SM51B-0527
Complex interplay of micro/macro scales in momentum creation and anomalous transport in magnetotail plasmas: simulation and comparison with laboratory experiments
We address the coupling of drift instabilities in the lower-hybrid range with the large scale dynamics of the magnetotail. We consider two ways in which microinstabilities affect large scales: anomalous resistivity and large scale momentum creation. First, on anomalous resistivity, we present a new approach to analyze non- linear kinetic simulations and to extract the role of wave-particle interaction in momentum creation. The approach is applied to the lower-hybrid drift instability where it is shown that the anomalous resistivity generated does not penetrate in the plasma even when electromagnetic fluctuations are considered. Second, on large-scale momentum creation we show how fluctuations in the drift range lead to large scale momentum creation over the whole magnetotail region. An analogy with spontaneous momentum creation in laboratory plasmas (focusing especially on Alcator C-Mod [W. D. Lee and et al., Phys. Rev. Lett. 91, 205003 (2003)]) will be presented.
SM51B-0528
On the Plasma Sheet Boundary Layer and Bursty Bulk Flow Connection
What has for many years been referred to as the "plasma sheet boundary layer," or the PSBL, is proving not to be a near-planar high-latitude layer of continuous proton field-aligned flows, but a high-latitude region of recurring bursts of protons (and electrons) with time-dispersed thermal energies and narrow filamentary structures. This is evident from Polar and Cluster ion composition measurements made at 4 to 7 Earth radii (RE) distance. As first implied by the Polar observations and later confirmed by the multipoint Cluster observations, these proton bursts have a transverse fine structure that may span but a few gyroradii of a 10-keV proton at these altitudes. The rate of energy dispersion varies a great deal, indicating a burst source that is more than 100 RE down the tail at times, but may be inside of 20 RE at other times. The latter is where most observations of earthward directed "bursty bulk flows" of protons, or BBFs, have been made near the equatorial plane. That there is a likely connection between the two kinds of proton flows is suggested by (1) the similarly bursty and structured nature of both and (2) the fact that the BBFs are invariably associated with a transient local increase of the northward tail Bz component, without an increase in the Bx; a process that probably allows the equatorial plasma to expand earthward along higher-latitude field lines. That this is indeed a plausible scenario is illustrated by Cluster magnetic field and ion data from about 19 RE near local midnight in the equatorial plane.
SM51B-0529
On the Earth's Magnetospheric Nonequilibrium Dynamics and the Fluctuation theorem
The Earth's magnetosphere evolves as an out-of-equilibrium system due to the continuous coupling with the solar wind and the Earth's ionosphere. Here, we test the Fluctuation Theorem for the magnetospheric dynamics by investigating the long time evolution of the Earth's magnetospheric ring-current, as monitored by the geomagnetic Dst-index. We find that the symmetries implied by the Fluctuation Theorem are all verified, thus providing a proof of the existence of a steady-state far-from-equilibrium for the Earth's magnetosphere.
SM51B-0530
MHD and Hall MHD simulations of 3-D turbulence lead by the Kelvin-Helmholtz instability
The entry process of the solar wind plasma into the magnetosphere during the northward IMF condition has been controversial in contrast to the Dungey's reconnection model for the southward IMF case. The major candidate processes are the double lobe reconnection model [Song et al., 1999], in which newly closed magnetic field lines on the dayside magnetopause capture the solar wind plasma, and the turbulent transport by the Kelvin- Helmholtz instability (KHI) driven by the fast solar wind flow. We have shown by simulation studies that the strong flow turbulence is a natural consequence of the nonlinear development of the KHI through the secondary instability [Matsumoto and Hoshino, 2004, 2006], which significantly contribute to the formation of a large scale mixing area (e.g., LLBL). Recently, we have studied the 3-D nonlinear evolution of the KHI by performing MHD simulations [Matsumoto and Seki, 2007]. The KH vortex is also susceptible to "the 3-D secondary instability" which converts the rotating energy into the magnetic energy by generating large amplitude magnetic fluctuations which finally lead the system to turbulent state. The fundamental mechanism is similar to the magneto-rotational instability (MRI) which has usually been applied to the accretion disk. Sano and Stone [2002] showed that the Hall term (ion kinetic) effect is important in the nonlinear saturation of the MRI as well as in the linear growth [Balbus and Terquem, 2001]; the direction of the initial magnetic field with respect to the angular velocity separates the fate of the instability. By analogy with their studies on the MRI, we have also examined an ion kinetic effect on the 3-D nonlinear evolution of the KHI. 3-D Hall MHD simulation showed a faster and more turbulent evolution of the secondary instability when the magnetic field directed opposite to the angular velocity of the vortex. On the other hand, it was inhibited when the magnetic field was set in the same direction. The results indicate importance of the ion dynamics in rapidly rotating plasma in which a vortex finally collapses into turbulence. The detailed mechanism which separates the natures of the secondary instability is also addressed in this presentation.
