SM21C-01 08:00h

Nonlinear Evolution of Kelvin-Helmholtz Instability in MHD Plasma

Lai, S (lucky@jupiter.ss.ncu.edu.tw) , National Central University, Institute of Space Science, National Central University , Chung-Lu, 320-01 Taiwan
* Lyu, L (lyu@jupiter.ss.ncu.edu.tw) , National Central University, Institute of Space Science, National Central University , Chung-Lu, 320-01 Taiwan

Kelvin-Helmholtz (K-H) instabilities at a magnetohydrodynamic (MHD) tangential discontinuity (TD) are studied by means of two-dimensional MHD simulation. Our simulation results indicate that nonlinear evolution of MHD surface wave at TD depends on the fast-mode Mach numbers of the surface wave on two sides of the TD. When the fast-mode Mach numbers of the surface wave on both sides of the TD are less than 1, K-H instability can grow into vortices or kink-type surface wave, depending on the orientation of the ambient magnetic field. When the fast-mode Mach number on either side of the TD is greater than 1, nonlinear fast-mode plane waves are developed from the ridges on the surface wave. A theoretical model based on magnetosonic-cone formation is proposed to explain the formation of these nonlinear plane waves in high-Mach-number K-H instability. Mach angle of magnetosonic cone is derived as a function of Mach number, orientation of ambient magnetic field, and plasma beta of the background medium. Flaring angles of these nonlinear plane waves obtained in our simulations are in good agreement with the Mach angles predicted by our theoretical model. Nonlinear evolution of K-H instability generated by a fast jet flow after magnetic reconnection will also be presented. Application of our results to magnetopause and nonlinear waves in magnetosheath and magnetosphere will be discussed.

SM21C-02 08:15h

Mirror Mode Waves in the Jovian Magnetosheath

* Joy, S P (sjoy@igpp.ucla.edu) , University of California, Los Angeles Institute of Geophysics and Planetary Physics, 405 Hilgard Ave, Los Angeles, CA 90095-1567 United States
* Joy, S P (sjoy@igpp.ucla.edu) , University of California, Los Angeles Dept. of Earth and Space Sciences, 405 Hilgard Ave, Los Angeles, CA 90095-2567 United States
Kivelson, M G (mkivelson@igpp.ucla.edu) , University of California, Los Angeles Institute of Geophysics and Planetary Physics, 405 Hilgard Ave, Los Angeles, CA 90095-1567 United States
Kivelson, M G (mkivelson@igpp.ucla.edu) , University of California, Los Angeles Dept. of Earth and Space Sciences, 405 Hilgard Ave, Los Angeles, CA 90095-2567 United States
Paterson, W (william.paterson@uiowa.edu) , Hampton Univ, Center Atmospheric Sciences, Hampton, VA 23668
Schwarzl, H (hannes@igpp.ucla.edu) , University of California, Los Angeles Institute of Geophysics and Planetary Physics, 405 Hilgard Ave, Los Angeles, CA 90095-1567 United States
Vo, S (svo@igpp.ucla.edu) , University of California, Los Angeles Institute of Geophysics and Planetary Physics, 405 Hilgard Ave, Los Angeles, CA 90095-1567 United States

Mirror modes waves are commonly observed in planetary magnetosheaths, cometary sheaths, and other plasmas with anisotropic pressure distributions. In this paper we present results derived from observations from many spacecraft that have sampled the Jovian magnetosheath over a wide range of radial distances and local times (Pioneer 10 & 11, Voyager 1 & 2, Ulysses, and Galileo). Several magnetic field signatures are associated with mirror mode waves at Jupiter. The are {\it spikes} where the field strength is briefly elevated above a slowly varying background level, {\it dips} where the opposite occurs, and {\it other} mirror mode waves where there is no clearly defined background field in the wave region. Here we report on the radial distance, local time, and spatial scale size distributions of each of these three magnetic structures. We examine the plasma parameters (Beta, number density, temperature, velocity) associated with each of these magnetic waveforms. We examine the relationship between the properties of the ambient plasma and the presence of waves and their structure.

SM21C-03 08:30h

ULF waves in the solar wind, their coupling to the magnetosphere and associated higher-frequency pulsations.

