Universal Physical Processes in the Solar System I Posters
Presiding: J M Davila, NASA Goddard Space Flight Center; H Singer, NOAA Space Environment Center
SH51A-01 0830h
Search for solar quakes induced by the proton flares on 28 October 2004 and 20 January 2005
We present the analysis of the SOHO/MDI 1 minute cadence dopplergrams obtained for the proton-rich flares on 28 October 2004 and 20 January 2005 and search for the helioseismic ripples induced by these flares. The obtained time-distance diagrams are used to deduce possible heliosesimic characteristics induced by these flares. These are compared with the theoretical models produced by electron or proton beam precipitation after their ejection from an RCS with the guiding magnetic field. We compare the responses to the momentums delivered by these particles with those deduced from the RHESSI observations.
http://kinetics.inf.brad.ac.uk
SH51A-02 0830h
Energy spectra of fully or partially separated electron beam at ejection from an current sheet with the guiding magnetic field
Electron and proton energy spectra gained at acceleration by a super-Dricer electric field are investigated in the non-neutral reconnecting current sheet (RCS) with a non-zero longitudinal component of magnetic field (a guiding field) directed along the electric field. The other transverse and tangential magnetic component are considered varying with the distances from the X null-point. The proton and electron energy spectra are calculated numerically from a motion equation using the particle-in-cell approach for the model RCSs with constant and variable densities. In the presence of a strong or moderate guiding field protons were found fully or partially separated from electrons at ejection from a RCS into the opposite semiplanes, 'electron' and 'proton' ones while for a weak guiding field they are ejected symmetrically as neutral beams. The particles ejected from a RCS with a very strong guiding field have the power-law energy spectra with spectral indices about 1.5 for protons and 2.0 for electrons. For a moderate guiding field the electron and proton spectra are a combination of power law and thermal-like ones.
http://kinetics.inf.brad.ac.uk
SH51A-03 0830h
Towards a Universal Physics-based "Coronal Heating Function" for Electrons, Protons, and Heavy Ions in the Accelerating Solar Wind
The Sun is often highlighted as a benchmark for the study of other stars, and as a stepping stone to the study of galaxies and cosmic distances. Not to be outdone, the solar wind is rapidly becoming a key baseline for the understanding of basic plasma phenomena such as MHD turbulence, kinetic wave-particle interactions, and nonlinear wave-mode coupling. In keeping with the IHY focus on these kinds of universal processes, we present a distillation of recent modeling efforts to understand how Alfven waves are generated, reflected, cascaded, and damped throughout the solar wind. A physical understanding of solar wind turbulence is crucial to the modeling of energetic particle transport in the heliosphere and the interaction with interstellar neutrals. The goal of this work is to derive a useful "recipe" for solar wind modelers that, given the background zero-order plasma properties, yields the wave amplitudes, the turbulent cascade rates, and the kinetic partitioning of the resultant heating into electrons, protons, and heavy ions (differentiating between parallel and perpendicular heating as well). We also discuss preliminary ideas concerning how the collisionless particle heating is modified if the turbulent cascade ends with the production of small-scale reconnection current sheets.
SH51A-04 0830h
Magnetic Reconnection and the Deduced Properties of Plasma inside the CME/Flare Current Sheet
In the present work, we display our results of studying and analyzing the observational data from UVCS and other remote sensing instruments for three CME/flare events that obviously developed a long current sheet during the eruptions. These results include the thickness of the current sheets, magnetic diffusivities and electrical conductivities (resistivities) of the plasma inside the current sheets. This is the first time that the electrical conductivity (resistivity) within magnetic reconnection region during the real eruptive processes has been deduced since the theory of magnetic reconnection was applied to the solar eruptions about 6 decades ago. The thickness of the current sheet developed during the January 8, 2002 event varies from 7 × 104 km to 2.2 × 105 km for altitudes between 2.5 R⊙ and 5.5 R⊙, with the average thickness of 1.4× 105 km, and the speed of magnetic reconnection inflow near the current sheet is about 10 km s-1. These results suggest a magnetic diffusivity of the plasma inside the current sheet to be 0.7 × 1012 m2 s-1 (compared to the classical value for the quiet corona of 1 m2 s-1, and to the corresponding value for the "turbulent plasma" of 3.4× 106 m2 s-1). For the event occurring on November 18, 2003, the data from UVCS indicate that the upper limit of the current sheet thickness at altitude of 1.7 R⊙ is about 2.8 × 104 km, and that the velocity of magnetic reconnection inflow near the current sheet ranges from 10.5 km s-1 to 106 km s-1. Combining these results yields a range of magnetic diffusivity from 1.4× 1011 m2 s-1 to 1.4× 1012 m2 s-1. During the event observed on March 23, 1998, the upper limit of the thickness of the current sheet in the wake of a CME is about 105 km according to data from UVCS. No data for the velocity of the magnetic reconnection near the current sheet in this event were obtained. Considering the fact that this event was more gradual than the other two cases, we assume the inflow speed in this event to be 5 km s-1. So, we obtain that the magnetic diffusivity of the plasma inside the current sheet has an upper limit of 2.5× 1011 m2 s-1. We notice that values of magnetic diffusivity deduced for three different events are within the range of magnitude.
