SH33A-1071
Stereoscope Observations of a Kreutz Sungrazing Comet by the SECCHI COR1 Coronagraphs Aboard STEREO
On June 8, 2007, a sungrazing comet was seen by the COR1 and COR2 coronagraphs on both the STEREO Ahead and Behind spacecraft. At that time, the two spacecraft had a heliocentric separation of just under 12 degrees, allowing for the first time the triangulation of the position and shape of the comet as it approaches the Sun. Additional observations were made by the C2 and C3 coronagraphs on SOHO. As is usual with Kreutz sungrazers, the comet did not survive perihelion passage. However, the tail remnant was seen to drift slowly outward after perihelion. Data from the two COR1 telescopes will be combined to derive 3D positions, and compared with other observations.
SH33A-1072
The Relation between low density events in the Solar Wind and CMEs
This paper discusses nine periods of time observed by Wind between 1999 and 2002 when the density of the solar wind plasma fell to values below 1/cc for periods between an hour and a day. All except one of these events could be associated with CMEs, which had plasma moving at about 1400 km/s as it passed 20Rs from the Sun. We suggest that when spacecraft enter rarefactions in this plasma, they observe extreme rarefactions. Thus two coincident conditions, a normal solar wind rarefaction and the arrival of material from an ICME are required for these events to be observed
SH33A-1073
Influence of Temperature Anisotropy and Alpha-Particle Parameters on Calculated Interplanetary Shock Parameters
In order to determine interplanetary shock parameters, we use Wind and ACE observations of shock passages in the solar wind. Magnetic field and plasma measurements by individual spacecraft are used with the nonlinear least squares fitting technique of Szabo [1994] with an improved error analysis to calculate the local shock parameters. Further improvement of the technique includes taking into account proton temperature anisotropy and alpha-particle parameters which results in higher accuracy of the calculated shock parameters. The shock parameters calculated at the locations of both spacecraft are then compared to estimate the global shapes of the observed shocks. We present statistics of the influence of proton temperature anisotropy and alpha particle parameters on the calculated shock parameters and discuss deviation of the shock global shape from the widely used planar assumption. The improved technique can be used to analyze STEREO and near-Earth observations of interplanetary shocks.
SH33A-1074
Energy Spectra and Composition of Low-Energy Ions during Solar Quiet Times
Although the Sun is never completely quiet, various studies over the last 40 years have reached the conclusion that there exist some minimum quiet-time intensities of low-energy ions <10 MeV/nucleon that may vary over the solar cycle, but are more or less reproducible. Recently, Fisk and Gloeckler have reported that quiet-time energy spectra of protons measured by Ulysses in the suprathermal energy range from 10 to 60 keV have a common spectral shape with a spectral index of –5 in velocity space (corresponding to a power law in energy with a spectral index of -1.5). We present the results of a survey that extends the work of Fisk and Gloeckler to somewhat higher energies, based on data from ACE and STEREO ranging from 0.1 to 30 MeV/nucleon. We find that the spectra of the H, He, O and Fe from 0.1 to 1 MeV/nucleon are typically somewhat steeper than reported by Fisk and Gloeckler. We compare the composition and spectral shapes of major species from H to Fe over the years from 1997 to 2007, and discuss the implications for the origin of the quiet-time intensities in the suprathermal energy range.
SH33A-1075
Multi-Spacecraft observations of nonlinear spatial correlation properties of solar wind fluctuations- Mutual Information estimates and solar cycle dependence
The WIND and ACE spacecraft spend extended (from weeks to years) intervals in the solar wind, potentially providing observations of the spatial correlation properties of both coherent structures and evolving turbulence. We estimate the correlation length scale in the solar wind using a nonlinear measure- mutual information- and linear cross correlation, the latter to facilitate comparison with previous work. We consider quantities such as Elsässer variables expected to characterize Alfvénic turbulent fluctuations alongside "non cascade" quantities such as the magnetic field magnitude and the proton density. We find that the magnetic field magnitude and the proton density have different correlation length scales to each other. We also consider variation with the solar cycle; this strongly modulates the correlation lenghtscale seen in ρ and |B|, but not that seen in the Elsässer variables for example. Our quantitative estimates of correlation lengthscales relate directly to the phenomenology of the solar wind, either in the context of turbulence, or that of propagating structures of coronal origin.