SM51B-0531
Asymmetry in seasonal variations of geomagnetic activity
Seasonal variations in geomagnetic activity were studied for the period of 1990-2007 using Dst and AE indices. Over 150 events characterised by the increase in geomagnetic activity of varying strength (from -90nT up to -1800 nT) were statistically analysed. Although Russell –McPherron effect plays major role in the equinoctial asymmetry in the geomagnetic activity, other effects may also take place. During this study we found a statistically significant October-November peak in geomagnetic activity for Northern Hemisphere, which is sufficiently larger than March- April peak. Several hypotheses for the cause of such effect are discussed.
SM51B-0532
Using Self-affine and Multifractal Testbeds to Calibrate Tests for "SOC" and "IT".
There is by now abundant evidence for scaling in many fluctuating quantities in the coupled solar-terrestrial system (solar wind, magnetosphere and ionosphere). Physical explanations have thus naturally been sought (see e.g. the reviews [1-3]) in descriptions such as low dimensional chaos, intermittent turbulence (IT) and self-organised criticality (SOC). These latter two descriptions differ, however: SOC was directly inspired by a wish to unify spatial (fractal) and temporal ("1/f") scaling; whereas, although the study of turbulence has of course placed increasing emphasis on scaling and multiscaling phenomenology since the seminal work of Kolmogorov [1941], scaling is just one aspect of the subject. In this presentation we discuss a complementary approach ([4,5]), the use of deliberately oversimplified mathematical "testbeds" that allow examination of the logical inferences made in constructing hypotheses such as SOC. The model we will dwell on is Linear Fractional Stable Motion (LFSM). This unites the long range dependence exemplified by fractional Brownian motion (fBm) with the heavy tailed jumps seen in Lévy flights. LFSM is not purely a toy but has known links to extremal dynamics. Intriguingly, LFSM exhibits the appearance of multiaffine behaviour, like IT, while giving (at least in 1D) "avalanche" phenomenology in the sense of power law- tailed pdfs for burst "sizes" and "durations", like SOC. We will discuss numerical simulations, some analytical scaling arguments and our newly found diffusion-like equation for LFSM. We will also present early results from simulations of multifractal processes derived from fBm in order to give insight into how properties of LFSM may carry over into the multifractal domain. The implications for the inference of IT and SOC behaviour from uncontrolled natural datasets will be discussed. 1. Chapman and Watkins, Space Science Reviews, 2001 2. Freeman and Watkins, Science, 2002 3. Vassiliadis, Reviews of Geophysics, 2006 4. Watkins, Nonlinear Processes in Geophysics, 2002 5. Watkins et al., Space Science Reviews, 2005 [Stimulating suggestions from Vadim Uritsky, Mervyn Freeman and Shaun Lovejoy are acknowledged].
SM51B-0533
Studies of Magnetotail Dynamics and Energy Evolution During Substorms Using MHD Simulations
Substorms are an important part of magnetotail dynamics that occur in response to increased energy input from the solar wind. The amount and evolution of the energy contained in the magnetotail over the course of a substorm is very difficult to determine with single point measurements. We have therefore used the Lyon-Fedder- Mobarry global magnetohydrodynamic code to simulate and analyze substorms that occured on March 9, 1995, December 10, 1996, and August 27, 2001. These events have been studied previously, and the simulation results have been shown to reproduce important features of the substorms. We calculate the total energy in the closed field line region and show that the time evolution of this quantity has the same pattern in all three events. The energy of the closed field line region decreases during the growth phase and increases during the expansion phase. We will discuss our results in terms of the relative timing of the onset of magnetotail reconnection on both closed and open field lines.