SH51A-05 0830h
Alfvenic Reconnection and Particle Energization in Solar-Terrestrial Plasmas
Magnetic reconnection and particle energization are two universal and important physical processes occurring in solar-terrestrial plasmas. The generation of electric fields, in particular, parallel electric fields, is a necessary condition for both processes. Most previous calculations of electric fields have been based on the generalized Ohm's Law. However, the generalized Ohm's law, which is essentially the electron momentum equation, only describes force balance, not the generation of the electric fields themselves. Magnetic reconnection often occurs when a pre-existing current sheet is compressed locally by external plasma forces. The parallel electric field responsible for breaking the frozen-in condition must be maintained long enough to provide for the observed particle energization during reconnection. Dynamical equations for the generation of electric fields during the compression of current sheets have been derived. These dynamical equations show that the generation of a sustained parallel electric field favors low plasma density. The continued presence of these electric fields requires a continuous energy supply by the release of localized magnetic or mechanical stresses. This implies that parallel electric field generation is a reactive process. While the basic dynamical equations for the generation of electric fields in current sheets are universal, the external stresses that drive these processes depend on the structure of the magnetic topology being considered. We will demonstrate how these stresses evolve in a number of important configurations, such as the Earth's magnetopause and geomagnetic tail, the auroral acceleration region, and in coronal loops.
SH51A-06 0830h
Optimum Cross-Section of the Current Flowing Through Magnetic Field Lines
Electric current flowing along magnetic fields occurs commonly in both the ionosphere-magnetosphere coupling system and the solar photosphere-corona loop system. In the former case, the current flows from one area of the ionosphere to one area of the magnetosphere or vice versa; in the latter case, the current flows from one foot of the coronal loop to its other foot. In either case, we assume that the total current flowing along the magnetic field lines is determined by the electrodynamics at the end areas of the loop but that the cross-section of the current and, hence, the current density, may vary. The parallel current produces a magnetic field perpendicular to the background magnetic field and causes field lines to twist. The magnetic flux also changes because a current perpendicular to the original field lines appears. For a uniform background magnetic field, analysis based on the magnetic energy shows that the cross-section of the current tends toward that value that produces a magnetic field comparable to the original magnetic field. When the cross-section changes, there is a transformation of magnetic field energy into particle energy.
SH51A-07 0830h
Using Total Perpendicular Pressure to Diagnose Stream Interactions
The total perpendicular pressure (thermal plus magnetic) has a very characteristic pattern at the interface between fast and slow streams. The total pressure rises to a maximum at the interface and then decline. This pattern may include sudden changes in pressure at forward and/or reverse shocks. A necessary condition is that the solar wind speed increases through the enhanced pressure region. This aids in the positive identification of the stream interaction. Usually, there are abrupt changes in the plasma properties at the peak in the pressure profile signifying the interface between the two distinct solar wind source regions. The height of the pressure maximum indicates the strength of the interaction. This strength often falls in a narrow range over an extended period of time. Shocks or shock-like jumps in pressure are surprisingly frequent, appearing in about 30 percent of the stream interactions in 1997.
SH51A-08 0830h
Sunward-Flowing Suprathermal Ion Populations Associated With IP Shocks
Anomalous sunward-flowing suprathermal ion populations were observed from in-situ measurements made by the Wind spacecraft. These ions immediately follow certain IP shocks and can be seen for up to several hours after the shock passage. Nine such IP shock events with sunward-flowing ion number densities large enough to allow for further investigation have been identified. Numerical analysis routines aided in characterizing the particle distribution. The numerical analysis was run on all selected events using several model distribution functions. We then identified the model distribution function that best reproduced the observations. The distribution was found to be of the form of a truncated isotropic exponential function. Correlations between best-fit parameter values and magnetic field angles will be presented. The functional form of the sunward-flowing ion distribution and the parameter values will be related to macroscopic parameters of the associated shocks. The acceleration mechanisms hypothesized to be responsible for the creation of these sunward-flowing ion populations, a major aim of this investigation, will be presented. Lastly, hypotheses as to why the studied ion populations are associated with only a fraction of observed IP shocks will be discussed.
SH51A-09 0830h
Ion Reflection at Collisionless Perpendicular Shocks: The Earth's Bow Shock as a Test Case
A very prominent feature at the Earth's bow shock is the presence of back-streaming ions. This feature can also be observed at interplanetary traveling shocks and is expected at the solar wind termination shock. Important questions are which physical processes cause particle reflection, acceleration, and escape upstream of the shock and what is the source of these ions. Assuming that these are common processes for all collisionless shocks throughout the heliosphere, and in other circumstellar environments we can use the Earth's bow shock is the prime candidate for a detailed study. We use data from the multi-spacecraft mission CLUSTER to study reflection, thermalization, and acceleration of ions at the (quasi-) perpendicular bow shock. Using a database of shock crossings covering a wide range of parameters, such as the shock normal angle, plasma beta, Mach number, as well as the cross shock potential and magnetic field profile, we investigate the intensity of gyrating and reflected ions relative to the solar wind flux. We correlate the aforementioned parameters with the ion fluxes to determine the main controlling parameters. This correlation study has already provided new insights into the source of these ions and the reflection process and has led to a new model for ion reflection.