Anatoliy Filonov

El Niño 1997–98 monitoring in mixed layer at the Pacific Ocean near mexico's West Coast

The field data collected on monthly polygonal hydrographic surveys off the West Coast of Mexico in 1996–98 are analyzed. Monthly measured temperature and salinity profiles have been computed from the experimental data. The profiles for the 1997 summer-fall and 1998 winter periods differ essentially from profiles computed for the same months in the year 1996. The inferred cause of the difference is the ingress of large volumes of relatively warm and fresh water whose T,S-characteristics identify these water masses as the Pacific Tropical Surface Water. By January 1998, those water masses had filled the entire upper 90-m layer. The heat storage of a 150-m column increased to 15.3 GJ/m², as compared with its January 1996 value of 10.1 GJ/m². The process which caused sea surface temperature anomalies in region B of the Pacific, occurred one month before the rise in temperature and drop down in salinity were observed on the site.

Features of the nonlinear internal wave spectrum in the coastal zone

This paper studies two examples of internal wave band temperature fluctuation spectra from moored instruments on the central Mexican Pacific Shelf and the western shelf of the Japan/East Sea. It is observed that for band f << ω << N, where N is the buoyancy frequency and f is the inertial frequency, the spectral falloff rate with frequency ω tends to ω -3 . These features of spectra are simulated by the model spectrum of nonlinear internal waves in the shallow sea. It is shown that nonlinear internal waves with frequencies f « ω » N are governed by the modified simple wave equation. This equation underlie of the model spectrum of nonlinear internal waves on the shelf. The model spectrum shows ω -3 falloff rate with frequency in contrast with model spectrum proposed with Garrett and Munk, which shows ω -2 falloff rate.

Internal waves in a tropical crater lake: Alchichica, Central Mexico

Lakes with sustained stratification always possess interna! waves. The factors determining the period, amplirude, length and direction of propagation of interna! waves are the character of the stratification, the thermocline position, the bottom relief of the lake and the location of its generating source (LEBLOND & MYSAK 1978). In strongly stratified, deep lakes, interna! waves are frequently the only mechanism enhancing the vertical exchange of heat, oxygen, nutrients, and other substances (KONYAEV & SABININ 1992, WETZEL 200 l). A sharp thermocline usually enhances the formation of interna! gravitational waves. Interna! waves have been studied in many lakes around the world (THORPE 1971, 1992, 1998, THORPE et al. 1996); however, studies undertaken in Mexican lakes are limited to the shallow Lake Chapala (FILONOV & TERESHCHENKO 1999a, b). On this basis, the presence of interna! waves in Lake Alchichica was tested by means of field hydrophysical measurements. The purpose of the present research was to present the initial results of studies on interna! waves in a deep, tropical warm monomictic lake.

Researchers study tsunami generated by Mexican earthquake

Barra de Navidad is a small Mexican tourist town on the coast of a lagoon that is buffered from the Pacific Ocean by a narrow strip of sand. The town is a favorite rest spot of American and Canadian tourists. On October 9, 1995, at 9:36 local time (1536 GMT), a strong earthquake that measured Mx = 8.0 disrupted the lives of the townspeople. The epicenter of the earthquake was located in the ocean at 18°51.5′N and 104°8.4′W [Ortiz and Synolakis, 1996], but it destroyed many hotels and homes, and the shifting of the land tore up the highway that connects Barra de Navidad and Manzanillo. Crevices of up to 3 m wide opened across the road, and bridges over small rivers were knocked down. In an instant, the town was disconnected from the outside world. Frightened townspeople roamed the streets, assessing the destruction.

