The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
N. Nakajima - One of the best experts on this subject based on the ideXlab platform.
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excitation of macromagnetohydrodynamic mode due to multiScale Interaction in a quasi steady equilibrium formed by a balance between microturbulence and zonal flow
Physics of Plasmas, 2007Co-Authors: A Ishizawa, N. NakajimaAbstract:This is the first numerical simulation demonstrating that a macromagnetohydrodynamic (macro-MHD) mode is excited as a result of multi-Scale Interaction in a quasi-steady equilibrium formed by a balance between microturbulence and zonal flow based on a reduced two-fluid model. This simulation of a macro-MHD mode, a double tearing mode, is accomplished in a reversed shear equilibrium that includes zonal flow and turbulence due to kinetic ballooning modes. In the quasi-steady equilibrium, a macroScale fluctuation that has the same helicity as the double tearing mode is a part of the turbulence. After a certain period of time, the macro-MHD mode begins to grow. It effectively utilizes free energy of the equilibrium current density gradient and is destabilized by a positive feedback loop between zonal flow suppression and magnetic island growth. Thus, once the macro-MHD appears from the quasi-equilibrium, it continues to grow steadily. This simulation is more comparable with experimental observations of growin...
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excitation of macromagnetohydrodynamic mode due to multiScale Interaction in a quasi steady equilibrium formed by a balance between microturbulence and zonal flow
Physics of Plasmas, 2007Co-Authors: A Ishizawa, N. NakajimaAbstract:This is the first numerical simulation demonstrating that a macromagnetohydrodynamic (macro-MHD) mode is excited as a result of multi-Scale Interaction in a quasi-steady equilibrium formed by a balance between microturbulence and zonal flow based on a reduced two-fluid model. This simulation of a macro-MHD mode, a double tearing mode, is accomplished in a reversed shear equilibrium that includes zonal flow and turbulence due to kinetic ballooning modes. In the quasi-steady equilibrium, a macroScale fluctuation that has the same helicity as the double tearing mode is a part of the turbulence. After a certain period of time, the macro-MHD mode begins to grow. It effectively utilizes free energy of the equilibrium current density gradient and is destabilized by a positive feedback loop between zonal flow suppression and magnetic island growth. Thus, once the macro-MHD appears from the quasi-equilibrium, it continues to grow steadily. This simulation is more comparable with experimental observations of growing macro-MHD activity than earlier MHD simulations starting from linear macroinstabilities in a static equilibrium.
A Ishizawa - One of the best experts on this subject based on the ideXlab platform.
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excitation of macromagnetohydrodynamic mode due to multiScale Interaction in a quasi steady equilibrium formed by a balance between microturbulence and zonal flow
Physics of Plasmas, 2007Co-Authors: A Ishizawa, N. NakajimaAbstract:This is the first numerical simulation demonstrating that a macromagnetohydrodynamic (macro-MHD) mode is excited as a result of multi-Scale Interaction in a quasi-steady equilibrium formed by a balance between microturbulence and zonal flow based on a reduced two-fluid model. This simulation of a macro-MHD mode, a double tearing mode, is accomplished in a reversed shear equilibrium that includes zonal flow and turbulence due to kinetic ballooning modes. In the quasi-steady equilibrium, a macroScale fluctuation that has the same helicity as the double tearing mode is a part of the turbulence. After a certain period of time, the macro-MHD mode begins to grow. It effectively utilizes free energy of the equilibrium current density gradient and is destabilized by a positive feedback loop between zonal flow suppression and magnetic island growth. Thus, once the macro-MHD appears from the quasi-equilibrium, it continues to grow steadily. This simulation is more comparable with experimental observations of growin...
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excitation of macromagnetohydrodynamic mode due to multiScale Interaction in a quasi steady equilibrium formed by a balance between microturbulence and zonal flow
Physics of Plasmas, 2007Co-Authors: A Ishizawa, N. NakajimaAbstract:This is the first numerical simulation demonstrating that a macromagnetohydrodynamic (macro-MHD) mode is excited as a result of multi-Scale Interaction in a quasi-steady equilibrium formed by a balance between microturbulence and zonal flow based on a reduced two-fluid model. This simulation of a macro-MHD mode, a double tearing mode, is accomplished in a reversed shear equilibrium that includes zonal flow and turbulence due to kinetic ballooning modes. In the quasi-steady equilibrium, a macroScale fluctuation that has the same helicity as the double tearing mode is a part of the turbulence. After a certain period of time, the macro-MHD mode begins to grow. It effectively utilizes free energy of the equilibrium current density gradient and is destabilized by a positive feedback loop between zonal flow suppression and magnetic island growth. Thus, once the macro-MHD appears from the quasi-equilibrium, it continues to grow steadily. This simulation is more comparable with experimental observations of growing macro-MHD activity than earlier MHD simulations starting from linear macroinstabilities in a static equilibrium.
Garry D Peterson - One of the best experts on this subject based on the ideXlab platform.
