SH31A-1146 0800h
Near-Relativistic Electron 1/V Onset Plots
It is often assumed that the first arriving electrons of a near-relativistic (E $>$ 30 keV) electron event propagate scatter-free to one Astronomical Unit (AU). In that case, the arrival time, Ta, should scale as D/V, where D is the travel distance and V the electron speed. A plot of Ta versus 1/V for various electron energies should then yield the solar injection time t and the travel distance D. In some electron events D is about 1.2 AU, but the inferred injection times are characteristically about 10 minutes after the start of metric/decametric type III radio bursts that are the assumed signatures of electron injection. This may indicate a delayed injection not directly associated with the type III burst, or it may result from significant coronal/interplanetary electron scattering, even for well beamed events. We use data from the 3DP electron detectors on the Wind spacecraft to do 1/V onset plots for a number of near-relativistic solar electron events. We find that the inferred travel distances are broadly distributed and do not peak at the nominal 1.2 AU value. This may invalidate the scatter-free assumption. If the problem were due to energy independent scattering, the value found for the travel distances should be systematically longer than the nominal value. Most of our values, however, seem to be shorter than the length of the magnetic field lines between the injection point and 1 AU. An energy-dependent scattering with higher scattering at higher energies could make the measured time delays systematically longer at the higher energies and the inferred travel distances systematically shorter. A significant decrease in the efficiency of gyroresonant scattering by whistler mode waves between a few hundred keV and 30 keV might be the cause.
SH31A-1147 0800h
Latitudinal dependence of solar proton flux derived from interplanetary Lyman alpha emission
There is a uniform flow of the interplanetary hydrogen in the solar system. The distribution of interplanetary neutral hydrogen is sensitive to solar wind proton flux, which has a latitudinal distribution, because interplanetary neutral hydrogen atoms are mainly ionized through a process of charge-exchange with solar wind protons (contributing to 80% of the total ionization rate). Rucinski et al. [1996] estimated the ionization rate of the interplanetary hydrogen in an average solar activity condition: 6.4 0.14 [10E-7/s] for charge exchange with protons. The most practical technique for determining the latitudinal dependence of the interplanetary hydrogen is observation of resonant backscatter of solar Lyman ? emission at 121.6 nm. The interplanetary Lyman ? emission has been measured by the ultraviolet imaging spectrometer (UVS) on board the Nozomi spacecraft crusing on its Mars transfer orbit with a periapsis of 1 AU and an apoapsis 1.5 AU from the Sun. The field-of-view of UVS is perpendicular to the spin axis of the spacecraft, which is controlled toward the Earth. The spatial resolution of UVS is 1.41 degrees in a plane perpendicular to the spin axis and 0.29 degrees in a plane including the spin axis. Spatial distributions are obtained from the full sky scanning of UVS with spin and orbital motions of the Nozomi spacecraft. One-year UVS data enable us to construct a full sky image of Lyman ? emission. We present the results obtained from Nozomi/UVS data analysis for the period of 1999-2002. From a fitting of model calculations to the observed data, it is confirmed that a latitudinal anisotropy with the higher ionization region at the equator is reduced toward solar maximum. Finally, higher ionization region are found at the poles than at the equator near solar maximum. Basically, this change is produced by variations in the latitudinal dependence of persistent solar wind proton flux. However, proton flux from transient CMEs also affects the distribution of the interplanetary hydrogen. We identify the effect of CMEs on the distribution of interplanetary hydrogen from the analysis of CME data collected by SOHO/LASCO.
SH31A-1148 0800h
Spectra of the X-ray Emission from the Heliospheric Gas
Spectra of the heliospheric EUV and X-ray emission induced in the charge-transfer collisions of the highly charged solar wind ions with the interstellar gas have been calculated. Cascading photon spectra of individual O$^{q+}$, C$^{q+}$, N$^{q+}$, and Ne$^{q+}$ ions have been constructed using recent data on ion radiative transition probabilities and the state selective population cross sections for charge-transfer collisions of the most abundant heavy solar wind ions with H and He atoms. Emission spectra have been calculated for slow and fast solar winds interacting with the heliospheric H and He gas. Relative intensities of the brightest lines have been predicted. The volume power distribution of the charge-transfer EUV and X-ray emission has been computed for simplified models of the solar winds and the interstellar gas. X-ray images of the heliosphere have been composed for the region of the heliosphere inside 10 AU from the Sun.
SH31A-1149 0800h
Enhancements of He$^+$ at Interplanetary Disturbances: A Survey
Recent observations with ACE/SEPICA and SOHO CELIAS STOF have shown that energetic He$^+$ is after H$^+$ and He$^{2+}$ the third most abundant energetic particle population in the heliosphere. The He$^+$/He$^{2+}$ ratio in the energetic particle population can reach unusually high values; in the energy range of 250keV/n -800keV/n ratios close to unity. The major source of the energetic He+ has been identified to be interplanetary pickup ions that are preferentially accelerated at CIR's, TIR's, and interplanetary traveling shocks. Since, compared to solar wind ions pickup ions are already suprathermal, any accelerator can create an enhancement in the energetic He$^+$/He$^{2+}$ ratio. In our survey of energetic helium over three years (1998-2000) from STOF and SEPICA we have identified additional discontinuities and magnetic field signatures, such as current sheet crossings, flows, and enhanced magnetic turbulence, which are associated with an enhancement in He$^+$/He$^{2+}$ ratio.
SH31A-1150 0800h
First Solar Wind Measurements by the Rosetta Ion and Electron Sensor (IES)
We report here results of the first operation in space of the Ion and Electron Sensor (IES) on board the European Space Agency's Rosetta spacecraft, on its way to rendezvous with comet Churyumov-Gerasimenko in 2014. The instrument became fully operational on the night of 8/9 September 2004, at which time Rosetta was about 1.04 AU from the Sun and 30 deg ahead of Earth's orbital motion. IES is comprised of 2 toroidal top-hat electrostatic analyzers, one each for electrons and ions, providing a 360 deg view in azimuth onto the 2 microchannel plate detectors. A set of deflection plates provides a +/- 45 deg view in elevation. Results of observations of solar wind plasma and comparison with observations by other near-Earth spacecraft will be discussed.