SH33A-1076
Solar Wind Structure at Solar Minimum: 3D MHD Solar Wind Model Results Compared with STEREO and ACE Observations
During the present period of low solar activity, STEREO-A and -B have been observing solar wind structure where quasi-steady corotating interaction regions (CIRs) are prevalent. We recently used several models developed by CISM (Center for Integrated Space weather Modeling), now available at the Community Coordinated Modeling Center (CCMC), to analyze the solar control of the declining phase solar wind observed by ACE at L1. The WSA/ENLIL and MAS/ENLIL models describe the steady solar wind structure and its origins in the corona, based on photospheric magnetic field synoptic maps. We extend our study by comparing the model results with spacecraft measurements on both STEREO spacecrafts. This comparison demonstrates the ability of these 3D MHD models to describe multi-point observations. In particular, the results provide a test on the steadiness of CIR structures over modest baselines around solar minimum.
SH33A-1077
The September 2004 Event at Ulysses and ACE: Influence of Large-Scale Interplanetary Structures on Energetic Particle Propagation
An intense solar energetic particle (SEP) event was detected in September 2004 by near-Earth spacecraft and by Ulysses at 5.4 AU. The characteristics of the intensity and anisotropy time profiles at both heliospheric locations were determined by the presence of a corotating low-density, low-speed, and low-proton-beta (βp) solar wind stream. This low-βp stream was followed by a faster and denser solar wind resulting in the formation of a strong compression region. The bulk part of SEPs at 1 AU was observed in the downstream region of this compression region. Only those SEPs either able to leak from behind the compression region or accelerated by the associated CME-driven shock as it penetrated into the low-βp region, or both, were observed prior to the main component of the SEP event. Anisotropic ion intensity enhancements observed upstream of this shock most likely resulted from both particle acceleration in a corrugated shock surface and particle propagation within the low-βp region. The particle event at Ulysses was exceptional in terms of the large and long-lasting (>4 days) field-aligned anisotropies. These large anisotropies resulted from both the leakage of energetic particles from behind the compression region and their propagation within the low-βp region. We propose a scenario that explains the characteristics of the SEP event at both 1 AU and Ulysses. The effects that large-scale interplanetary structures have on the energetic particle transport determine the properties of the event at both spacecraft by modifying the time history of both particle intensities and anisotropies. These effects must be carefully considered by models of energetic particle transport in the heliosphere.
SH33A-1078
Multi-point Data and Tools From STEREO's IMPACT Investigation
STEREO's IMPACT (In-situ Measurements of Particles and CME Transients) investigation provides the first opportunity for long duration, detailed observations of 1 AU magnetic field structures, plasma and suprathermal electrons, and energetic particles at points bracketing Earth's heliospheric location. The IMPACT team has developed both human-friendly web portals and API's (application program interfaces) which provide straight- foward data access to scientists and the Virtual Observatories. A new web browser tool provides easy access to imaging data related to events measured in-situ, and the Virtual Heliospheric Observatory incorporates STEREO data into its data system providing another powerful venue for multi-point, multi-spacecraft analysis of the heliosphere. This variety of data access techniques and the development of cross-spacecraft data analysis tools allow the larger scientific community to combine STEREO's unique in-situ data with those of other missions and, therefore, to maximize STEREO's scientific potential in gaining a greater understanding of the heliosphere. http://sprg.ssl.berkeley.edu/impact
SH33A-1079
Wind and STEREO - Combined Observations
After serving to facilitate intercorrelation, the Wind spacecraft will provide a third point from which observations can be made for the remainder of the mission. In this paper, we analyze the orbits and compare the instrumentation of the two spacecraft. Apart from magnetic field and plasma correlations as a function of distance in several directions and time, Wind and STEREO will explore both magnetic and plasma structures as they are convected past in the solar wind, collecting, for example, a statistical data base related to magnetic clouds. Other similar examples will be discussed.