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connecting social networks with ecosystem services for watershed governance a social ecological network perspective highlights the critical role of bridging organizations
Ecology and Society, 2012Co-Authors: Kaitlyn Rathwell, Garry D PetersonAbstract:In many densely settled agricultural watersheds, water quality is a point of conflict between amenity and agricultural activities because of the varied demands and impacts on shared water resources. Successful governance of these watersheds requires coordination among different activities. Recent research has highlighted the role that social networks between management entities can play to facilitate cross-Scale Interaction in watershed governance. For example, bridging organizations can be positioned in social networks to bridge local initiatives done by single municipalities across whole watersheds. To better understand the role of social networks in social-ecological system dynamics, we combine a social network analysis of the water quality management networks held by local governments with a social-ecological analysis of variation in water management and ecosystem services across the Monteregie, an agricultural landscape near Montreal, Quebec, Canada. We analyze municipal water management networks by using one-mode networks to represent direct collaboration between municipalities, and two- mode networks to capture how bridging organizations indirectly connect municipalities. We find that municipalities do not collaborate directly with one another but instead are connected via bridging organizations that span the water quality management network. We also discovered that more connected municipalities engaged in more water management activities. However, bridging organizations preferentially connected with municipalities that used more tourism related ecosystem services rather than those that used more agricultural ecosystem services. Many agricultural municipalities were relatively isolated, despite being the main producers of water quality problems. In combination, these findings suggest that further strengthening the water management network in the Monteregie will contribute to improving water quality in the region. However, such strengthening requires developing a network that better connects both agricultural and tourism oriented municipalities. Furthermore, these findings show that consideration of the social-ecological context of social networks, can help explain the structure of networks and reveal social-ecological clusters and disconnects in a network.
L Bardoczi - One of the best experts on this subject based on the ideXlab platform.
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impact of neoclassical tearing mode turbulence multi Scale Interaction in global confinement degradation and magnetic island stability
Physics of Plasmas, 2017Co-Authors: L Bardoczi, T A Carter, R J La Haye, T L Rhodes, G R MckeeAbstract:Recent measurements of turbulent density ( n) and electron-temperature ( Te) fluctuations have reported turbulence modifications by Neoclassical Tearing Mode (NTM) islands: turbulence decreases (increases) inside (outside) the island region when the island width (W) exceeds a threshold (WT), in qualitative agreement with gyrokinetic simulations. As the cross-field transport in tokamaks is dominantly driven by turbulence, these observations call into question the conventional understanding of confinement degradation by NTMs and magnetic island stability physics. The experimental data presented here support the following points: (i) When profiles flatten at the O-point and gradients increase outside of the island, n decreases (increases) inside (outside) the island. Along with the parallel transport resulting in increased fluxes inside the island, the increase of n outside of the island offers an explanation for the temporal increase of fluxes in that region. As the plasma stored energy (WMHD) gradually...
Bin Wang - One of the best experts on this subject based on the ideXlab platform.
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impacts of upScale heat and momentum transfer by moist kelvin waves on the madden julian oscillation a theoretical model study
Climate Dynamics, 2013Co-Authors: Fei Liu, Bin WangAbstract:The Madden–Julian oscillation (MJO) is observed to interact with moist Kelvin waves. To understand the role of this Interaction, a simple Scale-Interaction model is built, which describes the MJO modulation of moist Kelvin waves and the feedback from moist Kelvin waves through upScale eddy heat and momentum transfer. The backward-tilted moist Kelvin waves produce eddy momentum transfer (EMT) characterized by the lower-tropospheric westerly winds and eddy heat transfer (EHT) that warms the mid-troposphere. The EHT tends to induce the lower-tropospheric easterly winds and low pressure, which is located in front of the “westerly wind burst” induced by the EMT. Adding the eddy forcing to a neutral MJO skeleton model, we show that the EHT provides an instability source for the MJO by warming up the mid-troposphere, and the EMT offers an additional instability source by enhancing the lower-tropospheric westerly winds. The eddy forcing selects eastward propagation for the unstable mode, because it generates positive/negative eddy available potential energy for the eastward/westward modes by changing their thermal and dynamical structures. The present results show that moist Kelvin waves can provide a positive feedback to the MJO only when they are located within (or near) the convective complex (center) of the MJO. The EHT and EMT feedback works positively in the front and rear part of the MJO, respectively. These theoretical results suggest the potential importance of moist Kelvin waves in sustaining the MJO and encourage further observations to document the relationship between moist Kelvin waves and the MJO.
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A Model for the Interaction between 2-Day Waves and Moist Kelvin Waves*
Journal of the Atmospheric Sciences, 2012Co-Authors: Fei Liu, Bin WangAbstract:The eastward-propagating tropical low-frequency disturbances, such as the moist Kelvin waves or the Madden‐Julian oscillation (MJO), are often observed to experience convective enhancement when meeting with the westward-propagating 2-day waves. A Scale Interaction (SI) model is built to understand the nature of the Interaction between the 2-day waves and moist Kelvin waves or MJO. In this model, the convective complex of moist Kelvin waves modulates the strength and location of the 2-day waves, which feed back through the upScale eddy transfer. An ageostrophic model describing the 2-day waves is first solved, and the resultant westward-propagating, backward-tilted disturbances are consistent with the observed 2-day waves. An explicit representation of eddy momentum transfer (EMT), eddy heating transfer (EHT), and eddy moisture transfer (EQT) arising from the 2-day waves is then formulated. The SI model shows that the 2-day waves in front of moist Kelvin waves produce an EMT accelerating the low-frequency easterly in the lower troposphere, an EHT cooling down the middle troposphere, and an EQT moistening the middle troposphere. These three transfer terms have comparable magnitude. Although the negative EHT tends to damp the moist Kelvin waves, both the EMT and EQT provide instability sources for the moist Kelvin waves. The 2-day waves also slow down the moist Kelvin waves, mainly through the advective effects of the EMT. So the unstable moist Kelvin waves may exhibit convective enhancement when meeting with the 2-day waves. The theoretical results presented here point to the need to further observe the multiScale structures within the moist Kelvin waves and the MJO.