SH31A-1151 0800h
Kappa distribution and Probability Density Functions in Solar Wind
A signature of a statistical intermittency is the presence of large deviations from the average value: this increased probability of finding extreme deviations is characterized by Probability Density Functions (PDFs) which exhibit non Gaussian power-law tails. Such power-law distributions were observed over decades in biology, chemistry, finance and other fields. Known examples include heartbeat histograms, price distribution, turbulent fluid flow and many other non-equilibrium systems. It is shown that the Kappa distribution represents a good description of PDFs observed in Solar wind. The asymmetric fluctuations in variance over time observed in solar wind PDFs are Gamma distributed. It is shown that, by assuming such a distribution of variance, the Kappa distribution can be analitically derived.
SH31A-1152 0800h
Acceleration of the Weakly Collisional Solar Wind
A major assumption inherent to the usual fluid solar wind models is that the plasma is dominated by collisions. Therefore the fluid approach implies that the particle velocity distribution functions are close to Maxwellians. However the observed solar wind electron distributions depart significantly from Maxwellians, indicating the limited validity of this hypothesis. Collisionless models are not fully justified either, but should bring some insights into the physics since heat transport is mainly driven by suprathermal particles which are virtually collisionless because of the rapid increase with energy of the Coulomb free path. A proper theory should take into account the transition from a fully collisional regime to a weakly collisional one. If we neglect interactions with waves, the existence of a transonic plasma wind depends mainly on the electrostatic field and the heat flux which are determined by the velocity distributions of particles. In this work we present recent developments of a kinetic collisionless model of the solar wind and compare them with results obtained by numerical simulations that include collisions. Two important results emerge: a suprathermal tail in the electron velocity ditribution function enables to explain the fast wind and both models give the same speeds over a large range of parameters.
SH31A-1153 0800h
Comparison between impulsive energetic electron events and $^{3}He$-rich events
We present a comparison between electron data by WIND/3DP and $^{3}He$ data by ACE/ULEIS. Our study shows that impulsive energetic electron events occur more often than impulsive $^{3}He$-rich events. For a set of 41 $^{3}He$-rich events from 1997 November to 2003 April, WIND/3DP has good measurements during 29 events. An injection analysis shows that among the 29 $^{3}He$-rich events, 13 events with the $^{3}He$/$^{4}He$ ratio ($\sim$0.002-0.34) have an electron event with an injection time difference $<$ 1 hour, 6 events with the $^{3}He$/$^{4}He$ ratio ($\sim$0.081-6.2) have an electron event with an injection time difference of 1-2 hours, and the other 8 events with the $^{3}He$/$^{4}He$ ratio ($\sim$0.0054-0.25) have an electron event with a injection difference $>$ 2 hour or have no electron events. Further analysis including type III bursts and energy spectra may provide important information about the association between $^{3}He$-rich events and electron events.
SH31A-1154 0800h
Non-Resonant Pitch-Angle Scattering of Sub-MeV Electrons
As the translational energy of charged particles decreases, so does the wavelength of the waves with which these particles can gyroresonate. For sub-MeV electrons, the resonant processes of wave-particle interaction involve waves that contain only a small fraction of the turbulent wave energy, even for small pitch-angles. It is very uncertain whether these resonant processes can dominate the scattering in pitch-angle. We therefore estimate the contribution of that part of the turbulence spectrum that contains most of the turbulent wave energy, but interacts with the electrons by a non-resonant process. The study of such non-resonant interaction has been restricted so far to very small pitch-angle cosines $\mu$ and higher energies. We now calculate the effect of the non-resonant waves at larger $\mu$. We find that the non-resonant interaction of sub-MeV electrons with low-frequency waves produces an anomalous scattering. The electron pitch-angle sines can subdiffuse or supradiffuse in logarithmic space as a function of the elapsed distance along the average magnetic field. In the solar wind, subdiffusion seems to be the rule. The average pitch-angle variation due to non-resonant interaction on lengthscales of the order of a fraction of the electron travel distance from the Sun is found to be comparable to the initial pitch-angle of the electrons, and much larger than the pitch-angle reduction due to magnetic focusing in slow solar wind. Therefore, unless the electrons are injected along the magnetic field and do not encounter any enhanced whistler turbulence, or the fast mode component of the turbulence is much lower than the measured compressive component of the turbulence, already only a few percent of the whole turbulence, sub-MeV electrons in the inner heliosphere do not propagate scatter free. A simulation of the electron dynamics based on the direct integration of the equations of motion, involving some $10^{15}$ modes, confirms these results. Electrons with small initial pitch-angles keep small pitch-angles. On the other hand, electrons with large initial pitch-angles have much larger pitch-angle variations, and within a finite range from 90 degrees, can be reflected very quickly. So, while the non-resonant scattering process is consistent with the first electrons arriving at one AU being strongly beamed along the magnetic field in some solar events, it also offers the possibility of significant scattering and delay of the electrons before their beaming.
SH31A-1155 0800h
Heavy Element Abundances in the Heliospheric Plasma Sheet
Using sample crossings of the heliospheric plasma sheet by the Ulysses spacecraft, we compare the abundances of heavy elements (Z $>$ 2) near and within the sheet with the abundances found generally in the solar wind. The primary motivation for this study is to ascertain first if the sheet abundances are in fact different from those in the general solar wind, and, if so, to what extend the abundances reflect those known to be at the sun. A close relationship would confirm the sun to be the source of the plasma sheet, and may identify the source region. Variations of the abundances measured in the sheet from those near the sun will yield details of the transport mechanism.