SH33A-1080
Analysis and Interpretation of Comet Measurements from SMEI
The Solar Mass Ejection Imager (SMEI) has observed several comets and traced their plasma tails as far as 108 km from their nucleus. A time sequence of SMEI orbital sky maps displays considerable tail motion and disruption for several of these comets. Tracking these motions versus time, when combined with ephemeris information about their distance from the Earth allows a determination of solar wind speeds and their variation with the location of the comet. In the case of comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), which passed within about 0.3 AU of Earth in April and May of 2004, the SMEI observations show that speeds during disruptions are typically 50 to 100 km s-1 less than speeds before and after. Time durations of the disturbances vary between 3 and 8 hours, and correspond to distances traversed by the comets of ~106 km (0.007 AU). We compare these observations with interplanetary scintillation (IPS) three-dimensional tomographic reconstructions and find no evidence that the comet-tail features are due to large-scale density or velocity structures. We also compare these with near-by spacecraft measurements such as the Advanced Composition Explorer (ACE), and find a similar result. This suggests that the comet-tail disruptions are caused by small-scale changes in the solar wind acting over distances that are short compared with 1 AU. http://smei.ucsd.edu/
SH33A-1081
A 3D view of coronal mass ejections in interplanetary space
Ground-based measurements of interplanetary scintillation (IPS) have been used to study the solar wind for many years, but interpretation of the results has always been rendered more difficult by uncertainty about the electron density distribution along the extended line-of-sight from radio source to antenna. This has been particularly marked in the case of Earth-directed coronal mass ejections (CMEs). The launch of the STEREO spacecraft, with its Heliospheric Imager (HI) instruments, provides us with the first detailed view of structures in the Sun-Earth line, revealing the motion of large-scale density structures, and greatly reducing the uncertainties in interpreting IPS observations of the speeds of small-scale irregularities embedded within the larger structures. In this poster we present results from a co-ordinated programme of measurements which brings together STEREO HI and two different IPS experiments. We consider two events, one from 2005 in which we use a combination of long-baseline IPS measurements from EISCAT and MERLIN, tomographically-reconstructed 3D density distributions from STELab IPS observations, and SOHO EIT and LASCO images to track the development of an Earth-directed CME. We discuss the remaining uncertainties in this approach and the ways in which STEREO HI images would have assisted with the analysis. In the second event we combine STEREO HI observations of structures in the solar wind with IPS measurements of solar wind speed from EISCAT and MERLIN and tomographic reconstructions of 3D structure. We discuss the results and present suggestions for future co-ordinated campaigns.
SH33A-1082
Do Large Solar Energetic Particle Events Observed at 1 AU Include Particles Accelerated by the Associated Solar Flare?
Many large solar energetic particle (SEP) events observed at 1 AU start with a high Fe/O ratio (measured at a fixed MeV/nucleon) that then decays to a lower value. One possible explanation is that particles in these events are a combination of flare particles, with high Fe/O, and shock accelerated particles with a lower ratio. In this scenario, one would expect that when there is good magnetic connection to the flaring region, flare particles would be detected at the start of the event. The Fe/O ratio would decrease with time to an extent dependent on the strength of the associated shock and the energy of the observations. A second possible explanation is that only shock-accelerated particles are observed, and that the time-varying Fe/O ratio is a result of escape from the shock: at a fixed MeV/nucleon, Fe particles, with their higher rigidity, escape more readily than O and therefore arrive earlier at 1 AU. Yet a third suggestion is that Fe and O have similar injection profiles near the Sun and then undergo rigidity-dependent interplanetary scattering. We will present data from the ACE Solar Ion Spectrometer (SIS) from a variety of SEP events and consider the implications for these three scenarios. We will also consider the possibility that, by combining observations from the two STEREO spacecraft and near-earth spacecraft (ACE and WIND), we may be able to rule out one or even two of these scenarios.
SH33A-1083
Solar Wind and Suprathermal Ion Populations at the STEREO Spacecraft Approaching Solar Minimum
The two STEREO spacecraft, which were launched in October 2006, have been gradually separating in longitude at a rate of about 22 degrees per year. During this past year, the dominant heliospheric features have been a series of recurrent high and slow speed solar wind and their interaction regions, an occasional transient event (e.g., May 22), and "background" suprathermal populations such as interstellar pick up ions. In this poster we present an overview of the plasma and suprathermal signatures observed by the STEREO spacecraft using data from the Plasma and Suprathermal Ion Composition (PLASTIC) and Magnetometer (IMPACT/MAG) investigations. Complementary STEREO PLASTIC related presentations in this session are by Popecki et al., Klecker et al. (invited), and Simunac et al.
