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Spatio-temporal variability in the Brazil-Malvinas Confluence Zone (BMCZ), based on spectroradiometric MODIS-AQUA chlorophyll-a observations

Telesca L., Pierini J. O., Lovallo M., Santamaría-del-Angel E.

Oceanologia

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2018

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No. 60 (1)

76--85

EN

The Brazil-Malvinas Confluence Zone (BMCZ) is characterized by high environmental variation, which could be reflected in several optical types of water, from one containing only phytoplankton and sea water to other optically more complex. In this paper, we analyze the spatio-temporal variability of the Chlorophyll-a detected by the ocean color sensor (CHLAsat) in BMCZ in order to understand its environmental variability. We use the MODIS-Aqua CHLAsat monthly composites imagery from 2002 to 2015, and applied two statistical methods: the correlogram-based robust periodogram to identify, over a broad spectrum of temporal, the most significant periodicities, and the pixel gradient distribution to study the spatial-temporal gradients within the BMCZ and variations over the continental shelf and coastal waters. Our results point out to the predominance of the annual cycle over most of the investigated area, although an area from latitude 37°S in direction NE, alongshore of Uruguay to Brazil, evidences interannual periodicities, possibly related to variations in the discharge of the Rio de la Plata associated with the El Niño phenomena. The ocean color spectroradiometric signature in terms of pixel gradient presents a relatively high variability (∼0.0 to 0.65 mg m−3); in particular the high values of the pixel gradient correspond to saline front of the estuarine system of Rio de la Plata, and to the strip of the platform that extends along the isobaths of 80 m (coast of Uruguay), especially in the center and south of the study area.

2

Investigating dynamical features in the long-term daily maximum temperature time series recorded at Adrián Jara, Paraguay

Telesca L., Benitez J. B.

Acta Geophysica

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2018

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Vol. 66, no. 3

393--403

EN

In this study, we analyse the daily series of maximum temperature measured at Adrián Jara, Paraguay, to disclose features possibly linked with climatological indices that are thought to regulate, in general, the climatic variability of South America. This station is well suited to perform this investigation because it is located in a rural not urbanized area. Our findings reveal that the analyzed series is modulated by several cycles: the annual and half-annual cycle; the 8-year cycle that could be driven by 8-year cycle of the baroclinic waves at the Southern Hemisphere; the 2–3-year periodicity, which seems linked with the Pacific Decadal Oscillation; the 15–16 years periodicity that seems to be induced by the low-frequency fluctuations of SST in the North Atlantic. It is also found an apparent shift in the maximum temperature in the late 1989 that seems to be in agreement with similar findings by other studies that documented such potential jump in the climate system.

3

Fisher–Shannon analysis of the time variability of remotely sensed sea surface temperature at the Brazil–Malvinas Confluence

Pierini J. O., Lovallo M., Gómez E. A., Telesca L.

Oceanologia

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2016

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No. 58 (3)

187--195

EN

The collision of the warm and salty southward flowing Brazil Current and the cold and relatively fresh northward flowing Malvinas Current produces a strong frontal zone known as the Brazil–Malvinas Confluence Zone (BMCZ). This is featured by intense presence of eddies and meanders and is one of the most energetic areas of the world oceans. We apply the statistical method of Fisher–Shannon (FS) to the time series of sea surface temperature, derived from the satellite Advanced Very High Resolution Radiometer (AVHRR) imagery, acquired from 1984 to 1999. The FS method consists of the joint application of Fisher information measure (FIM) and Shannon entropy (SE), measuring respectively the degree of organization and the disorder of a system. Our findings indicate that the FS method is able to locate very clearly the BMCZ, which corresponds to the less organized and more disordered area within the area of confluence between the Brazil and Malvinas Currents.

4

Site Specific Ground Motion Modeling and Seismic Response Analysis for Microzonation of Baku, Azerbaijan

Babayev G., Telesca L.

Acta Geophysica

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2016

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Vol. 64, no. 6

2151--2170

EN

We investigated ground response for Baku (Azerbaijan) from two earthquakes of magnitude M6.3 occurred in Caspian Sea (characterized as a near event) and M7.5 in Shamakhi (characterized as a remote extreme event). S-wave velocity with the average shear wave velocity over the topmost 30 m of soil is obtained by experimental method from the VP values measured for the soils. The downtown part of Baku city is characterized by low VS30 values (< 250 m/s), related to sand, water-saturated sand, gravel-pebble, and limestone with clay. High surface PGA of 240 gal for the M7.5 event and of about 190 gal for the M6.3 event, and hence a high ground motion amplification, is observed in the shoreline area, through downtown, in the north-west, and in the east parts of Baku city with soft clays, loamy sands, gravel, sediments.

