SH34A-01 INVITED
Isotropic, homogeneous, incompressible fully developed turbulence in polar wind: observation of the inertial range
Theoretical results shows that, under the hypotheses of isotropy, local homogeneity and incompressibility, the high Reynolds number solar wind should present a linear scaling law for the pseudo-energy flux. This is the analogous of the celebrate 4/5 law for neutral fluids. Recent observations have shown that such range is indeed present in some streams of polar wind, as recorded by the Ulysses spacecraft. In this work we point out the main characteristics of the wind when the scaling is observed, in comparison with regions of non-scaling. Spectral properties shows that the role of the interplanetary magnetic field is crucial, as well as the compressibility of the wind.
SH34A-02 INVITED
Magnetic and velocity fluctuations of solar magnetic fields observed with Hinode
Solar Optical Telescope aboard Hinode satellite has a filter instrument and spectro-polarimetric instrument. The filter instrument provides us with high resolution high cadence images with line-of-sight Dopplergram, while the spectropolarimter gives precise magnetic and velocity maps with lower time resolution. The quality of the data is unprecedented. We will present relevant data in terms of fluctuations. http://hinode.nao.ac.jp/index_e.shtml
SH34A-03 INVITED
Probability Density Functions of the Solar Wind Driver of the Magnetopshere-Ionosphere System
The solar-wind driven magnetosphere-ionosphere system is a complex dynamical system in that it exhibits (1) sensitivity to initial conditions; (2) multiple space-time scales; (3) bifurcation sequences with hysteresis in transitions between attractors; and (4) noncompositionality. This system is modeled by WINDMI--a network of eight coupled ordinary differential equations which describe the transfer of power from the solar wind through the geomagnetic tail, the ionosphere, and ring current in the system. The model captures both storm activity from the plasma ring current energy, which yields a model Dst index result, and substorm activity from the region 1 field aligned current, yielding model AL and AU results. The input to the model is the solar wind driving voltage calculated from ACE solar wind parameter data, which has a regular coherent component and broad-band turbulent component. Cross correlation functions of the input-output data time series are computed and the conditional probability density function for the occurrence of substorms given earlier IMF conditions are derived. The model shows a high probability of substorms for solar activity that contains a coherent, rotating IMF with magnetic cloud features. For a theoretical model of the imprint of solar convection on the solar wind we have used the Lorenz attractor (Horton et al., PoP, 1999, doi:10.1063\/1.873683) as a solar wind driver. The work is supported by NSF grant ATM-0638480.
SH34A-04
Intermittent Properties of Solar Wind Fluctuations
In this paper we offer a short review of the most significant non-Gaussian properties of solar wind fluctuations as observed in interplanetary space. Several decades of in-situ observations of plasma and magnetic field fluctuations have shown that the tails of their distributions do not follow a Gaussian statistics in the sense that the strongest events have a probability to happen much stronger than that they would have if they were normally distributed. Moreover, this feature becomes more and more evident as we observe shorter and shorter scales. This behavior is commonly identified as "intermittent" within the context of MHD turbulence. Recent studies focused on these intermittent events and tried to unravel their intrinsic nature and origin. It appears that the intermittent component of interplanetary fluctuations is due to static structures, flux-tube like, advected by the wind and possibly related to the complicate magnetic field topology existing at the base of the corona.
SH34A-05
Calculation of Intermittency in the Photosphere and Corona From Hinode Data
High spatial and temporal resolution observations of the photospheric magnetic field and solar corona, offered recently by Hinode instrument, provide us a unique opportunity to simultaneously estimate degree of intermittency in the photosphere and the corona and to track their variations in time. To do this, we adopted a flatness-function technique, where the slope of the function defines degree of intermittency. The function itself is calculated as the ratio of the sixth-order structure function to the cube of the second-order structure function. Three independent data sets, that were utilized to calculate the intermittency in the corona (XRT/Hinode, GOES, and Nobeyama 9.4 Hz polarization flux), showed a synchronous increase of intermittency during a 5-day time interval that ends with the occurrence of the X3.4 flare in the NOAA 10930. Photospheric intermittency, calculated from SOT-FG/Hinode magnetograms, peaked approximately 1.5 days before the flare onset. The result allows to suggest a preceding gain of intermittency in the photosphere with a following transport of intermittency into the corona.
SH34A-06
Using PEACE, FGM, and CIS Data from the Four Cluster Spacecraft to Measure Cross Helicity, Compressibility, and Vorticity in the Solar Wind
Determinations of compressibility and vorticity in the solar wind require a set of multi-point measurements that encompass a volume of space over which finite differences can be defined in analogy to computing divergences and cross products in finite difference numerical calculations. Because Cluster cannot provide four-point data of the ion velocity and density moments, it is of interest to try to make such measurements using the four-point thermal electron data provided by the PEACE instruments. PEACE provides an opportunity to compute the velocity and density moments and from them construct the divergence and curl of the velocity, thereby obtaining both a measure of the compressibility and the vorticity. From those moments, and together with the FGM magnetic field data, we have also constructed spectra of the cross helicity (the correlation between the fluctuating velocity and magnetic fields). We present early results in that project, including strong velocity shears associated with a Hot Flow Anomaly encountered by the four spacecraft in 2007. The analysis makes use of the Taylor frozen-in-flow approximation to artificially vary the spacecraft separation in the GSE -x direction in the solar wind.
SH34A-07 INVITED
Intermittent Emission of High-Frequency Waves by Magnetic Reconnection Between Canopy Field and Small-Scale Horizontal Field
The energy source of coronal heating and solar wind acceleration is the interaction of magnetic field and thermal convection in the photosphere. Magnetoconvection has complicated bifurcation structure, and the mode, spectra and power of the waves generated in the photosphere depend on the nature of magnetoconvection in the photosphere. In order to study the relation between magnetoconvection and coronal heating/solar wind acceleration, we performed three-dimensional magnetohydrodynamic simulation of a domain that includes from upper convection zone to the corona. We first ran the simulation without magnetic field until convection developed to quasi-steady state, and then imposed a vertical and uniform magnetic field. We found that, in addition to the well-known fact that vertical magnetic field is swept into the downflow region, small scale horizontal fields as strong as 800G intermittently emerge in the photosphere. Even though the initial magnetic field is vertical and uniform, magnetic field in the convection zone become turbulent, and occasionally a bundle of strong magnetic flux is driven by the upward convection flow and emerges in the photosphere. Such horizontal fields undergo magnetic reconnection with pre-existing magnetic field in the chromosphere (so called "canopy" field), and then emit high-frequency (>0.05mHz) waves into the corona. We discuss the possible role of these processes in heating, acceleration and turbulence of the corona and the solar wind.