SH33A-1084
Probing the 2-D Geometry of CIRs at Solar Minimum: Observations From STEREO
The twin STEREO observatories provide a unique opportunity to study the two-dimensional in-ecliptic geometry of structures in the solar wind. At the start of 2007 the AHEAD (A) and BEHIND (B) satellites were near Earth. By the end of the year they will each be separated from Earth by about 20 degrees longitudinally, and from each other by about 40 degrees. This arrangement is well suited to test the conceptual picture of CIRs in the ecliptic plane. The orbital radius of STEREO A is about 0.98 AU, while STEREO B is at about 1.03 AU. If A and B were at the same line of longitude they would be less than 2000 Earth radii apart. Observations show this small radial separation becomes important when predicting the arrival time at Earth of streams observed with STEREO B; stream fronts were seen to arrive at A and B almost simultaneously in mid 2007 when the spacecraft were separated by about 7 degrees. This suggests the leading edge of the stream is roughly aligned with the solar wind garden hose angle. We report on observations of the leading edges of co-rotating high-speed streams, and discuss the implications for space weather forecasting.
SH33A-1085
STEREO/SEPT Observations of Upstream Particle Events: Almost Monoenergetic Ion Beams
The presence of energetic particles (<~1 MeV) upstream of the Earth's bow-shock, which are preferentially streaming from the magnetosphere in the Sun direction is well known since the 1960s. The origin of upstream ion bursts often associated with energetic electrons (>~30 keV) was explained in two ways: (1) leakage of magnetospheric particles accelerated within the magnetosphere, and (2) acceleration at the bow-shock. Normally, the ion upstream bursts are characterized by power-law energy spectra with negative slope, independent of their origin inside the magnetosphere or at the bow-shock. But the recently observed "Almost Monoenergetic Ion" (AMI) bursts detected in the magnetosphere and near the Earth's bow-shock at INTERBALL-1 show that some events exhibit narrow spectral lines. These lines were explained as acceleration in a burst of electrostatic field inside the magnetosphere. We present observations of such AMI events in the energy range of 100-1000 keV detected with the SEPT instruments onboard both STEREO spacecraft. These AMI events were detected inside the magnetosphere at STEREO-B as well as unexpectedly far upstream of the bow-shock at distances up to 1100 RE (STEREO-B) and 1900 RE (STEREO-A). We discuss the origin of AMI events, the connection to the Earth's bow-shock and to the magnetosphere, and the conditions of the IP medium and magnetosphere under which these AMI bursts occur. There is evidence that the detected lines may be caused by quasi-monoenergetic beams of protons, helium, and heavier ions. Furthermore, we present spatial and temporal distributions and the occurrence rate of all electron and ion upstream events from December 2006 until July 2007.
SH33A-1086
Goniopolarimetry of the inner heliosphere radio emissions with the STEREO Spacecraft
The S/Waves instrument onboard the 3 axis stabilized STEREO spacecraft is composed of a set of 3 monopole antennas connected to a radio receiver. The receiver measures spectral and cross-spectral power densities on one, two or three antennas in the frequency range between 10 kHZ and 16 MHz. This package therefore have goniopolarimetric (GP), aka direction-finding, capabilities, allowing to determine the direction of arrival of an incoming wave, its flux and polarization properties. We present the first result GP results on solar radio bursts and terrestrial auroral radio emissions.