SH31A-1156 0800h
Elemental Abundance Variations of Gradual SEP Events at Low Energies as Measured by ACE/ULEIS and WIND/STEP Over the Last Solar Cycle
Solar energetic particles (SEPs) provide a measuring technique to probe the composition of the solar corona independent of spectroscopic measurements. However, SEP elemental abundances in large gradual events can vary considerably from event to event, exceeding one order of magnitude in some cases; this must be taken into account when using SEP measurements to deduce the coronal composition. The causes of these variations are unfortunately still not clear, and may be produced either by acceleration/transport effects or variations in the source abundances. Using the Ultra-Low-Energy-Isotope-Spectrometer (ULEIS) onboard the Advanced Composition Explorer (ACE) and the Supra-Thermal-through-Energetic-Particle (STEP) instruments onboard the WIND spacecraft, we have measured the fluxes of Fe and the C-N-O at energies between 0.02 and 0.6 MeV/nucleon and extracted the C to O ratios for a survey of gradual SEP events between 1995 and 2003. In this presentation, we will report on preliminary results of this study.
SH31A-1157 0800h
Ulysses COSPIN/KET and EPAC observations of Jovian electron bursts during the distant Jupiter encounter
The Ulsses Energetic PArticles Composition instrument (EPAC) consists out of four detector heads and was designed to provide information on the flux, directional three-dimensional anisotropy as well as chemical composition of energetic particles in interplanetary space. Ions and electrons can be measured separately. During the mission it became evident that important informations about a few hundred keV electrons can be extracted from the four EPAC telescopes. The COSPIN/KET experiment on board Ulysses has been monitoring the flux of 3-20 MeV electrons in interplanetary space since the launch in October 1990. Between 1 and 10 AU Jovian, and galactic particles contribute continously to the few-MeV electron intensities. During it's recent descend to low latitudes the Ulysses spacecraft approached the planet Jupiter within 1~AU. However, in addition to the average intensity level well accounted for by diffusion, we report about very short duration electron events, which are called Jovian electron jets, characterized by: (i) a sharp increase and decrease of flux: (ii) a spectrum identical to the electron spectrum in the Jovian magnetosphere; and iii) a trong anisotropy. We compare our results with similar events, observed during the Jupiter flyby of Ulysses in 1992.
SH31A-1158 0800h
A Statistical Study On Kinematical And Geometrical Properties Of Halo CMEs.
Kinematical and geometrical properties of the halo CMEs in the period from 1997 to 2000 have been determined using the cone model proposed by Zhao, Plunkett and Liu (2002). A statistical study is performed to classify these CMEs. The properties of the CMEs are also examined against their geomagnetic activities.
SH31A-1159 0800h
Microstructures of interplanetary coronal mass ejections during solar cycle 23
Magnetic cloud structure of interplanetary coronal mass ejections (ICMEs) and their surrounding regions during solar cycle 23 are investigated, using solar wind data obtained from Wind and ACE spacecraft. Selected events are 27 ICMEs that satisfy the criteria of maximum solar wind speed >600 km/s and maximum magnetic field strength >20 nT. In order to understand the geometry of ICMEs, flux rope model fitting, minimum variance analysis, and coplanarity theorem are applied for magnetic clouds, interplanetary magnetic field (IMF) discontinuities, and interplanetary shocks, respectively. Typical microstructures are categorized into three types; 1) post-shock stream with turbulent IMF, 2) deflected stream with less turbulent IMF, and 3) transition layer from sheath temperature to cloud temperature with density enhancement. From the comparison with obtained ICME geometry, it is found that these three types of microstructures can be interpreted in terms of the interaction between the ICME and background solar wind.
SH31A-1160 0800h
Properties of the Heliospheric Current and Plasma Sheets at 5 AU: Ulysses Observations
Several studies have addressed the properties of the Heliospheric Current Sheet (HCS) and the surrounding Heliospheric Plasma Sheet (HPS) at or near 1AU. Statistics are available regarding the thickness of both, the orientation of the current sheet, etc. The structure of the current sheet, i.e., how the field changes from one side to the other, and the location of the current sheet within the plasma sheet have also been examined. Recent studies have explored the relation between the current sheet and the solar wind electron heat flux. The latter has been used to define the "sector boundary" and on occasion the location has been found to differ from the HCS, a surprising result. No such analyses have been carried out previously at larger heliospheric distances. We have identified HCS crossings in Ulysses data during the recent Jupiter Distant Encounter between November 2003 and March 2004. We studied the same properties of the HCS/HPS near 5 AU as the earlier analyses. A comprehensive set of data near these structures, consisting of the magnetic field, solar wind and heat flux measurements, was analyzed with the results to be presented.
