Remarks on Parametric Surface Waves in a Nonlinear and Non-Ideally Excited Tank

We studied free surface oscillations of a fluid in a cylinder tank excited by an electric motor with limited power supply. We investigated the possibility of parametric resonance in this system, showing that the excitation mechanism can generate chaotic response. Numerical experiments are carried out to present the existence of several types of regular and chaotic attractors. For the first time powers (power of the motor, power consumed by the damping force under fluid free surface oscillations, and a total power) are calculated, investigated, and shown for different regimes, regular and chaotic ones for parametric resonance interactions. [DOI: 10.1115/1.4005844]

Impact of biannual rossby waves on the Indian Ocean Dipole

Topex/Poseidon sea surface height anomalies during 1993-2002 are decomposed using 2-D finite impulse response filters which showed biannual Rossby waves (BRWs) in the equatorial Indian Ocean (peak at 1.5 degrees S) and in the southern tropical Indian Ocean (peak at 10.5 degrees S) during Indian Ocean Dipole (IOD) years. Anomalous downwelling BRWs in the equatorial Indian Ocean triggered by the wind stress curl-induced Ekman pumping near the eastern boundary started propagating westward from the eastern boundary in July/August 1993 and 1996, i.e., more than one year prior to the formation of the IOD events of 1994 and 1997 respectively. These strong downwelling signals reach the western equatorial Indian Ocean during the peak dipole time.

Global interannual trends and amplitude modulations of the sea surface height anomaly from the TOPEX/Jason-1 altimeters

This study uses the global Ocean Topography Experiment (TOPEX)/Jason-1 altimeters` time series to estimate the 13-yr trend in sea surface height anomaly. These trends are estimated at each grid point by two methods: one fits a straight line to the time series and the other is based on the difference between the average height between the two halves of the time series. In both cases the trend shows large regional variability, mostly where the intense western boundary currents turn. The authors hypothesize that the regional variability of the sea surface height trends leads to changes in the local geostrophic transport. This in turn affects the instability-related processes that generate mesoscale eddies and enhances the Rossby wave signals. This hypothesis is verified by estimates of the trend of the amplitude of the filtered sea surface height anomaly that contains the spectral bands associated with Rossby waves and mesoscale eddies. The authors found predominantly positive tendency in the amplitude of Rossby waves and eddies, which suggests that, on average, these events are becoming more energetic. In some regions, the variation in amplitude over 13 yr is comparable to the standard deviation of the data and is statistically significant according to both methods employed in this study. It is plausible that in this case, the energy is transferred from the mean currents to the waves and eddies through barotropic and baroclinic instability processes that are more pronounced in the western boundary current extension regions. If these heat storage patterns and trends are confirmed on longer time series, then it will be justified to argue that the warming trend of the last century provides the energy that amplifies both Rossby waves and mesoscale eddies.

Investigation of the Goias Alkaline Province, Central Brazil: Application of gravity and magnetic methods

We investigate the strong magnetic and gravity anomalies of the Goias Alkaline Province (GAP), a region of Late Cretaceous alkaline magmatism along the northern border of the Parana Basin, Brazil. The alkaline complexes (eight of which are present in outcrops, two others inferred from magnetic signals) are characterized by a series of small intrusions forming almost circular magnetic and gravimetric anomalies varying from -4000 to +6000 nT and from -10 to +40 mGal, respectively. We used the Aneuler method and Analytical Signal Amplitude to obtain depth and geometry for mapped sources from the magnetic anomaly data. These results were used as the reference models in the 3D gravity inversion. The 3D inversion results show that the alkaline intrusions have depths of 10-12 km. The intrusions in the northern GAP follow two alignments and have different sizes. In the anomaly magnetic map, dominant guidelines correlate strongly with the extensional regimes that correlate with the rise of alkaline magmatism. The emplacement of these intrusions marks mechanical discontinuities and zones of weakness in the upper crust. According to the 3D inversion results, those intrusions are located within the upper crust (from the surface to 18 km depth) and have spheres as the preferable geometry. Such spherical shapes are more consistent with magmatic chambers instead of plug intrusions. The Registro do Araguaia anomaly (similar to 15 by 25 km) has a particular magnetic signature that indicates that the top is deeper than 1500 m. North of this circular anomaly are lineaments with structural indices indicating contacts on their edges and dikes/sills in the interiors. Results of 3D inversion of magnetic and gravity data suggest that the Registro do Araguaia is the largest body in the area, reaching 18 km depth and indicating a circular layered structure. (C) 2011 Elsevier Ltd. All rights reserved.