Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm51a1278c&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SM51A-1278
Physics
7829 Kinetic Waves And Instabilities, 7839 Nonlinear Phenomena (4400, 6944), 7863 Turbulence (4490), 7868 Wave/Wave Interactions
Scientific paper
Ultralow frequency compressional magnetic turbulence has been observed in the Earth's magnetosphere for decades. Many linear theories have been proposed to describe these observations, such as Drift-Mirror modes, compressional trapped particle modes, and drift compressional modes; however, there are no ``self-consistent'' nonlinear theories. The observed fluctuation levels δ B|/B are on the order of 10% and the nonlinear frequency derived from the turbulence induced drift velocity is on the order of the linear frequency. Therefore, nonlinear effects must be important. Starting from the nonlinear gyrokinetic equations of Frieman and Chen (1982) the perturbed magnetic compressional component may be systematically isolated from both the electrostatic component and the shear Alfvén component assuming a cold electron population and a mode frequency less than the parallel Alfvén frequency. Using a pressure closure scheme consistent with the linear limit, a nonlinear single-field equation similar to the Charney-Hasegawa-Mima equation (describing both geostrophic flow and electrostatic drift waves) can be derived. In the absence of growth or dissipation this equation conserves magnetic energy and enstrophy (``current density''). The nonlinear interactions spectrally redistribute the energy and enstrophy through a dual cascade process in wavenumber space. Numerical simulations of the single-field nonlinear equation will also be discussed.
Chen Leon L.
Crabtree Chris
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