SH31A-1161 0800h
WIND Magnetic Clouds for Years 1995 - 2003 : A Summary of Model-Fitted Parameters
Almost a decade's worth of WIND interplanetary magnetic clouds (MCs) has been identified, and their magnetic field structures have been parameter-fitted by a static force free cylindrically symmetric model [Lepping et al., 1990], with various levels of success, measured by an objective figure of quality. Quality (good, fair, or poor) is estimated from a quantitative consideration of a large set of parameters such as the chi-squared of the model fit, symmetry of the $|$B$|$ profile, a comparison of the model-estimated radius vs. that from the duration of passage, etc. This paper summarizes various aspects of the results of the model fitting, including presenting of the estimated seven fit-parameter values for each of the 82 MCs that were discovered, their quality estimates, closest approach vector (in two coordinate frames), fit-parameter errors for the cases of acceptable quality (50 or 61%), axial magnetic fluxes, and axial current densities - as well as updated average MC profiles for various conditions. This set of MCs (called set 1) was initially identified by visual inspection of relevant field and plasma data. The resulting MC candidate is then "tested" through the use of the field model which also helps to better refine the boundary-times. Another, significantly larger, set of magnetic cloud-like (MCL) interplanetary structures (called set 2) are identified through an automated program whose criteria are based on MC plasma and field characteristics determined from the study of the earlier identified cases, set 1. Set 2 contains most of the set 1 cases, as expected, but in fact, its occurrence frequency of MCs better matches that of the sunspot cycle. However, cases in the difference-set (set 2 - set 1) are less intense (i.e., lower $<|$B$|>$) and have shorter durations than those in set 1, and almost never are they well represented as good flux ropes through force free parameter modeling. Nevertheless, many of the MCL structures are geoeffective often having long periods of negative BZ, somewhat similar to most MCs. We present a discussion of how a MC's front boundary is specifically identified in terms of multi-parameter considerations (i.e., any one or more of: increase in $|$B$|$, directional discontinuity, magnetic hole in $|$B$|$, drop in proton plasma beta, B-fluctuation level change, proton temperature drop, etc.), as well as through the application of the flux rope model. Also presented are examples of unusual MCs, including a case with a core and annulus in which the axial field changes polarity from the core to the annulus, as well as some commonly occurring relationships, such as the existence and frequency (about 1/2 of the time) of upstream interplanetary shocks, and less frequent internal shocks. Ref: Lepping et al. (1990), J. Geophys. Res., 95, 1957.
SH31A-1162 0800h
Ulysses Observations of the Heliospheric Current Sheet at Solar Maximum.
Since 1990, the Ulysses mission has studied the previously unexplored third dimension of the heliosphere from an elliptical orbit tilted at approximately 80\deg to the solar equatorial plane. Here we present an ongoing attempt to understand the topology of the heliospheric magnetic field through solar maximum by studying spacecraft observations of the heliospheric current sheet (HCS). The dataset studied (April 2000 - June 2002) is centred on aphelion, includes the solar maximum south and north polar passes, and extends either side back down to latitudes of 50\deg and 40\deg in the south and north, respectively. Encounters with the HCS by Ulysses are observed at all latitudes in the southern hemisphere and up to 67\deg in the north. For each encounter the local orientation of the HCS has been obtained using the minimum variance technique. The results show an increase in the spread of the north-south elevation angle of the orientations with increasing latitude, most pronounced at high ($>$50\deg) southern latitudes. The orientations are consistent with the single highly tilted HCS previously inferred from the latitudinal distribution of Ulysses encounters during the second orbit at solar maximum.
SH31A-1163 0800h
Solar cycle variation of long-duration radial IMF at 1 AU
Intervals of long-duration radial interplanetary magnetic fields (IMFs) were studied using the OMNI database for the period of approximately forty years. Long-duration radial IMF events were detected in various regimes of solar wind. It was found that long-duration radial IMF events frequently occur around solar minimum and are rarer near solar maximum. The events tend to occur in decreasing solar wind speed through solar cycle. The decreasing rates of solar wind speed associated with the events do not clearly depend on the solar activity.
SH31A-1164 0800h
Variability of the Heliospheric Magnetic Flux
There has been considerable controversy in recent years over the slow evolution of the Sun's open field, which extends out to become the heliospheric magnetic field. In the standard solar model [e.g., Wang and Sheeley, 1993] the open flux can increase or decrease in response to the emergence or cancellation of magnetic flux at the photosphere. In particular, the appearance of a new active region can lead to the formation of a new coronal hole, or the growth of an old one, which should be detectable as a long-term increase in the radial component of the magnetic field throughout the heliosphere. In the Fisk et al. [1999a, 1999b] model, on the other hand, the open flux is conserved and evolves primarily via interchange reconnection with closed field. This model predicts no long-term variations in the amount of heliospheric flux. To compare and test these competing theories, we measure the behavior of the open magnetic flux in the global heliospheric magnetic field. Using multi-point measurements from both the MAG instrument on the Advanced Composition Explorer (ACE) and the VHM instrument on the Ulysses spacecraft, we analyze in-situ magnetic field data. In particular, we examine the radial component of the magnetic field in data from 1998 through 2004 in order to determine the variablity of the open flux and its relation to variations in the area of coronal holes. We describe the implications of our results for the two theories. This work has been supported in part by NSF and NASA.
SH31A-1165 0800h
Radial evolution of cross helicity in the solar wind at high latitudes: Ulysses observations and turbulence modeling results
We employ a turbulence transport theory to explain the high latitude radial evolution of cross helicity, or Alfv\'enicity, observed by the Ulysses spacecraft. Although evolution is slower than at low latitudes, the plasma evolves towards a low cross helicity state under influence of shear driving, which is weaker at high latitudes owing to the absence of stream interaction regions. The flattening of the cross helicity versus radius has been previously observed and attributed to a saturation effect; here this result emerges from the turbulence equations as a consequence of weakened shear. It is of potential interest that very small or vanishing shear driving might in principle allow the cross helicity to again increase with radius, since it is mainly shear that opposes dynamic alignment, the tendency of freely evolving MHD turbulence to increase the Alfvenic correlation. Here we compare the theory, including weakened but non-zero shear driving, with Ulysses observations during solar minimum conditions. We analyze hourly averages of velocity and magnetic field data along with temperature data. Cross helicity, turbulence energy and correlation length are computed. We find that the observations significantly constrain combinations of model parameters and initial conditions that allow agreement with theory. Many parameter combinations are thus eliminated, leaving ranges of parameters that ``span'' the statistical spread of the observed data. Notably the analysis suggests that the turbulence energy at 0.3 AU is higher at high latitudes than at low latitudes. This may have important consequences, for example, for cosmic ray modulation. This work supported in part by NASA NAG5-11603 and NSF ATM-0105254
SH31A-1166 0800h
On the Generation of Rotational Discontinuities in the Solar Wind
Magnetic hodogram of rotational discontinuities (RDs) observed in the solar wind are characterized by mixed magnetic polarity (Neugebauer, 1989). This type of magnetic hodogram is part of the nonlinear wave solutions obtained in our previous theoretical study. Unfortunately, previous simulation studies fail to reproduce this type of RDs from a circularized nonlinear Alfven wave. Our recent MHD simulation study of velocity-shear instability indicates that no vortex but nonlinear plane waves can be formed if the velocity shear is greater than twice of the fast-mode speed. Phase-steepened nonlinear Alfven waves with mixed magnetic polarity can be found on both sides of the velocity-shear layer. Wave normal of these nonlinear Alfven waves is nearly anti-sunward in the slow solar wind region but sunward in the fast solar wind region. Our hybrid simulation study shows that RDs with mixed magnetic polarity can be developed from this type of nonlinear Alfven waves. Thus, we propose that RDs can be generated by velocity-shear instability in the solar wind. Comparison between our simulation results and previous solar-wind observations of RDs (Neugebauer, 1989) and nonlinear Alfven waves (Mavromichalaki et al., 1988) will be discussed.
