scholarly journals Contribution of low-frequency climatic/oceanic oscillations to streamflow variability in small, coastal rivers of the Sierra Nevada de Santa Marta (Colombia)

2018 ◽  
Author(s):  
Juan Camilo Restrepo ◽  
Aldemar Higgins ◽  
Jaime Escobar ◽  
Silvio Ospino ◽  
Natalia Hoyos
Keyword(s):  
Energy Spectrum ◽  
Sierra Nevada ◽  
Large Scale ◽  
Low Frequency ◽  
Maximum Power ◽  
Simultaneous Occurrence ◽  
Atmospheric Processes ◽  
Low Frequency Oscillations ◽  
Streamflow Variability

Abstract. This study evaluated the influence of low-frequency oscillations that are linked to large-scale oceanographic/atmospheric processes, on streamflow variability in small tropical coastal mountain rivers of the Sierra Nevada de Santa Marta, Colombia. We used data from six rivers that had > 32 years of complete, continuous monthly streamflow records. This investigation employed spectral analyses to (1) explore temporal characteristics of streamflow variability, (2) estimate the net contribution to the energy spectrum of low-frequency oscillations to streamflow anomalies, and (3) analyze the linkages between streamflow anomalies and large-scale, low-frequency oceanographic/atmospheric processes. Wavelet analyses indicate that the 8–12-yr component exhibited a quasi-stationary state, with a peak of maximum power between 1985 and 2005. These oscillations were nearly in phase in all rivers. Maximum power peaks occurred for the Palomino and Rancheria Rivers in 1985 and 1995, respectively. The wavelet spectrum highlights a change in river variability patterns between 1995 and 2015, characterized by a shift towards the low-frequency oscillations domain (8–12 yr). The net contribution of these oscillations to the energy spectrum was as high as 51 %, a value much larger than previously thought for rivers in northwestern South America. The simultaneous occurrence of hydrologic oscillations, as well as the increase in the amplitude of the 8–12-yr band, defined periods of extremely anomalous wet seasons during 1989–1990, 1998–2002 and 2010–2011, reflecting the role of low-frequency oscillations in modulating streamflow variability in these rivers. Cross Wavelet Transform and Wavelet Coherence revealed high common powers and significant coherences in low-frequency bands (> 96 months) between streamflow anomalies and Atlantic Meridional Oscillation (AMO), Pacific Decadal Oscillation (PDO) and the Tropical North Atlantic Index (TNA). These results show the role of large-scale, low-frequency oceanographic/climate processes in modulating long-term hydrological variability of these rivers.

scholarly journals Contribution of low-frequency climatic–oceanic oscillations to streamflow variability in small, coastal rivers of the Sierra Nevada de Santa Marta (Colombia)

2019 ◽  
Vol 23 (5) ◽  
pp. 2379-2400 ◽  
Author(s):  
Juan Camilo Restrepo ◽  
Aldemar Higgins ◽  
Jaime Escobar ◽  
Silvio Ospino ◽  
Natalia Hoyos
Keyword(s):  
Energy Spectrum ◽  
Sierra Nevada ◽  
Large Scale ◽  
Low Frequency ◽  
Maximum Power ◽  
Simultaneous Occurrence ◽  
Atmospheric Processes ◽  
Low Frequency Oscillations ◽  
Streamflow Variability

Abstract. This study evaluated the influence of low-frequency oscillations, that are linked to large-scale oceanographic–atmospheric processes, on streamflow variability in small tropical coastal mountain rivers of the Sierra Nevada de Santa Marta, Colombia. We used data from six rivers that had > 32 years of complete, continuous monthly streamflow records. This investigation employed spectral analyses to (1) explore temporal characteristics of streamflow variability, (2) estimate the net contribution to the energy spectrum of low-frequency oscillations to streamflow anomalies, and (3) analyze the linkages between streamflow anomalies and large-scale, low-frequency oceanographic–atmospheric processes. Wavelet analyses indicate that the 8–12-year component exhibited a quasi-stationary state, with a peak of maximum power between 1985 and 2005. These oscillations were nearly in phase in all rivers. Maximum power peaks occurred for the Palomino and Rancheria rivers in 1985 and 1995, respectively. The wavelet spectrum highlights a change in river variability patterns between 1995 and 2015, characterized by a shift towards the low-frequency oscillations' domain (8–12 years). The net contribution of these oscillations to the energy spectrum was as high as 51 %, a value much larger than previously thought for rivers in northwestern South America. The simultaneous occurrence of hydrologic oscillations, as well as the increase in the amplitude of the 8–12-year band, defined periods of extremely anomalous wet seasons during 1989–1990, 1998–2002 and 2010–2011, reflecting the role of low-frequency oscillations in modulating streamflow variability in these rivers. Cross-wavelet transform and wavelet coherence revealed high common powers and significant coherences in low-frequency bands (>96 months) between streamflow anomalies and Atlantic Meridional Oscillation (AMO), Pacific Decadal Oscillation (PDO) and the Tropical North Atlantic Index (TNA). These results show the role of large-scale, low-frequency oceanographic–climate processes in modulating the long-term hydrological variability of these rivers.

