SH32B-01 INVITED 

Anisotropies and Helicities in the Solar Wind Inertial and Dissipation Ranges at 1 AU

* Smith, C W (Charles.Smith@unh.edu), University of New Hampshre, Department of Physics and Astronomy, Space Science Center, Morse Hall, University of New Hampshire, Durham, NH 03824, United States Vasquez, B J (Bernie.Vasquez@unh.edu), University of New Hampshre, Department of Physics and Astronomy, Space Science Center, Morse Hall, University of New Hampshire, Durham, NH 03824, United States Leamon, R J (leamon@grace.nascom.nasa.gov), ADNET Systems, Inc., ADNET Systems, Inc., NASA/Goddard Space Flight Center, Code 671.1, Greenbel, MD 20771, United States Hamilton, K (kmz4@cisunix.unh.edu), UC/Riverside, Department of Physics and Astronomy, UC/Riverside, Riverside, CA 92521, United States

We have constructed a data base of ACE observations at 1 AU based on 960 intervals spanning the broadest possible range of solar wind conditions including magnetic clouds. Using spectral analysis of high resolution magnetic field data we compare inertial range characteristics with properties in the measured dissipation range. We find that previous conclusions by Leamon et al. [1998a,b,c] are upheld: average wave vectors are more field-aligned in the dissipation range than in the inertial range, magnetic fluctuations are less transverse to the mean field in the dissipation range, and cyclotron damping plays an important, but not exclusive role in the formation of the dissipation range. However, field-aligned wave vectors play a larger role in the formation of the dissipation range than was previously found. In the process we examine characteristics of the inertial range that are relevant to the manner in which the dissipation range is created. We find significant contrast between these inertial range results and the conclusions of Dasso et al. [2005] who examine larger scale fluctuations within the inertial range. Dasso et al. found a dominance of field-aligned wave vectors in the high-speed wind and a dominance of 2D wave vectors in low-speed winds. We find that the orientation of the wave vectors for the smallest scales within the inertial range are not organized by wind speed and that on average all samples show the same distribution of energy between perpendicular and field-aligned wave vectors. We conclude that this is due to the time required to evolve the spectrum toward a 2D state where the smaller inertial range scales examined here evolve more quickly than the larger scales of earlier analysis. Likewise, we find no such organization by to wind speed within the dissipation range.

SH32B-02 INVITED 

Properties of Compressible MHD Turbulence

* Lazarian, A (lazarian@astro.wisc.edu), University of Wisconsin-Madison, 475 Charter St., Madison, WI 53706, United States

Recent years have been marked by substantial advances in understanding of compressible turbulence in magnetized plasma. This includes better understanding of theory as well as its numerical and observational testing. In my talk I shall discuss MHD turbulence in fully and partially ionized plasma. I shall also discuss the case of turbulence being imbalanced, i.e. when the flow of energy from one direction is larger than the flow of energy in the opposite direction, as well as the backreaction of energetic particles on turbulence. I shall show that a number of long-standing puzzles related to energetic particle propagation and the observed fluctuations of plasma density can be resolved within the framework of present-day turbulence theory.

SH32B-03 

Measured constraints on the suprathermal electron temperature anisotropy in the solar wind

* Bale, S D (bale@ssl.berkeley.edu), Space Sciences Laboratory, University of California, Berkeley, CA 94720, United States Xu, K), Space Sciences Laboratory, University of California, Berkeley, CA 94720, United States Salem, C), Space Sciences Laboratory, University of California, Berkeley, CA 94720, United States Kasper, J C), Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, United States Quataert, E), Astronomy Department, University of California, Berkeley, CA 94720, United States Howes, G G), Astronomy Department, University of California, Berkeley, CA 94720, United States

We report on a statistical analysis of the measured electron temperature anisotropy in the solar wind using the 3DP instrument on the Wind spacecraft. Approximately one million independent measurements of the electron velocity distribution were integrated in two energy ranges corresponding to the solar wind 'core' and 'halo' components. The parallel and perpendicular (to the local magnetic field) temperatures were computed from the pressure integral and compared with the parallel electron beta parameter β_{e, \parallel} and the electron 'collisional age' A_e,e. The low-energy core distribution remains relatively isotropic, due to its larger density and correspondingly large Coulomb collision frequency. However, the temperature anisotropy of the halo distribution (E ≥ ~80 eV) shows a striking signature which suggests that it is bounded by a whistler-mode instability from above (T_\perp/T_\parallel > 1) and the electron firehose instability from below (T_\perp/T_\parallel < 1). These results confirm that solar wind electron expansion and compression are limited fundamentally by these instabilities.

SH32B-04 

Observations of Magnetic Reconnection in the Turbulent, High-Speed Solar Wind

* Gosling, J T (jack.gosling@lasp.colorado.edu), Laboratory for Atmospheric and Space Physics, University of Colorado, 1234 Innovation Drive, Boulder, CO 80303, United States

The high-speed (greater than 600 km/s) solar wind that originates in coronal holes is permeated by evolved Alfvenic-type fluctuations associated with MHD turbulence. We have used high temporal resolution (3-s) plasma and magnetic field measurements by the Wind spacecraft at 1 AU to identify and study Petschek-like reconnection exhausts in this turbulent flow for the first time. Despite the fact that the turbulent cascade produces numerous thin current sheets at 1 AU, such exhausts are relatively rare: we have identified only 34 reconnection exhausts in 1358 hours of high-speed solar wind data. With 3 exceptions, each exhaust was embedded within a relatively sharp, outward-propagating Alfvenic fluctuation. Local field shear angles across these reconnection exhausts ranged from 24 to 160 degrees, with average and median values being close to 90 degrees. The vast majority (88%) of these exhausts had maximum local widths less than 4 x 10⁴ km and were convected past the spacecraft in less than 66 s, which is why they have not previously been identified in lower temporal resolution (1- min) data. Multi-spacecraft observations indicate that current sheets, and thus also reconnection X-lines, in the turbulent, high-speed wind tend to be considerably more localized than in the low-speed wind or in interplanetary coronal mass ejections. The Wind observations demonstrate that reconnection is one way in which solar wind turbulence is dissipated and the high-speed wind heated far from the Sun, although it is not yet clear how effective reconnection is overall in this regard.

