We study the statistics of wind-driven open ocean currents. Using the Ekman layer model for the integrated currents, we investigate, analytically and numerically, the relation between the wind distribution and its temporal correlations... more
We study the statistics of wind-driven open ocean currents. Using the Ekman layer model for the integrated currents, we investigate, analytically and numerically, the relation between the wind distribution and its temporal correlations and the statistics of the open ocean currents. We find that temporally long-range correlated wind results in currents whose statistics is proportional to the wind-stress statistics. On the other hand, short-range correlated wind leads to Gaussian distributions of the current components, regardless of the stationary distribution of the winds, and therefore, to a Rayleigh distribution of the current amplitude if the wind stress is isotropic. An interesting result is the existence of an optimum in the amplitude of the ocean currents as a function of the correlation time of the wind stress. The results were validated using an oceanic general circulation model.
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Psammophilous plants are special plants that flourish in sand moving environments. There are two main mechanisms by which the wind affects these plants: (i) sand drift exposes roots and covers branches--the exposed roots turn into new... more
Psammophilous plants are special plants that flourish in sand moving environments. There are two main mechanisms by which the wind affects these plants: (i) sand drift exposes roots and covers branches--the exposed roots turn into new plants and the covered branches turn into new roots; both mechanisms result in an enhanced growth rate of the psammophilous plant cover of the dunes; (ii) strong winds, often associated with sand movement, tear branches and seed them in nearby locations, resulting in new plants and an enhanced growth rate of the psammophilous plant cover of the dunes. Despite their important role in dune dynamics, to our knowledge, psammophilous plants have never been incorporated into mathematical models of sand dunes. Here, we attempt to model the effects of these plants on sand dune dynamics. We construct a set of three ordinary differential equations for the fractions of surface cover of regular vegetation, biogenic soil crust and psammophilous plants. The latter r...
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Previous estimates of the surface temperature of Jupiter's moon, Europa, neglected the effect of the eccentricity of Jupiter's orbit around the Sun, the effect of the emissivity and heat capacity of Europa's ice, the effect of... more
Previous estimates of the surface temperature of Jupiter's moon, Europa, neglected the effect of the eccentricity of Jupiter's orbit around the Sun, the effect of the emissivity and heat capacity of Europa's ice, the effect of the eclipse of Europa (i.e., the relative time that Europa is within the shadow of Jupiter), the effect of Jupiter's radiation, and the effect of Europa's internal heating. Here we estimate the diurnal, seasonal and annual mean surface temperature of Europa, when Europa's obliquity, emissivity, heat capacity, eclipse, Jupiter's radiation, internal heating, as well as the eccentricity of Jupiter, are all taken into account. For a typical internal heating rate of 0.05 W m^-2, the equator, pole, and global mean annual mean surface temperatures are 96 K, 48 K, and 90 K, respectively. We found that the temperature at the high latitudes is significantly affected by the internal heating, especially during the winter solstice, suggesting th...
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Previous estimates of the surface temperature of Jupiter's moon, Europa, neglected the effect of the eccentricity of Jupiter's orbit around the Sun, the effect of the emissivity and heat capacity of Europa's ice, the effect of... more
Previous estimates of the surface temperature of Jupiter's moon, Europa, neglected the effect of the eccentricity of Jupiter's orbit around the Sun, the effect of the emissivity and heat capacity of Europa's ice, the effect of the eclipse of Europa (i.e., the relative time that Europa is within the shadow of Jupiter), the effect of Jupiter's radiation, and the effect of Europa's internal heating. Here we estimate the diurnal, seasonal and annual mean surface temperature of Europa, when Europa's obliquity, emissivity, heat capacity, eclipse, Jupiter's radiation, internal heating, as well as the eccentricity of Jupiter, are all taken into account. For a typical internal heating rate of 0.05 W m^-2, the equator, pole, and global mean annual mean surface temperatures are 96 K, 48 K, and 90 K, respectively. We found that the temperature at the high latitudes is significantly affected by the internal heating, especially during the winter solstice, suggesting th...