scholarly journals PORT RESONANCE MITIGATION MODELED INTRODUCING ARJ-R STRUCTURES

2020 ◽  
pp. 38
Author(s):  
Jose A. GONZALEZ-ESCRIVA ◽  
Josep R. MEDINA ◽  
Joaquin M. GARRIDO
Keyword(s):  
Reflection Coefficient ◽  
Physical Model ◽  
Large Scale ◽  
Low Frequency ◽  
Model Tests ◽  
Wave Interference ◽  
Low Frequency Oscillations ◽  
Physical Model Tests ◽  
Similar Cost ◽  
Interference Mechanism

ARJ-R caissons are based on the "long-circuit" concept (Medina et al, 2016) that allows the extension of the destructive wave interference mechanism to mitigate low frequency oscillations without enlarging the width of the caisson. The performance of the ARJ-R caissons is referred to its reflection coefficient (Cr) which was obtained through large-scale physical model tests (Gonzalez-Escriva et al, 2018). In this paper, the effectiveness of Anti-Reflective Jarlan-type structures for Port Resonance mitigation (ARJ-R) has been assessed numerically for the port of Denia (Spain). ARJ-R structures are constructible, with similar dimensions as conventional vertical quay caissons and with a similar cost (15percent more than conventional vertical caisson).Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/LomQEVpvjik

The Role of Low-frequency Neural Oscillations in Speech Processing: Revisiting Delta Entrainment

2019 ◽  
Vol 31 (8) ◽  
pp. 1205-1215 ◽  
Author(s):  
Victor J. Boucher ◽  
Annie C. Gilbert ◽  
Boutheina Jemel
Keyword(s):  
Speech Processing ◽  
Low Frequency ◽  
Phase Coherence ◽  
Theta Oscillations ◽  
Neural Oscillations ◽  
Acoustic Cues ◽  
Low Frequency Oscillations ◽  
Temporal Grouping ◽  
Delta Oscillations

Studies that use measures of cerebro-acoustic coherence have shown that theta oscillations (3–10 Hz) entrain to syllable-size modulations in the energy envelope of speech. This entrainment creates sensory windows in processing acoustic cues. Recent reports submit that delta oscillations (<3 Hz) can be entrained by nonsensory content units like phrases and serve to process meaning—though such views face fundamental problems. Other studies suggest that delta underlies a sensory chunking linked to the processing of sequential attributes of speech sounds. This chunking associated with the “focus of attention” is commonly manifested by the temporal grouping of items in sequence recall. Similar grouping in speech may entrain delta. We investigate this view by examining how low-frequency oscillations entrain to three types of stimuli (tones, nonsense syllables, and utterances) having similar timing, pitch, and energy contours. Entrainment was indexed by “intertrial phase coherence” in the EEGs of 18 listeners. The results show that theta oscillations at central sites entrain to syllable-size elements in speech and tones. However, delta oscillations at frontotemporal sites specifically entrain to temporal groups in both meaningful utterances and meaningless syllables, which indicates that delta may support but does not directly bear on a processing of content. The findings overall suggest that, although theta entrainment relates to a processing of acoustic attributes, delta entrainment links to a sensory chunking that relates to a processing of properties of articulated sounds. The results also show that measures of intertrial phase coherence can be better suited than cerebro-acoustic coherence in revealing delta entrainment.

Depth-integrated equation for hydro-acoustic waves with bottom damping

2015 ◽  
Vol 766 ◽  
Author(s):  
Ali Abdolali ◽  
James T. Kirby ◽  
Giorgio Bellotti
Keyword(s):  
Acoustic Waves ◽  
Large Scale ◽  
Model Equation ◽  
Low Frequency ◽  
3D Models ◽  
Sediment Layer ◽  
Sea Bed ◽  
Weakly Compressible ◽  
Acoustic Wave Generation

AbstractWe present a depth-integrated equation for the mechanics of generation, propagation and dissipation of low-frequency hydro-acoustic waves due to sudden bottom displacement in a weakly compressible ocean overlying a weakly compressible viscous sediment layer. The model is validated against a full 3D computational model. Physical properties of these waves are studied and compared with those for waves over a rigid sea bed, revealing changes in the frequency spectrum and modal peaks. The resulting model equation can be used for numerical prediction in large-scale domains, overcoming the computational difficulties of 3D models while taking into account the role of bottom dissipation on hydro-acoustic wave generation and propagation.

scholarly journals The 2010/2011 snow season in California's Sierra Nevada: Role of atmospheric rivers and modes of large-scale variability

2013 ◽  
Vol 49 (10) ◽  
pp. 6731-6743 ◽  
Author(s):  
Bin Guan ◽  
Noah P. Molotch ◽  
Duane E. Waliser ◽  
Eric J. Fetzer ◽  
Paul J. Neiman
Keyword(s):  
Sierra Nevada ◽  
Large Scale ◽  
Atmospheric Rivers ◽  
Snow Season
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