* Lessard, M R (marc.lessard@dartmouth.edu) , University of New Hampshire, Space Science Center Morse Hall, Durham, NH 03824 United States
Arnoldy, R L (roger.arnoldy@unh.edu) , University of New Hampshire, Space Science Center Morse Hall, Durham, NH 03824 United States
Thomson, D (djt@mast.queensu.cca) , Queens University, 252 Albert St., Kingston, ON K7L 3V5 Canada
Engebretson, M (engebret@augsburg.edu) , Augsburg College, 2211 Riverside Avenue, Minneapolis, MN 55454 United States

Recent work has shown the existence at geosynchronous orbit of wave power at frequencies substantially below that of fundamental field-line resonances. The existence of spectral power below that of fundamental frequencies indicates that the driver must be external to the magnetosphere, i.e, that the source is contained in the solar wind. Other work has shown that frequencies matching field-line resonances can sometimes also be observed in the solar wind. The combined spectrum that includes power at fundamental frequencies and lower maps precisely to {\it p}-mode helioseismic spectra and the question has been raised whether these helioseismic modes may stimulate the magnetospheric fluctuations. Coherences have been calculated between the magnetometers on {ACE} and Ulysses (in the solar wind) and {GOES-10} (within the magnetosphere), and show several frequencies where nine coherences are significant. This presentation reviews previous work regarding possible coupling of helioseismic modes to the magnetosphere and provides new results to support the conjecture. In addition, we revisit the interesting higher frequency signatures (10-15 mHz), associated with at least one of these events, observed in space and on the ground. These higher-frequency waves are observed as bursts of pulsations, occurring simultaneously over an extended region in local time, but having different polarizations and frequencies at each station.

SM21C-04 08:45h

A Statistical Survey of the ULF Spectrum and Wave Characteristics Observed by the Polar and ISEE Satellites

* Chi, P J (pchi@igpp.ucla.edu) , UCLA, Institute of Geophysics and Planetary Physics, Box 951567, Los Angeles, CA 90095-1567 United States
Russell, C T (ctrussell@igpp.ucla.edu) , UCLA, Institute of Geophysics and Planetary Physics, Box 951567, Los Angeles, CA 90095-1567 United States

In this study we analyze the statistical properties of the wave spectrum in the Ultra-low-frequency (ULF) band by using the magnetometer data collected by Polar and ISEE satellites. The combined dataset consists of more than 25 years of observations covering a large portion of the magnetosphere, and therefore they provide the empirical knowledge of ULF wave characteristics as well as their spatial and temporal variations. In order to conduct the statistical analysis, two useful databases of the ULF waves are generated: (1) the spectral density in the ULF band, and (2) a catalog of the ULF wave events selected by applying a statistical criterion on the wave spectrum obtained in (1). Wavelet analysis is used in producing the two databases because of its computational efficiency. The catalog of ULF waves consists of the events whose waves are more monochromatic, and it is useful for identifying the occurrence of different types of ULF waves as well as understanding their generation mechanisms. Initial results show that the compressional Pc~3 waves occur more often in the subsolar region of the magnetosphere, consistent with the model of which the upstream waves being the source, whereas some compressional Pc~5 waves are found at high-latitude regions, possibly associated with the surface waves on the magnetospheric boundary. For the transverse component of the Pc~3-5 waves, the wave frequency decreases statistically with the $L$-value, in agreement with with the field line resonance effects. The wave catalog can also facilitate the selection of interesting events for in-depth studies. On the other hand, the wave spectrum database provides a useful input to the research of particle energization in the radiation belt, for which a simplified formula for the ULF spectrum is broadly assumed because of the limitations in observations. Our study also attempts to define a standard of fast generation of ULF wave databases so that similar computer algorithms can be applied to the electromagnetic field data acquired by future satellite missions.

SM21C-05 09:00h

Investigation of the origin and characteristics of {ULF} waves driven by the solar wind

* Elkington, S R (scot.elkington@lasp.colorado.edu) , LASP, University of Colorado, 1234 Innovation Drive, Boulder, CO 80303 United States
Wiltberger, M J (wiltbemj@ucar.edu) , HAO/NCAR, 4985 Twin Lakes Rd, Boulder, CO 80301 United States
Chan, A A (aac@rice.edu) , Rice University Dept Physics & Astronomy, POB 1892, Houston, TX 77251
Baker, D N (Daniel.Baker@lasp.colorado.edu) , LASP, University of Colorado, 1234 Innovation Drive, Boulder, CO 80303 United States
Fei, Y (yfei@rice.edu) , Rice University Dept Physics & Astronomy, POB 1892, Houston, TX 77251

ULF waves, with frequencies in the mHz range, are known to efficiently energize and transport relativistic electrons through resonant interactions leading to radial diffusion. However, the global structure, occurrence, and characteristics of the ULF waves are not well known. ULF waves may result from internal geomagnetic processes, such as excitation by ring current ions, or they may result as a consequence of the external interactions between the solar wind and the geomagnetic field. In the latter category, possible sources of ULF wave energy include (i) impulsive variations resulting from changes in the solar wind dynamic pressure; (ii) shear interactions occurring at the magnetopause; and (iii) dynamic variations in the IMF-$B_z$ which lead to changes in the global convection electric field. In this work, we use the Lyon-Fedder-Mobarry MHD code to investigate the nature of magnetospheric ULF waves driven by these three interactions, under controlled, idealized solar wind conditions. In each case, the spatial and temporal characteristics of the waves will be investigated, including the radial penetration, spectral profile, and azimuthal mode structure of the waves.