SH31A-1167 0800h
Hydrodynamics of Shock Waves with Reflected Particles: Rankine-Hugoniot Relations
The exact mechanism of pickup ion (PUI) acceleration up to anomalous cosmic ray (ACR) energies at the heliospheric termination shock (TS) is a central problem in the physics of outer heliosphere. If we are to properly address shock energization of suprathermal particles, we must answer the question of how suprathermal particles self-consistently interact with a quasi-perpendicular shock and how they modify the structure of the shock. In the outer heliosphere, there is a substantial population of PUIs. Zank et al., (1996), Lee et al., (1996) and Lipatov and Zank (1999) have suggested that PUIs can be reflected preferentially by the cross-shock electrostatic potential. They proposed a new mechanism for the acceleration of PUIs which is often called mutiply reflected ion (MRI) acceleration or shock surfing. In this work we investigate the role of reflected particles in modifying of Rankine-Hugoniot (RH) relations in a simple hydrodynamical framwork. We included the momentum and energy terms introduced by reflected particles into the shock and studied RH conditions on the basis of a geometric formulation of entropy condition. We distinguish those solutions to the RH conditions which correspond to a physically realizable downstream state. It is seen that such shocks have some common features with the combustion shocks. We show that for shocks with reflected particles decelerated solutions of RH condition can exist under some specific conditions as well as subsonic-supersonic transitions. We have considered both perpendicular and highly oblique shocks, finding them to be strongly sheared. Such shear may destabilize the shock.
SH31A-1168 0800h
Injection rate in quasi-perpendicular shocks without cross-field diffusion
We have performed hybrid simulations to investigate the injection process at quasi-perpendicular shocks. The simulations are performed in one-dimensional system, therefore the injection is done without cross-field diffusion. For detailed investigations of the low density of the back-streaming ions which run into further upstream region (over Lamor radius), we have used over 10 thousand particles in simulation cell. This enable us to analyze the contribution of the reflected ions to the excitation of the upstream wave. The growth rate of the wave is smaller than the case in quasi-parallel shocks, but has finite value both in the oblique propagation angle and in a low density cases less than 0.1 percent of the incoming upstream thermal ions. We have observed the wave excitation by the reflected ions even in quasi-perpendicular shocks. This wave is different from the dispersive Whistler wave. This wave can boost up the ion reflection at the shock surface after convected from the upstream region to the shock surface.
SH31A-1169 0800h
Perpendicular shock structure: a small amplitude model
Reflection of ions by the cross-shock electrostatic potential is the primary dissipation mechanism at a quasi-perpendicular shock in the solar wind. Recently, the role of pickup ions and their greater facility for reflection by the cross-shock potential has raised important questions for injection and acceleration of pickup ions at, for example, the heliospheric termination shock. However, before these questions can be fully addressed, a better understanding of ion reflection and shock structure at a quasi-perpendicular shock is needed. We revisit the question of ion reflection and shock structure based on a fluid model and appropriate source terms that take into account the energization of the reflected ions by the motional electric field immediately upstream of the shock. By assuming that the source terms remain small, we develop a perturbation expansion solution of the model equations and derive a modified form of the classical Burgers equation. However, the dissipation term in our Burgers' equation is determined by the efficiency of the ion reflection process at the shock front, demonstrating explicitly that ion reflection should be viewed as a dissipative process and one that determines the scale length of the quasi-perpendicular shock.
SH31A-1170 0800h
Polytropic Index at the Bow Shock Inferred From Density and Field Compression
Data from the Cluster spacecraft obtained during crossings of the earth's bow shock is studied to attempt to obtain a value for the polytropic index $\gamma$ of the plasma in that region. Specifically, the compression ratio (average downstream density / average upstream density) and magnetic field ratio (average downstream magnetic field / average upstream magnetic field) are found for numerous instances of the shock and then used to determine the polytropic index, through the use of the MHD Rankine-Hugoniot equations. We find that in both cases, the polytropic index is consistent with a value falling in the range $5/3 < \gamma < 2$ over a wide range of Mach numbers.
SH31A-1171 0800h
The Diffusion Mean Free Path Upstream of Earth's Quasi-Parallel Bow Shock
We have analyzed a number of diffuse upstream particle events observed by Cluster when the spacecraft separation was between 1 and 1.5 Earth radii. The spatial gradient of the partial ion densities parallel to the magnetic field has been determined in several energy bands as a function of distance from the bow shock. For the events investigated the e-folding distance increases with decreasing solar wind speed. Assuming that upstream diffusion is balanced by downstream convection we can determine the spatial diffusion mean free path as a function of energy. Since the mean free path is proportional to the e-folding distance and proportional to the solar wind speed the mean free path is approximately independent of solar wind velocity.