5

Discriminating Between Different Streamflow Regimes by Using the Fisher-Shannon Method : An Application to the Colombia Rivers

Pierini J. O., Restrepo J. C., Lovallo M., Telesca L.

Acta Geophysica

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2015

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Vol. 63, no. 2

533--546

EN

The Fisher-Shannon (FS) information plane, defined by the Fisher information measure (FIM) and the Shannon entropy power (NX), was robustly used to investigate the complex dynamics of eight monthly streamflow time series in Colombia. In the FS plane the streamflow series seem to aggregate into two different clusters corresponding to two different climatological regimes in Colombia. Our findings suggest the use of the statistical quantity defined by the FS information plane as a tool to discriminate among different hydrological regimes.

6

Analysis of long-term fluctuations in stream flow time series: An Application to Litani River, Lebanon

Shaban A., Telesca L., Darwich T., Amacha N.

Acta Geophysica

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2014

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Vol. 62, no. 1

164--179

EN

Litani River is the largest river in Lebanon and has been affected by several physical and anthropogenic factors that influenced its flow dynamics. By means of the Singular Spectrum Analysis (SSA), the time dynamics of the stream flow of seven sites along the course of Litani River was investigated, extracting for each site the long-term trend. A clear decreasing trend characterizes all the long-term trends of the stream flow. Furthermore, several peaks were identified, consistent with the rainfall rate and snow cover variability.

7

Investigating the time dynamics of monthly rainfall time series observed in northern Lebanon by means of the detrended fluctuation analysis and the Fisher-Shannon method

Lovallo M., Shaban A., Darwich T., Telesca L.

Acta Geophysica

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2013

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Vol. 61, no. 6

1538--1555

EN

We investigate the time dynamics of monthly rainfall series intermittently recorded on seven climatic stations in northern Lebanon from 1939 to 2010 using the detrending fluctuation analysis (DFA) and the Fisher-Shannon (FS) method. The DFA is employed to study the scaling properties of the series, while the FS method to analyze their order/organization structure. The obtained results indicate that most all the stations show a significant persistent behavior, suggesting that the dynamics of the rainfall series is governed by positive feedback mechanisms. Furthermore, we found that the Fisher Information Measure (the Shannon entropy power) seems to decrease (increase) with the height of the rain gauge; this indicates that the rainfall series appear less organized and less regular for higher-located stations. Such findings could be useful for a better comprehension of the climatic regimes governing northern Lebanon.

8

Investigating prediction performance of an artificial neural network and a numerical model of the tidal signal at Puerto Belgrano, Bahia Blanca Estuary (Argentina)

Pierini J., Lovallo M., Telesca L., Gómez E.

Acta Geophysica

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2013

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Vol. 61, no. 6

1522--1537

EN

In the present study we compare performances of the prediction of hourly tidal level variations at Puerto Belgrano, a coastal site in the Bahia Blanca Estuary (Argentina), by means of the MOHID model, which is a numerical model designed for coastal and estuarine shallow water applications, and of an artificial neural network (ANN). It was shown that the ANN model is able to predict the hourly tidal levels over long term duration with at least seven days of observations and with a better performance in respect to the numerical model. Our findings can be useful to implement ANN-based tools for future studies of the hydrodynamics of Bahía Blanca estuary.

9

Statistical mechanics in earth physics and natural hazards

Vallianatos F., Telesca L.

Acta Geophysica

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2012

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Vol. 60, no. 3

499-501

10

Non-extensivity analysis of seismicity within four subduction regions in Mexico

Valverde-Esparza S., Ramirez-Rojas A., Flores-Marquez E., Telesca L.

Acta Geophysica

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2012

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Vol. 60, no. 3

833-845

EN

The non-extensivity approach based on the Tsallis entropy has been applied to seismicity that occurred from 1988 to 2010 along the Mexican South Pacific coast. We analyzed four different regions, characterized by different subduction patterns. Our results indicate a possible correlation between the non-extensive parameters and the seismicity pattern associated with the inclination angle of each subduction region.

11

Discriminating quarry blasts from earthquakes in Vértes Hills (Hungary) by using the Fisher-Shannon method

Telesca L., Lovallo M., Kiszely M.M., Toth L.

Acta Geophysica

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2011

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Vol. 59, no. 5

858-871

EN

The Fisher-Shannon information (FS) plane, defined by the Fisher information measure (FIM), and the Shannon entropy power, N x , is a robust tool for investigating the complex dynamics of time series. In the FS plane, earthquakes and quarry blasts measured in Vértes Hills (Hungary) are significantly discriminated from each other. Furthermore, the results of the receiving-operating characteristics (ROC) analysis reveal that FIM is a classifier more efficient than N x in discriminating earthquakes from quarry blasts.