean are functions of temperature, water velocity and other salient oceanographic properties and that the ocean is nearly transparent to low-frequency sound waves. These felicitous circumstances combine to allow signals transmitted over hundreds to thousands of kilometers to be processed with inverse methods to obtain estimates of large-scale fields of ocean properties. An especially advantageous feature of this method is that, given the 3000 knot speed of sound in the ocean, reasonably synoptic fields can be constructed. The chief problems presently encountered in this field are those related to engineering sufficiently accurate transmitters and receivers for the task.
Industry:Earth science
An undersea ridge that is not seismically or volcanically active. Examples of aseismic ridges are the Walvis Ridge, the Rio Grande Plateau, the Kerguelen Plateau, the Seychelles Ridge and the Lomonosov Ridge.
Industry:Earth science
An air-deployed, expendable, ocean temperature profiling probe. The AXBT consists of a temperature probe, 300-1000 meters of cable, a VHF transmitter and antenna, and a salt water activated battery. When the AXBT hits the ocean surface and stabilizes, the transmitter is activated and the temperature probe released. The surface transmitter telemeters the temperatures measured by the falling probe to a data gathering system on the aircraft that released it.
Industry:Earth science
A quantity first derived in Lorenz (1955) in an investigation to discover what portion of total potential energy could be transformed into kinetic energy under the constraint of quasi-hydrostatic and adiabatic processes. Available potential energy (APE) was defined as the difference between a system's mass integrated total potential energy and the total potential energy of a hydrostatic reference state, i.e. the difference in potential energy between the actual physical state and the reference state, where the latter is defined as the state of minimum potential energy that can be reached through reversible adiabatic processes. In the reference state, all density surfaces are level. This was extended in Van Mieghem (1956) to deal with non-hydrostatic states.
Industry:Earth science
The degree of freedom from error. The total error compared to a theoretically true value. Contrast with and see precision for an example.
Industry:Earth science
The tendency of the crust of the earth (i.e. the lithosphere) to maintain a near equilibrium state in relation to the denser, underlying asthenosphere or upper mantle. For example, a continental block might sink or rise due to the presence or absence of an ice sheet in a process called glacial isostatic adjustment.
Industry:Earth science
In meteorology, a line on a chart joining points of equal specific volume, the volume of unit mass.
Industry:Earth science