SH31A-1172 0800h
Cosmic Ray Modulation: Improving the Agreement Between Modelling and Observations
We compare the effects of two different models for perpendicular diffusion on the modulation of galactic cosmic ray protons in the heliosphere during solar minimum conditions. These two models correspond to the newly developed non-linear guiding center (NLGC) theory [Matthaeus et al., 2003] and the theory of Bieber and Matthaeus [1997] (known as BAM in several of our earlier publications). A steady-state two-dimensional numerical modulation model is used in this ab initio study, which incorporates a state-of-the-art turbulence model. Factors relevant to an improvement in the agreement between the ab initio modulation model and cosmic ray observations are discussed.
SH31A-1173 0800h
Conservation Laws and Ponderomotive Force for Non-WKB, MHD Waves in the Solar Wind
The interaction of non-WKB Alfv\'en waves in the Solar Wind was investigated by Heinemann and Olbert (1980), MacGregor and Charbonneau (1994) and others. MacGregor and Charbonneau (1994) investigated non-WKB Alfv\'en wave driven winds. We discuss both the canonical and physical wave stress energy tensors for non-WKB, MHD waves and the ponderomotive force exerted by the waves on the wind for the case where both compressible (magneto-acoustic type waves) and incompressible waves (Alfv\'en waves) are present. The equations for the waves include the effects of wave mixing (i.e. the interaction of the waves with each other via gradients in the background flow). Wave mixing is known to be an important element of turbulence theory in the Solar Wind. However, only the wave mixing of Alfv\'enic type disturbances have been accounted for in present models of Solar Wind turbulence (e.g. Zhou and Matthaeus, 1990), which use Elss\"asser variables to describe the perturbations. The relationship between the present analysis and nearly incompressible MHD (reduced MHD) is at present unclear. Also unclear is the relationship between the present analysis and theories using wave-mean field interactions (e.g. Grimshaw (1984), Holm (1999)). The analysis is based on a theory for wave and background stress-energy tensors developed by Webb et al. (2004a,b) using a Lagrangian formulation of the total system of waves and background plasma (see e.g. Dewar (1970) for the WKB case). Conservation laws for the total system of waves and background plasma result from application of Noether's theorems relating Lie symmetries of the action to conservation laws.
SH31A-1174 0800h
Linear Beam-Plasma Instabilities in the Presence of Finite Amplitude Backward Propagating Waves
In previous works finite amplitude circularly polarized waves propagating forward relative to the background magnetic field were shown to affect the behavior of linear proton beam-plasma instabilities [1-4]. We now study the behavior of these instabilities in the presence of finite amplitude circularly polarized backward propagating waves. We find that the presence of both right-hand and left-hand polarized backward propagating waves stabilize linear beam-plasma right-hand instabilities when their amplitude is above a treshold value. It has been shown than forward propagating waves can stabilize right-hand instabilities [1-3]. Here we show that the threshold wave amplitude required to stabilize the right-hand instabilty is larger for forward propagating waves than the amplitude threshold for backward propagating waves. Thus, backward propagating waves can be in some physical conditions a more efficient mechanism to stabilize linear right-hand instabilities. Also we find that the presence backward propagating waves can produce electrostatic instabilities by making the phase velocities of the linear ion acoustic waves become equal above a treshold amplitude value. These results can be relevant in various space plasma enviroments. \vspace{12pt} \parindent=0pt {\bf References} [1] L. Gomberoff, Stabilization of linear ion beam right-hand polarized instabilities by nonlinear Alfven/ion-cyclotron waves, {\em J.Geophys.Res.}, 108 (A6), 1261, doi: 10.1029/2003JA009387, 2003. [2] L. Gomberoff, J. Hoyos, and A. L. Brinca, Effect of a large amplitude circularly polarized wave on linear beam-plasma electromagnetic instabilities, {\em J. Geophys. Res.}, 108 (A12), 1472, doi: 10.1029/2003JA010144, 2003. [3] J. Araneda and L. Gomberoff, Stabilization of right-hand beam plasma instabilities due to a large amplitude left-hand polarized wave: A simulation study, {\em J. Geophys. Res.}, 109, A01106, doi: 10.1029/2003JA010189, 2003. [4] L. Gomberoff, J. Hoyos, A. L. Brinca and R. Ferrer, Electrostatic instabilities induced by large amplitude left-hand polarized waves, {\em J. Geophys. Res.}, 109, A07108, doi:10.1029/2004JA 010466, 2004.
SH31A-1175 0800h
Ion-Acoustic Instabilities in the Solar Wind
It has been shown that ion-acoustic waves can be estabilized by finite amplitude left-hand polarized waves propagating in the direction of the external magnetic field [Gomberoff et al., 2004, J. Geophys. Res. 10(A0718),10.109/20004JA010466]. This result was shown to apply in plasma systems composed of electrons, protons and a proton beam. Later on, it was shown that the same instability is possible even in the absence of the proton beam [Gomberoff et al., 2004b J. Res. Lett. (submitted)]. It is shown here that the instability can actually be triggered quite generall by circularly polarized finite amplitude waves propagating either forward or backward relative to the external field. The instability occurs when the amplitude of the finite amplitude wave is larger than a threshold value. These waves are shown to have the properties of the ion-acoustic waves observed in the solar wind: (a) they do not seem to be Landau damped for proton temperatures larger that the electron temperatures, $T_p \geq T_{e}$, (b) they are more likely to occur closer to the Sun, and (c) the may exist independently of the proton beam velocity.