The multiple equilibria of the thermohaline circulation (THC, used here in the sense of the meridional overturning circulation) as function of the surface freshwater flux has been studied intensively following
We construct directed and weighted climate networks based on near surface air temperature to investigate the global impacts of El Nino and La Nina. We find that regions which are characterized by higher positive or negative network in... more
We construct directed and weighted climate networks based on near surface air temperature to investigate the global impacts of El Nino and La Nina. We find that regions which are characterized by higher positive or negative network in weighted links, are exhibiting stronger correlations with the El Nino basin and are warmer or cooler during El Nino or La Nina periods. These stronger in-weighted activities are found to be concentrated in localized areas, as compared to non-El Nino periods, whereas a large fraction of the globe is not influenced by the events. The regions of localized activity vary from one El Nino (La Nina) event to another; still some El Nino (La Nina) events are more similar to each other. We quantify this similarity using network community structure. The results and methodology reported here may be used to improve the understanding and prediction of El Nino or La Nina events and also may be applied in the investigation of other climate variables.
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We thank Reviewer 1 for her/his thoughtful comments. Reviewer 1 concludes that “In my opinion, the paper is in principle clearly written, regarding methods and results. However, to truly appreciate the added value of this study, I think... more
We thank Reviewer 1 for her/his thoughtful comments. Reviewer 1 concludes that “In my opinion, the paper is in principle clearly written, regarding methods and results. However, to truly appreciate the added value of this study, I think the motivation of the study should be better articulated (including the choice of bays) as well as the wider implications and overall significance of the results.” We are grateful for the reviewer’s comments which helped us to improve the paper. Below is our detailed response.
Numerical modeling of the circulation and mixing processes in the extreme environment of the Dead Sea (DS) is a very challenging task, so progress has been very limited since the development of the first coarse-resolution circulation... more
Numerical modeling of the circulation and mixing processes in the extreme environment of the Dead Sea (DS) is a very challenging task, so progress has been very limited since the development of the first coarse-resolution circulation models of this lake more than three decades ago (Ezer, 1984; Sirkes, 1986). Therefore, the current study, using advanced high-resolution, non-hydrostatic MITgcm, provides new insights
The COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, is spreading rapidly throughout the world, causing many deaths and severe economic damage. It is believed that hot and humid conditions do not favor the novel coronavirus,... more
The COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, is spreading rapidly throughout the world, causing many deaths and severe economic damage. It is believed that hot and humid conditions do not favor the novel coronavirus, yet this is still under debate due to many uncertainties associated with the COVID-19 data. Here we propose surrogate data tests to examine the preference of this virus to spread under different climate conditions. We find, by mainly studying the relative number of COVID-19 deaths, that the disease is significantly (above the 95% confidence level) more common when the temperature is ∼10 °C, the relative humidity is ∼60%, the specific humidity is ∼5 g kg−1, and the ultraviolet radiation is less than ∼50 kJ m−2 (per hour). We also find, but less significantly, that the relative number of COVID-19 deaths is high when the wind is weak and low when the wind is strong. The results are supported based on global and regional data, spanning the time period ...
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A prominent feature of earthquakes is their empirical laws including memory (clustering) in time and space. Several earthquake forecasting models, like the EpidemicType Aftershock Sequence (ETAS) model, were developed based on earthquake... more
A prominent feature of earthquakes is their empirical laws including memory (clustering) in time and space. Several earthquake forecasting models, like the EpidemicType Aftershock Sequence (ETAS) model, were developed based on earthquake empirical laws. Yet, a recent study showed that the ETAS model fails in reproducing significant long-term memory characteristics found in real earthquake catalogs. Here we modify and generalize the ETAS model to include short- and long-term triggering mechanisms, to account for the short- and long-time memory (exponents) recently discovered in the data. Our generalized ETAS model reproduces accurately the short- and long-term/distance memory observed in the Italian and South California earthquake catalogs. The revised ETAS model is also found to significantly improve earthquake forecasting.
The deep (~100 km) ocean of Europa, Jupiter’s moon, covered by a thick icy shell, is one of the most probable places in the solar system to find extraterrestrial life. Yet, its ocean dynamics and its interaction with the ice cover have... more
The deep (~100 km) ocean of Europa, Jupiter’s moon, covered by a thick icy shell, is one of the most probable places in the solar system to find extraterrestrial life. Yet, its ocean dynamics and its interaction with the ice cover have received little attention. Previous studies suggested that Europa’s ocean is turbulent using a global model and taking into account non-hydrostatic effects and the full Coriolis force. Here we add critical elements, including consistent top and bottom heating boundary conditions and the effects of icy shell melting and freezing on ocean salinity. We find weak stratification that is dominated by salinity variations. The ocean exhibits strong transient convection, eddies, and zonal jets. Transient motions organize in Taylor columns parallel to Europa’s axis of rotation, are static inside of the tangent cylinder and propagate equatorward outside the cylinder. The meridional oceanic heat transport is intense enough to result in a nearly uniform ice thickn...