SH32B-05 

Solar Wind Measurements of the Alignment Between Vector Velocity and Magnetic Field Fluctuations and Comparisons to Boldyrev's Phenomenological Theory

* Podesta, J J (j.podesta@unh.edu), Center for Integrated Computation and Analysis of Reconnection and Turbulence, University of New Hampshire, Durham, NH 03824, United States Bhattacharjee, A (amitava.bhattacharjee@unh.edu), Center for Integrated Computation and Analysis of Reconnection and Turbulence, University of New Hampshire, Durham, NH 03824, United States Chandran, B D (benjamin.chandran@unh.edu), Center for Integrated Computation and Analysis of Reconnection and Turbulence, University of New Hampshire, Durham, NH 03824, United States

Boldyrev's phenomenological theory of incompressible MHD turbulence predicts that as energy cascades from large to small scales through the inertial range the components of velocity and magnetic field fluctuations perpendicular to the mean magnetic field become progressively more aligned with each other so that the angle between them decreases monotonically like λ^1/4, where λ is the length scale of the fluctuations perpendicular to the mean magnetic field. Studies undertaken to search for this scaling law in solar wind data have shown that such a scaling law holds at the largest inertial range scales but then breaks down at intermediate to small scales. Analysis of data from the Wind spacecraft at 1 AU show a power law scaling exists from roughly 5× 10⁴ to 10³ seconds with a power law exponent similar to the predicted value 1/4. The scaling law disappears at smaller scales with the alignment angle reaching a minimum between 10³ and 10² seconds and then increasing as the scale size decreases further down to 10 seconds or so.

SH32B-06 

Waves/Turbulence in the Heliospheric Plasma Sheet: Ulysses Observations

* Zhou, X (Xiaoyan.Zhou@jpl.nasa.gov), Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, United States Smith, E J (Edward.J.Smith@jpl.nasa.gov), Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, United States

The Heliospheric Current Sheet (HCS) and Heliospheric Plasma Sheet (HPS) are the largest structures in the heliosphere and carry important information of fast and slow solar wind interaction and magnetic field variations. The HPS is distinguished by relatively high Beta, slow speed plasma that surrounding the HCS. Here, we report studies of waves/turbulence in the HPS. The data used in the investigation are current sheet and plasma sheet crossings in Ulysses data. The advantage of using these data is that the HPS is thicker at large radial distances and the spacecraft spends longer intervals inside the plasma sheet. We find that, if Alfvén waves are present in the HPS, they are weak and are dominated by variations in the field magnitude, |B|, and solar wind density, NP, that are anti-correlated. To distinguish between slow mode waves, Pressure Balance Structures (PBS) and Mirror Modes, correlations between magnetic, kinetic and total static pressures (pB, pK, and pT) are studied. The slopes of the pB - pK, and pK - pT regression lines are qualitatively consistent with slow mode waves and rule out the other possibilities. In principle, the slopes are measures of the wave speed relative to the Alfvén and sound speeds and imply the direction of propagation with respect to the ambient field.

SH32B-07 

Wave Number Spectra in the Solar Wind as Seen by CLUSTER Spacecraft

* Narita, Y (y.narita@tu-bs.de), Institute of Geophysics and Extraterrestrial Physics, Technical University of Braunschweig, Mendelssohnstr. 3, Braunschweig, 38106, Germany Glassmeier, K (kh.glassmeier@tu-bs.de), Institute of Geophysics and Extraterrestrial Physics, Technical University of Braunschweig, Mendelssohnstr. 3, Braunschweig, 38106, Germany Goldstein, M L (melvyn.l.goldstein@nasa.gov), Geospace Physics Laboratory, Code 673, NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States Treumann, R A (treumann@issibern.ch), Department of Geoscience, Geophysics Section, Ludwig-Maximilians-University Munich, Theresienstr. 41, Munich, 80333, Germany Gary, S (pgary@lanl.gov), Mail Stop D466, Los Alamos National Laboratory, Los Alamos, NM 87545, United States

We present direct measurement of wave number spectra in the solar wind. We use magnetic field data obtained by the four CLUSTER spacecraft and apply the wave telescope method, which is particularly suited for multi- spacecraft data analyses, to determine the spectra of two-dimensional, Alfvénic, and compressible turbulence. The wave number spectra are characterized by the power law on intermediate scales (1000-10,000 km) and spectral breaks on smaller scales (100 km), reminiscent of turbulence. The wave number spectra also exhibit dominance of two-dimensional turbulence and only small contribution of compressible turbulence, which justifies the assertion of incompressible fluctuations in the solar wind and accounts for why the mean free paths of the cosmic rays are larger than predicted by the quasi-linear theory. On the other hand, the wave number spectra exhibit some different properties from that of the frequency spectra derived from the single spacecraft measurements. We discuss possible reasons and implications of the spectral differences between the wave number and frequency domain.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.