SH31A-1176 0800h
Quasilinear Simulation of Harmonic Electromagnetic Emission via Beam-driven Langmuir Waves in the Solar Wind
The linked nonlinear processes of electrostatic Langmuir decay and electromagnetic emission are important for type III solar radio emissions, and other emissions in space plasmas. For instance, to generate the observed levels of emission at the second harmonic plasma frequency in most type III bursts, it is usual to invoke nonlinear three-wave processes where beam-driven Langmuir waves coalescence with Langmuir products from Langmuir electrostatic decay. In this work, second harmonic emission is studied using quasilinear theory for situations where the Langmuir waves are driven by an electron beam. An approximate method for studying wave decay and emission in three spatial dimensions is developed, based on the Langmuir and ion-acoustic wave dynamics in one spatial dimension. The numerical results are explored for illustrative parameters in the solar wind at the corona and at 1 AU. The evolution of the transverse waves shows the combined effects of local emission and propagation away from the source. At a given location, the emission rate shows a series of coalescences of Langmuir waves driven by the beam and those produced by successive decays. The effects of solar wind parameters on the emission are compared and discussed.
SH31A-1177 0800h
Stochastic Waves in Space Plasmas
Burstiness of observed wave emissions and related processes in space plasmas has been addressed via various stochastic theories of wave growth. These include elementary burst theories (EBT) of solar microwave spike bursts, and stochastic growth theory (SGT) of type II and III radio bursts and other planetary and heliospheric sources. These theories are analytically unified here, the SGT and EBT regimes are elucidated, and new regimes are uncovered. It is predicted that all the subregimes have lognormal wave-intensity statistics. This is verified using published data on type III solar radio bursts, magnetospheric waves, pulsar radio emissions, and simulations, leading to data collapse onto a single theoretical curve with no free parameters. Simplified model equations for the dynamics of generalized SGT are proposed and their results are compared with quasilinear and PIC simulations, and with theory. These are the first simulations to show direct evidence of SGT. Evidence for divergence of correlation lengths as a critical point is approached is also presented, possibly pointing to existence of a self-organized critical regime.
SH31A-1178 0800h
Orientation Of Interplanetary Magnetic Clouds Associated With Filament Eruptions And Major Geomagnetic Storms
As a major source of non-recurrent geomagnetic storms, more than half of magnetic clouds in the interplanetary medium are associated with filament eruptions [Subramanian and Dere, 2001]. The strength of south component of the magnetic field inside magnetic cloud and its duration are consider the very important factors in causing geomagnetic storm. Obviously, these factors are related to the orientation of magnetic cloud in terms of flux rope model. By investigating the observations of SOHO and ACE spacecraft from 2000 to 2003, the relationship between the orientation of interplanetary magnetic clouds which were associated with filament eruptions and major geomagnetic storms are studied. Two issues are discussed: (1) the effect of magnetic cloud's orientation on the intensity of geomagnetic storm, and (2) the possible factors in influencing the cloud's orientation. The results will be worked out.
http://staff.ustc.edu.cn/~ymwang/mc_orientation.htm
SH31A-1179 0800h
Solar Cycle During the Maunder Minimum
Cyclicity of solar activity during the Maunder Minimum (1645-1715 AD) has been investigated by using the records of radiocarbon content in annual tree-rings. The spectral analysis of the records have shown a weak peak around fourteen years, suggesting that the length of the $``$eleven-year$''$ cycle had been stretched and that there had been only five $``$eleven-year$''$ cycles during this period. We also report possible features of polarity reversal of the Sun during this period.
SH31A-1180 0800h
Imaging Three-Dimensional Heliosphere in EUV with Ultra-High Spectral Resolution
A high-throughput, high-resolution spectrometer for diffuse radiation at 30.4 nm allows a way to map the heliopause and to image the three-dimensional flow pattern of the solar wind, including in the regions over the sun's poles. The radiation reaching an observer would include glow of the interstellar plasma beyond the heliopause and emissions produces by charge exchange of solar wind alpha-particles on interplanetary atomic hydrogen. We show that high spectral resolution would separate these two sources of radiation and distinguish between the high (ecliptic) and slow (polar) solar wind flows. This enabling instrumentation should be able to measure 1 milli-Rayleigh irradiance in 1000 seconds with a 0.005-nm spectral resolution with an angular pixel of a few degrees. The desired performance characteristics can be achieved by combining multiple entrance slits with an optimized spectrometer design.
SH31A-1181 0800h
A high-throughput, high-resolution spectrometer for mapping the heliopause and 3-D Solar Wind using He+ 30.4nm
The He+ ion provides a valuable tracer of solar wind dynamics and the heliospheric boundary. Mapping the heliosphere from 1 AU in 30.4nm with high spectral resolution will open access to the heliopause and reveal the three-dimensional flow of the solar wind. The scattered and emission fluxes are however faint, just a few milli-Rayleighs (mR), which poses a serious limitation on the mapping rate at high signal-to-noise ratio. We explore a spectrometer concept for narrowband EUV emission that offers important advantages over previous designs: high throughput (~1cps/mR), high spectral resolution (several thousand), no moving parts, and modest instrument size and mass. The concept combines a conventional normal-incidence Rowland mount grating and an efficient multilayer coating, with a microchannel plate detector performing two dimensional photon counting. One key innovation is the use of a large-area multi-slit at the spectrometer entrance. This multislit is a one dimensional sequence of open and opaque zones, against which pattern the accumulated spectral image can be correlated to recover the incident spectrum. The other innovation is arranging that each member of the multislit group is curved in such a way that the off-plane grating aberrations (which extend and rotate the image of each object point) do not introduce significant wavelength broadening. The curved slit arrangement yields a large well-corrected image field, and a high throughput for diffuse emission is achieved. This presentation concentrates on the design of the wide-field mount that maximizes the working area populated by the slits. The curved-multislit Rowland spectrometer will have a variety of other applications in astrophysics, aeronomy, and space physics sensing diffuse fluxes with high spectral resolution and sensitivity.