SM51B-0534
Relative Order of Auroral Transient Structure During Substorm Activation
Variability of auroral structures is a manifestation of the magnetosphere-ionosphere plasma dynamics. During the last decade the complexity of magnetosphere-ionosphere plasma has been widely discussed in numerous papers. The most popular approaches are based on turbulence or/and self-organized criticality paradigms. However, there is no clear evidence that the dynamics during the discussed events is really organization, and not disorganization. The problem is that the magnetosphere-ionosphere system is an open non-equilibrium system, therefore classical thermodynamics is not directly applicable. Here we use an approach based on the S-theorem by Yu.L. Klimontovich. This approach allows us to compare the ordering which characterize the current (non- equilibrium) state of the system with experimental data. The considered characteristic is an analogy of entropy which has been extended to non- equilibrium states. Television observations of the auroral structure during substorm activation at the Barentsburg observatory (Svalbard) have been used as a data set. Dependence of the ordering on the spatial scale has been analyzed. We found that the ordering of the aurora increases during the substorm development. The same approach has been applied to data sets generated by cellular automata models. Evolution of the systems in time and dependence on external control parameters are compared and discussed. Acknowledgements. This work was supported by grant No 171076/V30 of the Norwegian Research Council and partly by the Division of Physical Sciences of Russian Academy of Science.
SM51B-0535
Scaling properties of the solar wind driver and the Akasofu's ε parameter at solar maximum.
Earth magnetosphere is constantly driven by turbulent and intermittent solar wind. Observations suggest that the multi-scale nature of this coupling is a fundamental aspect of magnetospheric dynamics. We examine the statistical properties of fluctuations in Akasofu's ε, which represents the energy input from the solar wind into the magnetosphere, and the magnetic field energy density of the solar wind at solar maximum. Previous studies suggested that, at solar maximum, these fluctuations are approximately self-similar and their probability distributions have similar functional form. We examine scaling properties of these quantities in detail, obtain values of their scaling exponents and examine a fractional Lévy walk as a possible model for their statistics.
SM51B-0536
A stochastic theory for temporal fluctuations in Self-Organized Critical systems.
In this work we use a mean field assumption to derive simple stochastic differential equation for the toppling activity in the Bak-Tang-Wiesenfeld (BTW) sandpile models, modelling the activity as an anti persistent fractional Brownian "super-walk", where the diffusion coefficient is proportional to the activity level itself. Through analysis of the stochastic differential equation and analytical solutions of the corresponding Fokker- Planck equation it is possible predict all the essential statistical properties of the toppling signal, including its spectral properties and the probability density functions for duration-times and the fluctuations in the signal itself. The methods used are insensitive to the particular details of the BTW class models, and can easily be modified to include other sandpile models.
SM51B-0537
First Results on the Variability of Mid- and High-Latitude Ionospheric Electric Fields at 1- Second Time Scales
The electric fields at high latitudes are often modeled as a static pattern in the absence of variation in solar wind parameters or geomagnetic disturbance. However, temporal variability in the local electric fields on time scales of minutes for stable conditions has been reported and characterized statistically as an intrinsic property amounting to turbulence. We describe the results of applying a new technique to SuperDARN HF radar observations of ionospheric plasma convection at middle and high latitudes that gives views of the variability of the electric fields at sub-second time scales. We address the question of whether there is a limit to the temporal scale of the electric field variability and consider whether the turbulence on minute time scales is due to organized but unresolved behavior. The basis of the measurements is the ability to record raw samples from the individual multipulse sequences that are transmitted during the standard 3 or 6–second SuperDARN integration period; a backscattering volume is then effectively sampled at a cadence of 200 ms. The returns from the individual sequences are often sufficiently well-ordered to permit a sequence-by-sequence characterization of the electric field and backscattered power. We attempt a statistical characterization of the variability at these heretofore inaccessible time scales and consider how variability is influenced by solar wind and magentospheric factors.