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J Shukla - One of the best experts on this subject based on the ideXlab platform.
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modeling the effects of vegetation on mediterranean climate during the roman Classical Period part ii model simulation
Global and Planetary Change, 2000Co-Authors: Oreste Reale, J ShuklaAbstract:Abstract The purpose of this study is to perform a high-resolution general circulation model (GCM) experiment to quantify the sensitivity of regional climate to change in vegetation around the Mediterranean basin, corresponding to vegetation change during the Roman Classical Period (RCP), about 2000 years BP. First, an RCP vegetation distribution based on fossil pollen maps and historical records was defined. Second, the RCP vegetation inferred from palynology and other proxies was converted to the 12 vegetation types required by the biosphere model implemented in the GCM. The albedo change due to the change in vegetation significantly alters the atmospheric circulation over northern Africa and the Mediterranean. The consequences of this change involve a northward shift of the ITCZ in the African continent and a coupled circulation between northwestern Africa and the Mediterranean Sea. A large increase of precipitation occurs over the Sahel, the Nile valley and northwestern Africa. A smaller increase of precipitation occurs also over the Iberian Peninsula and the region corresponding to the south of the Caucasus range (Armenia). The increase of precipitation over northern Africa, the Iberian Peninsula and the Armenian region are consistent with the pollen, historical and geographical data. These results suggest that deforestation around the Mediterranean during the last 2000 years contributed to the dryness of the current climate.
Oreste Reale - One of the best experts on this subject based on the ideXlab platform.
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modeling the effects of vegetation on mediterranean climate during the roman Classical Period part ii model simulation
Global and Planetary Change, 2000Co-Authors: Oreste Reale, J ShuklaAbstract:Abstract The purpose of this study is to perform a high-resolution general circulation model (GCM) experiment to quantify the sensitivity of regional climate to change in vegetation around the Mediterranean basin, corresponding to vegetation change during the Roman Classical Period (RCP), about 2000 years BP. First, an RCP vegetation distribution based on fossil pollen maps and historical records was defined. Second, the RCP vegetation inferred from palynology and other proxies was converted to the 12 vegetation types required by the biosphere model implemented in the GCM. The albedo change due to the change in vegetation significantly alters the atmospheric circulation over northern Africa and the Mediterranean. The consequences of this change involve a northward shift of the ITCZ in the African continent and a coupled circulation between northwestern Africa and the Mediterranean Sea. A large increase of precipitation occurs over the Sahel, the Nile valley and northwestern Africa. A smaller increase of precipitation occurs also over the Iberian Peninsula and the region corresponding to the south of the Caucasus range (Armenia). The increase of precipitation over northern Africa, the Iberian Peninsula and the Armenian region are consistent with the pollen, historical and geographical data. These results suggest that deforestation around the Mediterranean during the last 2000 years contributed to the dryness of the current climate.
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modeling the effects of vegetation on mediterranean climate during the roman Classical Period part i climate history and model sensitivity
Grid and Pervasive Computing, 2000Co-Authors: Oreste Reale, Paul A DirmeyerAbstract:Abstract This is the first of a two-part study to construct a vegetation map around the Mediterranean Sea that is an accurate representation of conditions two millennia ago, and to use this data in general circulation model experiments to better understand historical climate and climate change. Particularly, we want to evaluate the sensitivity of the atmospheric circulation around the Mediterranean Sea to changed land surface conditions. The idea that 2000 years BP, during the Roman Classical Period (RCP), northern Africa and the Mediterranean countries were moister than today is widely acknowledged but has not been discussed within a scientific framework until a few decades ago. Archeological and historical documents provide some qualitative agreement that moister conditions prevailed during Roman times, and interdisciplinary scientific research provides some confidence through proxies that the Mediterranean has been experiencing a trend towards drier conditions. The first step of this work is the multidisciplinary task of organizing all the available information coming from historical and archeological sources, together with what is known from scientific methods, into a coherent history of climate and vegetation. The second step is to run a 25-year general circulation model (GCM) experiment, with a forcing that represents an idealized RCP vegetation distribution. The forcing produces a noticeable effect on the climate, namely a northward shift of the intertropical convergence zone during summer over the African continent.
J Kengne - One of the best experts on this subject based on the ideXlab platform.