SH33A-1087
Discovery of Accelerating Plasmoids in the Tail of Comet Encke
Comet 2P/Encke was the second comet to have its return correctly predicted (in 1819). Encke is a Jupiter-family comet with a period of 3.30 years and a perihelion distance of 0.338 AU. The interaction between cometary plasma and the solar wind plasma provides the potential for remote monitoring of the solar wind. In this regard comet Encke is potentially a very useful probe of the solar wind because of its very short orbital period and therefore large number of close approaches to the Sun. However, for this reason it is likely to have exhausted most of its reserves of ice and therefore possess a less dense plasma tail. The comet could therefore respond faster and more dynamically to solar wind variations than the tail of a more active or higher gas production comet. The Heliospheric Imager (HI) of STEREO-A (HI-1A), observed comet 2P/Encke during April, 2007. The comet was predicted to have reached perihelion on April 19th 0 UT. This paper will only consider the observations obtained by HI-1A on April 25th to 27th, 2007. At this time the comet was around 0.63 AU from Earth and 0.39 AU from the Sun. The comet was seen to exhibit a distinct "flick" of its plasma tail on April 26th and a series of "whiplash" events. However, the most interest phenomena seen was a whole series of "plasmoids" that were observed to break off from the brighter part of the tail near the nucleus and accelerate along the tail for 4-5 million kilometres down-wind of the nucleus.
SH33A-1088
The Spatial Evolution of 26-Day Recurrent Particle Intensity Variation: Correlated ULYSSES, SOHO, and STEREO Particle Observations
The effects of corotating interaction regions (CIRs) on energetic particles were first studied in detail about 30 years ago. The three-dimensional extent of CIRs and its importance in structuring the quiet heliosphere, however, became obvious first from Ulysses observations at high heliolatitudes. Mid 2007 the energetic particle fluxes measured at the position of Ulysses at about 1.5 AU and about 30 degree South, at SOHO, close to Earth, and at the location of the two STEREO spacecraft show pronounced solar rotational variation. From July to September 2007 a series of CIRs are observed. In this paper we investigate the longitudinal and latitudinal variation of the paricle modulations and the correlation to coronal hole structures seen in synoptic maps.
SH33A-1089
Helium at Interplanetary Discontinuities: ACE STEREO Observations and Simulations
ACE/SEPICA observations showed that, on average, energetic He+ is after H+ and He2+ the third most abundant energetic particle species in the heliosphere. Depending on the type of the energetic population the He+/He2+ ratio can reach unusually high values in the energy range 250 - 800keV/n ratios up to unity. As a major source of energetic He+ interplanetary pickup ions have been identified that are preferentially accelerated at co-rotating interaction regions (CIRs), transient interaction regions (TIRs), and interplanetary traveling shocks. Most recent data from STEREO/PLASTIC in the energy range of 0.2-80keV/Q show clear evidence of abundant He+ at interplanetary discontinuities. Thus PLASTIC extends the energy range into injection region of the source. Furthermore, ACE/ULEIS and ACE/SEPICA measurements showed that very often 3He2+ and He+ are also accelerated simultaneously at CME-driven IP shocks. This is surprising because, these to species originate from different sources. However, this may indicate that the injection, or the acceleration efficiency of the accelerator for different source population may be similar. From observations, however, this cannot be differentiated easily. In numerical simulations this can be done because there is control over species and distribution functions. In a numerical study we applied test particle simulations and multi-dimensional hybrid simulations to address the contribution of source, injection and acceleration efficiency at shocks to the variability of the helium ratio. These, simulations with and without superimposed turbulence in the shock region will be compared with observations.
SH33A-1090
Multipoint Observations of Stream Interaction Regions
A stream interaction region (SIR) forms when a fast stream overtakes a preceding slow stream. These SIR structures continue to evolve as they move away from the Sun. During short intervals of Ulysses' perihelion and aphelion passes, Ulysses was at almost the same helio-latitude as ACE and Wind, and the three spacecraft observed several of the same SIRs. Based on multipoint observations of the same events, we study the evolution of SIR properties over a relatively large temporal and spatial scale. In particular, we examine the associated shock, duration, width, total perpendicular pressure, magnetic field and velocity variation, and compare them with our previous statistical results of SIR evolution from 1 to 5.3 AU. We also compare the observations of STEREO and ACE, to study the structures of SIRs and their evolution over shorter spatial and temporal scales.