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Abstract We investigate the effect of interannual variability of the wind-stress over the Eastern Mediterranean on Adriatic Deep Water (ADW) formation using an oceanic general circulation model of the Mediterranean Sea driven by monthly... more
Abstract We investigate the effect of interannual variability of the wind-stress over the Eastern Mediterranean on Adriatic Deep Water (ADW) formation using an oceanic general circulation model of the Mediterranean Sea driven by monthly ERA-Interim wind-stress of the years 1979–2014. This is done by using climatological annual cycle of the surface temperature and freshwater flux but interannually varying wind-stress. A connection between the wind-stress magnitude over the Rhodes Gyre region and ADW outflow is found in association with the formation of Levantine Intermediate Water (LIW). 720 years artificially generated wind-stress fields were constructed based on the first 50 Empirical Orthogonal Functions (EOFs) of the wind-stress monthly anomalies. This simulation strengthen the connection that was found and also reveal a centennial internal variability of both the LIW and the ADW outflow. It is also found that the intensity of the Rhodes Gyre is almost linearly related to the wind-stress amplitude. However, the ADW outflow is non-monotonically related to the wind-stress amplitude. There is an optimal wind-stress amplitude for which the ADW formation is maximal. When the wind-stress amplitude is more than 50% the climatological mean wind-stress amplitude, the ADW outflow is weakened. This implies a different balance between the saline LIW and the fresh Atlantic Water, entering the Eastern Mediterranean from Sicily Strait, under stronger than present wind-stress amplitude.
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Oceanic variability and eddy dynamics during snowball Earth events, under a kilometer of ice and driven by a very weak geothermal heat flux, are studied using a high-resolution sector model centered at the equator, where previous studies... more
Oceanic variability and eddy dynamics during snowball Earth events, under a kilometer of ice and driven by a very weak geothermal heat flux, are studied using a high-resolution sector model centered at the equator, where previous studies have shown the ocean circulation to be most prominent. The solution is characterized by an energetic eddy field, equatorward-propagating zonal jets, and a strongly variable equatorial meridional overturning circulation (EMOC), on the order of tens of Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1), restricted to be very close to the equator. The ocean is well mixed vertically by convective mixing, and horizontal mixing rates by currents and eddies are similar to present-day values. There are two main opposite-sign zonal jets near the equator that are not eddy driven, together with multiple secondary eddy-driven jets off the equator. Barotropic stability analyses, the Lorenz energy cycle (LEC), and barotropic-to-baroclinic energy conversion rates together indicate...
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Escribano, C. & Reyes, M., Analysis of functions defined on fractal sets 7 (1999) 197–204 Fleury, V. & Schwartz, L., Diffusion limited aggregation from shear stress as a simple model of vasculogenesis 7 (1999) 33–39 Frame, M. & Lanski, J., When is a recurrent IFS attractor a standard IFS attracto...more
ABSTRACT
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Research Interests: Engineering, Computer Science, Biophysics, Electrophysiology, Medicine, and 15 moreElectrocardiography, Complex System, Humans, Mathematical Sciences, Physical sciences, Heart rate, Heart, Oscillations, Mathematical Model, Time Factors, Statistical Properties, Sudden Cardiac Death, Qualitative Method, Heart Diseases, and Model simulation
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Although the relations between climate and settlement are not straightforward, there is a general agreement that arid conditions are less favorable for human settlement in the semiarid Near East than humid conditions. Here we show that... more
Although the relations between climate and settlement are not straightforward, there is a general agreement that arid conditions are less favorable for human settlement in the semiarid Near East than humid conditions. Here we show that humid conditions resulted in the abandonment of settlements along the Israeli coastal plain. We first present archaeological evidence for a drastic decline in settlement along the Israeli coast during most of the third millennium BC (Early Bronze Age II–III). Then, based on archaeological and climatic evidence, we link this decline to an environmental change occurring at that time. We propose that increased precipitation intensified the already existing drainage problems and resulted in flooding, which led to the transformation of arable land into marshes and to the spread of diseases, gradually causing settlement decline and abandonment.
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We present results of an exact computation of the properties of the development of the wave function in the presence of a potential barrier in a bounded well. We find that the complex behavior of this evolution, associated with tunneling,... more
We present results of an exact computation of the properties of the development of the wave function in the presence of a potential barrier in a bounded well. We find that the complex behavior of this evolution, associated with tunneling, is very similar to that expected from a chaotic dynamical system.