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Dynamical analysis of a simple autonomous jerk system with multiple attractors
Nonlinear Dynamics, 2016Co-Authors: J Kengne, Z. T. Njitacke, H. B. FotsinAbstract:In recent years, tremendous research efforts have been devoted to simple chaotic oscillators based on jerk equation that involves a third-time derivative of a single variable. In the present paper, we perform a systematic analysis of a simple autonomous jerk system with cubic nonlinearity. The system is a linear transformation of Model MO5 first introduced in Sprott (Elegant chaos: algebraically simple flow. World Scientific Publishing, Singapore, 2010 ) prior to the more detailed study by Louodop et al. (Nonlinear Dyn 78:597–607, 2014 ). The basic dynamical properties of the model are investigated including equilibria and stability, phase portraits, frequency spectra, bifurcation diagrams, and Lyapunov exponent plots. It is shown that the onset of chaos is achieved via the Classical Period-doubling and symmetry-restoring crisis scenarios. One of the key contributions of this work is the finding of a window in the parameter space in which the jerk system experiences the unusual and striking feature of multiple attractors (e.g. coexistence of four disconnected Periodic and chaotic attractors). Basins of attraction of various coexisting attractors are computed showing complex basin boundaries. Among the very few cases of lower-dimensional systems (e.g. Newton–Leipnik system) capable of displaying such type of behaviour reported to date, the jerk system with cubic nonlinearity considered in this work represents the simplest and the most ‘elegant’ prototype. An appropriate electronic circuit describing the jerk system is designed and used for the investigations. Results of theoretical analyses are perfectly traced by laboratory experimental measurements.
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Periodicity chaos and multiple attractors in a memristor based shinriki s circuit
Chaos, 2015Co-Authors: J Kengne, Njitacke Z Tabekoueng, Kamdoum V Tamba, Nguomkam A NegouAbstract:In this contribution, a novel memristor-based oscillator, obtained from Shinriki's circuit by substituting the nonlinear positive conductance with a first order memristive diode bridge, is introduced. The model is described by a continuous time four-dimensional autonomous system with smooth nonlinearities. The basic dynamical properties of the system are investigated including equilibria and stability, phase portraits, frequency spectra, bifurcation diagrams, and Lyapunov exponents' spectrum. It is found that in addition to the Classical Period-doubling and symmetry restoring crisis scenarios reported in the original circuit, the memristor-based oscillator experiences the unusual and striking feature of multiple attractors (i.e., coexistence of a pair of asymmetric Periodic attractors with a pair of asymmetric chaotic ones) over a broad range of circuit parameters. Results of theoretical analyses are verified by laboratory experimental measurements.
Gerard J M Versteegh - One of the best experts on this subject based on the ideXlab platform.
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short term climate variability during roman Classical Period in the eastern mediterranean
Quaternary Science Reviews, 2011Co-Authors: Liang Chen, Karin A F Zonneveld, Gerard J M VersteeghAbstract:Abstract To obtain insight into character and potential forcing of short-term climatic and oceanographic variability in the southern Italian region during the “Roman Classical Period” (60 BC–AD 200), climatic and environmental reconstructions based on a dinoflagelate cyst record from a well dated site in the Gulf of Taranto located at the distal end of the Po-river discharge plume have been established with high temporal resolution. Short-term fluctuations in accumulation rates of the Adriatic Surface Water species Lingulodinium machaerophorum, the freshwater algae Concentricystes and species resistant to aerobic degradation indicate that fluctuations in the trophic state of the upper waters are related to river discharge of northern and eastern Italian rivers which in turn are strongly related to precipitation in Italy. The dinoflagellate cyst association indicates that local sea surface temperatures which in this region are strongly linked to local air temperatures were slightly higher than today. We reconstruct that sea surface temperatures have been relatively high and stable between 60 BC–AD 90 and show a decreasing trend after AD 90. Fluctuations in temperature and river discharge rates have a strong cyclic character with main cyclicities of 7–8 and 11 years. We argue that these cycles are related to variations of the North Atlantic Oscillation climate mode. A strong correlation is observed with global variation in Δ14C anomalies suggesting that solar variability might be one of the major forcings of the regional climate. Apart from cyclic climate variability we observed a good correlation between non-cyclic temperature drops and global volcanic activity indicating that the latter forms an additional major forcing factor of the southern Italian climate during the Roman Classical Period.
Farhan Saif - One of the best experts on this subject based on the ideXlab platform.
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Atom optics quantum pendulum
Journal of Russian Laser Research, 2009Co-Authors: Muhammad Ayub, Khalid Naseer, Manzoor Ali, Farhan SaifAbstract:We explain the dynamics of cold atoms, initially trapped and cooled in a magneto-optic trap, in a monochromatic stationary standing electromagnetic wave field. In the large-detuning limit, the system is modeled as a nonlinear quantum pendulum. We show that the wavepacket evolution of the quantum particle probes parametric regimes in the quantum pendulum that support the Classical Period and quantum-mechanical revival and superrevival phenomena. Interestingly, complete reconstruction, in particular the parametric regime at quantum revival times, is independent of the potential height.
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Atom optics quantum pendulum
Journal of Russian Laser Research, 2009Co-Authors: Muhammad Ayub, Khalid Naseer, Manzoor Ali, Farhan SaifAbstract:We explain the dynamics of cold atoms, initially trapped and cooled in a magneto-optic trap, in a monochromatic stationary standing electromagnetic wave field. In the large detuning limit the system is modeled as a nonlinear quantum pendulum. We show that wave packet evolution of the quantum particle probes parametric regimes in the quantum pendulum which support Classical Period, quantum mechanical revival and super revival phenomena. Interestingly, complete reconstruction in particular parametric regime at quantum revival times is independent of potential height.