Hydro-meteorology of Lake Chapala

The purpose of this work is to examine fluctuations of the hydrometeorological characteristics of Lake Chapala, such as air temperature, precipitation, evaporation, atmospheric pressure, wind, water level in the lake and volume of flow of the rivers in the Lake Chapala region. Linear and nonlinear (maximum likelihood) methods of spectral analysis were used to investigate these phenomena. The main periods were identified in the range from hours to decades, obtaining estimates of the mean square amplitudes. The thermodynamic mode of Lake Chapala was also investigated, particularly the vertical-horizontal distribution of temperature of the water and currents. For this purpose, measurements of the distributions of currents and temperatures were performed. Measurements show that Lake Chapala has a quite complex thermodynamic regime and a significant vertical stratification. The differences in temperatures detected between the surface and bottom in the center of the lake were between 0.5 and 1°C and in the eastern part, from 2 to 3°C. The warmest water was located in the lake’s eastern shallow part. The temperature of the water in the central and southern parts of the lake was 1–2°C lower than that of the water at the northern shore. In all the cross-sections, ordinary spatial variations of 3°C on a distance of just 100 to 500 m were registered with a towed device. A buoy station registered the movements of the internal thermal front with a temperature fluctuation of 2°C. The advanced part of the front was accompanied by intense internal waves. The measurements show that the currents in the lake depend strongly on the intensity of the daytime breeze, which enhances wind velocities up to 10 cm s−1 resulting in increases of the water levels of up to 10–30 mm near the shoreline.

Diurnal frequency internal waves in the southern part of the California Current ecosystem as a nutrient source

Although the semidiurnal internal tide dominates internal motions at all sites studied to date off Mexico, a diurnal signal was detected on the shelf of the California Current System off Baja California Sur, even though the barotropic tide is exponentially stronger in the semidiurnal frequency along this coastline. In this study, diurnal thermocline shoaling events were measured in kelp beds in late summer and fall of 2004, very near their southern limit in the Northern Hemisphere. Sub-thermocline water bathed the base of the kelp beds at a diurnal frequency. Nitrate concentrations up to 1.4 μmol·L–1 were found in this sub-thermocline water of almost 20 oC entering the kelp beds, which is a much greater concentration of nitrate at this temperature than is typical for the California Current. Nitrate-rich pulses lasted from 35 min to 19 h and reduced bottom temperatures up to 5 oC in 1 h. The periodicity of temperature variability at the moorings showed significant coherence with the diurnal variability in zonal winds (>95% confidence interval) and was not coherent with the semidiurnal tide. We propose that windforced, diurnal internal motions may provide an important nutrient source for primary producers during reduced upwelling periods and merit further study as a fertilization source in the southern part of the California Current System. A pesar de que la marea semidiurna predomina en las ondas internas de casi todos los sitios estudiados hasta la fecha en Mexico, se detecto una marea interna diurna sobre la plataforma continental del Sistema de la Corriente de California frente a las costas de Baja California Sur, aunque la marea barotropica es exponencialmente mas fuerte en la frecuencia semidiurna. En este estudio, se midio la subida diurna de la termoclina en los mantos de kelp, localizados cerca del limite sureno de su distribucion en el hemisferio norte, durante el verano y el otono de 2004. Agua profunda cubrio la base de los mantos de kelp una vez al dia donde se encontraron concentraciones de nitrato de hasta 1.4 μmol·L–1 en agua de casi 20 oC, lo cual representa una concentracion elevada de nitrato a esa temperatura para la corriente de California. Los pulsos de agua rica en nitrato duraron de 35 min a 19 h en los mantos y redujeron la temperatura del fondo hasta 5 oC en 1 h. La periodicidad de la variabilidad de la temperatura mostro una coherencia significativa con la variabilidad diurna de los vientos zonales (>95% intervalo de confianza) y no fue coherente con la marea semidiurna. Proponemos que las ondas internas diurnas, forzadas por el viento, podrian proveer una fuente importante de nutrientes a los productores primarios durante periodos en los cuales la actividad de surgencias es reducida y requieren de mas estudio para evaluar su capacidad de actuar como una fuente de fertilizacion en la parte sur del Sistema de la Corriente de California.