Energy transfer in two-dimensional magnetohydrodynamic turbulence: formalism and numerical results

The basic entity of nonlinear interaction in Navier-Stokes and the Magnetohydrodynamic (MHD) equations is a wavenumber triad ({\bf k,p,q}) satisfying ${\bf k+p+q=0}$. The expression for the combined energy transfer from two of these wavenumbers to the third wavenumber is known. In this paper we introduce the idea of an effective energy transfer between a pair of modes by the mediation of the third mode, and find an expression for it. Then we apply this formalism to compute the energy transfer in the quasi-steady-state of two-dimensional MHD turbulence with large-scale kinetic forcing. The computation of energy fluxes and the energy transfer between different wavenumber shells is done using the data generated by the pseudo-spectral direct numerical simulation. The picture of energy flux that emerges is quite complex---there is a forward cascade of magnetic energy, an inverse cascade of kinetic energy, a flux of energy from the kinetic to the magnetic field, and a reverse flux which transfers the energy back to the kinetic from the magnetic. The energy transfer between different wavenumber shells is also complex---local and nonlocal transfers often possess opposing features, i.e., energy transfer between some wavenumber shells occurs from kinetic to magnetic, and between other wavenumber shells this transfer is reversed. The net transfer of energy is from kinetic to magnetic. The results obtained from the studies of flux and shell-to-shell energy transfer are consistent with each other.Comment: 27 pages REVTEX; 14 ps figure

巨大衝突により生じた周惑星円盤からの天王星の衛星形成

京都大学新制・課程博士博士(理学)甲第23007号理博第4684号新制||理||1672(附属図書館)京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 嶺重 慎, 准教授 前田 啓一, 教授 太田 耕司学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDFA

Calculation of renormalized viscosity and resistivity in magnetohydrodynamic turbulence

A self-consistent renormalization (RG) scheme has been applied to nonhelical magnetohydrodynamic turbulence with normalized cross helicity $\sigma_c =0$ and $\sigma_c \to 1$. Kolmogorov's 5/3 powerlaw is assumed in order to compute the renormalized parameters. It has been shown that the RG fixed point is stable for $d \ge d_c \approx 2.2$. The renormalized viscosity $\nu^*$ and resistivity $\eta^*$ have been calculated, and they are found to be positive for all parameter regimes. For $\sigma_c=0$ and large Alfv\'{e}n ratio (ratio of kinetic and magnetic energies) $r_A$, $\nu^*=0.36$ and $\eta^*=0.85$. As $r_A$ is decreased, $\nu^*$ increases and $\eta^*$ decreases, untill $r_A \approx 0.25$ where both $\nu^*$ and $\eta^*$ are approximately zero. For large $d$, both $\nu^*$ and $\eta^*$ vary as $d^{-1/2}$. The renormalized parameters for the case $\sigma_c \to 1$ are also reported.Comment: 19 pages REVTEX, 3 ps files (Phys. Plasmas, v8, 3945, 2001

Panel 3 Paper 3.2: Nature, agriculture and rural resilience: Interdependencies between natural protected areas and rural landscapes in Satoyama/Satoumi in Japan

The Capacity Building Workshops on Nature-Culture Linkages in Heritage Conservation (CBWNCL), held at the University of Tsukuba in Japan, gather Asia-Pacific heritage professionals with the aim of creating a platform of mutual-learning and exchange between the culture and nature sectors. In the first workshop on Agricultural Landscapes, from 14 case studies, 5 showed natural protected areas in tense relations with their rural landscape surroundings. However, these agricultural landscapes are essential for protecting natural values, as they form part of their larger ecosystems. In the second workshop on Sacred Landscapes, from 16 case studies, 5 case studies were also agricultural landscapes, and 8 case studies featured natural protected areas which embody spiritual values for their surrounding rural communities. In the third workshop on Disasters and Resilience, from 15 case studies, 7 presented the struggles faced by rural communities in the conservation of their natural environment and their cultural practices in a context of increasing disasters. By looking at the Japanese experience, we learned from the concepts of Satoyama and Satoumi, that the protection of nature can be interlinked with the maintenance of agricultural landscapes, that the continuity of spiritual practices is essential for identity and community cohesion, and that the maintenance of cultural practices represent community’s strength for post-disaster recovery. These lessons demonstrated that resilience lies in people and their community networks -beyond human, and underpinned on their natural and cultural heritage (both tangible and intangible)-, and that the stronger these networks are, and the more autonomy and decision-making power is recognized at local level, the higher level of resilience a landscape would show. This finding, however, raises concern, as these landscapes are facing pressures not only from urban development, but mostly from depopulation due to migration and ageing communities, processes that are eroding these networks and consequently, rural landscape resilience