SH33A-1091
IPS observations of the inner-heliosphere and their comparison with multi-point in-situ measurements
Interplanetary scintillation (IPS) observations of the inner-heliosphere have been carried out on a routine basis for many years using metre-wavelength radio telescope arrays. By employing a kinematic model of the solar wind, we reconstruct the three-dimensional (3D) structure of the inner-heliosphere from multiple observing lines of sight. From these reconstructions we extract solar wind parameters such as velocity and density, and compare these to "ground truth" measurements from multi-point in situ solar wind measurements from ACE, Ulysses, STEREO, and the Wind spacecraft, particularly during the International Heliophysical Year (IHY). These multi- point comparisons help us improve our 3D reconstruction technique. Because our observations show heliospheric structures globally, this leads to a better understanding of the structure and dynamics of the interplanetary environment around these spacecraft. http://ips.ucsd.edu/index_ss.html
SH33A-1092
STEREO SECCHI Observations of Space Debris: Are They Associated with S/WAVES Dust Detections?
White-light coronagraphs are optimized to reject stray light in order to accomplish their primary science objective - - the observation of coronal mass ejections (CMEs) and the corona. Because they were designed to detect these faint signals while pointing at the Sun, many spacebased coronagraphs in the past (Skylab, SMM, SOHO) have detected "debris" apparently associated with the vehicle. These appear to be sunlit particles very near the front of the telescope aperture (~meters). In at least one case, these earlier debris sightings were interpreted as deteriorating insulation from the thermal blankets on the spacecraft (St. Cyr and Warner, 1991ASPC...17..126S); and for the earlier Sklyab observations, the sightings were believed to be associated with water droplets (Eddy, "A New Sun: The Solar Results from Skylab", NASA SP-402, p119, 1979.) The STEREO SECCHI suite of white-light coronagraphs represents the most recent instantations of these specialized instruments, and for the first time we are able to track CMEs from their initiation at the Sun out to 1 A.U. Since observations commenced, the SECCHI white-light telescopes have been sporadically detecting debris particles. Most of the detections are individual or small numbers of bright objects in the field which therefore do not affect the primary science goals of the mission. But on several occasions in the eight months' of observation there have been "swarms" of these bright objects which completely obscure the field of view of one or more instrument for a brief period of time. Here we report on the intriguing possibility that the SECCHI debris sightings represent particles of thermal insulation, ejected from the spacecraft by interplanetary dust impacts. Because of the large field of view and high duty cycle of the Heliospheric Imagers on STEREO, we may be able to demonstrate that some of these have also been detected by STEREO S/WAVES as sporadic plasma emissions.
SH33A-1093
Correlation of Solar Wind Features from Well-Separated Spacecraft
Observations of correlated features in the solar wind from two well-separated spacecraft, such as Wind and ACE in 2001-2002, yield information about the variability of the solar source of the wind as well as about evolution of features between the observation points. If their solar sources were independent of time, one would expect features that are not radially expanding as portions of spherical shells to be co-rotating with the Sun as Parker spirals. Previous correlation studies have shown that the average propagation times of features between spacecraft lie between those expected for spherically expanding shells and those expected for co-rotation. Nevertheless, we have found that individual pressure-balanced structures well-correlated in several parameters are consistent with co-rotation provided that the associated magnetic fields are close to the Parker spiral direction. That dependence on field orientation has not been pointed out previously.
