1,703 research outputs found
Thermic structure and intense internal waves on the narrow continental shelf of the Black Sea
No full textMeasurements results of the thermic structure taken from the waters of the narrow continental shelf of the south coast of Crimea are discussed. Continuous observations were performed in July-August 1993, from a stationary oceanologic platform (depth 30 m) using an antenna with three temperature distribution sensors and two temperature gradient distribution sensors situated at the platform comers (in a 19 x 22 m plane) covering the thermocline completely. Probes were also made of the water layer down to the bottom using a CTD, and also the currents at 5, 10 and 20 m were observed. A continuous register of the sea level waves, wind and atmospheric pressure was taken. The thermic structure showed oscillations in three time-scales: synoptic, related to the surge phenomena (3-5 days); inertial (17-18 h) and short period (less than 1 h). The thermocline was completely extended with a strong negative setup, and was close to the bottom with a positive setup, possessing vertical gradients of up to 2°C/m. Inertial movements showed up in the current oscillations and also produced vertical displacements in the thermocline up to 8-10 m, happening constantly while the measurements were taken. These displacements were usually related to groups of intense internal short period waves with amplitudes of 4-9 m, periods of 14-28 min and wavelengths of 250-360 m. An intense movement, with diurnal period related to the breeze processes on the coast, was also found in the currents. The relationship between the parameters of the intense waves in groups and those of the medium dispersion and non-linearity as well as the parameters of the calculated solitons in the Korteweg and de Vries equation, are analyzed. (C) 2000 Elsevier Science B.V
Spatial structure of the temperature and salinity fields in the presence of internal waves on the continental shelf of the states of Jalisco and Colima (Mexico)
No full textA method to filter fluctuations in the hydrophysical properties of the continental shelf, caused by intense internal tides, is proposed. The method is based on a smoothing of the field of the properties analyzed with a filter, the parameters of which are determined by the shape of the spatial correlation function of the field pulsations. The filtering method was tested on data from a fast oceanographic survey, conducted in an area of the monitoring polygon of the waters around Barra de Navidad. The survey was conducted on 25 and 26 November 1995, with an undulating CTD. In one day, 86 vertical profiles of temperature and salinity were obtained from nine transects perpendicular to the coast (survey area of 100 x 25 km) to a depth of 100 m. The filtering algorithm of the internal waves is studied in detail. The field measurements present an analytical shape obtained from an equation in which the elements describe the components: low frequency, pulsating and related to daily behavior. The results of the analysis of the initial temperature and salinity fields with respect to homogeneity and isotropy are discussed, as well as the structural peculiarities of the estimates of the spatial correlation functions. It is observed that the temperature and salinity fields along the shelf, within the limits of the polygon scale, are neither homogenous nor isotropic. The correlation functions of the field pulsations analyzed are more clearly observed in the thermocline. The characteristic scales perpendicular to the coast are smaller than along it. Examples of smoothing the temperature and salinity fields in the thermocline are given
On the dynamical response of lake Chapala, Mexico to lake breeze forcing
No full textFluctuations in the atmospheric characteristics, as well as variations in the water level of Lake Chapala are discussed. Field measurements of the atmospheric characteristics and lake level during December 1996 through January 1997 are described; using spectrum analysis of synchronous time series. The findings suggest that the variability is due to the diurnal cycle of atmospheric elements. Lake breeze circulation plays an important role in the area of Lake Chapala; since it was registered in 83% of the data. Periodic fluctuations in atmospheric pressure and wind generate significant seiche amplitudes in the lake, with the periods of about 6 h. With the help of a simple model, the seiche parameters are estimated. The amplitude of one-nodal seiches on one of the edges of the lake; is on average equal to 18 mm. This wave should generate currents of approximately 0.012 m s-1 at the lake's centre in the area of the nodal line. The experimental results on the thermal regime and circulation of Lake Chapala are discusssed as well. Surface temperature variations were registered at the eastern part of the lake. In all cross-sections, typical spatial variations of 3°C were registered, over a distance of 100-300 m. A bouy station registered movements of an internal thermal front in the body of the water. The leading edge of the front was accompanied by intense internal waves, in the form of internal KdeV solitones. The front near the buoy station was produced by the movement of a warm body of water travelling from the shallow eastern part of the lake and trigered by morning breeze
Tsunami waves on the shelf near the west coast of Mexico (October 9, 1995)
No full textThe materials obtained by submerged buoy stations on the shelf of the west coast of Mexico were analyzed. The stations were equipped with autonomous sensors of temperature, electric conductivity, and pressure. The parameters of tsunami waves in the open sea were measured, and their interaction with the internal tide was registered
Tsunami waves on the shelf near the west coast of Mexico (October 9, 1995)
No full textThe materials obtained by submerged buoy stations on the shelf of the west coast of Mexico were analyzed. The stations were equipped with autonomous sensors of temperature, electric conductivity, and pressure. The parameters of tsunami waves in the open sea were measured, and their interaction with the internal tide was registered
On the interpretation of short-period fluctuations in the thermocline obtained from a towed sensor [Acerca de la interpretaci�n de las fluctuaciones de corto periodo de la termoclina obtenidas por medio de un sensor en movimiento]
No full textAspects related to the interpretation of data from temperature oscillations in the thermocline obtained from a towed sensor are presented. A simple model of dispersion relation for linear internal waves with a decrease in energy in the spectrum, isotropic with regard to direction and uniform in frequency, shows that, at determined tow speeds of the sensor, a fictitious spectral density peak may appear in the frequency spectrum measured. The results of the study on the dependency of the spectral density in the internal wave spectra with respect to the tow speed of the sensor, the nature of the decrease in energy and wave number for specific hydrological conditions are also analyzed. How to avoid or decrease Doppler deformations in the spectra measured is discussed
On the interpretation of short-period fluctuations in the thermocline obtained from a towed sensor [Acerca de la interpretación de las fluctuaciones de corto periodo de la termoclina obtenidas por medio de un sensor en movimiento]
No full textAspects related to the interpretation of data from temperature oscillations in the thermocline obtained from a towed sensor are presented. A simple model of dispersion relation for linear internal waves with a decrease in energy in the spectrum, isotropic with regard to direction and uniform in frequency, shows that, at determined tow speeds of the sensor, a fictitious spectral density peak may appear in the frequency spectrum measured. The results of the study on the dependency of the spectral density in the internal wave spectra with respect to the tow speed of the sensor, the nature of the decrease in energy and wave number for specific hydrological conditions are also analyzed. How to avoid or decrease Doppler deformations in the spectra measured is discussed
Internal tides in the Northern Gulf of California
No full textThe characteristics of the internal tide in the Northern Gulf of California are described using data from two moored arrays of temperature and current sensors, one for summer and one for winter, located between Angel de la Guarda Island and the mainland. From the summer six-sensor mooring it was found that: (1) the current fluctuations are dominated by the semidiurnal frequency band, while the quarterdiurnal frequency dominated the temperature fluctuations. (2) The baroclinic semidiurnal horizontal current fluctuations are aligned with the gulf axis, and have amplitudes of 10-15 cm s-1; the vertical displacements reached 4 m in this frequency band. (3) The vertical modal structure for the temperature and velocity oscillations was dominated by the first and third modes. (4) The energy of the semidiurnal internal tide is 45% of that of the barotropic tide. (5) Vertical wave number spectra showed slightly asymmetric peaks in the high wave number components, indicating that their downflowing energy is larger than that flowing upward. From the winter two-sensor mooring, it was found that the vertical oscillations were mainly semidiurnal, with root mean square amplitudes of 7 m
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