SH31A-1182 0800h
First Results of an ADIS Type Charged Particle Detector, Taken at the NSCL Accelerator Facility
We report here the first results from a working ADIS-type charged particle detector for use in space missions. The ADIS system consists of three detectors, two of which are inclined at an angle to the telescope axis, forming the first detectors in a multi-element charged particle instrument. By comparing signals from the ADIS detectors, the angle of incidence of incoming particles can be determined. The ADIS system can thus replace hodoscopes using conventional position sensing detectors (PSD's). PSD's add significant complexity and require additional electronics, increasing instrument mass, power usage and, in many cases telemetry requirements. The ADIS system's angle determination requires only the processing of simple equations, easily within the capabilities of even the slowest on-board processors. Thus a light-weight, low-power ADIS based charged particle telescope is a good candidate for studying high energy charged particles in deep space. We have built a prototype ADIS telescope for laboratory testing. While the detector housing is made specifically for this system, this test model used off-the-shelf components. The prototype model was taken to the National Superconducting Cyclotron Laboratory at Michigan State University. There the instrument was subjected to a primary beam of 48Ca, and fragment beams from that primary. Various detector systems are compared to show how the instrument response varies with respect to detector thickness and orientation. The preliminary results show that the ADIS instrument can distinguish element in the sub-Ca region with charge resolution of ~0.25e.
SH31A-1183 0800h
Neutron Monitor Temperature Coefficients: Measurements for BF$_3$ and $^3$He Counter Tubes
The Bartol neutron monitor network, part of the Spaceship Earth (SSE) project, utilizes a combination of BF$_3$ and $^3$He counter tubes. In order to make the datasets from these stations as comparable as possible, we have found it necessary to apply temperature corrections to the data. By analysis of several years of data we have measured the absolute temperature coefficients for both BF$_3$ and $^3$He counter tubes; in addition, we find that end tubes have a different coefficient than middle tubes. We will report on comparisons with Monte-Carlo simulations of the temperature response which include the effects of monitor structure and temperature-dependent cross-sections. These corrections have been applied to all of the Bartol network data for which we have adequate temperature measurements. Supported by NSF grant ATM-0000315.
SH31A-1184 0800h
A new Instrument Mode for Electrons on the Wind Spacecraft
The SWE instrument on the Wind spacecraft consists of two Faraday cups used to measure solar wind, two ion-electron spectrometers (VEIS), and an additional instrument to measure the electrons making up the "Strahl". To recover from a failure of a high voltage power supply in the year 2002, the VEIS and the Strahl instruments have been combined in a new form to measure electron phase density and pitch angle distributions. This paper describes the new data obtainable in this way. As a result of providing additional telemetry capability to the Strahl sensor, the new mode has greater time and angular resolution than the previous arrangement. The new mode is an arrangement of data taking using telemetry capacity previously allotted to the VEIS sensor. This takes 9 seconds and each spin is divided in eight sectors. Elevation (pitch angle) coverage is provided by the six Strahl detectors, at $\pm 26.6^\circ, \pm17.1^\circ$, \pm 7.34^\circ.$ These details are described in the paper, examples of the new observations are given, and details of access are provided.
SH31A-1185 0800h
SARISA: an instrument for analysis of Genesis mission returned samples
To analyze elemental and isotopic composition of solar wind samples returned to Earth by the Genesis spacecraft of NASA's Discovery Program, a special advanced analytical instrument facility was constructed at Argonne National Laboratory. This facility is based on a new time-of-flight mass spectrometer and laser post-ionization of neutral species ion sputtered or laser desorbed from the solar wind collectors. The constructed instrument is called SARISA. It was specifically designed to efficiently use sample during laser post-ionization analysis. Since neutrals are the predominant species in ion sputtering and laser desorption, and laser post-ionization efficiently converts neutrals into ions, this instrument minimizes consumption of sample during analysis so that pieces of the collectors as small as 25 mm$^{2}$ can be characterized. This is very important for the precious solar wind samples. Also incorporated in the instrument is the capability for ultra-shallow depth profiling analysis with resolution of a few nanometers. This is accomplished by implementing a dual beam technique, which includes low-energy normal-incidence ion bombardment for removing atomic monolayers from the sample surface and micro-focused ion or laser beams for generating secondary neutrals from the exposed surface in order to probe the sample composition. The lateral resolution of the probe beams is 50 nm for ions from a liquid-metal ion source and 0.6 $\mu$m for photons from a desorption laser. Built into SARISA are an in-vacuum all-reflecting optical microscope and a capability of secondary electron imaging using a dedicated detector. The imaging capabilities of SARISA will allow identification of particulate contaminants on the collector surface in order to perform analysis on uncontaminated regions of this surface. Small sample consumption, high analysis resolution and imaging capabilities all are particularly important features of the SARISA instrument because of the condition of the returned Genesis samples. Details of the instrument design and results from test samples will be presented. This work is supported by the U. S. Department of Energy, BES-Materials Sciences, under Contract W-31-109-ENG-38, and by NASA under Work Orders W-19,895 and W-10,091.
SH31A-1186 0800h
Revisiting the "Perfect Detector Concept": Electron Moments From Thermal Noise Spectroscopy and Other Techniques
Space plasma measurements by classical particle spectrometers and Langmuir probes are intrinsically limited by the spacecraft potential. This limitation does not affect passive wave measurements at long wavelengths, since they perform an average over a large plasma volume. Thermal noise spectroscopy is based on a passive measurement of the plasma wave spectrum with a long electric antenna, and yields directly the density and the kinetic temperature of a stable electron velocity distribution. This technique does not suffer of the difficulties in plasma resonance identification that impede some other wave techniques as the resonance sounder and the quadripolar probe, and, contrary to them, does not perturb the other in-board instruments. We summarize the limitations and achievements of different plasma detectors in a variety of planetary and plasma environments, and examine how they might be combined on future missions. Finally, we examine how thermal noise spectroscopy might be implemented on a Solar Probe.