SH33A-1094
Cosmic Ray Observations from the COSPIN High Energy Telescope (HET) during Ulysses' Current Fast Latitude Scan
Ulysses reached its maximum southern heliographic latitude in February, 2007 and is now performing its third fast latitude scan. This scan will cover all latitudes between 79.7° S and 79.7° N at radii between 2.35 and 1.39 AU within 1 year, a time short compared to significant evolution of the solar activity cycle, which is now near its minimum phase. During this solar minimum the solar dipole magnetic field is opposite that observed during the first solar minimum fast latitude scan in 1994-95, a fact which is expected to lead to observable differences in the latitudinal structure of modulated cosmic ray intensities. Measurements of protons, helium, and heavy ions during the recent slow latitude scan, when Ulysses rose from near the ecliptic to maximum southern latitude between 2004 and 2007, a period of declining solar activity, revealed no measurable latitude gradients in HET observations above a threshold (for protons) of about 35 MeV/n. Because of its short duration and restricted radial range, observations during the fast latitude scan provide the best chance for a definitive measure of latitudinal gradients in the cosmic intensity through comparison of Ulysses observations with observations from near-Earth spacecraft, fixed in radius and latitude. However the recent loss of the IMP-8 spacecraft, which had served as a 1 AU baseline for COSPIN HET cosmic ray measurements since the launch of Ulysses, has presented a difficulty for measurement of the small gradients that seem likely given previous observations and the lack of clearly visible latitude effects in the Ulysses cosmic ray data alone. We will present results for heavy ions from the fast latitude scan through the most recent data available, using measurements from Ulysses compared to ACE/CRIS as the 1 AU baseline. For protons and helium, we will present Ulysses observations and evaluate available possible 1 AU baselines, including ERNE data from SOHO, STEREO HET observations, and possible extrapolations from available lower or higher energy measurements which can be used to define the modulation parameter at 1 AU as a function of time, and thus the expected flux variations in Ulysses' energy range at 1 AU. (This work was supported in part by NASA/JPL Contract 1247101)
SH33A-1095
STEREO observations of electron beams and Langmuir waves in the terrestrial electron foreshock
In the early phase of the STEREO mission, the two spacecraft entered a petal orbit and made multiple crossings of the terrestrial bow shock. The Suprathermal Electron Telescope (STE) made spectacular observations of foreshock electron beams at these crossings. The improved sensitivity and energy range of the STE measurements over previous Wind measurements reveals previously unseen fine structure in the electron beams. STE shows electron beams with energies up to 100 keV associated with the quasi-perpendicular bow shock. In addition, the new instruments allow high time resolution measurements of electron beam energy spectra and time-of-flight features. These results are presented in conjunction with STEREO/WAVES (S/WAVES) observations of Langmuir waves concurrent with the electron beams.
SH33A-1096
Nonlinear Energy Balance Model of Particle Acceleration by Parallel Shock Waves
A new theoretical/numerical model of particles acceleration by quasi-parallel shocks is developed and results of numerical analysis are discussed. The model assumes that resonant wave--particle interaction is the most important physical mechanisms relevant to motion and acceleration of particles as well as to excitation and dumping of waves. The treatment of plasma and waves is self-consistent and time dependent. The model uses conservation laws and resonance conditions to find where waves will be generated or dumped and hence particles will be pitch--angle scattered. Since the total distribution function (for bulk plasma and high energy tail) is included in the model, no any special bootstrap or termination assumptions are required (neither introduction of separate population of seed particles nor some ad-hoc escape rate of accelerated particles are needed). The preliminary results show not only remarkable agreement with diffusive shock acceleration (DSA) models in prediction of power spectra for accelerated particles in upstream region but also reveal presence of spectral break in high energy part of the spectra. The role of the second order Fermi acceleration at the initial stage of acceleration is discussed.
SH33A-1097
Benchmarking 1D Hydrodynamic Codes for Steady State Solutions
Recent studies that investigate the coronal heating problem use numerical codes to solve the 1D hydrodynamic equations. Many different numerical solutions are involved for solving the equations, however, only a few comparison have been made between the different numerical results. In this study, we begin a benchmarking process by comparing steady state solutions from the NRL Solar Flux Tube Model(SOLFTM), AAD's code and Serio's Scaling Law by calculating percentage differences in their simulated temperatures and densities.
SH33A-1098
Electric Field and Density Measurements with STEREO-SWaves.
The STEREO experiment SWaves has a low frequency part which is designed to make measurements of low frequency electric fields and rapid measurements of density fluctuations, using the three 6 meter stacer monopole antennas. The short antennas of STEREO respond both to density fluctuations and to electric fields. Therefore, it is desired to obtain four quantities, density and 3 components of electric field, from three measurements, the potentials on the three orthogonal antennas relative to the spacecraft, which requires some additional information. One possibility is to add a fourth equation implied by the large plasma conductivity, so large that electric field parallel to the magnetic field is zero, a condition which has often been used in electric field measurements. Under selected conditions, this seems to work. There are also conditions, for example ion acoustic waves, where the responses to density fluctuations and to electric fields are available from dispersion relations, and this provides another possible solution. A situation where it is not likely that the parallel electric field is zero is the case of solitary, intense bursts of Langmuir waves. For this case, it is expected that there is an electron density depression due to the ponderomotive pressure, and a resulting low frequency electric field from the non-neutrality which would be expected to have components parallel to the magnetic field. Examples will be discussed.