SM21C-06 09:15h

Magnetospheric Waveguide Modes: Coupling to Cavity Modes and Responses to Changes in the Global Magnetospheric Configuration

* McWilliams, K A (kathryn.mcwilliams@usask.ca) , Dept. of Physics & Engineering Physics, University of Saskatchewan, 116 Science Place, Saskatoon, SK S7N 5E2 Canada
Yeoman, T K (yxo@ion.le.ac.uk) , Dept of Physics & Astronomy, University of Leicester, University Road, Leicester, LE1 7RH United Kingdom
Sibeck, D G (david.sibeck@gsfc.nasa.gov) , NASA/GSFC, Code 696, Greenbelt, MD 20771 United States

A sequence of observations from a variety of instruments measured a ten-minute wave, along with related harmonics, in the solar wind, at the magnetopause, inside the magnetosphere, and from the ground. The location and temporal ordering of the wave phenomena reveal information about the causal relationships of the wave excitation and the development of harmonics for this interval. Coupling of a waveguide mode to a compressional, or cavity, mode was observed. Global changes in the magnetospheric configuration lead to changes in the frequency response observed at several locations in the magnetosphere and the ionosphere, such that the observed frequencies remained the same, but the dominant harmonics changed.

SM21C-07 09:30h

Nonlinear Electron Heating and Pedersen Conductivity Enhancements in the Evolution of Dispersive Field Line Resonances

* Rankin, R (rankin@phys.ualberta.ca) , University of Alberta, Department of Physics, University of Alberta, Edmonton, AB T6G 2J1 Canada
Lu, J (jlu@space.ualberta.ca) , University of Alberta, Department of Physics, University of Alberta, Edmonton, AB T6G 2J1 Canada
Marchand, R , University of Alberta, Department of Physics, University of Alberta, Edmonton, AB T6G 2J1 Canada
Kabin, K , University of Alberta, Department of Physics, University of Alberta, Edmonton, AB T6G 2J1 Canada
Tikhonchuk, V , Universite Bordeaux 1, Centre Lasers Intenses et Applications, 33405 Talence Cedex, Bordeaux, 33405 France

We examine the effect of ionospheric electron heating by resonant standing shear Alfven waves in Earth's magnetosphere. It is demonstrated that for realistic parameters of dispersive field line resonances, heated electrons cause ionization that changes the Pedersen conductivity of the ionosphere by a large factor. We show that this leads to a strong feedback effect on the FLR amplitude and resulting dynamics. Our simulations using a 2D finite element code indicate that the primary mechanisms responsible for the variation in the electron temperature, are Ohmic heating by the electron component of the Pedersen current, and electron cooling due to ionization losses and collisions with neutrals. The Pedersen conductivity is also spatially modulated, influencing the electric field and the FLR dissipation. These effects are found to be quantitatively more important than those associated with direct collisional ionization produced by precipitating electrons. In particular, the latter can only reduce the initial ionospheric dissipation by at most a factor of two.

SM21C-08 09:45h

Low-frequency Plasma Waves Within an AKR Source Region: Possible Wave Stimulation

* Menietti, J D (jdm@space.physics.uiowa.edu) , The University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242 United States
Santolik, O (ondrej.santolik@mff.cuni.cz) , Charles University, Faculty of Mathematics and Physics, Prague, CZ-18000 Czech Republic
Scudder, J D (jack-scudder@uiowa.edu) , The University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242 United States
Mutel, R L (robert-mutel@uiowa.edu) , The University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242 United States

We report the results of an investigation of waves observed by the Cluster wideband instrument (WBD) during an orbital conjunction with the Polar spacecraft. During this perigee pass Polar was at the upper extent of the AKR source region in the southern hemisphere nightside auroral region, Cluster was located at higher altitude above this region and observed AKR with clear signatures of ordered fine structure striations (rain). Using electron particle data observed by HYDRA on board Polar, we have modeled the electron distribution function within the AKR source region, This distribution function is unstable to a number of low-frequency wave modes and supports EMIC waves propagating up the magnetic field line. We investigate the role of these waves in stimulating the growth of AKR and producing the ordered fine structure observed by WBD on board Cluster.

Author(s) (2004), Title, Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract #####-##.